CN117395111A

CN117395111A - Subcarrier spatial arrangement index method for MIMO-OFDM system

Info

Publication number: CN117395111A
Application number: CN202311306435.4A
Authority: CN
Inventors: 张璐麟; 郑兴; 彭宇辉
Original assignee: Hangzhou Dianzi University
Current assignee: Hangzhou Dianzi University
Priority date: 2023-10-10
Filing date: 2023-10-10
Publication date: 2024-01-12

Abstract

The invention discloses a subcarrier spatial arrangement index method for a MIMO-OFDM system. This method groups the source bits at the transmitter and performs QAM modulation and index modulation respectively. The index-modulated bits are mapped into a subcarrier spatial arrangement matrix, multiplied by the QAM-modulated constellation, and then subjected to space-time mapping to obtain the data to be sent by the subcarriers of each transmitting antenna. The time domain signal to be sent by each antenna is then generated through IDFT changes. At the receiving end, the subcarrier space arrangement matrix and QAM symbols are obtained through demodulation in the corresponding manner. The mapping between the subcarrier space arrangement matrix and the index bits is performed on the same subcarrier space, and the source bit data is obtained through serial-to-parallel conversion. This method starts from the utilization of space resources, which can improve spectrum utilization and achieve a certain degree of reception diversity. The bit error rate and demodulator complexity are both better than the existing technology, so that communication quality and spectrum utilization can reach a balance.

Description

Subcarrier space arrangement indexing method of MIMO-OFDM system

Technical Field

The invention belongs to the technical field of wireless communication, relates to a digital signal processing method of index modulation in baseband modulation, and in particular relates to a subcarrier space arrangement index method of a MIMO-OFDM system.

Background

The huge number of users of 5G wireless networks will greatly increase the energy consumption. Therefore, in the design process of communication between devices, spectrum sharing, ultra-dense network, millimeter wave network, internet of things communication, multiple Input Multiple Output (MIMO) system, and the like, the high data rate and high energy efficiency of the wireless communication system have high priority. The proposal of the MIMO technology enables the space resource to be better utilized, has obvious improvement in the aspects of channel capacity and error performance, and is the basis of the next generation wireless communication system. MIMO systems increase throughput and coverage on the one hand and on the other hand provide capacity and diversity gains by exploiting the multi-channel capability. MIMO systems enable the use of spatial resources, and one of the key goals is to increase the data transmission rate and spectrum utilization by using distinguishable spatial information. Conventional space-time block codes (STBC) or vertical layered space-time coding (V-BLAST) can maximize diversity and multiplexing gain, but the requirements on the channel are very demanding, and when the channel conditions cannot be met, there is severe inter-subcarrier interference (ICI).

Spatial Modulation (SM) technology is an important MIMO technology that has emerged in recent years. In the SM scheme, in order to obtain the space diversity of rich scattering environments, the receiving end and the transmitting end are provided with a plurality of antennas, but in each transmitting time slot, the transmitting end activates only one antenna, so that the problem of synchronization among antennas is solved, interference among channels is avoided, and the complexity of a communication system is greatly reduced. Furthermore, in the SM scheme, information is transferred using an active antenna index of a transmitter in addition to transmitting a data symbol. This scheme may allow the data rate to increase logarithmically with the number of transmit antennas. In a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system, since data transmitted by one OFDM symbol is far greater than data carried by an active antenna index of a transmitter, in the MIMO-OFDM system, an SM modulation technique improves a data transmission rate very little, but a transmitter and a receiver become relatively complex.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a subcarrier space arrangement indexing method of an MIMO-OFDM system, which is characterized in that subcarriers of OFDM signals are grouped according to the number of antennas, and subcarriers in each group are respectively transmitted in different antennas according to different arrangement modes, so that the data transmission rate can be improved without increasing the bandwidth, and the frequency band utilization rate is improved.

A method for novel spatial index modulation of a MIMO-OFDM system, comprising the steps of:

step 1, in the MIMO-OFDM system of the P X Q antenna, the source data after channel coding is divided into m groups, whereinAnd m is an integer. The +.>The m groups get the QAM symbols { s } carried by N sub-carriers altogether ₁ ,s ₂ ,…,s _N N, where N _QAM Is a QAM modulation index. Initial space-frequency arrangement data block matrix M formed by ith group of subcarriers _i The method comprises the following steps:

the matrix M _i Is P, where i=1, 2, … m, s _n Represents QAM data carried by the nth subcarrier of OFDM, n=1, 2, … N.

Step 2, D of the rest part in the ith group of source data _imb Mapping bit data into subcarrier space arrangement index matrix I _i ，D _imb Satisfy the following requirementsThe index matrix I _i The size of the vector is P, the vector is composed of P mutually orthogonal unit vectors, and each arrangement mode of the P unit vectors corresponds to one D _imb Bit data.

Step 3, the initial space frequency number is calculatedData block M _i And index matrix I _i Multiplying to obtain space frequency data block matrix X carrying index information _i Index matrix I _i The arrangement modes of the unit vectors are different, the QAM symbols carried by the subcarriers are not changed, and only the transmitting antennas corresponding to the subcarriers are changed. Each space frequency data block X _i Carry D _imb +N _QAM * P-bit data. Splicing the m space frequency data block matrixes according to the positive sequence of the subcarriers to obtain space frequency data matrixes S= [ X ] of the P antennas ₁ X ₂ X ₃ …X _m ]。

Step 4, IDFT calculation is sequentially performed on each row of the spatial data matrix S, so before IDFT calculation, each row of the matrix S needs to be constructed into a conjugate symmetric matrix form as shown in formula (4) in order to make the calculation result of IDFT be a pure real number:

in the aboveRepresenting the QAM symbols carried by the nth subcarrier on the p-th antenna. s represents the conjugation of s.Is of a size of 1 XN _zp All zero matrices of (a). Setting the oversampling rate C, c=n according to the number of 0 _DFT /(N _DFT -N _zp ) Wherein N is _DFT For the calculated length of IDFT and DFT, a large oversampling rate can reduce the error rate of the system. After IDFT calculation, the discrete form OFDM real signal x to be transmitted by the p-th antenna can be obtained _p ：

Wherein k=0, 1,2, …, N _DFT -1。S[p][n]Data representing the nth row and nth column of the space frequency data matrix S. p=1, 2,..p. After IDFT operation, space frequency data matrix S to be transmitted by the antenna is mapped into space time matrix blocks, x ₁ ,x ₂ ,…,x _P Respectively emitted simultaneously through the P antennas.

And 5, grouping the received data according to a mode of transmitting subcarrier grouping. After receiving the signal, the receiving end performs OFDM demodulation and conversion to the frequency domain through DFT. In the MIMO-OFDM system, the perfect channel estimation is assumed, the MIMO channel has good scattering environment, the channel space is uncorrelated, the channel coherence time is far longer than the duration of the space-time block, and the transmission system model is as follows through the frequency selective fading channel:

wherein the method comprises the steps ofThe signal carried by the nth subcarrier received by the receiving antenna q.The channel responses corresponding to the nth sub-carrier on the transmitting antenna p and the receiving antenna q are obtained.Is the QAM signal carried by the nth subcarrier of the transmit antenna p.Representing the additive noise of the nth subcarrier of the receiving antenna q.

According to the space frequency data matrix S, each subcarrier exists in only one antenna, namelyOnly one of which is not 0. Therefore->Can watchThe method is shown as follows:

wherein the method comprises the steps ofRepresented by the number t _n N-th subcarrier data transmitted by the antenna, [ t ] ₁ t ₂ t ₃ …t _N ]Representing subcarrier spatial arrangement index information, t _n ∈[1,2,…,P]。Indicating the receiving antenna q, numbered t _n The channel response of the nth subcarrier is transmitted by the transmitting antenna. Since the N subcarriers of OFDM are divided into m groups of P subcarriers, the data received by each group of subcarriers is regarded as a vector:

number t in the m-th sub-carrier packet received by the receiving antenna q _p The channel response of the p-th subcarrier of the transmit antennas of (c). Wherein->A data vector representing the mth packet received by the receiving antenna q.And the QAM symbol carried by the p-th subcarrier in the m-th subcarrier group.

Step 6, antenna and QAM symbol detection is carried out on the received data vectors of the m groups of subcarrier groups by using a Maximum Likelihood (ML) detector:

wherein the method comprises the steps ofSpatial index information carried by the data vector for the mth group of subcarriers, and QAM symbols. Carry QAM data->The sub-carriers are numbered +.>Is provided.

And 7, performing QAM reflection on the data information subjected to ML demodulation of each group, demapping antenna index information, and finally obtaining a restored source bit stream after data sequencing.

The invention has the following beneficial effects:

aiming at the method that the transmitting end of the MIMO-OFDM system uses subcarrier grouping space arrangement, the number of OFDM subcarriers transmitted on each antenna is consistent, the frequency band utilization rate can be effectively improved by reasonably setting the grouping of the subcarriers, the data rate in the MIMO-OFDM system is increased logarithmically along with the number of transmitting antennas, and the PAPR (peak-to-average power ratio) on each transmitting antenna can be reduced. The receiving end can demodulate through a Maximum Likelihood (ML) demodulator to obtain a transmitting antenna index and QAM data. In addition, an MMSE equalizer can be used for noise removal and channel equalization, so that adverse effects on the transmission reliability of the system are avoided.

Drawings

Fig. 1 is a schematic diagram of a MIMO-OFDM system based on subcarrier spatial arrangement indexes;

the embodiment of fig. 2 enriches the system error rate results of different antenna combinations under scattering environment channels;

the system error rate results for different antenna combinations in the weak scattering environment channel in the embodiment of fig. 3.

Detailed Description

The invention is further explained below with reference to the drawings;

example 1

The present embodiment assumes that 24 original binary bit data after source coding is { 01110110100_1100101101101 }, using 4QAM modulation, the number of subcarriers n=8 of OFDM, the number of transmit antennas p=4, and the number of packets m=2, the original binary bit data is divided into {10110100_11011101} and {0111_1100}, where { 10100_11011101} is mapped into two initial space-frequency arrangement data blocks M by 4QAM modulation ₁ ,M ₂ ：

{0111_1100} is mapped to subcarrier spatially arranged index matrix I ₁ ,I ₂ ：

The mapping relationship is shown in table 1:

TABLE 1

The initial space frequency data block M _i And index matrix I _i Multiplying to obtain space frequency data block matrix X carrying index information _i ：

Each space-frequency data block matrix X _i Carrying 12 bits of data. Para [ X ] ₁ X ₂ ]Rearranging according to the subcarrier positions to obtain a space frequency data matrix S to be transmitted by the antenna:

each row of the matrix S is to represent data to be transmitted by one antenna. After receiving the signal, the receiving end can estimate the transmitted space arrangement index matrix I through maximum likelihood estimation, modulate the data M with QAM, and then obtain the original sequence through reflection.

Example 2

In an embodiment, after channel coding, QAM mapping, index matrix mapping, space-time mapping, a conjugate sequence is constructed for the obtained signal of each antenna, after IDFT calculation, an OFDM signal of each antenna is generated, and finally, the OFDM signal is transmitted through a radio frequency transmitting antenna. A corresponding MMSE frequency domain equalizer is designed on a receiving end, a QAM demodulator is cascaded at the back, and the ML subcarrier space arrangement decoder is firstly transmitted after the QAM demodulation. And finally, combining the index bit with the data bit, and obtaining a source bit stream after channel decoding. Specifically, the oversampling rate c=4, the ifft and FFT length is 1024, and the number of subcarriers n=400.

The error rates of different signal-to-noise ratios of the method under 10 multipath Rayleigh fading channels are calculated, the performances of the MISO-OFDM system, the double-transmission double-reception MIMO-OFDM system and the double-transmission four-reception system are compared, the result is shown in figure 2, the number of receiving antennas is increased, and the error rate can be obviously improved. It can be seen that MIMO-OFDM subcarrier spatial arrangement index modulation can effectively achieve receive diversity, and in a rich scattering environment, use spatial information to improve spectrum utilization and simultaneously enable reliable communication quality. Fig. 3 shows bit error rates of the method under different signal-to-noise ratios in a rayleigh fading channel with a multipath number of 2. Compared to fig. 2, it can be seen that the present system has better communication quality when multipath effects are weak. Compared with V-BLAST coding, the method reduces the requirement on scattering environment, improves the spectrum utilization rate and can obtain better communication quality. Can be applied to various channel environments. The method can realize a certain degree of receiving diversity, the error rate is superior to that of a space index (SM-OFDM) and a MIMO system based on V-BLAST coding, and the complexity of a demodulator is lower than that of the SM-OFDM and the MIMO system based on V-BLAST coding.

Claims

1. A subcarrier spatial arrangement indexing method for a MIMO-OFDM system, characterized by the following steps:

Step 1: At the transmitter of the MIMO-OFDM system with P antennas, the source data after channel coding is first divided into m groups, where... And m is an integer; for each group of source data Each data point is mapped to a QAM symbol, resulting in the QAM symbols { _s1 , _s2 , ..., _sN } carried by N subcarriers at the transmitter, where _NQAM is the QAM modulation index; then the initial space-frequency arrangement data block matrix _Mi formed by the QAM symbols on the i-th subcarrier is:

The size of the matrix _Mi is P*P, where i = 1, 2, ..., m;

Step 2: Map the remaining _{Di_imb} bits in the i-th group of source data to a subcarrier spatial permutation index matrix _{I_i} , where _{Di_imb} satisfies The index matrix I _<sub>i </sub> consists of P mutually orthogonal unit vectors of size P*P, and each arrangement of the P unit vectors corresponds to a _Dimb bit of data.

Step 3: Multiply the initial space frequency data block _Mi by the index matrix _I to obtain the space frequency data block matrix _Xi carrying index information. Each space frequency data block _Xi carries _Dimb + N _QAM * P bits of data. Concatenate the m space frequency data block matrices in the forward order of the subcarriers to obtain the space frequency data matrix S = [ _X1 _X2 _X3 … _Xm ] for P antennas.

Step 4: Perform IDFT calculation on the space frequency data matrix S, map it into a timing signal, and then transmit it using the corresponding antenna; at the receiving end, use ML to perform antenna and QAM symbol detection on the received data vector, then perform QAM inverse mapping, and demap the antenna index information according to the index matrix in step 2. Finally, after data sorting, the restored source data is obtained.

2. The subcarrier spatial arrangement indexing method for a MIMO-OFDM system as described in claim 1, characterized in that: before performing IDFT calculation on the space-frequency data matrix S, the following conjugate symmetric matrix is constructed sequentially for each row of the matrix:

in s represents the QAM symbol carried by the nth subcarrier on the p-th antenna, where p = 1, 2, ..., P; s ^* represents the conjugate of s; It is a zero matrix of size 1×N _zp ; the oversampling rate C and the computation length N _DFT of IDFT are set according to the number of zeros, C＝N _DFT /(N _DFT -N _zp );

Calculate the timing signal x _<sub>p</sub> transmitted by the p-th antenna:

Where S[p][n] represents the data in the p-th row and n-th column of the space frequency data matrix S.

3. The subcarrier spatial arrangement indexing method for a MIMO-OFDM system as described in claim 1, characterized in that: at the receiving end, assuming the number of receiving antennas is Q, the transmission system model is:

in, To receive the signal carried by the nth subcarrier received by the receiving antenna q; This represents the QAM signal carried by the nth subcarrier transmitted by the antenna numbered _{t_n} , where [ _{t_1} _{t_2} _{t_3} … _{t_N} ] represents the spatial arrangement index information of the subcarriers, and _{t_n} ∈ [1,2,…,P]. Let represent the channel response of the nth subcarrier under the receiving antenna q and the transmitting antenna numbered _tn ; then the data received by the receiving subcarrier is represented as:

in, This represents the channel response of the p-th subcarrier of the transmitting antenna numbered _tp in the m-th subcarrier packet received by the receiving antenna q; This represents the data vector of the m-th packet received by the receiving antenna q; The QAM symbol carried by the p-th subcarrier in the m-th subcarrier group.

4. The subcarrier spatial arrangement indexing method for a MIMO-OFDM system as described in claim 3, characterized in that: a maximum likelihood detector is used to perform antenna and QAM symbol detection on the data vectors of the received m groups of subcarrier packets.

in The data vector of the m-th subcarrier carries spatial index information and QAM symbols; it also carries QAM data. The subcarriers are numbered as The antenna transmits.