• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    A wireless communication system with multiple access (5) contains a forward link (31) to a terminal (41) and a terminal (40). The return link (32) uses a medium that is shared by multiple terminals (40) based on time and frequency. A terminal (40) sends a return link sign (32) with a sequence of transmission slots (51, 52, 53), each transmission slot being determined by a time slot, carrier frequency, and wherein the carrier frequency and the symbol rate can change between transmission slots. The return link signal (32) is sent continuously over the sequence of transmission slots (51.52.53). The terminal can send a return link signal (32) that is phase-continuous over the transmission slots.
    公开号:BE1019923A5
    申请号:E2011/0558
    申请日:2011-09-21
    公开日:2013-02-05
    发明作者:Alain Rolle；Dirk Breynaert；Daniel Delaruelle
    申请人:Newtec Cy N V；
    IPC主号:
    专利说明:

    TRANSMISSION SCHEDULE WITH MULTIPLE ACCESS FOR A WIRELESS COMMUNICATION SYSTEM
    SCOPE OF THE INVENTION
    This invention relates to a multi-access transmission scheme for a wireless communication system, such as the return link (or return connection) of an interactive satellite communication system, and to equipment for performing the scheme.
    BACKGROUND OF THE INVENTION
    Multiple interactive satellite communication systems have already been proposed. With such systems, terminals receive data from a hub via a forward link and can also send data to the hub via a return link. Both the forward and the return link are sent via satellite. One such system is standardized as a Digital Video Broadcasting-Return Channel via satellite (DVB-RCS) ETSI EN 301 790.
    DVB-RCS uses a medium, multiplexed on a time and frequency shared basis between the terminals. This scheme is called Multiple-Frequency Time-Division Multiple Access (MF-TDMA). MF-TDMA allows a group of terminals to communicate with a gateway via a set of carrier sequences, each divided into time slots. A scheduler (scheduling program, planner) assigns a series of slots to each active terminal, each slot being determined by a frequency, a bandwidth, a start time and a duration. Figure 1 shows one of the MF-TDMA schemes, the so-called fixed MF-TDMA. A grid of time slots 10 is shown. The slots have the same duration and the same bandwidth. The arrows in Figure 1 indicate a sequence of slots 11, 12, 13 assigned by the planner to a terminal in the system.
    Another form of MF-TDMA is the Dynamic-Slot MF-TDMA. This shape changes the bandwidth and duration of consecutive slots assigned to a terminal. In addition to changing carrier frequency and burst duration, the terminal can also change the transfer rate and the coding ratio between successive bursts. The advantage of the more flexible terminal is a more efficient adaptation to the widely differing requirements in connection with transmission specific to multimedia applications. Figure 2 shows a sequence of slots 15, 16, 17 assigned by the planner to a terminal in the system. It is clear that slot 16 has a larger bandwidth than slots 15 and 17. Slots 15 and 16 are longer than slot 17.
    The MF-TDMA schemes described in ETSI EN 301 790 have limitations in terms of bandwidth efficiency.
    SUMMARY OF THE INVENTION
    A component of the present invention provides a method for a terminal in a wireless communication system with multiple access, comprising, inter alia, a forward link to the terminal and a return link from the terminal, the return link using a medium provided by the terminals is shared based on time and frequency. This method comprises: transmitting a return link signal from the terminal over a series of transmission slots, each transmission slot being defined as a time slot and a carrier frequency, whereby carrier frequency and Symbol rate can change between the transmission slots, and where the return link signal is continuously transmitted over the series of transmission slots.
    The term "continuously broadcast" includes: the continuous transmission with no waiting time; continuous transmission with a small number of zero energy, or reduced energy, transmission symbols at the beginning and / or end of a transmission slot. Advantageously, the return link signal is transmitted in a phase-continuous manner over the series of the transmission slots. This means that even when the transmitted signal contains zero-energy transmission symbols, the total duration of the sequence of zero-energy transmission symbols is an integer multiple of symbol transmission period.
    Transmission in a continuous manner avoids the need for the terminal signal to be acquired by the receiver each time the signal passes to a new frequency and / or symbol rate, since the receiver can remain locked (or locked) on a signal. This has the advantage that the need for a considerable amount of overhead data can be avoided, such as a long preamble for synchronization purposes. Conventional transmission schemes transmit bursts with significant waiting time between bursts and require a significant amount of overhead (non-payload) data, such as a long synchronization sequence, in each transmitted burst, for the sole purpose of enabling synchronization by the receiver.
    The term "wherein the carrier frequency and symbol rate can change between transmission slots" means that the frequency carrier and symbol rate can switch between adjacent transmission slots, and that the terminal is capable of operating in this manner. It is clear that this method does not require that both the carrier frequency and the symbol rate have to be changed between each adjacent pair of transmission slots. Depending on the specific combination of transmission slots, and the specific implementation of the transmission scheme, the terminal may either: maintain the carrier frequency and the symbol rate of the return link signal at the values used in the previous transmission slot; or only the carrier frequency of the return link signal with respect to the carrier frequency value used for the previous transmission slot; or only the symbol rate of the signal from the return link relative to the symbol rate used in the previous transmission slot; or both the carrier frequency and the symbol rate of the return link signal change compared to the values of the carrier frequency and the symbol rate used for the previous transmission slot.
    Advantageously, the method comprises receiving, on the forward link, information identifying a next transmission slot. The information allows the terminal to determine the number of transmission symbols to be transmitted during a subsequent transmission slot. The information can determine a symbol rate from which the terminal can derive a number of transmission symbols, or the information can also directly define the number of transmission symbols.
    Advantageously, this method also allows transmitting with a symbol rate selected from a set of different symbol rates, the set of symbol rates being selected in such a way that each symbol rate of the set counts an integer number of symbols during a final period, and where the terminal can change the symbol rate at the start of each new transmission slot.
    Advantageously, this method includes synchronizing the frequency with the forward link and sending in the return link with a symbol rate and carrier frequency based on the synchronized frequency of the forward link.
    Advantageously, this method includes synchronizing with a hub of the system by: receiving from the hub an instruction to begin sending identification symbols; sending, on the return link, identification symbols, and counting the number of identification symbols sent; receiving an instruction to begin sending a user data payload during a first transmission slot, after a certain number of transmitted identification symbols; sending in the first transmission slot of a user data payload after sending a certain number of identification symbols.
    Advantageously, the method comprises receiving an instruction to adjust the symbol rate on the return link. The terminal can receive an instruction to raise or lower the symbol rate. This guarantees that the terminal remains synchronized with the hub, without the terminal having to maintain a time reference for this.
    Another aspect of the invention provides a method for operating a hub of a wireless multiple access communication system with a forward link from the hub to terminals in the system and a return link from each terminal to the hub, the return links from terminals sharing a transmission medium that is distributed based on time and frequency, containing, in the hub: assigning a series of transmission slots to a terminal in the system, each transmission slot being characterized by a time slot and a carrier frequency, the carrier frequency and symbol rate can change between transmission slots; assigning a receive function to receive the return link signal from each terminal in the network; and, possibly substantially, changing the carrier frequency of the receiver in synchronization with a change in the carrier frequency of the signal received from the terminal, the return link being sent continuously over the series of transmission slots.
    Conventional MF-TDMA requires accurate planning with sufficient resolution, with the characteristic of using short bursts, which implies that short error protection code words must be used to fit into those short bursts. For a given available signal / noise ratio, it is more difficult to develop a spectrally efficient code with short code words than with long code words. Advantageously, in realizations of this invention there is a continuous transmission (this means: without "bursts"), making it possible to determine the length of the code words by weighing allowed processing time against desired spectral efficiency in function of the signal / noise ratio, as known in the art, with little or no nuisance from the MF-TDMA context. This improves the spectral efficiency as a whole thanks to: more efficient codes (longer code words) and less overhead since there is no waiting time between the slots, and moreover less synchronization data to be transmitted for a given amount of payload data. Another advantage of substantially continuous transmission is that a signal can be more easily monitored with regard to the saturation of the outdoor unit of the terminal. Monitoring saturation allows saturation prevention, which in turn makes it possible to use the power amplifier of the outdoor unit against the saturation point, instead of transmitting with inefficiently low power, allowing the outdoor unit to be used more efficiently. Monitoring saturation is very difficult for short-term bursts that are typical of classic MF-TDMA.
    Other features of the invention provide devices for realizing all of the methods described or the methods in the claims. Thus, one aspect of the present invention provides a wireless communication terminal that can be used in a multi-accessible wireless communication system, comprising: a receiver to receive a forward link signal; and a transmitter to be able to send a return link signal, wherein the return link uses a medium that is shared by the terminals on a time and ifequence basis, and wherein the transmitter is set to send a return link signal from the terminal using which is made from a series of transmission slots, and wherein each transmission slot is defined as a time slot and carrier frequency, whereby carrier frequency and symbol rate can change between the slots, and wherein the return link signal is continuously transmitted over the series of transmission slots.
    Another feature of the invention provides a wireless communication system for use in a hub of a multi-accessible wireless communication system, comprising: a transmitter to send a forward link to terminals in the system; a receiver to receive a return link signal from each of the terminals, the return link signals sharing a transmission medium based on time and frequency; a scheduling function intended to schedule a sequence of transmission slots for the return link of each terminal, wherein each transmission slot is defined on the basis of a time slot and a carrier sequence, wherein carrier sequence and symbol rate may change between transmission slots; with - possibly substantially - changing the carrier frequency in the receiver, synchronous with a change in the frequency of the return link signal received from the terminal, the return link signal being continuously transmitted throughout the sequence of the transmission slots.
    The system can adopt any of the following topologies: star network; multi-star network; and a partially meshed star network where terminal to hub and terminal to terminal communication links can share bandwidth.
    The functionality described here can be implemented in hardware, or in software executed by a processing unit, or by a combination of hardware and software. The processing unit may consist of a computer, a processor, a finite state machine, a logic matrix (logic array) or any other suitable processing device. The processing device may be a general-purpose processor that executes software for the purpose of causing the general-purpose processor to perform the required tasks, or the processing unit may be specially designed to perform the required tasks itself. Another aspect of the invention provides (software) instructions in machine language which, when executed by a processor, perform any of the methods already described. The machine language instructions can be stored in an electronic memory, on a hard disk, an optical disk or another type of machine-readable storage medium. The machine language instructions can be downloaded to the storage medium via a network connection.
    BRIEF DESCRIPTION OF THE DRAWINGS
    Realizations of this invention will be described, by way of example only, with reference to the accompanying drawings in which:
    Figure 1 represents a conventional MF-TDMA scheme;
    Figure 2 represents another conventional MF-TDMA scheme;
    Figure 3 represents an interactive satellite communication system according to an embodiment of the present invention;
    Figure 4A represents a transmission scheme according to an embodiment of the present invention;
    Figure 4B shows a transmission scheme according to another realization of the present invention, with a fixed-duration lock;
    Figure 4C shows a transmission scheme according to another realization of the present invention, with a fixed-duration slot and a fixed frequency distribution
    Figure 5A shows the operation of a terminal, according to a conventional MF-TDMA transmission scheme; .
    Figure 5B shows the operation of a terminal using a transmission scheme according to an embodiment of the present invention;
    Figure 6 shows a state diagram of a terminal in the system of Figure 3;
    Figure 7 shows the operation of the hub and a terminal in the system of Figure 3;
    Figure 8 shows an exemplary structure of a frame in the physical layer;
    Figure 9 shows a baseband signal from a terminal;
    Figure 10 shows a device in a terminal of the system in Figure 3;
    Figure 11 shows a device in a hub of the system in Figure 3.
    DESCRIPTION OF PREFERRED REALIZATIONS
    This invention will be described taking into account certain realizations and referring to certain drawings; however, the invention is not limited thereto merely by the claims. The described drawings are only schematic and not restrictive. For the sake of clarity, the dimensions of some elements in the drawings may be exaggerated and not to scale. Where the term "containing" is used in the present description and claims, this does not exclude other elements or steps. Furthermore, the terms first, second, third etc. used in the description and the claims are used to distinguish between similar elements without necessarily serving to represent a sequential or chronological order. It is clear that the terms used as such are interchangeable under appropriate circumstances and that the realizations of the invention described herein are capable of functioning in sequences other than those described or explained herein.
    Figure 3 shows an interactive satellite communication system 5 according to an embodiment of the present invention. The main parts of the communication system 5 are a hub 20, a satellite 30 and terminals 40. The hub 20 comprises a forward link transmission function 21 and a set of receivers 22 to receive the signals from terminals 40 on the return links 32. When active, the forward link transmission function 21 will send a forward link (FW) signal 31 to satellite 30, and satellite 30 in turn transmits the forward link signal 31 to terminals 40. Each active terminal 40 sends a return link (RL) signal 32 to satellite 30 and satellite 30 in turn sends the return link signal 32 to the receivers 22 in the hub. Advantageously, a receiver is assigned to receive the return link signal 32 from each active terminal 40. The hub also contains a time reference 25 of the network. A return link planner 26 assigns transmission slots to the terminals 40 based on the requests for data traffic through the terminals, and on the observed return link quality (e.g., signal-to-noise ratio) for each terminal-to-hub link. Planner 26 sends information to terminals, via the forward link 31, whereby it is determined which transmission slots a terminal 40 should use to send its data. System 5 is essentially a star network that serves N users (N = 3 in Figure 3) with hub 20. A terminal 40 can be either an indoor unit or an outdoor unit. The forward link (FW) 31 from hub 20 to terminals 40 is typically a single broadband carrier with information for all users through a time-sharing mechanism such as Time-Division Multiple Access (TDMA).
    In realizations of this invention, the access medium is shared between all return links 32 through a Multiple-Frequency Time-Division Multiple Access (MF-TDMA). At all times, the signals sent from all terminals (users) 40 are separated in frequency and the frequency and bandwidth occupied by each terminal can change over time. Consequently, it is clear that the transmission scheme is a combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA). Nevertheless, unlike conventional MF-TDMA systems, a terminal 40 continuously broadcasts, and no conventional waiting time interval is used between transmissions with different frequencies and / or symbol rates. The conventional waiting time interval is shown in the prior art (prior art) drawings. Figures 1 and 2 as the lines in bold 14,18.
    Figures 4A to 4C show transmission schemes according to realizations of the present invention. For clarification, each Figure shows a sequence of transmission slots assigned to two terminals (Terminal A, Terminal B). It will be understood that other terminals may function simultaneously with these terminals, using other transmission slots that differ in time and / or frequency from the slots assigned to Terminal A and Terminal B.
    In the diagram of Figure 4A, a terminal transmits over a sequence of transmission slots. The slots differ in duration. They also differ in bandwidth, making it possible for the terminal to broadcast with different symbol rates. Frequency carriers are not permanently assigned to transmission slots with a certain symbol rate. Terminal A uses a sequence of transmission slots 51, 52, 53 for its transmission.
    In the diagram of Figure 4B, a terminal transmits using a sequence of transmission slots with the same and fixed duration. The slots do not vary in duration. The slots vary in bandwidth, making it possible for the terminal to transmit with different symbol rates. There is no fixed allocation of frequency carriers to the transmission slots with a certain symbol rate.
    In the diagram of Figure 4C, a terminal transmits over a sequence of transmission slots of equal and fixed duration. The slots do not change in duration. The slots change in bandwidth, making it possible for the terminal to transmit with different Symbol rates. Nevertheless, frequencies are assigned to slots with a certain bandwidth.
    Although, advantageously, transmission slots are completely separated in frequency and time, it is possible that there is some controlled overlap in frequency between the transmission slots. This causes some loss in error performance (for example due to an increased bit error rate or loss of packages). Some frequency overlap between transmission slots can occur to the extent that the error caused by the overlap is still acceptable to the network operator.
    Figures 5A and 5B show the return link signal sent by an individual terminal in a specific time period. Figure 5A shows a conventional MF-TDMA terminal, and Figure 5B shows a terminal that functions according to an embodiment of the present invention. Figure 5A shows a frequency versus time graph for a return link (RL), illustrating transmission slots of a single conventional dynamic slot MF-TDMA terminal. Figure 5A also shows a graph of possible power versus time for a conventional MF-TDMA terminal over the same time period.
    Figure 5B shows a frequency versus time graph for a return link (RL), with an example of a sequence of transmission slots 51, 52 and 53 of a single terminal 40 according to an embodiment of the present invention. Figure 5 also shows a graph of possible power versus time over the same time period. The power level can vary during a transmission slot (as shown in Figure 5B) or can remain constant. The transition between the transmission slots at the time points t1 and t2 is almost instantaneous and does not interrupt the transmitted signal. Figure 5B also shows that the bandwidth of the reverse link signal sent by a terminal 40 can vary between slots. The bandwidth of slot 52 is larger than the bandwidth of slots 51, 53. Figure 5B also shows that the duration of a transmission slot can change between slots, although it may sometimes be advantageous in view of the simplicity of operation to opt for one fixed duration for the transmission slot. Terminals 40 change neither the transmission frequency nor the Symbol rate (used spectrum) without prior knowledge in the hub 20. In one realization, the time and frequency schedule for the return link is periodically revised by planner 26 at hub 20 and communicated via the forward link 31 to each terminal 40.
    A hub in system 5 knows in advance, and this in sufficient accuracy, when it can expect frequency changes and / or symbol rate changes in a return link. Terminals change frequency and symbol rate synchronously with the symbol clock for transmission, the precise moments for this being determined in advance by the hub. This allows the hub to anticipate and respond to frequency changes so that the hub remains synchronized with the return link signal, without the need for re-acquisition after a frequency or symbol rate transition, as would normally happen in MF-TDMA burst receivers.
    The benefits of a continuous transmission transmission scheme include: optimum utilization of the satellite channel capacity (in terms of achievable bits / s / Hz); minimum complexity of the receiver hardware, and therefore lower costs, for a given total bandwidth to be processed from a return link.
    We will now describe in detail the steps of synchronizing the terminals. The synchronization of the system ensures continuous communication between hub 20 and each individual terminal, as well as minimal interference between the RL signals 32 sent by the terminals 40 in the system. It also prevents breaches of transmission regulations. The system synchronization mechanism supports variable RL symbol rate and variable RL carrier frequencies. The system synchronization mechanism is also robust enough to handle typical statistics of channel parameters that can occur in a satellite channel, for example accuracy and drift of the local oscillator in the terminal, accuracy and drift of the local oscillator in the satellite , variations in propagation time due to satellite motion (resulting in a variable round-trip time), and variations in propagation time within the satellite's footprint.
    Each terminal 40 acquires frequency synchronization with a stable common reference in the system. This has two intentions. First, as soon as a hub demodulator is synchronized with the signal from a terminal 40 on a transponder (and therefore has also established the LO frequency offset of the satellite that can go up to a few 100 kHz), the frequency uncertainty of the other terminals that transmissions in this transponder are limited to the order of a few kHz. This reduces the time required for starting the network. Secondly, it is also a guarantee that the carrier frequency of the terminal always respects the transmission regulations. In a realization of the invention, a GEO satellite is used and the forward link (FW) symbol clock is considered as a reference in the system. Each terminal receives the FW link 32, and automatically knows the used FW symbol clock by synchronizing with it. This allows a terminal to compile any other frequency by considering the received symbol clock as a reference. The expected doppler effect and doppler rate effect on the symbol rate are the result of periodic fluctuations in the distance between the hub, satellite and terminal. For GEO satellites, this is only a negligible periodic deviation from the nominal Symbol rate.
    A terminal 40 has four operandi modes or states 101-104, as shown in the state diagram in Figure 6. Figure 7 shows the time course of communication between hub 20 and terminal 40. At time 110, hub 20 starts out a forward link signal send. Terminal 40 starts in the "IDLE" state 101 and remains in this state until it is frequency locked with the forward link symbol clock. The terminal receives the FW link at time 111 and reaches its frequency synchronization at time 112. When the terminal is synchronized, it receives RL "Look-Up" Tables in the FW link signal. These tables contain information about the finite set of allowed RL frame structures (linked to the finite set of nominal RL transmission speeds). Once these conditions are met, the terminal enters the "RL WAITING" state 102. The transmission circuit of the terminal is muted while in "IDLE" state 101 or "RL WAITING" state 102.
    The terminal remains in the "RL WAITING" state 102 until it has received an <RL START> signal from hub 20, which indicates the RL carrier frequency and power level of the indoor unit at which it may start transmitting an identification sequence. A suitable identification sequence is, for example, a Pseudo-Random Binary Sequence (PRBS) with a given polynomial and initial state. The hub sends the <RL START> signal at time 113. When this <RL START> signal is received by the terminal, it passes to "RL LOGGING ON" state 103 and starts transmitting the PRBS symbol sequence (at time 114 ) with the requested carrier frequency. In a realization, the PRBS sequence is BPSK modulated. This means that the terminal sends BPSK symbols that represent the PRBS sequence. The terminal 40 continues to transmit this PRBS sequence, while keeping track of the number of PRBS symbols already transmitted, until at a certain moment it receives either an <RL SYNO or an <RL STOP> message from hub 20. The hub transmits the <RL SYNO message at time 117. The <RL SYNO message indicates that hub 20 was able to synchronize the signal sent by the terminal, and determines how many PRBS symbols the terminal must have already sent in total, before it was the very first symbol of the first operational frame may send. This symbol will be called the Start of Frame (SOF) symbol. As soon as the <RL SYNO message is received, the terminal goes to the "RL LOGGED ON" state 104.
    The hub 20 may decide at any time to send an <RL STOP> message, whereby the terminal suppresses its transmission signal and returns to the <RL WAITING> state. For example, the hub 20 can also send an <RL STOP> message while the terminal 40 is still in the "RL LOGGING ON" state 103, because the HUB fails to synchronize with the RL signal from this terminal.
    In the "RL LOGGED ON" state 104, the terminal 40 sends its first frame with real payload data only after it has sent the required number of PRBS symbols, as communicated in the <RL SYNC> message. All the parameters required to fully define the first frame are contained in the <RL SYNO message. These parameters are: the Symbol rate, the modulation and coding scheme for the payload data (called modcod), carrier frequency and power level. If the terminal has to change the symbol rate and / or the carrier frequency at the first symbol of the operational frame, it does this phase-continuously, synchronized with the SOF symbol.
    The terminal leaves the "RL LOGGED ON" state 104 for the "RL WAITING" state 102 when it receives an <RL STOP> message from the hub (this may be due to a policy decision by the planner in the hub regarding bandwidth , or simply because the hub can no longer synchronize on the signal from the terminal and wants to switch it off for security reasons).
    When the terminal is in the "LOGGED ON" state 104, it must receive a <UPDATE> message from the hub before sending the last symbol of the current frame. At time 119, the hub sends a <UPDATE> message which instructs the terminal 40 regarding signal parameters to be used from the next SOF symbol. These parameters include: carrier frequency, symbol rate, modulation scheme, coding scheme and transmission power. The <UPDATE> message is received by the terminal at time 120. After sending the correct number of PRBS symbols (see earlier), the terminal sends the first symbol 121 (SOF) of the second operational frame. The hub 20 receives this SOF symbol 121. The <UPDATE> message is also a sign for the terminal that the hub is still active. If the return link demodulator function in the hub unexpectedly drops out, <UPDATE> messages will no longer be sent, and the terminal will return to the 'RL WAITING' state 102. Regardless of the state of the terminal, synchronization with the forward link 31 always a reason to immediately switch back to the 'IDLE' state 101.
    The following is a summary of the process described above. A terminal 40 initially synchronizes to the frame - or heartbeat - of the system by keeping a count of the transmitted PRBS symbols, and this count and the information received from the hub 20 in the <SYNC> message, to determine the time when the first symbol of an operational frame is sent. The terminal can then receive an instruction to adjust the symbol rate to ensure that the symbols sent by the terminal arrive at the desired time in the hub 20. In Figure 7 it can be seen that the difference δΐ between the time that the hub receives the SOF symbol and the time that the hub expects that SOF symbol is already smaller for SOFm + i than for SOFm. This time difference δί must converge to a very small value, once the terminal has been registered for a while.
    HUB operation
    The notion of time in the hub will be called tH. For example, one can view tu as a time in seconds ranging from minus infinity to plus infinity. A common time reference is distributed to all receivers in a hub 20. It is not required that this time reference is also distributed to the terminals, nor is it required for a terminal to have any notion of time, contrary to what is customary in MF-TDMA networks. The dynamic adjustment of the return link parameters takes place at the rhythm of the frame rate. The system frame period will be called Tp (order of magnitude: 1 second). All return link receivers 22 know the sequence of values for îh, for receiving SOFm.i; SOFm; SOFm + i; ... corresponding to the frame boundaries. When the system is properly synchronized, the SOF symbols sent by all terminals 40 will reach the hub antenna, known at a point in time by the hub as a frame boundary. This is possible, despite the fact that the terminals can transmit with different symbol rates, because only a finite set of nominal symbol rates is supported in the return link. Moreover, the frame period is chosen such that a whole number of symbol periods exactly fits into a frame period for all permitted nominal symbol rates.
    As described above, the hub activates the return link of an individual terminal by sending a <RL-START> message. The hub assumes that the terminal is correctly synchronized on the forward link, and will respond promptly to this activation message. Before a terminal can send its first real frame with expected arrival time at the hub given by tn = t (SOFm.i), the hub must send an activation message <RL-START> around the time tn = t (SOFm.i) - 2 · At, where 2 At is the round-trip propagation delay (hub-satellite-terminal-satellite-hub). In this way, the hub can activate a corresponding demodulation process in a receiver to start acquisition attempts from tn = t (SOFm.i).
    If a demodulation process in a receiver 22 is correctly synchronized to the signal transmitted by a terminal, it will at a certain moment be able to identify a particular PRBS symbol as the nth symbol of the PRBS sequence. The receiver 22 knows the hub time tn associated with this nth symbol. The receiver 22 also knows the hub time tn associated with the reception of the next expected SOF symbol (in Figure 7 this is SOFm). The receiver 22 calculates the time difference between the hub time tn associated with the reception of the next expected SOF symbol and the hub time tn associated with the reception of the nth symbol. This time difference can be converted (by rounding) into a whole number of symbol periods, which we call 'x'. By means of a <SYNC> message, the receiver instructs the terminal to send a total of (n + x) PRBS symbols before sending the first SOF symbol of an operational frame containing a payload of user data. The receiver remains in synchronization with the signal from the terminal and now assumes that the first SOF symbol of the first frame with payload x symbols will be found later than the symbol identified as the nth PRBS symbol. Thus, the receiver can also switch its nominal carrier frequency and symbol rate, in a phase-continuous manner, to the new values, after counting (n + x) received PRBS symbols. This mechanism guarantees that the next SOF symbol will be received around the time tH = t (SOFm). The error 6t is largely due to the rounding operation when determining the nearest integer x.
    Once the terminal has been correctly registered, the synchronization between this terminal and the hub 20 is based on counting sent or received symbols. Both the hub and the terminal have access to a static look-up table (LUT) which, for each combination of modcod and symbol rate, specifies how many symbols must be sent (or received) in a frame 10. Terminal 40 and receiver 22 know so both when the next SOF symbol is to be sent / expected.
    As long as a terminal is registered, the hub in the running frame signals which return link parameters (modcod, symbol rate, carrier frequency, power) should be used in the next frame (i.e. from the next SOF symbol). This is done by means of <UPDATE> messages as shown in Figure 7. Each <UPDATE> message contains the knowledge of the number of symbols to be sent / received in the next frame. The hub sends a <UPDATE> message at a time point 2 · Δί + ε before the next frame border, where ε represents a suitable time margin. If a terminal has not received a new <UPDATE> message when all the symbols of the current frame have already been sent, then it assumes that an error has occurred in the return link process of the hub, and returns to the 'RL -WAITING 'condition 102 as a precaution.
    As long as a terminal is registered, the receiver 22 in the hub compares the carrier frequency of the received terminal signal with the nominal expected value. This information is only used for monitoring the condition of the system.
    A demodulation process in the hub typically synchronizes to the signal from each terminal separately in a closed loop, and thus effectively captures frequency deviations without additional complexity.
    Advantageously, terminals with neighboring frequencies use different polynomials for their PRBS sequence during the sign-in process.
    So far, it has been described how an individual return link 32 can remain synchronized between a particular terminal and the hub by counting symbols on either side of the link. In the following it is described how it can be achieved that the return link signals from all terminals change their carrier frequency and Symbol rate more or less at the same time, with the intention of minimizing the interference between the terminals 40. The receiver in the hub constantly compares the measured hub time of a synchronized SOF symbol with the expected hub time for receiving that SOF symbol, as defined by the hub. This time difference can have different origins. For this difference to converge to zero, the 'next Symbol rate' value in the <UPDATE> message contains a nominal value (belonging to a known set of allowed values), and an offset value (typical single ppm (millionths) of the nominal value). This means that, even if the planner in the hub temporarily does not impose a change in the Symbol rate, the receiver 22 in the hub may have detected a progressive time shift and, via the 'offset' field, may request a change in the symbol rate to compensate for a part of the time shift over the length of the next frame.
    The purpose of this slow time correction loop over satellite is to improve the time alignment of the SOF symbols of all terminals, as well as to compensate for slow drift of the symbol clock. Initially, the SOF alignment error (5t) can be large due to the rounding error when determining 'x' in the logon phase (see above). After a while, the time correction loop will have reduced this error to a level that can be expected as a result of satellite movements. After registration, the deviation of the received SOF time from the different terminals compared to the SOF time expected by the hub is not statistically correlated. After a while, this deviation is no longer determined by the rounding error when the last symbol of an operational frame is zero-energy symbols. In this way the frequency plan is changed while the return link is suppressed. The suppression is done in a spectrally pure way, because it takes place before the pulse-forming filter. If required, the signal level of the terminal can also be adjusted between the zero energy symbols to maintain a desired spectral power density, despite possible changes in Symbol rate.
    Advantageously, the system 5 periodically reviews the frequency link of the return link and sends this information (the sequence information) to all terminals 40. The time between two consecutive revisions is called the heartbeat period, and may have a value of, for example, 500 milliseconds to 1 second. Advantageously, the heartbeat period is (exactly) equal to a whole multiple of the channel's symbol period, regardless of the return link symbol rate used. This, in turn, requires a limitation of the available return link symbol rates to a finite set, such that the heartbeat period can be expressed as an integer number of symbol periods for each symbol rate in the finite set. The system has a dynamic return link, whereby several terminals share the same frequency band but individually change their spectral occupation (center frequency and / or occupied bandwidth) over time. Terminals are controlled in such a way that changes in spectral occupation of all terminals occur substantially simultaneously. If this condition is not met, the demodulation of each return link signal can be seriously hampered by (frequency) interference with other terminals. One way to ensure system synchronization is to define a common heart rate sequence for all return links 32. This heart rate is the frame rate 1 / Tp. Terminals may only change their spectral occupancy at the start of a new frame (Start Of Frame, SOF), in other words: once every TF seconds. The system synchronization algorithms described above require that this frame period TF is nominally equal to a whole number of symbol periods, regardless of the symbol rate used. More formal: set {R} is the set of allowed return link symbol rates, then: TF Rj is whole, Vz
    Any symbol rate is allowed, provided that it is a rational multiple of any other allowed symbol rate.
    Figure 8 shows an example of a frame structure 120 in the physical layer. The frame is designed to contain as much useful data as possible, with a minimum amount of overhead, to maximize the bandwidth efficiency of the return link. A possible realization of the frame contains absolutely no overhead, only payload. Still a small one
    Any symbol rate is allowed, provided that it is a rational multiple of any other allowed symbol rate.
    Figure 8 shows an example of a frame structure 120 in the physical layer. The frame is designed to contain as much useful data as possible, with a minimum amount of overhead, to maximize the bandwidth efficiency of the return link. A possible realization of the frame contains absolutely no overhead, only payload. A small amount of overhead is nevertheless beneficial. An adjustable number of "null" (zero energy) symbols 121 can be included at the beginning and, optionally, at the end of the frame 120. No carrier is transmitted during a null symbol. The null symbols help to counter the possible interference between the terminals that is a result of small errors in time synchronization of the frame transitions. The preamble 122 consists of a configurable sequence of symbols. It is used in the receiver to help lock the phase of the carrier, and to estimate the density of the thermal noise power in the link. A code word has a certain length (number of bits), and a symbol of a certain modulation scheme has a finite capacity (bits per symbol). For some combinations of symbol rate, modulation scheme and coding scheme, a number of 'fill' symbols may be required because the payload portion of the frame (expressed in number of symbols) is not an integer multiple of the length of the codeword (also expressed in number symbols). Advantageously, these padding symbols are included after the preamble 122, and not at the end of the frame, because padding symbols do not carry useful information, and they can be used to detect any remaining transition phenomena due to carrier synchronization that may occur immediately after the preamble 122. The remaining portion of the frame contains an integer number of code words 124. Each code word consists of a number of transmission symbols. Figure 8 is not drawn to scale. Typically, a frame has a length of about 1 second, and the null symbols only take a few ps.
    Figure 9 shows an example of a BPSK symbol sequence, and the phase progression of the carrier 0 (t). Two complete frames 131, 132 are shown, along with a part of the third frame 133. Each new frame starts with "Start Of Frame" (SOF) symbol, respectively 134, 135, 136. Each frame has the same duration Tf. In this example, frames 131, 132, 133 each have a different symbol rate, frame 132 has a lower symbol rate than frame 131, and frame 133 has a higher symbol rate than frames 131 and 132. It will be appreciated that Figure 9 shows a baseband signal sequence, and that the symbols in each of the frames 131, 132, 133 can be sent with different carrier frequencies.
    If, in the hub, the SOF symbols are received exactly at the moments associated with the ffame transitions in the hub, then the terminal is perfectly synchronized with the system 'heart rate': the frame rate. Note that the phase of the carrier 0 (t) follows a continuous path, composed of connected straight lines. The slope of these line segments (in other words the carrier frequency) may change exactly before the SOF symbols 134-136.
    Figure 10 schematically shows a terminal 40 for use in the satellite transmission system. The terminal includes an antenna 72 for receiving the forward link RF signal 31 and transmitting the return link RF signal 32, a receiver 80 and a transmitter 90. Typically, the forward link RF signal 31 coming from the antenna 72 undergoes a downward frequency translation to an IF band and applied to the receiver 80. Receiver 80 receives the forward link signal 31 (after downward frequency translation) and performs demodulation and decoding on the received signal. The resulting data is available on output 81. Receiver 80 extracts, from the forward link signal, information about the sequence of transmission slots assigned to the terminal in the return link 32. This information 83 is received in <UPDATE> messages and forwarded to the controller 92. Receiver 80 also extracts, from the forward link signal, information 84 which imposes a change in transmission speed. This informate 84 is received in an 'offset' field within <UPDATE> messages, and forwarded to the controller 92. Receiver 80 also extracts, from the forward link signal, information about the forward link transmission clock speed. Information 84, 86 and an output of a local oscillator 85 are supplied to a frequency reference unit 93. Unit 93 maintains a stable clock speed synchronized with the hub frequency reference, which contributes to compliance with the transmission regulations by terminal 40.
    Advantageously, each terminal 40 generates a return link (RL) signal 32 in multiple steps. In a first step 94, a modulated signal is generated that contains transmission symbols (commonly referred to as "baseband signal" in the art), and in a second step 95, a frequency translation to RF is applied to this generated signal. This step is a broadband transmitter that selectively transmits the transmission symbols on one (or more) of a series of carriers used by the transmission scheme. Step 94 dynamically adjusts the carrier frequency and the symbol rate in a phase-continuous manner. The carrier sequence can change within a frequency band. Frequency changes are synchronized with the symbol timing of the channel.
    Signal level changes for the purpose of maintaining a predetermined power spectral density at jumps in symbol rate are also performed in step 94. Step 94 generates transmission symbols at a required speed. These symbols contain encrypted user data. Advantageously, RF step 95 is not dynamically changed, and is programmed to statically transmit in the L-band frequency range that will result in the proper transmit frequency of the outdoor unit after upward frequency translation. Transmitter 90 has an input 91 for receiving data. Controller 92 determines the time and frequency band and symbol rate to be used for each transmission slot, based on sequence information 83. A storage function 96 contains a look-up table (LUT) of symbol rates and the corresponding numbers of transmission symbols. The LUT is used to translate the symbol rate, as sent in the <UPDATE> message, into a number of symbols that the terminal must send in the next frame.
    Figure 11 shows, schematically and in more detail, the device provided in the hub 20 of the satellite transmission system. The hub 20 generates the forward link RF signal 31 and receives the return link RF signal 32. The actual transmission and reception of these signals by means of an antenna can take place in a remote ground station (remote from the hub). The hub comprises a transmitter 21 for generating the forward link signal 31 and a receiver 22 for receiving the return link signal 32. The transmitter 21 receives data to be transmitted, performs coding and modulates the signal; it also takes care of the mutliplexing of the signals destined for different terminals 40. Transmitter 21 also adds data in the forward link 31, which contains information about the sequence of transmission slots assigned by planner 26 to each terminal 40 in the return link 32. A stable frequency reference (e.g., a local oscillator) is applied to the transmitter 21 and used by it to generate transmission symbols at a controlled speed over the forward link 31. Advantageously, there is a set of return link receivers, with one receiver 22 is assigned to every active terminal 40 in the system. Receiver 22 has an input for receiving an RF signal (typically after frequency translation to IF). A tuner 223 tunes into the frequency band that is known to be used by the terminal 40 at any time. The symbol demodulation function 224 demodulates the received transmission symbols at the required speed. This also includes decoding the received data. Controller 221 receives the sequence information from the scheduler 26 and uses this information to cause the tuner 223 to set the frequency band, for which it is known for each transmission slot that it will be used by a particular terminal, at a time when it is known that it corresponds to the beginning of the transmission slot. Controller 221 also controls the symbol demodulation function 224 to vary the symbol rate in accordance with the sequence information. Planner 26 receives requests from the active terminals in which the transmission needs of the terminals are specified. Planner 26 assigns a sequence of transmission slots to each active terminal based on their transmission needs, and can use different priority criteria to distribute the available resources fairly among the terminals. Various planning algorithms are known in the art.
    Advantageously, all terminals 40 change the carrier frequency and / or symbol rate in a phase-continuous manner, or with a predictable and limited phase discontinuity. This makes it easier to meet the requirements of transmission regulation, as there are no abrupt changes in signal value that could give rise to unwanted frequency components (with too much energy). This phase continuity requirement allows further simplifications in the design of the hub receiver, and allows return link efficiencies that are very close to the capacity of the satellite channel.
    In the system described above, a planner attempts to assign a transmission slot to each terminal that meets the bandwidth needs of the terminal at that time. Different portions of the frequency have slots with different bandwidth (e.g. in Figure 5B, slot 52 has a larger bandwidth than slots 51 and 53). If a terminal has no data to send, either (i) a slot with nominal bandwidth can be assigned, or (ii) the terminal can be deregistered returning to state 102. Option (i) has the advantage that it is in the terminal allows him to continue sending, so that he can later send a bandwidth request and be granted a transmission slot with minimal delay, without the need to resubmit. Whether the terminal will work according to option (i) or option (ii) depends on factors such as the number of free transmission slots.
    The realization described in detail is a dynamic scheme in which the terminal symbol rate and / or carrier frequency changes as instructed by the hub. A static schedule is also possible, whereby the return link frequency plan is never changed. In this alternative realization it is not necessary that the SOF (start-of-frame) symbols of all terminals are synchronized. In this alternative realization, the terminal can switch to a normal frame mode, with a (static) operational symbol rate, after sending a static number of PRBS symbols that are also known by the hub. As a result, all terminals continue to send SOF symbols at random time offsets relative to the hub SOF. This does not interfere with individual communication between a terminal and the hub, since it is sufficient for an RL receiver to know where to find the code words in a received symbol sequence. In practice, it only involves a small cost to align the SOFs of all terminals, especially when the system also supports the dynamic scheme. That is why it is possible to have the system align the SOFs even in a static RL plan scenario, with a view to a uniform solution and a shorter test phase.
    The system can have any of the following topologies: star network; multi-star network; partially meshed star network, where communication links from terminal to hub and from terminal to terminal can share bandwidth. The partially meshed star network has a 'master' hub and several 'slaving' hubs / terminals with 'remote' return link receivers. All 'remote' receivers synchronize on one common time reference. The time reference can be the GPS (Global Positioning System) time. Remote receivers execute instructions that are sent by the planner in the master hub.
    The invention is not limited to the realizations described here. These can be changed without departing from the scope of this invention.
    权利要求:
    Claims (13)
    [1]
    A method for operating a terminal in a multi-access wireless communication system, comprising a forward link to the terminal and a return link from the terminal, the return link using a medium shared by terminals based on time and frequency, and wherein the method comprises: sending a return link signal through the terminal over a sequence of transmission slots, each transmission slot being determined by a time slot and a carrier frequency, wherein carrier frequency and Symbol rate can change between transmission slots, and wherein the return link signal is sent continuously over the sequence of transmission slots; and receiving, via the forward link, information defining the next slot and allowing the terminal to derive the number of symbols to be sent during the next transmission slot.
    [2]
    A method according to claim 1, wherein the return link signal is sent in a phase-continuous manner over the sequence of transmission slots.
    [3]
    A method according to any one of the preceding claims wherein the terminal can transmit with one from a set of different Symbol rates, wherein there is such a relationship between the symbol rates of the set that each Symbol rate of the set contains an integer number of symbol within a frame period, and where the terminal changes the symbol rate at the start of a new transmission slot.
    [4]
    A method according to any one of the preceding claims, further comprising: acquiring frequency synchronization with the forward link and transmitting on the return link with a symbol rate and a carrier frequency based on the acquired frequency synchronization.
    [5]
    A method according to claim 4, further comprising acquiring synchronization with the hub of the system by: receiving, coming from the hub, an instruction to start sending identification symbols over the return link; sending identification symbols over the return link, and counting the number of sent identification symbols; receiving an instruction to start sending a payload of user data in a first transmission slot after a predetermined number of sent identification symbols; and sending, in a first transmission slot, a payload of user data after sending the determined number of identification symbols.
    [6]
    A method according to claim 4 or 5, wherein each terminal sends a start-of-frame symbol at the start of each transmission slot, further comprising receiving an instruction to adjust the symbol rate in the return link to the start-up or frame symbol sent by the terminal to synchronize with the start-of-frame symbol of other terminals in the system.
    [7]
    7. A method for operating a hub in a wireless communication system with multiple access with a forward link from the hub to the terminals in the system and a return link from a terminal to the hub, the return links from the terminals being a medium sharing based on time and frequency, containing, in the hub: assigning a sequence of transmission slots to a terminal in the system, wherein each transmission slot is determined by a time slot and a carrier frequency, and wherein the carrier frequency and the symbol rate can change between transmission slots; assigning a return link receiver function to receive the return link from each of the terminals in the network; - possibly substantially - changing the carrier frequency in the receiver, corresponding to the change of carrier frequency of the signal received from the terminal, wherein the return link signal is sent continuously over a sequence of transmission slots; and monitoring the timing of the terminal and sending an instruction to the terminal to adjust the symbol rate without substantial interruption of the return link signal.
    [8]
    A method according to claim 7, further comprising sending information through the hub to the terminal with identification of a next transmission slot, and wherein the information enables the terminal to determine the number of symbols to be sent during the next transmission slot.
    [9]
    A method according to claim 8, further comprising periodically determining the transmission needs of the terminals in the system and sending information including the sequence of transmission slots based on the determined transmission needs and return link quality indicators such as signal / noise ratio and saturation level of the power amplifier of the terminal.
    [10]
    A method according to any of claims 7 to 9, further comprising acquiring synchronization with a terminal in the system by: sending an instruction to the terminal to send identification symbols over the return link; receiving, via the return link, identification symbols sent by the terminal, and counting the number of identification symbols received from the terminal; determining a start time for the terminal to send user payload data in a first transmission slot based on the number of sent identification symbols; sending an instruction to the terminal to begin sending user payload data in the first transmission slot after the determined number of identification symbols.
    [11]
    A terminal for wireless communication for use in a wireless communication system with multiple access, comprising: a receiver configured to receive a forward link signal; and a transmitter configured to send a return link signal, wherein the return link uses a medium that is shared based on time and frequency by multiple terminals, and wherein the transmitter is configured to send a return link signal with a sequence of transmission slots, wherein each transmission slot is determined by a time slot and a carrier frequency, wherein the carrier frequency and the Symbol rate can change between transmission slots, and wherein the return link signal is sent continuously over the sequence of transmission slots.
    [12]
    A wireless communication device for use in the hub of a multi-access wireless communication system, comprising: a transmitter configured to send a forward link signal to the terminals in the system; a receiver configured to receive a return link signal from one of the terminals, the return link signals from the terminals sharing a transmission medium, divided on a time and frequency basis; a scheduling function performed to schedule a sequence of transmission slots for the return link of each terminal, each transmission slot being defined as a time slot and a carrier frequency, wherein carrier frequency and symbol rate may change between the transmission slots; a mechanism that causes the frequency of the receiver to be changed - possibly substantially - in synchronization with a change in frequency of the return link signal received from the terminal, the return link signal being transmitted continuously over the sequence of transmission slots .
    [13]
    A computer program containing instructions which, when executed by a processor, enable the processor to implement the method of any claim from 1 to 10.
    类似技术:
    公开号 | 公开日 | 专利标题
    BE1019923A5|2013-02-05|TRANSMISSION SCHEDULE WITH MULTIPLE ACCESS FOR A WIRELESS COMMUNICATION SYSTEM.
    US10819419B2|2020-10-27|Timing synchronization for a beam hopping satellite
    NL194188C|2001-08-03|Linearisation of a power amplifier in a mobile TDMA radio system. Mobile time-division multiplex radio system with linearization of the power amplifiers belonging to the transmitters of the remote units belonging to the system.
    EP0606236B1|1998-01-07|Simulcast synchronization and equalization system
    JP2018521582A|2018-08-02|Method and apparatus for efficient data transmission in a half-duplex communication system with large propagation delay
    US10305578B2|2019-05-28|Method of exchanging communications between a satellite and terminals associated therewith
    JP2000269887A|2000-09-29|Method and device for communication
    JPH11113049A|1999-04-23|Radio communication system
    EP2472736A1|2012-07-04|Frequency and timing synchronization and error correction in a satellite network
    US9674804B2|2017-06-06|Apparatus and method for synchronizing communication between systems with different clock rates
    CN110289901A|2019-09-27|A kind of star towards on-board processing beam-hopping satellite communication system ground synchronous method
    AU2010341826C1|2015-12-03|Wireless mesh network using plural radio channels
    US10694479B2|2020-06-23|Timing synchronization with a modified DVB-S2X waveform for a beam hopping satellite
    EP3579458B1|2020-09-30|System for synchronizing a ground segment to a beam hopping satellite
    US7133395B2|2006-11-07|Multiple access bandwidth-on-demand using MSPK with an embedded tracking channel
    JPH1175253A|1999-03-16|Inconstant output bcch carrier and measurement method for signal level of the carrier received by mobile station
    US20190379448A1|2019-12-12|Dynamic Receiver
    US20020089946A1|2002-07-11|System and method for providing a timing reference for data transmissions in a satellite-based communications network
    KR20210114762A|2021-09-24|Synchronization acquisition method for satellite communication system and apparatus performing the same
    CN113645687A|2021-11-12|Multi-user time synchronization method based on agile spot beam
    KR970011683B1|1997-07-14|Satellite system
    EP1089464A2|2001-04-04|Synchronization method for a processing communication satellite
    同族专利:
    公开号 | 公开日
    BR112013006647A2|2016-06-28|
    DE11781457T1|2014-03-13|
    BR112013006647B1|2022-01-04|
    EP2619924B1|2017-06-28|
    IL225370A|2017-11-30|
    EP2619924A1|2013-07-31|
    IL225370D0|2013-06-27|
    CN103201966A|2013-07-10|
    KR20130141486A|2013-12-26|
    JP2013538533A|2013-10-10|
    ZA201302087B|2013-11-27|
    EA027585B1|2017-08-31|
    AU2011304416B2|2015-09-24|
    EA201370067A1|2013-06-28|
    DE11781457T9|2014-04-17|
    AU2011304416A1|2013-05-02|
    CN103201966B|2017-04-26|
    CA2812224A1|2012-03-29|
    MX2013003164A|2013-08-01|
    SG188608A1|2013-04-30|
    US20130176937A1|2013-07-11|
    GB201015801D0|2010-10-27|
    WO2012038380A1|2012-03-29|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    FI945978A|1994-12-20|1996-06-21|Nokia Telecommunications Oy|The base station|
    US7027498B2|2001-01-31|2006-04-11|Cyntrust Communications, Inc.|Data adaptive ramp in a digital filter|
    EP1366587A4|2001-02-06|2005-06-29|Harris Corp|System and method for real time adaptive capacity scheduling|
    WO2004093386A1|2003-04-16|2004-10-28|Koninklijke Kpn N.V.|Sytem and method for measuring data network quality|
    FR2874147B1|2004-08-05|2006-09-22|Cit Alcatel|DEVICE FOR ALLOCATING SHARED RESOURCES OF A COMMUNICATION NETWORK BY ALLOCATING TEMPORAL INTERVALS OF A DYNAMICALLY ADAPTABLE TIME / FREQUENCY PLAN|
    US7515566B2|2004-12-09|2009-04-07|Viasat, Inc.|Partial mesh communication in hub based system|
    US7729372B2|2005-07-27|2010-06-01|Sharp Corporation|Communicating in a network that includes a medium having varying transmission characteristics|
    US7397400B2|2005-12-02|2008-07-08|Viasat, Inc.|Variable length data encapsulation and encoding|
    US8032073B2|2006-05-03|2011-10-04|Stm Networks, Inc.|Satellite communication with multiple active gateways|
    US20080279300A1|2007-05-10|2008-11-13|Walker Glenn A|System and method of transmitting and receiving satellite digital radio signals over an odd number of frequency slots|
    WO2009155002A2|2008-05-27|2009-12-23|Viasat, Inc.|Time of day encryption using tdma timing|
    US8670373B2|2009-05-05|2014-03-11|Gilat Satellite Networks Ltd.|Elastic access scheme for two-way satellite communication systems|US9247512B2|2011-08-25|2016-01-26|Ubiquiti Networks|Adaptive synchronous protocol for minimizing latency in TDD systems|
    US10368327B2|2014-05-14|2019-07-30|Satixfy Israel Ltd.|Method and system for signal communications|
    US10305578B2|2014-05-14|2019-05-28|Satixfy Israel Ltd.|Method of exchanging communications between a satellite and terminals associated therewith|
    CN106537788B|2014-05-20|2019-09-03|萨迪斯飞以色列有限公司|Method for reducing interference in satellite communication network|
    US10033509B2|2014-05-20|2018-07-24|Satixfy Israel Ltd.|Method and system for satellite communication|
    US10349401B2|2015-01-30|2019-07-09|Telefonaktiebolaget Lm Ericsson |Burst slot numbering for licensed assisted access|
    US10693574B2|2015-07-02|2020-06-23|Qualcomm Incorporated|Method and apparatus for efficient data transmissions in half-duplex communication systems with large propagation delays|
    CN105812046B|2016-03-10|2018-11-02|中国人民解放军国防科学技术大学|A kind of realization system and method for satellite mobile communication system heartbeat message|
    EP3772187B1|2019-07-29|2021-06-16|ST Engineering iDirectCy NV|Satellite communication system|
    法律状态:
    2019-06-12| MM| Lapsed because of non-payment of the annual fee|Effective date: 20180930 |
    优先权:
    申请号 | 申请日 | 专利标题
    GB201015801|2010-09-21|
    GBGB1015801.2A|GB201015801D0|2010-09-21|2010-09-21|Multiple access transmission scheme for a wireless system|
    [返回顶部]