Low-complexity decoding method for quasi-orthogonal space-time coded spatial modulation systems

Abstract

The present invention belongs to the technical field of anti-interference of Massive Multiple Input Multiple Output (MIMO) communication, and specifically relates to a low-complexity decoding method for a receiving end of a Quasi-Orthogonal Space-Time Block Coded Spatial Modulation (QOSTBC-SM) system. The present invention adopts a quasi-orthogonal space-time block code pattern with the lowest decoding complexity at the transmitting end, selects a group of antennas from the transmitting antenna to send QOSTBC code words, and the bit information is transmitted through the antenna index and the code word, and is demodulated at the receiving end by traversing the antenna combination using a single symbol decoding algorithm. The system maintains system performance while reducing the decoding complexity of the receiving end. The present invention adopts a single symbol decoding algorithm for the QOSTBC code pattern with the lowest decoding complexity. Compared with the traditional ML decoding algorithm, the decoding complexity of the receiving end is reduced, and the system BER performance is close to ML.

Description

Technical Field

[0001] The present invention belongs to the technical field of anti-interference of Massive Multiple Input Multiple Output (MIMO) communications, and specifically relates to a low-complexity decoding method for a receiving end of a Quasi-Orthogonal Space-Time Block Coded Spatial Modulation (QOSTBC-SM) system. Background Art

[0002] Spatial Modulation (SM) technology is a new type of low-complexity, sparse RF-supported MIMO transmission technology, which is characterized by activating only one antenna in each transmission time slot. SM is generalized to activate multiple transmit antennas at a time to transmit more data symbols, which is called generalized spatial modulation (GSM). From the perspective of modulation design, in SM, the information bit is modulated not only by the constellation symbol, but also by the activated antenna index. An information bit block is mapped to two information-bearing units, one of which is the symbol selected from the traditional APM constellation diagram, and the other is the symbol selected from N T The number of bits carried on a set of transmitting antenna indices selected in the antenna improves the spectrum efficiency log 2 N T SM combines digital and spatial dimensions to enhance the freedom of constellation modulation, thereby achieving unique advantages over traditional MIMO technology, while considering the trade-off between the number of RF chains, detection complexity and transmission rate to achieve a flexible structure.

[0003] Space-Time Block Coded (STBC) is an efficient transmit diversity technology using multiple antennas. When Nt>3, the maximum transmission rate is 3 / 4, which will lead to spectrum expansion and cannot achieve full diversity. Therefore, Quasi-Orthogonal Space-Time Block Coded (QOSTBC) is proposed, which relaxes the orthogonality between the columns of orthogonal STBC, sacrificing some diversity gain in exchange for an increase in transmission rate. At the same time, the complexity of the maximum likelihood decoding algorithm is increased due to the need for paired decoding. The QOSTBC-SM system is designed for MIMO transmission, and by obtaining the advantages of each, it improves the spectrum efficiency compared with the traditional space-time block coded spatial modulation (STBC-SM) system.

[0004] The decoding complexity of the QOSTBC-SM system increases exponentially with the modulation order and the number of transmit antennas in traditional ML detection, and is not applicable when high-order modulation and large-scale transmit antenna transmission are used. Therefore, reducing the decoding complexity of the system at the receiving end and ensuring system performance has become one of the main research directions of the system. Summary of the invention

[0005] Based on the purpose of reducing the decoding complexity of the system receiving end and maintaining the system performance, the present invention proposes a low-complexity decoding algorithm design scheme for the receiving end of the multi-antenna QOSTBC-SM system. The scheme adopts the quasi-orthogonal space-time block code pattern with the lowest decoding complexity at the transmitting end, selects a group of antennas from the transmitting antennas to send the QOSTBC codeword, and the bit information is transmitted through the antenna index and the codeword. At the receiving end, the single symbol decoding algorithm is used for demodulation by traversing the antenna combination. The system maintains the system performance while reducing the decoding complexity of the receiving end.

[0006] For ease of understanding, the multi-antenna QOSTBC-SM system is defined as follows:

[0007] For a N T ×N R The multi-antenna QOSTBC-SM system, N T is the number of transmit antennas, N R is the number of receiving antennas, N u is the number of antennas activated in each transmission slot. u In N time slots, spatial modulation is based on the information bits. T Select N of the transmitting antennas u (1≤N u ≤N T ) transmit data symbols. After quasi-orthogonal space-time coding, the selected N u The root antenna is activated and transmits the QOSTBC coded transmission symbol. At the same time, the unselected N T -N u The root antenna remains silent, that is, the transmitted symbol is 0. It can be seen that there are C(N T ,N u ) activation antenna combination modes, and the transmission probability of each combination is equal. The information bits of the QOSTBC-SM system are divided into two parts after serial-to-parallel conversion. One part is used to select the transmitting antenna combination, where the number of available combinations is C(N T ,N u ); the other part is used to modulate into PSK / QAM constellation symbols, and after QOSTBC encoding, it is u The selected antenna combination is used for transmission in each time slot. Since each antenna can carry log 2 M bits, so Nu The number of bits that can be transmitted by an antenna is N u log 2 M, where M is the modulation order. The number of codewords used to transmit QOSTBC is And the maximum spectrum efficiency of the QOSTBC-SM system is

[0008] The technical solution of the present invention is:

[0009] The low-complexity decoding algorithm for the receiving end of the quasi-orthogonal space-time block code spatial modulation system includes:

[0010] Transmitter:

[0011] Step 1: Generate information bit stream. The sender converts the bit data to be transmitted into B by serial-to-parallel conversion. k Divided into Two parts, the first part The bit is used as the antenna combination index to select a codeword, with a total of C (N T ,N u ) antenna combination, and the second part After the traditional APM modulation, the bit is modulated into N u M-QAM / PSK symbols are used for quasi-orthogonal space-time coding to obtain the codewords required for transmission. A code word.

[0012] Step 2: Perform quasi-orthogonal space-time block coding on the APM symbols to obtain the transmitted QOSTBC codebook. In the case of 4 transmitting antennas, assuming Z 1 and Z 2 are two Alamouti STBC codewords, and an Alamouti STBC codeword is as follows:

[0013]

[0014] where z 1 , z 2 is the transmitted APM symbol. The columns and rows correspond to the transmitting antennas and symbol intervals respectively. Common QOSTBC codewords are constructed into the following three code types:

[0015]

[0016]

[0017]

[0018] The QOSTBC codeword type used in the present invention is the MDC-QOSTBC code type with the smallest decoding complexity, and its specific form is as follows:

[0019]

[0020] in() R and() I denote the real and imaginary parts of the sign respectively.

[0021] Step 3: Spatial modulation maps a partial bit vector to select the activated transmit antenna index. Assume s k (k=1,2,3,4) is the kth row of QOSTBC codeword, 0 pxq Representing a matrix of size pxq, depending on the activated antenna combination, the QOSTBC transmission codebook with the following structure can be obtained:

[0022]

[0023]

[0024]

[0025] The information data is spatially modulated and mapped and then sent through the activated transmitting antenna.

[0026] Receiver:

[0027] Step 4: Model the received k-th space-time block. The signal to be detected at the receiving end is Transmission channel matrix Each entry of is a Gaussian random variable CN(0,1), and the noise matrix Each term is also a Gaussian random variable CN(0,σ 2 ), the received signal can be modeled as:

[0028] Y k =H k Z k +N k

[0029] Step 5: Decode the received signal using a single symbol detection algorithm. In the context of a static Rayleigh stationary fading MIMO channel, the detection of the above MDC code pattern by the QOSTBC-SM system can be expressed as the sum of the following four functions:

[0030]

[0031]

[0032]

[0033]

[0034] Among them, the parameters a, β, γ, χ,δ is:

[0035]

[0036]

[0037]

[0038]

[0039]

[0040] The decoding metric of the MDC code type QOSTBC can be expressed as 4 f i The sum of functions, each f i The function is a joint test of two real symbols, that is and in() R and() I denote the real and imaginary parts of the desired transmission symbol respectively. For 1≤i≤4, when i≠k, z k are independent, so the decoding is equivalent to minimizing the four f independently i Function, the decoding complexity is greatly reduced compared with the traditional ML metric. Use the single symbol detection algorithm to calculate under each antenna combination and find the 4 f i The activated antenna combination corresponding to the minimum function sum is used to obtain the bit corresponding to the symbol in the corresponding QOSTBC codeword.

[0041] Step 6: Demodulate the antenna index and symbol to recover the bit stream. Demodulate the bit corresponding to the activated antenna combination index to obtain the bit information carried by the antenna index. The 4 symbols in the obtained QOSTBC codeword are demodulated to obtain the bit information carried by the modulation symbol Recover the sent data bit stream.

[0042] The present invention aims at the QOSTBC code type with the lowest decoding complexity and adopts a single symbol decoding algorithm. Compared with the traditional ML decoding algorithm, the decoding complexity of the receiving end is reduced, and the system BER performance is close to ML. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is the block diagram of the QOSTBC-SM system. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments:

[0045] Embodiment 1:

[0046] Next, we take the transmitting antenna N T is 6, receiving antenna N R =4, the number of transmission antennas activated in each time slot is N u The modulation symbol is 4, BPSK is used, each QOSTBC codeword contains 4 transmission symbols, each symbol carries 1 bit, each group of activated antenna combinations carries 2 bits, and the corresponding relationship between antenna index and bit is as follows:

[0047]

[0048] When the antenna index transmits "00", the first antenna combination "1 2 3 4" is activated. The channel is quasi-static stationary Rayleigh fading, and the receiving end is known. The specific implementation of the present invention is introduced as an example. Figure 1 As shown, the specific processing method for this example is:

[0049] Transmitter:

[0050] Step 1: Generate information bit stream. The sender converts the bit data to be transmitted into B by serial-to-parallel conversion. k =6 points Two parts. Part 1 Bit [1 0] is used as an antenna combination index to select a codeword. Assume that there are 4 antenna combinations, and each combination corresponds to a set of antenna index bits. The bit [1 1 0 1] is modulated by BPSK to obtain 4 symbols, which are used for quasi-orthogonal space-time coding to obtain the codeword required for transmission. Taking the jth QOSTBC codeword as an example, the information bit is generated, and its transmission bit is [1 1 0 1]. The bit is mapped by BPSK constellation to obtain the modulation symbol z j =[z j,1 ,z j,2 ,z j,3 ,z j,4 ].

[0051] Step 2: Perform quasi-orthogonal space-time block coding on the BPSK modulated symbols to obtain the transmitted QOSTBC codeword. The QOSTBC codeword type used is the MDC-QOSTBC code type with the lowest decoding complexity, and the specific form is as follows:

[0052]

[0053] in() R and() IRepresent the real and imaginary parts of the symbol respectively. Substitute the modulation symbol for encoding and map it to spatial modulation to obtain the transmission codeword Z k as follows:

[0054]

[0055] Step 3: Spatial modulation maps part of the bit vector to select the activated transmit antenna index. There are 6 transmission antennas in total, 4 antennas are activated for each transmission, and the QOSTBC codeword is mapped to the 4 antenna combinations to obtain the following 4 codewords:

[0056]

[0057]

[0058]

[0059]

[0060] Where Z i , i = 1, 2, 3, 4, represents the QOSTBC-SM system codebook containing the lowest decoding complexity QOSTBC, the row represents the transmit antenna, 0 means the antenna remains silent, so the index of the activated antenna can be used to carry the information bit. The information data is sent through the activated transmit antenna after spatial modulation mapping.

[0061] Receiver:

[0062] Step 4: Model the received k-th space-time block. The signal to be detected at the receiving end is Transmission channel matrix Each entry of is a Gaussian random variable CN(0,1), and the noise matrix Each term is also a Gaussian random variable CN(0,σ 2 ), the received signal can be modeled as:

[0063]

[0064] Step 5: Decode the received signal using the single symbol detection algorithm. In the context of a static Rayleigh stationary fading MIMO channel, the receiver is aware of the channel. The received signal to be detected Y k as follows:

[0065]

[0066] Substituting the channel information used in the formula for calculation corresponds to each antenna combination. For example, if the calculation is performed under the first antenna combination (1 23 4), the channel information is H = H k(1:4,:), H is substituted into the formula for calculation. The symbols after BPSK modulation are "-1" and "1" respectively. The real and imaginary parts of these two symbols are taken and the following four functions f are substituted into these four antenna combinations. i Perform the calculation:

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076] Calculate the sum of the four f functions for each antenna combination i=1,2,3,4, The corresponding antenna combination is the required antenna index, corresponding to the symbol z i , i=1,2,3,4, which are the 4 symbols in the required QOSTBC codeword.

[0077] Step 6: Demodulate the symbol and antenna index to recover the transmitted data bit stream. The calculation shows that the third antenna combination is the required antenna index. According to the corresponding relationship between the antenna index and the bit, the antenna index bit is [1 0], the corresponding symbol in the obtained QOSTBC codeword is demodulated to obtain the bit [1 1 0 1], and finally the transmitted data bit stream [11 0 11 0] is recovered.

Claims

1. A low-complexity decoding method for a quasi-orthogonal space-time coded spatial modulation system, the system comprising N T Transmitting antennas, N R Root receiving antennas, defined in N consecutive u In N time slots, the system T Select N of the transmitting antennas u The number of antennas transmitting data symbols is 1≤N. u ≤N T ; It is characterized in that, The method comprises: Transmitter: Step 1: The sender converts the bit data B to be transmitted by serial-to-parallel conversion k Divided into Two parts, the first part The bit is used as the antenna combination index to select a codeword, with a total of C (N T ,N u ) antenna combination modes, each combination corresponds to a set of antenna index bits; the second part After APM modulation, the bit is modulated into N u M-QAM / PSK symbols are used for quasi-orthogonal space-time coding to obtain the codewords required for transmission. codewords, where M is the modulation order; Step 2: Perform quasi-orthogonal space-time block coding on the APM modulation symbols to obtain the transmitted quasi-orthogonal space-time block code codeword Z k ; Step 3: Map the quasi-orthogonal space-time block code codeword to C(N T ,N u ) antenna combinations to obtain the corresponding codeword, thereby using the index of the activated antenna to carry the information bit; the information data is sent through the activated transmitting antenna after spatial modulation mapping; Receiver: Step 4: Define the signal to be detected at the receiving end as Transmission channel matrix Each entry of is a Gaussian random variable, the noise matrix Each term of is also a Gaussian random variable, so the received signal is modeled as follows: Y k =H k Z k +N k Step 5: Use the single symbol detection algorithm to detect the received signal Y k Decoding is performed by using a single symbol detection algorithm to perform calculations under each antenna combination. Substituting the channel information calculated by the formula into the corresponding antenna combination "antenna_combination", taking the real and imaginary parts of the modulation symbol, the channel information H = H k (:,antenna_combination), according to the antenna combination index parameter corresponding to the channel matrix H k The corresponding column will be H and the received signal Y k Substitute the following formula to calculate: where h n,r is the channel fading factor between the nth receiving antenna and the rth transmitting antenna. The sum of the four fi functions is calculated for each antenna combination. i=1,2,3,4,j=1,...,C(N T ,N u ), The corresponding antenna combination is the required antenna index, corresponding to the symbol z i , () R and() I Respectively represent the real part and imaginary part of the symbol, that is, the four symbols in the desired quasi-orthogonal space-time block code codeword, thereby obtaining the bits corresponding to the symbols in the corresponding quasi-orthogonal space-time block code codeword; Step 6: Demodulate the bit corresponding to the activated antenna combination index to obtain the bit information carried by the antenna index The obtained quasi-orthogonal space-time block code codeword is demodulated to obtain the bit information carried by the modulation symbol. Recover the sent data bit stream.

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