EP3827528A1 - Reliable channel state information in multi-beam satellite communications - Google Patents
Reliable channel state information in multi-beam satellite communicationsInfo
- Publication number
- EP3827528A1 EP3827528A1 EP19742230.6A EP19742230A EP3827528A1 EP 3827528 A1 EP3827528 A1 EP 3827528A1 EP 19742230 A EP19742230 A EP 19742230A EP 3827528 A1 EP3827528 A1 EP 3827528A1
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- fields
- signal
- receiver
- waveform
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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
- H04B7/204—Multiple access
- H04B7/2041—Spot beam 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
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/18578—Satellite systems for providing broadband data service to individual earth stations
Definitions
- the invention lies in the field of satellite communication systems, and relates in particular to a method and device for providing reliable channel state information for a plurality of carriers in a multi-beam satellite communication system relying on aggressive frequency reuse among its available carriers.
- Communication satellites have evolved to provide broadband data transfer from a transmitting ground station via the satellite to a geographical area on the ground, which is defined by the area covered by the satellite’s transmission beam.
- Multibeam architectures have been proposed, in which information is simultaneously transmitted to a plurality of spot beams on the ground.
- the first subset of beams is not transmitting, and a second subset of beams, preferably serving a second set of ground spots, transmits at the same frequency.
- This approach allows to flexibly allocate scarce on-board resources over the service coverage.
- precoding takes the estimated interference levels into account, which the signal that is to be transmitted on a beam is likely to suffer. If, during transmission of the signal, the signal is indeed subject to the estimated interference, the precoding allows for a high probability of correct detection of the signal at a receiver located within the corresponding ground spot.
- the channel state information that is estimated by the receivers and made available at the transmitter or at the gateway where the precoding step if performed, must be as reliable as possible. The more accurate the available channel state information is, the more efficient the quality of the received signal using precoding will be.
- any system using precoding benefits from accurate and reliable channel state information.
- Patent document WO 2015/192995 Al describes a method for synchronization and channel estimation in a DVB-S2x system (see ETSI EN 302 307-2 DVB“ Second Generation framing structure, channel coding and modulation systems for Broadcasting, interactive Services, news gathering and other broadband satellite applications, Part II: S2-Extensions”, www.etsi.org).
- a complete chain for precoding is described and the method is designed to work even for asynchronous co-channel carriers.
- it has the drawback of detecting the interference carriers as a first step, when signals are not synchronized and, as a consequence, most of the impairments are not compensated. Aside from being computationally expensive, this considerably limits the possibility of detecting carrier at very low signal-to-noise plus interference ratios.
- a known sequence-based detection method is proposed for the detection of the adjacent co-channel carriers, which occurs in the presence of strong timing/phase impairments.
- a method for generating reliable channel state information in a wireless multi-user multiple input single output, MISO, satellite communication system employing precoding comprises the following steps:
- each frame unit comprises a first field that is not subjected to precoding and that indicates a start of the respective frame unit and at least one second field that is not subjected to the precoding, said second field comprising a pilot sequence;
- phase values of said plurality of second fields determining phase values of said plurality of second fields; d) if the standard deviation of said plurality of phase values is lower than a predetermined threshold value, generating a reliable channel coefficient corresponding to the waveform component based on the determined phase values, otherwise, discarding the phase values as being unreliable.
- a method for generating reliable channel state information in a wireless multi-user MISO satellite communication system employing precoding comprises the following steps:
- a) at a receiver receiving a signal from a satellite, the signal comprising a plurality of
- each waveform component being subdivided into frame units, wherein each frame unit comprises a first field that is not subjected to precoding and that indicates a start of the respective frame unit and a plurality of second fields that are not subjected to the precoding, each of said second fields comprising a pilot sequence;
- the predetermined threshold value may be p/2.
- the threshold may be selected as a function of the carrier noise levels.
- step b) may further comprise :
- step c) may further comprise: cl) at the receiver, determining the absolute phase values of said pilot sequences comprised in said plurality of second fields in the frame unit of the re-sampled reference waveform component.
- step b) may further preferably comprise a step of applying a matched filter on said received signal in order to increase the signal-to-noise ratio SNR.
- the matched filter may be determines based on the estimated frequency of the references waveform component.
- step c) may further comprise determining a phase offset value for said second fields of said the waveform component, relative to the phase value of said reference waveform component.
- the received signal may have been transmitted from a multi-beam satellite using aggressive full frequency reuse, wherein each beam serves a different ground spot.
- said reference waveform may have said receiver as its destination, while said remaining waveform components may have receivers located in different ground spots as their respective destinations.
- Said phase offset value may preferably be determined based on an average value of said phase values determined for the plurality of said second fields of said waveform component.
- the offset value may preferably be determined with respect to an average of the absolute phase values that are determined for said second fields of said reference waveform component.
- Said determination of phase values may preferably be made based on the second fields within one frame unit of a waveform component.
- said determination of phase values may preferably be made based on the second fields within a plurality of subsequent frame units of a waveform component.
- information identifying said first and second fields of said waveform components is pre-provided at the receiver.
- said waveform components of the received signal are substantially synchronized in time with respect to each other.
- said waveform components of the received signal are synchronized in time with respect to each other.
- the method may preferably comprise a subsequent step of transmitting said reliable channel coefficient using a data communication channel to a transmission gateway of said satellite communication system.
- a device for generating reliable channel state information in a wireless multi-user MISO satellite communication system employing precoding comprises signal receiving means, for example an antenna for receiving satellite transmitted signals and/or a wireless receiving interface, signal processing means, for example a signal processor, and a memory element, for example a random-access memory, RAM, device, a Hard Disk, a solid-state drive, SDD, or other data storage devices.
- signal receiving means for example an antenna for receiving satellite transmitted signals and/or a wireless receiving interface
- signal processing means for example a signal processor
- a memory element for example a random-access memory, RAM, device, a Hard Disk, a solid-state drive, SDD, or other data storage devices.
- the receiving means are configured for receiving a signal from a satellite, the signal comprising a plurality of waveform components, each waveform component being subdivided into frame units, wherein each frame unit comprises a first field that is not subjected to precoding and that indicates a start of the respective frame unit and a plurality of second fields, each of said second fields comprising a pilot sequence, and wherein the signal processing means are configured for
- the signal processing means are further configured to perform the method in accordance with aspects of the invention.
- a computer program comprising computer readable code means is provided, which when run on a computer, causes the computer to carry out the method according to aspects of the invention.
- a computer program product comprising a computer-readable medium on which the computer program according to the previous aspect of the invention is stored.
- aspects of the present invention allow for providing reliable channel state information, CSI, in scenarios where a receiver obtains a signal that comprising multiple waveforms: a reference waveform, the destination of which is the receiver at hand, and a plurality of interfering waveforms, having other receivers as their intended destination.
- a receiver obtains a signal that comprising multiple waveforms: a reference waveform, the destination of which is the receiver at hand, and a plurality of interfering waveforms, having other receivers as their intended destination.
- This is typically the case in signals transmitted via broadband satellites using full frequency reuse among a plurality of satellite beams, each beam serving different ground spots.
- the receiver is able to estimate the reliability of the computed channel state information for the reference channel as well as for the interfering channels. This reliability indicator substitutes the detection and verification procedure over interferer carriers. Only if the reliability is estimated to be sufficiently high, the channel state information is eventually provided o the transmitter gateway for further use, for example as input to a precoding step.
- Embodiments of the present invention allow to reliably estimate co-channel carriers with very low signal to noise plus interference ratio. As a consequence, precoding gain in terms of throughput are larger and the degradation due to non-perfect CSI is smaller as compared to known solutions.
- the reference signal when a signal including a reference signal and interferer signals is received, the reference signal only is synchronized and as a consequence, the complexity of the receiver for the synchronization part is reduced compared to known solutions.
- coherent accumulation pilots and correct estimation of the channel coefficients becomes feasible.
- the procedure facilitate the phase compensation of the precoded fields since, by reporting the phase difference, the phase of the precoded and the not precoded fields become the same.
- figure 1 provides a workflow diagram illustrating the main steps of a method in accordance with a preferred embodiment of the invention
- figure 2a provides a schematic view of a communication system in which a method in accordance with a preferred embodiment of the invention may be put to use;
- figure 2b provides an illustration of the structure of various components comprised in a received signal, in accordance with an embodiment of the invention
- figure 3 provides a schematic view of steps involved in implementing a method in accordance with a preferred embodiment of the invention.
- the proposed method assumes a broadband multi-beam satellite system where each i-th beam has an associated area of coverage or ground spot, and an associated signature in terms of pilot sequences. While the invention is not limited to such systems, it finds particular use in a system having a structure and using transmission signals as defined in Annex E, format 2 and 3 of the DVB-S2x specification, which is hereby incorporated by reference in its entirety: ETSI EN 302 307-2 DVB“ Second Generation framing structure, channel coding and modulation systems for Broadcasting, interactive Services, news gathering and other broadband satellite applications, Part II: S2 -Extensions" , www.etsi.org. The multiple carriers are supposed to be aligned in time.
- Figure 1 illustrates the main steps of a method according to a preferred embodiment of the invention.
- the method aims at generating reliable channel state information, CSI, in a wireless multi-user MISO satellite communication system employing precoding.
- CSI channel state information
- a plurality of signals 1, ... , N beam is generated at one or at a plurality of gateway stations 10 in the communication system, which relay the signals to a broadband multi-beam satellite 20.
- Each of the signals is due to be transmitted on one of the N beam beams the satellite is forming, and serves receivers located within a corresponding ground spot, covered by said beam.
- three beams are represented, but the invention extends of course to a different plurality of beams, for example up to tens or hundreds of beams.
- Beam 1 serves receivers in the first ground spot, such as receiver 100
- beam 2 serves receivers 100(2)
- beam i serves receivers l00(i), and so on.
- the satellite may for example use aggressive frequency reuse on all its beams, so that the signal actually received by a receiver suffers from both spatial and co-channel interference.
- the signal 110 received at receiver 100 not only comprises the reference waveform component 1 that it wants to decode, but it also comprises interference from waveform components 2, .. i, ... N beam , that are transmitted on the same channel frequency.
- the gateways 10 use a precoding technique. Precoding is as such known in the art and will not be explained in details in the context of the present invention. Details may for example be found in patent document WO 2015/192995 Al, which is hereby incorporated by reference in its entirety. In order to form the adequate precoding matrix that is multiplying the data signals formed at the gateways, the latter have to know channel state information describing the behaviour of each one the communication channels formed by each of the satellite’s beams, as observed by the respective receivers.
- each of the waveform components 1, 2, ..., i, ..., N beam comprises a first field Start(l), Start(i), ... that marks the start of a frame unit within the waveform component.
- each waveform component comprises a sequence of second fields, or pilot fields Pil(l), Pil(i), ..., that comprise respective pilot sequences.
- the signal 110 comprising the plurality of waveform components is received at the receiver 100, for which only the reference waveform component 1 is intended.
- the signal also comprises a data payload, which will however not be described in the context of the present invention.
- the start of the frame unit and of the pilot sequences are determined.
- the locations of the ground spots are static and the receiver 110 knows the
- the phase values of the pilot sequences are determined, and at step d), the reliability of the estimated values is evaluated. Only if he phase values are deemed to be reliable, the corresponding channel state coefficient for the selected waveform component (corresponding to one of the beam channels) is generated, and eventually fed back 120 to the gateway(s) 10, either via a terrestrial or a satellite communication channel.
- the receiver 100 estimates a frequency value, time-synchronizes the waveform component and resamples it to obtain a re-sampled waveform component only for the reference waveform component 1, which was intended for reception by receiver 100.
- the absolute phase values of the pilot sequences in the frame unit of the re-sampled waveform component are determined.
- Frequency misalignments amongst carriers/beams can in practice be mitigated through the use of an Ultra Stable Oscillator on the payload of the satellite, which drives all the downconverters. If the payload cannot incorporate it, a frequency calibration procedure, similar to the one used for timing, can be performed through dedicated terminals, see for example S. Andrenacci et al,
- timing misalignments amongst carriers are effective only for large baudrates of carriers.
- a pre-compensation procedure shall preferably be used to limit the degradation effects on both the channel estimations and the precoding gains.
- the reliability test at step d) relies on the finding that when a co-channel carrier is present in the received signal, the phase estimation on successive pilot fields should yield a value which has a small standard deviation window, while on the other hand, when the signal is not present, the phase estimation should vary randomly between p and ⁇ p. According to these considerations, a coefficient is classified as being reliable (and, as a consequence, the corresponding carrier is detected at receiver 100) if the standard deviation of the estimated phase is below a certain predetermined value, for example but not limited to p/2.
- the phase values are determined as offset values with respect to the absolute phase value that has been determined for the reference waveform 1.
- the offset value is for example computed by computing the difference between the average of the reference waveform component’s sequence of pilot field phase values, and the average of an interfering waveform component’s sequence of pilot field phase values.
- each beam is defined by its own signature (in a frequency-reuse fashion for large systems since the number of Walsh-Hadamard sequences is limited) and since the beams are fixed (in terms of coverage over the earth), the receiver shall know the signature of the neighbour beams and it should try to estimate ideally all of them.
- all SF-Pilot fields in a superframe should be used (for example, in format 2 of DVB-S2x,
- step d) in accordance with embodiments with the invention is provided.
- a 3 ⁇ 4eam where N p u is the number of pilot sequences (second field) in one frame (or alternatively, the number of pilot sequences contained in the desired length to be considered for the procedure) and L pil is the length of the SF- Pilot for which orthogonality is maintained for up to beams.
- r® be the received and compensated signal (based on the reference signal) of the k-th receiver in the i-th beam, before the CSI estimation procedure, as; where ⁇ h kn ⁇ is the amplitude of the channel coefficient from the n-th antenna to the k-th user terminal, is the phase of the channel from the n-th antenna to the k-th user terminal or receiver, 9 k is the phase of the reference signal of the k-th user, x n is the transmitted signal from the n-th antenna, which can be precoded or not precoded depending on the index of the symbol according to the DVB-S2x specification.
- the received signal is given by the superposition of co-channel carriers, each of them coming from the n-th antenna. Since in one frame (for example the superframe duration) there are more pilots.
- an estimated coefficient is defined as reliable, and as a consequence correctly detected, if:
- N a ⁇ N pi J 20 is the number of pilots coherently accumulated inside the frame according to: arg ( ⁇ r ⁇ k (p)c * /L pil );
- CSI coefficients can be also calculated accordingly:
- the estimation through pilot symbols for interferer carriers shall be almost coherent, so that the gaussian noise is almost completely mitigated thanks to the coherent accumulation over various pilot fields.
- the reference signal is used to estimate the frequency/phase noise errors and then the tracking can be applied on the interferer carriers to compensate for frequency errors.
- the procedure assumes the interferer carriers to be synchronous in frequency amongst beams. If the frequency coherence cannot be guarantee, a pre-compensation procedure similar to the one used for synchronize the timing misalignments is needed.
- FIG. 3 illustrates how the method that has been described is implemented in particularly preferred embodiment of the invention.
- the receiver 200 implements the following steps:
- coarse frequency acquisition 250, by means of frequency estimation algorithm: while the use of the quadricorrelator is one option, any coarse carrier frequency offset algorithm can be used.
- the aim is to reduce the frequency uncertainty and, as a consequence, increase the coherence window for the start of superframe detection procedure;
- a matched filtering, 251 through a Square Root Raised Cosine, SRRC, filter as specified in the DVB-S2x specification;
- a start of superframe detection of the reference signal only, 252, through its own signature a start of superframe detection of the reference signal only, 252, through its own signature.
- the start of superframe detection depending on the considered Baudrate of the signal, can make use of the post detection integration procedure to account for the residual frequency offset.
- the start of superframe detection provides also a coarse timing synchronization in terms of samples, to be used to find the positions of the different fields; a timing synchronization for the reference signal only, 253, based on the known signature.
- a modified Early Late Gate working on the correlation function instead of the received waveform can be used.
- the timing estimation drives the re-sampling procedure through interpolation, 254;
- a channel state information estimation for each cannel coefficient, 257 the estimation is based on the synchronization with the reference signal only for frequency, timing and phase. Only the phase difference between the i-th carrier and the reference signal is reported. Using this procedure, an almost coherent accumulation over pilot fields can be implemented, which drastically reduce the bias of the estimation when low signal to noise plus interference carriers are considered;
- a detection of the channel state coefficient through evaluation of the reliability of the estimate, 258 the procedure is mandatory to decide whether the estimated coefficient comes from a carrier or not.
- the receiver 200 comprises a frequency acquisition unit 250 (a frequency estimation unit), a matched filter 251 (a matched filter unit), one frame synchronization unit 252, one symbol re-sampling unit 254 (resampling units), one demultiplexer (demultiplexer units), one time recovery unit 253 (time offset determination units), and a decoding unit for the reference waveform 260 comprising an SN1R estimation unit.
- the receiver further comprises a fine frequency tracking unit and phase noise tracking unit 256, a channel estimation unit 257 as well as a reliability test/detection unit 258.
- This method relates to estimating a channel (channel state vector, channel vector) between a transmitter and a receiver, the transmitter wirelessly transmitting a plurality of first signals in a plurality of beams through a plurality of transmit feeds in accordance with a weighting procedure (precoding), wherein each of the plurality of first signals is subdivided into frame units (e.g. super- frames) each having a first field that is not subjected to the weighting (precoding) and that indicates a start of the respective frame unit (i.e.
- the receiver receiving a second signal resulting from transmission of the plurality of first signals through the plurality of transmit feeds in accordance with the weighting procedure and subsequent interference at the receiver location, wherein the second signal comprises a waveform component for each of the plurality of transmit feeds.
- this method relates to estimating a channel vector (channel state vector) in a wireless MISO (satellite) communication system employing precoding, wherein a receiver receives a signal comprising a plurality of waveform components, each waveform component being subdivided into frame units, wherein each frame unit has a first field that is not subjected to precoding and that indicates a start of the respective frame unit and one or more second fields and that each comprise a predetermined pilot sequence ln a preferred embodiment, the frame unit comprises two or more second fields, and the steps described below are applied to said two or more second fields.
- the signal After reception of the signal, the signal is sampled in a sampling unit (not shown in Fig.3) to obtain a sequence of samples corresponding to the received signal.
- a first frequency estimation (coarse frequency estimation) of the carrier frequency of the received signal is performed.
- the coarse frequency estimation may be performed for instance by the algorithm proposed in Kim et al. in "Robust frame synchronization for the DVB-S2 system with large frequency offsets," lnt. J. Satell. Commun. Network., vol. 27, no. 1, pp. 35-52, 2009, which is hereby incorporated by reference.
- Frame synchronization is performed by searching the received signal for the known sequences of symbols (codewords) indicating the start of the super-frames (frame units) in the respective beams (i.e. respective waveform components) ln other words, a start of a frame unit of a waveform component, e.g. waveform component m, is determined by searching (using a correlator), in the received signal, for a first field indicating the start of the respective frame unit.
- the received signal contains, in each waveform component, first fields indicating the starts of respective frame units, wherein the first fields in different waveform components are mutually orthogonal.
- the start of a frame unit in a given waveform component can be determined by correlating the received signal with a known codeword corresponding to the content of the first field of the frame units of the given waveform component.
- Demultiplexing is performed for the reference waveform component in order to separate the start of the super-frame (SoSF, i.e. a first field indicating a start of the frame unit), the pilots (i.e. one or more second fields each indicating (comprising) non-precoded pilot sequences), the precoded pilots (PLH and P2, i.e.
- the first, second and third fields as well as actual data (fourth field) can be separated and extracted.
- the first field and the one or more second fields are separated (extracted) from the received signal on the basis of the determined start of the frame unit and a known (predetermined) structure of the frame unit. This step is performed in the illustrated demultiplexer.
- Data aided time tracking and resampling is performed on the basis of the SoSF and precoded pilots of the reference waveform.
- a time offset of the waveform component is determined by referring to the first field and the one or more second fields.
- this step relates to (data aided) determining a time offset of the waveform component by referring to the first field in the frame unit and the one or more second fields in the frame unit.
- this is achieved by correlating the demultiplexed waveform component with a known codeword corresponding to the content of the first field and known codewords corresponding to the contents of the one or more second fields, respectively, e.g. using a (pilot-aided) early/late gate.
- the reference waveform component is resampled on the basis of the determined time offset, whereby the time offset is eliminated from the resampled waveform component, i.e. the frame units in the reference waveform component are aligned with a local clock of the receiver 200.
- This step is performed in the symbol re-sampling and time recovery units 253, 254.
- Frequency and phase tracking on precoded pilots of the reference waveform component is performed.
- This step relates to (data-aided) determining a frequency offset and a phase offset of the re-sampled waveform component by referring to the one or more second fields in the frame unit.
- the known codewords corresponding to the contents of the one or more second fields are compared to the one or more second fields in the frame unit (same for the one or more third fields, if applicable), and the frequency offset and phase offset are determined on the basis of the comparison.
- Channel estimation is performed on the basis of the non-precoded or precoded pilots (i.e. the one or more second fields) for each waveform component, wherein the estimated channel is to be sent back to the gateway only if it is deemed to be reliable, as it has been described in the context of the previous embodiments.
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Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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LU100879A LU100879B1 (en) | 2018-07-25 | 2018-07-25 | Reliable channel state information in multi-beam satellite communications |
PCT/EP2019/070018 WO2020021001A1 (en) | 2018-07-25 | 2019-07-25 | Reliable channel state information in multi-beam satellite communications |
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EP3827528A1 true EP3827528A1 (en) | 2021-06-02 |
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EP19742230.6A Withdrawn EP3827528A1 (en) | 2018-07-25 | 2019-07-25 | Reliable channel state information in multi-beam satellite communications |
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EP (1) | EP3827528A1 (en) |
LU (1) | LU100879B1 (en) |
WO (1) | WO2020021001A1 (en) |
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WO2007084681A1 (en) * | 2006-01-20 | 2007-07-26 | Atc Technologies, Llc | Systems and methods for satellite forward link transmit diversity using orthogonal space coding |
EP2958249B1 (en) | 2014-06-18 | 2017-10-25 | European Space Agency | Joint transmitter signal processing in multi-beam satellite systems |
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- 2018-07-25 LU LU100879A patent/LU100879B1/en active IP Right Grant
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2019
- 2019-07-25 WO PCT/EP2019/070018 patent/WO2020021001A1/en active Application Filing
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