Multi-channel time division multiplexed access method and system

Abstract

SUMMARY OF THE INVENTION [0005] A device, system, and method for high utilization, low latency, multi-channel time division multiplexed access (TDMA) is described. One exemplary method for wireless communication includes: transmitting a first data unit over a first logical channel of a plurality of logical channels in a first time interval of a time division multiplexed access (TDMA) slot; refraining from transmitting for a second time interval immediately following the first time interval following completion of the transmission of the first data unit; and, for each data unit of (N-1) subsequent data units in the TDMA slot, performing (N-1) transmissions in (N-1) time intervals, such that a transmission of an nth data unit of the (N-1) subsequent data units is performed over the nth logical channel of the plurality of logical channels.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This patent document claims priority to and the benefit of U.S. Nonprovisional Patent Application No. 17 / 006,644, filed August 28, 2020. The entire contents of the aforementioned patent application are incorporated by reference as part of the disclosure of this patent document.

[0002] FIELD OF THE INVENTION This patent document is directed to cooperative wireless communication between nodes in a wireless network. [Background technology]

[0003] In certain wireless communication applications, signals traveling between nodes can experience long propagation delays. For example, using geostationary satellites to communicate between mobile stations and base stations across continents can result in delays of hundreds of milliseconds. In another example, the propagation delay of underwater acoustic channels across ocean depths can be many seconds. Traditional time-slotted medium access control (MAC) schemes trade off channel utilization to accommodate these long propagation delays. Enabling high utilization and low latency communications on these channels can significantly expand new communication capacity. Summary of the Invention

[0004] This patent document relates to high utilization, low latency multi-channel time-division multiplexing access (TDMA). Embodiments of the disclosed technology can be configured to provision multiple bursts on multiple orthogonal radio resources during a single TDMA slot, which advantageously increases link utilization and reduces timing uncertainty.

[0005] In one example, a method is disclosed for wireless communication over a wireless medium including a plurality of logical channels, the method including: transmitting a first data unit over a first logical channel of the plurality of logical channels in a first time interval of a time division multiple access (TDMA) slot; refraining from transmitting for a second time interval immediately following the first time interval following completion of the transmission of the first data unit; and, for each data unit of (N-1) subsequent data units in the TDMA slot, performing (N-1) transmissions in (N-1) time intervals such that the transmission of an nth data unit of the (N-1) subsequent data units is performed over the nth logical channel of the plurality of logical channels, where n and N are positive integers and 2≦n≦N, each of the plurality of logical channels corresponds to a distinct transmission resource, the wireless medium is characterized by a maximum propagation delay, and a duration of the TDMA slot is greater than the maximum propagation delay.

[0006] In another example, a method is disclosed for wireless communication over a wireless medium including a plurality of logical channels, the method including: receiving and detecting a first data unit by a first logical channel of the plurality of logical channels at a first time of a time division multiple access (TDMA) slot; and receiving and detecting at least one of (N-1) subsequent data units at each of (N-1) times in the TDMA slot, such that reception of an nth data unit of the (N-1) subsequent data units is performed by the nth logical channel of the plurality of logical channels, where n and N are positive integers and 2≦n≦N, each of the plurality of logical channels corresponds to a distinct transmission resource, the wireless medium is characterized by a maximum propagation delay, and a duration of the TDMA slot is greater than the maximum propagation delay.

[0007] In yet another example, a wireless communication system is disclosed that includes a transmitter, a first receiver coupled to the transmitter by a wireless medium including a plurality of logical channels, each of the plurality of logical channels corresponding to a distinct transmission resource, the wireless medium being characterized by a maximum propagation delay, a distance between the transmitter and the first receiver corresponding to a first propagation delay that is smaller than the maximum propagation delay, and a second receiver coupled to the transmitter by the wireless medium, the distance between the transmitter and the second receiver corresponding to a second propagation delay that is smaller than the first propagation delay, wherein the transmitter transmits a first data unit to the first receiver and the second receiver via a first logical channel of the plurality of logical channels in a first time interval of a time division multiple access (TDMA) slot, and The receiver is configured to refrain from transmitting for a second time interval immediately following the first time interval following completion of transmission of the unit, and to perform (N-1) transmissions in (N-1) time intervals for each data unit of the (N-1) subsequent data units in the TDMA slot, such that transmission of the nth data unit of the (N-1) subsequent data units is performed by the nth logical channel of the plurality of logical channels; the second receiver is configured to receive and decode at least one of the N subsequent data units within the TDMA slot, the first receiver is unable to receive and decode each of the N subsequent data units, the duration of the TDMA slot is greater than the first propagation delay, n and N are positive integers, and 2≦n≦N.

[0008] In yet another example, the above-described methods are embodied in the form of processor-executable code and stored on a computer-readable program medium.

[0009] In yet another example, a device configured or operable to perform the above-described method is disclosed.

[0010] These examples and other aspects and their implementations are described in more detail in the drawings, description, and claims. [Brief explanation of the drawings]

[0011] [Figure 1A] 1 shows slot allocation for a multi-hop network. [Figure 1B] 1 shows slot allocation for a multi-hop network. [Figure 1C] 1 shows slot allocation for a multi-hop network. [Figure 2] 1 illustrates an example of a broadcast flooding scheme for a barrage relay network. [Figure 3A] An example of TDMA slot utilization is shown below. [Figure 3B] An example of TDMA slot utilization is shown below. [Figure 3C] An example of TDMA slot utilization is shown below. [Figure 4] 1 shows an example of a transmitter and multiple receivers using multiple channels in a single TDMA slot. [Figure 5] 1 shows an example of multiple cooperative transmitters simultaneously using different channels in the same TDMA slot. [Figure 6] 1 shows a flowchart of an exemplary method for wireless communication. [Figure 7] 10 illustrates a flowchart of another exemplary method for wireless communication. [Figure 8] 1 is a block diagram representation of a portion of a wireless device that may be used to implement embodiments of the disclosed technology. DETAILED DESCRIPTION OF THE INVENTION

[0012] Propagation delay is the amount of time it takes for a communication signal to travel from source to destination over a given transmission medium, i.e., D p = d / c, where D pwhere ∑ is the propagation delay, d is the distance between the source and destination, and c is the speed of the signal. In most terrestrial wireless systems, such as mobile cellular and Wi-Fi networks, the propagation delay is typically small compared to the packet size, and the effects of the propagation delay can be mitigated using techniques such as guard periods. However, using guard periods in systems with long propagation delays (e.g., underwater acoustic channels, satellite communications, etc.) results in poor channel utilization. Furthermore, configuring a system to use the worst-case round-trip time (RTT) results in significant inefficiencies for devices in systems with RTTs smaller than the worst-case RTT. Embodiments of the disclosed technology enable high utilization and low latency communication in time-slotted networks over channels with long propagation delays.

[0013] Some embodiments described herein are directed to single-hop and multi-hop time-slotted wireless networks, i.e., wireless networks that may implement a time division multiple access (TDMA) scheme, dividing a unit of time, e.g., one second, into slots, each dedicated to the transmission and reception of messages from nodes that may be multiple hops away from each other.

[0014] In one example, the representative slot allocations shown in Figures 1A, 1B, and 1C define virtual channels for different types of messages, including synchronization, data, and voice messages. Table 1 provides a legend for some of the types of slots allocated within a frame.

[0015] [Table 1]

[0016] A barrage relay network (BRN), which is an example of a time-slotted multi-hop wireless network, is shown in Figure 2. The BRN in Figure 2 illustrates a wireless network in which independent medium allocation is obtained via a TDMA scheme. While BRNs can be defined according to various medium allocation schemes (e.g., time slots, different frequency channels, different frequency hopping patterns, different antenna radiation patterns, low cross-correlation spreading sequences, etc.), embodiments of the disclosed technology are described in the context of a time-slotted barrage relay network but are intended to be applicable to other medium allocation schemes.

[0017] Specifically, time is divided into frames, which are further divided into multiple slots per frame (e.g., Figure 2 uses three slots per frame, labeled "A," "B," and "C"). The data transmitted in a given time slot is denoted as a "packet." Two packets transmitted by two different nodes are said to be identical if all data, including all protocol header information contained in the respective packets, is identical.

[0018] In one embodiment, for example, central node 101 transmits a packet on slot A of the first TDMA frame. All nodes that successfully receive this packet are, by definition, one hop away from the source. These nodes are labeled 111-117 in FIG. 2. These nodes transmit the same packet on slot B, thus relaying it to nodes two hops away from the source (nodes 121-129), which then transmit the same packet on slot C. Nodes three hops away from the source node (nodes 131-137) relay the packet on slot A of the second TDMA frame. Thus, the packet is transmitted outward from the source via a decode-and-forward technique.

[0019] In the embodiment shown in Figure 2, multiple two-hop nodes receive the same packet from different one-hop nodes. These packets do not collide due to the physical (PHY) layer processing used by the BRN. Specifically, the BRN uses a PHY layer that allows identical packets to be combined at the receiver in a manner similar to multipath mitigation in conventional wireless receivers. That is, multiple time-shifted copies of the received signal occurring at the BRN can be interpreted at the receiver as resulting from, for example, reflections off buildings when a single source transmits, rather than from different transmitting nodes.

[0020] For two packets to be identical, both the payload data and all protocol header data must be identical. Therefore, protocol headers in a barrage relay network can only be modified in a common manner across all nodes at a given hop distance from the source. This is in stark contrast to traditional hierarchical network architectures that use a point-to-point link abstraction at Layer 2, where protocol headers can be modified in a node-specific, as opposed to hop-specific, manner.

[0021] In some embodiments, spatial reuse of time slots allows packets to be pipelined to the source for transmission every three slots. Specifically, as shown in FIG. 2, the one-hop node will not receive a packet broadcast by a three-hop node during slot A of the second TDMA frame. Therefore, the source can safely transmit a second packet during that slot. In this way, a throughput of W / 3 can be achieved for broadcasting in a single source BRN (W is the capacity of a single point-to-point link). This efficient injection of messages for broadcast transmission is referred to as "spatial pipelining" to emphasize its reuse of time slots between spatially separated nodes.

[0022] More generally, spatial pipelining can be achieved by having the source node inject a new packet for each barrage relay broadcast every M slots, resulting in a throughput of W / M. In this context, M is referred to as the spatial pipelining factor (SPF). In some embodiments, when the size of any wireless network is not known to the source in advance, M must be at least 3 to avoid collisions. A larger spatial pipelining factor (e.g., 4) may be selected to increase robustness in highly mobile network topologies.

[0023] Furthermore, to encompass the scope of a given barrage relay transmission, two fields can be incorporated into the header (preamble) of each data packet: a time-to-live (TTL) field and a hop count (HC) field. The TTL field is unchanged by relay nodes, while the HC field is initially set to 1 by the packet's source and incremented during relaying. In the context of FIG. 2, the central node 101 may set the TTL field to 8, allowing the packet to propagate across 8 hops through the BRN. A one-hop neighbor of this central node receives such a packet and relays the modified packet with the HC field set to 2. Similarly, a two-hop neighbor sets HC to 3, and so on. Relaying continues whenever a received packet has an HC field less than or equal to the TTL field, but stops if this condition cannot be met.

[0024] Although the discussion of the interaction between the TTL and HC fields is in the context of a BRN, the concept of incrementing the HC field during relaying and stopping the relaying process when a packet with equal TTL and HC fields is received is not limited to BRNs and is generally compatible with other wireless networks. For example, a time-slotted multi-hop network with a single node at each hop can support the interaction between TTL and HC, as well as spatial pipelining, in the manner described above.

[0025] In a time-slotted network (e.g., the BRN described above), a TDMA-based MAC can be configured to use a slot guard time to overcome propagation delay and timing reference error to avoid overlap of two consecutive signals between two consecutive TDMA slots at the receiver. Typically, propagation time is the main source of timing uncertainty, and the slot guard time is provisioned based on the maximum propagation delay of the link.

[0026] In terrestrial RF communications, link propagation delays (100 μs for 30 km) are typically small compared to signal transmission (burst) times (hundreds of microseconds to a few milliseconds), and therefore the relative overhead due to slot guard times is manageable. However, there are applications where long propagation delays are unavoidable. For example, line-of-sight aerial networks may operate over link distances of hundreds of kilometers, thereby requiring guard times of several milliseconds. Underwater acoustic communications (UWAC) also suffers from large propagation delays due to the relatively slow speed of wave propagation (approximately 1.5 km / s), which translate into delays of several seconds (e.g., to cover multiple kilometers over ocean depths).

[0027] Figures 3A, 3B, and 3C show an example of TDMA slot allocation. As shown in Figure 3A, a TDMA slot (310) has a signal duration S (320), a maximum propagation delay P (330), and a slot guard time G (340), where G>P. In this example framework, the slot-level channel utilization, U, is given by:

[0028]

number

[0029] The slot-level latency, L, is

[0030]

number

[0031] In some embodiments, MAC layer system utilization and latency are proportional to slot-level system utilization and latency metrics, respectively. Generally, a smaller S and a smaller P / S ratio are desirable for TDMA MAC.

[0032] Figure 3A shows an exemplary TDMA scheme with a small P (compared to the signal duration S) that operates with high efficiency and low latency. Figure 3B shows another exemplary TDMA scheme with a large P (compared to the TDMA slot length T) that operates with comparable latency but lower utilization. Figure 3C shows yet another TDMA scheme with a large P that operates with comparable utilization but higher latency. Thus, conventional TDMA schemes suffer from a trade-off between utilization and latency for a large P.

[0033] In some embodiments, for scenarios with large propagation delays, a random access MAC solution may be implemented to improve channel utilization, but this comes at the expense of desirable attributes of TDMA.

[0034] This patent document uses terminology including physical layer protocol data unit (PPDU) and interframe spacing (IFS) solely for ease of understanding and the disclosed techniques, and embodiments may be implemented in other wireless systems that use physical layer bursts and inter-burst spacing.

[0035] Embodiments of the disclosed technology are directed, for example, to communication systems experiencing high propagation delays, and may be configured to achieve high channel utilization and low latency (down to signal duration S) by provisioning multiple physical layer protocol data units (PPDUs) (or more generally, multiple bursts) with multiple orthogonal radio resources during a TDMA slot. In terms of terminology, each PPDU is assumed to be transmitted in a corresponding time interval of a TDMA slot. Here, the radio resources are referred to as channels or logical channels. In one example, logical channels may be configured in frequency, space (antenna directivity), polarization, or code domain.

[0036] According to the described embodiments, high utilization and low latency can be achieved regardless of how slots are organized and utilized at the TDMA frame level, and the described methods and techniques can be applied to existing wireless devices that have a single half-duplex transceiver (where the wireless device can either transmit or receive, but not both simultaneously).

[0037] In some embodiments, a transmitter of a TDMA slot transmits a first PPDU in a first time interval of the TDMA slot using a primary channel. Instead of idling for the remaining channel time in the transmission slot (e.g., the remaining time interval), the transmitter switches to one or more secondary channels to transmit additional PPDUs, each separated in time by a predefined inter-frame spacing (IFS) long enough to accommodate the time for the transmitter and / or receiver to switch from one channel to another. All transmitted PPDUs are contained entirely within the current TDMA slot. The larger the maximum propagation delay (P), the larger the TDMA slot, and therefore, the more PPDUs can be transmitted within a single TDMA slot. From the transmitter's perspective, previously unused guard time is fully utilized for disseminating information in the additional PPDUs.

[0038] In some embodiments, one or more specific logical channels within a BRN may be used to transmit PPDUs as described in the embodiments herein, and other logical channels may be used as originally designed. In one example, PPDUs may be transmitted within frames associated only with a synchronous logical channel (e.g., "S" in FIG. 1A), while other channels may be used for data (e.g., "D" in FIG. 1A), voice (e.g., "V" in FIG. 1A), etc.

[0039] In some embodiments, the receivers of a TDMA slot always tune to the primary channel and look for the first PPDU at the beginning of the TDMA time slot. Upon receiving the first PPDU, each receiver evaluates the time-of-arrival (TOA) and independently decides whether to switch to the secondary channel to receive subsequent PPDUs. If the TOA of the primary PPDU is too late (due to a time offset and propagation delay relative to the sender), a particular receiver may decide to remain on the primary channel and prepare for upcoming activity in the next time slot. Similarly, each receiver may independently decide to receive all or a subset of subsequent PPDUs based on its local timeline.

[0040] FIG. 4 shows an exemplary embodiment of the described technique configured for a transmitter (TX) and multiple receivers (RXn). The transmitter transmits a TDMA slot (410) of length T by transmitting a first PPDU (412) on a primary channel (CH1) followed by one or more PPDUs (414, 416, 418) on alternate channels (CH2, CH3, and CH4, respectively). The nth PPDU, denoted Sn, is followed by an interframe spacing IFSn (413, 415, 417, and 419 for n=1, 2, 3, and 4, respectively). In some embodiments, IFSn is chosen to be large enough to accommodate the time required to switch between channels, the maximum delay spread on CHn, and the receiver's processing latency for the PPDU. In some embodiments, there is no explicit slot guard governed by propagation time; in fact, IFSn can be much smaller than the maximum propagation delay on CHn, e.g., tens of milliseconds to several seconds for underwater acoustic channels. If the propagation delay of CH2 is expected to be significantly smaller than that of CH1, then IFS1 (413) may be selected to be larger than the subsequent IFSs (415, 417, 419) to ensure that S1 (412) arrives before the subsequent PPDU. The subsequent IFS durations can be similarly configured for the expected difference in channel propagation times.

[0041] Without loss of generality, it is assumed that all PPDUs in the example of FIG. 4 have a common duration S. The time of arrival (TOA) of the nth PPDU at the kth receiver is denoted by TOAnk. The TOA of a PPDU is estimated through reception processing, for example, by correlating with a predefined pilot and / or preamble sequence inserted into the PPDU.

[0042] As shown in FIG. 4, the first receiver (RX1) of the slot detects the first PPDU (422) having TOA11 + S < T(420 - 1). The remaining time Δ11 = T - (TOA11 + S)(423) is large enough for RX1 to attempt to decode S1 before the slot expires. However, subsequent PPDUs (Sn, n = 2, 3, 4) are received with TOAn1 + S > T and cannot be processed by RX1.

[0043] The second receiver (RX2) shown in FIG. 4 experiences a lower propagation delay across the channel compared to the first receiver (RX1). Here, the remaining time Δ12 = T - (TOA11 + S) is large enough for RX2 to attempt to decode S1 of the first PPDU (432) and, if S1 is successfully decoded, attempt to switch to CH2 to detect S2 of the second PPDU (434). If the remaining time Δ22 = T - (TOA22 + S) is large enough to process S2 and return to the primary channel (CH1) for subsequent TDMA slots, RX2 decides to decode S2; otherwise, S2 is not processed. Subsequent PPDUs (Sn, n = 3, 4) are received with TOAn2 + S > T and cannot be processed by RX2.

[0044] The third receiver (RX3) shown in FIG. 4 experiences an even lower propagation delay such that TOA13 + S < TOA23 + S < TOA33 + S < T, and as a result, RX3 can decode the first three PPDUs. Since TOA43 + S > T, it cannot process the slot of the last PPDU (S4).

[0045] Embodiments of the disclosed technology may also be configured for waveforms with cooperative communication capabilities, whereby there may be multiple transmitters of the same slot, with copies of that slot arriving at a particular receiver with different delays. To prevent interference between PPDUs from multiple transmitters with different propagation delays, each PPDU of a transmitted slot uses a different channel, as shown in Figure 5. As shown there, S1 (512) is transmitted on CH1 followed by a first inter-frame spacing time IFS1 (513), S2 (514) is transmitted on CH2 followed by a second inter-frame spacing time IFS2 (515), and so on.

[0046] In some embodiments, channels may be reused during a TDMA slot based on maximum propagation delay, eg, CH3=CH1 and CH4=CH2.

[0047] According to some embodiments of the disclosed technology, a first PPDU can be used to transmit a first type of information or data, and a subsequent PPDU can be used to transmit a second type of information or data. In one example, the first type of data and the second type of data are identical. In another example, the second type of data is different from the first type of data. The subsequent PPDU can be used for one or more redundant transmissions of data, for transmission of error-tolerant data, and to obtain additional user capacity for short-range links.

[0048] In some embodiments, subsequent PPDUs may be used for redundant transmissions based on the fact that not all links experience the maximum expected propagation delay. Receivers with smaller propagation delays may receive multiple copies of the same data within a TDMA slot and combine these signals to improve reliability. This advantage may be particularly important in difficult channels that experience signal fading, such as underwater acoustic channels.

[0049] In some embodiments, subsequent PPDUs can be used for redundant transmission in a multi-hop barrage relay network (BRN), e.g., as described in the context of FIG. 2. The barrage relay waveform realizes synchronous multi-hop cooperative relaying as part of the MAC layer function. The PPDU transmission sequence is associated with a downward propagation delay constraint, such that the first primary PPDU can be received by all links within the maximum propagation delay provisioned by the slot guard time. Each subsequent PPDU can only be received by a receiver experiencing a lower propagation delay. Successful detection and decoding of the PPDU depends on other factors, such as transient channel errors. Thus, in the case of a BRN, the PPDU sequence automatically provides different multi-hop relay paths consisting of all links or a subset of shorter (potentially more reliable) links. This can be advantageously exploited to increase the diversity and reliability of the end-to-end path.

[0050] In some embodiments, subsequent PPDUs can be used for the transmission of error-tolerant data. In one example, one type of error-tolerant data is the Position Location Information (PLI) service present in many tactical waveforms. In another example, various Layer 2 control and management functions (including ranging and time tracking between one-hop neighbors) are error-tolerant. In a conventional TDMA MAC, such information would consume its own time slot, but in the described embodiment, it can be advantageously disseminated via the secondary PPDU without additional overhead.

[0051] In some embodiments, the subsequent PPDUs may be used to support additional user capacity for short-range links. In a typical MANET network use case, high propagation links exist with only a single or few long-range links, and the majority of nodes are in close proximity to their one-hop neighbors. When ranging information is available, a cognitive TDMA MAC may intelligently utilize the additional PPDUs for the majority of short-range traffic to provide long-range communication capabilities without losing channel utilization efficiency.

[0052] FIG. 6 shows a flowchart of an example method 600 for high utilization, low latency multi-channel TDMA. The method 600 includes, at operation 610, transmitting a first data unit over a first logical channel of a plurality of logical channels in a first time interval of a time division multiplexing (TDMA) slot. In one example, the transmission may use a constant envelope (CE) waveform, such as continuous phase modulation (CPM) or CE-orthogonal frequency division multiplexing (CE-OFDM). In another example, the transmission may use OFDM with a high-order quadrature amplitude modulation (QAM) constellation (e.g., 64-QAM or higher) to achieve high data rates. In yet another example, the transmission may be more robust by using a lower-order QAM constellation (e.g., QPSK, 8-PSK).

[0053] Method 600 includes, at operation 620, refraining from transmitting for a second time interval immediately following the first time interval following completion of transmission of the first data unit. In one example, the first data unit may be S1 (412) or S1 (512) of Figures 4 and 5, respectively, and the corresponding second time interval may be IFS1 (413) and IFS1 (513), as shown in Figures 4 and 5, respectively.

[0054] The method 600 includes, at operation 630, for each data unit of the (N-1) subsequent data units in the TDMA slot, performing (N-1) transmissions at (N-1) time intervals, such that the transmission of the nth data unit of the (N-1) subsequent data units is performed by the nth logical channel of the plurality of logical channels. In some embodiments, n and N are positive integers, 2≦n≦N, each of the plurality of logical channels corresponds to a distinct transmission resource, the wireless medium is characterized by a maximum propagation delay, and the duration of the TDMA slot is greater than the maximum propagation delay. Operation 630 is shown in FIG. 4 for, e.g., N=4, where S2, S3, and S4 are transmitted on CH2, CH3, and CH4, respectively, all within the same TDMA slot (410) of length T.

[0055] In some embodiments, the method 600 further includes an operation of performing a switching operation from the nth logical channel to the (n+1)th logical channel following the transmission of the nth data unit, where 2≦n≦(N−1). As shown in the example of FIG. 4, following the transmission of S2 (414), a switching operation (from CH2 to CH3) is performed for a duration denoted as IFS2 (415).

[0056] In some embodiments, the distinct transmission resources include frequencies, frequency bands, antenna directions, polarizations, or codes.

[0057] In some embodiments, the maximum propagation delay is greater than tens of milliseconds. In one example, the maximum propagation delay of tens of milliseconds is due to a wireless medium that includes a line-of-sight (LOS) air link spanning hundreds of kilometers. In another example, the maximum propagation delay is due to a wireless medium that includes an underwater acoustic link with a relatively slow wave propagation speed (e.g., approximately 1.5 km / sec).

[0058] In some embodiments, the second time interval is the interval between bursts (eg, IFS1, shown as 413 and 513 in FIGS. 4 and 5, respectively).

[0059] In some embodiments, the duration of the interval between bursts is based on at least the maximum delay spread, hi one example, the interval between bursts is selected to be large enough to include switching time, the maximum delay spread, and the receiver processing latency of the data unit to allow subsequent data units to be processed.

[0060] In some embodiments, the data in each of the N subsequent data units is identical to the data in the first data unit. By sending redundant data, the message completion rate (MCR) is increased and / or the bit error rate (BER) and packet error rate (PER) are reduced.

[0061] In some embodiments, the first data unit includes high-speed data, and each data unit of the N subsequent data units includes error-tolerant data. In one example, the error-tolerant data includes position location information (PLI) or Layer 2 control and management functions, and the high-speed data includes video or audio data. In another example, the error-tolerant data uses a low-rate error correcting code (ECC), such as a low-density parity check (LDPC) code. In yet another example, the high-speed data includes information having a data rate on the order of several megabytes (MB), while the error-tolerant data includes information having a data rate on the order of several kilobytes (kB).

[0062] In some embodiments, the duration of each of the (N-1) time intervals is the same as the duration of the first time interval. In one example, the duration may be the same when the N-1 subsequent data units are used to retransmit data transmitted in the first data unit to achieve a higher MCR or a lower BER / PER through redundant transmission.

[0063] In some embodiments, the duration of each of the N-1 data units may be the same but may differ from the duration of the first time interval. In one example, this may be the case when the first data unit is used for high-speed data and the subsequent data unit is used for PLI data.

[0064] 7 shows a flowchart of another example method 700 for high utilization low latency multi-channel TDMA. The method 700 includes, at operation 710, receiving and detecting a first data unit by a first logical channel of a plurality of logical channels at a first time in a time division multiple access (TDMA) slot.

[0065] The method 700 includes, at operation 720, receiving and detecting at least one of the (N-1) subsequent data units at each of (N-1-1) times in the TDMA slot, such that reception of an nth data unit of the (N-1) subsequent data units is performed by an nth logical channel of the plurality of logical channels. In some embodiments, n and N are positive integers, 2≦n≦N, each of the plurality of logical channels corresponds to a distinct transmission resource, the wireless medium is characterized by a maximum propagation delay, and the duration of the TDMA slot is greater than the maximum propagation delay.

[0066] In some embodiments, the method 700 further includes an operation of performing a switch operation from the nth logical channel to the (n+1)th logical channel following receipt of the nth data unit, where 2≦n≦(N−1).

[0067] In some embodiments, detecting the first data unit is based on the first data unit including a predefined pilot sequence.

[0068] In some embodiments, the distinct transmission resources include frequencies, frequency bands, antenna directions, polarizations, or codes.

[0069] In some embodiments, the number of at least one of the (N-1) subsequent data units received and detected is based on the duration between the first time and the end of the TDMA slot.

[0070] As described in this patent document, embodiments of the disclosed technology solve the technical problems of poor channel utilization and increased latency typically associated with systems having long propagation delays.

[0071] Preferred embodiments of the disclosed technology are listed in the solution list below. 1. A method for wireless communication over a wireless medium including a plurality of logical channels, the method including: transmitting a first data unit by a first logical channel of the plurality of logical channels in a first time interval of a time division multiple access (TDMA) slot; and, following completion of the transmission of the first data unit, refraining from transmission for a second time interval immediately following the first time interval; and for each data unit of (N-1) subsequent data units in the TDMA slot, performing (N-1) transmissions in (N-1) time intervals so that the transmission of an nth data unit of the (N-1) subsequent data units is performed by the nth logical channel of the plurality of logical channels, wherein n and N are positive integers, 2≦n≦N, each of the plurality of logical channels corresponds to a distinct transmission resource; the wireless medium is characterized by a maximum propagation delay, and the duration of the TDMA slot is greater than the maximum propagation delay. 2. The method according to solution 1, further comprising performing a switching operation from the nth logical channel to the (n+1)th logical channel following transmission of the nth data unit, where 2≦n≦(N-1). 3. The method according to solution 1 or 2, wherein the separate transmission resources include frequencies, frequency bands, antenna directions, polarizations, or codes. 4. The method according to any one of solutions 1 to 3, wherein the maximum propagation delay is greater than several tens of milliseconds. 5. The method according to any one of solutions 1 to 4, wherein the second time interval is the interval between bursts. 6. The method of solution 5, wherein the duration of the interval between bursts is based on at least the maximum delay spread of the wireless medium. 7. The method according to any one of solutions 1 to 6, wherein the wireless medium comprises a line-of-sight (LOS) air link or an underwater acoustic link. 8. The method according to any one of solutions 1 to 7, wherein the data in each data unit of the N subsequent data units is identical to the data in the first data unit. 9. The method according to any one of solutions 1 to 8, wherein the first data unit comprises high-speed data and each data unit of the N subsequent data units comprises error-tolerant data. 10. The method according to solution 9, wherein the error-tolerant data includes position location information (PLI) or layer 2 control and management functions. 11. The method according to any one of solutions 1 to 10, wherein the duration of each of the (N-1) time intervals is identical to the duration of the first time interval. 12. A wireless communication system comprising: a transmitter; a first receiver coupled to the transmitter by a wireless medium including a plurality of logical channels, each of the plurality of logical channels corresponding to a distinct transmission resource, the wireless medium being characterized by a maximum propagation delay, a distance between the transmitter and the first receiver corresponding to a first propagation delay that is smaller than the maximum propagation delay; and a second receiver coupled to the transmitter by the wireless medium, a distance between the transmitter and the second receiver corresponding to a second propagation delay that is smaller than the first propagation delay, wherein the transmitter transmits a first data unit to the first receiver and the second receiver via a first logical channel of the plurality of logical channels in a first time interval of a time division multiple access (TDMA) slot, abstaining from transmission for a second time interval immediately following the first time interval following completion of transmission of the (N-1) subsequent data units, and performing (N-1) transmissions in the (N-1) time intervals for each data unit of the (N-1) subsequent data units in the TDMA slot, such that transmission of the nth data unit of the (N-1) subsequent data units is performed by the nth logical channel of the plurality of logical channels; a second receiver configured to receive and decode at least one of the N subsequent data units within the TDMA slot, the first receiver being unable to receive and decode each of the N subsequent data units, the duration of the TDMA slot being greater than the first propagation delay, n and N being positive integers, and 2≦n≦N. 13. The system of solution 12, wherein the size of the first data unit and the size of each of the (N-1) subsequent data units are identical. 14. The system of solution 12 or 13, wherein the first time interval is greater than or equal to the sum of the time required to perform a switching operation between two of the plurality of logical channels, the maximum delay spread of the first logical channel, and the processing latency of the first data unit. 15. The system of any one of solutions 12 to 14, wherein the separate transmission resources include frequencies, frequency bands, antenna directions, polarizations, or codes. 16. A method for wireless communication over a wireless medium including a plurality of logical channels, the method including: receiving and detecting a first data unit by a first logical channel of the plurality of logical channels at a first time of a time division multiple access (TDMA) slot; and receiving and detecting at least one of (N-1) subsequent data units at each of (N-1) times in the TDMA slot, such that reception of an nth data unit of the (N-1) subsequent data units is performed by the nth logical channel of the plurality of logical channels, wherein n and N are positive integers, 2≦n≦N, each of the plurality of logical channels corresponds to a distinct transmission resource; the wireless medium is characterized by a maximum propagation delay, and the duration of the TDMA slot is greater than the maximum propagation delay. 17. The method of solution 16, further comprising performing a switching operation from the nth logical channel to the (n+1)th logical channel following reception of the nth data unit, where 2≦n≦(N−1). 18. The method of solution 16 or 17, wherein detecting the first data unit is based on the first data unit including a predefined pilot sequence. 19. The method according to any one of solutions 16 to 18, wherein the separate transmission resources include frequencies, frequency bands, antenna directions, polarizations, or codes. 20. The method according to any one of solutions 16 to 19, wherein the number of at least one of the (N-1) subsequent data units received and detected is based on the duration between the first time and the end of the TDMA slot.

[0072] According to an embodiment of the disclosed technology, a wireless communication system includes a transmitter; a first receiver coupled to the transmitter by a wireless medium including a plurality of logical channels, each of the plurality of logical channels corresponding to a distinct transmission resource, the wireless medium being characterized by a maximum propagation delay, a distance between the transmitter and the first receiver corresponding to a first propagation delay that is smaller than the maximum propagation delay; and a second receiver coupled to the transmitter by the wireless medium, the distance between the transmitter and the second receiver corresponding to a second propagation delay that is smaller than the first propagation delay, wherein the transmitter performs transmission of a first data unit to the first receiver and the second receiver via a first logical channel of the plurality of logical channels in a first time interval of a time division multiple access (TDMA) slot. the first receiver is configured to transmit the N subsequent data units over the TDMA slot, refrain from transmitting for a second time interval immediately following the first time interval following completion of the transmission of the first data unit, and for each data unit of the (N-1) subsequent data units in the TDMA slot, perform (N-1) transmissions in the (N-1) time intervals, such that the transmission of the nth data unit of the (N-1) subsequent data units is performed by the nth logical channel of the plurality of logical channels; the second receiver is configured to receive and decode at least one of the N subsequent data units within the TDMA slot, the first receiver is unable to receive and decode each of the N subsequent data units, the duration of the TDMA slot is greater than the first propagation delay, n and N are positive integers, and 2≦n≦N.

[0073] In some embodiments, the first time interval is greater than or equal to the sum of the time required to perform a switching operation between two of the plurality of logical channels, the maximum delay spread of the first logical channel, and the processing latency of the first data unit.

[0074] 8 is a block diagram representation of a portion of a wireless device in accordance with some embodiments of the techniques of this disclosure. The wireless device 811 may include processor electronics 801, such as a microprocessor, that implements one or more of the techniques presented in this patent document. The wireless device 811 may include transceiver electronics 803 for transmitting and / or receiving wireless signals via one or more communication interfaces, such as an antenna 809. The wireless device 811 may include other communication interfaces for transmitting and receiving data. The wireless device 811 may include one or more memories 807 configured to store information, such as data and / or instructions. In some implementations, the processor electronics 801 may include at least a portion of the transceiver electronics 803. In some embodiments, at least some of the disclosed techniques, modules, or functions (including, but not limited to, methods 600 and 700) are implemented using the wireless device 811.

[0075] Embodiments of the disclosed technology are directed to overcoming problems faced by conventional time-slotted MAC schemes operating in systems with large propagation delays: time slots in these systems are typically configured to take into account the maximum propagation delay, resulting in low utilization or long latency.

[0076] In the exemplary technical solution described herein, multiple bursts are transmitted on separate channels within a single TDMA time slot, and each transmitted burst is followed by a duration during which the transmitter refrains from transmitting and switches to a channel for the next burst transmission. Multiple data units are transmitted on different channels within the same time slot, which advantageously allows a receiver close to the transmitter to receive and process some of the multiple data units, while a receiver further away from the transmitter can receive and process at least the first data unit transmitted.

[0077] Some of the embodiments described herein are described in the general context of methods or processes, which may be implemented in one embodiment by a computer program product embodied in a computer-readable medium including computer-executable instructions, such as program code, executed by computers in a networked environment. The computer-readable medium may include removable and non-removable storage devices, including, but not limited to, read-only memory (ROM), random access memory (RAM), compact discs (CDs), digital versatile discs (DVDs), and the like. Thus, computer-readable media may include non-transitory storage media. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions or processor-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes.

[0078] Some of the disclosed embodiments can be implemented as devices or modules using hardware circuits, software, or a combination thereof. For example, a hardware circuit implementation may include discrete analog and / or digital components integrated, for example, as part of a printed circuit board. Alternatively or additionally, the disclosed components or modules can be implemented as Application Specific Integrated Circuit (ASIC) and / or Field Programmable Gate Array (FPGA) devices. Some implementations may additionally or alternatively include a digital signal processor (DSP), which is a dedicated microprocessor having an architecture optimized for the operational needs of digital signal processing associated with the disclosed functionality of the present application. Similarly, various components or subcomponents within each module may be implemented in software, hardware, or firmware. Connectivity between modules and / or components within a module may be provided using any one of connectivity methods and mediums known in the art, including, but not limited to, communication via the Internet, a wired network, or a wireless network using an appropriate protocol.

[0079] While this patent document contains many details, these should not be construed as limitations on the scope of the claimed invention or what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as acting in a particular combination and may even initially be claimed as such, one or more features from a claimed combination can, in some cases, be deleted from that combination, and the claimed combination may be directed to a subcombination or variations of the subcombination. Similarly, while operations are shown in the figures in a particular order, this should not be understood as requiring such operations to be performed in the particular order shown, or in any sequential order, or that all illustrated operations be performed, to achieve desired results.

[0080] Only some implementations and examples have been described; other implementations, extensions, and variations can be made based on what is described and illustrated in this disclosure.

Claims

1. A method for wireless communication between a transmitter and at least one receiver over a wireless medium including a plurality of logical channels, said method comprising: transmitting, by the transmitter, to the at least one receiver, a first data unit over a first logical channel of the plurality of logical channels during a first time interval of a time division multiple access (TDMA) slot; refraining from transmitting for a second time interval immediately following the first time interval following completion of the transmission of the first data unit; For each data unit of the (N-1) subsequent data units in the TDMA slot, performing (N-1) transmissions at (N-1) time intervals, so that transmission of an n-th data unit of the (N-1) subsequent data units is performed by an n-th logical channel of the plurality of logical channels; n and N are positive integers, 2≦n≦N, and each of the plurality of logical channels corresponds to a distinct transmission resource; the first time interval, the second time interval, and the sum of the (N-1) time intervals are less than or equal to the duration of the TDMA slot; the at least one receiver is configured to determine whether to receive and decode one or more of the (N-1) subsequent data units based on comparing a time of arrival (TOA) of the first data unit with an end of the TDMA slot. method.

2. 2. The method of claim 1, further comprising: performing a switching operation from the nth logical channel to an (n+1)th logical channel following the transmission of the nth data unit, where 2≦n≦(N−1).

3. The method of claim 1 , wherein the distinct transmission resources include frequencies, frequency bands, antenna directions, polarizations, or codes.

4. The method described in claim 1, wherein the maximum propagation delay in the wireless medium is less than the duration of the TDMA slot and greater than several tens of milliseconds.

5. The method of claim 1 , wherein the second time interval is an inter-burst interval.

6. 6. The method of claim 5, wherein the duration of the inter-burst interval is based on at least a maximum delay spread of the wireless medium.

7. The method of claim 1 , wherein the wireless medium comprises a line-of-sight (LOS) air link or an underwater acoustic link.

8. 2. The method of claim 1, wherein data in each of the (N-1) subsequent data units is identical to data in the first data unit.

9. 2. The method of claim 1, wherein the first data unit comprises high-speed data and each data unit of the (N-1) subsequent data units comprises error-tolerant data.

10. 10. The method of claim 9, wherein the error-tolerant data includes position location information (PLI) or layer 2 control and management functions.

11. 2. The method of claim 1, wherein a duration of each of the (N-1) time intervals is the same as a duration of the first time interval.

12. 1. A wireless communication system, comprising: A transmitter; a first receiver coupled to the transmitter by a wireless medium including a plurality of logical channels, each of the plurality of logical channels corresponding to a distinct transmission resource, the wireless medium being characterized by a maximum propagation delay, and a distance between the transmitter and the first receiver corresponding to a first propagation delay that is less than the maximum propagation delay; a second receiver coupled to the transmitter by the wireless medium, wherein a distance between the transmitter and the second receiver corresponds to a second propagation delay that is smaller than the first propagation delay; The transmitter: transmitting a first data unit to the first receiver and the second receiver via a first logical channel of the plurality of logical channels during a first time interval of a time division multiple access (TDMA) slot; refraining from transmitting for a second time interval immediately following the first time interval following completion of the transmission of the first data unit; and for each data unit of the (N-1) subsequent data units in the TDMA slot, (N-1) transmissions are performed at (N-1) time intervals, so that transmission of an n-th data unit of the (N-1) subsequent data units is performed by an n-th logical channel of the plurality of logical channels; the second receiver is configured to receive and decode at least one of the (N-1) subsequent data units within the TDMA slot, the first receiver is unable to receive and decode each of the (N-1) subsequent data units, a duration of the TDMA slot is greater than the first propagation delay, n and N are positive integers, and 2≦n≦N.

13. 13. The system of claim 12, wherein the size of the first data unit and the size of each of the (N-1) subsequent data units are the same.

14. 13. The system of claim 12, wherein the first time interval is greater than or equal to the sum of a time required to perform a switching operation between two of the plurality of logical channels, a maximum delay spread of the first logical channel, and a processing latency of the first data unit.

15. The system of claim 12 , wherein the distinct transmission resources include frequencies, frequency bands, antenna directions, polarizations, or codes.

16. 1. A method for wireless communication over a wireless medium including a plurality of logical channels, said method comprising: receiving and decoding a first data unit by a first logical channel of the plurality of logical channels at a first time in a time division multiple access (TDMA) slot, the first time corresponding to a time of arrival (TOA) of the first data unit; comparing a TOA of the first time with the end of the TDMA slot; determining whether to receive and decode at least one of the (N-1) subsequent data units at each of the (N-1) time periods in the TDMA slot based on the comparison, whereby reception of an n-th data unit of the (N-1) subsequent data units is performed by an n-th logical channel of the plurality of logical channels; n and N are positive integers, 2≦n≦N, and each of the plurality of logical channels corresponds to a distinct transmission resource; a time length between the first time and the (N-1) times is equal to or less than a duration of the TDMA slot; method.

17. 17. The method of claim 16, further comprising: performing a switch operation from the nth logical channel to an (n+1)th logical channel following the reception of the nth data unit, where 2≦n≦(N−1).

18. 17. The method of claim 16, wherein the decoding of the first data unit is based on the first data unit including a predefined pilot sequence.

19. The method of claim 16 , wherein the distinct transmission resources include frequencies, frequency bands, antenna directions, polarizations, or codes.

20. 17. The method of claim 16, wherein the number of the at least one of the (N-1) subsequent data units received and decoded is based on a duration between the first time and an end of the TDMA slot.

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