CN111884975B - Index modulation and demodulation method and system based on time delay-Doppler domain - Google Patents

Index modulation and demodulation method and system based on time delay-Doppler domain Download PDF

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CN111884975B
CN111884975B CN202010694362.0A CN202010694362A CN111884975B CN 111884975 B CN111884975 B CN 111884975B CN 202010694362 A CN202010694362 A CN 202010694362A CN 111884975 B CN111884975 B CN 111884975B
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CN111884975A (en
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王�华
赵航
何东轩
康子奇
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Beijing Institute of Technology BIT
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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Abstract

The invention discloses an index modulation and demodulation method based on a delay-Doppler domain, which can greatly reduce the detection performance on the basis of ensuring the detection performanceComplexity. The transmitting end divides the information bits to be transmitted into a plurality of groups, the information bits in each group are divided into index bits and data bits, and the modulation type of the data bits is determined by the index bits
Figure DDA0002590358090000012
Or
Figure DDA0002590358090000011
Further generating an OTFS sub-block; mapping the generated OTFS sub-blocks to a delay-Doppler domain to form an OTFS frame, and transforming the OTFS frame to a time domain for sending; and the receiving end groups the OTFS sub-blocks according to the size of the OTFS sub-blocks to obtain the modulation mode of each received OTFS sub-block, judges whether the modulation mode is a legal modulation mode or not and corrects the illegal modulation mode.

Description

Index modulation and demodulation method and system based on time delay-Doppler domain
Technical Field
The invention belongs to the technical field of communication, and particularly relates to an Orthogonal Time Frequency Space (OTFS) system and an Index Modulation (IM) technology based on a delay-Doppler domain.
Background
OTFS is a communication scheme based on the delay-doppler domain which has been studied in recent years. The method converts a time-varying multipath channel into a time-invariant two-dimensional delay-Doppler channel, and simultaneously carries information in a delay-Doppler domain, so that all symbols in one OTFS frame obtain relatively constant channel gain. Research shows that the error rate performance of the OTFS is obviously better than that of the conventional Orthogonal Frequency Division Multiplexing (OFDM) technology in a high-speed motion scene (such as high speed rail).
In recent years, researchers have proposed the concept of Index Modulation (IM) technology, and the main idea is to transmit extra information bits by using indexes inherent in the communication system, such as antenna Index, subcarrier Index, and slot Index, to further improve the spectrum efficiency of the system.
The basic principle of the early IM technique for multi-carrier systems is to divide the data into individual sub-blocks, and the symbols in each sub-block are divided into active and silent states, and the active symbols normally transmit modulation informationAnd the silent symbol is set to zero, no information is transmitted, and the transmitting end transmits additional index bits through the symbol state. Although the spectral efficiency gain brought by the index is ensured to a certain extent, the existence of the silent symbol makes the spectral efficiency gain brought by the index unable to make up for the spectral efficiency lost by the zero-setting when a high-order mapping mode is adopted. In view of the above, the researchers have proposed a Dual-mode Index Modulation (DM-IM) technique, i.e. changing the symbol state in a sub-block from active and silent to two distinguishable Modulation types (defined as two distinguishable Modulation types)
Figure RE-GDA0002663677240000011
And
Figure RE-GDA0002663677240000012
) The modulation type of the symbol is determined according to the index bit, so that the problem of spectrum efficiency loss caused by silent symbols is solved. Meanwhile, to perform index modulation and demodulation more conveniently, a lookup table is usually defined to determine the mapping relationship between index bits and sub-block modulation modes.
For DM-IM, the receiving end recovers the index bit by detecting the modulation type of the received symbol, and further recovers the data bit. The conventional detector has an optimal Maximum Likelihood (ML) detector and a sub-optimal Log-Likelihood Ratio (LLR) detector.
If an ML detector is used, the detection of each sub-block can be expressed as:
Figure RE-GDA0002663677240000021
wherein the content of the first and second substances,
Figure RE-GDA0002663677240000022
representing all legal modulation mode sets of the sub-block,
Figure RE-GDA0002663677240000023
constellation symbol for representing legal modulation modeThe set of numbers, d, represents the sub-block size,
Figure RE-GDA0002663677240000024
denotes the x-th data symbol, S, in the beta sub-blockI，χDenotes the x-th symbol in the I-th legal modulation mode,
Figure RE-GDA0002663677240000025
and
Figure RE-GDA0002663677240000026
respectively representing the modulation mode obtained by ML detection and the corresponding constellation symbol. It can be seen that although the ML detector is an optimal detector, its complexity grows exponentially with the sub-block size, the modulation pattern distribution and the modulation order of the different modulation patterns, without taking advantage of practical use.
If an LLR detector is employed, the detection of each symbol can be expressed as:
Figure RE-GDA0002663677240000027
wherein the content of the first and second substances,
Figure RE-GDA0002663677240000028
MAand MBRespectively correspond to modulation types
Figure RE-GDA0002663677240000029
And
Figure RE-GDA00026636772400000210
modulation order of, yαAnd gammaαRespectively, representing the alpha-th data symbol and its corresponding LLR value. As can be seen, the LLR detector ignores the prior information of the legal modulation mode, and directly performs likelihood ratio calculation on each received data symbol, so that the complexity is greatly reduced; but the disadvantage is mainly that the performance at low signal-to-noise ratio is far from the same as the ML detector. In addition, due to the effects of channel and noise, LLR demodulation may occur at the time of decisionThe resulting modulation mode is not a legitimate modulation mode (i.e., not present in the look-up table), and the sign with the smaller LLR needs to be modified in the opposite direction.
In summary, the detector needs to be designed scientifically to achieve the tradeoff between detection performance and complexity.
Disclosure of Invention
In view of this, the present invention provides an index modulation and demodulation method and system based on a delay-doppler domain, which greatly reduces complexity on the basis of ensuring detection performance.
The invention mainly comprises two contents, one is that index modulation is introduced into an OTFS system (the OTFS-DM-IM is used for referring to the system in the following), and the frequency spectrum efficiency of the system is improved while the existing OTFS system architecture is compatible; and secondly, providing an improved LLR detector design method based on the minimum Hamming distance under the system. Simulation results show that the error rate performance of the improved LLR detector is consistent with that of the optimal ML detector, but the complexity is greatly reduced.
The specific invention content is as follows:
firstly, the method comprises the following steps: an OTFS-DM-IM system based on a delay-Doppler domain is proposed. The transmitting end divides the information bits to be transmitted into a plurality of groups, simultaneously the information bits in each group are divided into index bits and data bits, and the modulation type of the data bits is determined by the index bits (
Figure RE-GDA0002663677240000031
Or
Figure RE-GDA0002663677240000032
) Further generating an OTFS sub-block; mapping the generated OTFS sub-blocks to a delay-Doppler domain to form an OTFS frame; and finally, sending the time delay-Doppler domain OTFS frame carrying the extra index bit through a traditional OTFS transmitter, namely firstly converting the time delay-Doppler domain signal into a time-frequency domain signal through Inverse Symplectic Finite Fourier Transform (ISFFT), and then converting the time delay-Doppler domain signal into a time-frequency domain signal through Heisenberg Transform for transmission. Assuming that the number of sub-blocks of the system in the delay-Doppler domain is G, each sub-block comprises L data symbols, letThe modulation type of K data symbols in the built-in block is
Figure RE-GDA0002663677240000033
(modulation type)
Figure RE-GDA0002663677240000034
Denoted by 1), the modulation type of the remaining L-K data symbols is
Figure RE-GDA0002663677240000035
(modulation type)
Figure RE-GDA0002663677240000036
Denoted by 0), one OTFS frame may be additionally transmitted
Figure RE-GDA0002663677240000037
And the index bit is used for further improving the frequency spectrum efficiency of the system.
II, secondly: an improved LLR detector based on minimum Hamming distance is presented. Considering that the conventional LLR detector has a large gap compared to the optimal ML detector performance at low snr, this gap is mainly due to the fact that the LLR detector ignores the constraint relation between symbols in the block, which results in the case that the LLR decision result is not a legal modulation mode in the look-up table, and the lower the snr, the more likely this occurs. In order to solve the problem, the invention provides that: and correcting the illegal decision result (namely, the decision result is not the legal modulation mode in the lookup table) by using the minimum Hamming distance, and ensuring the accuracy of the error correction result as much as possible while correcting the illegal modulation mode into the legal modulation mode. The operation process is as follows:
after the LLR value of each symbol is obtained through calculation, carrying out logic judgment on the LLR value (judgment criterion: the LLR value is judged to be 1 when the LLR value is larger than 0, and is judged to be 0 when the LLR value is smaller than or equal to 0); when an illegal decision result exists, the range of a legal modulation mode set possibly corresponding to the illegal decision result is narrowed by calculating the minimum Hamming distance, the position of the illegal decision result different from the position corresponding to the possible set is determined, and the illegal decision result is corrected by reversing the logic value of the position corresponding to the smaller LLR value.
Based on the above analysis, the index modulation and demodulation method based on the time delay-doppler domain of the present invention specifically includes the following steps:
the transmitting end divides the information bits to be transmitted into a plurality of groups, the information bits in each group are divided into index bits and data bits, and the modulation type of the data bits is determined by the index bits
Figure RE-GDA0002663677240000041
Or
Figure RE-GDA0002663677240000042
Further generating an OTFS sub-block; mapping the generated OTFS sub-blocks to a delay-Doppler domain to form an OTFS frame, and transforming the OTFS frame to a time domain for sending;
after receiving the time domain signal and converting the time domain signal to the delay-Doppler domain, the receiving end firstly calculates LLR value gamma of each delay-Doppler domain symbolαAccording to γαConverting the positive and negative values into 1/0 values, and grouping according to the size of the OTFS subblocks to obtain the modulation mode of each received OTFS subblock
Figure RE-GDA0002663677240000043
The value range of beta is 1-G, and G is the total number of the OTFS subblocks; judgment of
Figure RE-GDA0002663677240000044
If the modulation mode is legal, the illegal modulation mode is recorded as
Figure RE-GDA0002663677240000045
Computing
Figure RE-GDA0002663677240000046
Finding the minimum Hamming distance d from the Hamming distance of each legal modulation mode in the lookup tableminThe corresponding possible legal modulation modes are noted
Figure RE-GDA0002663677240000047
By using
Figure RE-GDA0002663677240000048
For illegal modulation mode
Figure RE-GDA0002663677240000049
Error correction is carried out; finally, the index bit and the data bit are demodulated by using the modulation mode after error correction.
Preferably, said factor γαPositive and negative of (d) converts it to an 1/0 value of: gamma rayα>At the time of 0, the number of the first,
Figure RE-GDA00026636772400000410
γαwhen the content is less than or equal to 0,
Figure RE-GDA00026636772400000411
preferably, said utilization
Figure RE-GDA0002663677240000051
For illegal modulation mode
Figure RE-GDA0002663677240000052
The error correction is carried out as follows:
for dminIn case of 1, will
Figure RE-GDA0002663677240000053
With each legal modulation mode
Figure RE-GDA0002663677240000054
Comparing to obtain bits with different modulation types and LLR value corresponding to the bits, and inverting the bit corresponding to the LLR value with the minimum absolute value as the correction bit
Figure RE-GDA0002663677240000055
Correcting the data on the bits to correct the illegal modulation mode into a legal modulation mode in the lookup table;
for dminIn case of ≧ 2, the illegal modulation mode is first reversed
Figure RE-GDA0002663677240000056
Bit corresponding to LLR value with minimum inner absolute value to reduce illegal modulation mode
Figure RE-GDA0002663677240000057
Minimum hamming distance from the set of legal modulation modes in the look-up table; repeating the reverse illegal modulation pattern
Figure RE-GDA0002663677240000058
Operation of the bit corresponding to the minimum LLR value up to dminReuse of d as 1minError correction is performed in the processing method of 1.
The invention also provides an index modulation and demodulation system based on the time delay-Doppler domain, which comprises a sending modulation module and a receiving demodulation module;
a sending modulation module for dividing the information bits to be transmitted into several groups, the information bits in each group are divided into index bits and data bits, and the modulation type of the data bits is determined by the index bits
Figure RE-GDA00026636772400000516
Or
Figure RE-GDA00026636772400000517
Further generating an OTFS sub-block; mapping the generated OTFS sub-blocks to a delay-Doppler domain to form an OTFS frame, and transforming the OTFS frame to a time domain for sending;
a receiving demodulation module for receiving the time domain signal and converting to the delay-Doppler domain, and first calculating LLR value gamma of each delay-Doppler domain symbolαAccording to γαConverting the positive and negative values into 1/0 values, and grouping according to the size of the OTFS subblocks to obtain the modulation mode of each received OTFS subblock
Figure RE-GDA0002663677240000059
The value range of beta is 1-G, and G is the total number of the OTFS subblocks; judgment of
Figure RE-GDA00026636772400000510
If the modulation mode is legal, the illegal modulation mode is recorded as
Figure RE-GDA00026636772400000511
Computing
Figure RE-GDA00026636772400000512
Finding the minimum Hamming distance d from the Hamming distance of each legal modulation mode in the lookup tableminThe corresponding possible legal modulation modes are noted
Figure RE-GDA00026636772400000513
By using
Figure RE-GDA00026636772400000514
For illegal modulation mode
Figure RE-GDA00026636772400000515
Error correction is carried out; finally, the index bit and the data bit are demodulated by using the modulation mode after error correction.
Preferably, the receiving and demodulating module includes: the device comprises a transformation submodule, a subblock modulation mode determining submodule, a syndrome submodule and a demodulation submodule;
the conversion submodule is used for receiving a time domain signal and converting the time domain signal into a received signal of a delay-Doppler domain;
the sub-block modulation mode determining sub-module is used for calculating LLR value gamma of each symbolαAccording to γαConverting the positive and negative values into 1/0 values, and grouping according to the size of the OTFS subblocks to obtain the modulation mode of each received OTFS subblock
Figure RE-GDA0002663677240000061
The value range of beta is 1-G, and G is the total number of the OTFS subblocks;
the correction submodule is used for judging
Figure RE-GDA0002663677240000062
If the modulation mode is legal, the illegal modulation mode is recorded as
Figure RE-GDA0002663677240000063
Computing
Figure RE-GDA0002663677240000064
Finding the minimum Hamming distance d from the Hamming distance of each legal modulation mode in the lookup tableminThe corresponding possible legal modulation modes are noted
Figure RE-GDA0002663677240000065
For dminIn case of 1, will
Figure RE-GDA0002663677240000066
And each of said legal modulation modes
Figure RE-GDA0002663677240000067
Comparing to obtain bits with different modulation types and LLR value corresponding to the bits, and inverting the bit corresponding to the LLR value with the minimum absolute value as the correction bit
Figure RE-GDA0002663677240000068
Correcting the data on the bits to correct the illegal modulation mode into a legal modulation mode in the lookup table;
for dminIn case of ≧ 2, the illegal modulation mode is first reversed
Figure RE-GDA0002663677240000069
Bit corresponding to LLR value with minimum inner absolute value to reduce illegal modulation mode
Figure RE-GDA00026636772400000610
Minimum hamming distance from the set of legal modulation modes in the look-up table; repeating the reverse illegal modulation pattern
Figure RE-GDA00026636772400000611
Operation of the bit corresponding to the minimum LLR value up to dminReuse of d as 1min1 processing methodCorrecting errors;
and the demodulation submodule is used for demodulating the index bits and the data bits by using the modulation mode after error correction.
Has the advantages that:
the core of the invention lies in the design of an OTFS-DM-IM system based on a time delay-Doppler domain and the design of an improved LLR detector based on a minimum Hamming distance. At present, no index modulation based on a delay-Doppler domain and a detector design method based on a minimum Hamming distance exist. Index modulation is introduced in a time delay-Doppler domain, so that the frequency spectrum efficiency of the OTFS system is improved; and correcting the LLR detection result by the minimum Hamming distance, ensuring low complexity and obtaining the same detection precision as the optimal ML detector, and realizing reasonable compromise between complexity and detection performance. By combining the two, under the same spectrum efficiency, the OTFS-DM-IM system can obtain the error rate performance superior to that of the traditional OTFS system.
Drawings
FIG. 1 is an overall block diagram of an OTFS-DM-IM system designed by the present invention;
FIG. 2 is a specific transmitter structure of OTFS-DM-IM;
FIG. 3 is an example of the delay-Doppler domain of an OTFS sub-block carrying index bits;
FIG. 4 is a comparison of the error correction performance of a conventional LLR detector and a proposed minimum Hamming distance based improved LLR detector in the presence of an illegal modulation mode;
FIG. 5 is a comparison graph of the overall error rate performance of a conventional OTFS system and an OTFS-DM-IM system using an ML detector, a conventional LLR detector and the proposed improved LLR detector, wherein the conventional OTFS system has a modulation method of 8PSK, and the two modulation methods in the OTFS-DM-IM system are QPSK and 8PSK, respectively;
fig. 6 is a schematic diagram of an index modem system based on the delay-doppler domain according to the present invention.
Detailed Description
The invention provides an index modulation and demodulation scheme based on a delay-Doppler domain, which has the main idea that: by introducing the idea of index modulation into the OTFS system, modulation information carrying index bits is transmitted in a delay-Doppler domain, so that the spectrum efficiency of the OTFS system is improved; and the reasonable compromise between the detection performance and the complexity is realized at the receiving end through the design of the improved LLR detector based on the minimum Hamming distance, and the transmission performance is further improved.
In order to more clearly illustrate the objects, technical solutions and advantages of the present invention, the present invention will be described in further detail with reference to the following embodiments and accompanying drawings.
Step 1: setting a system to have M subcarriers, wherein the subcarrier interval is delta f; there are N symbols, each symbol being of duration T. This means that one OTFS frame occupies a bandwidth of M Δ f for a duration of NT.
Step 2: fig. 1 shows the overall structure of the OTFS-DM-IM system of the present invention, and fig. 2 shows the specific structure of the transmitter. Firstly, dividing c bit information to be transmitted into G groups, wherein each group has p bits; dividing the p bits of each group into two parts corresponding to index bit p1And a data bit p2Determining the modulation type of the data bits by the index bits (
Figure RE-GDA0002663677240000081
Or
Figure RE-GDA0002663677240000082
Corresponding modulation order MAAnd MB) That is, if the index bit is 1, the modulation type of the corresponding data bit is
Figure RE-GDA0002663677240000083
Conversely, if the index bit is 0, the corresponding data bit modulation type is
Figure RE-GDA0002663677240000084
Thereby generating OTFS sub-blocks of length L. L is the length of the data bits after modulation into symbols. Suppose there are K data symbol modulation types in a sub-block as
Figure RE-GDA0002663677240000085
(L-K) data symbol modulation types of
Figure RE-GDA0002663677240000086
Then p at this time1、p2Can be calculated from the following formula:
Figure RE-GDA0002663677240000087
p2＝Klog2(MA)+(L-K)log2(MB) (4)
wherein the content of the first and second substances,
Figure RE-GDA0002663677240000088
representing the coefficients of a binomial expression.
And step 3: and mapping the OTFS subblocks carrying the index bits to a delay-Doppler domain to form an OTFS frame. Fig. 3 shows a specific mapping manner of the OTFS-DM-IM system in the delay-doppler domain according to the delay index, where the relevant parameter is set to (L, K) ═ 4, 2; indicating modulation type by dark color as
Figure RE-GDA0002663677240000089
Symbol of (2), light color indicates modulation type of
Figure RE-GDA00026636772400000810
The symbols of (1) are shown in Table 1, and sub-blocks 1 to 4 carry index bits [0,0 ] respectively]，[0,1]，[1,1]，[1,0]. As shown in fig. 3, the sub-blocks are mapped one by one in the delay domain, the doppler value is changed, and the mapping is continued. In practice, the sub-blocks may be mapped one by one in the doppler domain, then the delay value is changed, and then the mapping is continued, so that the vertically arranged sub-blocks in fig. 3 are arranged horizontally. It can be seen that one OTFS frame can be additionally transmitted
Figure RE-GDA00026636772400000811
And the index bit is used for improving the spectrum efficiency of the OTFS system.
And 4, step 4: and transforming the OTFS frame to a time-frequency domain by utilizing ISFFT (inverse fast Fourier transform), and transforming the OTFS frame to a time domain by Heisenberg transformation for sending. And the receiving end transforms the time domain receiving signal to a time-frequency domain through Wigner transformation, and finally obtains the receiving signal of the time delay-Doppler domain through SFFT.
The above steps complete the process from the initial index modulation to the generation of the delay-doppler domain signal to the transmission and finally to the reception of the delay-doppler domain signal in the OTFS-DM-IM system. The following steps are the use of an improved LLR detector based on minimum hamming distance.
And 5: after receiving the delay-Doppler domain signals, calculating LLR value gamma of each received delay-Doppler domain symbol according to equation (2)αSimultaneously for gammaαMaking a logical judgment to obtain
Figure RE-GDA0002663677240000091
(criterion is γ)α>At 0 time
Figure RE-GDA0002663677240000092
γαWhen the temperature is less than or equal to 0
Figure RE-GDA0002663677240000093
)；
Step 6: to the obtained
Figure RE-GDA0002663677240000094
Grouping
Figure RE-GDA0002663677240000095
β ═ 1, 2, …, G being the total number of sub-blocks, to determine the modulation mode of each received OTFS sub-block, wherein,
Figure RE-GDA0002663677240000096
indicating the modulation mode corresponding to the beta sub-block,
Figure RE-GDA0002663677240000097
denotes a modulation type corresponding to the χ -th symbol in the β -th sub-block, and χ ═ 1, 2, …, L;
and 7: judgment of
Figure RE-GDA0002663677240000098
Whether the modulation mode is legal or not and correcting the illegal modulation mode:
1) if it is
Figure RE-GDA0002663677240000099
If the modulation mode is legal, the index bit and the data bit are demodulated normally;
2) if it is
Figure RE-GDA00026636772400000910
If it is an illegal modulation mode, calculating
Figure RE-GDA00026636772400000911
Finding the minimum Hamming distance d from the Hamming distance of each legal modulation mode in the lookup tableminAnd (4) descending the corresponding possible legal modulation modes, thereby reducing the range of the possible legal modulation mode set. Note that the minimum Hamming distance dminIs related to the sub-block size L (number of symbols contained in the block), i.e. the range of possible values of (c) is related to the sub-block size L (number of symbols contained in the block), i.e. the number of symbols
Figure RE-GDA00026636772400000912
Representing a positive integer field. At this time, it is necessary to dominCase-by-case discussion is carried out: for dminIn the case of 1, find the corresponding dminLegal modulation mode set of 1
Figure RE-GDA00026636772400000913
Determining
Figure RE-GDA00026636772400000914
And
Figure RE-GDA00026636772400000915
in different positions of the corresponding bit, reversed
Figure RE-GDA00026636772400000916
Bit with minimum absolute value of corresponding LLR value
Figure RE-GDA00026636772400000917
Thereby correcting the illegal modulation pattern to a legal modulation pattern in the look-up table so as to finally demodulate the index bits and the data bits using the corrected modulation pattern. Wherein the LLR values represent probability log-likelihood ratios of the received symbols for the two modulation types, as shown in equation (2). This means that if the LLR is positive, the larger the absolute value thereof, the more likely it is a modulation type
Figure RE-GDA00026636772400000918
If the LLR is negative, the larger the absolute value of the LLR, the more likely it is a modulation type
Figure RE-GDA00026636772400000919
Therefore, the absolute value of the inverse LLR value is relatively small
Figure RE-GDA00026636772400000920
That is, the probability of the correct decision is small
Figure RE-GDA00026636772400000921
I.e. the more likely it is that an erroneous bit is present.
For dminIn case of > 2, first reverse
Figure RE-GDA00026636772400000922
Bit with minimum inner corresponding LLR absolute value
Figure RE-GDA00026636772400000923
Reducing its minimum hamming distance d from the set of legal modulations in the look-up tableminRepeating the above steps until d min1, and finally reusedminError correction is performed in the manner of 1. Here d can be reduced by inverting the bit with the smallest absolute value of the corresponding LLRminIs based on the following principle:
hamming distance refers to the number of corresponding bits in the two arrays that differ. Suppose a modulation pattern preliminarily obtained according to equation (2)
Figure RE-GDA0002663677240000101
The modulation mode is an illegal modulation mode, the minimum Hamming distance between the modulation mode and the 4 legal modulation modes in the lookup table 1 is 2, and the number of the modulation modes which is different from the corresponding bits of the 4 legal modulation modes is 2; then reverse direction
Figure RE-GDA0002663677240000102
Any bit in the set of bits, which corresponds to a different number of bits, must be increased by a little 1 and decreased by a little 1, which means that the minimum hamming distance from the 4 legal modulation modes must be decreased by 1. For example, assume a preliminary estimated sub-block modulation mode
Figure RE-GDA0002663677240000103
The Hamming distances between the modulation mode and the four legal modulation modes in the lookup table are all 2, and the minimum Hamming distance is determined to be 2 at the moment; if it is reversed
Figure RE-GDA0002663677240000104
Bit 1 in (1) makes it become [ 0111]Then it matches the legal modulation pattern in the look-up table [ 1010]And [ 1001 ]]The Hamming distance of (b) is increased to 3, corresponding to the legal modulation mode [ 0101 ]]And [ 0110]Is reduced to 1, and finally the minimum hamming distance is determined to be reduced to d min1. In the same way, reverse
Figure RE-GDA0002663677240000105
Bits 2, 3 and 4 in the above description may also reduce the minimum hamming distance from the legal modulation mode, and are not described in detail here.
Table 1 look-up table example when L is 4 and K is 2
Figure RE-GDA0002663677240000106
The following illustrates embodiments and capabilities of the present invention by way of specific examples:
suppose an OTFS subblock length L is 4, and a modulation type with 2 symbols K is 4 in the block
Figure RE-GDA0002663677240000107
Modulation type of 2 symbols for the remaining (L-K) ═ 2 is
Figure RE-GDA0002663677240000108
A look-up table as shown in table 1 is provided. According to the sub-block modulation mode of column 2 of the table, pair 2 can be obtainedL16 possible LLR decision results, corresponding to the minimum hamming distance dminIs L/2-2, d is described belowmin1 and dminCase 2.
The first condition is as follows: suppose that the index bit [0,0 ] is actually sent]Corresponding to subblock modulation mode [ 1010%]And the LLR value obtained by the preliminary calculation of the receiving end is gamma(β)＝[6.01，-0.85，-1.17，-5.15]TThe logic judgment is carried out on the modulation scheme, and the preliminary estimation subblock modulation mode is [ 1000 ]]. It can be seen that the preliminary decision result is not in the look-up table, and is an illegal modulation mode. At this time, the Hamming distance between the modulation condition of the legal subblocks in the lookup table and the modulation condition of the legal subblocks in the lookup table is calculated, and the minimum Hamming distance d is determinedmin1, corresponding to a set of possible legal modulations of [ 1010 []And [ 1001 ]]The positions with different corresponding positions are a third position and a fourth position; due to the fact that
Figure RE-GDA0002663677240000111
Therefore, the preliminary estimation sub-block modulation scheme [ 1000 ] is reversed]To [ 1010 ] with error correction]Error correction result corresponds to index bit [0,0 ]]And the error correction is successful according to the actual transmission index bit.
Case two: suppose that the index bit [1,1 ] is actually sent]Corresponding to subblock modulation mode [ 0101 ]]And the LLR value obtained by the preliminary calculation of the receiving end is gamma(β)＝[0.10，1.42，2.00，4.96]TThe logic judgment is carried out on the modulation scheme, and the preliminary estimation sub-block modulation mode is [ 1111 ]]It can be seen that the preliminary decision result is also an illegal modulation mode. At this time, the Hamming distance between the modulation condition of the legal subblocks in the lookup table and the modulation condition of the legal subblocks in the lookup table is calculated, and the minimum Hamming distance d is determinedmin2. Due to dminNot less than 2, so that it needs to be reversed first
Figure RE-GDA0002663677240000112
Having the smallest internally-corresponding LLR value
Figure RE-GDA0002663677240000113
To reduce the hamming distance of the legal modulation patterns in the decision result and the look-up table. It is noted that
Figure RE-GDA0002663677240000114
At a minimum, therefore, reverse
Figure RE-GDA0002663677240000115
The first bit in [ 1111 ]]The preliminary error correction is [ 0111 ]]At this time dminIs reduced to 1 corresponding to a set of possible legal modulations of [ 0101 ]]And [ 0110]. The subsequent error correction process is similar to case one, since
Figure RE-GDA0002663677240000116
Figure RE-GDA0002663677240000117
So the preliminary error correction result [ 0111 ] is reversed]The third bit of the error correction data to obtain the final error correction result [ 0101 ]]Corresponding to index bit [1,1 ]]And the error correction is successful according to the actual transmission index bit.
As can be seen from the simulation results of fig. 4, the improved LLR detector based on the minimum hamming distance provided by the present invention has significantly better error correction performance than the conventional LLR detector when the preliminary decision result is illegal. As can be seen from the simulation result of fig. 5, in the index modulation and demodulation system OTFS-DM-IM based on the delay-doppler domain proposed by the present invention, the error rate performance of the improved LLR detector is substantially consistent with that of the optimal ML detector, which is superior to that of the conventional LLR detector. Meanwhile, as can be seen from the following detector complexity analysis, the complexity of the proposed improved LLR detector is greatly reduced, and a reasonable compromise between detection performance and complexity is better achieved compared to the ML detector. Meanwhile, under the same spectrum efficiency, the performance of the OTFS-DM-IM system is superior to that of the traditional OTFS system when the EbN0 is more than or equal to 14 dB.
TABLE 2 Detector computation complexity comparison
Figure RE-GDA0002663677240000121
Table 2 shows a comparison of the complexity of the different detectors. Suppose that the dual-mode modulation modes are QPSK and 8PSK respectively, corresponding to MA＝4,MBIn a given lookup table (L is 4, K is 2), the conventional LLR detector needs to perform error correction at most 4 times when there is an illegal decision result, whereas the improved LLR detector based on the minimum hamming distance proposed by the present invention needs only 2 times of error correction at most; meanwhile, although the ML detector does not need to carry out error correction operation, 4096 multiplications are needed, the complexity is high, and the complexity is greatly reduced because the invention only needs 48 multiplications.
It can be seen from the above that, the invention improves the spectrum efficiency of the OTFS system by blocking the transmission symbols (the symbols in the blocks adopt different modulation types, and then the symbols of different modulation types are mapped to the delay-Doppler domain, thereby transmitting the modulation information carrying the index bits in the delay-Doppler domain, and meanwhile, if the receiving end judges the modulation mode of the sub-blocks only by the LLR value of each symbol, the condition of illegal modulation mode may occur, and the lower the signal-to-noise ratio, the higher the possibility of the condition, and the design of the improved LLR detector based on the minimum Hamming distance corrects the illegal modulation mode, improves the detection precision, realizes the reasonable compromise between the detection performance and the complexity, and improves the transmission performance.
In order to implement the above method, the present invention further provides an index modulation and demodulation system based on the delay-doppler domain, as shown in fig. 6, the system includes a transmitting modulation module and a receiving demodulation module;
a sending modulation module for dividing the information bits to be transmitted into several groups, the information bits in each group are divided into index bits and data bits, and the modulation type of the data bits is determined by the index bits
Figure RE-GDA0002663677240000131
Or
Figure RE-GDA0002663677240000132
Further generating an OTFS sub-block; mapping the generated OTFS sub-blocks to a delay-Doppler domain to form an OTFS frame, and finally transforming the OTFS frame to a time domain to be sent;
a receiving demodulation module for receiving the time domain signal, converting it to the delay-Doppler domain, and firstly calculating LLR value gamma of each delay-Doppler domain symbolαAccording to γαConverting the positive and negative values into 1/0 values, and grouping according to the size of the OTFS subblocks to obtain the modulation mode of each received OTFS subblock
Figure RE-GDA0002663677240000133
The value range of beta is 1-G, and G is the total number of the OTFS subblocks; judgment of
Figure RE-GDA0002663677240000134
If the modulation mode is legal, the illegal modulation mode is recorded as
Figure RE-GDA0002663677240000135
Computing
Figure RE-GDA0002663677240000136
Finding the minimum Hamming distance d from the Hamming distance of each legal modulation mode in the lookup tableminThe corresponding possible legal modulation modes are noted
Figure RE-GDA0002663677240000137
By using
Figure RE-GDA0002663677240000138
For illegal modulation mode
Figure RE-GDA0002663677240000139
Error correction is carried out; finally, the index bit and the data bit are demodulated by using the modulation mode after error correction.
Wherein, the receiving demodulation module comprises: the device comprises a transformation submodule, a subblock modulation mode determining submodule, a syndrome submodule and a demodulation submodule;
the transformation submodule is used for receiving the time domain signal and transforming the time domain signal into a received signal of a delay-Doppler domain;
a sub-block modulation mode determining sub-block for calculating LLR value gamma of each symbolαAccording to γαConverting the positive and negative values into 1/0 values, and grouping according to the size of the OTFS subblocks to obtain the modulation mode of each received OTFS subblock
Figure RE-GDA00026636772400001310
The value range of beta is 1-G, and G is the total number of the OTFS subblocks;
a correction submodule for judging
Figure RE-GDA00026636772400001311
If the modulation mode is legal, the illegal modulation mode is recorded as
Figure RE-GDA00026636772400001312
Computing
Figure RE-GDA00026636772400001313
Finding the minimum Hamming distance d from the Hamming distance of each legal modulation mode in the lookup tableminThe corresponding possible legal modulation modes are noted
Figure RE-GDA00026636772400001314
For dminIn case of 1, will
Figure RE-GDA00026636772400001315
With each legal modulation mode
Figure RE-GDA00026636772400001316
Comparing to obtain bits with different modulation types and LLR value corresponding to the bits, and inverting the bit corresponding to the LLR value with the minimum absolute value as the correction bit
Figure RE-GDA0002663677240000141
Middle correction of data at bits, thereby preventing illegal modulationCorrecting the system mode into a legal modulation mode in a lookup table;
for dminIn case of ≧ 2, the illegal modulation mode is first reversed
Figure RE-GDA0002663677240000142
Bit corresponding to LLR value with minimum inner absolute value to reduce illegal modulation mode
Figure RE-GDA0002663677240000143
Minimum hamming distance from the set of legal modulation modes in the look-up table; repeating the reverse illegal modulation pattern
Figure RE-GDA0002663677240000144
Operation of the bit corresponding to the minimum LLR value up to dminReuse of d as 1minError correction is carried out in a processing mode of 1;
and the demodulation submodule is used for demodulating the index bits and the data bits by using the modulation mode after error correction.
The above description of the present invention is provided in connection with the accompanying drawings, and not intended to limit the scope of the invention. It will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the invention and these are intended to be included within the scope of the invention.

Claims (4)

1. An index modulation and demodulation method based on a time delay-Doppler domain is characterized in that:
the transmitting end divides the information bits to be transmitted into a plurality of groups, the information bits in each group are divided into index bits and data bits, and the modulation type of the data bits is determined by the index bits
Figure FDA0003007873120000011
Or
Figure FDA0003007873120000012
Further generating an OTFS sub-block; mapping the generated OTFS subblocks to a delay-Doppler domain to form an OTFS frame, change to the time domain to send;
after receiving the time domain signal and converting the time domain signal to the delay-Doppler domain, the receiving end firstly calculates LLR value gamma of each delay-Doppler domain symbolαAccording to γαConverting the positive and negative values into 1/0 values, and grouping according to the size of the OTFS subblocks to obtain the modulation mode of each received OTFS subblock
Figure FDA0003007873120000013
The value range of beta is 1-G, and G is the total number of the OTFS subblocks; judgment of
Figure FDA0003007873120000014
If the modulation mode is legal, the illegal modulation mode is recorded as
Figure FDA0003007873120000015
Computing
Figure FDA0003007873120000016
Finding the minimum Hamming distance d from the Hamming distance of each legal modulation mode in the lookup tableminThe corresponding possible legal modulation modes are noted
Figure FDA0003007873120000017
By using
Figure FDA0003007873120000018
For illegal modulation mode
Figure FDA0003007873120000019
Error correction is carried out; finally, demodulating the index bit and the data bit by using the modulation mode after error correction;
said utilization
Figure FDA00030078731200000110
For illegal modulation mode
Figure FDA00030078731200000111
The error correction is carried out as follows:
for dminIn case of 1, will
Figure FDA00030078731200000112
With each legal modulation mode
Figure FDA00030078731200000113
Comparing to obtain bits with different modulation types and LLR value corresponding to the bits, and inverting the bit corresponding to the LLR value with the minimum absolute value as the correction bit
Figure FDA00030078731200000114
Correcting the data on the bits to correct the illegal modulation mode into a legal modulation mode in the lookup table;
for dminIn case of ≧ 2, the illegal modulation mode is first reversed
Figure FDA00030078731200000115
Bit corresponding to LLR value with minimum inner absolute value to reduce illegal modulation mode
Figure FDA00030078731200000116
Minimum hamming distance from the set of legal modulation modes in the look-up table; repeating the reverse illegal modulation pattern
Figure FDA00030078731200000117
Operation of the bit corresponding to the minimum LLR value up to dminReuse of d as 1minError correction is performed in the processing method of 1.
2. The method of claim 1, wherein: said according to gammaαPositive and negative of (d) converts it to an 1/0 value of: gamma rayα>At the time of 0, the number of the first,
Figure FDA00030078731200000118
γαwhen the temperature is less than or equal to 0，
Figure FDA00030078731200000119
3. An index modulation-demodulation system based on a delay-Doppler domain is characterized in that: the device comprises a transmitting modulation module and a receiving demodulation module;
a sending modulation module for dividing the information bits to be transmitted into several groups, the information bits in each group are divided into index bits and data bits, and the modulation type of the data bits is determined by the index bits
Figure FDA0003007873120000021
Or
Figure FDA0003007873120000022
Further generating an OTFS sub-block; mapping the generated OTFS sub-blocks to a delay-Doppler domain to form an OTFS frame, and transforming the OTFS frame to a time domain for sending;
a receiving demodulation module for receiving the time domain signal and converting to the delay-Doppler domain, and first calculating LLR value gamma of each delay-Doppler domain symbolαAccording to γαConverting the positive and negative values into 1/0 values, and grouping according to the size of the OTFS subblocks to obtain the modulation mode of each received OTFS subblock
Figure FDA0003007873120000023
The value range of beta is 1-G, and G is the total number of the OTFS subblocks; judgment of
Figure FDA0003007873120000024
If the modulation mode is legal, the illegal modulation mode is recorded as
Figure FDA0003007873120000025
Computing
Figure FDA0003007873120000026
And each legal in the look-up tableHamming distance of modulation mode, finding minimum Hamming distance dminThe corresponding possible legal modulation modes are noted
Figure FDA0003007873120000027
By using
Figure FDA0003007873120000028
For illegal modulation mode
Figure FDA0003007873120000029
Error correction is carried out; finally, demodulating the index bit and the data bit by using the modulation mode after error correction;
said utilization
Figure FDA00030078731200000210
For illegal modulation mode
Figure FDA00030078731200000211
The error correction is carried out as follows:
for dminIn case of 1, will
Figure FDA00030078731200000212
With each legal modulation mode
Figure FDA00030078731200000213
Comparing to obtain bits with different modulation types and LLR value corresponding to the bits, and inverting the bit corresponding to the LLR value with the minimum absolute value as the correction bit
Figure FDA00030078731200000214
Correcting the data on the bits to correct the illegal modulation mode into a legal modulation mode in the lookup table;
for dminIn case of ≧ 2, the illegal modulation mode is first reversed
Figure FDA00030078731200000215
Bit corresponding to LLR value with minimum inner absolute value to reduce illegal modulation mode
Figure FDA00030078731200000216
Minimum hamming distance from the set of legal modulation modes in the look-up table; repeating the reverse illegal modulation pattern
Figure FDA00030078731200000217
Operation of the bit corresponding to the minimum LLR value up to dminReuse of d as 1minError correction is performed in the processing method of 1.
4. The system of claim 3, wherein the receive demodulation module comprises: the device comprises a transformation submodule, a subblock modulation mode determining submodule, a syndrome submodule and a demodulation submodule;
the conversion submodule is used for receiving a time domain signal and converting the time domain signal into a received signal of a delay-Doppler domain;
the sub-block modulation mode determining sub-module is used for calculating LLR value gamma of each symbolαAccording to γαPositive and negative of (d) converts it to an 1/0 value: gamma rayα>At the time of 0, the number of the first,
Figure FDA0003007873120000031
γαwhen the content is less than or equal to 0,
Figure FDA0003007873120000032
and grouping according to the size of the OTFS subblocks to obtain the modulation mode of each received OTFS subblock
Figure FDA0003007873120000033
The value range of beta is 1-G, and G is the total number of the OTFS subblocks;
the correction submodule is used for judging
Figure FDA0003007873120000034
If it is legal modulation mode, recording the illegal modulation modeIs composed of
Figure FDA0003007873120000035
Computing
Figure FDA0003007873120000036
Finding the minimum Hamming distance d from the Hamming distance of each legal modulation mode in the lookup tableminThe corresponding possible legal modulation modes are noted
Figure FDA0003007873120000037
For dminIn case of 1, will
Figure FDA0003007873120000038
And each of said legal modulation modes
Figure FDA0003007873120000039
Comparing to obtain bits with different modulation types and LLR value corresponding to the bits, and inverting the bit corresponding to the LLR value with the minimum absolute value as the correction bit
Figure FDA00030078731200000310
Correcting the data on the bits to correct the illegal modulation mode into a legal modulation mode in the lookup table;
for dminIn case of ≧ 2, the illegal modulation mode is first reversed
Figure FDA00030078731200000311
Bit corresponding to LLR value with minimum inner absolute value to reduce illegal modulation mode
Figure FDA00030078731200000312
Minimum hamming distance from the set of legal modulation modes in the look-up table; repeating the reverse illegal modulation pattern
Figure FDA00030078731200000313
Operation of the bit corresponding to the minimum LLR value up to dminReuse of d as 1minError correction is carried out in a processing mode of 1;
and the demodulation submodule is used for demodulating the index bits and the data bits by using the modulation mode after error correction.
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