# Patent

## Title
Dynamic time division duplex (DTDD) access for satellite RAN

## Abstract

A ground station communicates with a satellite having a field of view (FOV), the satellite directly communicating with user equipment (UE) over uplink signals and downlink signals. The ground station has a Dynamic Time Division Duplex (DTDD) controller configured to establish UE uplink time slots during which the UE sends UE uplink signals, the UE uplink time slots based on a unique delay for the UE, whereby UE uplink signals are received at the satellite during a same satellite uplink time slot. The controller avoids overlapping uplink and downlink signals being received at the satellite, as well as at the UE.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority of U.S. Application Ser. No. 63/222,633 filed Jul. 16, 2021, the content of which is relied upon and incorporated herein by reference in its entirety.


BACKGROUND
Radio access network (RAN) has two types: FDD (frequency division duplex) and TDD (time division duplex) are two spectrum usage techniques, both forms of duplex, used in mobile or fixed wireless broadband links. It is essential to these links that transmission can occur in both directions simultaneously so that data can flow downlink (DL) and uplink (UL) at the same time. TDD uses a single frequency band for both transmit and receive. TDD alternates the transmission and reception of station data over time. Time slots may be variable in length.
The real advantage of TDD is that it only needs a single channel of frequency spectrum. Furthermore, no spectrum-wasteful guard bands or channel separations are needed. The downside is that successful implementation of TDD needs a very precise timing and synchronization system at both the transmitter and receiver to make sure time slots do not overlap or otherwise interfere with one another.
SUMMARY
A ground station communicates with a satellite having a field of view (FOV), the satellite directly communicating with user equipment (UE) over uplink signals and downlink signals. The base station has a Dynamic Time Division Duplex (DTDD) controller configured to establish UE uplink time slots during which the UE sends UE uplink signals, the UE uplink time slots based on a unique delay for the UE, whereby UE uplink signals are received at the satellite during a same satellite uplink time slot. The controller avoids overlapping uplink and downlink signals being received at the satellite, as well as at the UE.



BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a diagram that shows a TDD channel applied to satellite communications;
FIG. 2(a) is a diagram showing TDD over satellite and supporting ground infrastructure for a single satellite embodiment;
FIG. 2(b) shows TDD over satellite and supporting ground infrastructure for a multiple satellite embodiment;
FIG. 2(c) is a flow diagram;
FIG. 3 is a diagram showing TDD Tx/Rx rings;
FIGS. 4(a), 4(b) are diagrams showing TDD channel using satellite;
FIG. 5(a) is a timing diagram for a GateWay Station (GWS), a single satellite (SAT) and UEs located in rings of FIG. 3;
FIG. 5(b) is a timing diagram for a GateWay Station (GWS), two satellites (SAT1, SAT2) and UEs located in rings of FIG. 3; and
FIG. 6 is a diagram showing the Tx/Rx frequency split.



DETAILED DESCRIPTION
In describing the illustrative, non-limiting embodiments illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents that operate in similar manner to accomplish a similar purpose. Several embodiments are described for illustrative purposes, it being understood that the description and claims are not limited to the illustrated embodiments and other embodiments not specifically shown in the drawings may also be within the scope of this disclosure. For example, “gNodeB” illustrations and texts are equally applicable to eNodeB.
FIG. 1 shows a standard LTE (Long-Term Evolution) TDD frame of 10 ms. As illustrated, the satellite has predetermined time slots during which an uplink signal is received and predetermined time slots during which a downlink signal is transmitted. In the example embodiment shown, the uplink and downlink time slots alternate with one another. At the ground station processing device, such as an eNodeB, a 10 ms TDD frame has ten subframes 0-9. In the example embodiment shown, the first subframe 0 is when the eNodeB transmit a downlink signal to the UE via the satellite. That is followed by a second subframe, which is a special subframe having a Downlink Pilot Time Slot (DwPTS), a Guard Pilot (GP) and an Uplink Pilot Time Slot (UpPTS). That is followed by two Uplink subframes 2, 3, during which the UE transmits an uplink signal to eNodeB at the ground station, and then two Downlink subframes 4, 5, another special subframes, then another two uplink subframes 7, 8, and then a downlink subframe 9 and the next subframe 0 of the next frame, just like the subframe 0 of this frame at the beginning. Such cycle repeats to deliver continuous DL and UL communications. There can be a few different ratio and granularity of DL and UL slots by RAN system configurations.
As further illustrated in FIG. 1, the User Equipment (UE) on earth communicate with the eNodeB. Here, the UE initially receives a signal from the eNodeB during subframe 0, and receives a control signal during the DwPTS half-subframe, then transmits a signal during the UpPTS half-subframe. The UE then switches to transmit during the subframes 2, 3 for the Uplink signals. The DwPTS and UpPTS provide time to allow downlink/uplink switching to be performed. When the UE switches back to receive during the Downlink signal, it accounts for a Timing Advance (TA) (e.g., 20 μs). The eNodeB instructs the UE to transmit a bit early to meet the time slot at the eNodeB and avoid overlapping signals at the eNodeB. And, there is some offset between the satellite and the eNodeB to allow for switching from downlink to uplink and from uplink to downlink.
TDD is more flexible and efficient in spectrum usage, as the DL and UL traffic is asymmetric and dynamically changing. NR Mid band and High band only have TDD, and FDD stays only for Low band (FR1: below 6 GHz). It can work better than FDD, as the same frequency for Tx and Rx there is no switch insertion loss. The TDD D/U ratio can be dynamically adjusted to suit for the needs, especially for wider bandwidth (BW). The future will have more TDD for UE HW and e/gNB TR/Rx is simpler than FDD, the spectrum usage is more efficient.
Timing is often synched to precise GPS-derived atomic clock standards. Guard times are also needed between time slots to prevent overlap. This time is generally equal to the send-receive turnaround time (transmit-receive switching time) and any transmission delays (latency) over the communications path.
FIG. 2(a) shows a Dynamic Time Division Duplex (DTDD) access system and method according to the present disclosure. The DTDD system 100 includes a gateway 150 that communicates with one or more Low Earth Orbit (LEO) satellites 20 over Transmit and Receive beams Tx/Rx 12. The satellite 20 directly communicates with one or more User Equipment (UE) 10 located in cells 7 on earth over respective Transmit and Receive beams Tx/Rx 14. The gateway 150 has a gateway antenna 152, a gateway site 154, a first processing device 156a, a second processing device 156b, and a DTDD controller 160. In the embodiment shown, the first processing device 156a includes one or more gNodeBs or eNodeBs, each to control communications over beams 12, 14 with a first cell 7, and the second processing device 156b includes one or more gNodeBs, each to control communications over beams 12, 14 with a second cell 7.
In FIG. 2(a), a single satellite 20 is utilized to communicate with UEs 10 over different frequencies. Time slots are used for transmit signals Tx and receive signals Rx. The DTDD controller 160 separates the transmit signal Tx and receive signal Rx in different frequencies. The DTDD controller 160 dynamically controls operation of the system 100 to coordinate communication between the satellite 20 and the ground station 150 via the antennas 152, and the direct communication between the satellite 20 and the UEs 10. The controller 160 controls the frequency and timing amongst all of the UEs communicating on all of the plurality of gNodeBs 156 to avoid any overlap of communication at the satellite 20. The controller 160 can also receive information on the orbit, Field of View (FOV), etc., and control communications based on that information. The controller 160 handles the frequency and time DL and UL signals with their cell IDs to the plurality of gNodeBs 156, which then provide the synchronization and time slot assignment as normal. That information is then transmitted to and received by the UEs 10 via the satellite 20, to control operation of the UEs to communicate on the designated frequencies and time resource allocations.
FIG. 2(b) is an example of another embodiment of the disclosure utilizing multiple satellites, a first satellite 20a and a second satellite 20b. However, additional satellites can be utilized, as a particular cell 7 may be in communication with four or more satellites at any given time. As illustrated, the first satellite 20a communicates a feeder link signal with the GW site 154 over a first beam 12 and the first satellite 20a directly transmits downlink signals to the UEs on earth over a second beam 14. And the second satellite 20b communicates a signal with the GW site 154 over a third beam 13 and directly receives uplink signals from the UE on earth over a fourth beam 16. And, as further shown, the second satellite 20b can transmit a downlink signal to different cells than the downlink signal 14 from the first satellite 20a. 
As the satellites orbit, the setting satellite 20a can conduct handover to transfer the uplink signal, then the downlink signal, for the cells to the setting satellite 20b; thus, when the second satellite 20b takes over the uplink signal, then 20a can release. However, in the embodiment shown, one satellite (the first satellite 20a) communicates the downlink signal and a different satellite (the second satellite 20b) communicates the uplink signal; though in other embodiments a single satellite can conduct both uplink and downlink (FIG. 2(a)). In some embodiments, the transmit signal Tx is over a first frequency, and the receive signal Rx is over a second frequency different than the first frequency for different regions/cells, while the Tx and Rx of the same frequency from the same cell are handled separately by two satellites so that with multiple satellites, TDD TRx collision can be avoided completely, and the GWS 154 can route the TRx signal to two satellites over different feeder links and combine the relevant DL and UL signal for the BBUs, and the UEs can communicate uplink signals and downlink signals as they do normally without causing timing collision issue on the same satellite, as two satellites are handling Tx and Rx at different position in the space. They have their own Tx and Rx beams for the same cell. It is the ground gateway site managing the feeder links and take the spatial diversity to resolve such challenges.
Accordingly, at any given time, the DTDD 160 dynamically controls the operation of the system 100 in real time to coordinate communications between the first and second satellites 20a, 20b with the ground station 150 over the antennas 152, and between the first and second satellites 20a, 20b directly with the UEs 7. The controller 160 can also receive information on the orbit, Field of View (FOV), etc., and control communications based on that information. The UEs 7 directly transmit signals to the second satellite 20b at a certain time subchannel and receive signals from the first satellite 20a at a certain time channel, so that there is no interference or overlap of communications at the satellites 20a, 20b, and the satellites 20a, 20b are fully utilized.
Referring to the time vs. distance chart of FIG. 2(b), the FOV are generally large enough to find cells using LB or HB, so two satellites can be arranged for taking care of two different bands, for example, 20a Tx LB cells, but Rx the HB cells; while 20b Tx HB cells, but Rx the LB cells. In this way they can avoid TDD collision effectively.
FIG. 2(c) shows the operation 200 of the DTDD 160 in accordance with one example embodiment of the present disclosure. Starting at step 202, the satellite control center provides information about the system, including for example the cells, RAT, frequencies, satellite(s) and gate way site. At step 204, the satellite control center also provides the TDD low band (Tx) cells and high band (Rx) cells and visible satellites 20 by each and every cell 7. And, step 206, the satellite control center also provides the field of view for each satellite 20 when serving a cell 7. The information from steps 202, 204, 206 can be accessed by or communicated to any of the DTDD 160 or the gNodeB.
At step 208, the DTDD 160 determines, for the information obtained from the NCC and the satellite control center, the best satellite transmit signal Tx and satellite receive signal Rx for each cell. At step 210, the DTDD 160 allocates a frequency and time resource for each cell, step 210. The controller 160 also determines (with respect to two satellites), step 212, the routing arrangement of the feeder links, as well as the direct digital control (DDC) parameters and, step 214, the routing arrangement (mapping) for satellite hand over. It then updates the satellite's position and field of view at the satellite control center, step 216. That information is then transmitted to the UEs via the gNodeBs and satellite(s). The gNodeB operates in accordance with its standard compliant procedures, and here configures the signal to a baseband signal for communication with the satellite(s). Thus, the DTDD controller 160 determines the frequency and time resource allocation for each cell, step 210, and utilizes that information to configure operation of the UL and DL signals at the satellite(s), UEs, and gate way station 154.
The entire operation at the DTDD 160 (as well as the satellite control center) is conducted automatically and without any manual interaction. Accordingly, unless indicated otherwise the process can occur substantially in real-time without any delay or manual action.
FIG. 3 is a diagram showing a FOV for a single satellite 20. The gNodeBs 156 each separate the FOV into a plurality of concentric TDD Tx/Rx rings 5 based on a distance (pathlength) from the satellite 20 to the ground. The shortest pathlength is at the center of the FOV at the first ring 5a, which is located directly below the satellite 20. Each subsequent surrounding ring 5b-5g extends further outward from the first ring 5a and is associated with a further distance from the satellite 20. The satellite 20 directly communicates with the UEs 7 positioned in each of the rings 5a-5g via a respective transmit beam 14a-14g and a respective receive beam 16a-16g. 
The outermost ring 7g is furthest from the satellite 20 and defines the outer perimeter of the FOV for the satellite 20. The beams 14g, 16g communicating with the outermost ring 7g typically form an angle of about 20 degrees (though larger or smaller angles can be utilized) from the UEs 7 on the ground to the satellite 20. The FOV and rings 5 follow the satellite 20 as it orbits earth. One or more cells 7a-7g are located in a respective ring. For synchronization, area is in rings so the latency to the satellite 20 is similar for all the UEs in each ring, and all the cells 7 in the FOV have the same ratio for DL/UL.
The beams 14, 16 track the cells and hence the cell tracking beams change their rings every few seconds, which means the gNBs 156 shift the special time slot from one subframe to the next, so that all the FOV would roughly align the TRx switching time on the same subframe. Such dynamic changes are actually changing slowly and UEs are able to adapt to the changes. There are points where the special subframe need to shift when they are close to 1 ms drift due to satellites orbiting at high speed, so that the changes match the protocol periodicity and the smooth shifts of Tx-Rx time. Must follow the 1 ms granularity for the ring sliding over the fixed cell. The Network Control Center (NCC), which is at the gate way site 154, and the NCC has a controller that guides the ring switching for each Base Band Unit (BBU) of the gNodeB 156, as well as handling communications at the satellites 20a, 20b for each cell 7 (e.g., the operating parameters for the Tx/Rx beams of the cell 7). Each gNodeB 156 can have a plurality of BBUs, each of which has a controller that controls a single cell 7.
The solution for better use of the TDD spectrum resources by having different DL/UL ratio (the respective number of DL and UL subframe) would be a new use of TDD bandwidth part (BWP) in smaller granularity (say 20 MHz) into multiple TDD BWPs (4×5 MHz) and do the different DL/UL ratio for each partition of BWs, so that there will be different frequency sub-band usage by all the cells to avoid phase array Rx suffer from interference of the strong Tx. Dynamic adjusting of the TDD resources according to the needs as shown in FIG. 6. Thus, within the TDD, each BWP can have a different frequency. For example, any overlap in DL and UL processing can be resolved by assigning a different frequency for the DL and UL signals.
The width of each ring 5 can be smaller with HB (high band, i.e., approximately 2 GHz), as the cell size reduces, hence ring changing would be quicker than LB (low band, approximately 1 GHz), but a few seconds for a ring change is not too much for a gNodeB. Scheduling is parameterized with any ring.
One objective of the above description is to be able to run the TDD with a modified gNodeB but minimizing additional changes. Running an engine that can recover the frequency dimension lost when working on TDD instead of FDD. The DTDD controller 160 provides a dynamic and real-time assignment of the frequencies depending on the position on the ring 5 and makes the operation transparent to the gNodeB 156 and the UE 10.
It cross-correlates and assigns in real-time the frequency plan, with each carrier assigned to either to Tx or Rx; there is a scheduler that determines the best means of transmitting each carrier in real time, using carrier planning that continuously adjusting itself in real time. Each carrier is assigned just for Tx or Rx and they're assigned in different ring levels to minimize the delay difference impact.
Turning to FIG. 4(a), a timing diagram is shown to illustrate an issue with TDD when used for a single satellite having ten frames 0-9. A downlink signal is transmitted from the satellite 20 to the UE 10, which is transmitted from the satellite 20 during a satellite downlink frame DL-SAT and received at the UE during a UE downlink frame DL-EU. The downlink signal starts at a first time period T=0, but due to the pathlength from the satellite 20 to the UE 10, there is a delay until the downlink signal is first received at the UE, at T=1. In addition, an uplink signal is transmitted from the UE to the satellite, which is transmitted from the UE during a UE uplink frame UL-EU and received at the satellite during a satellite uplink frame UL-SAT.
That delay in transmission between the satellite and the UE causes an overlap in operation when the satellite 20 changes from transmitting data to the UEs 10 in the downlink frames, to receiving data from the UEs 10 in the uplink frames, as shown where the DL-UE and UL-UE overlap at T=5 to T=8. For example, the satellite 20 continues to transmit the downlink signal until time T=6, and from T=7 to T=10 the satellite 20 receives uplink data. In addition, at time T=5, the UE must begin to transmit data to the satellite 20 in order for that data to be received at the beginning of the uplink frames at T=7 to make full use of the satellite and maximize satellite operations. Consequently, any transmission from the satellite to the UE after a certain time, say T=6, will be received at the UE when the UE is in the transmission mode, at T=8. More specifically, the UE will both be receiving data from the satellite and also transmitting data to the satellite from T=5 to T=8. That period of overlapping operation cannot be reliably performed by the UE and is likely to have errors and interference.
In FIG. 4(b) it is shown that the greater the distance in the FOV between the satellite and the UE, the greater the pathlength, and the longer the delay in the UL and DL transmissions, which can be further based on orbital position, FOV and other factors. Where the delay is long enough, it can resolve the overlapping operation at the UE; as shown, there is no overlap between the DL-UE frame and the UL-UE frame. However, a longer delay causes an overlapping operation at the satellite 20 when the satellite converts from downlink during the DL-SAT frames to uplink during the UL-SAT frames, which also is undesirable. Accordingly, a delay is needed that avoids overlapping operations at both the UE and the satellite.
FIG. 5(a) shows a timing diagram for a single satellite operation (FIG. 2(a)) to maximize capacity at the satellite 20, and FIG. 5(a) shows a timing diagram for two satellite operation (FIG. 2(b)) to maximize capacity at the satellites 20a, 20b. Referring first to FIG. 5(a), the figure shows an example where UEs 10b, 10d, 10g are active in three of the rings, namely rings 5b, 5d and 5g, respectively. As shown, the UEs 10b, 10d, 10g transmit respective signals on respective distinctive beams 16b, 16d, 16g during respective uplink time frames UL-UEb, UL-UEd, UL-UEg to the satellite 20 to be processed at the satellite 20 during an uplink frame UL-SAT from T=6 to T=7. For the uplink beams 16b, 16d, 16g to be received at the same time T=6, the UE 10g in the furthest ring 5g must begin transmitting at the earliest time T=0 to T=3, time frame UL-UEg, since that UE transmission has the longest pathlength and the longest delay. The UE 10d in the next furthest ring 5d in the example must begin transmitting at the next earliest time T=1 to T=4, time frame UL-UEd. And the UE 10b in the closest ring 5b begins transmitting at the latest time T=2 to T=5, time frame UL-UEb. Accordingly, the beams from each of the rings 5g, 5d, 5b arrive simultaneously at the satellite time slot UL-SAT at T=6 to T=7.
The satellite 20, also during the satellite uplink time frame UL-SAT, transmits the uplink signals 12 UL to the gate way site 154 and after a delay is received at T=8 to T=9 during an uplink time slot at the gate way site UL-GWS. At the next downlink time slot at the gate way site DL-GWS, at time T=9 to T=10, the gate way site 154 transmits a downlink signal 12DL to the satellite 20. It is received at the satellite during a satellite downlink time slot DL-SAT from T=11 to T=12. Thus, the UL subframe for the UEs in different rings are offset with respect to one another so that the UL signals are synchronized when received at the satellite.
At that same time, the satellite simultaneously transmits that downlink signal on respective distinctive downlink beams 14b, 14d, 14g, all starting at the same time T=11 and ending at the same time T=12. The closest UEs 10b (i.e., the UEs in ring 5b, FIG. 3) receives the downlink signal 14b first, at DL-UEb, because it has the least delay in communication with the satellite based on its pathlength and other factors. The next closest UE 10d (i.e., the UEs in ring 5d, FIG. 3) receives the signal 14d next, at DL-UEd, and the furthest UE 10g (i.e., the UEs in ring 5g, FIG. 3) receives the downlink signal 14g last, at DL-UEg. Thus, the DTDD controller 160 provides different delays for the UEs located in the various rings 5a-5g of FIG. 3, to avoid overlapping UL and DL frames at the GWS 154, the satellite 20, and/or the UEs 10. That is, the UEs 10 located in the closest ring 5a will all be associated with a first delay, the UEs 10 located in the next closest ring 5b will all be associated with a second delay longer than the first delay, and the UEs located in the furthest ring 5g will all be associated with a seventh delay longer than the first-sixth delays for rings 5a-5f. Thus, the DL signal is synchronized at the satellite 20.
Accordingly, UE uplink frames for the three UEs, namely uplink frames UL-UEb, UL-UEd, UL-UEg, are offset with respect to one another, and can overlap (or not) with one another. However, the UE closest to the satellite, UEb, has an uplink frame UL-UEb that starts and ends last at T=2 to T=5 and a downlink frame DL-UEb that starts and ends first, at T=13 to T=16; the next closest UEd has an uplink frame UL-UEd that starts and ends after the closest UEb starts and ends, at T=1 to T=4, and a downlink frame DL-UEd that starts and ends after the closest UEb starts and ends, at T=14 to T=18; and the furthest UEg has an uplink frame UL-UEg that starts and ends last (after UL-UEb and UL-UEd start and end), at T=15 to T=18. The UE frames can be stretched to accommodate that timing. However, for a single satellite (FIG. 2(a)), the TDD Tx signals may interfere with the Rx signals.
As further illustrated in FIG. 5(a), there is no overlapping operation at any of the gate way site 154, the satellite 20 or the UEs 10. That is, none of those elements need to receive and transmit at the same time. And, communications occur without collision between transmit and receive for all UEs 10 in all cells 7. And, the satellite uplink can start and end at the same time, T=6 to T=7; and the satellite downlink can start and end at the same time, T=11 to T=12. That entire operation is coordinated by the DTDD controller 160.
Though FIG. 5(a) is illustrated for a single satellite (FIG. 2(a)) for a particular case to avoid Tx Rx collision, such case is with constraints of cell position, U/D periods matching the delay, it is clear that the next frame will run into collision. So, with one satellite TDD is challenging. However, the solution does exist when the full constellation of satellites are available, as in that case each cell can see normally 4 satellites. Hence a better TDD solution can be formed from two satellites (FIG. 2(b)), one does the Tx only while the other does the Rx, as shown for example in FIG. 5(b). The 3D diagram (FIG. 2(b)) illustrates spatial, time and frequency diversity to avoid the interference from Tx of 2 or 2+ satellites. The 2+ satellites handling TDD case would be the preferred one as there is no restrictions on the DL and UL fractions, and can fit in the demand better.
Referring to FIG. 5(b), a timing diagram is shown where there are two satellites (FIG. 2(b)), where a first satellite (SAT1) 20(a) only conducts uplink (U), and a second satellite (SAT2) 20(b) only conducts downlink (D), for a given UE or cell or FOV. Thus, starting at a first time period, T=0 to T=1, all of the UEs from all of the rings 5b, 5d, 5g transmit an uplink signal 16 during its uplink frame, UL-UEb, UL-UEd, UL-UEg. Because the UEs are in different rings and at different distances from the second satellite 20(b), those signals arrive at the second satellite 20(b) at different times. Namely, the uplink signal from the closest UEb, UL-UEb arrives at a frame that starts and ends first, at times T=2 to T=4; the uplink signal from the next closest UEd, UL-UEd arrives at a frame that starts and ends after the first signal UL-UEb, at times T=3 to T=6; and the furthest UEg, UL-UEg arrives at a frame that starts and ends after the first and second signals, UL-UEb and UL-UEb, at times T=5 to T=7.
The second satellite 20(b) operates as a pass through and sends those offset signals to the gate way site 154. The DTDD 160 applies a respective delay to each signal. The signal 16b from frame UL-UEb arrived first, so the DTDD applies the longest delay, Delay b. The second signal 16d to arrive is from UL-UEd, and the DTDD 160 gives that a Delay d, which is shorter than the first delay, Delay b. And the last signal 16g to arrive is from frame UL-UEg, which receives the shortest delay, Delay g. The delays b, d, g are configured so that all of the uplink signals are recognized at the DTDD 160 at a same time, starting at T=8 and ending at time T=9. Thus, although the signals 16b, 16d, 16g arrived at the second satellite 20(b) at different times, they are all synchronized at the gate way 154, for example at the DTDD 160. It is noted that although all the uplink signals 16b, 16d, 16g are shown being sent at the same time (T=0 to T=1 in the example embodiment shown) from the UEs 10b, 10d, 10g, they can be sent at different times and an appropriate delay can be applied to each respective signal by the DTDD 160. However, in some embodiments, the uplink signals from the UEs are all on the same band, and can be the same or different frequencies. The downlink signals 14b, 14d, 14g can be treated in a similar manner, with a delay being applied at the gate way such as by the DTDD 160, so that the downlink signals are sent at different times (though shown in the figure at the same time), so they arrive at the UEs at a same time period.
One goal in FIGS. 2(a), 2(b), 5(a), 5(b) is to make the TRx switching on the same subframe timing that can be achieved by each eNB to configure the timeslots for downlink and uplink with and/or without frequency scheduling resources according to the needs of the active UEs. Thus, the DL and UL do not occur at the same time, same distance and same frequency.
Turning to FIG. 6, another embodiment of the disclosure is illustrated. Here, the uplink and downlink signals can be on different frequencies to eliminate interference at the GWS 154, satellite 20 and/or UE 10, either on a same beam or different beams. FIG. 6 shows the Tx/Rx frequency split: the frequency dimension and Tx/Rx separation is recovered with an external controller. This is transparent for the gNodeB, but a coordinated mapping of the radio resources: 1 and 2 here are timeslots for smaller scale FDD within a TDD system in this context. The further introduction of such FDD can avoid the interference between Tx and Rx, and can be very dynamic. In time collision case in a TDD case, using different sub carriers for Tx and Rx can help avoid interference.
The DTDD system 100 addresses two issues. First, Satcom RF path length delay is much longer than the TDD DL and UL cycle (10 ms in general). Unlike FDD, where there is an extra dimension of frequency to make the Tx and Rx independent of each other, and full duplex works gracefully without restriction to each other. The DTDD provides that extra dimension back to the TDD link in a transparent way for the cellular system (gNodeB to UE connection).
Second, RF path length differences to the cells in the satellite FoV would mean that the delay normalisation would make satellite beams TRx not aligned between all the cells 7 in the FoV, and that would cause some cells that are transmitting Tx to interfere with the cells that are receiving Rx. With the addition of the concept of rings (FIG. 3) the synchronization is done in each of them, so the latency to the satellite is similar for all the UEs in each ring.
In addition to the above solution, with full constellation, a cell would be covered by more than one beam from different satellites, the overlapping FOV can have the advantage of solving the above TDD Tx/Rx collision on one satellite. The multiple satellites can do independent Tx/Rx for each other and avoid collision 100% if coordinated well. There is no restriction with regards to the Tx and Rx switching time, as there is only Tx or Rx for that band. The gNodeB needs to configure the scheduler and keep the same ratio of D/U on all the cells the satellite 20 is serving. The gNodeB and/or DTDD controller 160 can handle Doppler compensation for the UEs.
It is implemented at the gateway, outside the gNodeB. The flow chart should have a transmission from gNodeB in frequency A, then a frequency conversion to get to the satellite in V band, then another frequency conversion to transmit in frequency B, within the same band but with an offset. Then the UE will transmit back in frequency A, this will be converted also to V band, and sent back to the gNodeB in frequency A.
It is noted that the FOV is divided into concentric rings or circles. However, any suitable separation can be provided.
In the embodiments disclosed, the DTDD controller 160 (as well as the BBU controller and the NCC controller) can include a processing device to perform various functions and operations in accordance with the disclosure, though operation can alternatively be performed at the gNodeB 156 and/or the satellite 20. The processing device can be, for instance, a computer, personal computer (PC), server or mainframe computer, or more generally a computing device, processor, application specific integrated circuits (ASIC), or controller. The processing device can be provided with one or more of a wide variety of components or subsystems including, for example, wired or wireless communication links, input devices (such as touch screen, keyboard, mouse) for user control or input, monitors for displaying information to the user, and/or storage device(s) such as memory, RAM, ROM, DVD, CD-ROM, analog or digital memory, flash drive, database, computer-readable media, floppy drives/disks, and/or hard drive/disks. All or parts of the system, processes, and/or data utilized in the system of the disclosure can be stored on or read from the storage device(s). The storage device(s) can have stored thereon machine executable instructions for performing the processes of the disclosure. The processing device can execute software that can be stored on the storage device. Unless indicated otherwise, the process is preferably implemented in automatically by the processor substantially in real time without delay. In some embodiments, the system 100 of the present disclosure is configured to operate and communicate with standard UEs 10. That is, the UE can be a standard UE without any special electronic components or operating software. In addition, the entire process is conducted automatically by the processor, and without any manual interaction. Accordingly, unless indicated otherwise the process can occur substantially in real-time without any delay or manual action.
The description and drawings of the present disclosure provided in the paper should be considered as illustrative only of the principles of the disclosure. The disclosure may be configured in a variety of ways and is not intended to be limited by the preferred embodiment. Numerous applications of the disclosure will readily occur to those skilled in the art. Therefore, it is not desired to limit the disclosure to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the disclosure.

## Claims

1. A ground station configured for communication with a satellite having a field of view (FOV), the satellite configured for directly communicating with user equipment (UE) over uplink signals and downlink signals, said ground station comprising:
a Dynamic Time Division Duplex (DTDD) controller configured to establish a first UE uplink time slot for a first UE at a first distance of the first UE from the satellite and having a first delay, and a second UE uplink time slot for a second UE at a second distance of the second UE from the satellite and having a second delay greater than the first delay;
wherein the first UE uplink time slot occurs after the second UE uplink time slot; and
whereby UE uplink signals are received at the satellite during a same satellite uplink time slot.

2. The ground station of claim 1, said DTDD controller configured to segregate the satellite FOV into a plurality of concentric rings, each of said plurality of concentric rings associated with a unique delay.

3. The ground station of claim 2, further comprising a first center ring and a second concentric ring around the first center ring, wherein said DTDD controller associates UEs in the first center ring with a first UE uplink time slot and UEs in the second concentric ring with a second UE uplink time slot.

4. The ground station of claim 3, wherein the first center ring is directly below the satellite.

5. The ground station of claim 1, wherein UE uplink signals are simultaneously received at the satellite during a same satellite uplink time slot.

6. The ground station of claim 1, wherein the uplink signals are separated to different frequencies.

7. The ground station of claim 6, wherein the frequencies minimize interference and is at subcarrier (15 kHz) or radio block (180 kHz) granularity.

8. The ground station of claim 1, said DTDD configured to communicate uplink signals via a first satellite and downlink signals via a second satellite.

9. The ground station of claim 1, further comprising a processing device configured to control communication with UEs in the FOV, said processing device configured to receive communication time slots for the satellite and the UE from the DTDD controller.

10. The ground station of claim 9, wherein the processing device comprises an eNodeB or a gNodeB.

11. The ground station of claim 9, wherein the processing device includes a plurality of base band units each configured to control communications with UEs in a single cell within the FOV.

12. A ground station configured for communicating with a satellite having a field of view (FOV), the satellite configured for directly communicating with user equipment (UE) over uplink signals and downlink signals, said ground station comprising:
a Dynamic Time Division Duplex (DTDD) controller configured to segregate the satellite FOV into a first center ring and a second concentric ring arranged concentrically about the first center ring, and associating first UEs in the first center ring with a first UE uplink time slot based on a first delay realized at the first center ring and second UEs in the second concentric ring with a second UE uplink time slot based on a second delay realized at the second concentric ring, whereby the first UE uplink time slot occurs before the second UE uplink time slot.

13. The ground station of claim 12, wherein the first UEs directly communicate with the satellite over a first UE uplink signal during the first UE uplink time slot and the second UEs directly communicate with the satellite over a second UE uplink signal during the second UE uplink time slot.

14. The ground station of claim 13, whereby the first and second UE uplink signals are received at the satellite during a same satellite uplink time slot.

15. A ground station configured for communicating with a satellite having a field of view (FOV), the satellite configured for directly communicating with user equipment (UE) over uplink signals and downlink signals, said ground station comprising:
a Dynamic Time Division Duplex (DTDD) controller configured to receive the uplink signals and apply a unique delay to each of the uplink signals to synchronize the uplink signals to a same uplink subframe time slot, wherein the DTDD is configured to establish a first UE uplink time slot having a first delay for a first UE, and a second UE uplink time slot having a second delay for a second UE, the second delay being greater than the first delay;
wherein the first UE uplink time slot occurs after the second UE uplink time slot; and
wherein UE uplink signals are received at the satellite during a same satellite uplink time slot.