EP3542469A1 - Procédé et système pour une communication par satellite - Google Patents

Procédé et système pour une communication par satellite

Info

Publication number
EP3542469A1
EP3542469A1 EP17872022.3A EP17872022A EP3542469A1 EP 3542469 A1 EP3542469 A1 EP 3542469A1 EP 17872022 A EP17872022 A EP 17872022A EP 3542469 A1 EP3542469 A1 EP 3542469A1
Authority
EP
European Patent Office
Prior art keywords
signal
communication
module
time
operable
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP17872022.3A
Other languages
German (de)
English (en)
Other versions
EP3542469A4 (fr
Inventor
Doron Rainish
Arie KESHET
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Satixfy Israel Ltd
Original Assignee
Satixfy Israel Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US15/354,913 external-priority patent/US10368327B2/en
Priority claimed from US15/361,281 external-priority patent/US10033509B2/en
Application filed by Satixfy Israel Ltd filed Critical Satixfy Israel Ltd
Publication of EP3542469A1 publication Critical patent/EP3542469A1/fr
Publication of EP3542469A4 publication Critical patent/EP3542469A4/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/18578—Satellite systems for providing broadband data service to individual earth stations
    • H04B7/18582—Arrangements for data linking, i.e. for data framing, for error recovery, for multiple access
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/204—Multiple access
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/204—Multiple access
    • H04B7/208—Frequency-division multiple access [FDMA]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/204—Multiple access
    • H04B7/212—Time-division multiple access [TDMA]

Definitions

  • the present disclosure relates to the field of communications and in particularly to communications being held between satellites and terminals associated therewith in a satellite communications network.
  • SMS Tellite system(s)
  • LEO Low Earth Orbit
  • MEO Medium Earth Orbit
  • HAP High-Altitude Platforms
  • HALE UAV High-altitude Platforms
  • a portion of the available capacity is allocated for hub-to-satellite communications in the forward link.
  • a portion of the return link capacity is allocated for satellite-to-hub communications.
  • Frequency Division Duplexing In various satellite communication systems Frequency Division Duplexing (FDD) is used. Different frequencies are used for the forward traffic (i.e. traffic transmitted from the satellite to the terminals) and for the return traffic (i.e. traffic transmitted from terminals to the satellite) of the RF link.
  • FDD Frequency Division Duplexing
  • the allocated frequency is substantially different from the frequency allocated for carrying out downlink communications (i.e. satellite to hub communications and satellite to terminal communications), using the capacity portion allocated therefor.
  • Interference to communications exchanged along satellite links is one of the major factors limiting the capacity of satellite communication.
  • Modern satellites include numerous transponders transmitting at different frequencies, different antennas (single beam or multiple beam), and different polarizations per antenna.
  • a ground receiver of a satellite link is susceptible to interference that may arise, for example, from co-frequency transmissions at the same frequency, same beam but different polarization (co-frequency, co-beam, cross polarization), same frequency but a different beam (co-frequency, adjacent beam), and adjacent frequency channel from the same or from different beams.
  • interference on the uplink may leak into the desired channel as well. Additionally, unwanted interference originating from an adjacent satellite may also occur as well as interfering signals from terrestrial sources.
  • Active interference cancellation means are available. Such means typically involve building a dedicated receiver to capture the interfering signal and then cancel it by subtraction from the wanted signal. Obviously, this technique is rather costly while perfect cancellation is never possible. Even when the interfering signal is known (which is the case when dummy frames are transmitted), cancellation requires synchronization and channel estimation of the interference, which might still require installation of additional circuitry.
  • terminal refers in general to an end station of a communication system connected to the end user of the system.
  • the term refers to the ground station used by the consumer while the term hub or gateway refers to the ground station which serves the service provider.
  • One approach for scheduling the transmissions is to perform on-the-fly transmit- receive conflict resolution without imposing any limitation on the terminals by inducing a framing mechanism thereon.
  • a scheduler must ensure that packets are only multiplexed onto the forward link at such times that they arrive at the terminal when it is not transmitting. This means, in turn, that the forward link multiplexer must maintain a separate queue for each (active) terminal and, in addition, track the propagation delay between the satellite and that very same terminal.
  • the scheduler would use the delay information to consult the return link capacity allocation matrix in order to check whether, at the projected time of forward link packet reception, the terminal is scheduled to transmit or not.
  • the scheduler must then serve fairly the non-blocked queues.
  • scheduling must allow terminals certain pre-agreed short transmission windows for random-access return link transmissions.
  • return link capacity allocation must keep a terminal's transmission duty cycle below 100% to ensure that it can send forward link traffic without excessive delay.
  • Transmit-receive scheduling also impacts terminal handover between beams and satellites.
  • the scheduler must be involved in each handover in order to make sure that forward link data is correctly re-routed.
  • Satellite communication it often used for broadcast transmissions, distribution and contribution links, cellular and Internet connection backhaul traffic, and/or for many other communication purposes.
  • a large part of the communication traffic transferred via satellites is communicated over continuous transmission channel/link, in which non information coded transmission signals are transmitted in the time gaps between information coded transmission section of the transmitted signals.
  • the conventional use of continuous transmissions is aimed at obviating a need for receivers, to re-acquire and re-synchronize to separate transmission bursts of information coded signals.
  • continuous transmission mode enables the receiver to track the various transmission parameters relatively in a straightforward operation.
  • satellite communications' standards such as DVB-S2 and DVB-S2X define a continuous transmission mode of operation in the forward link (transmissions being sent from the satellite(s) towards the terminals), and define that whenever the (hub) transmitter has no data to transmit, "dummy frames" will be transmitted, which contain no information.
  • beam and/or communication-beam is used herein to designate a beam of transmitted electromagnetic (EM) waves (typically of a radio frequency), which is directed (optionally by suitable antenna module) and/or constructed by beam forming (e.g. utilizing beam former and phase array antenna) to propagate to cover a certain designated region of interest.
  • EM transmitted electromagnetic
  • suitable antenna module e.g. utilizing beam former and phase array antenna
  • beam hopping operation mode multiple such beams may be continuously or discontinuously be transmitted from the satellite whereby the data bandwidth directed to different coverage regions may be dynamically allocated by hopping one or more of the beams from one coverage zone to another (e.g. in a time interlaced fashion) so that multiple zones can be served by a lower number of coexisting simultaneously transmitted beams via a time domain dynamic beam allocation to zones.
  • channel and/or communication-channel and/or link and/or communication-link are used herein interchangeably to designate a communication channel formed between the satellite and one of the terminals it serves.
  • each beam simultaneously carries one or more communication channels to one or more terminals in the zone covered thereby.
  • continuous communication links/channel e.g. the latter is hereinafter also referred to as continuous communication links/channel.
  • Interactive communications for example, are bursty by nature, and an assembly of such links forms links of non-constant rate.
  • the allocated bandwidth of a link is typically determined by the difference between the peak information rate for transferring the information to the average information rate that can be supported.
  • the dummy frames, used in the continuous communication mode e.g. by the DVB-S2 and DVB-S2X standards) are used in order to compensate for this difference.
  • SINR signal to noise and interference ratio
  • Another deficiency of the continuous transmission mode is associated with the inefficient allocation/distribution of the total data bandwidth of the satellite/transmitter. This is because in this continuous mode of transmission, certain of the data bandwidths is allocated for transmitting the dummy frames which actually carry no data (no meaningful data), and this may result in a lower number of communication channel/beams as would have being possible in cases where non continuous transmission mode (no dummy frame transmission) is used.
  • the transmission time, during which the dummy frames are communicated in the continuous mode might instead be allocated for the transmission of one or more additional beams/channels/links and thereby facilitate coverage of additional zones and/or allocating larger data bandwidths to each beam/zone. Accordingly in this manner a beam hopping system whereby transmission resources are used to serve different zones by different beams may be facilitated.
  • conventional satellite communication techniques are implementing continuous transmission mode, in which dummy frames (and/or other dummy transmission sections which do not encode any meaningful/required information) are transmitted in the time gaps between information coded transmission sections. This is made in order to facilitate efficient acquisition of the transmitted signal to be received, by the signal receivers (satellite terminals) that should receive the signal.
  • a bursty communication mode in which no signal is transmitted in the time gaps between transmissions of information coded signal sections, may result in much more efficient communication in terms of SINR (signal to interference and noise), data bandwidth, beam hopping coverage, and energy consumption.
  • SINR signal to interference and noise
  • conventional satellite communication techniques such as DVB-S2 and DVB-S2X standards, generally use the continuous communication mode. This is because the conventional receivers used in satellite communication, require significant time and resources to acquire (perform signal acquisition) and possibly synchronize to each communication burst of the separated communication bursts provided by the bursty communication mode. More specifically as will be explained in more details below, a receiver configured according to the conventional technique would require to receive at least two, and typically more than two, communication frames in order to lock-on-to (acquire) the signal, which is to be received thereby.
  • conventional receivers require a significant amount of time, extending over several/plurality of communication frames in order to analyze the signal, to scan over the possible carrier frequency of the signal, until the correct carrier frequency is determined, and the signal is acquired. This results with the effective loss of several communication frames after every discontinuity in the transmitted/received signal, which in turn makes the use of burst communication mode impractical/inefficient with the conventional receivers.
  • the term communication frame is used herein to designate a section (time portion) of a transmitted (EM) signal including a header part (typically encoding data indicative of at least the parameters of the physical layer of the communication) and a data payload part, in which the actual data that should be communicated to the receiver is encoded.
  • the communication- frame further includes additional sections, such as pilot sections and/or other.
  • a dummy frame is used herein to designate a communication frame in which the transmitted data section of the signal does not encode any useful information for the receiver.
  • a data coded frame is used herein to designate a communication frame in which the transmitted data section of the signal encodes information useful for the receiver/terminal (e.g. payload data).
  • a communication transmission system including: a data provider configured and operable for providing data to be communicated to one or more terminals over one or more forward communication channels; a communication frames generator module configured and operable to segregate the data into a plurality of data payload portions to be communicated to at least one terminal of the terminals over at least one forward communication channel of the forward communication channels and generate a sequence of communication frames to be sequentially transmitted over the communication channel (each communication frame including a header portion and a data payload portion); and a transmission channel signal encoder configured and operable for generating a transmission signal for transmission via the forward communication channel with the sequence of communication frames encoded in the signal.
  • the transmission channel data encoder is configured and operable in burst communication mode such that transmission signal includes transmission data time slots at which one or more of the communication frames are encoded in the signal and one or more recess time slots between them.
  • the communication transmission system also includes a transmission module configured and operable for transmitting the transmission signal in burst communication mode such that during the recess time slots no signal is transmitted.
  • the communication transmission system is configured and operable in a multi-beam mode for transmitting a plurality of beams having different respective geographical coverages.
  • Each communication channel of the one or more forward communication channels is associated with at least one beam of the beams and designated for one or more terminals residing in a geographical coverage of said at least one beam.
  • the system may be configured and operable in a beam-hopping mode, such that two or more groups of beams, each including at least one of the plurality of beams, are transmitted at distinct time intervals.
  • the communication transmission system includes a transmission scheduler module configured and operable for scheduling transmission of the two or more groups of beams.
  • the transmission scheduler module is configured and operable for scheduling the transmission data time slots of the communication frames of the at least one forward communication channel of each group of beams is transmitted, so as to aggregate a plurality of recess timeslots together to form a prolonged recess time slot at which different group of one or more of the beams can be transmitted.
  • the transmission scheduler module is configured and operable in a dynamic scheduling mode for assigning dynamically determined time durations to the transmission of each beam during a beam hopping operation.
  • a communication receiver module adapted for processing signals of a burst mode communication channel from a remote communication system.
  • the communication receiver is configured and operable for processing at least a portion of a signal received in the communication channel after a recess time period during which communication frames were not transmitted in said communication channel to determine a carrier frequency of the communication channel, based on a single communication frame appearing in the communication channel after said recess time period.
  • a method for reducing interference to transmissions that occur due to other transmissions sent from/to neighboring satellites utilizing the same frequencies and/or interference that occur due to other communications transmitted along different satellites beams using the same frequencies, wherein the method comprises the step of replacing full dummy frames that should be transmitted in a TDM continuous satellite forward channel, with dummy frames' headers.
  • the method provided further comprising a step of inserting at least one pilot sequence at least one gap formed when a full dummy frame associated with the dummy frame's header and comprises a respective payload, was replaced by a dummy frame's header.
  • dummy frame's header is transmitted at a reduced power. Also, if at least one pilot sequence has been inserted at the at least one gap formed, it will be transmitted at a reduced power.
  • the method provided further comprising a step of inserting dummy frames at least one of the satellite's transmission beams, when there is data available for transmission along that at least one beam.
  • the timing of the dummy frames is optimized so that the system performance is enhanced (e.g. the system throughput is increased).
  • the transmitting timing of dummy frames, dummy frames headers or dummy frames headers and pilot signals in each beam is controlled in such a way that the inter-beam interference is minimized (at the cost of some additional delays).
  • dummy frames would be inserted in transmissions conveyed along a beam, even if this beam's queue is not empty, in order to reduce interference to a certain frame or frames being transmitted along another beam or beams.
  • the decision on whether to insert a dummy frame, and thus delaying transmission of a frame may depend on that frame time sensitivity or other quality of service parameters associated therewith.
  • dummy frames are transmitted only when there is no data to send.
  • dummy frames, dummy frame headers or dummy frames headers and pilot signals are inserted at some of the beams (preferably at those that are less occupied with communications), also when there is data to send in order to reduce interference to other beams, at a cost of delaying the data frames.
  • a receiver configured for use in a satellite communications network, wherein the receiver is configured to receive communications wherein full dummy frames that should have been transmitted in a TDM continuous satellite forward channel, were replaced with dummy frames' headers.
  • the receiver is further configured to receive communications in which at least one pilot sequence was inserted at least one gap formed when a full dummy frame associated with that dummy frame's header and comprises a respective payload, had been replaced with the dummy frame's header.
  • the signal acquisition system includes:
  • an input module adapted to obtain a received signal (e.g. EM signal), which encodes communicated data over a certain unknown carrier frequency.
  • the certain unknown carrier frequency may be any one of a plurality of possible carrier frequencies residing within a predetermined frequency band.
  • a signal time frame processor connectable to the input module and configured and operable for continuous processing of time frame portions of the received signal to identify at least one code word of a group of one or more predetermined code words, being encoded in a time frame portion of the received signal.
  • the signal time frame processor includes:
  • a carrier frequency analyzer module configured and operable for analyzing the time frame portion of the received signal in conjunction with the plurality of possible carrier frequencies simultaneously. This is achieved by transforming the time frame portion to generate carrier-data including a plurality of carrier-data-pieces associated with each possible carrier frequency of the plurality of possible carrier frequencies respectively. Each of the carrier-data pieces is indicative of data encoded in the time frame portion over a carrier frequency associated with the respective carrier-data piece;
  • a convolution module configured and operable for processing the time frame portion of the signal to simultaneously identify whether the time frame portion encodes said at least one code word, over any one of the a plurality of possible carrier frequencies.
  • the signal acquisition system may also include an output module configured and operable for outputting identification data indicative of identification of said code word in the signal.
  • the signal acquisition system may be adapted to determine a time index of said code word in the received signal based on the time frame portion of the received signal at which said the code word is identified, and the output module is adapted to output the time index.
  • the time frame processor is adapted to process the carrier data to identify the carrier-data piece, which encodes significant data and thereby determine the carrier frequency of the received signal.
  • the output module is further adapted to output the determined carrier frequency.
  • a satellite communication terminal including the signal acquisition system described above.
  • the invention also provides a satellite communication terminal adapted for receiving a plurality of designated communication frames transmitted in a forward link from a satellite to said terminal, wherein said satellite operates in a beam-hopping mode and said communication terminal is associated with a certain group of one or more respective groups of communication terminals associated with respective beams transmitted by said satellite in said beam-hopping mode ;
  • the satellite communication terminal comprises a signal receiving module configured and operable for performing signal receipt operation during a forwards link transmission of a respective beam of the beam-hoping mode which is associated with the certain group for receiving and processing the communication frame transmitted in said forward link from said satellite;
  • said signal receiving module comprises the above-described signal acquisition system configured and operable to process at least a part of the communication frame received in the forward link from said satellite and to apply carrier locking on to a carrier frequency of said respective beam by identifying at least one code word in the respective communication frame and determine a time index at which said code word is encoded in the received signal and a carrier frequency over which said code word is encoded in the received signal.
  • the air interface of the communication between the satellite and the terminals includes a forward link established by one or more TDM carriers, and a return link that utilizes a reservation access scheme such as Multi-Frequency Time Division Multiple Access (MF-TDMA).
  • MF-TDMA Multi-Frequency Time Division Multiple Access
  • the air-interface used by the present invention may be characterized by its ability to accommodate the inability of the terminal to receive communications while being in a mode of transmitting communications.
  • a frame that is used for the forward link is divided into N - for example 4 - equal length sub-frames.
  • a forward link stream carried by each sub-frame will serve 1/N - one fourth using the same example - of the terminal population in a beam.
  • the satellite return link scheduler will assign capacity to terminals, while taking into account their sub-frame association. This scheme simplifies scheduling by the satellite and allows the terminals to be grouped for addressing over the forward link, and to save receiver power.
  • a forward link super-frame structure taken together with signaling e.g. over a DVB-S2 (or any other applicable standard) PL ("Physical Layer") header, is used to alert terminals which are in stand-by mode to a forward link traffic that is queued and is about to be transmitted to them.
  • Beam and satellite handover may optionally but not necessarily rely on a system-wide GPS-grade time -base; terminal geo-location information; accurate satellite orbital data, communicated to the terminals through layer 2 signaling over the forward link; and the framing scheme described hereinabove.
  • Beam or satellite switchover for terminals that are in a stand-by mode or are currently receiving data may involve no signaling and may be done with no interruption to the traffic.
  • Return link transmission during switchover may include exchanging modified capacity request messages (e.g. preferably in a seamless manner) during intra- satellite switchover and nearly so between satellites.
  • each designated communication sub-frame is a respective portion of a communication frame, which transmitted from the data communication mediator (e.g. satellite) in the forwards link.
  • the designated communication sub-frame includes N communication sub-frames designated to serves respective one or more groups of communication terminals.
  • the satellite communication terminal includes:
  • the scheduling module may for example include:
  • a forward link scheduler configured and operable for assigning a forwards link schedule for receiving said designated communication sub -frame at said time slot
  • a return link scheduler configured and operable for assigning a return link schedule for transmitting information to the satellite during time slots other than said time slot of the designated communication sub-frame
  • a signal receiving module associated with the scheduling module and configured and operable for performing signal receipt operation during the forwards link schedule for receiving and processing said designated sub-frame of the communication frame transmitted in the forward link from the communication mediator (satellite).
  • the signal receiving module includes a signal acquisition system configured and operable to process at least a part of the communication frame received in the forward link from the communication mediator (satellite) and to lock on to the designated communication sub-frame by identifying at least one code word in the received signal designating the designated sub -frame, and determining a time index (sample position) at which the code word is encoded in the received signal and a carrier frequency over which the code word is encoded in the received signal.
  • a signal acquisition system configured and operable to process at least a part of the communication frame received in the forward link from the communication mediator (satellite) and to lock on to the designated communication sub-frame by identifying at least one code word in the received signal designating the designated sub -frame, and determining a time index (sample position) at which the code word is encoded in the received signal and a carrier frequency over which the code word is encoded in the received signal.
  • the terminals belonging to the at least one group of terminals are characterized in that they cannot receive communications while they are transmitting communications.
  • each of the at least one group of terminals is further divided into sub-groups, and a Physical Layer Header (PL-Header) of each of the forward link communication frames specifies at least one of the subgroups, and wherein each communication frame carries traffic addressed to the at least one sub-group specified in the respective PL-Header.
  • PL-Header Physical Layer Header
  • each terminal is configured to decode every PL- Header of the forward link communication frames, and wherein the method further comprises a step whereby if the PL-Header carries a an indication of a sub-group that matches the sub-group of terminals to which a respective terminal belongs, the respective terminal will decode the entire communication frame, and if the PL-Header carries an indication of a sub-group that does not match the sub-group of terminals to which a respective terminal belongs, the respective terminal will not decode the respective entire communication frame.
  • the respective terminal in a case where the PL-Header carries an indication of a sub-group that does not match the sub-group of terminals to which a respective terminal belongs, the respective terminal is configured to power down its receiver for the duration of the entire communication frame.
  • the method provided further comprises a step of alerting terminals from among the plurality of terminals which are currently in a stand-by mode, that traffic that is destined to them is currently being queued and is about to be transmitted to them.
  • each of the N sub-frames comprises a baseband frame, and wherein all of the base-band frames are of a fixed, pre-defined length, having different modulations and/or different codes.
  • a method for enabling communications between one or more satellites and a plurality of terminals, wherein the one or more satellites are configured to communicate with the plurality of terminals belonging to a public network through at least one gateway, and wherein the plurality of terminals and the at least one gateway are configured to execute identical, bit-exact satellite coverage calculation routines, synchronized for traffic routing and beam / satellite selection with minimal signaling.
  • each of the plurality of terminals is configured to generate requests for allocation of return link capacity in another beam or a different satellite, thereby when a terminal switches a beam or a satellite, it is able to immediately utilize said allocated capacity over the new (switched- to) beam or at the new satellite.
  • the terminal is configured to:
  • the one or more satellites are configured to:
  • gateway-referenced mechanism to establish a system-wide Time of
  • adaptive acquisition time is allocated for a period of time required for carrying out an inter-beam switchover and/or inter- satellite switchover.
  • the satellite system is a member selected from a group that consists of: a Geo Stationary system, a LEO system and a MEO system.
  • Fig. 1 illustrates a prior art transmission sequence of communications in a satellite network
  • Fig. 2 demonstrates one embodiment of the solution provided by the present invention whereby only the header of dummy frames are transmitted together with pilot signals, instead of full dummy frame's payload;
  • Fig. 3 demonstrates another embodiment of the solution provided by the present invention whereby only the header of dummy frames are transmitted instead of the full dummy frames;
  • Fig. 4A demonstrates a standard complying system (prior art) where no dummy frames are inserted at any of the beams when there is data to send along these beams;
  • Fig. 4B illustrates yet another embodiment of the solution provided by the present invention whereby dummy frames are inserted at some of the beams also at times when there is data to send along these beams;
  • Fig. 4C is a block diagram showing a communication transmission system configured according to an embodiments of the present invention
  • Figs. 4D and 4E are flow diagrams exemplifying the operation of a transmission scheduler module 350 of the communication transmission system of the present invention for carrying out a beam hopping transmission according to two embodiments of the present invention;
  • FIG. 5 illustrates an example scheme for transmit-receive scheduling
  • FIG. 6 illustrates an example scheduling scheme where the satellite accepts requests for capacity in the new beam that are received over the old beam
  • FIG. 7A is a block diagram of a communication terminal (e.g. satellite communication terminal) according to an embodiment of the present invention.
  • a communication terminal e.g. satellite communication terminal
  • FIG. 7B is a diagram schematically illustrating three possible frame structures of the DVB-S2X standard/protocol.
  • Figs. 8A to 8C are block diagrams of several examples of signal acquisition system according to various embodiments of the present invention.
  • DVB-S2 and DVB-S2X standard except for broadcasting with constant coding and modulation (CCM).
  • CCM constant coding and modulation
  • a dummy frame is a relatively short frame (having a length of between 3330 to 3510 symbols), which comprises a header of 90 or 180 symbols, and 3240 pre-determined symbols instead of data. It may also include 72 symbols of pilots, which are also known symbols transmitted within each frame to facilitate synchronization and channel estimation.
  • a typical DVB-S2/S2X frame varies in size between 3240 to 33720 symbols, and includes a header, data and pilot symbols. The frame size depends on the type of modulation selected, while the actual symbol rate is determined by the allocated bandwidth for the link.
  • dummy frames are transmitted while using a reduced transmission power.
  • S is the received signal power
  • N is the noise power
  • // is the interference power received from the interfering link.
  • the received signal power, S is in fact a random variable since the channel may undergo fading, so SINRo, - the operational SINR, is determined by its statistics, which is measured or taken from ITU- R Recommendation No. P.618 entitled “Propagation data and prediction methods required for the design of Earth-space telecommunication systems", 09/2013.
  • link / will be transmitting in full power and cause interference of // to the link of interest, while for 1- p, of the time it will transmit with reduced power and the interference caused thereby will be reduced to l ⁇ 1.
  • the power of interference caused by such a link may be described as multiplied by a stochastic variable with binomial distribution.
  • the total interference is thus given by:
  • the total interference is a random variable. Its exact statistics may depend on a number of parameters such as the number of interfering signals, their relative strength, the different average to peak ratio per link, and whether they are correlated (namely, if there is a correlation among dummy frames transmission times). However, similarly to the approach taken while considering the signal fluctuations, one can measure or estimate the margin required, when considering also the fact that the interference is reduced.
  • Controlled Links In case where all links are controlled by a central entity, (e.g. a scheduler), the stochastic process described hereinabove may be made more deterministic, and in this case, some maximal interference level may be ensured with high probability. For that purpose, the scheduler will transmit dummy frames (reduced power, header and pilots only) instead of frames which, according to their QoS requirement, can be delayed.
  • a central entity e.g. a scheduler
  • a single-carrier non-spread modulation is preferably used, e.g. as in the DVB-S2 and in DVB-S2X Standards (ETSI EN 302 307-1 and EN 302 307-2), while for the return link, a Multi-Frequency Time Division Multiple Access (MF-TDMA) may be used, e.g. DVB-RCS2 standard, (EN 301 542-2).
  • MF-TDMA Multi-Frequency Time Division Multiple Access
  • the forward link of the present invention is somewhat similar to a DVB- S2/S2X link but is characterized by having at least the following differences when compared with a DVB-S2/S2X link:
  • a modified Physical Layer (PL) header provided by the present invention that is characterized in that it: (a) enables combined low-SNR and high-SNR adaptive coding and modulation (ACM); and (b) includes a larger payload of mode- setting bits.
  • Base-band frames have a constant length in symbols (and may carry a number of bits that varies by the modulation currently used).
  • the return link of the present invention is somewhat similar to a DVB- RCS2 link but is characterized by having at least the following difference when compared with a DVB-RCS2 link: certain MAC messages include additional, nonstandard information such as the terminal's location and sub-population assignment.
  • the forward link PHY is somewhat similar to the definition provided in the DVB-S2/S2X standard, but is characterized by having at least the following differences when compared with a DVB-S2/S2X link:
  • An extended Physical Layer Header includes a longer Start Of Frame (“SOF”) sequence in order to ensure a first-time acquisition, and a longer Physical Layer Signaling (“PLS”) field which comprises more signaling bits.
  • SOF Start Of Frame
  • PLS Physical Layer Signaling
  • the PLS is preferably used to signal at least one of the following:
  • the baseline header described above may be extended to include a longer SOF sequence (based on the standard SOF), and additional FEC bits for the PLS field.
  • low-SNR frames may use punctured LDPC codes.
  • the forward link may be capable of supporting mixed operation of baseline (high-SNR) and low-SNR base-band frames.
  • the return link PHY is somewhat similar to that as defined by DVB-
  • the present invention provides a transmit-receive framing mechanism that greatly simplifies scheduling and streamline satellite and beam switchover. Moreover, it transfers most of the complexity of routing and handover from the satellite to the gateway and the terminals. This comes at the cost of modest framing delay and a somewhat lower terminal transmission duty cycle (75% for the example of 4 sub- frames, compared with a best-case of over 90%).
  • a baseband frame relates to a frame that contains a number of payload (user information) bits, which varies between 2432 to 53760.
  • the destination of this information can be to one user (a terminal) or to many users (when operating in a broadcast mode, or in a time- division mode).
  • a base-band header is added to these payload bits and the whole frame is then encoded, modulated to symbols and framed into a Physical Layer Frame (PL- Frame), which contains between 3330 to 33282 symbols.
  • PL- Frame Physical Layer Frame
  • a terminal receiving such a PL-frame has first to decode the header of the PL-frame, in order to be able to access the data contained in that frame.
  • the symbols may be transmitted at different rates, depending on the allocated bandwidth at the satellite.
  • a rate of 500 Msps (which is supported by High-Throughput satellites), so that if one takes for example a fixed PL-frame of 32400 symbols it would take 64.8 microseconds for that PL-frame to be transmitted.
  • 500Msps may be 36 Msps, or 72 Msps, which are currently more common. At these rates, the time required to transmit a 32400 symbols long PL-frame would be 0.9 msec or 0.45 msec, respectively.
  • a sub-frame of 0.5 msec comprises about 8 PL-Frames when using a 500 Msps rate.
  • the length of the frames according to the present disclosure will have to be modified, since a PL-frame cannot be divided into several sub-frames.
  • a time period of 2 msec is exemplified as being associated with a communication frame, which is the equivalent of having 16 PL- frames.
  • a super- frame that comprises 5 communication frames, will therefore comprise 80 PL-frames.
  • sub-frame refers herein throughout the specification and claims to an entity that comprises several PL-frames, each of which comprising a base-band frame.
  • Fig. 1 illustrates a prior art transmission sequence/channel of communications in a satellite network, where full dummy frames are transmitted between communication frames, when data is not available at the ingress of the transmitter.
  • the purpose of inserting these dummy frames is to achieve a rate matching between the allocated bandwidth for transmission and the actual transmission rate.
  • Figs. 2 and 3 illustrate two non-limiting examples of communication channel CH transmitted by the transmission method according to certain embodiments of the present invention.
  • the communication channel shows two transmitted communication data frames encoded in the channels signal, Data Frame i and Data Frame i+1 , whereby the signal is transmitted over a communication channel with a recess time slot R between the communication of certain consecutive data frames thereof Data Frame i and Data Frame During the recess time slot R no signal, and/or signal with substantially reduced power is transmitted over the communication channel.
  • dummy frame header(s) H and/or optionally pilot signals P are transmitted instead of a full dummy frame's payload (DD in Fig.l).
  • DD full dummy frame's payload
  • Fig. 3 demonstrates a case whereby only an optional header H of dummy frames are transmitted, instead of the full dummy frames. It should be understood, and also discussed below that actually both the dummy frame headers H and/or pilot signals P are optional and may be used to provide certain consistency/computability (to some degree of efficiency) with conventional continuous mode receivers.
  • Fig. 4A illustrates a conventional satellite multi-beam technique in which the satellite's S transmitter transmits a plurality of continuous mode communication beams CB simultaneously to cover different geographical regions.
  • Fig. 4B illustrates a multi- beam technique according to the present invention, in which the satellite's transmission system 300 configured and operable according to the technique of the present invention, (as described in more details below with reference to Fig. 4C) transmits a plurality of burst mode communication beams BB for covering a plurality of geographical regions.
  • Each burst communication beam may include a plurality of communication channels communicated to the respective geographical regions it covers.
  • recess time slots R in Figs. 2 and 3 e.g.
  • the timings of the recess time slots of different communication channels may be arranged by the scheduler so as to accommodate transmission of additional burst mode communication beams BB, (e.g. more than possible by the conventional continuous mode communication techniques). This may be achieved for example by dynamic scheduling of the communication frame transmission in each of the beams and/or communication channels thereof.
  • Fig. 4C is a block diagram showing a communication transmission system 300
  • the system 300 includes a data provider module 310 configured and operable for providing data to be communicated to one or more terminals (communication receivers) over one or more forward communication channels, a communication frames generator module 320 configured and operable to segregate the data into a plurality of communication frame data payload portions, and a transmission channel signal encoder 330, configured and operable for generating/encoding the communication frames in a transmission signal to be transmitted via the forward communication channel(s).
  • the transmission channel data encoder 330 is configured to operate in burst communication mode (or in other words is capable of operating in a non-continuous transmission mode), in which the transmission over the forward communication channel may include bursts of signal transmission (i.e. occurring during a certain statically or dynamically determined transmission time slots), in which a signal encoding one or more of the communication frames is transmitted, and one or more recess time slots between the transmission bursts (between some or all of the transmission time slots), during which no signal is transmitted over the channel, or possibly a signal of substantially reduced power is transmitted.
  • bursts of signal transmission i.e. occurring during a certain statically or dynamically determined transmission time slots
  • a signal encoding one or more of the communication frames is transmitted
  • recess time slots between the transmission bursts (between some or all of the transmission time slots)
  • the system also includes a transmission module 340 configured and operable for transmitting the transmission signal in burst communication mode.
  • the transmission module 340 is adapted for transmitting the encoded signals of the communication channels/beams in a time-division multiplexing (TDM) transmission.
  • TDM time-division multiplexing
  • the transmission module 340 may be adapted to operate during the transmission time slots associated with a respective communication channel for transmitting the communication frames of the respective communication channel during the these transmission time slots, and recess from transmitting signals associated with the respective communication channel during the recess time slots.
  • no signals pertaining to the respective communication channel are encoded/transmitted by modules 330 and/or 340, or possibly in some cases only a residual signal (e.g. which includes only headers and pilots comprising predetermined code words) with significantly reduced power is transmitted (e.g. which average power is reduced for example to not more than 0.1% of the power of the signal in the transmission time slots) at least as compared to the power of the signal transmission during the transmission time slots.
  • a residual signal e.g. which includes only headers and pilots comprising predetermined code words
  • significantly reduced power is transmitted (e.g. which average power is reduced for example to not more than 0.1% of the power of the signal in the transmission time slots) at least as compared to the power of the signal transmission during the transmission time slots.
  • headers and pilots which typically encode sequences including at least one of certain predetermined/known key-words and which may therefore be detercted by convolution with the keywords
  • SNR SNR as low as -2dB
  • a DVB- S2 waveform is used.
  • the header and/or pilots in cases where they are used, can be transmitted with down to about 1/1000 of the power used for transmittin data carrying postions of the signal.
  • the received signal strength may limit effective SNR to a level as low as 5dB.
  • the reduced power of the residual header and pilot signal could go down to 20% of the data power.
  • the total interference power to other beams is reduced as described above, while receivers which are not capable for burst reception can still be supported.
  • a beam hopping scenario where a recess gap in one beam transmission is used for transmission to other beams, it is not possible to transmit reduced power header or pilots in one beam simultaneously with other beams. Hence in this case only receivers capable of burst reception are supported.
  • the technique of the present invention obviates a need for transmitting dummy frames and/or dummy payload data in between the actual communication data frames which are transmitted over the communication channel. This is achieved by operating in burst communication mode for transmitting the required data communication frames during certain transmission time slots while not transmitting on that channel during the recess time slot between them.
  • the transmission channel signal encoder 330 is configured and operable for introducing one or more recess time slots in between the one or more of the communication data frames which are encoded in each channel/beams, so as to encode the data frames in the communication channel in a burst communication mode.
  • DD dummy payload data
  • the transmission channel signal encoder 330 is configured and operable for encoding the communication time frame in a time-division multiplexing (TDM) scheme in the communication channel signal(s) it generates.
  • TDM time-division multiplexing
  • the transmission channel signal encoder 330 may optionally include a TDM signal encoder module 334 configured and for applying time-division multiplexing to the data to be encoded in the channels signal.
  • TDM signal encoder module 334 configured and for applying time-division multiplexing to the data to be encoded in the channels signal.
  • Time-division multiplexing techniques and various configurations of TDM signal encoders are generally known to those versed in the art, and for conciseness will not be repeated here.
  • coping with the burst communication mode of the present invention may be difficult for conventional communication receivers which are operable in continuous communication mode. This is because during the recess time periods, at which no signal is transmitted, such receivers may lose synchronization with the communication channel and/or dis-acquire the channels' carrier frequency (e.g. due to differences in the internal clocks of the receiver and transmitter), and therefore may require prolonged time extending over several communication frames to re-acquire and/or re-synchronize with the signal of the communication channel once it re-appears after a recess time slot/period.
  • novel communication receiver configuration which is configured to operate/receive signal from a burst mode communication channel.
  • a receiver will be complementary with the transmission system 300 operating in a burst communication mode.
  • the configuration and operation of such a communication receiver 200 according to some embodiments of the present invention are discussed in more details below with reference to Figs. 7 A to 8C. More specifically, the communication receiver 200 of the present invention is adapted to receive bursts of communication signals from a remote communication system (e.g.
  • the transmission channel signal encoder 330 is further configured and operable for introducing one or more intermediate/additional communication sequences into the signal of the communication channel, so as to practically shorten the durations at which no signal is transmitted over the communication channel to be below a certain predetermined maximal duration.
  • the transmission channel signal encoder 330 of the present invention is adapted to encode, a recess header data sequence H (also referred to herein above as dummy frame' header) in the signal of the communication channel.
  • the duration of the recess header data sequence H shortens the effective time of the recess time slot between the communication frames preceding and proceeding it.
  • recess header data sequences may be encoded at respective recess header time slots preceding respective recess time slots. This is illustrated for example in Figs. 2 and 3 above in which the optional recess header data sequences H in the channel are illustrated.
  • the transmission channel signal encoder 330 of the present invention is adapted to encode one or more (optional) pilot sequences P within the time duration of the recess time slots of the signal of the communication channel, so as to practically split the recess time slot to several parts which durations does not exceed the certain predetermined maximal duration. This is illustrated for example in Fig. 2 above in which the optional pilot sequences P in the channel are illustrated.
  • the transmission channel signal encoder 330 may be configured and operable such that the durations at which no signal is transmitted over the communication channel is below a certain predetermined maximal duration, whereby this certain predetermined maximal duration sets up a threshold limit above which, statistically, the signal (and/or it carrier frequency and/or its synchronization) are not expected to be lost by the receiver (except maybe to extreme/rare cases), even if the receiver would be operating in the conventional continuous communication mode.
  • the predetermined maximal duration threshold may generally be selected according to the bandwidth of the communication and the specified stabilities of the clocks' (e.g. internal-oscillators') used in the communicating transmission system 300 (transmitter 340) and communication receiver(s) 200 (or terminal(s) 100) which exchange the communication of that bandwidth.
  • the transmission channel signal encoder 330 may be configured and operable for introducing recess header data sequences H and/or pilot sequences P in to the recess time slots (at the beginning and/or middle thereof) in every case where total time duration of the recess time slots exceed this predetermined threshold.
  • the recess header data sequences H and/or pilot sequences sequence P may be encoded with predetermined code words identifiable by the receivers, so that to allow the receivers to maintain synchronization with (e.g. update-the/retune-to) the carrier frequency and/or timing of the communication channel.
  • the transmission module 340 is configured and operable for transmitting the recess header data H and/or said pilot sequences P is with reduced power as compared to the power of the signal transmission during said data time slots.
  • the transmission system 300 is configured and operable in a multi-beam mode for transmitting a plurality of beams having different respective geographical coverages respectively.
  • each communication channel of the one or more forward communication channels may be is associated with at least one beam of the plurality of beams, and designated for one or more terminals residing in a geographical coverage of the beam.
  • the phrases beam and/or communication beam is used herein to designate a transmission beam of electromagnetic (EM) radiation (typically radio frequency), which is transmitted by the transmission system 300 towards (to cover) a certain predetermined geographical coverage area.
  • EM electromagnetic
  • a beam may be for instance formed by the directional properties of the antenna 305 to which the transmitter 340 is connected and through which the signal is transmitted, and/or it may be controllably formed to be controllably/adju stably directed to cover predetermined geographical area by using a beam former module.
  • a beam former 345 is optionally included in the transmitter, and can be operated with the configuration of antenna 305 as a phased array antenna including a plurality of antenna elements.
  • the beam former 345 may be adapted to receive the signal(s) of the communication channels that are to be transmitted by each beam (e.g. the signals here may be being a sequence of data frames associated with the respective communication channels to be included in the beam), generate therefrom a plurality of corresponding elemental signals to be transmitted by respective elements of a phased array antenna (e.g. 305) with the phases and possibly frequencies of such elemental signals being adjusted such that the beam carrying the signals of the one or more channels is directed to cover a predetermined geographical location, to which the respective channels should be transmitted.
  • a phased array antenna e.g. 305
  • each group of beams may include one or more beams that can be simultaneously formed by the beam-former 345 and simultaneous transmitted by the transmitter 340 (via antenna 305) to concurrently cover several geographical areas.
  • the phrase communication channel is used herein to designate a data stream (typically burst/non-continuous data stream of data) which is communicated from the transmission system (e.g. of a satellite) to one or more communication receivers (e.g. being terminals adapted to receive data from the satellite).
  • the communication channel is generally formed as a plurality of data frames designated (e.g. by parameters encoded in their headers and/or by predetermined timings thereof and/or by their respective frequencies) to be received by certain on or more communication receivers (e.g. terminals), listening the forward communication channel from the satellite.
  • the present invention facilitates the transmission of plurality of groups of beams at distinct time schedules for each groups so as to accommodated broader geographical coverage.
  • the signals of each transmitted beam may include, or be composed of, the signals of one or more communication channels.
  • the transmitter module 340 may include a beam encoder module 342 configured and operable for receiving, from the transmission channel signal encoder 330, the signals (e.g. the encoded communication data frames) of a plurality communication channels, in association with the communication beam(s) BB over which each of the communication channels should be transmitted, and process the encoded communication data frames of channels that are associated with each respective beam to form a unified beam's signal encoding all these communication data frames of the channels participating/transmitted in the respective beam.
  • the beam encoder module 342 is adapted to encode the communication frames of the plurality of communication channels which are to be transmitted in each beam, in a time division multiplexing, in the beam's signal.
  • the beam encoder module 342 is adapted to encode the communication frames of the plurality of communication channels which are to be transmitted in each beam, in a frequency division multiplexing, in the beam's signal.
  • other techniques for multiplexing the plurality of channels on the same beam may be employed by the beam encoder module 342,
  • the beam signal in cases where the beam encoder module 342 is used, or the signals of the communication channels (as obtained from the transmission channel signal encoder 330) may be further processed by the optional beam former 345 to generated a beam formed signal of the beam which is then transmitted in directional manner via antenna 305 (being phase array in this case). Indeed, groups of a plurality (one or more beams) may be simultaneously generated ant transmitted.
  • the transmission system 300 is configured and operable for operating in a beam-hopping mode. In this mode, that two or more groups of beams which are transmitted at distinct time intervals.
  • Each group of beams may generally include one or more beam (up to the upper limit imposed by the data bandwidth and/or beamforming parameters) covering one or more respective geographical areas.
  • each group of beams establishes at least one of the forward communication channels transmitted by the system 300.
  • the system further includes a transmission scheduler module 350 configured and operable for scheduling transmission of the two or more groups of beams.
  • the transmission scheduler module 350 is configured and operable for scheduling the transmission data time slots at which the communication frames of the communication channel(s) of each group of beams are transmitted. More specifically according to some embodiments the transmission scheduler module 350 is adapted to schedule the communication frames of the channels of each group of beams so as to aggregate together the plurality recess timeslots R of those communication channels to form a prolonged recess time slot which duration is long enough so that the transmission of a different group of one or more beams can be accommodated in that prolonged time slot.
  • the transmission channel signal encoder 330 and/or the beam encoder module 342 may be connectable to the transmission scheduler module 350 and may be adapted to encode the communication frames of each of the one or more channels of each beam in accordance with the scheduling of the scheduler. Accordingly, in this way the system 300 may be provide an efficient beam hopping implementation.
  • Figs. 4D and 4E are flow diagrams exemplifying the operation of the transmission scheduler module 350 according to two embodiments of the present invention in which it is configured and operable in static or dynamic scheduling modes.
  • the transmission system 300 may include a data provider module 310 configured and operable for providing data to be communicated/transmitted by the system 300 towards different geographical areas, via different beams.
  • K geographical areas are considered which are covered by respective beams Beaml-BeamK.
  • the data provider 310 may be for example adapted to obtain/receive the data to be remitted in the beams in the form of data packet/frames communicated to the system 300 from a ground station, such as a data gateway, whereby each packet may designate the geographical area to which it should be transmitted and/or the channel/beam in the scope of which it should be transmitted.
  • Beaml-Data to BeamK-Data which include the data packets that should be transmitted via each beam.
  • the data packets in Beaml-Data to BeamK-Data may by themselves represent communication frames that should be transmitted by the respective beams, or in some cases they only include the pay load data that should be transmitted and the communication frame generator 320 encapsulate those in respective communication frames (e.g. by adding thereto respective headers, such as physical layer communication headers. Accordingly, the data provider 310 obtains a plurality of communication data frames which should be communicated by the different beams Beaml-BeamK.
  • the obtained communication data frames are classified to the different beams based on for example any one or more of the following:
  • the communication data frame are actually classified/placed in K bins BIN-1 to BIN-K respectively representing the collections of communication data frames that should be transmitted by the respective beams Beaml-BeamK.
  • the transmission scheduler module 350 operates a scheduler transmission procedure (e.g. loop), in which it schedules for transmission one or more of the communication data frames accumulated in each bin by the respective beam associated with the beam.
  • the scheduler 350 consecutively accesses the bins and upon accessing each bin (e.g. BIN2) it acquires certain numbers of communication data frames from the accessed bin (e.g. BIN2) and forwards those for encoding and transmission by the modules 330 and 340, while operating he transmitter 340 to transmitted those communication data frames of the specific bin (e.g. BIN2) in the framework of a corresponding beam (e.g. Beam2) directed to the respective geographical area to which those frames are designated.
  • a scheduler transmission procedure e.g. loop
  • the scheduler 350 consecutively accesses the bins and upon accessing each bin (e.g. BIN2) it acquires certain numbers of communication data frames from the accessed bin (e.g. BIN2) and forwards those for encoding and transmission by the modules 330 and
  • the transmission scheduler module 350 operates in a static scheduling mode.
  • Each beam is allocated with a certain fixed time duration FTD during which it is transmitted, regardless of the numbers/lengths of the communication data frames that should be transmitted by the beam.
  • the fixed time duration FTD may be a duration accommodating the durations of one or more super frames (e.g. DVB-S2 and DVB-S2X super frames), in which one or more communication data frames may be included.
  • the fixed time durations FTD of different beams may be different in their lengths however they are static in the sense that their duration does not change regardless of the quantity of data (accumulated in the bins) which should be transmitted by each beam.
  • this static scheme is implemented in order to accommodate backward compatibility with communication protocols requiring that the transmission duration of each beam burst, in a beam-hopping mode), would last a certain fixed duration (e.g. the duration of a predetermined super frame length) or an integer multiples of this fixed duration.
  • the scheduler module 350, and/or the transmitter 340 may be configured and operable such that the transmission of burst of a beam lasts a certain predetermined duration regardless of the amount of data to be transmitted.
  • the transmission channel signal encoder 330 may be adapted to generate, for each transmitted beam, complete super frame(s) of a predetermined fixed duration(s) while encoding therein the communication data frames that should be included in the beam and in case there is not enough data (not enough communication data frames) to fill an entire supper frame(s), further pad the rest of supper frame(s) with dummy symbols.
  • the transmitter 340 transmits the super frames (padded or not) in their respective beams.
  • Fig. 4E there is yet provided an alternative transmission scheduling scheme, dynamic scheduling mode, according to which the scheduler 350 is configured to operate in some embodiments of the present invention.
  • the dynamic mode there is no predetermined allocation time durations for the transmissions of each beam, but instead variable time durations TD1, TD2 to TDK, are dynamically allocated to the different beams, to each bursts thereof, as per demand/requirement so as to more efficiently exploit the resources of the transmission system.
  • variable time durations TD1, TD2 to TDK are dynamically allocated to the different beams, to each bursts thereof, as per demand/requirement so as to more efficiently exploit the resources of the transmission system.
  • there is no need to transmit dummy symbols and/or to pad super frames which such symbols and the time extent of super frames (if any) transmitted in each burst of each beam may vary per demand, and optimized to maximize the services provided by the transmission system.
  • the transmission scheduler module 350 is configured to operate in an un-prioritized dynamic scheduling mode.
  • the scheduler 350 may for example operate a scheduler's transmission procedure in which consecutively accesses the different bins (e.g. in a predetermined order BIN1 -> BIN2 -> ... BINK) and upon accessing each bin (e.g. BIN2) it acquires all of communication data frames accumulated in the accessed bin (e.g. BIN2) to that time, and forwards those for encoding and transmission by the modules 330 and 340.
  • the transmitter 340 operates to transmit all the communication data frames of the specific bin (e.g. BIN2) in the framework of a corresponding beam (e.g. Beam2), which is directed to the respective geographical area to which those frames are designated.
  • the transmission scheduler module 350 is configured to operate in a prioritized dynamic scheduling mode.
  • the data provider 310 further operates to classify the communication frames it puts in each bin, also to plurality of different priorities.
  • three priority classes are set as follows: PR1 (highest) , PR2 (intermediate) and PR3 (lowest).
  • PR1 (highest) , PR2 (intermediate) and PR3 may be associated with a certain maximal time delay threshold (e.g. PD1 to PD3 respectively) indicated in the maximal time delay on which the communication data frames of this priority are permitted to be delayed before transmission.
  • the classification to priorities may be conducted based on various considerations, for example any one or more of the following:
  • some channels may be associated with higher/better service levels and therefore higher priority and /or other channels may be associated with lower service levels and thus lower priorities.
  • the scheduler 350 may for example operate a scheduler's transmission procedure in which it consecutively accesses the different bins (e.g. in a predetermined order BIN1 -> BIN2 -> ... BINK) and upon accessing each bin (e.g. BIN2) it acquires all of communication data frames that are accumulated only in the highest level of priority (e.g. PD1) accumulated in the accessed bin (e.g. BIN2) to that time, and forwards those for encoding and transmission by the modules 330 and 340. Accordingly the highest level priority communication frames are transmitted as soon as possible,
  • the scheduler 350 may further operate an additional procedure, priority update procedure in which it updates the permitted time delays of the remaining communication data frames of the different priorities, and accordingly updates their current priorities (e.g. leave them in their previous priority and/or advancing them to higher priority) based on whether the relation between their updated permitted time delays and the maximal time delay threshold (e.g. PDl to PD3) of the respective priority levels (e.g. PR1 to PR3).
  • the maximal time delay threshold e.g. PDl to PD3
  • Fig.4E whereby transmission of a packet in a bin is made when the bin has reached a predetermined capacity level, or when some predetermined timer set according to the time delays (e.g. PDl- PDK) has expired, such that the order of transmission is not fixed yet no dummy frames are added to the transmission.
  • some predetermined timer set according to the time delays e.g. PDl- PDK
  • FIG. 5 illustrates an example scheme for transmit-receive scheduling, for an example set of parameters, wherein:
  • Forward link base-band frames are grouped into 2 mS long frames. Each frame is divided into four equal-length (0.5 mS long) sub-frames, each consisting of an integer number of e.g. DVB-S2 or DVB-S2X base-band frames.
  • the satellite forward link carries four equal-rate streams (e.g. DVB-S2 or DVB-S2X), each occupying one sub- frame within a frame (for example, for a single-carrier-per-beam 500 Msps carrier, there will be four 125 Msps streams).
  • the terminal population is divided into four equal- size sub-populations.
  • the division is done in a way that maximizes randomness across geography (and therefore within any single beam at any given time).
  • Each sub -population of terminals receives the stream carried by one sub-frame within a frame. This division is fixed (i.e. a static division).
  • Each sub-population (served by one of the four forward link sub-frames) may be further divided into groups. Each such group is served by a fraction of the sub -frame capacity, designated by a time- slice number (as defined for example by DVB-S2, Annex M) thereby representing the group.
  • a time- slice number as defined for example by DVB-S2, Annex M
  • Return link TDMA slots there is an integer number of return link TDMA slots within the time period of a forward link sub-frame.
  • a return link transmission time is allocated for a terminal during the three sub-frames within a frame, when it is not receiving communications.
  • Return link capacity allocation takes into account satellite-terminal delay to ensure that capacity assignments (made in the satellite's return link time frame) are compatible with the terminal's transmit time window (as illustrated for example in FIG. 1).
  • Increasing (or decreasing) the number n of sub-frames within a frame increases (or decreases) the transmit time window (to 1-1/n of a frame) and increases (or decreases) the delay somewhat (to 1-1/n of a frame).
  • Transmit-receive scheduling and return link capacity assignment are preferably signaled in layer 2. Their implementation in the satellite and the terminal is preferably managed by software.
  • the assignment of the terminal's sub-population and group is preferably carried out at the gateway.
  • Each packet sent over the gateway-to-satellite link carries this data as side-information, thereby relieving the satellite from the task of storing mappings for the entire terminals' population.
  • the terminal Upon session initiation (and preferably during hand-over), the terminal provides the satellite with the necessary information on its current location and sub -population assignment, and this data may then be cached at the satellite for the various active terminals.
  • terminals that are not transmitting or receiving communications enter preferably a stand-by mode in which all but a minimal set of their sub-systems, are powered down.
  • An inactive terminal comes out of its stand-by mode when either (a) a packet arrives at its local interface; or (b) it is addressed by the satellite over the forward link; or (c) it has to perform an infrequent housekeeping task such as receiving updated system information.
  • case (b) involves the following features of the air interface:
  • Each M - for example five - forward link frames will be grouped into a Super- frame (10 mS long for 5 X 2 mS frames). The start of a super- frame is signaled by the PLS.
  • Part of the PLS payload is dedicated to terminal alerting - signaling terminals that are currently in a stand-by mode that there is queued forward link traffic addressed to them, which will be transmitted within the next sub-frame.
  • the terminal altering channel within the PLS may use time division multiplexing over a super-frame in a way that any single terminal only needs to demodulate a small number of (and with very high probability only one) base-band frame PL headers at a known offset within a known sub-frame in the super-frame.
  • a terminal in a stand-by mode will power up - once every 10 mS for the above example - the receiver blocks needed for demodulating one forward link base-band frame PL header (and very infrequently, a small number of subsequent headers), before returning to its stand-by mode.
  • a 10 mS super-frame introduces an average / worst-case delay in start-up of forward link traffic of 5 / 10 mS, respectively.
  • a master oscillator at the satellite generates the time base for the Network Clock Reference ("NCR"), used by the terminals to time their return link bursts.
  • NCR Network Clock Reference
  • This oscillator is locked to the forward link symbol clock, and the frequencies are chosen so that the terminal can convert the timing of the start of a sub-frame to an NCR value. This makes it possible for a terminal that comes out of stand-by mode to re-acquire the NCR as soon as it has demodulated the first base-band frame header.
  • the terminal At installation, the terminal is programmed with its geo-location, with a high degree accuracy (for example within 50m). The terminal is also coarsely 3 -axis aligned (in North-South orientation and 2-axis tilt). b. During commissioning, the terminal executes a calibration routine that fine-align its orientation and tilt, based on the satellite reception.
  • the satellites use GPS receivers or an equivalent gateway-referenced mechanism to establish a system- wide Time of Day (ToD) time base, and the gateways are configured to align themselves to the time base.
  • the DVB-RCS2 NCR may serve for this purpose.
  • the satellites broadcast periodically over the forward link of each beam, Layer 2 information that specifies the system's satellite constellation - orbits and satellite positions - to an accuracy that would enable a terminal to predict the location of any satellite for a period such as up to 12 hours ahead, to within an accuracy of for example 100 m (300 nS one-way propagation time).
  • All gateways and terminals execute identical, bit accurate coverage mapping routines that use the information associated with (a) and (d) and timed by (c), in order to determine satellite coverage of a terminal.
  • the terminal's antenna is able to track satellites without relying on signal strength indication.
  • Coverage mapping routine (e) also provides the terminal with the satellite's Doppler frequency shift. The terminal may then use this information to:
  • All forward links generated by a satellite across all its beams may be synchronized at the symbol, base-band frame, sub-frame, frame and super- frame levels.
  • Coverage mapping routine (e) executed by the terminal, determines the frame at which the terminal must switch beams. The terminal programs its receive synthesizer during the preceding transmit sub-frame and it is then able to acquire the first receive sub- frame (or, in a stand-by mode, receive the alert signal) over the new beam, with the same accuracy as while dwelling in the former beam.
  • Satellite and beam routing to a terminal is preferably determined by the gateway and signaled to the satellite through side-information attached to every forward link packet.
  • the gateway running the same coverage mapping routine (e) as the terminal, determines the timing of terminal beam switching and route forward link traffic accordingly.
  • the gateway is made aware of sub-framing when managing forward link queuing, or (b) the satellite is provided with data "expiration" information and prioritize traffic to terminals that are about to switch away from one of its beams.
  • return link transmissions from a terminal can only be made after a capacity request was sent to the satellite and a capacity assignment was made and received in response to the request made.
  • the satellite responds to capacity request messages with a tightly controlled response time: the terminal receives the assignment a pre-defined number of sub-frames after it had made the request and - unless the return channel is heavily overloaded - the assignment will be for a (small) fixed number of sub-frames in the future.
  • forward- and return-link switching use the procedure illustrated in the following FIG. 6.
  • the satellite accepts requests for capacity allocation for the new beam that are received over the old beam.
  • the terminal makes - over the old beam - a request for capacity allocation in the new beam, at such time that the assignment is received just prior the switchover (Request 1 in FIG. 6). There will only be at most one other such request pending from a given terminal. While the request is pending, the terminal continues to receive forward link and transmit (as was previously assigned) return link traffic over the old beam.
  • the gateway re-routes traffic to the new beam at the time it should start arriving at the terminal, immediately following the switchover. There will be a transition phase (approximately coinciding with the time the cross-beam capacity request is pending) when the satellite receives the terminal's traffic over the old beam and transmits traffic to the very same terminal over the new beam.
  • the terminal re-programs its transmit and receive LO frequency synthesizers during the receive and transmit sub-frames, respectively.
  • inter-beam (intra- satellite) beam switching does not in itself involve any air interface messaging.
  • Beam selection and switching decisions are made by the gateway and the terminal: the satellite does not have to track the switchover process.
  • all the satellites in the system are preferably synchronized to a common ToD.
  • Their forward links are synchronized at the base-band frame, sub-frame, frame and super- frame levels, and their return links have synchronized slots.
  • the coverage mapping routine executed at the terminal determines the timing of the satellite switchover.
  • a terminal in a stand-by mode uses this information to switch to the new satellite and then proceeds to demodulate its terminal alert channel.
  • Forward link traffic to an active terminal that is switching satellites is re-routed by the gateway to the new satellite.
  • the gateway executes the same coverage -mapping algorithm as the terminal and will time the re-routing in advance so that, after propagating through the system, the forward link traffic arrives at the terminal aligned in time with the switchover without experiencing any switchover-related queuing delay.
  • the terminal sends, ahead of the switchover moment, a special capacity request message that is forwarded by the old (switched-from) satellite to the new (switched-to) satellite.
  • This message is either carried over an Inter- Satellite Link ("ISL"), if one extends between the two satellites, or goes through the gateway(s) serving them.
  • ISL Inter- Satellite Link
  • the capacity request specifies the time of switchover, allowing the new satellite to allocate the required capacity accordingly.
  • the terminal will time this request message to allow enough time for an assignment response to arrive back through the old satellite before implementing a switchover.
  • the terminal is then able to switch the return link transmission from the old to the new satellite with only a small hit in throughput.
  • the terminal re-programs its transmit and receive LO frequency synthesizers during the receive and transmit sub-frames respectively, immediately preceding the switchover, and steers its antenna from the old satellite to the new satellite during the back-end part of the transmit sub-frame immediately preceding switchover. This reduces by a small amount the return link transmit time window within the last frame before the switchover takes place. In addition, any difference in terminal -satellite path delay between the old and the new satellite will cause a shift in the frame, changing the duration of the first transmit window following the switchover.
  • the coverage-mapping routine preferably provides the carrier-frequency Doppler shift of the new satellite.
  • First-time return link transmissions arrive at the new satellite with a larger timing error than the follow-on traffic (500 nS, for the example parameters given above, or 1% of 50 ⁇ 8 for a relatively short 1024 bit burst at 20 Mbps).
  • return link capacity assigned through the procedure described above will leave entire slots as guard time intervals and, if needed, the satellite's return link receiver(s) will be alerted to perform burst acquisition over a larger search window.
  • Fig. 7 A showing a block diagram of a communication terminal 100 (e.g. satellite communication terminal) according to an embodiment of the present invention.
  • the communication terminal 100 is configured and operable for wirelessly communicating, directly or indirectly, with a designated data gate-way station (not specifically shown) for exchanging data therewith view a forward-link communication channel FL, by which data is received by the terminal 100, and a returned-link communication channel RL by which data is transmitted from the terminal 100.
  • the communication terminal 100 is a satellite communication terminal, which is configured and operable for communicating indirectly with the data gateway, via a communication mediator being presented here for example as a transmission system/satellite 300, such as that described above, furnished on a satellite.
  • the communication terminal 100 is configured and operable for establishing the forward communication channel FL and possibly the return communication channels RL with the communication mediator 300 (which is without loss of generality also referred herein as satellite 300).
  • the communication mediator 300 is configured and operable for making efficient use of its communication resources (data bandwidth/rate). As indicated above, this may achieved according to some embodiments of the present invention by omitting dummy frames from the communication channel(s) and timely aggregating (bunching) together the data bearing communication frames (which carry meaningful data payloads) of one or more of channels which should be transmitted from the communication mediator 300 in a common beam. Accordingly, a certain number of data bearing communication frames pertaining to the channels of the beam are communicated sequentially, with practically no time gaps between them, and thereafter a prolonged recess time is introduced (instead of the dummy frames which are omitted), in which the beam's signal may not be transmitted, and the transmission may direct its resources for transmission of other beams.
  • the communication terminal 100 perceives a bursty communication from the communication mediator 300, which includes bursts in which a certain numbers of communication frames are transmitted from the transmission system, and prolonged recess times between them during the terminal may receive no signal from the satellite.
  • the terminal 100 includes communication receiver 200 which is configured and operable according to the present invention and adapted for efficiently receiving and processing signals received in a burst communication mode from the transmission system
  • the communication receiver 200 may be configured and operable for example according to any one of the examples illustrated in Fig. 8A discussed below, and is adapted for processing at least a portion of the beam's signal, which is received after the prolonged recess time periods during which the beam may have not being transmitted from the satellite, to determine a carrier frequency of the beam's signal.
  • the communication receiver 200 is adapted to determine the carrier frequency based on only single communication frame that appears in the portion of the beam's signal which is received after the prolonged recess time period.
  • the communication receiver 200 includes a Signal Acquisition module 201 configured and operable for detecting the communication burst, acquiring its signals (namely determine the carrier frequency of the respective beam) and locating the timings of the communication frames therein by processing a single communication frame (typically the first communication frame), and optionally by processing only the header of the single/first communication frame, which appears in the burst. This is achieved for example in the manner described below with reference to any one of Figs. 8A to 8C. This detection and time location of the first/single communication frames in the timely separated bursts enable the receiver to efficiently process and decode the data encoded in the communication frames of the burst while without requiring re-transmission of communication frames.
  • a Signal Acquisition module 201 configured and operable for detecting the communication burst, acquiring its signals (namely determine the carrier frequency of the respective beam) and locating the timings of the communication frames therein by processing a single communication frame (typically the first communication frame), and optionally by processing only the header of the single/first communication frame,
  • the communication terminal 100 also includes a scheduling module 130 that is configured and operable for determining the designated time intervals (e.g., the timing and duration) during which communication bursts of the beam's transmission from the satellite may expected to be received by the specific terminal 100 (and/or by other terminals in the same geographical coverage area of the beam). For instance, some of the data previously received by the terminal, may contain transmission/reception plan (e.g. conveyed to from the gateway) and indicative of respective transmission/reception times of different beams (e.g. in a multi-beam/beam-hopping systems), as well as time stamp information, which is an indication of the frame/beam transmission time as measured by a network clock (e.g.
  • the scheduling module 130 schedules the reception time intervals during which the receiver 200 should be operated to receive the bursts of the communication beam which is directed to its geographical area by the satellite.
  • the scheduling module 130 includes a forward link scheduler module 135 that is configured and operable to utilize the time interval data and assign a forward link schedule for receiving the beam's burst.
  • the forward link scheduler module 135 generates operative instructions/signals for activating the communication receiver module 110 of the terminal 100 for receiving the designated burst of the beam during the respective time interval.
  • the forward link scheduler module 135 is configured and operable for generating operative instructions/signals for deactivating the communication receiver 200 of the terminal 100 during one or more time slots at which the forward link is occupied by sub-frames that are designated to other terminals/terminal-groups. This may be for example used for reducing/suppressing noise and/or crosstalk between the received forward link signal and the transmitted return link signals.
  • the communication receiver 200 may be connectable to the scheduling module 130 and configured and operable to be responsive to operative instructions therefrom for performing signal receipt operation during the forward link schedule.
  • This communication receiver 200 thereby receives and processes the bursts of the beam designated to the terminal 100 and/or it geographical area, at the correct time intervals at which they are transmitted.
  • the communication receiver 200 may include a receiving channel (not specifically shown in Fig. 7A) configured and operable for applying preprocessing to the analogue signal received from the antenna 105 associated with the terminal.
  • the receiving channel may include any one or more of the following modules, which may be implemented as analogue and/or digital modules: signal mixers and/or down-converters (e.g. for applying frequency shift/transform to the signal, such as reducing the signal frequency to the baseband) and/or bandpass filters (e.g.
  • matched filter for applying bandpass filtration to the received signal
  • Analogue to Digital converter(s)/samplers for Sampling the analogue signal from the antenna 105 to convert it to digital form
  • VQ signal converters for processing the received signal to the complex VQ signal representation form
  • PLLs phased locking loops
  • the signal receiver 110 may also include a Forward Link Data Adapter 160, adapted for processing the received signal (e.g. after its preprocessing by the receiving channel) and extracting forward link data therefrom. More specifically, the Forward Link Data Adapter 160 may be configured and operable for implementing a certain communication protocol (e.g. DVB-S2 or DVB-S2X) and may be configured and operable for processing the received designated sub-frames, which are designated to the terminal 100, in order to determine, in accordance with such protocol, the header segments and data segments of the designated frames/sub-frames and extract the data therefrom accordingly.
  • a certain communication protocol e.g. DVB-S2 or DVB-S2X
  • each or one or more communication frame in the forward link includes sub-frames that are transmitted in the forward link from the satellite/mediator/gateway 300.
  • the communication terminal 100 is associated (e.g. registered in or belongs to) a certain group of one or more respective groups of communication terminals. For example a plurality of satellite terminals are divided in several groups).
  • each of the designated communication sub- frames of the complete communication frame is designated to specific one (or more) of the terminal groups.
  • the communication frame includes a certain designated sub-frame (being a respective portion of the full communication frame) which is specifically designated to be received by the terminal 100 (and possibly by additional member terminals of the group to which terminal 100 belongs).
  • the full communication frame in the forward link may include a plurality of N communication sub-frames designated to serve respective one or more groups of (satellite) communication terminals.
  • the scheduling module 130 may be configured and operable for determining the time slot (e.g., the timing and duration within the forward link communication frame that is transmitted by the satellite/mediator 300) of the designated communication sub-frame which is designated to be received by the specific terminal 100 (and/or by other members of his terminal group).
  • the Signal Acquisition module 200 detects and locates the start of the reception frame, as described below. This detection and location enables the receiver to process and decode the data.
  • Some of the received data may contain time stamp information, which is an indication of the frame transmission time as measured by the network clock located at the gateway. This information, also known as Network Clock Reference is standardized. Based on this time stamp information the scheduling module 130 schedules the transmission time slot according to the transmission plan conveyed to it by the gateway.
  • the timeslot of the designated sub-frame is a data parameter (e.g. configuration parameter) that is stored in a configuration memory section of the terminal 100.
  • the scheduling module 130 includes a forward link scheduler module 135 that is configured and operable for utilizing said time slot data and assign a forward link schedule for receiving the designated communication sub- frame at said time slot.
  • the forward link scheduler module 135 generates operative instructions/signals for activating the signal receiver module 110 of the terminal 100 for receiving the designated sub-frame during the respective time slot at which it should be communicated over the forward link communication channel.
  • the scheduling module 130 also includes a return link scheduler 132 that is configured and operable for assigning a return link schedule for transmitting information to the satellite during time slots other than the time slot of the designated communication sub-frame.
  • the return link scheduler 132 may be configured an operable for generating operative instructions/signals for activating the signal transmitting module 120 of the terminal 100 for transmitting return link data during one or more time slots at which the forward link is occupied by sub-frames that are designated to other terminals/terminal-groups.
  • the terminal 100 includes a signal transmitting module 120 and also optionally a return link data provider module 150 connectable to the scheduling module 130 and configured and operable to be responsive to operative instructions therefrom for performing signal transmit operations for transmitting return link data during the return link schedule.
  • the return link data provider module 150 may be configured and operable to prepare and provide the return link data that should be transmitted to the satellite and the signal transmitting module 120, may be configured and operable for encoding the returned link data on a signal to be transmitted (e.g. by properly modulating the signal to be transmitted according to a certain modulation scheme associated with a predetermined data transmission protocol) and thereby generate the transmitted signal that is to be transmitted by the antenna 105.
  • a person of ordinary skill in the art will readily appreciate how to appropriately configure signal transmitting module 120 and/or a return link data provider module 150 for generating transmission signals according to a predetermined protocol.
  • the forward link scheduler module 135 is configured and operable for generating operative instructions/signals for deactivating the signal receiver module 110 of the terminal 100 during one or more time slots at which the forward link is occupied by sub-frames that are designated to other terminals/terminal- groups.
  • the return link scheduler module 132 is configured and operable for generating operative instructions/signals for deactivating the signal transmitted module 110 of the terminal 100 during the respective time slot at which it the designated sub-frame is communicated over the forward link communication channel. This provides for reducing/suppressing noise and/or crosstalk between the received forward link signal and the transmitted return link signals and therefore improves the signal to noise ratio - thereby enabling improvement in the communication data rate of the system.
  • the terminal 100 may include a signal receiving module 110 connectable to the scheduling module 130 and configured and operable to be responsive to operative instructions therefrom for performing signal receipt operation during the forward link schedule(namely during the time slot of the designated sub-frame).
  • This signal receiving module 110 thereby receives and processes the designated sub-frame designated to the terminal 100 at the correct time slot of the communication frame transmitted in the forward link.
  • the signal receiver 110 may include a receiving channel (not specifically shown in Fig. 7A) configured and operable for applying preprocessing to the analogue signal received from the antenna 105 associated with the terminal.
  • the receiving channel may include any one or more of the following modules, which may be implemented as analogue and/or digital modules: signal mixers and/or down-converters (e.g. for applying frequency shift/transform to the signal, such as reducing the signal frequency to the baseband) and/or bandpath filters (e.g.
  • the signal receiver 110 may also include a Forward Link Data Adapter 160, adapted for receiving the received signal (e.g.
  • the Forward Link Data Adapter 160 may be configured and operable for implementing a certain communication protocol (e.g. DVB-S2 or DVB-S2X) and may be configured and operable for processing the received designated sub-frames, which are designated to the terminal 100, in order to determine, in accordance with such protocol, the header segments and data segments of the designated sub -frames and extract the data therefrom accordingly.
  • a certain communication protocol e.g. DVB-S2 or DVB-S2X
  • DVB-S2X DVB-S2X
  • Fig. 7B is diagram schematically illustrating in self- explanatory manner three possible frame structures of the DVB-S2X standard/protocol.
  • three frame types are illustrated: A regular frame, a very low signal-to- noise ratio noise frame (referred to as VL-SNR frame), and super frame.
  • the code words e.g. unique words referenced UW in Figs. 8B and 8C below
  • UW very low signal-to- noise ratio noise frame
  • a start of frame (SOF) which is a 26 symbols sequence.
  • a VL-SNR frame of the DVB-S2X protocol may include code word (UW) in the form of a VL-SNR header which contains 900 symbols (there could be different sequences of this code word).
  • UW code word
  • a super frame of the DVB-S2X protocol may include SOSF (Start Of Super- Frame) code word (UW) in which contains 270 symbols (there could be different sequences of this code word).
  • SOSF Start Of Super- Frame code word
  • the communication terminal is further configured and operable for establishing the return communication channel RL with the communication mediator (satellite transmission system) 300 for transmitting data back to the satellite.
  • the terminal 100 further includes a signal transmitting module 120 and a data provider module 150 configured and operable for transmitting return link data during the return link schedule.
  • the data provider module 150 may be configured and operable to prepare and provide the return link data that should be transmitted to the satellite and the signal transmitting module 120, may be configured and operable for encoding the returned link data on a signal to be transmitted by the antenna 105 (e.g. by properly modulating the signal to be transmitted according to a certain modulation scheme associated with a predetermined data transmission protocol) and thereby generate the transmitted signal that is to be transmitted by the antenna.
  • the scheduler module 130 is configured and operable for activating the communication receiver 200 at time intervals at which the designated communication bursts from the satellite's beam should be received by the terminal and possibly deactivating the receiver module 100 at other time slots (e.g. for instance in order to reduce cross-talk between the receipt/transmit channels and/or reduce other noises and/or save energy).
  • the terminal 100 is configured such that the signal transmitting module 120 and the signal receiving module 110 thereof are configured for operating at mutually exclusive time slots for transmitting and receiving the respective return and forward link signals.
  • the communication receiver 200 may lose (dis-acquire) the signal of the beam from the transmission system 100, in the senses that it losses synchronization/locking with the carrier frequency of the signal.
  • the carrier frequency locking module(s) of the signal receiving module 110 is/are not activated during return link schedule, thereby allowing a carrier frequency of said forward link to drift out of tune.
  • signal loss may occur for example in cases where the beam to be received by the terminal 100 is communicated in bursty communication mode (with recess times between the burst), and/or in cases where the communication receiver 200 is deactivated at certain time recesses.
  • signal loss may occur in implementations of the system, in which the receiver does not receive the signal for relatively long periods of time (e.g. due to sleep/deactivated periods of the receiver and/or beam hopping scenarios when the satellite transmits its energy to different areas (cells) at different times).
  • the carrier frequency locking module(s) of the signal receiving module 200 e.g. such as a phase lock loop, and/or other frequency tracking mechanisms implemented digitally
  • the carrier frequency locking module(s) of the signal receiving module 200 is/are not functionally capable/operable/activated for locking on to the signal's carrier, thereby allowing the carrier frequency to drift out of tune.
  • the forward link signal drifts significantly, and/or in case the synchronization signal (clock signal) of the receiver 110, drifts, upon activation of the receiver it might not immediately lock/find the forwards link signal. This is because such a drift may cause a discrepancy between the carrier frequency at to which the receiver is tuned and the actual carrier frequency over which data is encoded on the forward link signal.
  • sequential carrier frequency scanning immediately after activation the receiver 110, by sequentially tuning the receiver to different carrier frequencies in an attempt to identify the correct carrier frequency about which the forward link signal data is encoded.
  • sequential carrier frequency scanning is time consuming operation (particularly in cases where the communication frames carry large data payloads - since it the duration of a complete communication frame is required at each such scanning step in order to identify the header of the frame).
  • conventional communication receiver may not be able to immediately lock/find the forwards link signal. This is because such a drift may cause a discrepancy between the carrier frequency to which the receiver is tuned and the actual carrier frequency over which data is encoded on the forward link signal.
  • the communication terminal 100 (e.g. the signal receiving module 110 thereof) includes a novel communication receiver 200 including a signal acquisition system 201, which is configured and operable for processing time frame of the received (forward link) signal (signal burst) to simultaneously, at the same time/processing-stage/step, determine the carrier frequency of the signal burst out of a plurality of possible carrier frequencies.
  • the processed time frame portion of the signal/burst may be a portion of the signal extending not more than one communication frame, or not more than a header of such communication frame, and including one or more predetermined code words expected in the header.
  • the signal acquisition system 201 is configured and operable to simultaneously determine (e.g.
  • the novel communication receiver 200 (signal acquisition system 201) of the present invention enables simultaneous locking on the carrier frequency of the forward link signal and therefore facilitates fast acquisition of the signal.
  • the signal acquisition system 201 is configured for operating upon activation of the receiver for process at least a part of the communication frame received in the forward link (e.g. from the satellite/mediator 300) to lock on to the forward link signal (e.g. on to the exact frequency thereof).
  • This allows to immediately (with no delays) identify at least one code word in the received signal designating whether the received signals encompasses a designated sub-frame of interest, and determine a time index (sample position) at which said code word is encoded in the received signal (namely determining the initial/reference time/sample of the sub-frame of interest in the received signal and the carrier frequency over which data (e.g. code word) is encoded in the received signal.
  • the communication terminal 100 of the present invention can implement an efficient beam hopping technology Relying inter-cilia on the ability of the communication receiver 200 of the present invention to efficiently locking on the carrier frequencies of unknown/newly received signals in real time (namely within one/first communication frame).
  • This allows the satellite's transmission system 300 beam to hop from one group of terminal to the other, and cause discontinuity in the forward link of each terminal, while without the cost of time consuming signal acquisition (carrier frequency locking) at the times of reestablishment of the forward link signals to a particular terminal.
  • the scheduling module 130 is further configured and operable for generating a request for allocation of return link capacity in another beam or a different satellite, thereby when a terminal switches a beam or a satellite, it is able to immediately utilize the allocated capacity over the new (switched-to) beam or at the new satellite.
  • FIG. 8A to 8C there are illustrated in block diagrams several examples of signal acquisition system 201 which may be included in the communication receiver 200 according to various embodiments of the present invention.
  • the signal acquisition system 201 includes: an input module 210 configured and operable to obtain a received signal (e.g. electro -magnetic (EM), typically radio frequency (RF), signal) which encodes communicated data over a certain carrier frequency;
  • a received signal e.g. electro -magnetic (EM), typically radio frequency (RF), signal
  • EM electro -magnetic
  • RF radio frequency
  • a signal time frame processor 220 that is connectable to the input module and configured and operable for continuous processing (e.g. in real time) of time frame portions of the received signal to identify at least one code word of a group of one or more predetermined code words, being encoded in a time frame portion of the received signal;
  • an output module configured and operable for outputting identification data indicative of identification of said code word in the signal.
  • the acquisition engine/system 201 is a part of the receiver 110, the purpose of which is to acquire the received signal, namely detect the existence of a received signal and synchronize to the basic frame structure.
  • the receiver might to acquire the received signal in two, rather different circumstances:
  • Synchronization procedures mainly include carrier frequency correction, sampling timing correction, frame synchronization, equalization and fine phase correction.
  • burst receiving conditions are more of the signal loss type rather than cold start, but, depending on the off-time interval, oscillator's drift and instability and dynamic changes may require that the receiver performs re-acquisition.
  • the acquisition engine/system 201 is designed to achieve recovery from a signal loss within a single transmission frame. Possible applications may include: operation as a terminal receiver in a Frame by frame beam-hopping environment, and operation when dummy frames are omitted hence the resulting transmission is discontinuous.
  • the actually carrier frequency of the signal to be received may be unknown at the receiver end (e.g. due to frequency drift) and may actually reside anywhere within a certain, e.g. predetermined, frequency band in which frequency shift due to drifting can occur.
  • the actual carrier frequency can at any one of a plurality of possible carrier frequencies within this frequency band.
  • the signal time frame processor 220 is adapted to overcome this problem of the carrier frequency drifting, and configured and operable for applying real time processing of the received signal to identify in real time the whether any one or more code words are encoded in the received signal over any of the possible one or more carrier frequencies.
  • the signal time frame processor 220 includes a carrier frequency analyzer module 230 configured and operable for analyzing a time frame portion (or one or more time frame portions) of the received signal in conjunction, simultaneously, with the plurality of possible carrier frequencies of the received signal. More specifically the carrier frequency analyzer module 230 is configured and operable for transforming the time frame portion of the received signal to generate (simultaneously) carrier-data which includes a plurality of carrier-data- pieces associated with each possible carrier frequency of the plurality of possible carrier frequencies of the received signal, respectively.
  • each of the carrier-data pieces are indicative of data is decoded from the processed time frame portion by in case such a decoding was made by assuming one of the possible carrier frequencies the received signal might have had acquired.
  • each carrier-data piece is indicative of a "pseudo" data (meaningful or not) encoded in the time frame portion over certain assumed one of the possible carrier frequencies associated with said carrier-data piece.
  • the carrier frequency analyzer module 230 includes an array of signal frequency transformers, (e.g. implemented as digital or analogue signal mixers and/or frequency-shifters) fi ... f n which are configured and operable for applying difference respective frequency shifts fi- f n to the time frame portion of the received signal thereby respectively generate n carrier-data pieces associated with differently frequency shifts of the received signal. Even more specifically, these simultaneously generated carrier-data pieces are actually frequency shifted replicas of the processed time frame portion of the received signal having their carrier frequencies shifted by the different predetermined frequency shifts fi- f n respectively relative to the certain undetermined/unknown carrier frequency of the received signal. Accordingly in this case each carrier-data piece is indicative of a "pseudo" data (meaningful or not) encoded in the time frame portion over certain assumed one of the possible carrier frequencies associated with said carrier-data piece.
  • signal frequency transformers e.g. implemented as digital or analogue signal mixers and/or frequency-shifters
  • the carrier frequency analyzer module 230 includes a time to frequency transformation module, which transforms the convolution results of the time frame portion of the received signal with a certain code word which might have being encoded in the signal, and transforms these convolution results from the time domain to the frequency domain.
  • the time to frequency transformation may be implemented for example using Fourier transform (e.g. Fast Fourier Transform (FFT) and/or Discrete Fourier Transform (DFT)) and/or via any suitable time-frequency transform. Accordingly, a result of the transform is generally a series of bins in the frequency domain.
  • FFT Fast Fourier Transform
  • DFT Discrete Fourier Transform
  • the bins actually present carrier-data pieces whereby the intensity (magnitude) of each bin number is indicative of whether the specific code word used in the convolution is encoded in the time frame portion of the signal under the assumption of a certain one of the possible carrier frequencies (or in other words under the assumption that the received signal is shifted by one of the frequency shifts fi- f n associated with the particular bin.
  • the bins together present a plurality of carrier-data pieces indicative of the plurality of possible frequency shifts of the carrier frequency of the received signal.
  • the signal time frame processor 220 also includes a convolution module 240 configured and operable for processing the time frame portion of the signal to simultaneously identify whether the time frame portion encodes the at least one code word, over any one of the a plurality of possible carrier frequencies simultaneously.
  • a convolution module 240 configured and operable for processing the time frame portion of the signal to simultaneously identify whether the time frame portion encodes the at least one code word, over any one of the a plurality of possible carrier frequencies simultaneously.
  • the convolution module 240 includes a plurality of at least n correlator modules connectable/connected to the plurality of n signal mixers (frequency- transformers/shifter; e.g. to their output) and respectively configured and operable for simultaneously convolving the n plurality of n carrier-data pieces (e.g. which are in this case constituted by respectively differently frequency shifted signal portions) with a certain code word (or possibly with a plurality of m code words).
  • each convolved signal representation is indicative of whether the convolved code word is encoded in the time frame portion of the signal with a certain corresponding one of the carrier frequency shifts fi- f n .
  • the convolution module 240 precedes the frequency analyzer module 230 with reference to the direction of the signal processing flow by the system.
  • each symbol-convolved signal representation indicates of whether a respective symbol/constituent is encoded in the time-frame portion.
  • a frequency representation of the code word convolution with the time frame portion of the received signal is obtained.
  • the frequency representation actually presents carrier data and includes a plurality of bins presenting carrier data portions indicating whether the code word and at which carrier frequency the code word is encoded in the time frame portion of the received signal.
  • the intensity of each bin numbers indicates whether the code word is actually encoded in the time frame portion of the received signal and a particular carrier frequency associated with the location of the bin in the frequency representation.
  • the carrier frequency of the received signal can be determined from the bin location in the frequency representation and the code word is identified as encoded over that carrier frequency in the respective time frame portion of the received signal.
  • the time frame processor 220 is adapted to determine a time index of code word in the received signal, based on the time frame portion of the received signal at which the code word is identified. Accordingly the output module may be further adapted to output this time index data, as this time index data actually designates/indicate a reference/initial location of a communicating data frame communicated over the received/forward link signal.
  • time frame processor 220 is adapted to process carrier data to identify the carrier-data piece which encodes significant data and thereby determines the carrier frequency of the received signal.
  • the output module 250 is further adapted to output said determined carrier frequency.
  • the carrier frequency analyzer module 230 of the signal acquisition system includes a plurality of n signal mixers/shifters (transformers) Afi-Af n configured an operable for simultaneously processing the received signal.
  • the signal mixers are adapted to apply a plurality of n respectively different predetermined frequency shifts to the received signals and thereby generate a plurality of n respectively different frequency shifted signals having their carrier frequencies shifted by said different predetermined frequency shifts relative to the certain undetermined carrier frequency of the received signal.
  • the convolution module 240 includes a plurality of at least n correlator modules connectable to the plurality of n signal mixers Afi-Af n respectively and configured and operable for simultaneously convolving the plurality of frequency shifted signals respectively with the code word, to thereby concurrently generate n convolved signal representations indicative of whether the code words is encoded in said the corresponding frequency shifted signals.
  • Fig. 8B depicts, in a self-explanatory manner, the operational principles of the signal acquisition system 201. It relies on a priori known information (UW - Unique/code Word) transmitted by the transmitter within the transmitter frame.
  • UW UW - Unique/code Word
  • the received signal at the output of the optionally provided matched filter of the receiving path is frequency shifted and then correlated with several possible unique/code words UW.
  • the output/comparator module 250 is used to determine the start of frame based on the convolved signal representations (representing the correlations with the frequency shifts). To this end, the maximal absolute value of the correlation among all possible frequency shifts is tested and compared to a threshold value, and the timing when this threshold is passed determines the start of frame (time index).
  • the convolution module 240 includes a plurality of at least nXm correlator modules, for simultaneously testing whether any one of number m (integer) of code words UW is encoded in the received signal (in the time frame portion thereof).
  • each group of m correlator modules is connectable to a respective one signal mixer of the n signal mixers Afi-Af n and configured for simultaneously convolving a respective frequency shifted signal obtained by the respective one signal mixer with up to m code words simultaneously.
  • the convolution module thus generates up to nXm convolved signal representations indicative of whether any one of the m code words is encoded in any one of the n frequency shifted signals respectively.
  • the output module may include a code word identification module adapted for comparing nXm convolved signal representations with predetermined criteria and thereby to determine whether any code word is encoded in the frequency shifted signal corresponding to the convolved signal representation.
  • the first word convolution stage S (1> further includes a plurality of kf 2> symbol convolution modules (e.g. signal multipliers).
  • Each symbol convolution module is connectable to a respective delay module of the plurality of delay modules, for receiving therefrom a corresponding time delayed signal, which is generated thereby, and is connectable to the code word provision module (shift register) for receiving corresponding symbol/constituent hi of the kf 2> symbol constituents whose location in the code word UW corresponds to the respective time delay of the time delayed signal of the respective delay module D. Also, each symbol convolution module is configured and operable for convolving the time delayed signal with the corresponding symbol/constituent to generate a respective symbol-convolved signal representations indicative of whether said symbol constituent is encoded in the corresponding time delayed signal.
  • the kf 2> symbol convolution modules generate kf 2> symbol-convolved signal representations indicative of whether the kf 2> symbol constituents of the code word are encoded in a timely order in the received signal.
  • the first stage S (1) yields n symbol-convolved signal representations.
  • the signal acquisition system 201 also includes the carrier frequency analyzer module 230 including a time to frequency transformation module (e.g. FFT or DFT) adapted for receiving the kf 2> symbol-convolved signal representations from the code word convolution module 240 and applying time to frequency transformation thereto to obtain a frequency based representation of the n symbol-convolved signal representations.
  • a time to frequency transformation module e.g. FFT or DFT
  • the input signal can be described as:
  • h n is the known symbol value of the UW
  • N is the number of symbols within the UW.
  • T s is the symbol time (1/Symbol rate) in seconds, no is the actual delay of the received signal.
  • the operation performed by the acquisition module is then:
  • the input signal is corrected by a frequency shift Af k and then correlated with the UW. If the frequency Af k shift equals that of the actual error, the result is the actual correlation between the received signal and the UW, which will peak at no.
  • Fig. 8C The actual implementation is exemplified in Fig. 8C, in which the correlation to a given UW (of which the symbols are described as hi) is performed first, and the hypotheses of the possible frequencies of the carrier signal are tested via DFT / FFT.
  • a selector module 245 is optionally used which is configured to selectively operate the time to frequency transformation module FFT based on the symbol-convolved signal representations obtained from a selected stage / of the set of stages. Accordingly, the frequency transformation module FFT transforms solely the kf 2> symbol-convolved of the selected one of the convolution stages thereby enabling controllable adjustment of processing power requirements and accuracy of identification of the code word in the received signal.
  • a peak in the frequency based representation indicates that the code word UW is encoded in the received signal.
  • the location of the peak in the frequency based representation indicates a shift of the carrier frequency of the received signal; and the intensity (absolute magnitude) of this peak indicates significance level of the code word being encoded in the received signal (in the processed time frame portion thereof).
  • the output module comprises a code word identification module may include a comparison module adapted for comparing said the peak intensity with a predetermined criteria and thereby determine whether the code word is encoded in the received signal.
  • the signal acquisition system 201 is configured an operable for concurrently determining whether any one of a plurality of m>l different code-words is encoded in the received signal.
  • the signal acquisition system 201 may for example include a plurality of at least m word convolution modules 240 similar to those described above, or additional one or more time frame signal processors 220' for processing different respective code words.
  • the signal acquisition system 201 configured as in any of the above described examples of Figs. 7 A and 8A-8C, may be configured as a digital signal processing chip (system on chip) or part of a system on a chip.
  • the input module may be associated with signal receiving channel connectable to an antenna module and including at least an analogue to digital converter adapted to sample an analogue signal from the antenna module and generate the received signal in digital form.
  • the input module may be adapted to extract the time frames portions from the received signal as successive time frame portions of predetermined length successively shifted from one another by at least one signal sample.
  • the signal acquisition system as described above may be configured and operable to process the received signal to identify the at least one code word encoded in the signal and determine a time index (sample position) and whether the code word is encoded in the received signal and a carrier frequency over which the code word is encoded in the received signal.
  • the signal acquisition system 201 and/or the entire communication receiver 200 described above can be implemented in the chip as H/W accelerator for the DSP, e.g. on the same chip of the DSP.
  • time synchronization may be performed in a hierarchal manner. This may, for example, be implemented as follows:
  • the signal, a communication frame thereof, is generally composed as a sequence of symbols. Considering for example the case of DVB-S2X, a symbol time can vary between 2nsec (500Msymbols per second) to 1 microsec (1M sps). Symbols are ordered in communication frames. In DVB-S2X frames are between 3000 to 35000 symbols, which translates to 6 microsec to 35msec.
  • Frames can be organized as superframes containing about 600000 symbols. A superframe size may then be between 1.2msec to 600msec. Frames or superframe transmission times are therefore an integer multiple of the above.
  • the acquisition engine/system 200 described above provides synchronization at a frame level. Symbol level synchronization can be performed at the modem itself using known algorithms (Gardner). Standardized methods (GPS, IEEE 1588 and Network Clock Reference (NCR) provide means to synchronize transmission times.
  • each of the verbs, "comprise” “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Radio Relay Systems (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

La présente invention concerne une technologie de communication (systèmes émetteur et récepteur) servant à communiquer des données de l'émetteur à un ou plusieurs récepteurs de terminaux sur un ou plusieurs canaux de communication. Le canal de communication est transmis dans un mode de communication par rafales de sorte qu'un signal de transmission comprend des intervalles de temps de données de transmission auxquels une ou plusieurs desdites trames de communication sont codées dans le signal et un ou plusieurs intervalles de temps d'inactivité entre eux. Le récepteur de communication est adapté pour traiter des signaux du canal de communication en mode rafale et peut être utilisé pour traiter au moins une partie d'un signal reçu dans le canal de communication après une période de temps d'inactivité durant laquelle des trames de communication n'ont pas été transmises afin de déterminer une fréquence porteuse du canal de communication, sur la base d'une seule trame de communication apparaissant dans le canal de communication après la période de temps d'inactivité.
EP17872022.3A 2016-11-17 2017-11-16 Procédé et système pour une communication par satellite Withdrawn EP3542469A4 (fr)

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US15/354,913 US10368327B2 (en) 2014-05-14 2016-11-17 Method and system for signal communications
US15/361,281 US10033509B2 (en) 2014-05-20 2016-11-25 Method and system for satellite communication
PCT/IL2017/051247 WO2018092132A1 (fr) 2016-11-17 2017-11-16 Procédé et système pour une communication par satellite

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IL266379A (en) 2019-06-30
WO2018092132A1 (fr) 2018-05-24
CN110121845A (zh) 2019-08-13
IL266379B (en) 2022-02-01

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