CN111988062B - Index modulation based multi-sequence spread spectrum system - Google Patents

Index modulation based multi-sequence spread spectrum system Download PDF

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CN111988062B
CN111988062B CN202010897103.8A CN202010897103A CN111988062B CN 111988062 B CN111988062 B CN 111988062B CN 202010897103 A CN202010897103 A CN 202010897103A CN 111988062 B CN111988062 B CN 111988062B
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CN111988062A (en
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徐位凯
全凌淼
王琳
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Xiamen University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B2001/70724—Spread spectrum techniques using direct sequence modulation featuring pilot assisted reception

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Abstract

A multi-sequence spread spectrum system and method based on index modulation belongs to the spread spectrum technical field in wireless communication. The system transmitting terminal comprises a binary system/decimal system conversion module, a natural number mapping and shifting selection module, a shifting module, a serial-parallel conversion module, a constellation mapping module, a CP adding module and a digital-to-analog conversion module; the receiving end comprises an analog-to-digital conversion module, a CP removing module, a channel estimation module, a de-spreading module, an index detection module, an index de-mapping module and a decimal/binary conversion module. And the sending end carries out index modulation on the additional information bits, selects a plurality of spreading sequences with different cyclic shifts to carry out spreading superposition on the original information bits to obtain a sending signal. The receiving end estimates the channel according to the pilot signal, and despreads the transmitting signal by using the estimated channel state information to obtain the estimated information bit and the index of the spreading sequence, thereby recovering the original information bit and the additional information bit. Interference can be well suppressed, and the information transmission rate can be improved.

Description

Index modulation based multi-sequence spread spectrum system
Technical Field
The invention belongs to the technical field of spread spectrum in wireless communication, and particularly relates to a multi-sequence spread spectrum system and method based on index modulation.
Background
In recent years, there has been an increasing demand for highly reliable underwater wireless communication in military, scientific and civilian applications. But at the same time, it becomes very difficult to achieve reliable communication in the underwater acoustic channel due to insufficient available bandwidth in the underwater acoustic environment and severe double spreading phenomenon in the time domain (multipath delay spread) and frequency domain (doppler spread).
Direct sequence spread spectrum takes advantage of frequency diversity in frequency selective hydroacoustic channels and benefits from spread spectrum gain, enabling communication with low signal-to-noise ratios. Direct sequence spread spectrum techniques are widely used in covert communications, but it typically requires complex RAKE receiver-based coherent detection at the receiver and requires the channel to remain time-invariant over the spreading sequence period, which is almost impossible for fast time-varying underwater acoustic channels. Thus, many scholars have improved direct sequence spreading.
A multi-sequence Spreading (MSS) system is proposed, which first obtains a plurality of cyclically shifted Sequences of an original Spreading sequence, simultaneously modulates a plurality of different symbols and superposes them. At the receiver, channel estimation is performed using the pilot signal, and the received signal is despread using the estimated channel state information, thereby achieving suppression of time-delay multipath interference. The MSS system exhibits good performance on fast time-varying channels because the pilot-bearing spreading sequence and the data-bearing spreading sequence pass through the same channel.
In order to improve data transmission rate and energy utilization efficiency, a multi-sequence spread spectrum system and method based on index modulation are provided. Index Modulation (IM) transmits additional information by extending a new dimension obtained based on a conventional two-dimensional signal constellation diagram, so that the scheme can simultaneously transmit original information and additional information, and the information transmission rate is improved.
Disclosure of Invention
The invention aims to provide a multi-sequence spread spectrum system and a method based on index modulation, which can improve the system information transmission rate and the system performance aiming at the problems of low information transmission rate and the like of the existing multi-sequence spread spectrum system.
The multi-sequence spread spectrum system based on index modulation comprises a sending end and a receiving end;
the transmitting end includes: the system comprises a binary system/decimal system conversion module, a natural number mapping and shifting selection module, J shifting modules, a serial-parallel conversion module, J constellation mapping modules, a CP adding module and a digital-to-analog conversion module;
the binary/decimal conversion module is used for converting the binary sequence into a decimal number; the natural number mapping and shifting selection module is used for carrying out index modulation; the J shift modules are used for carrying out different shifts on an original spread spectrum sequence c; the serial-parallel conversion module is used for converting serial data into parallel; the J constellation mapping modules are configured to perform constellation modulation on a transmission symbol, and the CP adding module is configured to add a cyclic prefix to an ith spread spectrum superposition signal x (i); the digital-to-analog conversion module converts a digital signal into an analog signal;
the receiving end includes: the device comprises an analog-to-digital conversion module, a CP removing module, a channel estimation module, a de-spreading module, an index detection module, an index de-mapping module and a decimal/binary conversion module;
the modulusThe conversion module is used for converting the received analog signal into a digital signal, the CP removing module is used for removing the cyclic prefix of the received signal, and the channel estimation module is used for obtaining the channel estimation quantity
Figure GDA0003186410660000021
The de-spreading module is used for correlating the channel estimator and the shift spread spectrum sequence to obtain a decision variable
Figure GDA0003186410660000022
The index detection module is used for selecting the maximum value of the absolute value of the decision variable and estimating the index, the index demapping module is used for mapping the estimated index into a natural number, and the decimal/binary conversion module is used for converting the decimal natural number into a binary sequence, namely the estimated additional information bit sequence
Figure GDA0003186410660000023
The multi-sequence spread spectrum method based on index modulation comprises the following steps:
1) at a sending end, a transmitter sends a data block consisting of an additional information bit sequence used for index modulation and an information bit sequence carried by a spread spectrum sequence, index modulation is carried out on the additional information bit sequence, and a plurality of spread spectrum sequences with different cyclic shifts are selected to carry out spread spectrum superposition on original information bits to obtain a sending signal;
2) at the receiving end, the receiver sends the received signal to the analog-to-digital conversion module for analog-to-digital conversion, estimates the channel according to the pilot signal, despreads the transmitted signal by using the estimated channel state information to obtain the estimated information bit sequence and the index of the spreading sequence, thereby recovering the original information bit sequence and the additional information bit sequence.
In step 1), the specific step of obtaining the transmission signal may be: the transmitter transmits an additional information bit sequence b for index modulationIMAnd an information bit sequence b carried by the spreading sequence, the transmitter transmitting the additional information bit sequence bIMConverted into decimal number Z by binary/decimal conversion module according to parameter Jmax-1 and J (J < J)max-1) mapping Z with natural numbers to obtain spreading sequence index j1...jJSelecting J displacement from the spread spectrum sequence according to the index, then shifting the original spread spectrum sequence c according to the selected displacement to obtain J spread spectrum sequences, then spreading the information symbols respectively, and superposing and outputting the spread signals.
In step 2), the receiver receives a signal r (t) affected by multipath fading and additive white gaussian noise, performs analog/digital conversion on the received signal r (t) and removes a cyclic prefix to obtain an ith received signal sequence r (i), estimates a channel according to a pilot signal to obtain a channel estimator, and shifts an original spreading sequence c to obtain a Jmax-1 spread spectrum sequence, then according to the channel estimator and the shifted spread spectrum sequence to make dispreading to obtain the decision variable sequence
Figure GDA0003186410660000031
And indices of spreading sequences
Figure GDA0003186410660000032
Constellation demodulation is carried out on the decision variable to obtain an estimated bearing information bit sequence
Figure GDA0003186410660000033
Mapping the estimated index into a natural number and converting the natural number into a binary sequence to obtain an estimated additional information bit sequence
Figure GDA0003186410660000034
The invention provides an index modulation-based multi-sequence spread spectrum (MSSS-IM) system, which carries out index modulation on additional information bits at a sending end, selects a plurality of spread spectrum sequences with different cyclic shifts, and carries out spread spectrum superposition on original information bits to obtain a sending signal. At the receiving end, the channel is estimated according to the pilot signal, and the estimated channel state information is used for de-spreading the transmitted signal to obtain the estimated information bit and the index of the spreading sequence, thereby recovering the original information bit and the additional information bit. The invention selects partial sequences to spread and superpose signals in a given maximum number of spread spectrum shift sequences, and the selected spread spectrum sequences are determined by the method of mapping additional information bits by using combined natural numbers, so that the additional information bits are carried by indexes of the spread spectrum sequences. The first of the selected spreading sequences carries a pilot signal that is used for channel estimation, and the rest is used to carry information bits. Therefore, the invention can well inhibit interference and can improve the information transmission rate. Computer simulation results show that the invention improves the information transmission rate under the multipath Rayleigh channel and improves the system performance.
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FIG. 1 is a block diagram of a system transmitting end;
FIG. 2 is a block diagram of a system receiving end;
FIG. 3 is a block diagram of channel estimation at the receiving end of the system;
fig. 4 is a graph comparing the bit error rate performance of the index modulation based multi-sequence spread spectrum system with that of the conventional multi-sequence spread spectrum system under different numbers of superimposed spread spectrum sequences under the multipath rayleigh fading channel. The number of channel paths is L104 and the total number of spreading sequences is Jmax9, the number of the superposed information bearing spread spectrum sequences is J7, 4 and 1 respectively;
fig. 5 is a graph comparing the bit error rate performance of the index modulation based multi-sequence spread spectrum system with that of the conventional multi-sequence spread spectrum system under different numbers of superimposed spread spectrum sequences under the multipath rayleigh fading channel. The number of channel paths is 204, and the total number of spreading sequences is JmaxThe number of superimposed information-bearing spreading sequences is J3, 1, respectively.
Detailed Description
In order to make the technical means, the creation features, the achievement purposes and the effects of the invention easy to understand, the following embodiments are further described with the attached drawings.
The transmitter transmits an additional information bit sequence b for index modulationIMAnd information bit sequence b carried by shift spread spectrum sequenceThe data block, the information bit sequence b carried by the spread spectrum sequence are processed by a serial-parallel conversion module and a constellation mapping module to obtain information symbols
Figure GDA0003186410660000041
Additional information bit sequence bIMConverted into decimal number Z by binary/decimal conversion module, and the natural number mapping and displacement selection module is used for selecting the natural number according to the parameter Jmax-1, Z and J carry out combined natural number mapping (index modulation) to obtain a displacement index J of a spread spectrum sequence1...jJ. The original spread spectrum sequence c is sent to shift modules 1, … and J respectively, and J is carried out on the original spread spectrum sequence c1(L+1),....,jJShifting (L +1) (L is the maximum time delay spread of the channel), obtaining the spread spectrum sequence of the J-path information symbols, and combining the spread spectrum sequence with the information symbols
Figure GDA0003186410660000042
The multiplication is spread while the pilot signal (pilot) is multiplied by the original spreading sequence c for spreading. Then, all the spread signals are superposed in the time domain to obtain the ith spread superposed signal x (i), and then a Cyclic Prefix (CP) is added and digital/analog conversion is carried out to obtain a sending signal s (t).
After receiving the signal r (t), the receiver sends the signal r (t) to an analog-to-digital conversion module, and after analog-to-digital conversion, the signal r (t) is sent to a CP removing module to remove the Cyclic Prefix (CP), and an ith receiving signal sequence r (i) is obtained. The receiving end carries out channel estimation according to the pilot signal (pilot) and the original spread spectrum sequence c to obtain the channel state information
Figure GDA0003186410660000043
The original spreading sequences c are simultaneously fed into Jmax-1 shift branches, performing (L +1),2(L +1). -, (J) on the original spreading sequence c, respectivelymax-1) (L +1) shift to obtain Jmax-1 spreading sequence, then the estimated channel state information, r (i), and the shifted spreading sequence are fed to the despreading module, Jmax-performing correlation calculations in 1 despreading module to obtain Jmax-1 decision variable
Figure GDA0003186410660000044
And respectively input to Jmax-1 absolute value taker, taking the absolute values of them, then sending them to the index detector, taking the J largest absolute values as the displacement estimators of the transmit-side shifted spread-spectrum sequence, i.e. the
Figure GDA0003186410660000045
Finally, the estimated index is sent to a decision quantity selector, J decision variables are selected and sent to a constellation demapping module, and an estimated information bit sequence is output
Figure GDA0003186410660000046
In addition, the estimated displacement is sent to an index mapping module to be mapped into natural numbers, and then the natural numbers are sent to a decimal/binary conversion module to be converted into binary sequences, and estimated additional information bit sequences are obtained
Figure GDA0003186410660000047
Fig. 1 is a block diagram of a transmitting end of a system, which includes: the binary/decimal conversion module converts a binary sequence into a decimal number, the natural number mapping and shift selection module performs index modulation, the J shift modules perform different shifts on an original spread spectrum sequence c, the serial-parallel conversion module converts serial data into parallel, the J constellation mapping modules perform constellation modulation on a transmission symbol, the CP adding module adds a cyclic prefix to an ith spread spectrum superposition signal x (i), and the digital-to-analog conversion module converts a digital signal into an analog signal, wherein the specific working process is as follows:
at the transmitting end, it is assumed that the transmitted data block contains an original information bit sequence b and an additional information bit sequence bIMThe transmitted signal may be expressed as:
Figure GDA0003186410660000051
wherein, the symbol s (i, J) is obtained by mapping an original information bit sequence b ∈ {0,1} constellation, and represents the jth symbol of the ith data block, c is an original spreading sequence with length M, L represents the maximum path number of the channel, J is the number of information-bearing symbols, T is a cyclic shift matrix, and the expression is:
Figure GDA0003186410660000052
wherein, IM-1Representing an identity matrix of order M-1. T in formula (1)j(L+1)c represents the sequence after the spreading sequence c is shifted by j (L +1) chips. In a multi-sequence spread spectrum system, the maximum number of superimposed spreading sequences J is determined by the maximum delay spread of the channel. For a given JmaxJ (2. ltoreq. J) may be selected to be transmitted simultaneouslymax) Information symbols to further reduce inter-symbol interference in low data rate systems, wherein JmaxIs determined by the following formula:
Figure GDA0003186410660000053
wherein,
Figure GDA0003186410660000054
indicating a rounding down. For the index modulation-based multi-sequence spread spectrum scheme provided by the invention, J is coexistedmax-1 possible cyclically shifted spreading sequences, only J of which are selected as spreading sequences, with an index J1...jJIn the presence of
Figure GDA0003186410660000055
And (6) selecting the mode. Index modulation corresponds each selection to a bit sequence, and thus the additional information bit sequence bIMThe method corresponds to an index, and also corresponds to a selection mode of a spread spectrum sequence, thereby achieving the purpose of carrying additional information bits by using the selection mode of the spread spectrum sequence and improving the information transmission rate.
For a data block-by-data block transmission over a multipath channel, the ith received signal sequence r (i) contains not only the signal of the ith transmitted block but also the inter-block interference IBI of the previous data block. The signal received by the receiving end can be expressed as:
r(i)＝H(i)x(i)+HIBI(i)x(i-1)+n(i) (4)
in the formula, the second term represents the interference between blocks IBI, H (i) and HIBI(i) Channel matrix of M × M, expression is [ H (i)]m,nH (i; m-n) and [ H ═ HIBI(i)]m,nH (i; M + M-n), and M, n 1, M, n (i) represents independently identically distributed additive white gaussian noise, and
Figure GDA0003186410660000061
in order to eliminate the effect of inter-block interference, a method of inserting a Cyclic Prefix (CP) at a transmitting end is used. After inserting and removing the Cyclic Prefix (CP), the relation of the system transmitting and receiving signals is expressed as:
Figure GDA0003186410660000062
wherein the equivalent channel matrix after removing the cyclic prefix
Figure GDA0003186410660000063
The expression is as follows:
Figure GDA0003186410660000064
substituting the formula (1) and the formula (6) into the formula (5) to obtain a received signal expression:
Figure GDA0003186410660000065
in order to recover the jth information symbol, a matched filter is designed
Figure GDA0003186410660000066
After the output of the matched filter is obtained, the output can be obtained from equation (7)The transmitted symbols s (i, j) and channel state information h (i; l) are extracted. The matched filter output expression is:
Figure GDA0003186410660000067
and due to the satisfaction of the relation TM＝IMAnd [ Ti]T＝TM-iEquation (8) can be:
Figure GDA0003186410660000068
the result of the above equation is obtained because, when the spreading sequence is an m-sequence, the following equation is satisfied:
Figure GDA0003186410660000069
when l ═ l 'and j ═ j', the first term of formula (9) can be represented as:
Figure GDA0003186410660000071
and when l ≠ l 'or j ≠ j', the second term of equation (9) can be expressed as:
Figure GDA0003186410660000072
the result of equation (9) contains three parts, mh (l) s (j) is the dominant component of the jth signal after channel tap weighting on the current data block; v. ofI(J; l) represents inter-symbol interference caused by multipath delay spread when J ≠ J ', and represents interference caused by simultaneously superposing other J-1 symbols when J ≠ J'; eta (j; l) represents channel noise, obedience
Figure GDA0003186410660000073
Distribution of (2). To overcome the time-variability of the channel, pilot signalsThe signals are also spread and superimposed for use as channel estimates. Assuming that the pilot signal is s (i,0), the estimated channel state information is:
Figure GDA0003186410660000074
for recovering the information bit sequence and the additional information bit sequence, channel estimators are used
Figure GDA0003186410660000075
The decision variables are obtained as:
Figure GDA0003186410660000076
wherein,
Figure GDA0003186410660000077
| · | represents a 2 norm. At JmaxOnly J of the-1 decision variables are required. To select the J, Ω { | z (1) |, | z (2) |, |max-1) | }, J indices are obtained using the following algorithm 1:
algorithm 1 estimation of cyclic shift spreading sequence index
Figure GDA0003186410660000078
1, initialization: let i equal to 1 and Φ equal to Ω
2: repetition
3：
Figure GDA0003186410660000079
4:: order to
Figure GDA00031864106600000710
5：i＝i+1
6: until i is J
7：
Figure GDA0003186410660000081
Ordering to obtain an estimate of the index
Estimating the amount of the obtained index
Figure GDA0003186410660000082
Index demodulation is carried out to obtain the additional information bit sequence
Figure GDA0003186410660000083
After determining the index of the spreading sequence, J modulation symbols of the ith data block carried on the spreading sequence can be represented as:
Figure GDA0003186410660000084
the J modulation symbols are subjected to constellation demapping to obtain an information bit sequence
Figure GDA0003186410660000085
FIG. 1 shows a block diagram of the transmitting end of the system; fig. 2 shows a block diagram of a receiving end of the system, which includes: the analog-to-digital conversion module converts the received analog signal into a digital signal, the CP removing module removes the cyclic prefix of the received signal, and the channel estimation module obtains the channel estimation quantity
Figure GDA0003186410660000086
The de-spread module correlates the channel estimator with the shifted spread spectrum sequence to obtain a decision variable
Figure GDA0003186410660000087
The index detection module selects the maximum value of the absolute value of the decision variable and estimates the index, the index demapping module maps the estimated index into a natural number, the decimal/binary conversion module converts the decimal natural number into a binary sequence, namely the estimated additional information bit sequence
Figure GDA0003186410660000088
FIG. 3 shows a block diagram of channel estimation at the receiving end, includingL +1 multipliers for multiplying the received signal y by the coefficients
Figure GDA0003186410660000089
And multiplying each shift sequence of the original spreading sequence c to obtain a channel estimator.
To better illustrate its effectiveness, some computer simulation results are presented herein. In the simulation, an M-sequence with a length M of 1023 is used as a spreading sequence, a channel is a multipath rayleigh fading channel, and the channel paths are respectively as follows: and L is 104, L is 204, and the channel power delay spectrum is equal power.
FIG. 4 shows simulation results of MSSS-IM system and original MSSS system on 104-path Rayleigh fading channel, wherein the MSSS system selects 9 spreading sequence superpositions, i.e. Jmax9, one of which carries a pilot signal and the other 8 carries information symbols; and for MSSS-IM systems, JmaxAnd-1-8, J-7, 4,1, that is, 7,4,1 information spreading sequences are respectively selected from the optional 8 sequences to be superimposed. As shown in the figure, when J is 7 and the modulation order is 4, the number of information bits transmitted in one spreading period by the MSSS system is 16, and the number of information bits transmitted by the MSSS-IM system is 17. At this time, the BER curve of the MSSS system shows slightly better performance than the MSSS-IM system at low snr, but the performance of the MSSS-IM system starts to be improved compared with the MSSS system when the snr is continuously increased to about-17 dB. This shows that the proposed new system improves the performance of the system in multipath rayleigh fading channels and increases the information transmission rate due to the simultaneous transmission of additional information bits. Note that when JmaxAt a certain time, the value of J has little effect on MSSS-IM systematic performance.
FIG. 5 shows simulation results of MSSS-IM system and original MSSS system on 204-path Rayleigh fading channel, wherein the MSSS system selects 5 spreading sequence superpositions, i.e. Jmax(ii) 5; and for MSSS-IM systems, Jmax-1-4, J-3, 1. As shown, the performance of the MSSS-IM system is still slightly better than the MSSS-IM system at low signal-to-noise ratios, and as the signal-to-noise ratio is continuously increased to about-15 dB, the performance of the MSSS-IM system starts to be improved but is slightly improved compared with the MSSS system. In addition, in the case where J values are 3 and 1Under the condition, the BER curves almost coincide, which is due to JmaxIs too small, different J values do not have much impact on system performance.
The foregoing has outlined the rather broadly the principles, features and advantages of the present invention. The multi-sequence spread spectrum system based on index modulation increases the information transmission rate of the system by adding partial information bits in a different mode of selecting the spread spectrum sequence, and can adjust the transmission efficiency and the system performance according to the number of the selected overlapped spread spectrum sequences, thereby realizing the balance between the system performance and the spectrum efficiency.

Claims (1)

1. The multi-sequence spread spectrum system based on index modulation is characterized by comprising a transmitting end and a receiving end;
the transmitting end includes: the system comprises a binary system/decimal system conversion module, a natural number mapping and shifting selection module, J shifting modules, a serial-parallel conversion module, J constellation mapping modules, a CP adding module and a digital-to-analog conversion module; the transmitting end divides the source bit sequence into an additional information bit sequence b for index modulationIMAnd information bit sequence b, b carried by spread spectrum sequenceIMEntering a binary/decimal conversion module to obtain a decimal number Z, entering the Z into a natural number mapping and shifting selection module to select J displacements, connecting J parallel shifting modules with the natural number mapping and shifting selection module, and shifting the shifting sequences simultaneously according to the J displacements to obtain J spread spectrum sequences; after entering a serial-parallel conversion module, an information bit sequence b carried by a spread spectrum sequence obtains J groups of sub-bit sequences, and then enters J constellation mapping modules to obtain J constellation symbols; the J constellation symbols are multiplied by the J spread spectrum sequences output by the shift module through a multiplier, and the result and the spread spectrum sequences carrying pilot signals are added together at an adder to obtain a spread spectrum superposition signal x (i); sending x (i) to a CP adding module to add a cyclic prefix, and then carrying out digital-to-analog conversion on signals through a connected digital-to-analog conversion module to obtain a sending signal s (t);
the receiving end includes: analog-to-digital conversion module, CP removing module, channel estimation module, de-spreading module, index detection module, index de-mapping module, decimal/binaryA system conversion module; the receiving end receives the signal r (t), sends the signal r (t) to the analog-digital conversion module for analog-digital conversion of the signal, enters the CP removing module to remove the cyclic prefix and obtains a signal r (i); r (i) firstly entering a channel estimation module to carry out channel estimation to obtain a channel estimator
Figure FDA0003206371010000011
The original spreading sequence c then enters parallel Jmax-1 shift module to get Jmax-1 different shifted sequences, andmax-1 different shifted sequences, r (i) and channel estimates
Figure FDA0003206371010000012
Are respectively fed into Jmax1 despreading module to get Jmax-1 decision variable Δ1,
Figure FDA0003206371010000013
The absolute values of the decision variables are obtained and sent to an index detection module to obtain the displacement estimator
Figure FDA0003206371010000014
Sending the displacement estimation quantity into an index demapping module to obtain a decimal number
Figure FDA0003206371010000015
Sending it into decimal/binary conversion module to convert it into binary bit sequence
Figure FDA0003206371010000016
Meanwhile, the decision variable selection module estimates the quantity J according to the displacementmax-1 decision variable selecting out corresponding J and sending them into constellation demodulation module to obtain recovered information bit sequence
Figure FDA0003206371010000017
The binary/decimal conversion module is used for converting the binary sequence into a decimal number; the natural number mapping and shifting selection module is used for carrying out index modulation; the J shift modules are used for carrying out different shifts on an original spread spectrum sequence c; the serial-parallel conversion module is used for converting serial data into parallel; the J constellation mapping modules are configured to perform constellation modulation on a transmission symbol, and the CP adding module is configured to add a cyclic prefix to an ith spread spectrum superposition signal x (i); the digital-to-analog conversion module converts a digital signal into an analog signal;
the analog-to-digital conversion module is used for converting the received analog signals into digital signals, the CP removing module is used for removing the cyclic prefix of the received signals, and the channel estimation module is used for obtaining channel estimation quantity
Figure FDA0003206371010000021
The de-spreading module is used for correlating the channel estimator and the shift spread spectrum sequence to obtain a decision variable
Figure FDA0003206371010000028
The index detection module is used for selecting the maximum value of the absolute value of the decision variable and estimating the index, the index demapping module is used for mapping the estimated index into a natural number, and the decimal/binary conversion module is used for converting the decimal natural number into a binary sequence, namely the estimated additional information bit sequence
Figure FDA0003206371010000023
At the transmitting end, it is assumed that the transmitted data block contains an original information bit sequence b and an additional information bit sequence bIMThe transmitted signal is expressed as:
Figure FDA0003206371010000024
wherein, the symbol s (i, J) is obtained by mapping an original information bit sequence b ∈ {0,1} constellation, and represents the jth symbol of the ith data block, c is an original spreading sequence with length M, L represents the maximum path number of the channel, J is the number of information-bearing symbols, T is a cyclic shift matrix, and the expression is:
Figure FDA0003206371010000025
wherein, IM-1Representing an M-1 order identity matrix; t in formula (1)j(L+1)c represents the sequence of the spread spectrum sequence c after shifting j (L +1) chips; in a multi-sequence spread spectrum system, the maximum number J of spread sequences superimposedmaxDetermined by the maximum delay spread of the channel; for a given JmaxSelecting to send J (J is more than or equal to 2 and less than or equal to J) at the same timemax) Information symbols to further reduce inter-symbol interference in low data rate systems, wherein JmaxIs determined by the following formula:
Figure FDA0003206371010000026
wherein,
Figure FDA0003206371010000027
indicating a rounding down.
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