阅读说明：本技术 一种空间频率索引调制传输方法 (Space frequency index modulation transmission method ) 是由 蒋婷敏 肖悦 但黎琳 于 2019-11-26 设计创作，主要内容包括：本发明属于无线通信技术领域，具体涉及一种空间频率索引调制传输方法。本发明首先引入空频索引调制，利用空间和频域索引调制的优势，避免了天线间干扰，降低PAPR以及对频偏的敏感性，以提高系统误码性能。同时利用空间和频域两个维度的索引信息来传递额外的比特信息，以弥补系统频谱效率的损失。其次通过利用信道信息预编码，在激活的子载波上进行天线偏移，进一步实现了系统误码率性能的提升。(The invention belongs to the technical field of wireless communication, and particularly relates to a space frequency index modulation transmission method. The invention firstly introduces space frequency index modulation, utilizes the advantages of space and frequency domain index modulation, avoids interference between antennas, reduces PAPR and sensitivity to frequency deviation, and improves the error code performance of the system. And simultaneously, the index information of two dimensions of space and frequency domain is utilized to transmit extra bit information to make up the loss of the spectrum efficiency of the system. And secondly, by utilizing channel information precoding, antenna offset is carried out on the activated subcarriers, and the improvement of the error rate performance of the system is further realized.)

1. A space frequency index modulation transmission method defines a multi-carrier space frequency index modulation system with N_tThe IFFT length of the OFDM signal transmitted by each transmitting antenna is N, so that each OFDM symbol period has N_tX N space frequency resource units, dividing the space frequency resource into G sub-blocks, each sub-block having N_SF＝N_txL elements, where L is the number of subcarriers selected per transmit antenna on each sub-block; the system performs bit mapping by taking a space frequency block as a unit, each subblock is independent, each subblock of the system only activates k space frequency resource units, and each activation unit can only be on different frequency domains; the transmission method comprises the following steps:

a sending end:

a. dividing the information bit stream: dividing the information bit stream into index bits and modulation bits, wherein the index bits are used to select a specific transmission pattern on each space-frequency resource block, i.e. to activateThe modulation bits are mapped into constellation point symbols through M-QAM modulation and transmitted on the activated space frequency resource units; for any sub-block, where the length of the index bits is

b. index modulation and information mapping are carried out: for each sub-block, according to p₁Activating corresponding resource units according to the mapping relation between the bit index bits and the transmission patterns; p is to be₂The bit modulation bits are modulated and mapped into constellation point symbols by an M-ary constellation point set omega, and are configured by the normalized power of rho ═ L/k and are placed on the activation unit;

c. generating OFDM blocks and interleaving: g sub-blocks are connected after information mapping to generate OFDM blocks which are distributed to N_tThe root antenna interweaves the OFDM block on each antenna;

d. antenna offset by block: for N after interleaving_tDividing the xN space frequency resource units into G sub-blocks, and for any sub-block, if the symbol on the nth sub-carrier is expressed as

d1. Offset antenna selection: for any sub-block, assume that the l-th legal space-frequency index modulation symbol is selected, where

d2. pre-coding: to enable the receiving end to correctly detect and recover the data, it is necessary to select a symbol S to be transmitted_i,mAnd (3) carrying out precoding processing:

e. frequency domain-time domain transformation: connecting the transmission vectors of the pre-coded G sub-blocks to generate OFDM blocks and distributing the OFDM blocks to corresponding N sub-blocks according to the selected offset antennas_tThe root antenna is transmitted after serial-parallel conversion, IFFT, parallel-serial conversion and cyclic prefix adding operation are sequentially carried out on the corresponding antenna;

receiving end:

when the transmission signal is transmitted from the transmitting antenna and experiences Rayleigh fading channel, the receiving end carries out the operation of removing cyclic prefix and FFT on the received signal, and if the index bit is mapped to the l legal space frequency index modulation signal mode X for any sub-block^lThe received signal in the frequency domain is:

the above formula can be further expressed as:

Y＝βHX^l+W

the receiving end adopts ML detection to recover the original data, and detects the original information of the corresponding sub-block by traversing all possible space frequency index modulation signal modes, namely:

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to a space frequency index modulation transmission method.

Background

With the increasing demand for communication services, wireless communication technologies with higher bandwidth efficiency and reliable transmission performance are being developed. Orthogonal Frequency Division Multiplexing (OFDM) technology is one of the most popular multi-carrier transmission technologies at present due to its high spectrum utilization rate, good anti-multipath fading capability, simple hardware and low cost.

Most of the Multiple-Input Multiple-Output (MIMO) transmission technologies can effectively improve data rate and system capacity without occupying additional spectrum resources by providing Multiple antennas at the transmitting and receiving ends for transmission, and have recently gained much attention and research. Spatial Modulation (SM), a novel multi-antenna technique, is known for its high transmission efficiency, high energy efficiency and low complexity transmitter design by using index information of antennas to transmit extra bit information. Because only one transmitting antenna is activated in each sending time slot, the problems of synchronization and interference among the antennas are avoided, and simultaneously, only one radio frequency unit is needed for transmitting data, compared with the traditional MIMO technology, the hardware implementation cost is reduced.

Index Modulation OFDM (OFDM-IM) is a new type of multicarrier transmission technology that has been proposed as an alternative to conventional OFDM. Inspired by SM, index modulation is applied to OFDM systems, with the index of the sub-carriers being used to transmit additional bit information. Different from the traditional OFDM, the OFDM-IM only activates partial subcarriers to transmit information, and has proved that the OFDM system has better error rate performance compared with the traditional OFDM under the medium and low frequency spectrum efficiency and can reduce the peak-to-average ratio of the OFDM system.

To further exploit the potential of IM, researchers propose to combine OFDM-IM and MIMO techniques to exploit the advantages of both, the system being defined as MIMO-OFDM-IM. Compared with the traditional MIMO-OFDM, the method can obtain higher signal-to-noise ratio gain. However, the system only performs subcarrier index modulation independently on each antenna, and ignores index information in the spatial dimension. To solve this limitation, a space-frequency index modulation scheme is proposed to further improve the spectrum efficiency and the transmission reliability.

Disclosure of Invention

The invention provides a novel space-frequency index modulation transmission scheme based on the purpose of improving the error code performance of a multi-carrier system. The invention firstly introduces space frequency index modulation, utilizes the advantages of space and frequency domain index modulation, avoids interference between antennas, reduces PAPR and sensitivity to frequency deviation, and improves the error code performance of the system. And simultaneously, the index information of two dimensions of space and frequency domain is utilized to transmit extra bit information to make up the loss of the spectrum efficiency of the system. And secondly, by utilizing channel information precoding, antenna offset is carried out on the activated subcarriers, and the improvement of the error rate performance of the system is further realized.

The technical scheme of the invention is as follows:

assume a multi-carrier space-frequency index modulation (SFIM-OFDM) system has N_tThe IFFT length of the OFDM signal transmitted by each antenna is N, so that each OFDM symbol period has N_tX N space frequency resource units, dividing the space frequency resource into G sub-blocks, each sub-block having N_SF＝N_tX L elements, where L is the number of subcarriers selected for each transmit antenna on each sub-block. The system uses the space-frequency resource block as a unit to carry out bit mapping, each sub-block is independent, so any space-frequency resource block can be taken as an example for explanation, and it is assumed that each sub-block of the system only activates k resource units, each activation unit can only be on different frequency domains, and the rest keep silent. The transmitter structure is shown in fig. 1, and the system implementation process includes the following steps:

a sending end:

a. dividing the information bit stream: and dividing the information bit stream into index bits and modulation bits, wherein the index bits are used for selecting a specific transmission pattern on each space-frequency resource block, namely, activated resource units, and the modulation bits are mapped into constellation point symbols through M-QAM modulation and transmitted on the activated resource units. For any sub-block, where the length of the index bits is

Represents rounding down; modulating the bit length p₂＝k·log₂And M. The index bit in the symbols of one frame of the system has m₁＝p₁G bits, modulation bits total m₂＝p₂G bits, total number of bits m_total＝m₁+m₂A bit.

b. Index modulation and information mapping are carried out: for each sub-block, according to p₁Between bit index bit and transmission patternActivating the corresponding resource unit according to the mapping relation; p is to be₂And the bit modulation bits are modulated and mapped into constellation point symbols by an M-ary constellation point set omega, and are configured by the normalized power of rho-L/k and placed on the activation unit.

c. Generating OFDM blocks and interleaving: g sub-blocks are connected after information mapping to generate OFDM blocks which are distributed to N_tThe root antenna and the OFDM block on each antenna are interleaved.

d. Antenna offset by block: for N after interleaving_tThe x N space-frequency resource units are subdivided into G sub-blocks. For any sub-block, if the symbol on the nth sub-carrier is expressed as

Wherein

The sub-block transmission symbol is X ═ X₁,X₂,…,X_L]^T. The channel information on the nth subcarrier is

Wherein | H_a,nI represents the corresponding channel frequency response between the a-th antenna and the receiving antenna on the nth subcarrier, and a e Φ ═ 1,2, …, N_tThe frequency domain channel matrix of the whole sub-block is

d1. Offset antenna selection: for any sub-block, assume that the l-th legal space-frequency index modulation symbol is selected, where

According to the index bit mapping relation, the ith transmitting antenna and the resource unit pointed by the mth subcarrier in the block are activated, and the sub-block symbols are

According to channel information H on activated sub-carriers_mSelectingThe transmitting antenna corresponding to the element with the largest modulus value is as follows:j denotes the optimal transmit antenna, i.e., offset antenna, selected by the activated mth subcarrier.

d2. Pre-coding: to enable the receiving end to correctly detect and recover the data, it is necessary to select a symbol S to be transmitted_i,mAnd (3) carrying out precoding processing:

the precoded transmit vector may be represented as:

wherein

Is a transmit signal power normalization factor and,

which may be considered as the precoding coefficient of the transmitted signal. i is the transmitting antenna corresponding to the resource element activated by the index bit in step d1, and j is the offset antenna selected on the mth subcarrier corresponding to the activated resource element.

e. Frequency domain-time domain transformation: connecting the transmission vectors of the pre-coded G sub-blocks to generate OFDM blocks and distributing the OFDM blocks to corresponding N sub-blocks according to the selected offset antennas_tAnd the root antenna is transmitted after serial-parallel conversion, IFFT, parallel-serial conversion and cyclic prefix adding operation are sequentially carried out on the corresponding antenna.

Receiving end:

when the transmission signal is transmitted from the transmitting antenna and experiences Rayleigh fading channel, the receiving end carries out the operation of removing cyclic prefix and FFT on the received signal, and for any sub-block, if the index bit is mapped to the l legal space-frequency index modulation signal mode X^lIts received signal in the frequency domain can be expressed as:and W clothesFrom a mean of 0 and a variance of N₀Complex gaussian distribution.

The expression can be written in particular in the form:

the above formula can be further expressed as:

Y＝βHX^l+W

and the receiving end recovers the original data by adopting ML detection, and detects the original information of the corresponding sub-block by traversing all possible space-frequency index modulation signal modes. Namely:

wherein X^κIs counted as

The kth signal pattern in the conventional spatial modulation signal.

The invention has the beneficial effects that: compared with the traditional multi-carrier spatial modulation system, the invention expands the spatial dimension to the frequency domain dimension on the basis of the spatial dimension, and utilizes the index information of the space and the frequency domain to carry out extra bit transmission, thereby improving the spectral efficiency of the system. Compared with the traditional space frequency index multi-carrier (SFIM-OFDM) technology, the invention introduces the concept of offset antenna, utilizes CSI information to precode the transmitted signal, and further improves the error rate performance of the system.

Drawings

Fig. 1 is a block diagram of a transmitting end of a novel space-frequency index modulation technique proposed by the present invention.

Fig. 2 is a simulation graph comparing the bit error rate performance of the embodiment.

Detailed Description

The technical scheme of the invention is described in detail in the following with reference to the accompanying drawings and embodiments: