CN109347781A - MIMO-OFDM-IM detection method based on the search of subcarrier tree - Google Patents
MIMO-OFDM-IM detection method based on the search of subcarrier tree Download PDFInfo
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Abstract
The invention discloses the MIMO-OFDM-IM detection methods searched for based on subcarrier tree, and by the conversion to signal is received, the problem of will test is converted into tree search problem, are then successively scanned for by subcarrier using K-best detection algorithm；In each layer, path metric value is calculated according to certain subcarrier order, and selects the node retained and the node abandoned compared with thresholding according to path metric value；When searching the last one subcarrier of first layer, the symbol in minimal path metric respective path is the testing result based on subcarrier K-best detection method；The method of subcarrier K-best detection based on thresholding is scanned for signal is received, and is on the one hand reduced the complexity of system detection, is on the other hand reached and performance similar in optimal detection.
Description
Technical Field
The invention relates to the research field of wireless communication technology, in particular to a MIMO-OFDM-IM detection method based on subcarrier tree search.
Background
In order to improve the capacity and performance of the system, MIMO technology using antenna multiplexing gain and diversity gain is proposed and is one of the key technologies of the fourth generation mobile communication system. However, the multiplexing gain of the conventional MIMO technology depends on the orthogonality of the transmitting and receiving antennas, and thus a new multi-antenna technology, i.e., spatial index modulation, which does not require the orthogonality of the transmitting and receiving antennas is proposed. In spatial index modulation, information is transmitted not only through constellation symbols but also through activated antenna sequence numbers. Compared with the traditional MIMO, the space domain index modulation avoids the interference among the antennas and reduces the complexity of the detector at the receiving end. The spatial domain index is modulated to be a very competitive MIMO technique in the next generation mobile communication.
Inspired by the idea of spatial domain index modulation, the application of index modulation to the frequency domain proposes an OFDM-IM system. The OFDM-IM system is a flexible subcarrier system, which activates a part of subcarriers to transmit constellation data through index modulation, and the rest subcarriers are silent. Due to the fact that a large number of silent subcarriers exist in the OFDM-IM, active subcarrier distribution is sparse, and therefore frequency offset can be effectively resisted. Meanwhile, the silent subcarrier does not need to send energy, and the energy efficiency of the system is improved. Due to the introduction of index modulation, OFDM-IM can flexibly configure the sub-carriers and can adjust between system performance and spectral efficiency as required.
Based on the advantages of the MIMO technology and the OFDM-IM technology, the MIMO-OFDM-IM system can be obtained by combining the MIMO technology and the OFDM-IM technology. In the system, a transmitting end antenna independently transmits OFDM-IM data frames, and a receiving end antenna demodulates the OFDM-IM subcarrier group detection. Compared with the traditional MIMO-OFDM system, the MIMO-OFDM-IM system has more excellent performance, can realize higher energy efficiency, and can realize compromise between spectrum efficiency and system performance by changing the number of active subcarriers. But due to the correlation of the subcarriers in the subcarrier group in MIMO-OFDM-IM, the detection of the positions of the constellation symbols and the active subcarriers in the subcarrier group becomes a challenging problem. Although the Maximum Likelihood (ML) detector achieves the optimal performance, the complexity is too high, and the number increases exponentially with the number of active subcarriers and the number of antennas, which is not favorable for practical implementation. Although the Minimum Mean Square Error (MMSE) based detector and the sequential coherent Interference Cancellation (OSIC) detector reduce the complexity, the performance of the detector is far from the performance of the ML detector at the cost of the system performance. How to design a detector with low complexity to approximate optimal ML detection performance remains a challenging problem in MIMO-OFDM-IM.
Disclosure of Invention
The invention mainly aims to overcome the defects of the prior art and provide a MIMO-OFDM-IM detection method based on subcarrier tree search.
The purpose of the invention is realized by the following technical scheme:
the MIMO-OFDM-IM detection method based on subcarrier tree search is characterized by comprising the following steps:
s1, source bit mapping;
source bit ANtBit information division into NtThe A bit information of each group corresponds to one transmitting antenna; dividing A bit information of each antenna into G groups through a bit splitter, wherein each group of the G groups has p bit information, A is pG, and the p bit information is mapped to an OFDM-IM group with the carrier length of N, wherein N is M/G, M is the number of subcarriers in one OFDM-IM block symbol, in each OFDM-IM group, L transmission constellation symbols exist in subcarriers with the carrier length of N, and the rest subcarriers are null subcarriers;
in one aspect, p1Bit information is sent to an index selector, and is used for selecting L subcarriers from subcarriers with the carrier length of N to activate, so that the bit number transmitted by the index selector is as follows:
wherein,is a pair ofThe lower part is taken as the whole,is a binomial coefficient;
on the other hand, p2The bit information is sent to the mapper, and is mapped to L transmission constellation symbols in the W dimension, and then the bit number transmitted by the mapper is:
p2＝Llog2W；
s2, OFDM modulation data is sent,
after index modulation, G group data of each transmitting antenna is subjected to group generator to obtain an OFDM-IM group symbol:
wherein,for the data of the nth carrier in the gth OFDM-IM carrier group of the tth antenna, t is 1,2t，g＝1,2,...,G，n＝1,2,...,N；
Sending the OFDM-IM group symbol into an interleaver to obtain the interleaved OFDM-IM group symbol
The OFDM-IM group symbol after interweaving is converted into a time domain through IFFT operation, and is sent out by a sending antenna after a CP is added;
s3, receiving multi-antenna signals, wherein the receiving end has NrEach receiving antenna firstly carries out CP operation and FFT conversion on the received signals and converts the data of a time domain into a frequency domain; for the r antenna, the received signal converted to the frequency domain after FFT is:
wherein,in order to receive the vector of signals, for the channel frequency domain response from the tth transmit antenna to the r-th receive antenna, in order to be a vector of the noise,
s4, deinterleaving the signal packet:
the signals obtained by the deinterleaving operation opposite to the interleaving operation at the transmitting end are:
wherein h isr,tIs composed ofDeinterleaved data, ηrIs composed ofDe-interleaving the data;
in order to detect the position of active sub-carrier in OFDM-IM group, the de-interleaved signal passes through signal grouping device, and is divided into G group with the same number as that of the sending end group, for the G group, there are:
wherein,for the channel through which the g-th group transmits data,noise vectors on the transmitted data for the g-th group;
the nth subcarrier in the g group receives a signal:
wherein N is 1, 2.. times.n;
s5, converting signals;
carrying out QR decomposition on the channel matrix of the nth subcarrier of the g group:
Hg(n)＝Qg(n)Rg(n)，
wherein Q isg(n) is an orthogonal headquarters matrix,Rg(n) is aboveThe matrix of the triangles is a matrix of the triangles,
the nth sub-carrier received signal formula in the g group in step S4 is pre-multiplied by (Q)g(n))HObtaining:
wherein z isg(n)＝(Qg(n))Hyg(n)，μg(n)＝(Qg(n))Hηg(n)；
According to index modulation, signals of N subcarriers need to be detected continuously, and therefore, the detection problem turns into:
to solve the above problem, a super symbol is defined as The super received symbol is The equivalent channel matrix is Noise is
The detection problem is as follows:
wherein z isg,Rg,xg,μgA combination of the g-th group of signals for all receiving antennas;
s6, detecting the K-best tree based on the subcarrier, wherein the detection of the transmitted signal is as follows:
where Ω is all possible realizations of the transmitted signal for a group,
n thtThe path metric values for the layers are calculated as follows:
wherein,denotes the NthtThe path metric value of the mth possible implementation form in the g subcarrier group of the layer,is the NthtAn mth transmit symbol in a gth subcarrier group of a layer;
n thtThe path metric values for the layers are calculated as follows:
wherein,denotes the NthtA path metric value for the g-th subcarrier group of the layer;
from the NthtLayer searching is started until the first layer antenna is searched, and in the searching process of each layer antenna, the calculation of the path measurement is carried out on the subcarrier level and is carried out in sequence, and the path measurement is determined by the channel factor passed by the subcarrier;
the channel factor of the nth subcarrier of the l-th layer antenna is as follows:
for the search of the antenna of the layer I, the larger the channel factor is, the smaller the channel attenuation passed by the subcarrier is, the more the subcarrier has the priority to calculate the path metric value, and the smaller the channel factor is, the subcarrier delays to calculate the path metric value;
according to the channel factors, the order of calculating the path metric values of the subcarriers of the antenna of the l layer is ordered as follows:
{1'l,2'l,...,n'l...,N'l}，
wherein, n'lThe serial number of the subcarrier of the antenna in the l layer arranged at the nth position is represented;
in each layer, calculating a path metric value according to the sequence of the subcarrier sequence, comparing the path metric value with a preset threshold value after calculating the path metric value each time, and reserving nodes lower than the threshold value; when the first layer N 'is searched'1And when each subcarrier is used, the super symbol value on the path corresponding to the minimum path metric value is a detection result.
Further, in step S6, specifically, the method includes:
y1, calculation of Path metric from NthtLayer antennaStart of one sub-carrier, NthtLayer oneThe path metric value of the mth node on the subcarrier is calculated as:
wherein,mapping symbols for an mth candidate constellation selected from 0 or data constellation points;
after the path metric value is calculated, the path metric value is compared with a threshold value, and the threshold value can be calculated as:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy; by comparing the path metric value with a threshold value, selecting nodes whose path metric values are below the threshold, and associating the path metric values of these nodes with corresponding symbolsStoring the number value; then continuing to expand to the next subcarrier, each node expanding to the (W +1) subcarrier of the next subcarrier;
at the NthtLayer antennaIn the search of subcarriers, the number of reserved nodes is κ, where min { K, n (W +1) }; after the Nth calculationtLayer antennaAfter the path value on the sub-carrier, the first oneThe sub-carrier continues to extend the sub-node to the next sub-carrier;
y2, NtLayer antennaThe [ (k-1) (W +1) + m on the sub-carriers]The path metric value of each node is:
wherein,is the NthtThe number of nodes reserved for one subcarrier on the layer antenna;is as followsA path metric value corresponding to the kth node of the subcarrier;is as followsThe k node of the subcarrier is extended toBranch metrics for the mth node of the subcarrier;
then there are:
wherein,is as followsThe m-th candidate symbol of which the subcarrier is selected from 0 or a data constellation point;
using additional metricsControlling the number of active subcarriers and null subcarriers in each OFDM-IM subcarrier group to ensure that each OFDM-IM subcarrier group has exactly L active subcarriers, and specifically calculating as follows:
wherein,the number of non-zero elements corresponding to the kth existing path in the first n-1 subcarriers is lambda as a constant, and omega is a data constellation point;
n thtLayer antennaThe threshold values of the sub-carriers are set as follows:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy; selecting nodes of which the path metric values are lower than a threshold by comparing the path metric values with a threshold value, and storing the path metric values of the nodes and corresponding symbol values; then continuing to expand to the next subcarrier, each node expanding to the (W +1) subcarrier of the next subcarrier;
y3, 1 'in K-best tree search detection based on subcarrier of layer 1 antenna'lThe [ (k-1) (W +1) + m on the sub-carriers]The path metric values for each node are calculated as follows:
wherein,is the N 'of the l +1 layer antenna'l+1A path metric value corresponding to the kth node of the subcarrier;is a l-layer antenna of 1'lBranch metrics for the mth node of the subcarrier;
then there are:
wherein,mapping symbols for an mth candidate constellation selected from 0 or data constellation points;is a j-th layer antenna 1'lA symbol value corresponding to a k path on a subcarrier;
the path metric values on other subcarriers of the layer 1 antenna are calculated as:
wherein, n'l＝2'l,3'l,...,N′l；
N 'of l-layer antenna'lThe path metric threshold values for the individual subcarriers are set to:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy. And NtThe layers operate identically, and the path is selected by comparing the path metric to a thresholdThe nodes with the metric value lower than the threshold store the path metric values and the corresponding symbol values of the nodes;
y4, N 'when searching the first layer'lSelecting a path corresponding to the minimum path metric value when each subcarrier is detected, wherein the symbol value on the path is a detection result;
further, the number of the transmitting antennas is NtThe number of the receiving antennas is NrAnd the number of transmitting antennas is equal to the number of receiving antennas, i.e. Nt≤Nr；
Further, in step S2, the interleaver is a group interleaver with dimension G × N;
further, in step S3, the fading channel is a rayleigh multipath fading channel;
further, in step S4, the deinterleaving process is the inverse operation of interleaving.
Compared with the prior art, the invention has the following advantages and beneficial effects:
the method converts the detection problem into a tree search problem by converting the MIMO-OFDM-IM received signals, and then searches the subcarriers layer by utilizing a threshold-based K-best detection algorithm; in each layer, calculating a path metric value according to a certain subcarrier sequence, and selecting a reserved node and a discarded node according to the comparison between the path metric value and a threshold value; when the last subcarrier of the first layer is searched, the symbol on the path corresponding to the minimum path metric value is the detection result based on the subcarrier K-best detection method; the threshold-based subcarrier K-best detection method searches the received signals, reduces the complexity of system detection on one hand, and achieves the performance similar to the optimal detection on the other hand.
Drawings
FIG. 1 is a flowchart of a method for MIMO-OFDM-IM detection based on sub-carrier tree search according to the present invention;
FIG. 2 is a block diagram of a model structure of a transmitting end of the MIMO-OFDM-IM system in an embodiment of the present invention;
FIG. 3 is a block diagram of a receiving end model of the MIMO-OFDM-IM system according to an embodiment of the present invention;
fig. 4 is a schematic diagram showing performance comparison of four detection methods under (N, L) ═ 2,1) and QPSK modulation in the embodiment of the present invention;
fig. 5 is a diagram illustrating the performance comparison of two detection methods under (N, L) ═ 2,1) and QPSK modulation in the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
Example (b):
a MIMO-OFDM-IM detection method based on subcarrier tree search, as shown in fig. 1, where a transmitting end and a receiving end of a MIMO-OFDM-IM system are shown in fig. 2 and fig. 3; here, the number N of transmitting antennas is settNumber of receive antennas N4rThe number of subcarriers M is 1024, the signal modulation is QPSK, the parameter λ in the detector is 100, and the channel used in the simulation is a rayleigh multipath fading channel.
The method comprises the following steps:
s1, source bit mapping;
will ANtBit information division into NtGroup NtThe A bit information of each group corresponds to a sending antenna; dividing the A bit information into G groups by a bit splitter, wherein each group of the G groups has p bit information, A is pG, mapping the p bit information to an OFDM-IM group with the carrier length of N, wherein N is M/G, M is the number of subcarriers in one OFDM-IM symbol, and in the OFDM-IM group, the carrier lengthL transmission constellation symbols are arranged in the subcarriers with the degree of N, and the rest subcarriers are null subcarriers;
in one aspect, p1Bit information is sent to an index selector, and is used for selecting L subcarriers from subcarriers with the carrier length of N to activate, so that the bit number transmitted by the index selector is as follows:
wherein,is a pair ofThe lower part is taken as the whole,is a binomial coefficient;
on the other hand, p2The bit information is sent to the mapper, and is mapped to L transmission constellation symbols in the W dimension, and then the bit number transmitted by the mapper is:
p2＝L log2W；
s2, OFDM modulation data is sent,
after index modulation, G group data of each transmitting antenna is subjected to group generator to obtain an OFDM-IM group symbol:
wherein,for the data of the nth carrier in the gth OFDM-IM carrier group of the tth antenna, t is 1,2t，g＝1,2,...,G，n＝1,2,...,N；
Sending the OFDM-IM group symbol into an interleaver to obtain the interleaved OFDM-IM group symbol
The OFDM-IM group symbol after interweaving is converted into a time domain through IFFT operation, and is sent out by a sending antenna after a CP is added;
s3, receiving multi-antenna signal with NrAfter passing through a fading channel, each receiving antenna firstly passes through CP operation and FFT conversion to convert time domain data into a frequency domain; for the r antenna, the received signal converted to the frequency domain after FFT is:
wherein,in order to receive the vector of signals, for the channel frequency domain response from the tth transmit antenna to the r-th receive antenna, in order to be a vector of the noise,
s4, deinterleaving the signal packet:
the signals obtained by the deinterleaving operation opposite to the interleaving operation at the transmitting end are:
wherein h isr,tIs composed ofDeinterleaved data, ηrIs composed ofDe-interleaving the data;
in order to detect the position of active sub-carrier in OFDM-IM group, the de-interleaved signal passes through signal grouping device, and is divided into G group with the same number as that of the sending end group, for the G group, there are:
wherein,for the channel through which the g-th group transmits data,noise on data sent for the g-th groupAn amount;
the nth subcarrier in the g group receives a signal:
wherein N is 1, 2.. times.n;
s5, converting signals;
carrying out QR decomposition on the channel matrix of the nth subcarrier of the g group:
Hg(n)＝Qg(n)Rg(n)，
wherein Q isg(n) is an orthogonal headquarters matrix,Rg(n) is an upper triangular matrix,
the nth sub-carrier received signal formula in the g group in step S4 is pre-multiplied by (Q)g(n))HObtaining:
wherein z isg(n)＝(Qg(n))Hyg(n)，μg(n)＝(Qg(n))Hηg(n)；
According to index modulation, signals of N subcarriers need to be detected continuously, and therefore, the detection problem turns into:
to is coming toTo solve the above problem, a superscript is defined as The super received symbol is The equivalent channel matrix is Noise is
The detection problem is as follows:
wherein z isg,Rg,xg,μgA combination of the g-th group of signals for all receiving antennas;
s6, detecting the K-best tree based on the subcarrier, wherein the detection of the transmitted signal is as follows:
where Ω is all possible realizations of the transmitted signal for a group,
n thtThe path metric values for the layers are calculated as follows:
wherein,denotes the NthtThe path metric value of the mth possible implementation form in the g subcarrier group of the layer,is the NthtAn mth transmit symbol in a gth subcarrier group of a layer;
n thtThe path metric values for the layers are calculated as follows:
wherein,denotes the NthtA path metric value for the g-th subcarrier group of the layer;
from the NthtLayer searching is started until the first layer antenna is searched, and in the searching process of each layer antenna, the calculation of the path measurement is carried out on the subcarrier level and is carried out in sequence, and the path measurement is determined by the channel factor passed by the subcarrier;
the channel factor of the nth subcarrier of the l-th layer antenna is as follows:
for the search of the antenna of the layer I, the larger the channel factor is, the smaller the channel attenuation passed by the subcarrier is, the more the subcarrier has the priority to calculate the path metric value, and the smaller the channel factor is, the subcarrier delays to calculate the path metric value;
according to the channel factors, the order of calculating the path metric values of the subcarriers of the antenna of the l layer is ordered as follows:
{1'l,2'l,...,n'l...,N'l}，
wherein, n'lThe serial number of the subcarrier of the antenna in the l layer arranged at the nth position is represented;
in each layer, calculating a path metric value according to the sequence of the subcarrier sequence, comparing the path metric value with a preset threshold value after calculating the path metric value each time, and reserving nodes lower than the threshold; (ii) a When the first layer N 'is searched'1And when each subcarrier is used, the super symbol value on the path corresponding to the minimum path metric value is a detection result.
Further, in step S6, specifically, the method includes:
y1, calculation of Path metric from NthtLayer antennaStart of one sub-carrier, NthtLayer oneThe path metric value of the mth node on the subcarrier is calculated as:
wherein,to select from 0 or data constellation pointsThe mth candidate constellation mapping symbol of (1);
after the path metric value is calculated, the path metric value is compared with a threshold, and the threshold value can be calculated as:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy; selecting nodes of which the path metric values are lower than a threshold by comparing the path metric values with a threshold value, and storing the path metric values of the nodes and corresponding symbol values; then continuing to expand to the next subcarrier, each node expanding to the (W +1) subcarrier of the next subcarrier;
y2, NtLayer antennaThe [ (k-1) (W +1) + m on the sub-carriers]The path metric value of each node is:
wherein,is the NthtThe number of nodes reserved for one subcarrier on the layer antenna;is as followsA path metric value corresponding to the kth node of the subcarrier;is as followsThe k node of the subcarrier is extended toBranch metrics for the mth node of the subcarrier;
then there are:
wherein,is as followsThe m-th candidate symbol of which the subcarrier is selected from 0 or a data constellation point;
using additional metricsControlling the number of active subcarriers and null subcarriers in each OFDM-IM subcarrier group to ensure that each OFDM-IM subcarrier group has exactly L active subcarriers, and specifically calculating as follows:
wherein,the number of non-zero elements corresponding to the kth existing path in the first n-1 subcarriers is lambda as a constant, and omega is a data constellation point;
n thtLayer antennaThe threshold values of the sub-carriers are set as follows:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy; selecting nodes of which the path metric values are lower than a threshold by comparing the path metric values with a threshold value, and storing the path metric values of the nodes and corresponding symbol values; then continuing to expand to the next subcarrier, each node expanding to the (W +1) subcarrier of the next subcarrier;
y3, 1 'in K-best tree search detection based on subcarrier of layer 1 antenna'lThe [ (k-1) (W +1) + m on the sub-carriers]The path metric values for each node are calculated as follows:
wherein,is the N 'of the l +1 layer antenna'l+1A path metric value corresponding to the kth node of the subcarrier;is a l-layer antenna of 1'lBranch metrics for the mth node of the subcarrier;
then there are:
wherein,mapping symbols for an mth candidate constellation selected from 0 or data constellation points;is a j-th layer antenna 1'lA symbol value corresponding to a k path on a subcarrier;
the path metric values on other subcarriers of the layer 1 antenna are calculated as:
wherein, n'l＝2'l,3'l,...,N′l；
N 'of l-layer antenna'lThe path metric threshold values for the individual subcarriers are set to:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy; and NtThe operation of the layer is the same, the nodes with the path metric value lower than the threshold are selected by comparing the path metric value with the threshold value, and the path metric values of the nodes and the corresponding symbol values are stored.
Y4, N 'when searching the first layer'1Selecting a path corresponding to the minimum path metric value when each subcarrier is detected, wherein the symbol value on the path is a detection result;
fig. 4 shows the performance comparison of different detection methods at the receiving end in the MIMO-OFDM-IM system, where (N, L) ═ 2,1, the modulation method is QPSK modulation, and the detection methods are MMSE-ML detection, K-best detection for subcarriers with fixed K values, and K-best detection for subcarriers based on thresholds in the present invention. As can be seen from the simulation diagram, the performance of the fixed K value subcarrier K-best detection when K is 8 and the threshold-based subcarrier K-best detection in the present invention approaches the optimal ML detection. There is a large gap between the performance of the fixed K-best detection with K4 and the MMSE-based detection method and the optimal ML detection.
The complexity comparison between the subcarrier K-best detection method with a fixed K value and the subcarrier K-best detection method based on a threshold in the QPSK modulated MIMO-OFDM-IM system with (N, L) ═ 2,1 is shown in fig. 5, the complexity is measured by the number of times of path metric calculation, the complexity of the ML detection method is constant to be O (4096), and the complexity is not shown in the figure because of a large difference from the complexity of the K-best detection method; from simulation, the complexity of the threshold-based subcarrier K-best detection method is reduced along with the increase of the signal-to-noise ratio; the threshold-based subcarrier K-best detection method is a fixed K value subcarrier K-best detection method when the complexity is lower than K-8, and is a fixed K value subcarrier K-best detection method when the signal to noise ratio is higher or even lower than K-4. By combining the simulations of fig. 4 and 5, we can obtain that the threshold-based subcarrier K-best detection method embodies performance advantages compared to MMSE and low-K subcarrier K-best detection methods; compared with the optimal ML and the subcarrier K-best detection method with the high K value, the threshold-based subcarrier K-best detection method has the advantage of complexity.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (6)
1. The MIMO-OFDM-IM detection method based on subcarrier tree search is characterized by comprising the following steps:
s1, source bit mapping;
source bit ANtBit information division into NtThe A bit information of each group corresponds to one transmitting antenna; dividing A bit information of each antenna into G groups through a bit splitter, wherein each group of the G groups has p bit information, A is pG, mapping the p bit information to an OFDM-IM group with the carrier length of N, wherein N is M/G, M is the number of subcarriers in one OFDM-IM symbol, and in each OFDM-IM groupIn the method, L transmission constellation symbols exist in subcarriers with the carrier length of N, and the rest subcarriers are null subcarriers;
in one aspect, p1Bit information is sent to an index selector, and is used for selecting L subcarriers from subcarriers with the carrier length of N to activate, so that the bit number transmitted by the index selector is as follows:
wherein,is a pair ofThe lower part is taken as the whole,is a binomial coefficient;
on the other hand, p2The bit information is sent to the mapper, and is mapped to L transmission constellation symbols in the W dimension, and then the bit number transmitted by the mapper is:
p2＝Llog2W；
s2, OFDM modulation data is sent,
after index modulation, G group data of each transmitting antenna is subjected to group generator to obtain an OFDM-IM group symbol:
wherein,for the data of the nth carrier in the gth OFDM-IM carrier group of the tth antenna, t is 1,2t，g＝1,2,...,G，n＝1,2,...,N；
Sending the OFDM-IM group symbol into an interleaver to obtain the interleaved OFDM-IM group symbol
The OFDM-IM group symbol after interweaving is converted into a time domain through IFFT operation, and is sent out by a sending antenna after a CP is added;
s3, receiving multi-antenna signal with NrEach receiving antenna firstly carries out CP operation and FFT conversion on the received signals and converts the data of a time domain into a frequency domain; for the r antenna, the received signal converted to the frequency domain after FFT is:
wherein,in order to receive the vector of signals, for the channel frequency domain response from the tth transmit antenna to the r-th receive antenna, in order to be a vector of the noise,
s4, deinterleaving the signal packet:
the signals obtained by the deinterleaving operation opposite to the interleaving operation at the transmitting end are:
wherein h isr,tIs composed ofDeinterleaved data, ηrIs composed ofDe-interleaving the data;
in order to detect the position of active sub-carrier in OFDM-IM group, the de-interleaved signal passes through signal grouping device, and is divided into G group with the same number as that of the sending end group, for the G group, there are:
wherein,for the channel through which the g-th group transmits data,noise vectors on the transmitted data for the g-th group;
the nth subcarrier in the g group receives a signal:
wherein N is 1, 2.. times.n;
s5, converting signals;
carrying out QR decomposition on the channel matrix of the nth subcarrier of the g group:
Hg(n)＝Qg(n)Rg(n)，
wherein Q isg(n) is an orthogonal headquarters matrix,Rg(n) is an upper triangular matrix,
the nth sub-carrier received signal formula in the g group in step S4 is pre-multiplied by (Q)g(n))HObtaining:
wherein z isg(n)＝(Qg(n))Hyg(n)，μg(n)＝(Qg(n))Hηg(n)；
According to index modulation, signals of N subcarriers need to be detected continuously, and therefore, the detection problem turns into:
to solve the above problem, a super symbol is defined as The super received symbol is The equivalent channel matrix is Noise is
The detection problem is as follows:
wherein z isg,Rg,xg,μgA combination of the g-th group of signals for all receiving antennas;
s6, detecting the K-best tree based on the subcarrier, wherein the detection of the transmitted signal is as follows:
where Ω is all possible implementations of a group of transmitted signals, | Ω | ═ 2p1WL；
N thtThe path metric values for the layers are calculated as follows:
wherein,denotes the NthtThe path metric value of the mth possible implementation form in the g subcarrier group of the layer,is the NthtAn mth transmit symbol in a gth subcarrier group of a layer;
n thtThe path metric values for the layers are calculated as follows:
wherein,denotes the NthtA path metric value for the g-th subcarrier group of the layer;
from the NthtLayer searching is started until the first layer antenna is searched, and in the searching process of each layer antenna, the calculation of the path measurement is carried out on the subcarrier level and is carried out in sequence, and the path measurement is determined by the channel factor passed by the subcarrier;
the channel factor of the nth subcarrier of the l-th layer antenna is as follows:
for the search of the antenna of the layer I, the larger the channel factor is, the smaller the channel attenuation passed by the subcarrier is, the more the subcarrier has the priority to calculate the path metric value, and the smaller the channel factor is, the subcarrier delays to calculate the path metric value;
according to the channel factors, the order of calculating the path metric values of the subcarriers of the antenna of the l layer is ordered as follows:
{1'l,2'l,...,n'l…,N'l}，
wherein, n'lThe serial number of the subcarrier of the antenna in the l layer arranged at the nth position is represented;
in each layer, calculating a path metric value according to the sequence of the subcarrier sequence, comparing the path metric value with a preset threshold value after calculating the path metric value each time, and reserving nodes lower than the threshold; when the first layer N 'is searched'1And when each subcarrier is used, the super symbol value on the path corresponding to the minimum path metric value is a detection result.
2. The MIMO-OFDM-IM detection method according to claim 1, wherein the step S6 specifically comprises:
y1, calculation of Path metric from NthtLayer antennaStart of one sub-carrier, NthtLayer oneThe path metric value of the mth node on the subcarrier is calculated as:
wherein,mapping symbols for an mth candidate constellation selected from 0 or data constellation points;
after the path metric value is calculated, the path metric value is compared with a threshold value, and the threshold value is calculated as:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy; selecting nodes of which the path metric values are lower than a threshold by comparing the path metric values with a threshold value, and storing the path metric values of the nodes and corresponding symbol values; then continuing to expand to the next subcarrier, each node expanding to the (W +1) subcarrier of the next subcarrier;
y2, NtLayer antennaThe [ (k-1) (W +1) + m on the sub-carriers]The path metric value of each node is:
wherein, is the NthtThe number of nodes reserved for one subcarrier on the layer antenna;is as followsA path metric value corresponding to the kth node of the subcarrier;is as followsThe k node of the subcarrier is extended toBranch metrics for the mth node of the subcarrier;
then there are:
wherein,is as followsThe m-th candidate constellation mapping symbol selected by the subcarrier from 0 or the data constellation point;
using additional metricsControlling the number of active subcarriers and null subcarriers in each OFDM-IM subcarrier group to ensure that each OFDM-IM subcarrier group has exactly L active subcarriers, and specifically calculating as follows:
wherein,the number of non-zero elements corresponding to the kth existing path in the first n-1 subcarriers is lambda as a constant, and omega is a data constellation point;
n thtLayer antennaThe threshold values of the sub-carriers are set as follows:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy; selecting nodes of which the path metric values are lower than a threshold by comparing the path metric values with a threshold value, and storing the path metric values of the nodes and corresponding symbol values; then continuing to expand to the next subcarrier, each node expanding to the (W +1) subcarrier of the next subcarrier;
y3, K-best tree search based on sub-carrier in the 1 st antenna, 1 'during detection'lThe [ (k-1) (W +1) + m on the sub-carriers]The path metric values for each node are calculated as follows:
wherein,is the N 'of the l +1 layer antenna'l+1A path metric value corresponding to the kth node of the subcarrier;is a l-layer antenna of 1'lBranch metrics for the mth node of the subcarrier;
then there are:
wherein,mapping symbols for an mth candidate constellation selected from 0 or data constellation points;is a j-th layer antenna 1'lA symbol value corresponding to a k path on a subcarrier;
the path metric values on other subcarriers of the layer 1 antenna are calculated as:
wherein, n'l＝2'l,3'l,...,N'l；
N 'of l-layer antenna'lThe path metric threshold values for the individual subcarriers are set to:
wherein,indicating the minimum PM value in this layer,indicating the next smallest PM value in this level, α is a constant value,is the noise energy. And NtThe operation of the layers is the same, nodes with the path metric value lower than the threshold are selected by comparing the path metric value with the threshold value, and the path metric values of the nodes and the corresponding symbol values are stored;
y4, N 'when searching the first layer'lAnd selecting the path corresponding to the minimum path metric value when each subcarrier is detected, wherein the symbol value on the path is the detection result.
3. The method of claim 1, wherein the number of transmit antennas is NtSaid receiving antennaNumber NrAnd the number of transmitting antennas is equal to the number of receiving antennas, i.e. Nt≤Nr。
4. The method for detecting MIMO-OFDM-IM according to claim 1, wherein the interleaver is a block interleaver of dimension gxn in step S2.
5. The method of claim 1, wherein the fading channel is a rayleigh multipath fading channel in step S3.
6. The method for detecting MIMO-OFDM-IM according to claim 1, wherein the de-interleaving process is an inverse operation of interleaving in step S4.
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