Using time division duplex systems in frequency division duplex networks

Abstract

Techniques are described herein to coordinate operation of access nodes in a communication system to enable efficient use of TDD systems (e.g., cellular equipment) in FDD networks (e.g., satellite networks). The two access nodes may be configured with complementary schedules such that the forward link slot of the first access node corresponds to the return link slot of the second access node, and vice versa. In this arrangement, all time slots of the satellite network are utilized except for the switching time slots. Advantageously, although the cellular equipment implements a TDD scheme, the coordinated operation of the access nodes allows the satellite network to operate in full duplex, and may make the duration of handover time slots in the scheduling relatively small. That is, the switching time slot is not affected by the propagation delay of the signal through the satellite network.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 297,623, filed on January 7, 2022, and entitled “TDD SYSTEM FOR FDD OVERSATELLITE,” the entire contents of which are expressly incorporated herein by reference for all purposes. Background Art Technical Field

[0003] The present disclosure generally relates to communication systems that employ both time division duplexing and frequency division duplexing.

[0004] Description of related technologies

[0005] A communication system may employ a variety of technologies to enable communication between devices on a network. A communication system may use terrestrial network links, non-terrestrial network links, or a combination of these network links to pass information between devices. These network links use duplexing to enable two-way communication over a communication channel. Two forms of duplexing include time division duplexing (TDD) and frequency division duplexing (FDD). In wireless communication systems, time division duplexing uses a single frequency band or channel for both transmission and reception, while frequency division duplexing uses different frequency bands or channels for transmission and reception. Summary of the invention

[0006] In some embodiments, the present disclosure relates to a method for coordinating the operation of a base station with a first access node and a second access node. The method includes generating a first TDD schedule for a first access node in a baseband, the first TDD schedule including a first plurality of forward link time slots and a first plurality of return link time slots, wherein there is a switching time gap between the first plurality of forward link time slots and the first plurality of return link time slots. The method also includes mapping the first TDD schedule to an uplink frequency for the first plurality of forward link time slots and mapping to a downlink frequency for the first plurality of return link time slots. The method also includes generating a second TDD schedule for a second access node in a baseband, the second TDD schedule including a second plurality of forward link time slots and a second plurality of return link time slots, wherein there is a switching time gap between the second plurality of forward link time slots and the second plurality of return link time slots. The method also includes mapping the second TDD schedule to an uplink frequency for a second plurality of forward link time slots and mapping to a downlink frequency for a second plurality of return link time slots. The first TDD schedule is complementary to the second TDD schedule such that the first plurality of forward link time slots coincide in time with the second plurality of return link time slots and the first plurality of return link time slots coincide in time with the second plurality of forward link time slots.

[0007] In some implementations, the method further includes synchronizing the first TDD schedule and the second TDD schedule in time based on the clock signal. In some implementations, the method further includes transmitting the first TDD schedule to the first access node to configure the operation of the first access node; and transmitting the second TDD schedule to the second access node to configure the operation of the second access node.

[0008] In some implementations, the switching time gap in the first TDD schedule coincides in time with the switching time gap in the second TDD schedule. In some implementations, the switching time gap is shorter than the shortest round trip propagation time between the first access node or the second access node and a user terminal with which the first access node or the second access node communicates. In some implementations, the duration of the switching time gap is independent of the round trip propagation time between the first access node or the second access node and a user terminal with which the first access node or the second access node communicates.

[0009] In some implementations, the number of time slots in the first plurality of forward link time slots is different from the number of time slots in the first plurality of return link time slots. In some implementations, the first access node and the second access node have the same carrier frequency and channel bandwidth. In some implementations, the first access node and the second access node share a radio frequency communication channel. In some implementations, the first access node and the second access node share an antenna.

[0010] In some embodiments, the present disclosure relates to a base station of a communication system. The base station includes a first access node; a second access node; a duplexer; an adder configured to generate a transmit signal by combining a transmit signal from the first access node with a transmit signal from the second access node, and send the transmit signal to the duplexer; a separator configured to separate a receive signal from the duplexer into a received signal for the first access node and a received signal for the second access node, send the received signal for the first access node to the first access node, and send the received signal for the second access node to the second access node; a clock configured to generate a clock signal to synchronize the first access node and the second access node; and a configuration module. The configuration module is configured to generate a first TDD schedule for a first access node in baseband, the first TDD schedule comprising a first plurality of forward link time slots and a first plurality of return link time slots, wherein there is a switching time gap between the first plurality of forward link time slots and the first plurality of return link time slots; map the first TDD schedule to an uplink frequency for the first plurality of forward link time slots and to a downlink frequency for the first plurality of return link time slots; generate a second TDD schedule for a second access node in baseband, the second TDD schedule comprising a second plurality of forward link time slots and a second plurality of return link time slots, wherein there is a switching time gap between the second plurality of return link time slots and the second plurality of forward link time slots; and map the second TDD schedule to an uplink frequency for the second plurality of forward link time slots and to a downlink frequency for the second plurality of return link time slots. The first TDD schedule is complementary to the second TDD schedule such that the first plurality of forward link time slots coincide in time with the second plurality of return link time slots, and the first plurality of return link time slots coincide in time with the second plurality of forward link time slots.

[0011] In some implementations, the base station further includes an antenna coupled to the duplexer, the antenna being configured to communicate with the satellite network. In some implementations, the switching time gap in the first TDD schedule coincides in time with the switching time gap in the second TDD schedule. In some implementations, the switching time gap is shorter than the shortest round-trip propagation time between the first access node or the second access node and a user terminal with which the first access node or the second access node communicates. In some implementations, the duration of the switching time gap is independent of the round-trip propagation time between the first access node or the second access node and the user terminal with which the first access node or the second access node communicates.

[0012] In some implementations, the first access node and the second access node are each half-duplex. In some implementations, the first access node and the second access node have the same carrier frequency and channel bandwidth. In some implementations, the first access node is configured to communicate with a first plurality of user terminals via a satellite network, and the second access node is configured to communicate with a second plurality of user terminals via a satellite network.

[0013] In some embodiments, the present disclosure relates to a communication system, which includes a base station having a first access node, a second access node, an antenna, and a configuration module. The configuration module is configured to generate a first TDD schedule for the first access node in a baseband, the first TDD schedule including a first plurality of forward link time slots and a first plurality of return link time slots, wherein there is a switching time gap between the first plurality of forward link time slots and the first plurality of return link time slots; map the first TDD schedule to an uplink frequency for the first plurality of forward link time slots and to a downlink frequency for the first plurality of return link time slots; generate a second TDD schedule for the second access node in a baseband, the second TDD schedule including a second plurality of forward link time slots and a second plurality of return link time slots, wherein there is a switching time gap between the second plurality of forward link time slots and the second plurality of return link time slots; and map the second TDD schedule to an uplink frequency for the second plurality of forward link time slots and to a downlink frequency for the second plurality of return link time slots. The communication system also includes a satellite network including a satellite; and a plurality of user terminals configured to communicate with at least one of a first access node and a second access node of the base station through the satellite network. The first TDD schedule is complementary to the second TDD schedule, so that the first plurality of forward link time slots coincide in time with the second plurality of return link time slots, and the first plurality of return link time slots coincide in time with the second plurality of forward link time slots.

[0014] In some implementations, the first access node is configured to communicate with a first group of user terminals in the plurality of user terminals, and the second access node is configured to communicate with a second group of user terminals in the plurality of user terminals. In some implementations, the user terminals in the plurality of user terminals are on a mobile platform. In some implementations, the user terminals in the plurality of user terminals are user devices configured to communicate directly with a satellite network.

[0015] In some implementations, the satellite network includes low earth orbit satellites. In some implementations, the satellite network includes geosynchronous satellites.

[0016] In some implementations, individual propagation times between the first access node and individual user terminals of the plurality of user terminals are different. In some implementations, at least one propagation time between the first access node and individual user terminals of the plurality of user terminals varies over time. In some implementations, a timing advance between a forward link time slot and a return link time slot in a first user terminal of the plurality of user terminals causes the return link time slot and the forward link time slot in the first user terminal to overlap. In some implementations, a timing advance between a forward link time slot and a return link time slot in a first user terminal of the plurality of user terminals is configured to cause a switching time gap.

[0017] For the purpose of summarizing the present disclosure, certain aspects, advantages, and novel features have been described herein. It should be understood that not all such advantages need be achieved according to any particular embodiment. Thus, the disclosed embodiments may be implemented or performed in a manner that achieves or optimizes one advantage or a group of advantages taught herein without necessarily achieving other advantages taught or suggested herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various embodiments are depicted in the drawings for purposes of illustration and should in no way be construed as limiting the scope of the present disclosure. Additionally, various features of different disclosed embodiments may be combined to form additional embodiments as part of the present disclosure.

[0019] Figure 1 A diagram of an example communication system that communicatively couples multiple user terminals and a gateway routing device to each other using a satellite network to provide access to the network is shown.

[0020] FIG. 2A shows an example of a typical TDD scheme in a cellular communication system.

[0021] Figure 2B A comparison of time slot allocation in a terrestrial communication system (eg, a cellular communication system) and time slot allocation in a satellite communication system is shown.

[0022] FIG. 2C shows an example of a typical FDD scheme in a satellite communication system.

[0023] FIG. 2D shows an example of a typical cellular communication system modified to operate over a satellite network.

[0024] Figure 3 An example communication system is shown that includes a base station configured to communicate over a satellite network, the base station including a first access node and a second access node configured to operate using complementary TDD scheduling.

[0025] Figure 4 An example base station including a configuration module that coordinates the operation of two access nodes is shown.

[0026] Figure 5 A flow chart illustrating an example method of coordinating operation of a TDD system (eg, a half-duplex access node) in an FDD network (eg, a satellite network) is shown.

[0027] Figure 6 A block diagram of an example configuration system configured to coordinate operation of a first access node and a second access node is shown. DETAILED DESCRIPTION

[0028] Subheadings provided herein, if any, are for convenience only and do not necessarily affect the scope or meaning of the claimed subject matter.

[0029] Overview

[0030] Some wireless communication systems such as cellular networks use time division duplex (TDD) to communicate between a base station and user equipment such as a cellular phone. This means that the same carrier frequency or channel is used for both downlink (DL) and uplink (UL) transmissions. Therefore, in a TDD frame, there is usually a series of DL time slots and a series of UL time slots separated by a gap period to allow the equipment to switch between transmission (Tx) and reception (Rx). The duration of the gap period is at least twice the propagation delay caused by the signal propagating between the base station and the user equipment.

[0031] Other wireless communication systems, such as satellite networks, may use frequency division duplexing (FDD) to communicate between ground stations and user terminals. This means that DL signals and UL signals use different carrier frequencies or channels, enabling DL and UL signals to communicate simultaneously. This means that unlike TDD systems, FDD systems can transmit DL signals and receive UL signals without requiring gap periods to switch between transmission and reception.

[0032] Cellular equipment and devices can be used to communicate via satellite networks by modifying the cellular system to operate in the frequency band used by satellites. However, even though the satellite network is capable of using an FDD scheme, cellular equipment and related protocols still utilize a TDD scheme for communication. Therefore, in this configuration, a large number of time slots in each frame remain unused. In addition, due to propagation delays on the satellite network, the Rx and Tx time slots on the user equipment side may overlap in time, which requires simultaneous Rx and Tx functionality (full duplex) at the user equipment.

[0033] Therefore, to address these and other problems, described herein is a technique for coordinating the operation of access nodes in a communication system to enable the use of a TDD system (e.g., cellular equipment) in an FDD network (e.g., a satellite network). Two access nodes may be configured to have complementary scheduling, such that a forward link (FL) time slot of a first access node corresponds in time to a return link (RL) time slot of a second access node, and the RL time slot of the first access node corresponds in time to the FL time slot of the second access node. However, for each access node, the scheduling does not include a FL time slot that overlaps in time with the RL time slot, so that each access node can implement a TDD scheme. The combination of complementary scheduling is configured to utilize all available time slots of a satellite link (except for a switching time slot), so that a satellite network can effectively implement an FDD scheme while merging a TDD system.

[0034] Advantageously, because the transmission of the signal utilizes the FDD scheme and the satellite network can operate in full duplex, the switching time gap can be made relatively small. In other words, the size of the switching time gap is not affected by the propagation delay of the signal through the satellite link. Advantageously, because the disclosed communication system is able to use the FDD scheme by coordinating the operation of the TDD system, a standard or typical TDD system (e.g., cellular equipment) can be incorporated into an FDD network (e.g., a satellite network) with little or no modification to the equipment. For example, this can be accomplished by implementing a configuration module that coordinates the operation of two or more access nodes in a base station.

[0035] Example Communication System

[0036] Figure 1 A diagram of an example communication system 100 is shown that communicatively couples a plurality of user terminals 110a, 110b and a gateway routing device 150 to each other using a satellite network 140 to provide access to a network, such as the Internet 190. The gateway routing device 150 includes a configuration module 151, a first access node 155a, and a second access node 155b. As described in greater detail herein, the operation of the first access node 155a and the second access node 155b are coordinated by the configuration module 151 so that the scheduling of the access nodes is complementary (e.g., a forward link time slot of the first access node 155a corresponds to a return link time slot of the second access node 155b, and vice versa).

[0037] The satellite network 140 includes satellites 105 to provide satellite links in the communication system 100. Each user terminal 110a, 110b is operably coupled to a corresponding client satellite transceiver 120a, 120b, which is configured to transmit and receive radio frequency (RF) signals with the satellite 105. In some implementations, the user terminals 110a, 110b and the corresponding client satellite transceivers 120a, 120b can be integrated together, such as integrated in a handheld terminal or a very small aperture terminal (VSAT) with an integrated antenna (e.g., a parabolic antenna). Similarly, the gateway routing device 150 is operably coupled to the gateway satellite transceiver 130, which is configured to transmit and receive signals with the satellite 105. The gateway routing device 150 and the gateway satellite transceiver 130 can be integrated into a base station 160, which can also be referred to as a ground station. As described in greater detail herein, base station 160 may be a base station of a cellular communication system that has been modified to be able to communicate with satellite network 140 .

[0038] The satellite network 140 provides a forward link (FL) for transmitting information from the gateway routing device 150 to the user terminals 110a, 110b and a return link (RL) for transmitting information from the user terminals 110a, 110b to the gateway routing device 150. The forward link includes a transmission path from the gateway routing device 150 through the gateway satellite transceiver 130, through the satellite 105 via a satellite uplink (UL) channel, to the client satellite transceivers 120a, 120b via a satellite downlink (DL) channel, and to the user terminals 110a, 110b. The return link includes a transmission path from the user terminals 110a, 110b through the respective client satellite transceivers 120a, 120b, through the satellite 105 via a satellite uplink channel, to the gateway satellite transceiver 130 via a satellite downlink channel, and to the gateway routing device 150. It should be understood that each communication path may utilize multiple satellites and transceivers. Satellite network 140 implements an FDD scheme, which means that a satellite UL channel uses a different frequency band than a satellite DL channel. Therefore, satellite network 140 may be referred to herein as an FDD network.

[0039] The gateway routing device 150 includes a configuration module 151 to coordinate the operation of the first node 155a and the second node 155b. In some implementations, the configuration module 151 is a separate component of the communication system 100. In some implementations, part or all of the gateway routing device 150 and / or the configuration module 151 can be located in a virtual device residing in a public or private computing cloud and / or as part of a distributed computing environment. The configuration module 151 can be configured to coordinate the scheduling of the access nodes 155a, 155b to enable a TDD system (such as a base station 160) to use an FDD network (such as a satellite network 140).

[0040] The configuration module 151 may be configured to perform one or more methods to coordinate the operation of two or more access nodes (such as a first access node 155a and a second access node 155b) sharing the same RF communication channel. The coordination of the access nodes 155a, 155b is accomplished by coordinating the scheduling of the first access node 155a and the second access node 155b. The configuration module 151 may be configured to generate a first schedule for the first access node 155a and a second schedule for the second access node 155b, the second schedule being complementary to the first schedule. For example, the configuration module 151 may allocate a plurality of FL time slots and a plurality of RL time slots separated by a switching time gap to form a first schedule. In order to make the second schedule complementary to the first schedule, the configuration module 151 may allocate an RL time slot in a time slot corresponding to the FL time slot in the first schedule and an FL time slot in a time slot corresponding to the RL time slot in the first schedule. Therefore, when the first access node 155a is scheduled to receive, the second access node is scheduled to transmit, and vice versa. The configuration module 151 may map the first schedule and the second schedule to the UL and DL frequencies of the satellite network 140. In this way, available time slots of the satellite network 140 are efficiently utilized. That is, FL or RL time slots not used by the first access node 155a are used by the second access node 155b, and vice versa.

[0041] In some implementations, user terminal 110a may or may not be co-located with user terminal 110b. In some implementations, user terminal 110a may represent a user terminal group, and user terminal 110b may represent another user terminal group, and different groups of user terminals may or may not be co-located. In some implementations, one or more of user terminals 110a, 110b may be mobile (e.g., located on a mobile platform or vehicle, such as an airplane, a ship, a bus, a train, etc.). In some implementations, one or more user devices are configured to be connected to individual user terminals. In some implementations, one or both of user terminals 110a, 110b include user devices configured to communicate with satellite network 140.

[0042] The user terminals 110a, 110b may include routers or other user equipment and may be configured to send and receive data routed through the communication system 100. The user terminals 110a, 110b may include or be communicatively coupled to any type of customer premises equipment (e.g., a phone, a modem, a router, a computer, a set-top box, etc.). The user terminals 110a, 110b are configured to send and receive data using the satellite network 140 via respective customer satellite transceivers 120a, 120b.

[0043] The communication system 100 can utilize various network architectures including space segments and ground segments. The satellite network 140 incorporates these elements to provide communication between multiple user terminals 110a, 110b and a gateway routing device 150. For example, the space segment may include one or more satellites (such as satellite 105), and the ground segment may include one or more satellite user terminals (such as user terminals 110a, 110b), gateway terminals (such as gateway routing devices 150), network operation centers (NOCs), satellite and gateway terminal command centers, ground stations, base stations, etc. For clarity, some of these elements are not shown in the figure. The satellite network 140 may include one or more geosynchronous earth orbit (GEO) satellites, one or more medium earth orbit (MEO) satellites, and / or one or more low earth orbit (LEO) satellites. It should be understood that the satellite 105 may represent one or more satellites, and the one or more satellites may include GEO satellites, MEO satellites, LEO satellites, or any combination of these satellites.

[0044] Example Duplex Scheme in Communication Systems

[0045] Figure 2A Figure 2B 2C and 2D show examples of duplexing schemes and time slot allocations in terrestrial and satellite systems. TDD and FDD schemes for a typical cellular communication system and a typical satellite communication system and time slot allocations in these systems are shown. These time slot allocations demonstrate the effect of propagation delay or round trip time (RTT) on the scheduling of communication system components. In particular, the time slot allocations demonstrate the effect of propagation delay on the size of the switching time gap in a TDD scheme and an FDD scheme using TDD equipment.

[0046] 2A shows an example of a typical TDD scheme in a cellular communication system 200a. The cellular communication system 200a includes a base station 232 and a user equipment 212. The base station 232 and the user equipment 212 are configured to implement a TDD scheme to communicate. The figure shows a typical composition of a TDD frame at the base station 232: a series of Tx (DL) time slots, followed by a gap period that allows the RF equipment to switch from Tx to Rx (or vice versa), followed by a series of Rx (UL) time slots.

[0047] For example, the base station 232 transmits and receives based on the BS schedule 201a. The BS schedule 201a has multiple DL time slots and multiple UL time slots, wherein a single time slot is allocated as a switching time gap between multiple DL time slots and multiple UL time slots. The switching time gap is configured to allow the RF subsystem to switch between transmission and reception. Similarly, the user equipment 212 transmits and receives based on the UE schedule 202a. The UE schedule 202a has multiple DL time slots and multiple UL time slots allocated based on the propagation delay between the base station 232 and the user equipment 212. In addition, to implement the TDD scheme, the UL signal and the DL signal use a single carrier frequency or frequency band for communication.

[0048] As can be seen in the UE schedule 202a, the DL time slot is later in time with respect to the DL time slot in the BS schedule 201a, the amount of time being related to the propagation time or delay. In addition, the UE schedule 202a has a timing advance for the UL time slot, which is configured so that the UL signal from the user equipment 212 arrives at the base station 232 at the specified time. In other words, there are few or no switching time gaps in the UE schedule 202a to reduce or minimize the switching time gaps in the BS schedule 201a, thereby reducing or minimizing the overhead associated with switching between Tx and Rx at the base station 232.

[0049] Figure 2B A comparison of time slot allocation in a terrestrial communication system (e.g., a cellular communication system) and time slot allocation in a satellite communication system is shown. This illustrates one of the challenges of implementing a TDD scheme in a satellite communication system: the size of the switching time slot becomes prohibitively large due to the relatively long round-trip time between the satellite and the ground equipment. For example, the round-trip time in a LEO satellite communication system may be approximately 30 milliseconds (ms), and the round-trip time in a GEO satellite communication system may be approximately 500 ms.

[0050] For a terrestrial communication system, a base station 292 (similar to the base station 232 described with reference to FIG. 2A ) transmits and receives according to a BS schedule 201b. The BS schedule 201b includes a plurality of time slots allocated to forward link (FL) or DL ​​traffic, followed by a switching time slot, followed by a plurality of time slots allocated to return link (RL) or UL traffic. A user equipment 294 (similar to the user equipment 212 described with reference to FIG. 2A ) transmits and receives according to a UE schedule 202b. The UE schedule 202b includes a plurality of time slots for FL or DL ​​traffic, followed by a plurality of time slots for RL or UL traffic. The propagation delay in this example is approximately the same as the duration of a single time slot in the schedule. Therefore, the round trip time is approximately the size of 2 time slots in the schedule, which is marked as the turnaround time in the figure. Therefore, after the BS schedule 201b allocates the start of FL traffic, the UE schedule 202b allocates the start of FL traffic 1 time slot. In addition, UE schedule 202b has a timing advance for RL traffic so that user equipment 294 is scheduled to transmit RL traffic in a time slot immediately after it is scheduled to complete receiving FL traffic from base station 292. Propagation delays result in a switching time gap at base station 292. In this example, the switching time gap is 2 time slots to account for the round trip time in terrestrial communication systems. In terrestrial communication systems, the turnaround time is relatively small and is part of the system overhead. This means that a standard TDD solution is feasible with limited overhead.

[0051] In contrast, for a satellite communication system, the gateway 250 (or ground station) transmits and receives according to the GS schedule 203a. The GS schedule 203a includes a plurality of time slots allocated for forward link (FL) or UL traffic, followed by a switching time slot, followed by a time slot allocated for return link (RL) or DL ​​traffic. The satellite 205 (similar to the reference Figure 1 105) transmits and receives according to a SAT schedule 204. The SAT schedule 204 includes a plurality of time slots for FL traffic (which includes both UL and DL traffic) followed by a time slot for RL traffic (which includes both UL and DL traffic). In this example, the propagation delay from the gateway 250 to the satellite 205 is approximately the same as the duration of the three time slots in the schedule. The user terminal 210 (similar to the reference 204) transmits and receives according to a SAT schedule 204. The SAT schedule 204 includes a plurality of time slots for FL traffic (which includes both UL and DL traffic) followed by a time slot for RL traffic (which includes both UL and DL traffic). Figure 1The user terminals 110a, 110b) described transmit and receive according to the UT schedule 206a. The UT schedule 206a includes multiple time slots for FL or DL ​​traffic, followed by time slots for RL or UL traffic. In this example, the propagation delay from the satellite 205 to the user terminal 210 is approximately the same as the duration of 5 time slots in the schedule. Therefore, the total propagation delay from the gateway 250 to the user terminal 210 is approximately the same as the duration of 8 time slots in the schedule, and the round-trip time is approximately the size of 16 time slots in the schedule, marked as the turnaround time in the figure. In this example, the switching time gap is 16 time slots to take into account the round-trip time between the gateway 250 and the user terminal 210. In satellite communication systems, the turnaround time is relatively long (for example, relative to ground communication systems). This means that standard TDD solutions are unpopular and inefficient because they require a relatively large number of unused time slots. Therefore, after the GS schedule 203a allocates the start of FL traffic, the UT schedule 206a allocates the start of FL traffic 8 time slots. Furthermore, UT schedule 206a has a timing advance for RL traffic, so that user terminal 210 is scheduled to transmit RL traffic immediately after it is scheduled to finish receiving FL traffic from gateway 250. Propagation delays result in a switching time gap at gateway 250.

[0052] It should be noted that although the RL and FL time slots are shown side by side, the above reference Figure 2B The description is applicable to the case where the UL and DL frequency bands are the same. The above explanation is particularly relevant to the TDD scheme or the case where one or more components of the communication system are half-duplex so that the equipment is not configured for simultaneous transmission and reception.

[0053] FIG. 2C shows an example of a typical FDD scheme in a satellite communication system 200c. The FDD scheme is used at least in part due to the relatively large latency of transmissions over the satellite link. Figure 2B As described, the switching time gaps required in the TDD scheme are excessive and undesirable, which is at least partly why it is advantageous to implement the FDD scheme in a satellite communication system. The FDD scheme allows the satellite communication system to transmit and receive simultaneously using different frequency bands or carrier frequencies. The figure illustrates the typical composition of a ground station FDD frame: a series of FL (UL) time slots in parallel with a series of RL (DL) time slots.

[0054] Satellite communication system 200c is similar to that of the Figure 1Depicted satellite communication system 100. Satellite communication system 200c includes satellite 205 that communicates via satellite network 240 with ground stations 260 (which includes gateway 250 and a gateway satellite transceiver 230 similar to gateway satellite transceiver 130) and user terminals 210 using client satellite transceivers 220 (similar to client satellite transceivers 120a, 120b).

[0055] The ground station 260 transmits and receives according to the GS schedule 203b including a plurality of FL time slots allocated in the UL frequency band and a plurality of RL time slots allocated in the DL frequency band. Similarly, the user terminal 210 transmits and receives according to the UT schedule 206b including a plurality of FL time slots allocated in the DL frequency band and a plurality of RL time slots allocated in the UL frequency band. The satellite 205 receives FL traffic from the ground station 260 in the UL frequency band, converts the FL traffic to the DL frequency band, and then transmits the FL traffic to the user terminal 210. Similarly, the satellite 205 receives RL traffic from the user terminal 210 in the UL frequency band, converts the RL traffic to the DL frequency band, and then transmits the RL traffic to the ground station 260. The FL time slots of the UT schedule 206b are later in time than the corresponding FL time slots of the GS schedule 203b to take into account the propagation delay between the ground station 260 and the user terminal 210. Similarly, the RL time slots of the UT schedule 206b are advanced in time relative to the corresponding RL time slots of the GS schedule 203b to account for the propagation delay between the ground station 260 and the user terminal 210. The timing advance of the RL time slots of the UT schedule 206b is configured so that the FL and RL time slots in the GS schedule 203b are aligned in time. In some implementations, interference between the UL transmissions of the ground station 260 and the user terminal 210 is negligible or not a problem because different polarizations are used for different UL transmissions or because the ground station 260 and the user terminal 210 are sufficiently separated geographically.

[0056] 2D shows an example of a typical cellular communication system 200d modified to operate on a satellite network 240, which includes a satellite 205. The satellite 205 is capable of full-duplex communication (e.g., using an FDD scheme), while the base station 282 can operate with half-duplex communication (e.g., using a TDD scheme). The user equipment 284 can be configured for full-duplex communication to utilize the FDD scheme via the satellite 205. In some specific implementations, the cellular communication system 200d including the base station 282 and the user equipment 284 utilizes 5G cellular equipment.

[0057] In order to communicate via the satellite network 240, the RF subsystem of the base station 282 and the RF subsystem of the user equipment 284 can be modified to operate in the satellite frequency band. At least in part because the UL frequency band is different from the DL frequency band, the modification of the RF subsystem allows the cellular communication system 200d to use the FDD protocol. However, because the base station 282 and the associated cellular equipment implement the TDD scheme, a large number of time slots remain unused.

[0058] For example, the base station 282 transmits and receives according to the BS schedule 201c including a plurality of FL time slots allocated in the UL frequency band and a plurality of RL time slots allocated in the DL frequency band. However, because the base station 282 operates according to the TDD scheme, the BS schedule 201c allocates the FL time slots, followed by a switching time slot of 1 time slot, followed by the RL time slot, similar to the BS schedule 201a described herein with reference to FIG. 2A. The user equipment 284 transmits and receives according to the UE schedule 202c including a plurality of FL time slots allocated in the DL frequency band and a plurality of RL time slots allocated in the UL frequency band. Due at least in part to the relatively large propagation delay through the satellite network 240, the FL time slots in the UE schedule 202c are later in time than the corresponding FL time slots in the BS schedule 201c. Relatedly, the RL time slots in the UE schedule 202c are allocated earlier in time, so that the switching time slot in the BS schedule 201c can be reduced or minimized (e.g., the switching time slot can be 1 time slot between the FL time slots and the RL time slots). This may result in the UE schedule 202 c having FL time slots that overlap in time with RL time slots, thereby requiring simultaneous transmit and receive capabilities at the user equipment 284 .

[0059] Due to the TDD scheme implemented at base station 282 and propagation delays over satellite network 240, there are many unused time slots in both the UL and DL bands of base station 282 and user equipment 284. It is desirable to utilize these unused time slots to improve efficiency and more fully utilize the capacity of satellite network 240.

[0060] Thus, the base station of the satellite communication system described herein is modified to include two access nodes with complementary TDD scheduling, which more fully utilizes the capacity of the satellite network by using time slots that would otherwise be unused in a specific implementation similar to the cellular communication system 200d. Figure 3 An example communication system 300 is shown that includes a base station 360 configured to communicate via a satellite network 340, the base station 360 including a first access node 355a and a second access node 355b configured to operate using complementary TDD scheduling. The communication system 300 also includes a plurality of user terminals 310a, 310b configured to communicate via the satellite network 340. The satellite network 340 is similar to the one described herein with reference to Figure 11 and 105. The base station 360 is a satellite network 140 as described herein and includes a satellite 305 similar to the satellite 105. Although not shown, the base station 360 includes one or more antennas or satellite transceivers as described herein to enable communication with the satellite 305. Similarly, although not shown, the user terminals 310a, 310b include antennas or satellite transceivers as described herein to enable communication with the satellite 305. The base station 360 is configured to communicate with multiple user terminals 310a, 310b.

[0061] The base station 360 includes a first access node 355a that communicates on the satellite network 340 according to a first TDD schedule 301a, the first TDD schedule including a plurality of FL time slots and a plurality of RL time slots separated by switching time slots. The base station 360 includes a second access node 355b that communicates on the satellite network 340 according to a second TDD schedule 301b, the second TDD schedule including a plurality of RL time slots and a plurality of FL time slots separated by switching time slots. The first TDD schedule 301a and the second TDD schedule 301b are referred to as TDD schedules because each access node 355a, 355b implements a TDD scheme in which the FL time slots and the RL time slots do not overlap. The first TDD schedule 301a and the second TDD schedule 301b are configured to be complementary, so that the first TDD schedule 301a includes FL time slots, wherein the second TDD schedule 301b includes RL time slots, and the first TDD schedule 301a includes RL time slots, wherein the second TDD schedule 301b includes FL time slots. These schedules are described as complementary because the time slots not used in the first TDD schedule 301a are used in the second TDD schedule 301b, and vice versa. The first TDD schedule 301a and the second TDD schedule 301b are coordinated so that the satellite network 340 operates according to an FDD scheme that uses all available time slots (except for the switching time slots in each TDD schedule). The first TDD schedule 301a and the second TDD schedule 301b can be generated in the baseband and then mapped to the UL and DL frequency bands of the satellite network 340. In some specific implementations, the first TDD schedule and the second TDD schedule have different UL / DL ratios. For example, the UL to DL ratio can be 1:1, 2:3 or 3:2, 3:7 or 7:3, 1:2 or 2:1, etc.

[0062] The switching time slots of each of the first TDD schedule 301a and the second TDD schedule 301b are aligned in time and are of the same duration. That is, the switching time slots of the first TDD schedule 301a and the switching time slots of the second TDD schedule 301b occupy the same time slot in the frame. The size of the switching time slot can be configured to take into account the uncertainty of the signal arrival time from the user terminal 310a, 310b. However, as described herein, the size of the switching time slot can be independent of and has nothing to do with the propagation delay through the communication system 300.

[0063] The first access node 355a and the second access node 355b each operate in a manner similar to the base station 282 of Figure 2D. However, in order to more fully utilize the capacity of the satellite network 340, the first TDD schedule 301a and the second TDD schedule 301b are coordinated to be complementary, as described herein. The first access node 355a transmits and receives according to the first TDD schedule 301a, which includes a plurality of FL time slots, followed by a switching time slot, followed by a plurality of RL time slots. The second access node 355b transmits and receives according to the second TDD schedule 301b, which includes a plurality of RL time slots, followed by a switching time slot, followed by a plurality of FL time slots. The base station 360 is configured to map the FL time slots of the first TDD schedule 301a and the second TDD schedule 301b to the UL frequency band, and to map the RL time slots of the first TDD schedule 301a and the second TDD schedule 301b to the DL frequency band. Therefore, the base station 360 transmits FL traffic and receives RL traffic according to the combination of the first TDD schedule 301a and the second TDD schedule 301b, thereby implementing an FDD scheme that uses all available time slots (except the switching time slot) on the satellite network 340. That is, the base station 360 is able to operate in full duplex. As a result, because the base station 360 can transmit and receive at the same time, the switching time slot can be made relatively small. In addition, the switching time slot does not need to consider the propagation time between the base station 360 and the user terminals 310a and 310b, which means that the size of the switching time slot is not affected by the round-trip time of the signal through the satellite network 340. For example, the switching time slot can be less than twice the propagation time and / or less than the round-trip time through the satellite network 340. In some specific implementations, the propagation delay is different for each user terminal 310a and 310b. In some specific implementations, the propagation delay of the user terminals 310a and 310b changes over time.

[0064] The first user terminal 310a and the second user terminal 310b are each operated in a manner similar to the user equipment 284 of Figure 2D. In some specific implementations, the first access node 355a is configured to communicate with the first user terminal 310a, and the second access node 355b is configured to communicate with the second user terminal 310b. As described herein, each user terminal 310a, 310b can represent multiple or a group of user terminals, so that the first access node 355a is configured to serve the first user terminal group (represented by the first user terminal 310a), and the second access node 355b is configured to serve the second user terminal group (represented by the second user terminal 310b). In addition, each user terminal 310a, 310b (or user terminal group) may or may not be co-located.

[0065] The first user terminal 310a transmits and receives according to the first UT schedule 302a, which includes a plurality of FL time slots allocated in the DL frequency band and a plurality of RL time slots allocated in the UL frequency band. Due at least in part to propagation delays through the satellite network 340, the FL time slots in the first UT schedule 302a are later in time than the corresponding FL time slots in the first TDD schedule 301a. Relatedly, the RL time slots in the first UT schedule 302a are allocated earlier in time so that the switching time gap in the first TDD schedule 301a can be reduced or minimized (e.g., the switching time gap can be 1 time slot between the FL time slot and the RL time slot). This may result in the first UT schedule 302a having FL time slots that overlap in time with RL time slots, thereby requiring simultaneous transmission and reception capabilities at the first user terminal 310a.

[0066] Similarly, the second user terminal 310b transmits and receives according to the second UT schedule 302b, which includes a plurality of FL time slots allocated in the DL frequency band and a plurality of RL time slots allocated in the UL frequency band. Due at least in part to propagation delays through the satellite network 340, the FL time slots in the second UT schedule 302b are later in time than the corresponding FL time slots in the second TDD schedule 301b. Relatedly, the RL time slots in the second UT schedule 302b are allocated earlier in time so that the switching time gap in the second TDD schedule 301b can be reduced or minimized (e.g., the switching time gap can be 1 time slot between the FL time slot and the RL time slot). This may result in the second UT schedule 302b having FL time slots that overlap in time with RL time slots, thereby requiring simultaneous transmission and reception capabilities at the second user terminal 310b.

[0067] The first access node 355a and the second access node 355b can be implemented in hardware or software. In some embodiments, the first access node 355a and the second access node 355b can each be a physical entity, such as a tower, or each can be a virtual entity, such as a software defined radio (SDR). In some specific implementations, the first access node 355a and the second access node 355b share the same RF communication equipment, such as an antenna, a decoder, an encoder, a regulator, a demodulator, a multiplexer, a filter, etc.

[0068] Figure 4 An example base station 450 including a configuration module 451 for coordinating the operation of two access nodes 455a, 455b is shown. As described herein, two access nodes 455a, 455b share a common RF subsystem and have a coordination configuration. Configuration module 451 can be configured to access computing resources that are sufficient to implement any method described herein for coordinating the operation of two access nodes 455a, 455b that share the same RF communication channel. In some specific implementations, two access nodes 455a, 455b are half-duplex and are connected to the same air interface (e.g., two access nodes 455a, 455b include 2 transmitters and 2 receivers connected to the same antenna) via an air interface. In some specific implementations, configuration module 451 is implemented in a computing device, a distributed computing environment, a cloud, etc.

[0069] Base station 450 includes two access nodes 455a, 455b and a configuration module 451 having an adder 453, a separator 454 and a duplexer 456. The same clock signal 452 is used to synchronize the two access nodes 455a, 455b to align the time slots. Therefore, as described herein, the first access node 455a can be assigned a first TDD schedule by the configuration module 451, and the second access node 455b can be assigned a second TDD schedule by the configuration module 451, wherein the first TDD schedule and the second TDD schedule are complementary (e.g., the first access node 455a is scheduled to transmit, and the second access node 455b is scheduled to receive, and vice versa). In other words, the allocation of the time slots of the access nodes 455a and 455b by the configuration module 451 is complementary.

[0070] Base station 450 demonstrates a modification of a standard base station in a typical cellular communication network to implement the techniques described herein. In particular, base station 450 has a modified RF front end, and base station 450 includes configuration module 451 .

[0071] First, the base station combines adder 453 and separator 454 to combine two Tx and Rx signals from two access nodes 455a, 455b. Adder 453 is configured to generate a transmit signal by combining the transmit signal from the first access node 455a with the transmit signal from the second access node 455b, and send the transmit signal to duplexer 456. Separator 454 is configured to separate the received signal from duplexer 456 into a received signal for the first access node and a received signal for the second access node, send the received signal for the first access node to the first access node 455a, and send the received signal for the second access node to the second access node 455b. Duplexer 456 manages the communication of the combined signal between adder 453 and separator 454 and antenna (not shown). Secondly, as described herein, configuration module 451 jointly configures the parameters of the two access nodes 455a, 455b so that their Tx time slots and Rx time slots are complementary. In some implementations, all additional PHY transmission parameters of the two access nodes 455a, 455b are configured to be the same (eg, carrier frequency, channel bandwidth, etc.).

[0072] In addition, the two access nodes 455a, 455b are driven by the same clock signal 452 so that they operate synchronously. The clock signal can be provided from the cloud via GPS, or using an internal or external clock source. By using the same clock signal 452, the scheduling of the two access nodes 455a, 455b can be aligned in time. In addition, using the same clock signal 452 can prevent the scheduling from deviating (e.g., becoming unsynchronized) over time.

[0073] The configuration module 451 is configured to generate a first TDD schedule for the first access node 455a in the baseband. The configuration module 451 is also configured to map the first TDD schedule to the UL and DL frequencies of the satellite link or network in which it is implemented. The configuration module 451 is also configured to generate a second TDD schedule for the second access node 455b in the baseband, and the first and second TDD schedules are complementary. The configuration module 451 is also configured to map the second TDD schedule to the UL and DL frequencies of the satellite link or network in which it is implemented. The result of the complementary TDD scheduling can be that each Rx time slot and each Tx time slot of the satellite link are scheduled in the first TDD scheduling or the second TDD scheduling, so that all Rx time slots and Tx time slots of the satellite link are used except for the switching time gap.

[0074] Method for coordinating operations of two access nodes

[0075] Figure 5A flow chart of an example method 500 for coordinating the operation of a TDD system (eg, a half-duplex access node) in an FDD network (eg, a satellite network) is shown. The method 500 may be referenced herein. Figure 1 , Figure 3 and Figure 4 The method 500 is performed in any base station or ground station described herein. For ease of description, the method 500 will be described as being performed by a configuration module. This should not be understood as limiting the scope of the present disclosure. Instead, any step or part of the method 500 may be performed by any component or combination of components of the communication system described herein.

[0076] In block 505, the configuration module generates a first TDD schedule for the first access node in baseband. The first TDD schedule includes a first plurality of forward link time slots and a first plurality of return link time slots, wherein there is a switching time gap between the first plurality of forward link time slots and the first plurality of return link time slots. In block 510, the configuration module maps the first TDD schedule to an uplink frequency for the first plurality of forward link time slots and to a downlink frequency for the first plurality of return link time slots.

[0077] In box 515, the configuration module generates a second TDD schedule for the second access node in the baseband. The second TDD schedule includes a second plurality of return link time slots and a second plurality of forward link time slots, wherein there is a switching time gap between the second plurality of return link time slots and the second plurality of forward link time slots. In box 520, the configuration module maps the second TDD schedule to an uplink frequency for the second plurality of forward link time slots and to a downlink frequency for the second plurality of return link time slots. The first TDD schedule is complementary to the second TDD schedule such that the first plurality of forward link time slots coincide in time with the second plurality of return link time slots, and the first plurality of return link time slots coincide in time with the second plurality of forward link time slots.

[0078] In some implementations, the configuration module synchronizes the first TDD schedule and the second TDD schedule in time based on the clock signal. In some implementations, the configuration module transmits the first TDD schedule to the first access node to configure the operation of the first access node, and transmits the second TDD schedule to the second access node to configure the operation of the second access node. In some implementations, the number of time slots in the first plurality of forward link time slots is different from the number of time slots in the first plurality of return link time slots.

[0079] In some specific implementations, the switching time gap in the first TDD schedule coincides in time with the switching time gap in the second TDD schedule. The switching time gap may be configured to be shorter than the shortest round trip propagation time between the first access node or the second access node and a user terminal with which the first access node or the second access node communicates. The duration of the switching time gap may be independent of the round trip propagation time between the first access node or the second access node and the user terminal with which the first access node or the second access node communicates.

[0080] Example Configuration Module

[0081] Figure 6 A block diagram of an example configuration system 770 configured to coordinate the operation of a first access node 755a and a second access node 755b is shown. The configuration system 770 is similar to the configuration system 770 described herein with reference to Figure 1 The configuration module 151 described herein and referenced herein Figure 4 Configuration module 451 described herein and can be implemented in any communication system described herein. Configuration system 770 can adopt any method described herein for coordinating the operation of access nodes with complementary scheduling, such as the method described herein with reference to Figure 5 An example method 500 is described.

[0082] Configuration system 770 may include hardware, software and / or firmware components for coordinating the operation of access nodes in a satellite communication system. Configuration system 770 includes data storage 771, one or more processors 773, access node interface 775, synchronization module 772, scheduling module 774 and mapping module 776. The components of configuration system 770 can use communication bus 779 to communicate with each other, communicate with external systems, and communicate with other components of the network. Configuration system 770 can be implemented using one or more computing devices. For example, configuration system 770 can be implemented using a single computing device, multiple computing devices, a distributed computing environment, or it can be located in a virtual device residing in a public or private computing cloud. In a distributed computing environment, one or more computing devices can be configured to provide modules 772, 774 and 776 to provide the described functions.

[0083] The configuration system 770 is configured to communicate with the first access node 755a and the second access node 755b via the access node interface 775. The access nodes 755a, 755b are similar to those described herein with reference to Figure 1 , Figure 3 and Figure 4The configuration system 770 communicates with the access nodes 755a, 755b to coordinate the operation of the access nodes 755a, 755b, synchronize the operation of the access nodes 755a, 755b, and / or transmit a schedule to the access nodes 755a, 755b.

[0084] Configuration system 770 includes synchronization module 772 to synchronize the operation of two access nodes 755a, 755b. This can be done using a clock signal for both access nodes 755a, 755b. The clock signal can be provided, for example, but not limited to, by an external clock source, GPS or cloud. Synchronization allows the time slots of the scheduling generated for each access node 755a, 755b to be synchronized in time to communicate through a satellite network. Configuration system 770 includes scheduling module 774 to generate TDD scheduling for access nodes 755a, 755b. As described herein, scheduling module 774 is configured to determine complementary scheduling for access nodes 755a, 755b. Scheduling module 774 is configured to generate TDD scheduling for two access nodes 755a, 755b in baseband. Configuration system 770 includes mapping module 776 to map the TDD scheduling generated by scheduling module 774 to the UL and DL frequencies of the satellite network.

[0085] Configuration system 770 includes one or more processors 773, which are configured to control the operation of modules 772, 774, 776 and data storage 771. One or more processors 773 implement and utilize software modules, hardware components and / or firmware elements configured to coordinate the operation of access nodes 755a, 755b. One or more processors 773 may include any suitable computer processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA) or other suitable microprocessor. One or more processors 773 may include other computing components configured to interface with various modules and data storage of configuration system 770.

[0086] Configuration system 770 includes a data storage 771 configured to store configuration data, analysis parameters, control commands, databases, algorithms, executable instructions (e.g., instructions for one or more processors 773), etc. Data storage 771 can be any suitable data storage device or combination of devices, including, for example, but not limited to, random access memory, read-only memory, solid-state drive, hard disk drive, flash drive, bubble memory, etc.

[0087] Additional Examples and Terminology

[0088] The present disclosure describes various features, wherein no single feature is solely responsible for the benefits described herein. It should be understood that the various features described herein can be combined, modified or omitted, as will be apparent to those of ordinary skill in the art. Other combinations and subcombinations other than the combinations and subcombinations specifically described herein will be apparent to those of ordinary skill in the art, and are intended to form a part of the present disclosure. Various methods are described herein in conjunction with various flow chart steps and / or stages. It should be understood that in many cases, certain steps and / or stages can be combined together so that the multiple steps and / or stages shown in the flow chart can be performed as a single step and / or stage. In addition, certain steps and / or stages can be divided into additional sub-components to be performed separately. In some cases, the order of steps and / or stages can be rearranged, and certain steps and / or stages can be completely omitted. In addition, the method described herein should be understood to be open, so that additional steps and / or stages of those steps and / or stages shown and described herein can also be performed.

[0089] Some aspects of the systems and methods described herein may be advantageously implemented using, for example, computer software, hardware, firmware, or any combination of computer software, hardware, and firmware. Computer software may include computer executable code stored in a computer-readable medium (e.g., a non-transitory computer-readable medium) that performs the functions described herein when the computer executable code is executed. In some embodiments, the computer executable code is executed by one or more general-purpose computer processors. According to the present disclosure, those skilled in the art will appreciate that any features or functions that can be implemented using software to be executed on a general-purpose computer may also be implemented using different combinations of hardware, software, or firmware. For example, such a module may be implemented entirely in hardware using a combination of integrated circuits. Alternatively or additionally, such features or functions may be implemented in whole or in part using a special-purpose computer designed to perform the specific functions described herein rather than by a general-purpose computer.

[0090] Multiple distributed computing devices may replace any one computing device described herein. In such distributed embodiments, the functionality of one computing device is distributed (eg, via a network) such that some functions are performed on each of the distributed computing devices.

[0091] Some embodiments can be described with reference to equations, algorithms and / or flow charts. These methods can be implemented using computer program instructions executable on one or more computers. These methods can also be implemented as computer program products separately, or as components of devices or systems. In this regard, the frame or steps of each equation, algorithm, flow chart and their combination can be implemented by hardware, firmware and / or software including one or more computer program instructions embodied in computer-readable program code logic. As will be appreciated, any such computer program instruction can be loaded onto one or more computers, including but not limited to general-purpose computers or special-purpose computers, or other programmable processing devices for producing machines, so that the computer program instructions executed on computers or other programmable processing devices realize the functions specified in equations, algorithms and / or flow charts. It should also be understood that the frame and their combination in each equation, algorithm and / or flow chart display can be implemented by a computer system based on special-purpose hardware or a combination of special-purpose hardware and computer-readable program code logic devices that perform specified functions or steps.

[0092] In addition, computer program instructions, such as those embodied in computer-readable program code logic, may also be stored in a computer-readable memory (e.g., a non-transitory computer-readable medium) that can direct one or more computers or other programmable processing devices to function in a particular manner such that the instructions stored in the computer-readable memory implement the functions specified in the blocks of the flowchart. The computer program instructions may also be loaded onto one or more computers or other programmable computing devices to cause a series of operational steps to be performed on one or more computers or other programmable computing devices to produce a computer-implemented process such that the instructions executed on the computers or other programmable processing devices provide steps for implementing the functions specified in the blocks of the equations, algorithms, and / or flowcharts.

[0093] Some or all of the methods and tasks described herein can be performed and fully automated by a computer system. In some cases, a computer system can include multiple different computers or computing devices (e.g., physical servers, workstations, storage arrays, etc.) that communicate and interoperate through a network to perform the functions described. Each such computing device typically includes a processor (or multiple processors) that executes program instructions or modules stored in a memory or other non-temporary computer-readable storage medium or device. The various functions disclosed herein can be embodied in such program instructions, although some or all of the disclosed functions can alternatively be implemented in a dedicated circuit system (e.g., ASIC or FPGA) of a computer system. In the case where a computer system includes multiple computing devices, these devices can be but need not be co-located. The results of the disclosed methods and tasks can be stored persistently by converting physical storage devices such as solid-state memory chips and / or disks into different states.

[0094] Unless the context clearly requires otherwise, throughout the specification and claims, the words "comprise", "comprising", etc. should be interpreted in an inclusive sense, rather than an exclusive or exhaustive sense; that is, in the sense of "including but not limited to"; that is, in the sense of "including but not limited to". As generally used herein, the word "coupled" refers to two or more elements that can be directly connected or connected by means of one or more intermediate elements. In addition, when used in this application, the words "herein", "above", "below" and words with similar meanings should refer to the application as a whole rather than any particular part of the application. Where the context permits, the words used in the singular or plural in the above specific embodiments may also include the plural or singular, respectively. With respect to the word "or" for a list of two or more items, the word covers all the following interpretations of the word: any item in the list, all items in the list, and any combination of items in the list. The word "exemplary" is used exclusively herein to mean "serving as an example, instance, or illustration". Any specific implementation described as "exemplary" herein is not necessarily interpreted as preferred or advantageous over other specific implementations.

[0095] The present disclosure is not intended to be limited to the specific implementations shown herein. Those skilled in the art may readily appreciate various modifications to the specific implementations described in the present disclosure, and the general principles defined herein may be applied to other specific implementations without departing from the spirit or scope of the present disclosure. The teachings of the present invention provided herein may be applied to other methods and systems, and are not limited to the above methods and systems, and the elements and actions of the various embodiments described above may be combined to provide additional embodiments. Therefore, the novel methods and systems described herein may be embodied in various other forms; in addition, various omissions, substitutions, and changes may be made to the forms of the methods and systems described herein without departing from the spirit of the present disclosure. The attached claims and their equivalents are intended to cover such forms or modifications that fall within the scope and spirit of the present disclosure.

Claims

1. A method for coordinating operations of a base station with a first access node and a second access node, the method comprising: generating a first TDD schedule for the first access node, the first TDD schedule comprising a first plurality of forward link time slots and a first plurality of return link time slots, wherein there are switching time gaps between the first plurality of forward link time slots and the first plurality of return link time slots; mapping the first TDD schedule onto an uplink frequency for the first plurality of forward link time slots and onto a downlink frequency for a first plurality of return link time slots; generating a second TDD schedule for the second access node, the second TDD schedule comprising a second plurality of forward link time slots and a second plurality of return link time slots, wherein the switching time gap exists between the second plurality of forward link time slots and the second plurality of return link time slots; as well as mapping the second TDD schedule onto the uplink frequency for the second plurality of forward link time slots and onto the downlink frequency for the second plurality of return link time slots, The first TDD scheduling is complementary to the second TDD scheduling, such that the first plurality of forward link time slots coincide in time with the second plurality of return link time slots, and the first plurality of return link time slots coincide in time with the second plurality of forward link time slots. 2 . The method of claim 1 , further comprising synchronizing the first TDD schedule and the second TDD schedule in time based on a clock signal.

3. The method according to claim 1, further comprising: transmitting the first TDD schedule to the first access node to configure operation of the first access node; as well as The second TDD schedule is transmitted to the second access node to configure operation of the second access node. 4 . The method according to claim 1 , wherein the switching time gap in the first TDD schedule coincides in time with the switching time gap in the second TDD schedule.

5. The method of claim 1, wherein the switching time gap is shorter than a shortest round trip propagation time between the first access node or the second access node and a user terminal with which the first access node or the second access node communicates.

6. The method of claim 1, wherein the duration of the switching time gap is independent of a round trip propagation time between the first access node or the second access node and a user terminal with which the first access node or the second access node communicates.

7. The method of claim 1, wherein the number of time slots in the first plurality of forward link time slots is different from the number of time slots in the first plurality of return link time slots.

8. The method of claim 1, wherein the first access node and the second access node have the same carrier frequency and channel bandwidth.

9. The method of claim 1, wherein the first access node and the second access node share a radio frequency communication channel.

10. The method of claim 1, wherein the first access node and the second access node share an antenna.

11. A base station of a communication system, the base station comprising: a first access node; a second access node; Duplexer; an adder configured to generate a transmit signal by combining a transmit signal from the first access node with a transmit signal from a second access node, and to send the transmit signal to the duplexer; a splitter configured to split a received signal from the duplexer into a received signal for the first access node and a received signal for the second access node, send the received signal for the first access node to the first access node, and send the received signal for the second access node to the second access node; a clock configured to generate a clock signal to synchronize the first access node and the second access node; as well as Configuration module, which is configured to: generating a first TDD schedule for the first access node, the first TDD schedule comprising a first plurality of forward link time slots and a first plurality of return link time slots, wherein there are switching time gaps between the first plurality of forward link time slots and the first plurality of return link time slots; mapping the first TDD schedule onto an uplink frequency for the first plurality of forward link time slots and onto a downlink frequency for a first plurality of return link time slots; generating a second TDD schedule for the second access node, the second TDD schedule comprising a second plurality of forward link time slots and a second plurality of return link time slots, wherein the switching time gap exists between the second plurality of return link time slots and the second plurality of forward link time slots; as well as mapping the second TDD schedule onto the uplink frequency for the second plurality of forward link time slots and onto the downlink frequency for the second plurality of return link time slots, The first TDD scheduling is complementary to the second TDD scheduling, such that the first plurality of forward link time slots coincide in time with the second plurality of return link time slots, and the first plurality of return link time slots coincide in time with the second plurality of forward link time slots.

12. The base station of claim 11, further comprising an antenna coupled to the duplexer, the antenna configured to communicate with a satellite network. 13 . The base station according to claim 11 , wherein the switching time gap in the first TDD schedule coincides in time with the switching time gap in the second TDD schedule.

14. The base station of claim 11, wherein the switching time gap is shorter than a shortest round trip propagation time between the first access node or the second access node and a user terminal with which the first access node or the second access node communicates.

15. The base station of claim 11, wherein a duration of the switching time gap is independent of a round trip propagation time between the first access node or the second access node and a user terminal with which the first access node or the second access node communicates.

16. The base station of claim 11, wherein the first access node and the second access node are each half-duplex.

17. The base station of claim 11, wherein the first access node and the second access node have the same carrier frequency and channel bandwidth.

18. The base station of claim 11, wherein the first access node is configured to communicate with a first plurality of user terminals via a satellite network, and the second access node is configured to communicate with a second plurality of user terminals via the satellite network.

19. A communication system comprising: A base station, comprising a first access node, a second access node, an antenna and a configuration module, wherein the configuration module is configured to: generating a first TDD schedule for the first access node, the first TDD schedule comprising a first plurality of forward link time slots and a first plurality of return link time slots, wherein there are switching time gaps between the first plurality of forward link time slots and the first plurality of return link time slots; mapping the first TDD schedule onto an uplink frequency for the first plurality of forward link time slots and onto a downlink frequency for a first plurality of return link time slots; generating a second TDD schedule for the second access node, the second TDD schedule comprising a second plurality of forward link time slots and a second plurality of return link time slots, wherein the switching time gap exists between the second plurality of forward link time slots and the second plurality of return link time slots; as well as mapping the second TDD schedule onto the uplink frequency for the second plurality of forward link time slots and onto the downlink frequency for the second plurality of return link time slots; Satellite networks, which include satellites; as well as a plurality of user terminals configured to communicate with at least one of the first access node and the second access node of the base station through the satellite network, The first TDD scheduling is complementary to the second TDD scheduling, such that the first plurality of forward link time slots coincide in time with the second plurality of return link time slots, and the first plurality of return link time slots coincide in time with the second plurality of forward link time slots.

20. The communication system of claim 19, wherein the first access node is configured to communicate with a first group of user terminals among the plurality of user terminals, and the second access node is configured to communicate with a second group of user terminals among the plurality of user terminals.

21. The communication system of claim 19, wherein a user terminal of the plurality of user terminals is on a mobile platform.

22. The communication system of claim 19, wherein a user terminal of the plurality of user terminals is a user equipment configured to communicate directly with the satellite network.

23. The communication system of claim 19, wherein the satellite network comprises low earth orbit satellites.

24. The communication system of claim 19, wherein the satellite network comprises geostationary satellites.

25. The communication system of claim 19, wherein individual propagation times between the first access node and individual ones of the plurality of user terminals are different.

26. The communication system of claim 19, wherein at least one propagation time between the first access node and an individual one of the plurality of user terminals varies over time.

27. A communication system according to claim 19, wherein a timing advance between a forward link time slot and a return link time slot in a first user terminal among the plurality of user terminals causes the return link time slot and the forward link time slot in the first user terminal to overlap.

28. The communication system of claim 19, wherein a timing advance between a forward link time slot and a return link time slot in a first user terminal of the plurality of user terminals is configured to result in the switching time gap.

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