Method and apparatus for handling communications between a spacecraft operating in an orbital environment and a ground-based telecommunications device

Abstract

To provide communication using a feature and equipment of a terrestrial telecommunications device typically used for terrestrial telecommunication.SOLUTION: A multiple-access transceiver in Earth orbit which handles communication with a mobile station in an environment beyond the design assumption of a mobile station without necessarily requiring modification of the mobile station closes the communication with the mobile station while the mobile station design assumptions are exceeded, such as greater distance, greater relative motion, and / or other conditions commonly found when the functionality of the terrestrial transceiver is performed by an orbital transceiver. The orbital transceiver includes a data analyzer that analyzes a frame data structure, a signal timing module that adjusts timing on the basis of orbit-to-ground propagation delay, a frequency shifter, and a programmable radio that can communicate from Earth orbit using multiple access protocols.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for handling communications between a spacecraft and a terrestrial telecommunications device, and more particularly to communications using features and facilities of terrestrial telecommunications devices typically used for terrestrial telecommunications.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and is a non-provisional application of U.S. Provisional Patent Application No. 62 / 465,945, entitled "Method for Low-Cost and Low-Complexity Inter-Satellite Link Communications within a Satellite Constellation Network for Near Real-Time, Continuous, and Global Connectivity," filed March 2, 2017.

[0003] This application claims priority to and is a non-provisional application of U.S. Provisional Patent Application No. 62 / 490,298, entitled "Method for Communications Between Base Stations Operating in an Orbital Environment and Ground-Based Telecommunications Devices," filed April 26, 2017.

[0004] The entire disclosures of the above-cited applications are incorporated herein by reference for all purposes as if fully set forth herein. [Background technology]

[0005] Mobile communications involve signals being transmitted between a mobile station (MS) and a transceiver, which may provide an interface for the MS to communicate with other network resources, such as a telecommunications network, the Internet, etc., to carry voice and data communications, and possibly location discovery features. The transceiver may be a component within a base transceiver station (BTS), which handles traffic from multiple transceivers. The BTS may also include antennas and encryption / decryption elements. The antennas may be selective, and different MSs at different locations may communicate to their respective transceivers through different antennas of the BTS. The BTSs may have wired, wireless, and / or optical channels to communicate with their other network resources. A BTS may support one or more transceivers, and a given base station for supporting mobile communications may have a base station controller (BSC) that controls one or more BTSs of that base station.

[0006] Examples of mobile stations include mobile telephones, cellular telephones, smart telephones, and other devices equipped to communicate with a particular BTS. While a mobile station is referred to herein by name, it should be understood that the operations, functions, or characteristics of a mobile station may also be the operations, functions, or characteristics of a station that is effectively or functionally a mobile station but is not currently mobile. In some examples, a mobile station may be considered a substitute for a portable station that may move from place to place but is stationary in operation, such as a laptop computer with several attached peripherals and a cellular connection, or a mobile station may be stationary, such as a cellular device embedded within an implemented home security system. All that is required is that the mobile station be capable of or configured to communicate using a mobile communications infrastructure.

[0007] A BTS may be controlled by a parent BSC through a base station control function (BCF). While each of these elements may be implemented using hardware and / or software and may include network management and maintenance functions, a base station may be described as having one or more transceivers that communicate with mobile stations according to an agreed-upon protocol. This may be by configuring, adapting, or programming the BTS to operate according to the BTS's agreed-upon protocol and configuring, adapting, or programming the MS to operate according to the MS's agreed-upon protocol. The protocol may include details of how to transmit data between the transceiver and the MS, how to handle errors, how to handle encryption, and how to transmit control instructions and status data between the BTS and the MS. For example, part of the protocol may include an interaction where the MS contacts the BTS and the BTS indicates to the MS the timing, carrier frequency, and other protocol options the MS will use. This interaction may include carrying voice data, carrying text data, carrying other data, providing intra-cell handovers, and other tasks.

[0008] For simplicity of explanation, in many examples herein, communications are described as being between a BTS and an MS for interaction with one MS, but it should be understood that the interaction may be a corresponding path in the other direction from the BTS to the transceiver, radio circuitry, antenna, MS antenna, MS radio circuitry, software / hardware within the MS, and from the MS to the BTS. Thus, in some examples where a BTS is communicating with an MS, the communications are via a transceiver, and the examples ignore any discussion of other transceivers that the BTS may control.

[0009] Examples of protocols that a BTS may use include the GSM (Global System for Mobile Communications, a trademark of the GSM Association) 2G+ protocol, which includes Gaussian minimum-shift keying (GMSK), and the EDGE protocol, which includes GMSK and 8-PSK keying. A BTS can handle multiple transceivers using multiple sets of carrier frequencies within a spectrum band of the radio spectrum allowed by the protocol. Thus, if a spectrum band is logically divided into a carrier frequency spectrum, a transceiver may use a channel to communicate with an MS using one (or more) of those carrier frequencies. For a given channel, the protocol may specify that there are uplink and downlink subchannels, and in some cases, the carrier frequencies are separated from one another. In some cases, the uplink subchannel has a carrier frequency adjacent to the carrier frequency of the downlink subchannel. In some cases, all uplink subchannels are in one spectrum band and all downlink subchannels are in another spectrum band. For ease of explanation, a channel may be described as having an uplink portion and a downlink portion, and as if they were one channel, even though the portions are widely separated within the carrier frequency.

[0010] Some BTSs may offer frequency hopping, in which the transceiver and mobile station together rapidly jump from carrier frequency to carrier frequency to improve the overall performance of the BTS. The protocol may specify the hopping sequence to use.

[0011] In the GSM protocol, transceiver-to-MS communications involve frames, with each frame having up to eight time slots. In the eight time slots, the transceiver transmits frames directed to up to eight MSs, each of which is assigned a unique time slot within the frame by the transceiver's BTS. MSs can send their transmissions within their assigned time slots, and each MS communicating with that transceiver knows which time slot to use so that similarly positioned MSs can communicate back to the transceiver within their assigned time slots. A transceiver does not use all eight time slots.

[0012] Signaling channels, such as the Common Control Channel (CCCH) of the GSM protocol, can be used to communicate to MSs their time slot and carrier frequency assignments. For example, some common control channels are used to make access requests (e.g., make RACH requests from the MS to the BTS) for paging (e.g., make PCH requests from the BTS to the MS), access grant (e.g., make AGCH requests from the BTS to the MS), and cell broadcast (e.g., make CBCH requests from the BTS to the MS). The Access Grant Channel (AGCH) is used to grant time slot assignments / carrier assignments. Another channel, the Broadcast Control Channel (BCCH), may or may not be used to transmit information to the MS such as the Location Area Identity (LAI), a list of neighbor cells to be monitored by the MS, a list of frequencies used within the cell, a cell identifier, a power control indicator, whether DTX is allowed, and access control (i.e., emergency calls, call barring, etc.).

[0013] Examples of BTSs include cellular telephone towers, macrocell transceivers, femtocell transceivers, picocells (which may have only one transceiver), etc. The BTS will communicate wirelessly with the MS. Some BTSs have a wired backhaul (the interface between the BTS and other network resources) such as a cellular telephone tower, while some may have a wireless backhaul such as a microwave point-to-point two-way communication channel. Thus, the BTS may be any of several different types of electrically powered devices that receive data streams from the MS, process them, and / or forward them to other network resources, as well as receive data streams from other network resources, process them, and / or forward them to the MS via BTS-MS link(s). In this sense, the BTS acts as an access point for the MS, allowing the MS to access network resources such as telecommunications networks, the Internet, private networks, etc. Access can be used to route voice calls, other calls, texting, data transfer, video, etc.

[0014] The telecommunications network behind the BTS may include network and switching subsystems that determine how to route data to the appropriate BTS and how to route data received from the BTS. The telecommunications network may also have infrastructure to handle circuit and packet-based Internet connections, as well as network maintenance support. In either case, the BTS may be configured to use some protocols with the MS and other protocols in the backhaul.

[0015] Protocols for communication between an MS and a BTS may be standardized so that any standard MS can communicate with any BTS, assuming range requirements are met and membership requirements are met (e.g., the MS identifies itself to the BTS in such a way that the BTS or the service used by the BTS determines that the MS is a member of an authorized group or is otherwise authorized to use the service provided by the BTS). Some example protocols include the GSM protocol, sometimes referred to as the 2G (i.e., second-generation) network protocol. Other examples include the General Packet Radio Service (GPRS), Enhanced Data rates for GSM Evolution (EDGE, or EGPRS), the 3G (third-generation) UMTS standard developed by the 3GPP body, or the fourth-generation (4G) LTE enhancement protocol.

[0016] These protocols have rules for spectrum band usage, timing, coding, and conflict resolution. Because a BTS may need to communicate with many MSs simultaneously, the available radio communication paths are divided according to the protocol. A given protocol may have available radio communication paths divided by frequency, time, code, or two or more of these. This allows multiple users to share the same radio communication path.

[0017] For example, in Time Division Multiple Access (TDMA), a BTS and multiple MSs agree to divide a period into time slots (or "burst periods"), and if a first MS might interfere with a second MS, the first MS is allocated a first time slot and the second MS is allocated a different one of the available time slots. Because different MSs use different time slots (and all MSs agree that the timing is adequate), the MSs can share a common carrier frequency and their respective transmissions do not interfere. An example would be if there were eight time slots of 576.92 μs (microseconds) each for each frame, so that an MS allocated to the first time slot could transmit some bits during the first time slot, stop transmitting at or before the end of that time slot, maintain silence, and then continue transmitting as needed during the first time slot of the next period. Similar allocations occur to determine when an MS hears something from the BTS (and when the BTS begins transmitting its data).

[0018] Thus, using a single carrier frequency, each transceiver in a BTS can communicate with up to eight MSs, with communications to those MSs grouped into TDMA frames and transmitted on downlink channels using that carrier frequency channel. The timing is such that each of those MSs can communicate with the BTS on uplink channels using that carrier frequency channel within their respective time slots. This is called a "TDMA frame," and the data rate across all eight MSs using that carrier frequency is 270.833 kilobits / second (kbit / s), with a TDMA frame duration of 4.615 milliseconds (ms) in either direction.

[0019] Frequency Division Multiple Access (FDMA) is another method of dividing and allocating available wireless communication paths. In FDMA, the available or allocated spectrum bandwidth for a wireless communication path is divided into different channels by carrier frequency. A first MS is allocated one carrier frequency and a second MS is allocated another carrier frequency so that both can simultaneously transmit and receive with a single BTS.

[0020] In the above example, multiple mobile stations may be communicating with the BTS simultaneously, and communication between the BTS and a particular MS involves transmitting information in signals from a particular MS or BTS, so collisions of radio signals are avoided by having the BTS and the particular MS agree on which time slots of multiple time slots to use (TDMA) and / or which carrier frequencies of multiple carrier frequencies to use (FDMA). These are examples of multiple access communications.

[0021] In another type of multiple access communication, called "Orthogonal Frequency Division Multiple Access (OFDMA)," mobile devices are allocated subsets of subcarriers and orthogonal narrow frequency subchannels to more efficiently use the allocated spectrum compared to FDMA.

[0022] In some frequency allocations, the allocation is per channel block, where a channel block is a set or group of bidirectional channels, each bidirectional channel using an uplink carrier frequency for its uplink subchannels and a downlink carrier frequency for its downlink subchannels. Channels may be grouped together into two or more sets of channels based on some logic of classification, such as each set sharing a common identifier or attribute.

[0023] In some protocols, the spectrum is divided into subspectrums of carrier frequencies, and the time period is also divided into time slots. Typically, the BTS includes logic for determining which channel to assign to which MS. When allocating channels for use by an MS, the BTS allocates a particular transceiver to use a particular carrier frequency, indicates to the MS that the BTS will use that particular carrier frequency, and may also use that carrier frequency to indicate which time slot to use from the transmitted / received frame. A channel may comprise an uplink subchannel and a downlink subchannel. While communication between a given transceiver and an MS may use more than one channel, e.g., more than one carrier frequency and / or more than one time slot, in many examples herein, the protocol is illustrated as relating to an MS using a channel comprising only one carrier frequency and only one time slot.

[0024] In yet another example of multiple access communications, called "Code Division Multiple Access" (CDMA), mobile devices may use the same time slots and carrier frequencies, but each mobile device is assigned a unique pseudo-random code for encoding signals to and from the BTS, so that even if the MSs transmit simultaneously using the same carrier frequency or approximately the same time, and / or the same time slots, applying unique CDMA codes when used allows multiple transmitters to occupy the same time and frequency such that a receiver can separate the different receptions by using the pseudo-random codes to decode each specific signal sufficiently appropriately for demodulation.

[0025] In practice, CDMA does not separate channels strictly by time or strictly by frequency. By using a chipping rate faster than the signal's bit rate, CDMA results in the transmission of a spread-spectrum signal that spreads across a wider bandwidth than would be possible without coding. Therefore, encoding a signal with a pseudorandom code replaces the timing and frequency elements typically found in TDMA / FDMA protocols, since each code represents some element of articulation in both the time and frequency domains. In CDMA communications, the signal propagation delay and timing between the MS and BTS are understood, so the pseudorandom code is applied to the received signal over several bits / chips, which naturally occupy both some discrete span in the time domain and some discrete span in the frequency domain.

[0026] Some multiple access protocols use more than one technique.

[0027] In a GSM protocol digital mobile radio telephone system, the MSs and BTSs utilize communication over both frequency division multiple access (FDMA) and time division multiple access (TDMA) channels, so that the MSs can share the same transmit and receive carriers with the allocation of separate time slots on each carrier frequency, and each carrier frequency can be handled by a separate transceiver or transceiver module or logic block.

[0028] In GSM, the BTS is responsible for allocating time slots to mobile stations (MSs) when they request access. In the GSM frame structure, there are eight time slots within each TDMA frame. The number of carrier frequencies used can vary. In some regions, some carriers license a large number of carrier frequencies, and MSs within those regions are configured to accept instructions to use one of as many as a thousand carrier frequencies (which the BTS will also support). For example, in Europe, the GSM 900 MHz spectrum band contains 25 MHz of spectrum. If this is logically assigned to 200 kHz carrier frequencies (e.g., carrier frequencies centered within each 200 kHz subspectrum band) and a transceiver transmits signals on those carrier frequencies, 125 carrier frequencies are provided. The use of guard bands (unused carrier frequencies) within the frequency domain can reduce this number, but may result in improved reliability or easier signal processing. If a TDMA frame allows for eight time slots, a BTS with a sufficient number of available logical or physical transceivers can support 8 * 125 = 1000 MS channels simultaneously. In time division and frequency division, there may be guard slots and guard frequencies, respectively, so that one division is somewhat isolated from adjacent divisions. In some protocols, more than one time slot and / or more than one carrier frequency can be allocated to one MS to provide greater bandwidth.

[0029] In some cases, there may be multiple BTSs within range of a supported MS, so MS support may be spread among the BTSs, which may coordinate to avoid neighboring BTSs using the same carrier frequency when possible. The BTS may be programmed to spread these frequencies across its towers using a particular reuse scheme. A BTS may also be limited in the number of MSs it can support by the size of its pipe to other network resources. In one example, a BTS may use 1-15 carrier frequencies (i.e., its transceiver transmits using 1-15 carrier frequencies within a transmit / receive frame, allowing it to support anywhere from 8-120 users simultaneously).

[0030] Each MS typically includes a processor, memory, radio circuitry, a power supply, a display, input elements, etc. to perform its functions. The processor can read from program memory to perform the desired functions. For example, the program memory may have instructions on how to form a data stream, how to pass it to the radio circuitry, how to read an internal clock to determine the value of the system clock to properly time listening and transmissions, and how to set the appropriate frequencies for transmission and reception.

[0031] To perform its functions, each BTS typically includes a processor, memory, radio circuitry, power supply(s), an interface with the telecommunications network, a diagnostic interface, etc. The processor of the BTS can read from program memory to perform the desired functions. For example, the program memory may have instructions on how to form a data stream, how to pass it to the radio circuitry, how to communicate with the telecommunications network, how to read an internal clock to determine the value of the system clock and properly time listening and transmissions, how to set appropriate frequencies for transmission and reception, how to keep track of various MSs and their status, location, assignments, etc., and possibly store it in locally available memory.

[0032] In the method described above, an MS contacts a BTS and is assigned several time slots within a frame of several carrier frequencies, and the BTS notifies the MS of the MS's assignment. Both the BTS and the MS have the same (or nearly the same) system clock and therefore communicate within those assigned time slots and carrier frequencies. The assignment and communication of the assignment to the MS may be done using a random access channel, which the MS uses to request an assignment. In the GSM protocol, this is called RACH processing.

[0033] In the GSM example, communications over the radio communication path are parsed into TDMA frames of 4.61538 ms duration, with eight time slots per TDMA frame. Each time slot is long enough to hold 156.25 bits of data. In one application, an MS or BTS transmits 148 bits of data in a time slot over 546.46 μs, with a guard time of 8.25 bits (30.46 μs) between the time slots. In the GSM 900 band, the radio communication path has a bandwidth of 25 MHz in each uplink and downlink direction, using the 890-915 MHz spectrum band for the uplink subchannel and the 935-960 MHz spectrum band for the downlink subchannel, providing 125 carrier frequencies (125 carrier frequencies in each direction, spaced 200 kHz apart). With a 200 kHz guard separation on either side of each spectrum band, 24.6 MHz of spectrum or 123 carrier frequencies remain for data in transit. The total capacity of such a radio path (in both directions) would then be 156.25 bits per time slot times 8 time slots per frame times 216.667 frames / sec * 123 carriers = 33.312 Mbits / sec.

[0034] Considering that the MS may be mobile, such as when a BTS is fixed to a cell phone tower but the MS is 10 km away and traveling at 100 KPH, and you carry on a voice conversation over a telecommunications network using the MS, the MS may be at some distance from the BTS, and that distance may vary. If the BTS and MS are within a few meters of each other and the MS is not moving, the signal propagation time and Doppler shift due to movement can be ignored. If the MS is traveling at 100 KPH relative to the BTS, it may be negligible in some cases, but if the MS is some distance away, propagation time must be taken into account, or alternatively, a transmission in one time slot may not be received completely in that time slot but arrive late in another time slot, which may cause communication loss.

[0035] To account for propagation delays, transmitters advance or delay their transmissions, sending bursts of radio frequency (RF) signals to account for the propagation delays, and receivers anticipate their assigned transmissions at the adjusted times. When there are many MSs and one BTS, it is often useful for the MSs to adjust their transmission times so that the BTS is the one where the time slots are all aligned. Similarly, the BTS can send its transmission within a designated time slot, but to account for propagation delays, the MSs delay or advance the time at which they expect to listen or receive the transmission. In addition to the BTS assigning a time slot or slots and carrier frequency(ies) to an MS, the BTS may indicate to the MS the propagation delay or distance between the BTS and the MS.

[0036] For a BTS operating using the GSM protocol, the BTS knows the propagation delay of an MS signal by how the signal arrives on the Random Access Control Channel (RACH). The RACH channel is an uplink-only time slot used when an MS needs access to the channel to transmit data. The MS requests channel access by transmitting an 87-bit long signal burst on the RACH. The RACH burst is designed to have a 69.25-bit guard period between it and the next time slot. As a result, the burst can slide up to 69.25 bits within the RACH slot without adverse effects. When the RACH burst arrives at the BTS, the BTS can measure the number of these guard bits the signal burst has slipped to the right (i.e., moved further in time) and therefore determine the propagation delay of the signal. When the BTS responds to the MS with information about its channel allocation, the BTS includes what is called a "timing advance" (TA), which is sometimes expressed as the number of bits the MS needs to advance its signal so that it reaches the BTS in the correct time slot and does not spill over into an adjacent time slot. In the GSM protocol, the value of the timing advance can range from 0 to 63 bits, with 0 bits corresponding to no round-trip propagation delay and 63 bits corresponding to the propagation delay that would be experienced by an MS 35 km away from the BTS, with the radio signal traveling at the speed of light.

[0037] Without careful time alignment, transmissions from MSs operating at different distances may arrive at the BTS within the same time slot, causing collisions or overlaps. These collisions create interference from the BTS's perspective, which hinders the quality and reliability of communications. Guard times (measured in bits and called "guard bits") can be used to prevent burst timing errors from creating signal collisions, but this can only account for small time alignment errors in the internal clocks, not differences over extended and variable propagation distances.

[0038] For example, there may be a 30.461 μs guard time (8.25 guard bits) between time slots. Therefore, if a first MS is 4.569 km (9.138 km round trip) from the BTS and is assigned the first time slot, and a second MS is very close to the BTS and is assigned the next time slot, the relative propagation delay of the signals will not cause interference. This is because the signal from the first MS will be delayed by 30.461 μs, but the BTS will receive the second half of the transmission during the guard time, which will end before the second MS's time slot begins. In many cases, the guard time is too short to accommodate all possible distances of MSs. For example, if an MS is 10 km (20 km round trip) away, the propagation delay of the transmission from that MS to the BTS will be 33.333 μs, which exceeds the guard time and causes the BTS to receive that transmission at the same time as another MS assigned the next time slot.

[0039] One solution to accommodate distant MSs sharing the same BTS is to use a timing advance mechanism. The GSM protocol provides an example of this. In the initial handshake between the MS and the BTS, such as using the Random Access Channel (RACH) in the GSM protocol, the BTS determines the distance between the MS and the BTS. The BTS may transmit and receive time stamps during the RACH handshake when calculating the distance between the MS and the BTS, if each MS is based on uplink propagation delay.

[0040] While the determined distance may not be the actual distance between the MS and the BTS, for many purposes, a pseudorange is sufficient. As used herein, a "pseudorange" is a value that may or may not be the actual value of a distance, but is used as a proxy or assumed distance. That is, a module in the MS, BTS, or elsewhere assumes that a value is a distance, and various components are designed so that use of that value works well enough when the value is close enough to the actual value. As an extreme example, suppose the MS and BTS are 2 meters apart, but there is something between them that blocks a direct signal, and the closest path is a 3 km path with numerous reflections. In such a case, the pseudorange would be 3 km, and the MS and BTS would operate as if they were 3 km apart. Because the signal path their transmissions follow is 3 km, using that as a value for the distance between them works.

[0041] Generally, a pseudo-distance or pseudo-range of distance measured between two objects may differ from the actual distance or range of distance that can be measured by determining the time it takes a radio frequency signal to propagate from one object to another. Due to signal reflections and multipath, the line-of-sight (or range of distance) between the source and receiver of a signal may differ slightly from the propagation distance of that signal, in which case the pseudo-distance (or range of pseudo-distance) differs from the actual distance (or range of distance). However, in consistent usage, many operations can function solely on pseudo-distance values. In other usages, "pseudo" may similarly be used to indicate an estimate, assumption, approximation, etc.

[0042] Once the BTS determines the pseudorange of the MS, it stores the pseudorange in a table it maintains for each parameter and variable of the MS active using its transceiver. The BTS communicates the value to the MS in a control message described elsewhere herein. The MS is then programmed to implement a "timing advance" so that it takes into account its copy of the system clock, subtracts the propagation delay corresponding to the pseudorange, and sends its transmission to the BTS earlier than the start of the scheduled time slot. The RACH process may include various steps, described in more detail below, to determine these values.

[0043] As used herein, propagation delay is expressed as a conversion factor or approximation thereof, c=3*10 8 The propagation delay can be calculated from the propagation distance using m / s, and vice versa. If there is a standardized bit rate for transmission, such as 270.833 kbits / s for GSM, the propagation delay or distance can be expressed as the number of bits. For example, a 12 km separation results in a round-trip propagation delay of 80 μs, with each bit being transmitted in 3.692 μs, so the 12 km separation and 80 μs propagation delay can be equivalently expressed as a separation or propagation of 22 (more precisely, 21.66) bits. Thus, the propagation of one "bit" is equivalent to a round-trip propagation distance of approximately 555 meters and 3.692 μs.

[0044] MSs operating at different distances from the BTS are assigned different timing advances to accommodate their respective communication ranges. For convenience, this is sometimes expressed as an integer number of bits. To account for the movement of the MS, this timing advance value is communicated to the MS and used by modules within the MS to determine when to transmit or receive, and may be updated periodically and frequently enough to accommodate moving targets that may have time-varying communication ranges relative to the BTS. For example, if a user is using an MS on a high-speed train traveling at 200 KPH, the range may need to be updated more frequently than if the user were walking on the street.

[0045] In the specific example of the GSM protocol, the timing advance is represented as a 6-bit value, with the minimum representing a 0-bit timing advance and the maximum representing a 63-bit timing advance. Since the GSM protocol assumes that each bit corresponds to 3.692 μs (and a round-trip propagation delay of approximately 555 meters), a 63-bit timing advance would be used if the pseudorange were approximately 555 m / bit * 63 bits = 34,965 m, or approximately 35 km. Therefore, this timing advance technique works well for MSs within a range of 0 to 35 km from the BTS. In the GSM protocol, the BTS is programmed not to respond to, or at least not anticipate, a request from an MS if it determines that the MS is farther away than 35 km from the BTS. This is not an issue when there are other, closer BTSs, or in a distribution of BTSs where all points are within 35 km of one or more BTSs.

[0046] With a timing advance, the MS sends a transmission before the start of its time slot (from the MS's clock timing), and when that transmission is received at the BTS after a propagation delay, the BTS will receive the transmission completely within the time slot where the timing advance corresponds to the propagation delay. The MS is able to do this correctly because it has been provided with a value for the amount of timing advance to use. Note that the actual distance, and therefore the actual propagation delay, may differ from the pseudorange, but in many cases this is not an issue because MS-BTS communications have some leeway to handle internal clock differences, transmitter variations, etc.

[0047] While this timing mechanism works well when there is always one or more BTSs within 35 km of any MS, this is not always the case. In some geographic areas, it may not be practical, feasible, or economical to have a BTS within 35 km of any point in the area. For example, in rural, remote, or island geographic areas, BTS infrastructure with such spacing may not be accessible, and users with MSs may be scattered and widespread, so BTSs may not be used or may not be able to be installed or powered. In such situations, an "extended range" mechanism can be used. The GSM protocol allows for such a mechanism.

[0048] With the extended range mechanism, each MS is allocated two consecutive time slots instead of one, so that the MS can communicate with the BTS without requiring any timing advance if it can delay its transmission at the BTS for the duration of one time slot. This increases the allowable MS-BTS distance (e.g., from 35 km to 120 km), but reduces throughput by half because only four allocable time slots are available in each TDMA frame instead of eight. This may not be important for rural, remote, or island areas where data rates are low. By using a combination of the timing advance and extended range mechanisms, the maximum allowable MS-BTS distance can be 35 km + 85 km = 120 km.

[0049] In the extended range mechanism, each MS is allocated an entire time slot as an additional guard period, reducing throughput by half. A variation of this is the "sorted extended range mechanism," similar to that shown in U.S. Pat. No. 5,642,355. In the sorted extended range mechanism, time slots are "consumed" to be used as guard bits, but the time slots are allocated to MSs by distance, with the closest MS getting the first time slot and the farthest MS getting the last time slot allocated to its MS, i.e., before any "consumed" time slots not allocated to any MS. Because the extended range of the MSs spreads out their transmissions, the consumed time slots are used for the necessary guard bits. In effect, this "splits" the unused time slots between bursts.

[0050] If the distance is greater than 85 km or for other reasons, a "ring extended range" mechanism can be used. In the ring extended range mechanism, a fixed minimum distance is assumed, timing at the BTS is adjusted by that fixed minimum distance, and the BTS assumes all MSs are at least that distance apart, so MSs closer than the minimum communication distance are not supported. This is similar to the approach shown in U.S. Patent No. 6,101,177. Using the 35 km range achieved using the timing advance mechanism, MS-BTS distances ranging from the minimum distance to the minimum distance plus 35 km can be supported without requiring any MS modifications. In one example, the minimum distance is 85 km, but a different minimum communication distance can be used. In this example, the BTS can then support MSs ranging from 85 km to 120 km from the BTS.

[0051] The ring extended range mechanism may be used using eight of the eight allocated time slots, allowing MSs with distances ranging from 85 km to 120 km from the BTS. However, this creates a physical coverage gap some radial distance away from the BTS, because any signal burst transmitted from that area would reach the BTS much faster than the BTS could see that time slot. Instead, the BTS provides coverage for the area ring. The ring extended range mechanism may be used in geographic areas with a physical separation, such as a lake or valley, between the BTS and the MSs it is designed to serve, so having areas inside the ring where MSs are not supported would not be a problem.

[0052] It should be noted that GSM systems use a TDMA frame offset between the uplink and downlink subchannels. In a typical GSM frame structure, the uplink TDMA frame (or MS Tx and BTS Rx) is offset by three time slots from the downlink TDMA frame (or BTS Tx and MS Rx) to ensure that the MSs do not have to transmit and receive at the same time. It will be apparent to those skilled in the art of TDMA communications that this offset between the uplink and downlink subchannels is irrelevant to communications over extended distances and is not the same as the time slot synchronization offset used in the uplink TDMA frame only within the ring extended range mechanism.

[0053] When combined with extended range features, ring extension range mechanisms can be used alone or in combination to provide BTS coverage that can exceed a 120 km radius. These techniques are often sufficient for terrestrial communications, as such communications are typically limited by the curvature of the Earth. For example, to provide a distance D for line-of-sight communications between a ground-based MS and a BTS transceiver, the BTS transceiver should be mounted at a height of at least h = [SQRT(6370^2 + D^2) - 6370] km. For D = 120 km and h = 1130 m, 1130 meters is taller than any structure built today, so tower height is far greater than the limiting factor for terrestrial communications, rather than distance. Therefore, techniques that extend distance beyond 120 km are not very useful for terrestrial communications of cellular voice, data, text, and similar capacity, except in selected locations with large geological structures upon which to mount transceivers.

[0054] Satellite communications can be used in areas where it is impractical to distribute base station towers to provide wide coverage, such as where it is impractical to place a base station anywhere close to several locations, for example, within 35 km or 85 km of several locations, or within 120 km where tall towers can be installed. Typically, satellite communications are very expensive and therefore only used in applications that support the costs of resource detection, search and rescue, etc.

[0055] As used herein, the term "satellite" refers to an artificial satellite launched from Earth with the goal of operating in orbit, and / or assembled wholly or partially on the Earth's surface and / or operating in orbit, whether assembled wholly or partially in orbit. A satellite may be assembled and / or operate in one orbit and move to another. A satellite may be propelled or operate without its own propulsion means and may or may not rely on other objects in orbit to provide propulsion. As used herein, a satellite operating in orbit and not under propulsion is in a more or less stable orbit. Such an orbit has a minimum distance above the Earth's surface due to atmospheric drag. There is no strict dividing line between a vacuum sufficient for orbit and excess atmosphere that can cause a satellite to deorbit; low Earth orbit (LEO), approximately 400-500 km above Earth, has been shown to be practical, although particularly dense spacecraft, such as nanosatellites, may go even lower than these altitudes.

[0056] The very large minimum practical orbital distances have traditionally meant that satellite communications have used entirely different technologies. In some cases, the surface stations were not mobile, and in other cases, the surface stations were mobile but required power-intensive, heavy, large, and specialized equipment. In addition to distance, the movement of the satellites within the orbit had to be addressed.

[0057] There are many solutions for communication between satellites and surface-based mobile handsets on Earth that use the TDMA protocol for communication. Some satellite providers, including Iridium™, Globalstar™, Thuraya™, and Inmarsat™, offer satellite systems based on custom-developed satellite phones or user terminals (i.e., unique hardware devices that attach to or connect to existing mobile phones via physical or RF connections). Specific user terminals can simplify system, satellite, and terminal design because each can be specifically designed to function with other user terminals. The drawback is the requirement for specific terminal equipment that may be needed for every end user or a small group of end users, which can be expensive and impractical. While the custom terminal approach simplifies system design, it locks users into a specific provider because operators have the freedom to configure details such as communication method, power levels, and frequencies. As a result, end users may be required to purchase satellite phones (or user terminals that connect to existing mobile phones) that cost hundreds to thousands of dollars, have large, cumbersome antennas, use significant power, and require exorbitant monthly subscription fees to operate, and may have to do this with two or more satellite providers. This has limited the market appeal of traditional satellite phones.

[0058] As an example, U.S. Patent No. 8,538,327 describes a modified user equipment that calculates delay measurements based on data indicative of the satellite's position and data indicative of the user equipment's position. The timing of uplink communications from the user equipment is adjusted for delay as it travels to the satellite. The user equipment also calculates a frequency offset based on data indicative of the satellite's position and velocity, and adjusts its uplink signal frequency accordingly to account for dynamic Doppler shifts within the communications system. Naturally, this requires specific user equipment on the Earth's surface designed for satellite communications.

[0059] As another example, U.S. Patent Publication No. 2006 / 0246913 describes a scheme for managing RF signal propagation delays using sub-coverage rings characterized by reducing round-trip propagation delay differences. It uses geosynchronous Earth orbit (GEO) satellites to act as relays, connecting remote mobile stations to base stations within its network. To address the much larger delays imparted by GEO satellites, separate processing devices serve separate sub-coverage rings or zones by configuring themselves to the range of allowable propagation delays of the rings / zones. The link between the mobile station and the GEO satellite cannot be closed without the assistance of additional user terminal hardware for power, signal directionality, and frequency manipulation.

[0060] There is a need for an improved system for satellite-based communication with portable or mobile devices. Summary of the Invention

[0061] A multiple access transceiver for communication with a mobile station in an environment, such as may be found in Earth orbit, handles conditions beyond the mobile station's design assumptions without necessarily requiring modification of the mobile station. The multiple access transceiver is adapted to close communications with the mobile station during conditions beyond the mobile station's design assumptions, such as greater distances, greater relative motion, and / or other conditions typically found when the terrestrial transceiver's functions are performed by an orbital transceiver. The orbital transceiver may include a data analyzer that parses frame data structures, a signal timing module that adjusts timing based on orbit-to-ground propagation delays, a frequency shifter, and a programmable radio capable of communicating from Earth orbit using a multiple access protocol so that communications are compatible with, or appear to the terrestrial mobile station to be, communications between a terrestrial cellular base station and a terrestrial mobile station.

[0062] The multiple access transceiver may support terrestrial mobile stations that are cellular telephone handsets, smart phones, and / or connected devices. The signal timing module may be adapted to adjust the frequency of the transmission signal to a terrestrial Doppler shift based on the orbit. The signal allocation logic may allocate capacity of the multiple access transceiver distributed across multiple time slots, multiple carrier frequencies, multiple orthogonal subcarriers, and / or multiple code sequences to multiple terrestrial mobile stations, including the terrestrial mobile station. The multiple access transceiver may include, for each ground mobile station, a range calculator that determines a distance from the multiple access transceiver to the terrestrial mobile station; and a signal timing module that determines timing of transmitted signals relative to a frame structure, the frame structure comprising a plurality of slots each having a zero or non-zero time slot synchronization offset that provides a variable transmission delay due to distance from the multiple access transceiver to the terrestrial mobile station; and an input signal allocator that assigns a listen time slot within the frame structure to listen for communications from the terrestrial mobile station, the listen time slot being timed based on the distance from the multiple access transceiver to the terrestrial mobile station, the listen time slot being one of a plurality of time slots that are variably delayed within the frame structure to account for the multiple access transceiver handling communications from a plurality of terrestrial mobile stations having a plurality of distances from the multiple access transceiver.

[0063] The multiple access transceiver may have multiple time slots, which are variably delayed within the frame structure to accommodate the multiple access transceiver handling communications from multiple terrestrial mobile stations at multiple distances from the multiple access transceiver by allocating each of multiple different distance ranges to each of multiple channel blocks. The different distance ranges may collectively cover a slant range from a zenith distance to a minimum elevation distance, where the zenith distance is the distance between the zenith position of the satellite carrying the multiple access transceiver relative to the terrestrial mobile station and the minimum elevation distance is the distance between the position of the satellite when the terrestrial mobile station enters the satellite's design footprint. The different distance ranges may each range approximately 34-35 kilometers, with the difference between the zenith distance and the minimum elevation distance being 210-250 kilometers. The satellite's design footprint may be circular, elliptical, rectangular, and / or independent of the antenna function and / or antenna beam shape, but in many instances is approximated as a circle.

[0064] the multiple access transceiver is adapted for operation in Earth orbit and configured to communicate with terrestrial mobile stations, the multiple access transceiver comprising: a data analyzer that determines a frame structure defining which time slots are assigned to which of a plurality of terrestrial mobile stations; a range calculator that determines, for each terrestrial mobile station, a distance from the multiple access transceiver to the terrestrial mobile station; a channel allocation module that allocates the plurality of terrestrial mobile stations to a plurality of channel blocks, the channel blocks having a terrestrial frequency and an orbital frequency offset; a signal timing module that determines timing of transmitted signals relative to the frame structure; and a signal modulator that modulates signals to the terrestrial mobile stations at terrestrial frequencies with an orbital frequency offset that corresponds at least approximately to an expected Doppler shift in signals transmitted to the terrestrial mobile stations due to relative movement of the multiple access transceiver and the terrestrial mobile stations, so that the terrestrial mobile stations receive the signals at terrestrial frequencies. The channel blocks may be assigned based on the relative positions of the satellite and terrestrial mobile station carrying the multiple access transceiver, with the orbital frequency offset varying in small increments, such as 5 kilohertz increments.

[0065] In certain embodiments, a multiple access base station having one or more transceivers handles communications with a plurality of terrestrial mobile stations, the terrestrial mobile stations being configured to anticipate base station communications with terrestrial cellular base stations that are within a limited distance from the terrestrial mobile station and / or are moving at less than a limited speed relative to the terrestrial mobile station. The multiple access base station comprises: a data analyzer that analyzes data received by the multiple access base station according to a frame structure, the frame structure defining which time slots are assigned to which of a plurality of terrestrial mobile stations, the frame structure including a plurality of slots each having a zero or non-zero time slot synchronization offset that results in variable transmission delays due to distances from the multiple access base station to the plurality of terrestrial mobile stations; a signal timing module that determines a signal timing adjustment to the frame structure of a transmission signal to the terrestrial mobile station based on a base-to-mobile distance between the multiple access base station and the terrestrial mobile station, the base-to-mobile distance exceeding a distance limit; and a programmable radio that can communicate communications from the multiple access base station to the terrestrial mobile station using a multiple access protocol and take into account the signal timing adjustment, so that the communications are compatible with, or appear to the terrestrial mobile station to be, communications between a terrestrial cellular base station and a terrestrial mobile station despite the base-to-mobile distance exceeding the distance limit.

[0066] The multiple access base station may be adapted to communicate with a plurality of terrestrial mobile stations, the plurality of terrestrial mobile stations comprising cellular telephone handsets, smart phones, and / or connected devices. The distance limit may be approximately 100 kilometers, 120 kilometers, or some other distance, and the base-to-mobile distance exceeds the distance limit. The multiple access protocol may be one of a CDMA-based protocol, an LTE protocol, a GSM protocol, an OFDMA-based protocol, an FDMA-based protocol, a TDMA-based protocol, an EGPRS protocol, or an EDGE protocol. The multiple access base station may be an orbital base station operating within Earth orbit, the distance limit being 120 kilometers, and the base-to-mobile distance of the plurality of terrestrial mobile stations being approximately 500 kilometers to approximately 750 kilometers. In another variation, the multiple access base station is a base station operable within the Earth's atmosphere, including being mounted on or in one or more of an airplane, a drone, and / or a balloon, the distance limit being 120 kilometers, and the base-to-mobile distance exceeding 120 kilometers.

[0067] The multiple access base station may include signal allocation logic for allocating the capacity of the multiple access base station, distributed across multiple time slots, multiple carrier frequencies, multiple orthogonal subcarriers, and / or multiple code sequences, to multiple terrestrial mobile stations, including the terrestrial mobile station. The programmable radio may be capable of listening for communications from the terrestrial mobile stations using a multiple access protocol, and may include a range calculator that determines, for each terrestrial mobile station of the multiple terrestrial mobile stations, a base-to-mobile distance of each terrestrial mobile station from the multiple access base station to the terrestrial mobile station, a receive timing module that determines the timing of the terrestrial mobile station's received signal relative to a frame structure based on the terrestrial mobile station's base-to-mobile distance, and an input signal allocator that allocates a listen time slot within the frame structure to listen for communications from the terrestrial mobile station, the listen time slot being timed based on the terrestrial mobile station's base-to-mobile distance, the listen time slot being one of multiple time slots, and the multiple time slots being variably delayed within the frame structure to account for the multiple access base station handling communications from multiple terrestrial mobile stations having multiple base-to-mobile distances.

[0068] The multiple time slots can be variably delayed within the frame structure to account for multiple terrestrial mobile stations having multiple base-to-mobile distances by allocating each of multiple different base-to-mobile distance ranges to each of multiple channel blocks. The multiple access base station can be an orbital base station operating in Earth orbit, and the multiple different base-to-mobile distance ranges collectively cover a slant range from a zenith distance to a minimum elevation distance, where the zenith distance is the distance between the zenith position of a satellite carrying the multiple access base station relative to a terrestrial mobile station and the minimum elevation distance is the distance between the position of the satellite when the terrestrial mobile station enters the satellite's design footprint.

[0069] The different base-to-mobile distance ranges may each range approximately 34-35 kilometers, and the difference between the zenith distance and the minimum elevation distance is 210-250 kilometers.

[0070] The design footprint of the satellite may be circular, elliptical, rectangular, etc., and may be independent of the antenna function and / or the shape of the antenna beam.

[0071] In some variations, a multiple access base station having one or more transceivers handles communications with a plurality of terrestrial mobile stations configured to expect base station communications with a terrestrial cellular base station that is within a limited distance from the terrestrial mobile stations and / or moving at less than a limited speed relative to the terrestrial mobile stations. The multiple access base station includes: a data analyzer that analyzes data received by the multiple access base station according to a frame structure that defines which time slots are assigned to which of the plurality of terrestrial mobile stations and according to a multiple access protocol that expects the terrestrial mobile stations to receive signals on specified frequencies and transmit signals on specified frequencies; a Doppler shift calculator that determines, for each terrestrial mobile station of the plurality of terrestrial mobile stations, a Doppler shift of each terrestrial mobile station due to the velocity of each terrestrial mobile station relative to the multiple access base station; and a channel allocation module that allocates each of the plurality of terrestrial mobile stations to a channel block within a plurality of channel blocks, each channel block having a terrestrial frequency and a Doppler frequency offset. a signal modulator that modulates a signal to a terrestrial mobile station at terrestrial frequencies with a Doppler frequency offset, the Doppler frequency offset corresponding at least approximately to an expected Doppler shift in a signal transmitted to the terrestrial mobile station due to relative motion of the multiple access base station and the terrestrial mobile station, so that the terrestrial mobile station receives the signal at terrestrial frequencies; and a programmable radio that is capable of receiving communications from the terrestrial mobile station using a multiple access protocol and that takes into account the Doppler frequency offset of the terrestrial mobile station, so that communications are, or appear to the terrestrial mobile station, compatible with communications between a terrestrial cellular base station and a terrestrial mobile station, even though the speed of the terrestrial mobile station relative to the multiple access base station exceeds a speed limit.

[0072] The velocity of a terrestrial mobile station relative to a multiple access base station may be a result of the multiple access base station being in Earth orbit, and the Doppler frequency offset may vary in 5 kilohertz increments.

[0073] The multiple access base station may have signal allocation logic for allocating the capacity of the multiple access base station distributed across multiple time slots, multiple carrier frequencies, multiple orthogonal subcarriers, and / or multiple code sequences to multiple terrestrial mobile stations, including the terrestrial mobile station.

[0074] The multiple access base station may provide uplink and downlink subchannels including a contiguous spectrum of uplink and downlink subchannels for each of a plurality of channel blocks, and the channel blocks may be allocated such that adjacent channel blocks are allocated at adjacent Doppler frequency offsets.

[0075] In a particular embodiment of a multiple access base station having one or more transceivers handling communications with a plurality of terrestrial mobile stations, the terrestrial mobile station is configured to anticipate base station communications with a terrestrial cellular base station that is within a limited distance from the terrestrial mobile station and / or is moving at less than a limited speed relative to the terrestrial mobile station, the multiple access base station further comprising a data analyzer configured to transmit signals received by the multiple access base station according to a frame structure defining which time slots are assigned to which of the plurality of terrestrial mobile stations, the frame structure comprising a plurality of slots each having a zero or non-zero time slot synchronization offset that results in a variable transmission delay due to distance from the multiple access base station to the plurality of terrestrial mobile stations, the multiple access protocol further comprising a multiple access protocol that identifies channel blocks within the plurality of channel blocks, each channel block having a designated terrestrial frequency and a designated time slot, the multiple access protocol identifying a channel block ... a data analyzer that analyzes the received data; a signal timing module that determines a signal timing adjustment for a frame structure of a signal transmitted to the terrestrial mobile station based on a base-to-mobile distance between the multiple access base station and the terrestrial mobile station, where the base-to-mobile distance exceeds a distance limit and each channel block is allocated a designated signal timing adjustment; a signal timing module that determines, for each terrestrial mobile station of the plurality of terrestrial mobile stations, a Doppler shift for each terrestrial mobile station due to the velocity of each terrestrial mobile station relative to the multiple access base station, where each channel block is allocated a designated Doppler frequency offset; and a dynamic channel allocator that assigns each of the plurality of terrestrial mobile stations to a designated channel block within the plurality of channel blocks based on the channel block's designated signal timing adjustment and designated Doppler frequency offset, where a number of channels within the designated channel block have or are expected to have the designated signal timing adjustment and the designated Doppler frequency offset.The system may include a dynamic channel allocator corresponding to a number of the plurality of terrestrial mobile stations; a signal modulator that modulates signals to the terrestrial mobile stations at terrestrial frequencies with a Doppler frequency offset, the Doppler frequency offset corresponding at least approximately to an expected Doppler shift in signals transmitted to the terrestrial mobile stations due to relative motion of the multiple access base station and the terrestrial mobile stations, so that the terrestrial mobile stations receive the signals at terrestrial frequencies; and a programmable radio that is capable of receiving communications from the terrestrial mobile stations using a multiple access protocol and that takes into account the Doppler frequency offset of the terrestrial mobile stations, so that communications are, or appear to the terrestrial mobile stations, compatible with communications between a terrestrial cellular base station and a terrestrial mobile station, despite base-to-mobile distance exceeding a distance limit and despite the terrestrial mobile station's speed relative to the multiple access base station exceeding a speed limit.

[0076] The following detailed description taken in conjunction with the accompanying drawings will provide a better understanding of the nature and advantages of the present invention. [Brief explanation of the drawings]

[0077] Various embodiments according to the present disclosure will now be described with reference to the drawings.

[0078] [Figure 1] 1 illustrates one environment in which the present invention may be used. [Figure 2] 2 illustrates additional examples of the environment of FIG. 1. [Figure 3] 1 illustrates an example of a frame-based protocol used between a base transceiver station and a mobile station. [Figure 4] 1 illustrates an example of the effect of propagation delay and the use of timing advance when using a time division protocol. [Figure 5] 1 illustrates an example of the use of the extended range feature of a time division protocol. [Figure 6]1 illustrates an example of the use of the extended range feature and timing advance in a time division protocol. [Figure 7] An example is shown of various MSs at different distances from a BTS, whose distances can be at least approximately determined. [Figure 8] FIG. 7 illustrates how various MSs at different distances are allocated time slots based on their determined distances to provide for sorted extended range communications. [Figure 9] 1 illustrates the coverage area of ​​a ring system using a synchronization offset. [Figure 10] 1 illustrates how timing is adjusted for a ring scheme. [Figure 11] 1 illustrates an example satellite footprint and the resulting distance range within that satellite footprint. [Figure 12] 1 shows an example of how different mobile stations are allocated different time slots based on their terrestrial location to implement a ring scheme and sorted extended range for TDMA communications. [Figure 13] 1 illustrates how different mobile stations are allocated different carrier frequencies based on their terrestrial location distance so that a ring scheme can be used with varying ring diameters for different carrier frequencies. [Figure 14] 1 shows how a satellite footprint can be subdivided into Doppler shift strips. [Figure 15] 1 is a flow chart of a measurement process for determining pseudorange and Doppler shift from an MS. [Figure 16] 1 illustrates how a satellite footprint can be subdivided into range rings, Doppler shift strips, and both range rings and Doppler shift strips. [Figure 17] 1 illustrates an example of range ring / Doppler shift cells of a satellite footprint. [Figure 18] 18 illustrates an example of allocation of the range ring / Doppler shift cells of FIG. 17 to specific carrier frequency and Doppler offset blocks. [Figure 19] 1 illustrates how the frequency spectrum is allocated to various Doppler offset blocks of a channel, taking into account the Doppler shift in communication between a BTS and an MS. [Figure 20] 1 illustrates an example of allocating cells in a satellite footprint based on the expected density of MSs per cell. [Figure 21] 21 illustrates an example channel allocation that may be used for the allocation and mapping illustrated in FIG. 20. [Figure 22] FIG. 1 is a swim diagram illustrating the process of setup and distance determination. [Figure 23] 1 illustrates an exemplary transceiver and associated components. DETAILED DESCRIPTION OF THE INVENTION

[0079] In the following description, various embodiments are described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that the embodiments may be practiced without the specific details. Additionally, well-known features may be omitted or simplified so as not to obscure the described embodiments.

[0080] The techniques described and proposed herein include the design of a satellite-based base transceiver station (BTS) that implements a transceiver for transmitting to and receiving from Earth-based devices such as a mobile station (MS), which is a satellite or part of a satellite that may operate in orbit and is a mobile station designed for use with a terrestrial BTS. In many cases, the MS can be used without requiring any physical modifications or even any software modifications, in which case the MS may be in communication with the transceiver and BTS and may not be aware that the BTS is not a terrestrial BTS, or more generally, that the BTS is operating outside of the design assumptions of the MS, such as at a relative distance greater than the design assumptions of distance, at a relative velocity much greater than the relative velocity for which the MS would be designed, and other design assumptions.

[0081] With an orbital transceiver and terrestrial MS, the BTS would be outside the design assumptions of the MS design, which assumes a maximum distance from the BTS to the MS of approximately 35 km, and that relative motion, such as the time derivative of the BTS-MS distance during communication, is either negligible or much less than the 7.2-7.8 km / s that would be experienced compared to an orbital transceiver. Other design assumptions may also play a role. For example, an orbital transceiver would have a limited time window to communicate because the satellite would rise above a minimum altitude relative to the MS until it was below the minimum altitude above the opposite horizon.

[0082] While many of the examples and details herein relate to orbital transceivers adapted, configured, programmed, etc., to close communications with MSs operating as if those design assumptions still apply, these techniques can be used outside of orbital examples. For example, they can be used for BTSs located high enough that the slant angle exceeds 120 km. For example, if a BTS can be mounted at an altitude of 1,130 meters, this is sufficient to enable line-of-sight (slant range) to MSs of 120 km or more. Platforms such as airplanes, UAVs, high-altitude drones, hot air balloons, high-altitude balloons, suborbital vehicles, spaceplanes, mountains, or even some very large towers may be conditions in which some or all of these techniques find useful. It is also worth noting that the described techniques can be deployed even with a ground-based BTS, provided the antenna is oriented to serve MSs operating on platforms that create long communication ranges (e.g., greater than 120 km) and / or high Doppler shift environments, such as above approximately 200 KPH. This may include conditions where the MS is operating on the Earth's surface, in the atmosphere, or in a space environment, and the BTS is on the Earth's surface, either mobile (e.g., on some vehicles) or possibly stationary.

[0083] These techniques may also prove useful when the MS is in orbit and needs to operate as if the design assumptions were true, and the BTS is terrestrial and operates even when the design assumptions are not true, and can be adjusted to accommodate those MSs. For example, the MS could be used on a moving airplane, or possibly a future space station. A base station tower on the Earth's surface with a large enough antenna could perform operations to close communications with the MS while dealing with violations of similar design assumptions, such as long distances and high Doppler shifts.

[0084] BSC and MSC (including home location register or HLR, and subscriber handling) functions may also be satellite-provided, or some of the functions not required in orbit may be implemented on the ground. The BTS, BSC, and / or MSC functions may be implemented using conventional off-the-shelf software-defined radios, or commercial-grade (or proprietary) hardware / software, so long as they can be programmed, configured, or adapted to perform the required functions.

[0085] The BTS may provide its functionality despite the extended distance between the BTS and the MS, which causes distance-induced power reduction and distance-induced flight time delay, as well as the effects of greater relative motion between the BTS and the MS beyond the typical Earth-based relative motion the MS might experience with respect to the BTS. The latter causes Doppler shifts, and conventional MSs, such as cell phones, may not be designed to handle Doppler shifts as large as those caused by a satellite moving relative to the MS at speeds of 7.6 km / s, sometimes experienced in LEO. These Doppler shifts will be variable, as they vary with the location of the MS within the satellite's footprint. Locations behind the satellite will see negative Doppler shifts, while locations in front of the satellite will see positive Doppler shifts.

[0086] Power levels should be addressed. As an example, the GSM specification requires mobile phones to spike their transmit power to 1–2 W (depending on frequency) when necessary. Mobile phones do this naturally on the RACH, and once a channel is allocated, the BTS can command it to be quiet when it does not need to transmit "loud." With a suitable BTS antenna capacity, 2 W may be enough transmit power to close a link at a reasonable elevation angle at an altitude of 500 km using an antenna with a form factor such as 50 cm, with the rate of data transfer adjusted as needed. For example, one implementation might focus on narrowband messaging with 2G speeds and short data bursts rather than attempting to support data rates such as 4G LTE, although the latter may be possible. In such an approach, lower power levels and higher data rates could still typically be supported by space-based base stations with sufficient antenna technology. However, lower power levels and faster data rates for devices on the surface tend to increase the power and mass requirements of the space segment.

[0087] As used herein, a "footprint" refers to an area on the Earth's surface that is within the range of closing a communication channel with a BTS on a satellite. While a circular footprint is used in the examples herein, it should be understood that the footprint may not be circular and may depend on obscuring factors, the shape of the Earth's surface, atmospheric conditions, etc. In some examples, the footprint is a "design footprint" that differs from the actual footprint. For example, a satellite may actually be some distance away and therefore be able to communicate with mobile devices within the satellite's actual footprint, but for selectivity, performance, or other reasons, a system using that satellite is designed for a different footprint, such as a footprint smaller than the actual footprint, i.e., a design footprint. The boundary of the design footprint may be a circle or ellipse projected by a satellite onto the Earth, centered at a point on the surface directly beneath the satellite and having a radius that the satellite is designed to cover, such as a particular slant range.

[0088] As used herein, "surface" refers to the location of an MS, but it should be understood that "surface" is not limited to the Earth's surface. When an MS is described as being surface-based or on the surface, the MS may be on the surface of the Earth, on the surface of a body of water, somewhat below the surface of the Earth or a body of water, on the upper floors of a building, in a structure that is not exactly at surface level, in an airplane or otherwise airborne but in the atmosphere, or in the hands of a person standing in a similar location. However, for clarity of explanation, the MS may be described as being on the surface of the Earth to distinguish it from elements that are in orbit. This is not to say that the systems described herein cannot be used with MSs in orbit. Where applicable, and unless otherwise stated, an MS in orbit may also be supported, even if the MS is not specifically modified to communicate with an in-orbit BTS, assuming the device is electrically, mechanically, and otherwise durable enough for on-orbit use.

[0089] As used herein, "in orbit" refers to being in a location, traveling at a speed relative to an inertial frame that is (more or less) stationary relative to the Earth's center of gravity, and experiencing little atmospheric resistance at that location so that orbit can be easily maintained. In some examples herein, orbital distances are given, which conventionally refer to approximate typical distances from a mean or normal point on the Earth's surface to describe orbits. "LEO" is used in some examples, and it should be understood that these examples can apply to orbits that are conventionally defined as LEOs but may still be somewhat outside the range considered to be orbits. Unless otherwise indicated, in orbit can also describe orbits around other celestial bodies, such as Mars, the Moon, moons of other planets, or even points of interest such as L1 or L2. In many of the examples herein, the BTS is in orbit around the Earth, and the MS is terrestrial. The teachings herein can be used for other situations, such as when the BTS and MS swap locations, or when similar challenges are encountered when, instead of Earth orbit, the BTS is in an airplane, unpiloted autonomous vehicle, balloon, etc., or more generally, when conditions exist where challenges such as distance, propagation delay, and / or Doppler shift exceed those that the MS is typically designed to support or experience, e.g., when design is envisioned going into the construction and / or programming of the MS.

[0090] In traditional TDMA communication systems, there are timing and signal power aspects that create conditions that close the communication link, i.e., that the received signal power is sufficiently higher than the noise / interference environment so that data can flow over the channel at the desired data rate and bit error rate, and that the communicating devices follow the expected protocol without abandoning at either end. As described herein, a satellite-based BTS can communicate with a surface-based MS designed for use with a surface-based BTS. The satellite-based BTS modifies TDMA communication with the MS in a manner that allows communication over some distance by accounting for variable propagation delays while remaining transparent to the MS. A constellation of satellites in LEO can provide continuous connectivity from orbits 400–500 km above Earth to MSs using traditional terrestrial communication technologies and protocols with acceptable economic deployment costs and reasonable service lifetimes. The BTS provides suitable timing for the TDMA frame structure, enabling orbital-range communications and a channel assignment or allocation scheme that supports the required range pseudorange and Doppler shift mitigation, addressing signal interference issues and mismatches associated with Doppler shift due to orbital interference. As a result, the BTS described herein can provide communications between spacecraft and terrestrial telecommunications devices, as well as communications using features and facilities of terrestrial telecommunications devices typically used for terrestrial telecommunications. This may extend the range of radio coverage of the communications system, enabling communications between spacecraft in orbit and mobile phones or other communications / wireless devices. The BTS may be used in communications systems that utilize multiple access techniques in the frequency and / or time domains (i.e., TDMA, FDMA, OFDMA, etc.) used by conventional mobile phones to communicate with spacecraft in orbit using GSM cellular communications protocols or similar terrestrial protocols.

[0091] The BTS may be implemented using a communication modality that employs multiple access schemes in the time and / or frequency domains, such as TDMA, FDMA, CDMA, OFDMA, etc., because the BTS handles RF signals that are sliding in both the time and frequency domains, which must handle the given distances involved and the associated velocities involved. Generally, unless otherwise indicated, the teachings herein can be applied to one or more of these example multiple access schemes and systems, where multiple mobile stations are communicating or attempting to communicate with the BTS, and to avoid interference, the protocol used provides multiple access by having each MS use a different time slot, carrier frequency, and / or code sequence. Thus, many examples are described with reference to TDMA / FDMA protocols, but can be extended to other protocols.

[0092] As used herein, distances may be expressed in units other than kilometers, and in those cases, certain conversions are assumed. For example, the speed of light in a vacuum may be a conversion factor where distances are expressed in units of seconds, such as microseconds and milliseconds. The propagation delay in a particular situation may be the speed of light in a vacuum or may be longer, but it will be clear to one skilled in the art how to determine a distance given a propagation delay expressed in seconds from the context.

[0093] Similarly, distance and / or time may be expressed in bits, assuming a particular bit rate. For example, if the bit rate is 270.833 kbit / s, a period represented by "156.25 bits" would refer to a period of 576.92 μs, and a distance represented by 10 bits would correspond to a distance of 5.538 km, since transmitting 10 bits occupies 36.92 μs, and in a period of 36.92 μs, a signal can travel a distance of 5.538 km (round trip) at the speed of light in a vacuum. The difference between the speed of light in a vacuum and the actual propagation speed may vary, and this may be taken into account, but these details may be omitted for illustrative purposes and to avoid complicating the explanation.

[0094] Description of an exemplary BTS and its operation The present invention will now be described in detail with reference to specific, though not necessarily preferred, embodiments of the invention. These specific embodiments are by way of example, and those skilled in the art of multiple access communication systems and orbital mechanisms will recognize, upon reading this disclosure, that other variations are possible and that the present disclosure pertains to many types of multiple access communication systems between MSs on the surface of a planetary body and spacecraft BTSs operating in various orbits around that body.

[0095] In many examples herein, the orbits of the satellites including the BTSs are given as circular orbits having an altitude of 500 km, but it should be understood that the teachings herein apply to other orbits adjusted accordingly. In some examples, the BTSs operate as or simulate the operation of a GSM BTS, or fully perform functions for communicating with terrestrial mobile stations (MSs) near the surface of the Earth, i.e., not in orbit.

[0096] In some of the examples herein, a satellite's footprint is given as the set of points on or near the Earth's surface where the satellite is at or above a minimum elevation angle when viewed from the MS. As used herein, when a satellite is directly overhead the MS, the MS "sees" the satellite at an elevation angle of 90 degrees (thus, the MS is at nadir relative to the satellite). In the examples herein, the slant range is 90 degrees to 40 degrees, although other slant ranges, greater or lesser, may be used. Those skilled in the art, after reading this disclosure, will understand how to modify the calculations herein accordingly.

[0097] Using a 6,370 km radius relative to the Earth and assuming a 500 km circular orbit, an MS within the footprint is 500 km from the BTS when the elevation angle is 90 degrees. Using basic geometry, it can be determined that from a point on the Earth's surface, a satellite in a 500 km circular orbit would appear at an elevation of approximately 40 degrees relative to the horizon at that point if the distance from the satellite to that point is approximately 741 km. The propagation delay of a signal between an MS and a satellite BTS is a function of distance, and the distance to a satellite in orbit is a function of the orbital radius and the elevation angle, which is the angle between the satellite's position vector and the MS's position vector. When the elevation angle is 90 degrees, i.e., the satellite is overhead and the MS is at a surface point in the direction of the satellite's nadir, the distance can be taken as, or approximately, the difference between the orbital radius and the Earth's radius. When the elevation angle is less than 90 degrees, the distance can be calculated. For some minimum elevation angle at which a connection is expected to be made, it is generally considered that the angle will correspond to the longest distance supported for such a connection. For a minimum elevation angle of 40 degrees, the interaction time between the MS and satellite BTS may be calculated at the BTS and / or MS as follows: For a 40 degree elevation angle, 500 km circular orbit, the Earth's central angle is ACOS(R_earth*COS(min_elev) / (R_earth+h))-min_elev=4.74 degrees, where R_earth=6370 km (Earth's radius), min_elev is the minimum elevation angle (40 degrees in this example), and h is the satellite altitude (500 km in this example). The time it takes for the MS to move from a minimum elevation angle of 40 degrees relative to a satellite on one horizon to a minimum elevation angle of 40 degrees relative to a satellite on the other horizon may be calculated as the time it takes the satellite to travel 2*4.74=9.47 degrees of the Earth's surface. As described herein, a satellite in a 500 km circular orbit is moving at 7.11 km / s relative to the Earth's surface. So the time in seconds it takes to travel 9.47 degrees across the Earth's surface at this speed is approximately 9.47 degrees * Pi / 180 * (R_earth + h) / 7.11 km / s = 159.86 seconds. Of course, other minimum elevation angles can be used and the calculations adjusted accordingly.This assumes that the MS travels directly through the center of the satellite footprint as it passes overhead. Under various conditions, the BTS and / or MS may take this value of 159.86 seconds into account to plan and adjust communications and scheduling.

[0098] Actual distances may vary depending on atmospheric effects and other physical interactions. In this example, the BTS is configured to support communications with devices within a range of approximately 500 km to 741 km between the BTS and the MS, and must support the MS if those MSs view the BTS at an elevation lower than 40 degrees above the local horizon. In some implementations, the lower limit is lowered from the orbital distance to allow communication with MSs well above the Earth's surface. For example, if the MS is located in an airplane flying at 15,000 meters, but the satellite assumes a minimum distance of 485 km, it cannot support that MS. In another example, a satellite in geostationary Earth orbit (GEO) may serve the BTS, in which case the minimum distance is approximately 35,786 km.

[0099] 1 illustrates one environment in which the present invention may be used. As shown therein, on the surface 102 of the Earth (or a planetary or celestial body related thereto) are several mobile stations (MSs) 104, which may be mobile, or in some cases may be portable or stationary but function as MSs. These MSs 104 communicate with orbiting BTSs 106 via BTS-to-MS links 108. As illustrated, each of the BTSs 106 has an orbital velocity relative to the surface 102 and some separation distance.

[0100] 2 illustrates an additional example of the environment of FIG. 1, in which person 202 has various devices 204, including elements that make up a mobile station, such as a smart phone 204(1), a laptop computer 204(2), and a tablet device 204(N), each of which is configured and / or adapted to communicate with a terrestrial BTS 206, and when person 202 desires to communicate or access the Internet 208 and / or Internet-connected resources 210, they can do so via BTS 206. Other examples of devices may be devices without a user interface (e.g., "Internet of Things" devices), such as industrial or domestic appliances that interact over a network.

[0101] FIG. 3 illustrates an example of a frame-based protocol used between a base transceiver station (BTS) 306 and a mobile station (MS) 304 over a surface-to-orbit link 308 using a protocol such as TDMA or other protocols that may also be used for terrestrial communications.

[0102] As described in the examples herein, the BTS uses various techniques that allow it to transparently support MSs configured solely for terrestrial cellular communications. Several examples will be described, but first, several schemes for range extension of TDMA systems will be described.

[0103] Figure 4 illustrates how a timing advance mechanism can be used. It should be understood that where a timing diagram is shown, it is implied that there is a corresponding module with logic that follows the timing diagram. Figure 4 also illustrates the effect of propagation delays and the use of timing advance when using a time division protocol.

[0104] In Figure 4, eight time slots of a TDMA frame are shown. These may be part of a larger data structure that is omitted for clarity of illustration. When an MS or BTS has time slots allocated for MS-BTS communications, each of the devices is programmed to use its local copy of the system clock to determine when to start transmitting, when to stop transmitting, when to start listening, and when it can stop listening, which will correspond to their allocated time slots.

[0105] In FIG. 4, the top line illustrates a transmission 402 from an MS. As used herein, "Tx" is an abbreviation for transmit, transmitter, or transmitting, as the context may require. Similarly, "Rx" is an abbreviation for receive, receiver, or receiving, as the context may require. As used herein, a "transmission" is something that is sent from a transmitter as part of a communication or signal, and a "reception" is something that is received. If the transmitter and receiver have the same system time and there is a measurable propagation delay, a transmission and its corresponding reception do not occur at the same system time. From the MS's perspective, the process of sending transmission 402 occurs entirely within time slot 1, and it is assumed here that the MS has been allocated time slot 1. If transmission 402 occupies a majority of the allocated time slot, it will be received at the BTS after the propagation delay as BTS Rx and then as reception 404, which is partially received during time slot 2. This is undesirable. In timing advance, the MS sends a transmission 412 before time slot 1 begins (from the MS's clock timing) and when it is received at the BTS after a propagation delay as reception 414, it is completed entirely within time slot 1 at the BTS.

[0106] Figure 5 shows an example of the use of the extended range feature of a time division protocol. The time slot duration in this example is approximately 0.28 milliseconds, representing a distance of 85 km, so that an MS can communicate with a BTS without requiring any timing advance if it can delay its transmission at the BTS by the duration of one time slot. The extra time slot serves as an additional guard period.

[0107] As illustrated in FIG. 5, the MSs have eight time slots, but only the first (slot 0), third (slot 2), fifth (slot 4), and seventh (slot 6) time slots are in use. As illustrated, MS1 transmits 502(0) during time slot 0, MS2 transmits 502(2) during time slot 2, MS3 transmits 502(4) during time slot 4, and MS4 transmits 502(6) during time slot 6. The BTS receives reception of such transmissions, receiving reception 504(0) (referred to as "(0)" in the figure) beginning any time after the start of time slot 0 and ending any time before the end of time slot 1. Similarly, the BTS receives reception 504(2) ("(2)") ending any time after the start of time slot 2 and before the end of time slot 3, and similarly for receptions 504(4) and 504(6).

[0108] FIG. 6 illustrates an example of the use of the extended range feature and timing advance in a time division protocol. As shown, MSs transmit 602 during their respective time slots, and the BTS receives such transmissions and receives reception 604 at the appropriate times. As illustrated in FIG. 6, with the timing advance and extended range features combined, the maximum allowable MS-BTS distance can be 35 km + 85 km = 120 km. Whether using the timing advance feature alone, the extended range feature alone, or both, the BTS can manage which one to use. The MS may not even be aware that the extended range feature is being used, since the BTS simply will not allocate every other time slot. For example, if the BTS determines that the MS is 60 km away, the BTS may tell the MS to use a 0-bit timing advance (i.e., no timing advance) and not allocate the next time slot to any MS. If the BTS determines that the MSs are 95 km away, the BTS may tell the MSs to use an 18-bit timing advance and not allocate the next time slot to either MS.

[0109] Figure 7 shows an example of various MSs at different distances from a BTS, where their distances are at least approximately determined. A ~d G There are seven MSs labeled A through G with respective pseudoranges between . This illustrates how MSs can be sorted by distance.

[0110] FIG. 8 illustrates how various MSs at different distances in FIG. 7 are allocated to time slots based on their determined distances to provide sorted extended-range communications. As shown in FIG. 8, time slot 0 is allocated to user G, which is closest to the BTS in FIG. 7, and time slot 6 is allocated to user E, which is farthest from the BTS in FIG. 7. Only seven time slots are allocated. Considering the range of propagation delays, transmissions 802 from various MSs are received as receptions 804, so that no transmission 802 overlaps with another transmission 802 and all of the receptions 804 are received within a TDMA frame period. As illustrated in FIG. 8, signal bursts are progressively delayed across the time slots, which may eliminate collisions and interference.

[0111] The sorted extended range scheme provides higher throughput than the extended range mechanism, but can still tolerate MS-BTS distances of up to 120 km and 7 / 8 of the maximum frame capacity (as long as the total distance separation between two sorted MSs does not exceed 85 km). In some cases, more than one time slot will be allocated to split the distance separation, so that if N time slots are allocated in this manner, where N is between 1 and 7, the throughput will be 1-(N / 8) of the maximum frame capacity. If a time slot is 156.25 bits, the separation can be allocated as the number of bits distributed between the time slots. If this logic is performed by the BTS, an implementation of the sorted extended range mechanism does not require any modifications to the MS logic or operation, since the BTS orchestrates the calculated time slot allocation.

[0112] Figure 9 illustrates the range of a BTS using the ring extension range mechanism and the coverage area of ​​a ring scheme using synchronization offset. The cross-hatched area is the area supported by the BTS. All MSs must be at least d * If the BTS assumes that the distance between the *MSs closer than d are not supported. Using the 35km range obtained using the timing advance mechanism, without requiring any MS corrections, * ~d * It can support distances between MS and BTS of up to 35 km. * = 85 km, but other minimum communication distances can be used, so in this example the BTS can support MSs in the range of 85 km to 120 km from the BTS.

[0113] Figure 10 illustrates the timing of transmission and reception and how the timing is adjusted for the ring system. * is directly scaled by the time slot synchronization offset selected for use by the BTS on the uplink subchannel. At the MS, transmission 1002, which the MS sees as time slot 0, is sent by the MS. At the BTS, the * The signal 404 is received after a propagation delay that is d times the speed of light. * Since the value of d is known, the BTS can adjust the timing of that time slot by a certain offset (T_offset=2×d * 1004 in time slot 0 of the BTS.

[0114] FIG. 11 illustrates an example of a satellite footprint, rings, and the resulting range ranges of the rings of that satellite footprint. Satellite 1102 would have a coverage footprint illustrated in FIG. 11 as footprint 1104 in an edge-on view and as footprint 1106 from above. Different cross-hatched areas within footprint 1106 indicate different range ranges between the surface and the BTS, forming rings. In this example, there are seven rings, but more or fewer rings may be present as needed. In this example, the rings are labeled r0 through r6, corresponding to BTS-to-MS distances (which may be pseudorange ranges) {500-534.4, 534.4-568.9, 568.9-603.3, 603.3-637.7, 637.7-672.1, 672.1-706.6, 706.6-741} (all in km). Each of these ranges happens to be just under 35 km, which is a useful design choice, as explained below. Other applications may use different design choices. In an initial handshake, such as the RACH process, the BTS-MS distance is determined, from which the MS can be allocated to one of the rings within the satellite footprint.

[0115] As explained below, all MSs allocated to a particular one of the rings may be allocated to one carrier frequency, or a block of carrier frequencies transmitted on a TDMA / FDMA frame, or other approaches may be taken. In some embodiments, the rings may overlap so that an MS may be in more than one ring. For example, the first two rings may be 490-540 and 530-580, so that an MS that is 535 km from the BTS may be in either of these rings.

[0116] Depending on the desired application, the Orbit BTS may change its protocol and operation in one of three ways: (1) a timing advance scheme; (2) an extended range scheme (using fewer than all available time slots and instead using unused time slots as guard bits); (3) a sorted extended range scheme (using fewer than all available time slots and instead using unused time slots as guard bits assigned between time slots where the time slots are allocated based on expected variable delays); or (4) a ring extended range scheme (where coverage is a ring with an inner circle not supported). (5) a multiple ring extended range scheme (similar to scheme (4) but with multiple rings to simultaneously cover different ranges of distance and MSs assigned to rings based on BTS-to-MS distance); and (6) a sorted channel-to-ring assignment scheme (similar to scheme (5) but with different rings associated with different carrier frequencies, where MSs within the distance range of that ring are assigned time slots using scheme (3)), or a combination of one or more of (1), (2), (3), (4), (5), and (6).

[0117] Timing advance, ring, and sorted extended range methods Figure 12 illustrates a first example of a BTS using the timing advance scheme, the ring extended range scheme, and the sorted extended range scheme, where different mobile stations can be allocated different time slots based on their terrestrial location to implement the sorted extended range scheme for TDMA communications, and the ring scheme is used to make the range terrestrial.

[0118] In this example, satellite 1202 is * The satellite is in orbit at an altitude of d * There is no need to support closer MSs and the maximum distance from the BTS is some d maxIt is assumed that there is no need to support remote MSs. * ~d max There are five MSs, MS1-MS5, labeled by their distance from the BTS, ranging from 1 to 7. MSs MS1-MS5 are allocated time slots 4-0, respectively, with time slots 5, 6, and 7 unallocated, allowing the sorted extended range scheme to be used with three time slots worth of guard time. This corresponds to approximately 486 bits and is illustrated in MS frame 1204. As a result of the distance between the MSs and the BTS, signal bursts for MS1-MS5 are received as shown in BTS frame 1206.

[0119] In this example, the timing advance is 22 bits (required for a 12 km range) and the ring synchronization offset is 875 bits, which corresponds to a distance of approximately 488 km, so d * The extended range guard time uses up three time slots, but the MS-BTS distance (i.e., d max -d * ) for timing advance. Assuming a maximum range of 35 km, which can be 0 to 63 bits, the range of the sorted extended range scheme can be from about 35 km to about 640 km, depending on the number of time slots allocated for guard time, as shown in Table 1. In Table 1, the range assumes that the full range of 0 to 63 bits of timing advance is available. [Table 1]

[0120] This TDMA frame structure allows for satellite-based wide cellular coverage over a wide geographic area. Even with this solution, there are still operational issues and challenges that must be resolved. First, each frame has barely more than half the potential throughput of a typical GSM frame. Second, in this configuration, each frame is subject to a variable Doppler shift of plus or minus approximately 35 kHz (which varies from solution to solution depending on orbit selection, slant range, frequency usage, etc.). However, the Doppler shift issue can be mitigated using the on-orbit BTS methods and apparatus described herein. The timing issue can be resolved using the following method.

[0121] Timing advance and sorted channel-to-ring allocation scheme Figure 13 illustrates how different mobile stations are assigned different channels based on their terrestrial location relative to the BTS, allowing for the use of ring schemes with varying ring diameters for different channels. As shown there, a scheme using timing advance (for a range of approximately 0-35 km) and a sorted channel-to-ring allocation scheme can provide another approximately 241 km of range without running out of time slots. In the sorted channel-to-ring allocation scheme, the satellite footprint is divided into rings, with each ring paired with a separate carrier frequency, as illustrated in Figure 11. Each ring operates at a different synchronization offset.

[0122] As used herein, a channel may include one or more specific frequency divisions within a protocol, such as a group of carrier frequencies. In FIG. 13, the supported pseudorange range between the nearest and farthest potential targets is 241 km, distributed among seven pseudorange range rings. This results in a coverage range of approximately 34 km per ring, and the synchronization offset may vary for different rings allocated to channel blocks or sets of channels. By making the offset between channel blocks less than approximately 35 km, full throughput is possible within each channel by eliminating the need for an extra slot guard period, and then the timing advance by itself is sufficient.

[0123] The RACH request burst can be used to determine the propagation distance of each MS from the signal. Using a broadcast channel (BCCH), the BTS can constantly or periodically inform MSs on the RACH about which carrier frequency and time slot the BTS will assign to that MS for uplink use. The BTS will know exactly when the MS transmits its RACH burst and can count the number of bits between that time and the time the actual burst arrives. By dividing that number of bits by the channel bit rate (270.83 kbps for GSM), the BTS can calculate the round-trip propagation delay. The BTS then calculates the propagation distance, or pseudorange, by dividing the speed of light by the round-trip propagation delay. Depending on the calculated pseudorange, each MS qualifies its allocation to channels within a particular channel block. For example, in the configuration shown in Figure 13, channels in channel block b0 are allocated to MSs that have calculated pseudoranges between 500 km and approximately 534 km, channels in channel block b1 are allocated to MSs that have measured pseudoranges between approximately 534 km and approximately 568 km from the on-orbit BTS, and similarly for the other ranges shown in Figures 11 and 13.

[0124] The first channel block b0 has its uplink TDMA frame offset from the transmitted uplink frame by the same amount as shown in Figure 12. The next channel block b1 has its frame offset by approximately an additional 62 bits from the frame of channel block b0. Thereafter, the frame of each channel block has an additional offset of approximately 62 bits compared to the previous channel block (i.e., channel block b i+1 The frame is divided into channel blocks b i (The range rings are offset approximately 62 bits from the frame of the GSM mobile station. Each bit of the frame offset corresponds to approximately 555 meters, and each ring / channel block extends approximately 34 km further than the previous one. This configuration utilizing 62 bits creates various coverage rings, each approximately 34 km long. By assigning various synchronization offsets, each channel block represents coverage for a different ring in space (and the Earth's surface). If the channel blocks are given synchronization offsets in 62-bit increments and a traditional GSM implementation is used, full throughput can be achieved on all channels, and very extensive coverage can be achieved. This can be done without requiring any modification of the GSM mobile station. A top-down view of the range rings is shown in Figure 11. The channel blocks in each range ring are defined by a characteristic "distance range," defined for this particular implementation in the key to the left of Figure 11.

[0125] Doppler shift handling While the above schemes and their variations may provide maximum throughput across all channel spectrums, the frequency of transmission may differ between transmit and receive due to the relative motion of the BTS and MS. Using the Doppler solution, scenarios can be considered in which multiple MSs are within similar pseudorange ranges from the on-orbit BTS but may experience a wide range of variation in perceived carrier frequency shift. For example, in Figure 11, consider two MSs calculated to be within the same ring / channel block b6. In this case, one MS is positioned at the top-forward tip of the satellite coverage footprint, and the other is positioned at the bottom tip of the satellite coverage footprint.

[0126] In Figure 11, the satellite is located directly above the center of the coverage area shown for channel block b0 (the origin of the arrow) and is moving in the direction of the arrow labeled "velocity." The first MS ahead of the satellite's velocity vector experiences a positive Doppler shift in the receive frequency, while the second MS behind the satellite's velocity vector experiences a negative Doppler shift in the receive frequency. If these MSs are allocated the same frequency, the satellite may receive signal burst frequencies from the MSs that are several kilohertz apart (up to 70 kHz apart for the 1800 / 1900 GSM band). Furthermore, allocating adjacent channels to MSs that experience significantly different Doppler shift environments can result in signal interference at the satellite.

[0127] FIG. 14 shows how a satellite footprint can be subdivided into Doppler shift strips in a manner that alleviates this problem. As illustrated therein, consider a satellite 1402 traveling at a certain velocity relative to the Earth's surface 1404. Satellite footprint 1406 is the view from the satellite at the velocity shown. MSs within area 1410 of the satellite footprint 1406's vector will experience a positive Doppler shift within the receive frequency of signals from satellite 1402, while MSs within area 1412 of the satellite footprint 1406's vector will experience a negative Doppler shift within the receive frequency of signals from satellite 1402. A specific Doppler shift within the receive frequency can be determined using simple geometry, and for a range of Doppler shifts, satellite footprint 1406 can be divided into strips bounded by contour lines, which can be assigned values ​​1420 for their respective Doppler shifts.

[0128] In three-dimensional space, given sufficient information, the Doppler shift at any point within the satellite footprint can be calculated by the BTS or MS. One way to do so may assume that all vectors are represented in the Earth-Centered, Earth-Fixed (ECEF) coordinate frame (also known as the Earth's rotating frame because it is the coordinate system that rotates the Earth around its axis in space). In this process, each vector is treated as a vector quantity with three component values, such that each component value in the vector represents a value along each dimension of the coordinate frame represented by the vector. Such numerical values ​​may be stored in memory for manipulation by a processor.

[0129]

number

number

number

number

number

number

number

number

number

number

number

[0130] In Equation 1, D is the calculated Doppler shift and λ is the wavelength of the carrier frequency, which can be calculated when the carrier frequency is divided by the speed of light.

[0131] As an example, consider a spacecraft operating in an equatorial orbit at an altitude of 500 km, which happens to be directly over the meridian at a particular moment (e.g., the direct nadir relative to the satellite is the intersection of the equator and the meridian). At the same particular moment, a stationary MS1430 is positioned almost below sea level on the spacecraft, but is resting on the equator at 1 degree east longitude (e.g., its latitude and longitude position may be written as [0, 1]).

[0132] In this scenario, the satellite's ECEF position coordinates are approximately [6870 km, 0 km, 0 km]. The spacecraft's velocity vector, in a circular orbit at 500 km, is approximately perpendicular to the position vector and (for an equatorial orbit) parallel to the equator. The magnitude of the velocity vector relative to the Earth's surface can be calculated as SQRT(mu_earth / (R_e+h))-w_earth*(R_e+h) = 7.11 km / s, where mu_earth is the Earth's gravitational constant (mu_earth=398658.366 km 3 / s 2 ), R_e is the radius of the Earth at the equator (R_e approximately 6370 km), and w_earth is the angular velocity of the Earth's rotation (w_earth=7.27*10 -5 where R_earth*cos(1 degree), R_earth*sin(1 degree), 0] = [6369 km, 111 km, 0]. The ECEF position of this stationary MS relative to the spacecraft is therefore [6369 km, 111 km, 0] - [6870 km, 0 km, 0 km] = [-501 km, 111 km, 0]. The Doppler shift of the 1900 MHz signal received by this MS from the spacecraft is therefore as shown in Equations 2, 3, and 4.

number

[0133] As explained above, the signal received at the BTS from the MS on the RACH can be used to calculate the pseudorange. That signal can also be used to approximate the Doppler shift from the MS. The BTS knows the carrier frequency on which the RACH is on, just as it knows the time slot on which it is on. Therefore, when the BTS receives a RACH burst, it can measure the center of the burst frequency and calculate the offset (difference) from the expected center frequency on the RACH. This may or may not require the satellite BTS to listen over a wider frequency range on the RACH, depending on the amount of Doppler shift the system experiences.

[0134] Figure 15 is a flowchart of a measurement process that can use the RACH for a BTS to determine pseudorange and Doppler shift from an MS. The RACH can be indicated when the MS wants to initiate a session (e.g., send an SMS text, make a phone call, send data). The Doppler shift value does not need to be measured / updated frequently. The Doppler shift value changes with the time it takes to request access to the channel and transmit data, and the payload is typically not large enough to impair the system's ability to transmit and receive signals. In cases where it may be an issue, the BTS can make predictive changes and assume the MS is not moving at high speed. This process can be used for satellite BTSs when managing pseudorange and Doppler shift measurements to adjust channel allocation / distribution.

[0135] As illustrated in the flowchart of Figure 15, at the start of the process, the satellite BTS broadcasts RACH timing information on the BCCH channel (step 1501), and then the MS learns the time slots in which the RACH is on (step 1502). Knowing this, the MS transmits a burst during the RACH time slots that the BTS instructed the MS to use (step 1503). The burst arrives at the BTS with a frequency delay and offset (step 1504). The BTS then has two threads: one for delay and one for Doppler shift. In the first thread, the BTS counts the number of bits the burst is delayed by (step 1505), divides the counted number of bits by the channel bit rate to calculate the round-trip delay (step 1506), and then divides the round-trip delay by twice the speed of light to calculate the pseudorange (step 1507). In the second flow, the BTS measures the center frequency of the burst (step 1508) and subtracts it from the center frequency of the RACH to calculate the Doppler shift (step 1509). The two threads are then combined, and the BTS checks the channel configuration matrix to allocate the MS a channel configured for its pseudorange and Doppler shift (step 1510). The BTS then checks whether a channel is already configured (step 1511). If yes, the BTS allocates the configured channel to the MS (step 1513); if no, the BTS configures a channel for the detected MS's pseudorange and Doppler shift environment (step 1512), and the process ends.

[0136] Because the BTS can acquire knowledge of the Doppler shift from each MS, it can assign a specific Doppler shift range to a particular channel. In doing so, each individual channel may have its own specific, locally reduced range of potential Doppler shift values. For example, some channels may only experience a 0-5 kHz shift within the carrier frequency because the channels are allocated to MSs within the specific strip shown in Figure 14, while other channels may only experience a 25-30 kHz shift within the carrier frequency. Because the Doppler range is well-defined and more localized for each channel, it can be used as a modifier for channel assignment and allocation. This approach makes it much simpler to handle wide Doppler shift variations across the set of serviceable MSs within a satellite footprint.

[0137] Referring back to Figure 14, that figure illustrates the Doppler shift perceived at various locations across a satellite coverage footprint. Intuitively, half of the satellite footprint in the direction of the velocity vector experiences a positive Doppler shift, and the other half experiences a negative Doppler shift. What is less intuitive is that the geometry of the Earth's curvature creates a Doppler shift map in the satellite footprint that is described by increasingly curved contours.

[0138] One approach described herein is to assign channel blocks to predetermined Doppler shift blocks in the same way that channel blocks are assigned to rings of predetermined pseudorange ranges, as described above. When carrier frequencies are assigned to specific pseudorange ranges and Doppler shifts, the actual Doppler shift experienced by each channel is unique to the frequency of that channel. An implementation of this scheme will take this into account. In one design, the Doppler shift contour map uses the center frequency of the spectrum in question, and the illustration assumes 1900 MHz GSM with a satellite at an altitude of 500 km and an elevation angle of 40 degrees.

[0139] In Figure 14, each dashed line defines the boundary of a Doppler shift strip used to localize the potential Doppler shift of each channel and thus minimize interference. The curvature of the contour lines on the map is a result of the geometry of the communication link and the frequency of the communication.

[0140] FIG. 16 illustrates how a satellite footprint can be subdivided into range rings, Doppler shift strips, and both range rings and Doppler shift strips. As illustrated, the pseudorange ranges form rings and the Doppler shift contours form strips. When these are overlaid on a grid (not necessarily a Cartesian or linear grid), the satellite footprint 1602 is divided into grid cells bounded by a first range value, a second range value, a first Doppler shift value, and a second Doppler shift value. Each of these grid cells thus corresponds to a combination of pseudorange range and Doppler shift range relative to an on-orbit BTS and is a qualifier of the MS allocated to a particular channel (or one of a set of particular channels).

[0141] Note that while the satellite footprints depicted herein are essentially circular, this is not required. The footprints may be more square or elliptical in shape depending on which antennas are used on the satellite and how they are configured. A non-circular footprint may offer advantages in that it may increase or decrease the propagation delay and / or Doppler shift environmental spread within the footprint.

[0142] This grid represents a combination of pseudorange ranges and Doppler shift ranges corresponding to the pseudorange and Doppler shift channel block modifications. The grid cells described above are assumed to be symmetric about the satellite's velocity vector. This means that each grid cell off the centerline of the satellite's coverage area has a "twin" grid cell on the other side of the satellite footprint. The term "twin" grid cells is used because both MSs in these grid cells operate at similar pseudoranges and Doppler shifts, and therefore these two grid cells share a "bucket" logically associated with a pseudorange range and a Doppler shift range (i.e., an MS is logically assigned to a bucket based on whether the MS's pseudorange is within the pseudorange range allocated to that bucket and whether the MS's Doppler shift is within the Doppler shift range allocated to that bucket).

[0143] Handling Doppler shift for certain MS devices Some protocols may be more resilient to Doppler shift when demodulating downlink signals, while others may not. For some devices or some protocols, a 2.5 kHz shift may be the Doppler shift threshold. However, even some low-end cellular phones may be able to demodulate BCCH signals at offsets of up to 20 kHz from what would typically be the center carrier frequency of that channel. This may be related to interactions between the BTS and the MS on the frequency correction channel (FCCH), another broadcast channel used to synchronize the local clock with the BTS. This synchronization is ultimately the information the phone needs to subsequently demodulate the BCCH and other downlink channels. Therefore, Doppler shift strips larger than the exemplary 5 kHz strip used in the example above can be used. For example, the buckets can be adjusted and stretched to accommodate a wider range of Doppler shifts, up to at least 20 kHz in either direction. In practice, this can obviate the need for Doppler shift bucketing if the satellite footprint is small enough that the highest Doppler shift case is less than 20 kHz. This may not be the case for other protocols such as NB-IoT, which use much smaller signal bandwidths. NB-IoT also has other differences, such as where the multiple access protocol is the LTE NB-IoT protocol and the distance limit is 40 km, which exceeds the base-to-mobile distance.

[0144] Channel Allocation As described herein, a BTS can support multiple transceivers, each using its own carrier frequency, and each of the multiple transceivers can in turn support up to eight MSs. Because a transceiver can be configured to use one of many possible carrier frequencies, a channel can be associated with the transceiver. In the above example, there are 123 available carrier frequencies. While some of these many carrier frequencies can be allocated to MSs as needed, some advantages can be gained if they are assigned by grid cells, so that buckets of similarly positioned MSs with similar distances from the BTS and similar Doppler shifts using the same carrier frequency(ies) can be strategically allocated. A channel (which, as described above, may logically comprise an uplink subchannel and a downlink subchannel) can be assigned one of multiple time slots and one of multiple carrier frequencies. A channel may be identified solely by its assigned characteristics, such as its carrier frequency and its time slot, although in some situations, each channel is given a channel label. The channel label may encode the channel's carrier frequency, the channel's time slot, and possibly the channel's timing advance and Doppler shift, but it may be simple, such as a sequential number, and the BTS and / or MS may contain a stored mapping of channel number labels to allocated characteristics (e.g., channel 1 uses carrier frequency f1 and time slot 0, channel 2 uses carrier frequency f7 and time slot 3, etc.).

[0145] Figure 17 illustrates an example of range rings / Doppler shift cells of a satellite footprint. The intersections of the pseudorange rings and Doppler shift strips form the footprint grid. Channels can be allocated to the grid cells, range rings / Doppler shift cells.

[0146] FIG. 18 illustrates an example of the allocation of the range ring / Doppler shift cells of FIG. 17 to specific carrier frequency and Doppler offset blocks. Logical channel blocks may be associated with one or more carrier frequencies and / or time slots on a TDMA frame using those carrier frequencies. In FIG. 17, the channels are shown with arbitrary channel labels, in this case 1 through 70. They happen to be labeled from bottom to top, i.e., from most negative Doppler shift to most positive Doppler shift. Channels 1 through 70 may correspond to channels allocated to each of the eight time slots in a frame using eight carrier frequencies, and six time slots in a frame for another carrier frequency.

[0147] The diagram in Figure 17 shows how channel numbers are assigned to the grid cells of the satellite footprint. While only the left side of the footprint is shown numbered, it should be understood that the twin cells on the right side are also assigned these channel numbers. The channel assignment table in Figure 18 shows how each channel number is assigned to the grid cells of the Doppler shift strip (D0 to D1). 13 17 and 18 illustrate a channel allocation scheme in which a Doppler offset block is associated with, assigned to, or allocated to the corresponding channel blocks (b0-b6). Note that in other embodiments, the number of channels may vary depending on how the MS's pseudoranges and Doppler shifts are "bucketized." Multiple channels may be allocated to a grid cell. In the examples of FIGS. 17 and 18, for simplicity, one channel number is allocated per grid cell. Because the grid cells are symmetric about the satellite's velocity vector, only half of the grid cells are filled with a channel allocation. In an actual implementation, unfilled grid cells would be allocated the same channel number in the opposite grid cell in the contour map. This is because symmetric grid cells are at different physical locations on the contour map (and in the real world), but they represent the same qualifying parameters in terms of pseudorange and Doppler shift from an on-orbit BTS.

[0148] Pinching and Fraying The "pinch and wear" feature of the BTS design is useful when the uplink subchannels are in a contiguous spectrum and the downlink subchannels are in a contiguous spectrum, and the Doppler shift can be greater than or equal to the signal bandwidth, but this does not have to be the case to implement the following technique.

[0149] The table in Figure 18 is a channel allocation matrix that an on-orbit BTS uses to determine how to allocate channels to MSs, allocating them in the same way that adjacent numbers are allocated adjacent carrier frequencies. When a signal burst is received on the RACH, the calculated Doppler shift and calculated pseudorange estimates are used to find the appropriate grid cell and determine which channel should be allocated to that MS by looking up the MS's channel number in the table. In this example, not all channel blocks (columns in Figure 18) have the same number of actual channels in use or available because not all channel blocks correspond to pseudoranges that can experience the full range of Doppler shifts. The BTS may store copies of this table and have different versions of it to use when allocating channel numbers based on grid cells.

[0150] The advantage of channel allocation, in which channels are allocated in order of grid cells having a particular Doppler shift, is illustrated in Figure 19. Because the spacecraft actively allocates channels based on the expected Doppler shift, it no longer needs to consider wide ranges of shifts in receive frequencies. Instead, an on-orbit BTS can instruct the existing MS infrastructure to communicate on a particular carrier frequency, but listen on a slightly shifted carrier frequency depending on how much Doppler shift is expected on that channel. This reduces interference of adjacent carrier frequencies on the spacecraft segment.

[0151] In this particular embodiment, the Doppler shift contours are spaced every 5 kHz, although other intervals can be used. Thus, for each channel allocated to an MS, the satellite BTS listens on a carrier frequency that is the average of the maximum and minimum Doppler shifts of that channel's carrier frequency to identify data bursts in the time slot allocated to that channel. For example, channel 70 has an MS allocated to it, and it listens on frequency F 70 and time slot TS 70 The BTS on the spacecraft is assumed to be logically associated with the TS 70 The BTS will listen for uplink signals from the MS on a carrier frequency of +27.5 kHz. In this way, no signal will be offset by more than 2.5 kHz from the frequency being listened to by the BTS. For the return link, the on-orbit BTS will listen for uplink signals from the MS on a carrier frequency of +27.5 kHz. 70 The signal on channel 70 can be transmitted by transmitting bursts of the signal at -27.5 kHz so that the signal is received at the MS within reasonable limits of the carrier frequency being listened to.

[0152] Figure 19 shows a map of uplink and downlink carrier frequencies used by the MS and BTS to communicate. Specifically, Figure 19 shows the Doppler blocks referenced in Figures 17 and 18, with Doppler blocks having widths that scale based on the number of channels they carry. If channels are allocated in order of increasing carrier frequency as a function of some known Doppler effect, uplink signals "wear" off each other, defining the channel the BTS chooses to listen on. This mitigates interference at the BTS in orbit. Instead of "wearing" off the downlink transmission frequency, it "pinches" it to ensure the signal has the appropriate carrier frequency when it reaches the MS. Note that the Doppler blocks are referenced in both uplink and downlink frequencies, which implies that each channel has an uplink and downlink component. Other variations are possible.

[0153] Figure 19 shows that the on-orbit BTS listens on frequencies slightly offset from those transmitted by the MS. This is the result of a new channel allocation scheme, which reduces Doppler shift interference and complexity when communicating with the MS. In downlink operation, the spacecraft transmits on more "pinch" channels so that the signal that reaches the target MS is at the correct frequency. Channel blocks are represented as Doppler blocks, referenced in Figures 17 and 18, and have widths that scale with the number of channels they carry.

[0154] Similarly, it will be noted that channels can be distributed to Doppler blocks in descending order of signal frequency. This scheme reverses the effect of received and transmitted signals from the BTS's perspective. It is reasonable to assume that this technique may actually be useful in enhancing the ability to block uplink signals from an MS. This is because the uplink signal will be "pinched" instead of "wearing off," as shown in Figure 19. Because the amount of "pinch" is fairly well understood, an on-orbit BTS could exploit this fact to intelligently narrow the bandwidth at which it "listens" to each uplink channel. This would mean that received uplink signals would be separated by less than 200 kHz (similar to GSM). In this case, the on-orbit BTS could theoretically listen on a narrower channel to reduce noise.

[0155] Some embodiments of the present invention may prefer "worn" or "pinched" channels at the BTS for both uplink and downlink subchannels. To accommodate this, implementers would allocate channels where the uplink signal frequency increases and the downlink signal frequency decreases. This would result in a "worn" channel for the BTS's uplink receive and downlink transmit functions. Conversely, a channel where the uplink signal frequency decreases and the downlink signal frequency increases would result in a "pinched" channel for the BTS's uplink receive and downlink transmit functions.

[0156] While Figure 19 illustrates channels as boxes, one per Doppler block, it should be understood that the worn or pinched boxes in Figure 19 may correspond to one or more carrier frequencies and one or more time slots. For example, in the example of Doppler block D9, Figure 18 shows channels 50-56 allocated to cells within the strip covered by that Doppler block. Channels 50-56 may represent seven time slots within a frame of one carrier frequency, one time slot within a frame of seven different carrier frequencies, or some other configuration.

[0157] Discovering Locations In addition to data communication between the BTS and the MS, the BTS can be used for location discovery, i.e., to determine the geographic location of the MS, at least approximately, or with sufficient resolution for various applications (e.g., supporting remote search and rescue operations). When a satellite passes over an MS, the BTS for that satellite determines the grid cell (actually a pair of twin grid cells) of the MS (as described above). When another satellite passes over the same MS, the BTS for the second satellite determines a pair of grid cells within the footprint of the second satellite. If the second satellite is in a different orbit from the first, the symmetry lines of its pseudorange range rings and Doppler shift contour strips will be somewhat different from those of the first satellite. The BTS assumes that the MS has not moved, or has moved only slightly, on the scale of the satellite footprint, so that the two pairs of grid cells are such that one grid cell of one satellite overlaps one grid cell of the other satellite, but the other two do not overlap, allowing the BTS to determine the likely location of the MS.

[0158] It may be used alone or in combination with other location discovery systems.

[0159] Software-defined radio, dynamic allocation by density The BTS performs various functions described herein. The BTS may be implemented with a commercially available software-defined radio or may be programmed or configured with the specific functions provided herein. The software-defined radio may be reprogrammed in orbit to shift around the channel configuration of the BTS channel allocation scheme. This may be valuable when MSs on the Earth's surface are not evenly distributed. For example, as illustrated in FIG. 20, if the BTS has a mapping of connected or expected MSs, or if the BTS is exhibiting a particular Doppler shift range and getting most of its requests from MSs operating within a similar pseudorange, the BTS may prefer more crowded grid cells with more channels. Therefore, Doppler shift and pseudorange data can be used to proportionally allocate channel allocations. The right side of FIG. 20 illustrates, for each grid cell, how many channels may be assigned to that grid cell. Only a semicircle is shown, assuming the satellite footprint is symmetric about the satellite's velocity vector.

[0160] Figure 21 illustrates an example of a channel allocation table that may be used for the allocation and mapping illustrated in Figure 20, where the channel distribution is mapped with ordered channels using a channel allocation scheme. To reconfigure a channel serving a grid cell, the transceiver for that channel is reconfigured with a different time slot synchronization offset than the transmission TDMA frame, and the transceiver obtains an update of the transceiver's configured frequency offset for receiving and transmitting on the uplink and downlink carriers, respectively. Once the channels are reconfigured and remapped to the channel allocation scheme, they may remain in counting order (ascending or descending) from the lower right corner to the upper left corner of the channel allocation table, as shown. The channel allocation table may be stored in an accessible computer-readable memory such that a processor controlling the software-defined radio may set the frequency and timing according to the channel allocation table.

[0161] In addition to remapping channels into blocks, on-orbit software-defined radios can also reconfigure their block mapping. For example, if MSs are densely packed, the BTS can reconfigure its channel allocation scheme with finer spacing of pseudorange and Doppler shift to improve service, especially throughput, in a particular geographic area. Furthermore, the on-orbit BTS can set its channel's minimum and maximum time slot synchronization offset and Doppler compensation based on the minimum and maximum measured values ​​of pseudorange and Doppler shift, respectively. This allows the BTS to more tightly define the grid cells of its satellite footprint and more efficiently allocate channels to serve dense pockets of MSs. Finer spacing of Doppler blocks further reduces the effect of Doppler shift on each channel, while finer spacing of pseudorange range rings increases the potential throughput at more specific ring locations to serve denser MSs.

[0162] On-orbit processing can also leverage known satellite velocities to predict the motion of the satellite footprint, and therefore the pseudorange and Doppler shift contours for the MSs it serves. This would allow the satellite BTS to predict which pseudorange and Doppler shift buckets will require channel allocation in the near future and which will not. Predictability would allow for more accurate reconfiguration of the channel allocation scheme. Because there is some lead time associated with channel reconfiguration, predictability can be heavily leveraged to ensure that channel downtime is limited. For example, to account for this channel reconfiguration lead time, an on-orbit BTS can "juggle" or reserve one or more channels so that it does not have to suddenly go out of service because the carrier frequency serving the MS is reconfigured. Because channels must be configured in ascending or descending frequency order, reconfiguration can sometimes create a domino effect, requiring many channels to be reconfigured to maintain this critical frequency ordering in the channel allocation scheme. For example, consider an on-orbit GSM BTS with access to 80 channels in the GSM spectrum. Assuming channels are labeled 1 through 124, all odd channels (i.e., 1, 3, 5, 7, etc.) can be configured to serve an MS, while all even channels (i.e., 2, 4, 6, 8, etc.) can be "juggled" or reserved. When the need for reconfiguration arises, the on-orbit BTS can reconfigure the "juggled" channel without having to disrupt service on one of the other 62 already configured channels. If a configured channel no longer serves an MS, that channel can be rotated back into the reserved or "juggled" channel set, and the process repeats, maintaining consistent service and limiting channel downtime.

[0163] Orbiting BTSs can be programmed to use real-time measurements of MS pseudoranges, Doppler shifts, and other data (i.e., GPS) to further enhance the quality of service of such networks. Examples include channel reassignment or shifts based on large data sets collected over time and many satellite passes (based on the relatively static location of the MS), as well as more dynamic real-time shifts based on changes in MS distribution detected by spacecraft that passed this location immediately before the current spacecraft, or even by the current spacecraft.

[0164] The dynamic channel allocation described above can also be performed in a manner that allows certain channels to be reserved for particular MSs or geographic locations over which the satellites pass. In other words, the Doppler shift and pseudorange configuration of a particular channel, when plotted over time, is described by a somewhat smooth function that matches the Doppler shift and pseudorange environment experienced by a particular MS or geographic location over its course. This embodiment can be strategic under conditions where a particular MS on the Earth's surface needs or benefits from maintaining a locked link with a satellite for a longer period of time (e.g., minutes rather than seconds).

[0165] Consider the example case illustrated in Figure 20, where the connected MSs are operating in a "clump," possibly a remote area. Note that the map shows only half of the satellite footprint because the pseudorange and Doppler shift buckets are symmetric about the satellite's velocity vector. If the spacecraft collects pseudorange and Doppler shift data from these users, it can strategically prorate the channel distribution in its channel assignment scheme and, based on this proration, reprogram its channels to shift their service configuration. Such techniques can also leverage predictive data analysis software. An on-orbit BTS can tightly combine historical MS data with GPS navigation data to predict where and when it will cross dense pockets of customers within its footprint. GPS data from MSs actually being served can also be used to further enhance predictive channel analysis and assignment, as well as tracking applications. This can help increase the quality of service of such networks.

[0166] Figure 22 illustrates a process for determining MS parameters in the RACH process. By measuring the propagation delay from the MS uplink burst, the BTS can calculate the timing advance required for each MS to transmit its burst at the correct time. The RACH process can be: (1) the MS listens to the BCCH when it is resident on the BTS; (2) the MS user types a text message and hits "send"; (3) the MS requests access to the channel by sending a burst on the RACH using information provided on the BCCH; (4) the BTS retrieves the channel allocation and responds with the channel allocation and timing advance (in bits); and (5) the MS uses the timing advance to advance its burst to the allocated time slot and use the allocated frequency carrier.

[0167] In a more schematic case illustrated in Figure 22, the MS requests allocation of a dedicated signaling channel to perform the call setup, and after allocation of the signaling channel, the MOC call setup request including the TMSI (IMSI) and final LAI is forwarded to the VLR. The VLR requests AC via the triple HLR (if necessary). The VLR then initiates authentication, cipher initiation, IMEI verification (optional), and TMSI reallocation (optional). If all this does not result in an error requiring the process to be canceled, the MS sends the setup information (requested subscriber number and detailed service description) to the MSC, and the MSC requests the VLR to verify (from the subscriber data) whether it can handle the requested service and number (or whether there are restrictions that prevent the call setup from being processed further).

[0168] If the VLR indicates that the call should be handled, the MSC instructs the BSC to allocate a traffic channel to the MS, and the BSC allocates a traffic channel TCH to the MS. The MSC then sets up a connection to the requested number (called party).

[0169] According to one embodiment, the techniques described herein are implemented by a single or generalized computing system programmed to perform the techniques according to program instructions in firmware, memory, other storage, or a combination. A dedicated computing device such as a desktop computer system, a portable computer system, a handheld device, a network device, or any other device embedded with hardwired and / or program logic to implement the techniques can be used.

[0170] For example, Figure 23 is a block diagram illustrating a computer system 2300 in which one embodiment of the present invention may be implemented. The computer system 2300 includes a bus 2302 or other communication mechanism for communicating information, and a processor 2304 coupled with the bus 2302 for processing information. The processor 2304 may be, for example, a general-purpose microprocessor.

[0171] Computer system 2300 also includes a main memory 2306, such as random access memory (RAM) or other dynamic storage device, coupled to bus 2302 for storing information and instructions executed by processor 2304. Main memory 2306 may also be used for storing temporary variables or other intermediate materials during execution of instructions executed by processor 2304. Such instructions, when stored on a non-transitory storage medium accessible to processor 2304, render computer system 2300 into a special-purpose machine customized to perform the operations specified in the instructions.

[0172] Computer system 2300 further includes a read only memory (ROM) 2308 or other static storage device coupled to bus 2302 for storing static information and instructions for processor 2304. A storage device 2310, such as a magnetic disk or optical disk, is provided and coupled to bus 2302 for storing information and instructions.

[0173] The computer system 2300 may be coupled via bus 2302 to a display 2312, such as a computer monitor, for displaying information to a computer user. An input device 2314, including alphanumeric and other keys, is coupled to the bus 2302 for communicating information and command selections to the processor 2304. Another type of user input device is a cursor control 2316, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor 2304 and for controlling cursor movement on the display 2312. The input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), allowing the device to specify a position in a plane.

[0174] Computer system 2300 can implement the techniques described herein using customized hardwired logic, one or more ASICs or FPGAs, firmware, and / or program logic that in combination with the computer system renders or programs computer system 2300 into a special-purpose machine. According to one embodiment, the techniques herein are performed by computer system 2300 in response to processor 2304 executing one or more sequences of one or more instructions contained in main memory 2306. Such instructions may be read into main memory 2306 from another storage medium, such as storage device 2310. Execution of the sequences of instructions contained in main memory 2306 causes processor 2304 to perform the process steps described herein. In alternative embodiments, hardwired circuitry may be used in place of or in combination with software instructions.

[0175] As used herein, the term "storage medium" refers to any non-transitory medium that stores data and / or instructions that cause a machine to operate in a specific fashion. Such storage media may include non-volatile media and / or volatile media. For example, non-volatile media include optical or magnetic disks, such as storage device 2310. Volatile media include dynamic memory, such as main memory 2306. For example, common forms of storage media include floppy disks, flexible disks, hard disks, solid-state drives, magnetic tape, or any other magnetic data storage medium, CD-ROMs, any other optical data storage medium, any physical medium with a pattern of holes, RAM, PROM, EPROM, FLASH-EPROM, NVRAM, or any other memory chip or cartridge.

[0176] Storage media are distinct from but may be used in conjunction with transmission media. Transmission media involves transferring information between storage media. For example, transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus 2302. Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications.

[0177] Various forms of media may be involved in carrying one or more sequences of one or more instructions to processor 2304 for execution. For example, the instructions may initially reside on a magnetic disk or solid state drive of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a network connection. A modem or network interface local to computer system 2300 may receive the data. Bus 2302 carries the data to main memory 2306, from which processor 2304 retrieves and executes the instructions. The instructions received by main memory 2306 may optionally be stored on storage device 2310 either before or after execution by processor 2304.

[0178] Computer system 2300 also includes a communication interface 2318 coupled to bus 2302. The communication interface 2318 provides a two-way data communication coupling to a network link 2320 that is connected to a local network 2322. For example, communication interface 2318 may be an integrated services digital network (ISDN) card, a cable modem, a satellite modem, or a modem to provide a data communication connection to a corresponding type of telephone line. A wireless link may also be implemented. In any such implementation, communication interface 2318 sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.

[0179] Network link 2320 typically provides data communication through one or more networks to other data devices. For example, network link 2320 may provide a connection through local network 2322 to a host computer 2324 or to data equipment operated by an Internet Service Provider (ISP) 2326. ISP 2326, in turn, provides data communication services through the world wide packet data communication network commonly referred to herein as the “Internet” 2328. Local network 2322 and Internet 2328 both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network link 2320 and through communication interface 2318, which carry the digital data to and from computer system 2300, are exemplary forms of transmission media.

[0180] Computer system 2300 can send messages and receive data, including program code, through the network(s), network link 2320 and communication interface 2318. In the Internet example, a server 2330 might transmit a requested code for an application program through the Internet 2328, ISP 2326, local network 2322 and communication interface 2318. The received code may be executed by processor 2304 as it is received, and / or stored in storage device 2310, or other non-volatile storage device for later execution.

[0181] The operations of the processes described herein may be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The processes described herein (or variations and / or combinations thereof) may be performed under the control of one or more computer systems configured with executable instructions and implemented as code (e.g., executable instructions, one or more computer programs, or one or more applications) that collectively execute on one or more processors, by hardware, or a combination thereof. The code may be stored in a computer-readable storage medium, for example, in the form of a computer program including a plurality of instructions executable by one or more processors. The computer-readable storage medium may be non-transitory.

[0182] Unless specifically stated otherwise or clearly contradicted by the context, connective language such as expressions of the form "at least one of A, B, and C" or "at least one of A, B, and C" will be understood differently depending on the context as generally used to indicate that an item, term, etc. may be either A or B or C, or any non-empty subset of the set A, B, and C. For example, in the example of an exemplary set having three members, the connective expressions "at least one of A, B, and C" and "at least one of A, B, and C" refer to any of the following sets: {A}, {B}, {C}, {A, B}, {A, C}, {B, C}, {A, B, C}. Thus, such connective expressions generally are not intended to imply that a particular embodiment requires that at least one of A, at least one of B, and at least one of C are each present.

[0183] The use of any and all examples or exemplary language (e.g., "such as") provided herein is intended merely to better illuminate embodiments of the invention and does not serve to limit the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0184] In the foregoing specification, embodiments of the present invention have been described with reference to numerous specific details that may vary between implementations. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense. The sole and exclusive indication of the scope of the invention, and what the applicant intends the scope of the invention to be, is the literal scope and equivalents of the set of claims issuing from this application, in the particular form in which such claims issue, including any subsequent amendments.

[0185] Further embodiments may be envisioned by those skilled in the art after reading this disclosure. In other embodiments, combinations or sub-combinations of the above-disclosed inventions may be advantageously made. It is to be understood that example arrangements of components are shown for illustrative purposes, and that combinations, additions, rearrangements, etc. are contemplated in alternative embodiments of the invention. Thus, while the invention has been described with reference to exemplary embodiments, those skilled in the art will recognize that numerous modifications are possible.

[0186] For example, the processes described herein may be implemented using hardware components, software components, and / or any combination thereof. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. It will be evident, however, that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims, and that the invention is intended to cover all modifications and equivalents within the scope of the following claims.

[0187] All references cited herein, including publications, patent applications, and patents, are herein incorporated by reference to the same extent as if each reference was individually and specifically indicated to be incorporated by reference. [Item 1] a multiple access base station having one or more transceivers for handling communications with a plurality of terrestrial mobile stations, wherein a terrestrial mobile station of the plurality of terrestrial mobile stations is configured to anticipate base station communications with a terrestrial cellular base station that is (1) within a limited distance from the terrestrial mobile station and / or (2) moving at less than a limited speed relative to the terrestrial mobile station, the multiple access base station comprising: a data analyzer that analyzes data received by the multiple access base station according to a frame structure that defines which time slots are assigned to which of the plurality of terrestrial mobile stations, the frame structure comprising a plurality of slots each having a zero or non-zero time slot synchronization offset that results in a variable transmission delay due to distance from the multiple access base station to the plurality of terrestrial mobile stations; a signal timing module that determines a signal timing adjustment to the frame structure of a signal transmitted to the terrestrial mobile station based on a base-to-mobile distance between the multiple access base station and the terrestrial mobile station, wherein the base-to-mobile distance exceeds the distance limit; and a programmable radio capable of communicating communications from said multiple access base station to said terrestrial mobile station using a multiple access protocol and taking into account said signal timing adjustments so that said communications are, or appear to said terrestrial mobile station, compatible with communications between a terrestrial cellular base station and said terrestrial mobile station even though the base-to-mobile distance exceeds said distance limit. [Item 2] Item 1. The multiple access base station of item 1, further adapted to communicate with the plurality of terrestrial mobile stations, the plurality of terrestrial mobile stations comprising cellular telephone handsets, smartphones, and connected devices. [Item 3] 3. The multiple access base station according to item 1 or 2, wherein the distance limit is 120 kilometers and the base-to-mobile distance is greater than 120 kilometers. [Item 4] 3. The multiple access base station according to item 1 or 2, wherein the multiple access protocol is an LTE protocol, the limit distance is 100 kilometers, and the base-to-mobile distance is greater than 100 kilometers. [Item 5] 3. The multiple access base station according to item 1 or 2, wherein the multiple access protocol is an LTE-IoT protocol, the limit distance is 40 kilometers, and the base-to-mobile distance is greater than 40 kilometers. [Item 6] 4. The multiple access base station according to any one of claims 1 to 3, wherein the multiple access protocol is one of a CDMA-based protocol, an LTE protocol, a GSM (registered trademark) protocol, an OFDMA-based protocol, an FDMA-based protocol, a TDMA-based protocol, an EGPRS protocol, or an EDGE protocol. [Item 7] 7. The multiple access base station of any one of claims 1 to 6, wherein the multiple access base station is an orbital base station operating within an Earth orbit. [Item 8] 8. The multiple access base station according to item 7, wherein the limit distance is 120 kilometers and the base-to-mobile distance of the plurality of terrestrial mobile stations is between approximately 500 kilometers and approximately 750 kilometers. [Item 9] 7. The multi-access base station of any one of claims 1 to 6, wherein the multi-access base station is a base station operable within the Earth's atmosphere and is mounted on or in one or more of an airplane, a drone, and / or a balloon. [Item 10] 10. The multiple access base station of claim 9, wherein the distance limit is 120 kilometers and the base-to-mobile distance is greater than 120 kilometers. [Item 11] 11. The multiple access base station of claim 1, further comprising signal allocation logic for allocating capacity of the multiple access base station distributed across multiple time slots, multiple carrier frequencies, multiple orthogonal subcarriers, and / or multiple code sequences to the multiple terrestrial mobile stations including the terrestrial mobile station. [Item 12] The programmable radio is further capable of listening for communications from the terrestrial mobile station using a multiple access protocol, and the multiple access base station: a range calculator that determines, for each of the plurality of terrestrial mobile stations, a base-to-mobile distance for each of the terrestrial mobile stations, the base-to-mobile distance being the distance from the multiple access base station to the terrestrial mobile station; a receive timing module that determines the timing of a received signal at the mobile terrestrial station relative to the frame structure based on the base-to-mobile distance of the mobile terrestrial station; 2. The multiple access base station of claim 1, further comprising: an input signal allocator that allocates listening time slots within the frame structure to listen for communications from the terrestrial mobile stations, wherein the listening time slot is timed based on the base-to-mobile distance of the terrestrial mobile station, the listening time slot being one of a plurality of time slots, and the plurality of time slots being variably delayed within the frame structure to account for the multiple access base station handling communications from the plurality of terrestrial mobile stations having a plurality of base-to-mobile distances. [Item 13] 13. The multiple access base station of claim 12, wherein the plurality of time slots are variably delayed within the frame structure to account for the plurality of terrestrial mobile stations having a plurality of base-to-mobile distances by assigning each of a plurality of different base-to-mobile distance ranges to each of a plurality of channel blocks. [Item 14] Item 14. The multiple access base station of item 13, wherein the multiple access base station is an orbital base station operating within Earth's orbit, and the plurality of different base-to-mobile distance ranges collectively cover a slant range from a zenith distance to a minimum elevation distance, the zenith distance being the distance between a zenith position of a satellite carrying the multiple access base station relative to a terrestrial mobile station, and the minimum elevation distance being the distance between the position of the satellite when the terrestrial mobile station enters the design footprint of the satellite. [Item 15] Item 15. The multiple access base station of item 14, wherein each of the plurality of different base-to-mobile distance ranges is approximately 34 to 35 kilometers, and the difference between the zenith distance and the minimum elevation distance is 210 to 250 kilometers. [Item 16] 16. A multiple access base station according to item 14 or 15, wherein the design footprint of the satellite is circular, elliptical, rectangular and is independent of the function of the antenna and / or the shape of the antenna beam, or is the function of the antenna and / or the shape of the antenna beam. [Item 17] A multiple access base station having one or more transceivers handling communications with a plurality of terrestrial mobile stations, the terrestrial mobile stations being configured to anticipate base station communications with terrestrial cellular base stations that are (1) within a limited distance from said terrestrial mobile stations and / or (2) moving at less than a limited speed relative to said terrestrial mobile stations, said multiple access base station comprising: a data analyzer that analyzes data received by the multiple access base station according to a frame structure that defines which time slots are assigned to which of the plurality of terrestrial mobile stations, and according to a multiple access protocol that expects the terrestrial mobile stations to receive signals on specified frequencies and transmit signals on specified frequencies; a Doppler shift calculator for determining, for each of the plurality of terrestrial mobile stations, a Doppler shift for each of the terrestrial mobile stations due to the velocity of each of the terrestrial mobile stations relative to the multiple access base station; a channel allocation module that allocates each of the plurality of terrestrial mobile stations to a channel block within a plurality of channel blocks, each channel block having a terrestrial frequency and a Doppler frequency offset; a signal modulator that modulates a signal to the terrestrial mobile station at the terrestrial frequency with the Doppler frequency offset, the Doppler frequency offset corresponding at least approximately to an expected Doppler shift in a signal transmitted to the terrestrial mobile station due to relative motion of the multiple access base station and the terrestrial mobile station, so that the terrestrial mobile station receives the signal at the terrestrial frequency; a programmable radio capable of receiving communications from the terrestrial mobile station using the multiple access protocol and taking into account the Doppler frequency offset of the terrestrial mobile station, so that the communications are, or appear to the terrestrial mobile station to be, compatible with communications between a terrestrial cellular base station and the terrestrial mobile station, even though the speed of the terrestrial mobile station relative to the multiple access base station exceeds the speed limit. [Item 18] Item 18. The multiple access base station of item 17, wherein the velocity of the terrestrial mobile station relative to the multiple access base station is a result of the multiple access base station being in orbit around the Earth, and the Doppler frequency offset varies in increments of 5 kilohertz. [Item 19] Item 19. The multiple access base station of item 17 or 18, further adapted to communicate with the plurality of terrestrial mobile stations, the plurality of terrestrial mobile stations comprising cellular telephone handsets, smartphones, connected devices. [Item 20] 20. The multiple access base station of any one of items 17 to 19, wherein the multiple access base station is an orbital base station operating within an Earth orbit. [Item 21] 20. A multi-access base station according to any one of items 17 to 19, wherein the multi-access base station is a base station operable within the Earth's atmosphere and is mounted on or in one or more of an airplane, a drone, and / or a balloon. [Item 22] 22. The multiple access base station of claim 17, further comprising signal allocation logic for allocating capacity of the multiple access base station distributed across multiple time slots, multiple carrier frequencies, multiple orthogonal subcarriers, and / or multiple code sequences to the multiple terrestrial mobile stations including the terrestrial mobile station. [Item 23] 23. A multiple access base station as described in any one of items 17 to 22, wherein each of the plurality of channel blocks has uplink subchannels and downlink subchannels including a contiguous spectrum of uplink subchannels and a contiguous spectrum of downlink subchannels, and the channel blocks are allocated such that adjacent channel blocks are allocated adjacent Doppler frequency offsets. [Item 24] A multiple access base station having one or more transceivers handling communications with a plurality of terrestrial mobile stations, the terrestrial mobile stations being configured to anticipate base station communications with terrestrial cellular base stations that are (1) within a limited distance from said terrestrial mobile stations and / or (2) moving at less than a limited speed relative to said terrestrial mobile stations, said multiple access base station comprising: a data analyzer that analyzes data received by the multiple access base station according to a frame structure and further according to a multiple access protocol, the frame structure defining which time slots are assigned to which of the plurality of terrestrial mobile stations, the data analyzer comprising a plurality of slots each having a zero or non-zero time slot synchronization offset that results in a variable transmission delay due to distance from the multiple access base station to the plurality of terrestrial mobile stations, the multiple access protocol transmitting with an expectation that the terrestrial mobile stations will receive signals at a specified frequency and transmit signals at a terrestrial frequency and received with a Doppler frequency offset, the multiple access protocol identifying channel blocks within a plurality of channel blocks, each channel block having a designated terrestrial frequency and a designated time slot; a signal timing module that determines a signal timing adjustment for the frame structure of a signal transmitted to the terrestrial mobile station based on a base-to-mobile distance between the multiple access base station and the terrestrial mobile station, wherein the base-to-mobile distance exceeds the distance limit and each channel block is allocated a designated signal timing adjustment; a Doppler shift calculator for determining, for each of the plurality of terrestrial mobile stations, a Doppler shift for each of the terrestrial mobile stations due to the velocity of the each of the terrestrial mobile stations relative to the multiple access base station, each channel block being assigned a designated Doppler frequency offset; a dynamic channel allocator that assigns each of the plurality of terrestrial mobile stations to a designated channel block within the plurality of channel blocks based on the channel block's designated signal timing adjustment and designated Doppler frequency offset, the number of channels within the designated channel block corresponding to the number of terrestrial mobile stations of the plurality of terrestrial mobile stations that have or are expected to have the designated signal timing adjustment and designated Doppler frequency offset; a signal modulator for modulating a signal to the terrestrial mobile station at the terrestrial frequency with the Doppler frequency offset, the Doppler frequency offset corresponding at least approximately to an expected Doppler shift in a signal transmitted to the terrestrial mobile station due to relative motion of the multiple access base station and the terrestrial mobile station, so that the terrestrial mobile station receives the signal at the terrestrial frequency; and a programmable radio capable of receiving communications from the terrestrial mobile station using the multiple access protocol and taking into account the Doppler frequency offset of the terrestrial mobile station, so that the communications are, or appear to the terrestrial mobile station to be, compatible with communications between a terrestrial cellular base station and the terrestrial mobile station, even though the base-to-mobile distance exceeds the distance limit and even though the velocity of the terrestrial mobile station relative to the multiple access base station exceeds the velocity limit. [Item 25] 25. The multiple access base station of claim 24, wherein the velocity of the terrestrial mobile station relative to the multiple access base station is a result of the multiple access base station being in Earth orbit and the Doppler frequency offset varies in 5 kilohertz increments. [Item 26] 26. The multiple access base station of claim 24 or 25, further adapted to communicate with the plurality of terrestrial mobile stations, the plurality of terrestrial mobile stations comprising cellular telephone handsets, smartphones, connected devices. [Item 27] 27. The multiple access base station of any one of items 24 to 26, wherein the multiple access base station is an orbital base station operating in Earth orbit. [Item 28] 27. A multi-access base station according to any one of items 24 to 26, wherein the multi-access base station is a base station operable within the Earth's atmosphere and is mounted on or in one or more of an airplane, a drone, and / or a balloon. [Item 29] 29. The multiple access base station of any one of claims 24 to 28, further comprising signal allocation logic for allocating capacity of the multiple access base station distributed across multiple time slots, multiple carrier frequencies, multiple orthogonal subcarriers, and / or multiple code sequences to the multiple terrestrial mobile stations including the terrestrial mobile station.

Claims

1. a multiple access transceiver configured to communicate between the multiple access transceiver and a plurality of terrestrial mobile stations, including at least a first terrestrial mobile station, along a communication path that passes at least through an orbit around the Earth; a data analyzer for analyzing data received by the multiple access transceiver into a structure suitable for a predetermined frame structure in a multiple access protocol; a Doppler shift calculator for determining, for each of the plurality of terrestrial mobile stations, its respective Doppler shift due to the velocity of each terrestrial mobile station in said communications path relative to said multiple access transceiver in said communications path; a channel allocation module that allocates each of the plurality of terrestrial mobile stations to a channel block within a plurality of channel blocks, each channel block configured according to a Doppler frequency offset; a signal modulator that modulates the frequency of a signal to the first terrestrial mobile station to a terrestrial frequency at which the first terrestrial mobile station receives the signal plus the Doppler frequency offset, the Doppler frequency offset being the negative of an expected Doppler shift in a signal transmitted to the first terrestrial mobile station due to relative motion of the first terrestrial mobile station and the multiple access transceiver, so that the first terrestrial mobile station receives the signal at the terrestrial frequency; Equipped with the communication appears to the first terrestrial mobile station to be compatible with communication between a terrestrial cellular base station and the first terrestrial mobile station, even if the speed of the first terrestrial mobile station relative to the multiple access transceiver exceeds a speed limit specified in the multiple access protocol. Multiple access transceiver.

2. 2. The multiple access transceiver of claim 1, wherein the velocity of the first terrestrial mobile station relative to the multiple access transceiver is a result of the first terrestrial mobile station or the multiple access transceiver being in orbit around the Earth and the Doppler frequency offset varies in 5 kilohertz increments.

3. 3. The multiple access transceiver of claim 1 or 2, wherein the plurality of terrestrial mobile stations comprise one or more of a cellular telephone handset, a smart phone, and a communication device.

4. 4. A multiple access transceiver according to any one of claims 1 to 3, wherein the multiple access transceiver is an orbital base station operating in orbit around the Earth.

5. 4. The multiple access transceiver of claim 1, wherein the multiple access transceiver is a base station operable within the Earth's atmosphere, including being mounted on one or more of an airplane, a drone, and a balloon.

6. 6. The multiple access transceiver of claim 1, further comprising signal allocation logic for allocating capacity of the multiple access transceiver distributed across multiple time slots, multiple carrier frequencies, multiple orthogonal subcarriers, and / or multiple code sequences to the multiple terrestrial mobile stations, including the first terrestrial mobile station.

7. 7. The multiple access transceiver of claim 1, wherein each of the plurality of channel blocks has uplink and downlink subchannels including a first contiguous spectrum for the uplink subchannel and a second contiguous spectrum for the downlink subchannel, and the channel blocks are allocated such that adjacent channel blocks are allocated at adjacent Doppler frequency offsets.

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