WO2009157833A1 - Codage spatio-temporel - Google Patents

Codage spatio-temporel Download PDF

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Publication number
WO2009157833A1
WO2009157833A1 PCT/SE2008/050786 SE2008050786W WO2009157833A1 WO 2009157833 A1 WO2009157833 A1 WO 2009157833A1 SE 2008050786 W SE2008050786 W SE 2008050786W WO 2009157833 A1 WO2009157833 A1 WO 2009157833A1
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WIPO (PCT)
Prior art keywords
space time
data element
coded data
time coded
transmitting
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PCT/SE2008/050786
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English (en)
Inventor
Peter Larsson
Jawad Manssour
Afif Osseiran
Slimane Ben Slimane
Original Assignee
Telefonaktiebolaget L M Ericsson (Publ)
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.)
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Application filed by Telefonaktiebolaget L M Ericsson (Publ) filed Critical Telefonaktiebolaget L M Ericsson (Publ)
Priority to PCT/SE2008/050786 priority Critical patent/WO2009157833A1/fr
Publication of WO2009157833A1 publication Critical patent/WO2009157833A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
    • H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
    • H04L1/0618—Space-time coding
    • H04L1/0637—Properties of the code
    • H04L1/0643—Properties of the code block codes

Definitions

  • the present invention generally relates to data communication and in particular such communication utilizing space time coding.
  • a main striving force in the development of wireless and cellular communication networks and systems is to provide, apart from many other aspects, increased coverage or support of higher data rate, or a combination of both. Further, the cost aspect of building and maintaining the system has been of great importance and is expected to become even more so in the future.
  • the main topology of wireless communication systems has been fairly unchanged, including the three existing generations of cellular networks.
  • the topology of existing wireless communication systems is characterized by the cellular architecture with the fixed radio base stations and the mobile stations as the only transmitting and receiving entities in the networks typically involved in a communication session.
  • MIMO Multiple-Input Multiple-Output
  • STC Space-Time Coding
  • S 1 and s 2 are two data symbols and * denotes complex conjugate.
  • a two-transmit antenna Alamouti system is the only STC system that today can achieve a code rate of one as other STC coding techniques and/or higher antenna number significantly reduces the achievable code rate.
  • the code rate is defined as the number of transmitted independent information elements, such as modulated symbols, divided by the number of transmit instances. In Alamouti diversity, two symbols are transmitted over two instances and hence gives a code rate one.
  • ML detection is technically feasible in theory, but is practically infeasible in particular for thin clients having limited processing capability and power supply.
  • the present invention involves data communication between a transmitting communication unit and a receiving communication unit in a wireless network.
  • the invention provides a novel form of space time encoding and decoding providing a selected balance of spatial multiplexing gain and diversity gain, which may be adopted based on the varying radio conditions of the network.
  • the transmitting unit has access to data elements, such as symbols, to be transmitted to the receiving unit.
  • data elements such as symbols
  • the invention can though also be applied to MISO systems, where the transmitting but not receiving unit has access to a multi- antenna system.
  • the transmitting unit combine space time encodes a first set of multiple data elements into a combined space time coded data element.
  • a set of at least one data element is space time coded into a space time coded data element.
  • These space time coded data elements are mapped to respective transmitting antennas and transmission slots according to a space time coder matrix.
  • the combined space time coded data element is provided to a first transmitting antenna of the multi- antenna system for transmission at a selected transmission slot.
  • the combined space time coded data element is provided to a second transmitting antenna of the antenna system for transmission at the selected transmission slot.
  • N space time coded elements are transmitted at the selected over t time slots to achieve a coding
  • the present invention therefore provides a flexible data communication that can efficiently trade off between the degree of spatial multiplexing and the degree of diversity.
  • the receiving communication unit receives the combined space time coded data element and the space time coded data element by the receiving antennas of its multi-antenna system.
  • the combined space time coded data element is space time decoded at least partly based on information of a previously space time decoded data element received by the multi- antenna system, preferably, from the transmitting unit.
  • correctly received data elements can be used to increase the diversity gain of other data elements and /or can be used to obtain multiplexing gain and still obtain code rates over one.
  • the present invention is directed towards data transmission and receiving methods in the wireless communication network in addition to the transmitting and receiving communication units.
  • Fig. 1 is a flow diagram of a data transmitting method according to an embodiment of the present invention
  • Fig. 2 is a flow diagram illustrating the combine STC encoding step of Fig. 1 in more detail according to an embodiment of the present invention
  • Fig. 3 is a flow diagram illustrating additional steps of the data transmitting method of Fig. 1 ;
  • Fig. 4 is a flow diagram of a data receiving method according to an embodiment of the present invention.
  • Fig. 5 is a flow diagram illustrating an additional step of the data receiving method of Fig. 4;
  • Figs. 6A to 6C illustrate flow diagrams of a particular implementation embodiment of the data receiving method
  • Fig. 7 is a diagram comparing the sum capacity achievable according to an embodiment of the present invention with the sum capacity achievable according to prior art arrangements;
  • Fig. 8 is a schematic overview of a wireless communication network according to the invention.
  • Fig. 9 is a schematic block diagram of a transmitting communication unit according to an embodiment of the present invention.
  • Fig. 10 is a schematic block diagram illustrating an embodiment of the STC encoder of Fig. 9;
  • Fig. 11 is a schematic block diagram of a receiving communication unit according to an embodiment of the present invention
  • Fig. 12 is a schematic block diagram illustrating an embodiment of the STC decoder of Fig. 11.
  • the present invention generally relates to data communication in a wireless communication system and in particular such data communication involving space time encoding/ decoding in connection with a multi-antenna transmitter.
  • the traditionally data transmission approaches in multi-antenna systems and in particular MIMO systems have been to either provide spatial multiplexing or high diversity coding.
  • a data stream is split into multiple lower data rate streams, where each stream is transmitted from a different transmit antenna in the same frequency channel.
  • the receiver can separate these streams, creating parallel channels for free. This allows increasing the channel capacity.
  • the latter approach transmit multiple, redundant copies of a data stream to the receiver in the hope that at least some of them is received in good enough state to allow reliable decoding.
  • the present invention provides a novel form of space time encoding that basically can be seen as a trade-off between spatial multiplexing and diversity coding. This allows increasing the transmission and STC code rate substantially as compared to the prior art transmit diversity schemes, such as in Alamouti coding MIMO systems.
  • the invention utilizes the fact that the space time encoding can use a combined STC encoding of multiple data elements, such as symbols, into a combined or composite STC data element. This combined data element is then transmitted according to a STC scheme at a selected time slot and by a selected antenna of the multi-antenna system. This means that with a multi- antenna system a coding rate of more than one can be achieved by
  • Fig. 1 is a flow diagram illustrating a data transmission method of the invention implementable in a wireless communication network, such a mobile or cellular communication network.
  • the method starts in step Sl , where a transmitting communication unit comprises data to be wirelessly transmitted over the network to a receiving communication unit.
  • the invention can be used regardless of the actual type of data to communicate.
  • the data can be generated at the transmitting unit or has previously been received by the unit and is to be forwarded to the receiving unit.
  • Step S 1 combine space time encodes a first set of multiple data elements to form a so-called combined space time coded data element.
  • the data elements are typically modulated symbols.
  • the invention is actually not limited thereto but can also be operated with other data entities. For instance, it is possible to perform the combine space time encoding of step Sl at the bit-level, i.e. data bits, instead of at the symbol-level.
  • the invention is discussed further in connection with operating on data symbols. This will, though, also cover other form of data entities, such as data bits, that can be used according to the invention.
  • the combine STC coding of step Sl processes (encodes) multiple, i.e. at least two, preferably two, symbols (data elements) into a single combined STC coded symbol.
  • Preferred such operations allowing combine STC coding is described further herein.
  • the operation and function /(K ) can of course also operate on more than two symbols.
  • P symbols s v s 2 ,K , s p can be combine STC coded to a combined symbol x and each of the P symbols can be retrieved during decoding given the combined symbol x and the remaining P - I symbols.
  • a next step S2 space time encodes a second set of at least one symbol (data element) to form a space time coded data element.
  • This step S2 can be conducted according traditional STC coding, in which a single input symbol is encoded to a single coded symbol.
  • An alternative embodiment of step S2 co-processes multiple symbols similar to step Sl to thereby combine STC encode these multiple symbols into a single combined symbol.
  • steps Sl and S2 may be performed in series as indicated by Fig. 1 or in the opposite order to what is illustrated in Fig. 1.
  • the encoding can be performed in parallel or at least partly overlapping in time.
  • step S3 involves transmitting the combined STC coded symbol from step S 1 by a first transmitting antenna of the multi- antenna system at an assigned transmission slot, such as time slot.
  • the STC coded symbol from step S2 is correspondingly transmitted at the assigned transmission slot but by a second transmitting antenna of the multi-antenna system.
  • the communication unit has access to a stream of symbols s v s 2 ,K that are STC encoded and mapped to transmit antennas according to the invention to form the coded matrix:
  • At least one c y is combine STC encoded using multiple modulated symbols.
  • Fig. 2 is a flow diagram illustrating a particular embodiment of the co- encoding multiple data symbols into a combined STC coded symbol.
  • the method starts in step SlO, which involves XOR encoding or XOR bitwise encoding the at least two symbols into a combined symbol: x - s x ⁇ s 2 .
  • the combined symbol is then STC encoded according to any prior art encoding technique just as any other data symbol.
  • the method then continues to step S2 of Fig. 1.
  • the combine coding that can be used according to the present invention is preferably a linear data combining.
  • linear methods include summation over a predetermined Z> -bit Galois field, such as bitwise XOR- operations, and modulus-operations.
  • XOR bitwise encoding is a very suitable encoding method because of its simplicity.
  • Other codes may also be used, such as an erasure code like Reed Solomon.
  • Other erasure codes or erasure code oriented encodings may instead be used in the combined STC coding.
  • segments of b bits may be used for the combine encoding.
  • a Galois field of 2 b may then be used, under which addition is the encoding operation. With this notation, the XOR operation is just an addition in the Galois field of 2 1 .
  • a further example of an encoding operation suitable to use is based on the modulus operation.
  • Per signal constellation symbol encoding is considered in the following, and the procedure can be repeated for multiple consecutive constellation symbols.
  • the modulus operation is in this example performed both for the real and imaginary part independently when handling complex numbers and utilize a definition of the modulus operation and the mathematical observation that:
  • a real valued signal B can be superimposed on a real valued signal A and allow undisturbed recovery of the signal A (as long as the signal A does not exceed the quantization level L ), while the amplitude and hence the power is limited of the (non-linearly encoded) composite signal.
  • the present Invention has the advantage of being able to adapt the STC coding to the current radio environment and system service.
  • This means that the STC code of the invention can provide different levels of spatial multiplexing and diversity coding by the selection of which symbols to combine STC encode and to which transmitting antenna and transmission slot such a combined STC symbols is mapped. For instance, during high Signal-to-Noise-Ratio (SNR) conditions, increased spatial multiplexing can be employed to increase channel capacity.
  • SNR Signal-to-Noise-Ratio
  • the present invention can be used in connection with a dynamic adjustment of the STC coding scheme or mode based on, for instance, different collected or estimated quality parameters.
  • a quality parameter is estimated at the communication unit or elsewhere and then reported to the communication unit.
  • This quality parameter is representative of the radio quality of the communication link(s) employed for transmitting the (combined) STC symbols to the receiving unit.
  • signal measurements and determining quality parameters are well-known in the art and are therefore not further described herein. For instance, such quality-related signal measurements can be performed using pilot signals.
  • the quality parameter can be channel estimates between the transmitting and receiving antennas of the MIMO system, in particular if the transmitting communication unit is a network node (base station) or if TDD-based communication is employed. Actually any quality parameter descriptive of the current radio situation can be employed and the invention is not limited to usage of channel estimates.
  • step S21 the STC encoding mode is dynamically updated based on the estimated quality parameter.
  • This updating can be performed by switching between different pre-defined encoding schemes providing different associated spatial multiplexing gains and diversity gains. For instance, a first STC mode provides high multiplexing gain at the cost of a lower diversity gain. A second STC mode would instead provide a high diversity gain but with lower multiplexing gain.
  • Each such STC mode then has its special coder matrix defining at what time slots and by which antennas the combined STC coded symbols and any regular STC coded symbols of an input stream should be transmitted. Furthermore, the different STC coded modes are adapted for usage at different particular radio environments and/or system services as reflected by the estimated quality parameter.
  • the quality parameter from step S20 therefore allows identification of the STC mode that is most suitable in terms of providing a balance or trade off between multiplexing and diversity gain for the current situation.
  • the method then continues to step Sl of Fig. 1, where the symbols of the stream are encoded according to the selected STC mode.
  • the encoder matrix of the STC mode can be given as:
  • the transmission is identical to the case of traditional horizontal spatial multiplexing.
  • the signal transmitted from an antenna of the 2-antenna system is the combination of the previously encoded symbol of the other antenna with a new symbol.
  • the two symbols S 1 and s 2 are also STC encoded separately for transmission in the first transmission slot. A code rate of two is achieved.
  • a 2x2 Alamouti scheme can provide a diversity order up to four but with a code rate equal to one. However, not all of this diversity gain might be useful. For instance, if the Signal-to-Interference-Ratio (SINR) for the link is already very high, not much can be gained by introducing more diversity. In clear contrast, it would be better to trade it off for a multiplexing gain.
  • SINR Signal-to-Interference-Ratio
  • the following STC scheme provides such a trade off between diversity and multiplexing gain.
  • the encoder matrix is given by:
  • the first and second symbols S 1 and S 2 are also STC encoded separately for transmission in the first transmission slot. This corresponds to a purely spatial multiplexing type transmission.
  • the scheme provides a pure diversity Alamouti type transmission.
  • * denotes complex conjugate.
  • a code rate of 4/3 is achieved in this illustrative STC scheme example.
  • Another STC scheme example that provides a trade-off between spatial and diversity gain is to use an encoder matrix according to:
  • This scheme provides an antenna mapping such that each of the original symbols _?, , s 2 , s 3 is transmitted on two different antennas, thus maximizing the transmit diversity.
  • the scheme also provides a code rate of 3/2.
  • Fig. 4 is illustrates a flow diagram of a data receiving method implementable in a wireless communication network. This receiving method involves receiving a stream of STC encoded symbols as previously described in connection with the data transmission method.
  • a receiving communication unit receives STC coded symbols (data elements) transmitted by the multi- antenna system of the transmitting communication unit.
  • the receiving unit preferably also comprises a multi-antenna system thereby having access to multiple receiving antennas to form a MIMO system.
  • the multiple number of receiving antennas can be equal to or different from the multiple number of transmitting antennas.
  • the invention is described further with a multi-antenna system at the receiving unit.
  • the invention can also be used in connection with a MISO system, i.e. where a single receiving antenna is employed in the receiving communication unit.
  • step S30 involves receiving a combined STC coded symbol by at least a first and a second receiving antenna of the multi-antenna system.
  • This combined STC coded data element is transmitted by a first transmitting antenna of the transmitting multi-antenna system at a given transmission slot.
  • Step S30 also comprises receiving a (combined or regular) STC coded symbol at the first and second receiving antennas. This symbol was transmitted by a second transmitting antenna of the transmitting antenna system in parallel with the combined STC coded symbol.
  • a next step S31 STC decodes the received combined STC coded symbol and the STC coded symbol to obtain STC decoded symbols.
  • the decoding of the combined STC coded symbol is performed at least partly based on information of another symbol of the stream received by the receiving antennas and decoded at the communication unit. This other symbol can be the symbol sent in parallel with the combined symbol, a symbol sent at a previous transmission slot or even a symbol sent at a following transmission slot.
  • the method ends or returns to step S30 for receiving further (combined) STC coded symbols of the data stream.
  • the receiving structure of the invention can be made simple and does not require the very complex maximum likelihood detection as the prior art schemes.
  • the received signals from the multiple receiving antennas are processed.
  • This signal processing preferably comprises estimating the power present in the received radio signal.
  • RSSI Received Signal Strength Indication
  • the processed output signal is digitized through an analog to digital conversion before being down converted to baseband. After down conversion the transmitted signal from each transmit antenna are estimated at each receiver antenna as described further herein.
  • transmissions through multi-path channels usually experience inter-symbol interference at the receiver.
  • Such interference can be mitigated by an equalizer at the receiver to compensate for channel distortion.
  • Such equalization can either be done before or during the signal estimation.
  • STC decoding is then performed on the output from the signal estimation to yield an estimation of the transmitted data symbols.
  • the STC decoding is preferably performed at least partly based on the power/ channel parameter determined at the receiver.
  • the present invention can be used in connection with different symbol detection algorithms and is not limited to the complex maximum likelihood detection.
  • the invention can be used with more technically feasible detection algorithms that are practically implementable also in thin clients, such as mobile telephones.
  • a preferred example of such a detection algorithm is successive interference cancellation.
  • Successive interference cancellation can also be used in combination with symbol detection algorithms as minimum mean squared error estimation, linear minimum means squared error estimation and maximum likelihood. It is also possible to use any of these other detection algorithms instead of successive interference cancellation.
  • ⁇ is the noise and inter-cell interference with ⁇ denoting the noise and inter-cell interference at the i"' receiver antenna for the transmission phase j .
  • Fig. 5 illustrates an additional preferred step of the data receiving method.
  • the method starts in step S40, where the channel matrix for the current MIMO system is estimated at the receiving communication unit.
  • the channel state information can be estimated using power estimations of a pilot signal and/or a training sequence S .
  • the channel matrix can be estimated based on:
  • step S30 the coded symbols are received.
  • the decoding of the symbols involves estimation of a respective signal quality parameter for the received (combined) STC coded symbols based on the channel matrix. These estimated quality parameters are further employed in the symbol detection of the decoding.
  • the decoding of the STC coded symbols furthermore preferably Involves the estimation of reception power of the multiple receiving antennas. This procedure is schematically illustrated in the decoding example of Figs. 6A to 6C.
  • the method continues in Fig. 6A from step S30 of Fig. 4.
  • Received powers from the transmitting antennas are estimated, such as RSSI or some other power descriptive parameter, in step S50 for a given time slot. These estimated power parameters are compared with each other in a next step S51.
  • step S51 involves checking whether max ⁇ h x x ,h X2 ⁇ > max (A 21 , A 22 ) in this illustrative example with a 2x2 MIMO system.
  • the decoding is described further in connection with SIC detection using a 2x2 MIMO system, where the transmitting communication unit STC encoded and sent symbols according to the following coded matrix:
  • Step S52 involves detecting, during the first time slot, the received coded symbol S 1 . This symbol detection involves estimating a signal quality parameter for the symbol S 1 :
  • T s denotes the SINR (signal quality parameter) for symbol s
  • p denotes half of the power available at the transmitter
  • h y denotes the channel between transmitting antenna i and receiving antenna j
  • ⁇ k denotes the noise term at antenna k .
  • the SIC detection continues by cancelling the detected symbol ⁇ 1 from the received signals y u , y 2] at the first and second receiving antennas in step S53.
  • the other signal transmitted by the transmitting antenna system during the first time slot is then detected in step S54:
  • step S58 of Fig. 6B The method then continues to step S58 of Fig. 6B.
  • step S55 where the STC coded symbol transmitted by the second antenna during the first time slot is detected:
  • the detected symbol signal is cancelled from the received signals in step S56 and the symbol J 1 transmitted by the first antenna during the first time slot is detected in step S57:
  • step S58 of Fig. 6B The method then continues to step S58 of Fig. 6B.
  • Step S58 estimates the best antenna branch for the second transmit slot, preferably based on the estimated received powers (channel estimates) of the first and second transmitting antennas for the second transmit slot. If the first transmitting antenna is determined to provide strongest received power at the receiving communication unit in step S59, the method continues to step S60. This step S60 detects the symbol x, transmitted by the first antenna during the second transmit slot:
  • the noise terms are assumed to be constant during the first and second transmit slots.
  • the detected signal is cancelled from the received signals y u , y 22 in step S61 and the signal s 2 sent by the second antenna during this time slot is detected in step S62:
  • step S66 the received power from the second antenna instead was stronger in the comparison of step S59.
  • step S63 which detects the symbol from the second antenna at the second time slot:
  • the detected symbol signal is cancelled from the received signals in step S64 and the symbol X 1 transmitted by the first antenna during the second time slot is detected in step S65:
  • step S66 of Fig. 6C The method then continues to step S66 of Fig. 6C.
  • the modulated symbols will be estimated by the STC decoder of the receiving communication unit.
  • the decoder investigates whether the STC coded symbols s x , s 2 (in other words the symbols that were not combined STC coded) were received with sufficient power by the communication unit in steps S66, S67 and S72. This investigation is preferably performed based on the SINR values estimated for the detected symbols according to the method disclosed in Figs. 6A and 6B using SIC detection or some other signal/ symbol detection algorithm.
  • step S66 investigates whether the first symbol S 1 was detected at sufficient power to enable efficient decoding. This investigation is preferably conducted by comparing the SINR estimated for the symbol with a minimum quality threshold T . If the SINR value exceeds the threshold, the method continues to step S67, where the SINR value for the second symbol s 2 is likewise compared to a minimum quality threshold, typically the same as was used in step S66.
  • both the received combined STC coded symbols x, , x 2 can be used to obtain the third symbol S 3 .
  • the equivalent SINR for the three symbols will then be given as follows:
  • both the combined STC coded symbols can be used for increasing the diversity gain and decoding the third symbol, thereby significantly increasing the decoding probability for that symbol. All the data symbols transmitted by the two transmitting antennas during the two time slots are thereby decoded at the receiving communication unit.
  • step S67 If the first symbol but not the second symbol was received with sufficient power, the method continues from step S67 to step S70. In this case we use the combined STC coded symbol X 1 to increase the diversity gain of the symbol s 2 not received with sufficient power. The other combined STC coded symbol x 2 is used to obtain multiplexing gain by decoding ⁇ 3 :
  • step S73 we use the combined STC coded symbol x 2 to increase the diversity gain of S 1 and the other combined STC coded symbol x, to obtain multiplexing gain by- decoding S 3 :
  • the comparison of the SINR values of the first and second symbols with the threshold of steps S66, S67 and S72 can be performed in any order.
  • first the first symbol can be investigated followed by comparing the SINR of the second symbol as illustrated in the figure.
  • SINR of the second symbol is first compared to the threshold followed by the investigation for the first symbol.
  • the comparisons may alternatively be performed in parallel.
  • SINR-threshold comparisons of steps S66, S67 and S72 may be omitted.
  • the equivalent SINR values are calculated for the three different cases described above and disclosed in steps S68, S70 and S73.
  • a respective sum capacity parameter is calculated for each of the three cases in steps S69, S71, S74, such as:
  • c sum iog 2 (i + r; ) + iog 2 (i + r. ) + iog 2 (i + r.
  • a next step S75 compares the three sum capacities C 1 , C 2 and C 3 and the largest sum capacity C f is identified.
  • the decoding algorithm selects, in this embodiment, the decoding scenario that gives the highest sum-capacity in step S76.
  • the embodiment that merely employs SINR-threshold comparisons to select one of the available decoding scenarios may be less computationally expensive as only the calculations according to one of the steps S68, S70 and S73 are performed.
  • the other embodiment may be more computationally expensive but may give a better result as an "exhaustive" search among the different scenarios is performed to identify the currently most suitable scenario. It is anticipated by the present invention that other selection criteria than the sum capacity may be used. Furthermore, the two embodiments may actually be combined.
  • Fig. 7 illustrates the sum capacity of the STC scheme of the invention (empirical Cumulative Distribution Function, CDF) as opposed to that of a 2x2 Alamouti scheme with Maximum Ratio Combining (MRC) at the receiver.
  • CDF empirical Cumulative Distribution Function
  • MRC Maximum Ratio Combining
  • the average sum capacity of the Alamouti scheme is 3.8524 b/s/Hz, whereas that of the invention is 5.7623 b/s/Hz.
  • the invention therefore yields an average sum-capacity gain of 50 %.
  • Fig. 8 is a schematic overview of a wireless communication network 1 according to the present invention comprising a transmitting communication unit 100 and a receiving communication unit 200 together forming a so- called MIMO system.
  • the communication units 100, 200 can represent any unit, terminal or node in a communication network 1 having access to a multi- antenna system 110, 220 and being capable to wirelessly communicate with another unit, terminal or node in the network 1.
  • Illustrative examples of such units 100, 200 include base stations and other stationary or mobile network nodes. Further examples include user terminals, such as mobile telephones and terminals, laptops, computers and PDAs with communication equipment.
  • the figure also schematically indicates the channels It 11 -Ii 22 between the individual transmitting antennas 112, 114 and the receiving antennas 212, 214.
  • Fig. 9 is a schematic block diagram of a transmitting communication unit 100 according to an embodiment.
  • the unit 100 comprises a transmit buffer 120 containing data to be transmitted to one or more other communication units in the network. This data can be previously received data originating from another communication unit. In such a case, the received data is entered in a receive buffer 130 of the unit 100 and is transferred, optionally following further processing to the transmit buffer 120.
  • the receive and transmit buffers 120, 130 co-exist in the same memory facility and the individual data elements therein in are simply flagged as either being received or to be transmitted.
  • the data to be transmitted can instead or also come from an application 140 present in the unit 100.
  • the data elements are fetched from the transmit buffer 120 and are forwarded to a connected STC encoder 150 according to the invention.
  • This STC encoder 150 is arranged for space time encoding sets of data elements into STC coded data elements as previously described herein.
  • the STC encoder 150 encodes a first set of multiple data elements into a combined STC coded data element.
  • the encoder 150 also encodes a second set of at least one data element into a STC coded data element (in the case of one data element in the second set) or a combined STC coded data element (in the case of multiple data elements in the second set).
  • the encoded data elements are forwarded from the encoder to a connected antenna mapping unit 160.
  • This mapping unit 160 is also connected to the transmitting antennas 114 of the multi-antenna system 110 in the communication unit 100.
  • the mapping unit 160 is arranged for providing the combined STC coded data element from the STC encoder 150 to the first transmitting antenna 112 for transmission at a given transmission slot.
  • the unit 160 also provides the (combined) STC coded data element from the encoder 150 to second transmitting antenna 114 for transmission at the given time slot.
  • This antenna mapping unit 160 is preferably implemented for mapping input STC coded data elements to correct transmitting antenna 112, 114 based on information from the STC encoder 150.
  • This information corresponds to the particular STC scheme employed by the STC encoder 150 when space time encoding the input data elements.
  • the information could the be coder matrix of the STC scheme, an indication allowing information of the particular coder matrix or some other information descriptive of the antenna units and transmit slots by which STC encoded data elements should be transmitted.
  • the communication unit 100 preferably also comprises a link quality unit 170.
  • This quality unit 170 provides a quality parameter representative of the communication quality of a communication link between the communication unit 100 and the destined receiving unit.
  • the unit 170 can perform quality estimations based on signals received from the external unit.
  • the antenna system 110 receives the quality estimates from an external unit, such as the receiving communication unit. In such a case, this received parameter is employed by the quality unit 170.
  • the units 140 to 170 of the communication unit 100 may be implemented in hardware, software or a combination of hardware and software.
  • the units 110 to 170 may all be implemented in the communication unit 100.
  • a distributed implementation is also possible, in particular for a network situated communication unit 100. In such a case, the units 110 to 170 may be distributed among multiple inter-connected network nodes.
  • Fig. 10 is a schematic block diagram of a possible implementation of the STC encoder 150 of Fig. 9.
  • the encoder 150 comprises an XOR encoder 152 arranged for performing XOR-based combination of at least two input data elements to form a combined data element. This XOR operation is preferably an XOR bitwise encoding of the multiple data elements.
  • another combining algorithm or function as previously described can be used by the STC encoder 150.
  • the STC encoder 150 has access to multiple STC schemes defining the particular antenna and transmit slot mapping for the data elements and in addition identifying the data elements that should be combine space time encoded according to the invention. As was mentioned above, these STC schemes provide different spatial multiplexing gain and diversity gain levels, and also different code rates. This means that the STC schemes are adapted to usage at different network conditions and /or in connection with different system services.
  • the encoder 150 thus, preferably comprises a mode selector 154 arranged for selecting between these available STC schemes or modes. The selector 154 preferably performs this mode or scheme selection based on input information. This input information typically comprises the quality parameter provided by the link quality unit of Fig. 9.
  • the mode selector 154 can select the particular STC mode that provides the most "optimal" mixture of multiplexing and diversity gains for the current radio condition as assessed from the quality parameter.
  • Other selection input information could be data indicating the current system service employed by the communication unit.
  • the STC encoder 150 then STC encodes input data elements from an input stream or indeed multiple such streams according to the selected STC scheme/mode.
  • the STC encoder 150 can operate according to any of the previously described STC schemes and coder matrices.
  • the units 152 and 154 of the STC encoder 150 may be implemented in hardware, software or a combination of hardware and software.
  • the units 152 and 154 may all be implemented in the STC encoder 150.
  • a distributed implementation is also possible with at least one of the units 152 and 154 implemented elsewhere in the transmitting communication unit.
  • Fig. 11 is a schematic block diagram of a receiving communication unit 200 according to an embodiment.
  • the unit 200 comprises a multi-antenna system 210 comprising at least first 212 and second 214 receiving antennas.
  • This antenna system 210 is arranged for receiving, from a transmitting communication unit having a transmitting multi- antenna system, a combined STC coded data element transmitted at a given time slot by a first transmit antenna and a (combined) STC coded data element transmitted by a second transmit antenna at the given time slot.
  • the receiving communication unit 200 only comprises a single receiving antenna 212, basically resulting in a MISO system with the multi-antenna transmitting communication unit.
  • the receiving unit 200 is described further in connection with a multi-antenna unit 200.
  • the invention is, though, not limited there to but can be applied to single-antenna units.
  • the signals received by the receiving antennas 212, 214 are forwarded to a codeword or signal quality estimator 220.
  • This estimator 220 estimates the transmitted signals from each transmit antenna at each receive antenna 212, 214.
  • the estimator 220 preferably estimates a respective signal quality parameter for the received (combined) STC coded data elements, such as respective SINR values.
  • the estimator 220 comprises or is connected to a channel estimator 240.
  • This channel estimator 240 is implemented for estimating a channel matrix descriptive of the individual communication channels (see Fig. 8) between the transmitting and receiving antennas 212, 214 of the MIMO system.
  • the estimator 240 preferably performs this channel estimation based on signals received from the transmit antennas, such as based on pilot signals.
  • the channel estimates are forwarded from the channel estimator 240 to the signal quality estimator 220. There the estimates are employed by the quality estimator 220 in calculating the SINR values for the received signals as previously described.
  • the channel estimator 240 or another dedicated unit in the communication unit 200 preferably also estimates a respective received power from the transmit antennas. This received power corresponds to the channel estimates if all transmit antennas transmitted with equal power. Otherwise the channel estimates can be used as received power estimates by providing antenna weights based on power division among the transmit antennas.
  • the determined power parameters are forwarded to a power or channel comparator 250 of the communication unit 200.
  • the comparator 250 compares the estimated power/ channel parameters for the purpose of deciding the transmit antenna contributing to the largest received power at the communication unit 200 at a given transmit slot.
  • This power comparison is employed by the quality estimator 220 for the purpose of determining the SINR values for the received STC coded data elements.
  • the quality estimator 220 uses the result from the power/ channel comparison in a successive interference cancellation procedure.
  • the estimated SINR values for the received data elements are fed to a STC decoder that is arranged for space time decoding the data elements.
  • the decoding of a combined STC coded data element is performed at least partly based on information (SINR value) of another space time decoded data element received by the multi-antenna system 210.
  • This decoded data element can be a data element transmitted at the same time slot as the combined STC coded data element, at a previous time slot or even a following time slot.
  • the STC decoder 230 uses the input SINR values (or some other signal quality estimates) from the estimator 220 and estimates the received data elements based on determined equivalent SINR values. These equivalent values are calculated based on the input SINR values and based on a particular decoding mode adopted by the STC decoder 230, which is discussed further herein.
  • the units 220 to 260 of the communication unit 200 may be implemented in hardware, software or a combination of hardware and software.
  • the units 210 to 260 may all be implemented in the communication unit 200.
  • a distributed implementation is also possible, in particular for a network situated communication unit 200. In such a case, the units 210 to 260 may be distributed among multiple inter-connected network nodes.
  • Fig. 12 is a schematic block diagram of a STC decoder 230 implementable in the communication unit 200 of Fig. 11.
  • STC decoder 230 comprises a quality determiner 232 arranged for calculating the equivalent SINR values based on the input SINR values from the signal quality estimator of Fig. 11. This calculation is dependent on the particular STC scheme and based the particular reception mode as has been previously described.
  • a mode selector 234 is arranged for selecting a particular decoding mode depending on whether one or multiple of the data elements were received with high enough power.
  • the mode selector 234 preferably compares the respective SINR values for those data elements that were encoded and transmitted as single STC coded data element with minimum power thresholds. This comparison determines which of the data elements that can be correctly decoded separately or which requires further diversity gain from a combined STC coded data element that is a combination of the given data element and at least one other data element.
  • the quality determiner 232 uses information of the particular decoding mode from the selector 234 and calculates the equivalent SINR values for all the received data elements using the multiplexing/ diversity gain dictated by the decoding mode. In such a case, the quality determiner 232 and mode selector 234 can operate as previously described in connection with Figs. 6A to 6C.
  • the quality determiner 232 calculates equivalent SINR values according to all of the available decoding modes, or at least a portion thereof.
  • a capacity determiner 236 calculates a respective capacity parameter, such as sum capacity, for each mode based on the equivalent SINR values determined for the particular modes.
  • the mode selector 234 selects which decoding mode that should be employed for the received data elements based on these capacity parameters, basically by selecting the mode that maximizes the sum capacity.
  • the units 232 to 236 of the STC decoder 230 may be implemented in hardware, software or a combination of hardware and software.
  • the units 232 to 236 may all be implemented in the STC decoder 230.
  • a distributed implementation is also possible with at least one of the units 232 to 236 implemented elsewhere in the transmitting communication unit.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Radio Transmission System (AREA)

Abstract

Un procédé de communication de données implique un codage spatio-temporel combiné d'un premier ensemble d'éléments de données multiples dans un élément de données codé de manière spatio-temporelle combiné. Un deuxième ensemble comprenant au moins un élément de données est codé de même de manière spatio-temporelle dans un élément de données codé de manière spatio-temporelle. L'élément de données combiné est transmis dans un intervalle de transmission par une première antenne (112) qui fait partie d'un système à plusieurs antennes (110) en même temps qu'une deuxième antenne (114) du système transmet l'élément de données codé de manière spatio-temporelle. Le codage STC de combinaison d’éléments de données multiples permet de fournir un équilibre entre un gain de multiplexage spatial et un gain de diversité dans la transmission de données et permet d'obtenir encore des débits de code supérieurs à un.
PCT/SE2008/050786 2008-06-27 2008-06-27 Codage spatio-temporel WO2009157833A1 (fr)

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Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
CHAU YUEN ET AL: "Bi-Directional Multi-Antenna Relay Communications with Wireless Network Coding", VEHICULAR TECHNOLOGY CONFERENCE, 2008. VTC SPRING 2008. IEEE, 11 May 2008 (2008-05-11) - 14 May 2008 (2008-05-14), pages 1385 - 1388, XP031255755 *
LALAM, M. ET AL.: "Space-time error correcting codes", WIRELESS COMMUNICATIONS, IEEE TRANSACTIONS ON, vol. 7, no. 5, May 2008 (2008-05-01), pages 1472 - 1476, XP011214987 *
LIZHONG ZHENG ET AL: "Diversity and multiplexing: a fundamental tradeoff in multiple-antenna channels", INFORMATION THEORY, IEEE TRANSACTIONS ON, vol. 49, no. 5, May 2003 (2003-05-01), pages 1073 - 1096, XP011074770 *
S. SEZGINER ET AL: "A Full-Rate Full-Diversity 2x2 Space-Time Code for Mobile WiMAX Systems", ISCPC 2007, November 2007 (2007-11-01), DUBAI, XP031380548, Retrieved from the Internet <URL:http://www.sequans.com/technology/tech_docs.php> *
SEZGINER, S. ET AL: "A High-Rate Full-Diversity 2x2 Space-Time Code with Simple Maximum Likelihood Decoding", SIGNAL PROCESSING AND INFORMATION TECHNOLOGY, 2007 IEEE INTERNATIONAL SYMPOSIUM ON, 15 December 2007 (2007-12-15) - 18 December 2007 (2007-12-18), pages 1132 - 1136, XP031234173 *

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