CN110719142B - CPM-based RCM coding method decoding method and system - Google Patents

CPM-based RCM coding method decoding method and system Download PDF

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CN110719142B
CN110719142B CN201910828762.3A CN201910828762A CN110719142B CN 110719142 B CN110719142 B CN 110719142B CN 201910828762 A CN201910828762 A CN 201910828762A CN 110719142 B CN110719142 B CN 110719142B
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CN110719142A (en
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鲁放
董燕
奉凤
周雨秋
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0047—Decoding adapted to other signal detection operation
    • H04L1/005—Iterative decoding, including iteration between signal detection and decoding operation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
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Abstract

The invention discloses a decoding method and a system of a CPM-based RCM coding method, belonging to the technical field of rate adaptive transmission in wireless communication.A RCM coding symbol obtains a constant envelope signal with a peak-to-average ratio of 0dB through CPM modulation; and performing multiple internal iterations by adopting a BP (back propagation) method, continuously updating the message from the code symbol to the random signal and the message from the random signal to the code symbol, outputting the prior probability corresponding to the code symbol when the maximum iteration number is reached, transmitting the prior probability to a CPM (continuous phase modulation) demodulator, updating the maximum posterior probability of the code symbol according to the transmitted prior probability of the code symbol, transmitting the updated maximum posterior probability to an RCM (robust random access memory) decoder, updating the message from the code symbol to the random signal, and acquiring the probability of taking the value of the random signal as 0 and 1. The invention avoids the problem that the RCM high-power signal falls in the nonlinear area of the power amplifier to generate nonlinear distortion.

Description

CPM-based RCM coding method decoding method and system
Technical Field
The invention belongs to the technical field of rate adaptive transmission in wireless communication, and particularly relates to a decoding method and a decoding system of a CPM-based RCM coding method.
Background
In wireless communications, the adaptive selection of transmission parameters according to different channel conditions is critical to the spectral efficiency of the system. RCM (Rate Compatible Modulation for blind Rate adaptive transmission) is a seamless Rate adaptive coding technique, and can continuously adjust the spectrum utilization Rate according to the channel conditions within a large signal-to-noise ratio range, thereby effectively improving the transmission efficiency under a time-varying wireless channel, and having a wide application prospect in wireless communication. However, RCM has a high peak-to-average ratio and requires a high linear amplification range for the power amplifier. If the power amplifier does not have a wide enough linear region, when the RCM high-power signal falls in the nonlinear region of the power amplifier, signal distortion is generated, and nonlinear distortion is generated, so that the system spectrum is widened and the transmission performance of the system is reduced, and although the effective power back-off can enable the signal to work in the linear region of the power amplifier, the efficiency of the power amplifier is reduced. Therefore, the reduction of the peak-to-average ratio of the RCM signal can effectively promote the application of the RCM in a practical system.
The currently published literature for reducing PAPR of RCM proposes a new non-linear Constellation Mapping (NLCM) scheme, in which each RCM code symbol is mapped into a complex Amplitude Phase Shift Keying (APSK) Constellation, but this method randomly selects weight values in a large weight set, resulting in increased decoding complexity and limited reduction of peak-to-average ratio, which still requires a certain power backoff.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a decoding method and a decoding system of a CPM-based RCM coding method, and aims to solve the problem that the transmission performance of a wireless communication system is poor due to the fact that the conventional RCM has high peak-to-average ratio.
To achieve the above object, in one aspect, the present invention provides a CPM-based RCM coding method, including:
(1) mapping the random signal into an RCM coding symbol through a sparse measurement matrix;
(2) and modulating the RCM coded symbol by a CPM modulator to obtain a constant envelope signal with the peak-to-average ratio of 0 dB.
Preferably, the constant envelope signal is:
Figure GDA0002845585940000021
Figure GDA0002845585940000022
Figure GDA0002845585940000023
wherein E is the average signal energy of the constant envelope signal; t is the duration of the code symbol;
Figure GDA0002845585940000024
is the phase of the constant envelope signal; h is the modulation index of the CPM modulator; y isjEncoding a symbol for the jth RCM; g (t) frequency pulses of constant envelope signalA pulse function; l is the memory length of the constant envelope signal.
Preferably, the relationship between the random signal vector and the RCM coded symbols is:
YT＝ΦXT
wherein X is a random signal vector; y is a set matrix of RCM number symbols; Φ is the sparse measurement matrix.
On the other hand, based on the CPM RCM coding method, the present invention provides a CPM RCM decoding method, including:
(1) the constant envelope signal passes through an AWGN channel to obtain a noise adding signal r (t);
(2) setting a maximum external iteration frequency A of a BCJR method for calculating the maximum posterior probability of the RCM coding symbol and a maximum internal iteration frequency B of a BP method;
(3) setting the external iteration frequency a as 1 and the internal iteration frequency b as 0, and initializing a probability mass function PMF of the RCM coding symbol;
(4) acquiring the maximum posterior probability of the RCM coded symbol output by the a-th external iteration according to a probability quality function PMF of the RCM coded symbol or the prior probability of the coded symbol, a constant envelope signal, noise power and a noise signal;
(5) initializing a message from a random signal to a coded signal according to the sparsity of a code element of the random signal;
(6) updating a probability quality function PMF of the RCM coding symbols according to the message from the random signal to the coding signal;
(7) calculating a message from the code symbol to a random signal according to the maximum posterior probability of the RCM code symbol output by the a-th external iteration and a probability quality function PMF of the RCM code symbol;
(8) outputting the probability that the (b +1) th internal iteration random signal is 1 and 0 according to the message from the coding symbol to the random signal, normalizing the probability and updating the information from the random signal to the coding signal;
(9) judging whether the internal iteration frequency B is the maximum internal iteration frequency B, if so, turning to the step (10); otherwise, if B is equal to B +1, returning to the step (6) until the internal iteration number B is the maximum internal iteration number B, and turning to the step (10);
(10) judging whether the external iteration times a are the maximum external iteration times A or not, if so, judging the random signal according to the probability that the normalized random signal is 1 and 0; otherwise, updating the prior probability of the code symbol according to the information from the random signal to the code signal, wherein a is a +1, turning to the step (4), and judging the value of the random signal until the external iteration frequency a is the maximum external iteration frequency A.
Preferably, the message of the initialized random signal to each encoded signal is:
Figure GDA0002845585940000031
wherein,
Figure GDA0002845585940000032
for the external iteration number of 1, the internal iteration number of 0, a random signal xiTo the coded signal yjThe message of (2); p is a radical of0Is the symbol sparsity.
Preferably, when b ≧ 1, the probability that the random signal is 0 or 1 is:
Figure GDA0002845585940000041
wherein,
Figure GDA0002845585940000042
and
Figure GDA0002845585940000043
at the a-th external iteration and the (b +1) -th internal iteration, respectively, according to the exclusion of the encoding symbol yjThe message updated random signal x of the coded symbol outputiProbabilities of 0 and 1;
Figure GDA0002845585940000044
and
Figure GDA0002845585940000045
encoding the symbol y at the a-th external iteration and the b-th internal iteration, respectivelyj'To a random signal xiThe probability of the message of (1) being 0 and 1; p is a radical of0Is an initial set value; miW is a symbol which does not include a code symbol yjM of (A)i；MiRepresenting a random code xiOf adjacent coded symbols.
Preferably, the maximum a posteriori probability of an RCM encoded symbol is:
Figure GDA0002845585940000046
wherein,
Figure GDA0002845585940000047
for the a-th external iteration, the symbol y is encoded while the noisy signal r (t) is obtainedjMaximum a posteriori probability of; p(a)(θj,θj+1L r (t)) is the phase state of the constant envelope signal from theta when the noise signal is obtained as r (t) in the a-th external iterationjTo thetaj+1The probability of (d); thetajTo code symbols yjThe phase of the corresponding noisy signal; (theta)j,θj+1) Is from thetajTo thetaj+1The phase state of the constant envelope signal.
Preferably, the branch metric is:
Figure GDA0002845585940000048
wherein, r (t) is a noise adding signal; s*(t) is the conjugate of the constant envelope signal;
Figure GDA0002845585940000049
a prior probability of an RCM-encoded symbol for the (a-1) th external iteration; n is a radical of0Is the noise power;
Figure GDA00028455859400000410
branch metrics for the a-th external iteration; t is the code symbol duration; jT is the code element interval corresponding to the jth coded symbol;
preferably, the criterion method for the random signal value is as follows:
comparing the probability that the random signal is 0 with the probability that the random signal is 1, and if the probability that the random signal is 0 is greater than the probability that the random signal is 1, judging the random signal to be 0; otherwise, the random signal criterion is 1.
In another aspect, the present invention provides a CPM-based RCM system, including: the device comprises an RCM coder, a CPM modulator, an AWGN channel, a CPM demodulator and an RCM decoder which are connected in sequence;
the RCM encoder is used for mapping the random signal vector into RCM encoding symbols through a sparse measurement matrix; the CPM modulator is used for modulating the RCM coded symbols into constant envelope signals with peak-to-average ratio of 0 dB; the AWGN channel is used for connecting the CPM modulator and the CPM demodulator to acquire a noise-added signal; the CPM demodulator is used for calculating the maximum posterior probability of the RCM coding symbol by adopting a BCJR method according to the prior probability corresponding to the random signal transmitted by the RCM modulator; the RCM decoder is used for calculating the probability of the random signal corresponding to the values of 0 and 1 by adopting a BP method according to the maximum posterior probability of the RCM coding symbol, and realizing the judgment of the random signal values.
The maximum a posteriori probability of an RCM encoded symbol is:
Figure GDA0002845585940000051
wherein,
Figure GDA0002845585940000052
for the a-th external iteration, the symbol y is encoded while the noisy signal r (t) is obtainedjMaximum a posteriori probability of; p(a)(θj,θj+1L r (t)) is the phase state of the constant envelope signal from theta when the noise signal is obtained as r (t) in the a-th external iterationjTo thetaj+1The probability of (d); thetajTo code symbols yjCorresponding toThe phase of the noisy signal; (theta)j,θj+1) Is from thetajTo thetaj+1The phase state of the constant envelope signal.
Preferably, the criterion method for the random signal value is as follows:
and comparing the probability that the random signal is 0 with the probability that the random signal is 1, if the probability that the random signal is 0 is greater than the probability that the random signal is 1, judging the random signal to be 0, otherwise, judging the random signal to be 1.
Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:
(1) the invention provides a method for demodulating a random signal by adopting a CPM modulator and a corresponding CPM demodulator to perform CPM modulation on a coded symbol output by an RCM modulator to obtain a constant envelope signal with a peak-to-average ratio of 0dB, and provides a method for demodulating a random signal based on the modulation of the random signal.
(2) The invention provides a method that an RCM decoder adopts BP, a CPM demodulator adopts BCJR, a BP method is adopted to carry out multiple internal iterations, the message from a code symbol to a random signal and the message from the random signal to the code symbol are continuously updated, when the maximum iteration number is reached, the prior probability corresponding to the output code symbol is transmitted to the CPM demodulator, the maximum posterior probability of the code symbol is updated according to the transmitted prior probability of the code symbol and transmitted to the RCM decoder, the message from the code signal to the random signal is updated, and the probability that the value of the random signal is 0 and 1 is obtained, therefore, the demodulation error rate of the random signal is lower through multiple internal iterations and external iterations.
Drawings
Fig. 1 is a flowchart of a CPM RCM coding method provided in the present invention;
FIG. 2 is a flowchart of a CPM RCM decoding method provided in the present invention;
FIG. 3 is a schematic diagram of a CPM RCM system provided by the present invention;
fig. 4 is an out-of-band power diagram of an RCM system and an RCM-QAM system of the CPM provided by the embodiments;
fig. 5(a) is a schematic error rate diagram of RCM-CPM when the number of RCM coded symbols under the nonlinear PA is 8192 according to the embodiment;
fig. 5(b) is a schematic diagram of the error rate of the RCM-CPM when the number of RCM coded symbols is 4096 under the nonlinear PA provided by the embodiment;
fig. 5(c) is a schematic diagram of the error rate of RCM-CPM when the number of RCM coded symbols is 2048 under the nonlinear PA provided by the embodiment;
fig. 5(d) is a schematic diagram of the error rate of RCM-CPM when the number of RCM coded symbols under the nonlinear PA is 1536 according to the embodiment;
fig. 6 is a schematic diagram of the spectral efficiency of RCM-CPM under a nonlinear PA provided by the embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, the present invention provides a CPM-based RCM coding method, including:
(1) mapping the random signal into an RCM coding symbol through a sparse measurement matrix;
specifically, let N be the length of the random signal frame, and X be { X ═ X be the random signal vector1,x2,…,xN}∈{0,1}NThe size of the sparse measurement matrix Φ is mxn, and the RCM encoded symbol vector Y is:
YT＝ΦXT
wherein Y is { Y ═ Y1,y2,…,yMThe symbols are RCM coding symbol vectors formed by the RCM coding symbols; the row repetition of the sparse measurement matrix is fixed to N (N < N), in other words, each row in the sparse measurement matrix has only N nonzero values; n non-zero values from weight set W ═ W1,w2,…,wnSelecting the materials; generally W is symmetrical, meaning for any WiIs e.g. W and all have-WiThe vector belongs to W, the PAPR of the RCM coding symbols is influenced by the weight set of the matrix, and the PAPRs of the RCM coding symbols are all above 7dB under the normal condition;
(2) and modulating the RCM coded symbol by a CPM modulator to obtain a constant envelope signal with the peak-to-average ratio of 0 dB.
Specifically, a constant envelope signal with a peak-to-average ratio of 0dB is:
Figure GDA0002845585940000071
wherein E is the average signal energy of the constant envelope signal; t is the duration of the code symbol;
Figure GDA0002845585940000072
is the phase of the constant envelope signal;
phase of constant envelope signal
Figure GDA0002845585940000073
Comprises the following steps:
Figure GDA0002845585940000081
wherein h is the modulation index of the CPM modulator; y isjEncoding a symbol for the jth RCM; g (t) is a frequency pulse function of the constant envelope signal; l is the memory length of the constant envelope signal; t is the duration of the code symbol.
At a receiving end, a joint iterative decoding method is adopted, a BCJR maximum posterior probability method is adopted for CPM demodulation, a BP decoding method is adopted for RCM decoding, and the BCJR maximum posterior probability method and the RCM decoding both belong to Soft Input Soft Output (SISOS) methods. The BCJR demodulator transmits the posterior probability to BP decoding, and the two exchange soft information through a joint iterative decoding method, thereby improving the decoding performance. Since the BP decoder of the RCM is an iterative decoder, there are two iterative processes in the soft information passed between the BCJR demodulator and the BP decoder; one iteration only executes BP iterative decoding, defined as internal iteration, and the other iteration executes information transfer between BCJR demodulation and BP decoding, defined as external iteration.
For RCM decoding, BP method is adopted, namely random signal x connected in Tanner graph is passed throughi(i-1, 2, …, N) and the coding symbol yjAnd (j ═ 1,2, …, M) continuously and mutually transmit information, finally obtaining the magnitude of the probability value of 0 and 1 of each bit in the information bit vector, and then judging to obtain the estimated value of the information bit vector.
wijRepresenting a random signal xiAnd the code symbol yjWeight value of the connected edge, NjRepresenting a coded symbol yjOf adjacent random signals, and NjI is a signal which does not include a random signal xiN of (A)jFor the same reason, MiRepresenting a random signal xiOf adjacent coded signals, and MiY is not includedjM of (A)iThen, then
Figure GDA0002845585940000082
Figure GDA0002845585940000083
Indicating that at the a-th external iteration, the b-th internal iteration of BP is from random signal xiTo the code symbol yjThe message of (a) is received,
Figure GDA0002845585940000084
indicating that at the a-th outer iteration, the b-th inner iteration of BP is encoded from the symbol yjTo a random signal xiThe message of (2).
As shown in fig. 2, the CPM-based RCM coding method of the present invention provides a CPM-based RCM decoding method, including:
(1) the constant envelope signal passes through an AWGN channel to obtain a noise adding signal r (t);
(2) setting a maximum external iteration frequency A of a BCJR method for calculating the maximum posterior probability of the RCM coding symbol and a maximum internal iteration frequency B of a BP method;
(3) setting the external iteration frequency a as 1 and the internal iteration frequency b as 0, and initializing a probability mass function PMF of the RCM coding symbol;
(4) acquiring the maximum posterior probability of the RCM coded symbol output by the a-th external iteration according to a probability quality function PMF of the RCM coded symbol or the prior probability of the coded symbol, a constant envelope signal, noise power and a noise signal;
specifically, CPM demodulation adopts BCJR maximum posterior probability algorithm, T is more than or equal to jT and less than or equal to (j +1) T (j is more than or equal to 0 and less than or equal to M-1) in each code element interval, and coded symbols yjThe maximum a posteriori probability of (c) is:
Figure GDA0002845585940000091
wherein,
Figure GDA0002845585940000092
for the a-th external iteration, the symbol y is encoded while the noisy signal r (t) is obtainedjMaximum a posteriori probability of; p(a)(θj,θj+1L r (t)) is the phase state of the constant envelope signal from theta when the noise signal is obtained as r (t) in the a-th external iterationjTo thetaj+1The probability of (d); thetajTo code symbols yjThe phase of the corresponding noisy signal; (theta)j,θj+1) Is from thetajTo thetaj+1The phase state of the constant envelope signal of (a);
further, the phase state of the constant envelope signal is from θjTo thetaj+1Probability P of(a)(θj,θj+1L r (t)) is:
Figure GDA0002845585940000093
wherein, P(a)(θj,θj+1L r (t)) is the phase state of the constant envelope signal from theta when the noise signal is obtained as r (t) in the a-th external iterationjTo thetaj+1The probability of (d);
Figure GDA0002845585940000094
from theta for the phase state of the constant envelope signal for the a-th iterationjTo thetaj+1A corresponding branch metric;
Figure GDA0002845585940000095
the phase state of the constant envelope signal at the a-th iteration is thetajA corresponding forward metric;
Figure GDA0002845585940000096
the phase state of the constant envelope signal at the a-th iteration is thetaj+1A corresponding backward metric;
further, the air conditioner is provided with a fan,
Figure GDA0002845585940000101
and
Figure GDA0002845585940000102
respectively as follows:
Figure GDA0002845585940000103
wherein,
Figure GDA0002845585940000104
the phase state of the constant envelope signal at the a-th iteration is thetajA corresponding forward metric;
Figure GDA0002845585940000105
the phase state of the constant envelope signal at the a-th iteration is thetaj-1A corresponding forward metric;
Figure GDA0002845585940000106
from theta for the phase state of the constant envelope signal for the a-th iterationjTo thetaj+1A corresponding branch metric;
Figure GDA0002845585940000107
constant envelope for the a-th iterationPhase state of signal from thetaj-1To thetajA corresponding branch metric;
Figure GDA0002845585940000108
the phase state of the constant envelope signal at the a-th iteration is thetaj+1A corresponding backward metric;
Figure GDA0002845585940000109
the phase state of the constant envelope signal at the a-th iteration is thetajA corresponding backward metric;
further, in the case of a gaussian channel,
Figure GDA00028455859400001010
comprises the following steps:
Figure GDA00028455859400001011
wherein, r (t) is a noise adding signal; s*(t) is the conjugate of the constant envelope signal;
Figure GDA00028455859400001012
a prior probability of an RCM-encoded symbol for the (a-1) th external iteration; n is a radical of0Is the noise power;
Figure GDA00028455859400001013
branch metrics for the a-th external iteration; t is the code symbol duration; jT is the code element interval corresponding to the jth coded symbol;
when the a is equal to 1, the second step is carried out,
Figure GDA00028455859400001014
a probability mass function PMF for RCM encoded symbols; for a > 1 of the sum of the values of a,
Figure GDA00028455859400001015
setting the prior probability obtained by the RCM decoder; calculated by CPM demodulator
Figure GDA00028455859400001016
As the a posteriori probability of the RCM encoded symbols, for RCM decoding.
(5) Initializing a message from a random signal to a coded signal according to the sparsity of a code element of the random signal;
specifically, for the first internal iteration, a is 1 and b is 0, from xiIs sent to yjIs initialized by a prior probability:
Figure GDA0002845585940000111
wherein,
Figure GDA0002845585940000112
for the random signal x with an external iteration number of 1 and an internal iteration number of 0iTo the coded signal yjThe probability of 0 for the message of (a);
Figure GDA0002845585940000113
for the random signal x with an external iteration number of 1 and an internal iteration number of 0iTo the coded signal yjThe probability of message of 1; p (x)i0) is the probability that the random signal is 0; p (x)i1) is the probability that the random signal is 1; p is a radical of0Is the symbol sparsity.
(6) Updating a probability quality function PMF of the RCM coding symbols according to the message from the random signal to the coding signal;
in particular, define
Figure GDA0002845585940000114
The probability mass function PMF of the RCM encoded symbols for the a-th outer iteration and the b-th inner iteration is then
Figure GDA0002845585940000115
The calculation is as follows:
Figure GDA0002845585940000116
wherein, yj\iTo remove the random signal xiSum of external and coded signals yjThe sum of the products of the connected random signals and their corresponding weight values;
Figure GDA0002845585940000117
a probability mass function PMF for the RCM encoded symbols of the a-th external iteration and the b-th internal iteration; w is ai'jThe weighted value of the ith row and the jth column in the sparse matrix; p(a,b)(wi'jxi') Is the a-th external iteration and the b-th internal iteration wi' jxi'The probability of (d); () represents a convolution operation;
further, in the present invention,
Figure GDA0002845585940000118
wherein,
Figure GDA0002845585940000119
for the random signal x when the number of external iterations is a and the number of internal iterations is bi'To the coded signal yjThe probability of 0 for the message of (a);
Figure GDA00028455859400001110
for the random signal x when the number of external iterations is a and the number of internal iterations is bi'To the coded signal yjThe probability of message of 1;
(7) calculating a message from the code symbol to a random signal according to the maximum posterior probability of the RCM code symbol output by the a-th external iteration and a probability quality function PMF of the RCM code symbol;
Figure GDA0002845585940000121
wherein,
Figure GDA0002845585940000122
for encoding a signal y with an external iteration number a and an internal iteration number bjTo a random signal xiThe probability of 0 for the message of (a);
Figure GDA0002845585940000123
for encoding a signal y with an external iteration number a and an internal iteration number bjTo a random signal xiThe probability of message of 1; k is RCM code symbol yjA value set of (a);
Figure GDA0002845585940000124
taking the value of the RCM code symbol of the a-th external iteration and the b-th internal iteration as a probability mass function PMF of k; pMAP (a,b)(k | r (t)) when the received noise signal is r (t), the RCM code symbol takes the maximum a posteriori probability of k; pMAP (a,b)(k+wijL r (t)) is the value of the RCM code symbol k + w when the received noise signal is r (t)ijMaximum a posteriori probability of;
(8) outputting the probability that the (b +1) th internal iteration random signal is 1 and 0 according to the message from the coding symbol to the random signal, normalizing the probability and updating the information from the random signal to the coding signal;
specifically, the probability that the random signal of the (b +1) th internal iteration is 1 and 0 is:
Figure GDA0002845585940000125
wherein,
Figure GDA0002845585940000126
encoding the symbol y for the a-th outer iteration and the (b +1) -th inner iterationjTo a random signal xiA probability of 0;
Figure GDA0002845585940000127
is the a-th external iterationThe (b +1) th internal iteration encodes the symbol yjTo a random signal xiA probability of 1;
Figure GDA0002845585940000128
for encoding a signal y with an external iteration number a and an internal iteration number bj'To a random signal xiThe probability of 0 for the message of (a);
Figure GDA0002845585940000129
for encoding a signal y with an external iteration number a and an internal iteration number bj'To a random signal xiThe probability of message of 1; miRepresenting a random signal xiA set of adjacent coded symbols; and MiW is not yjM of (A)i；
Figure GDA0002845585940000131
Wherein,
Figure GDA0002845585940000132
for the time of the external iteration number a and the internal iteration number b +1, the random signal xiTo the coded signal yjThe probability of 0 for the message of (a);
Figure GDA0002845585940000133
for the time of the external iteration number a and the internal iteration number b +1, the random signal xiTo the coded signal yjThe probability of message of 1;
Figure GDA0002845585940000134
encoding the symbol y for the a-th outer iteration and the (b +1) -th inner iterationjTo a random signal xiA probability of 0;
Figure GDA0002845585940000135
encoding the symbol y for the a-th outer iteration and the (b +1) -th inner iterationjTo random messageNumber xiA probability of 1;
(9) judging whether the internal iteration frequency B is the maximum internal iteration frequency B, if so, turning to the step (10); otherwise, if B is equal to B +1, returning to the step (6) until the internal iteration number B is the maximum internal iteration number B, and turning to the step (10);
(10) judging whether the external iteration times a are the maximum external iteration times A or not, if so, judging the random signal according to the probability that the normalized random signal is 1 and 0; otherwise, updating the prior probability of the code symbol according to the information from the random signal to the code signal, wherein a is a +1, turning to the step (4), and judging the value of the random signal until the external iteration frequency a is the maximum external iteration frequency A.
Specifically, the method for deciding the value of the random signal is as follows:
Figure GDA0002845585940000136
wherein,
Figure GDA0002845585940000137
Figure GDA0002845585940000138
for encoding a signal y with an external iteration number A and an internal iteration number Bj'To a random signal xiThe probability of 0 for the message of (a);
Figure GDA0002845585940000141
for encoding a signal y with an external iteration number A and an internal iteration number Bj'To a random signal xiIs 1.
As shown in fig. 3, the present invention provides a CPM-based RCM system, including: the device comprises an RCM modulator, a CPM modulator, an AWGN channel, a CPM demodulator and an RCM decoder which are connected in sequence;
the RCM modulator is used for mapping the random signal vector into an RCM coding symbol through a sparse measurement matrix; the CPM modulator is used for modulating the RCM coded symbols into constant envelope signals with peak-to-average ratio of 0 dB; the AWGN channel is used for connecting the CPM modulator and the CPM demodulator to acquire a noise-added signal; the signal; the AWGN channel is used for connecting the CPM modulator and the CPM demodulator to acquire a noise-added signal; the CPM demodulator is used for calculating the maximum posterior probability of the RCM coding symbol by adopting a BCJR method according to the prior probability corresponding to the random signal transmitted by the RCM modulator; the RCM modulator is used for calculating the prior probability corresponding to the random signal by adopting a BP method according to the maximum posterior probability of the RCM coding symbol, and realizing the judgment of the value of the random signal.
The maximum a posteriori probability of an RCM encoded symbol is:
Figure GDA0002845585940000142
wherein,
Figure GDA0002845585940000143
for the a-th external iteration, the symbol y is encoded while the noisy signal r (t) is obtainedjMaximum a posteriori probability of; p(a)(θj,θj+1L r (t)) is the phase state of the constant envelope signal from theta when the noise signal is obtained as r (t) in the a-th external iterationjTo thetaj+1The probability of (d); thetajTo code symbols yjThe phase of the corresponding noisy signal; (theta)j,θj+1) Is from thetajTo thetaj+1The phase state of the constant envelope signal.
The criterion method for the random signal value taking is as follows:
and comparing the probability that the random signal is 0 with the probability that the random signal is 1, if the probability that the random signal is 0 is greater than the probability that the random signal is 1, judging the random signal to be 0, otherwise, judging the random signal to be 1.
The core technical scheme is as follows: at a transmitting end, RCM coding is carried out on source bits to obtain RCM coding symbols yjHas a high PAPR, yjA signal with PAPR of 0dB is obtained by one CPM modulator. The RCM-CPM signal passes through a Gaussian white noise channel and is demodulated by CPMA BCJR maximum posterior probability method is adopted, a BP decoding method is adopted for RCM decoding, and soft information is exchanged between the BCJR maximum posterior probability method and the RCM decoding through a joint iterative decoding method. When both the inner iteration and the outer iteration reach the maximum iteration number, the iteration algorithm is stopped and the RCM decoder makes a decision and outputs a 0 and 1 bit stream.
Examples
To illustrate the effectiveness of the present invention, simulation comparisons of the present invention and conventional RCM-QAM are made below. Conditions for comparison of RCP-CPM (RCM system of CPM) and RCM-QAM performance: and in the presence of the nonlinear power amplifier, ensuring that the RCM-CPM and the RCM-QAM have the same bandwidth, and comparing the spectral efficiency of the RCM-CPM and the RCM-QAM.
In the embodiment in which a solid-state power amplifier (SSPA) is used as a non-linear power amplifier PA (power amplifier), an input model s of the SSPAin(t) and output model sout(t) are respectively:
sin(t)＝Ain(t)exp[jφin(t)]
sout(t)＝G[Ain(t)]exp[j{φin(t)+Φ[Ain(t)]}]
wherein s isin(t) is the input model of the SSPA; sout(t) is the output model of the SSPA; a. thein(t) is the amplitude of the SSPA input signal; phi is ain(t) is the phase of the SSPA input signal; g [ A ]in(t)]Is the conversion function between Amplitude and Amplitude (AM/AM); phi [ A ]in(t)]Is the conversion function between Amplitude and Phase (AM/PM);
the AM/AM and AM/PM conversions of SSPA are:
Figure GDA0002845585940000151
Φ[Ain(t)]＝0
wherein A issat,inIs the saturation threshold of the amplifier; p is an amplification factor and mainly influences the transition speed of the SSPA amplifier from a linear region to a saturation region;
the input power back-off is:
Figure GDA0002845585940000161
wherein IBO is input power backoff; e {. is the average power of the input signal;
the bandwidth of the RCM-CPM and RCM-QAM signals is measured by setting the amplification factor p to 3, setting the roll-off factor a of the shaping filter to 0.4 to obtain a minimum PAPR, and defining the frequency band in the 99% concentration of the signal power as the bandwidth (i.e., the out-of-band power is-20 dB). The receiving end of the RCM-CPM system adopts a joint iterative decoding method, and the iterative combinations are respectively A: B: 2:8 and A: B: 1: 16.
Since one constellation point of QAM modulation can carry two RCM symbols, and one constellation point of CPM modulation can only carry one RCM symbol, a proper parameter should be selected to make the-20 dB bandwidth of the RCM-CPM system half of the bandwidth of the RCM-QAM system. Fig. 4 shows the out-of-band power diagram of the RCM-CPM system and the RCM-QAM system under different modulation indexes, and it can be seen from the diagram that the modulation index h of CPM should be set to 1/30 to obtain the same symbol bandwidth as QAM.
Fig. 5(a), 5(B), 5(c) and 5(d) show the error rates of the four RCM-QAM signals with ideal SSPA and p 3, IBO 8dB,7dB,6dB for an RCM code symbol number of 8192,4096,2048,1536 and the two RCM-CPM signals with a: B2: 8 and a: B1: 16, respectively, with the abscissa indicating the signal-to-noise ratio taking into account the negative effect of the input power back-off, in dB, and the ordinate indicating the error rates of the six signals. The simulation was performed in the presence of a non-linear power amplifier, and it can be seen from the figure that RCM-CPM has a significant performance improvement over RCM-QAM under high signal-to-noise ratio conditions, with the main advantage that it does not require power back-off. Under the signal-to-noise ratio environment of the whole simulation, the RCM-CPM system with the A: B being 2:8 always has more excellent error rate performance than the RCM-CPM system with the A: B being 1: 16. When the RCM coding symbol is 1536, the RCM-CPM system with a: B ═ 2:8 is better than the RCM-CPM system with a: B ═ 1:16 by about 1.5dB and the RCM-CPM system with a: B ═ 2:8 is better than the RCM-QAM system with IBO ═ 8dB by about 3.5dB at high snr. For the case of more coded symbols, the IBO to obtain the best BER performance of RCM-QAM is 6dB, and at this time, the RCM-CPM system with a: B ═ 2:8 still has the best error rate performance, and the error rate performance of the RCM-CPM system with a: B ═ 1:16 is not significantly superior to that of the RCM-QAM system.
Fig. 6 shows the spectral efficiency of four RCM-QAM signals for ideal SSPA and p 3, IBO 8dB,7dB,6dB and two RCM-CPM signals for a: B2: 8 and a: B1: 16, with the abscissa indicating the signal-to-noise ratio in dB taking into account the negative effect of input power back-off and the ordinate indicating the spectral efficiency of six signals in bit/s/Hz. The simulation was performed in the presence of a non-linear power amplifier. For each source bit block, the transmitter continues to generate and transmit constellation symbols in a given step size until receiving feedback of successful decoding by the receiving end or reaching a maximum number of transmissions. At the receiver, the RCM symbols are accumulated for decoding. If the decoded bits pass through Cyclic Redundancy Check (CRC), immediately feeding back a signal of successful decoding to the transmitting end, otherwise, continuously receiving the incremental symbols to execute the next decoding round. In this simulation, the incremental symbol step is set to Δ m — 64. As can be seen from the figure, the RCM-CPM system with a: B-2: 8 has higher spectral efficiency than the RCM-CPM system with a: B-1: 16 under the snr environment of the whole simulation. Under the condition of high signal-to-noise ratio, the RCM-CPM system with the A: B ═ 2:8 is about 1.5dB better than the RCM-CPM system with the A: B ═ 1:16, and the RCM-CPM system with the A: B ═ 2:8 is about 3dB better than the RCM-QAM system with the IBO ═ 8 dB. However, when the signal-to-noise ratio is low, because the influence of the PA on the RCM-QAM system is reduced, when the IBO is 6dB, the RCM-CPM system performance of the a: B: 1:16 is not as good as that of the RCM-QAM system, when the IBO is 7dB, the RCM-CPM system performance of the a: B: 1:16 is equivalent to that of the RCM-QAM system, and when the IBO is 8dB, the RCM-CPM system performance of the a: B: 1:16 is better than that of the RCM-QAM system.
According to simulation and analysis, the following two conclusions are drawn:
(1) the combination of RCM and CPM can be used for solving the problem of PAPR related to RCM, and CPM modulation generates a 0dB PAPR constant envelope signal, so that the method is very suitable for a nonlinear PA and improves the efficiency of the PA;
(2) when the influence of nonlinear power amplification is considered, the RCM-CPM system is superior to the RCM-QAM system in the aspects of bit error rate and spectral efficiency when proper joint iteration times are adopted.
In summary, the present invention provides a method for performing CPM modulation on a coded symbol output by an RCM modulator by using a CPM modulator and a corresponding CPM demodulator to obtain a constant envelope signal with a peak-to-average ratio of 0dB, and provides a method for demodulating a random signal based on the modulation on the random signal, which is known from the modulation and demodulation processes of the random signal.
The invention provides a method that an RCM decoder adopts BP, a CPM demodulator adopts BCJR, a BP method is adopted to carry out multiple internal iterations, the message from a code symbol to a random signal and the message from the random signal to the code symbol are continuously updated, when the maximum iteration number is reached, the prior probability corresponding to the output random signal is transmitted to the CPM demodulator, the maximum posterior probability of the code symbol is updated according to the transmitted prior probability of the code symbol and transmitted to the RCM decoder, the message from the random signal to the code symbol is updated, and the prior probability of the code symbol is obtained, therefore, the demodulation error rate of the final random signal is lower through multiple internal iterations and external iterations.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (6)

1. A decoding method of a CPM-based RCM coding method is characterized by comprising the following steps:
(1) the constant envelope signal passes through an AWGN channel to obtain a noise adding signal r (t);
(2) setting a BCJR method to calculate the maximum external iteration times A of the maximum posterior probability of the RCM coding symbols and the maximum internal iteration times B of a BP method, wherein the BP method is a belief propagation algorithm;
(3) initializing the external iteration number a to be 1 and the internal iteration number b to be 0, and initializing a probability mass function PMF of the RCM coding symbol;
(4) acquiring the maximum posterior probability of the RCM coding symbol output by the external iteration for the a-th time according to the probability quality function PMF of the initialized RCM coding symbol, the constant envelope signal, the noise power and the noise signal; or acquiring the maximum posterior probability of the RCM coding symbol output by the a-th external iteration according to the prior probability of the RCM coding symbol, the constant envelope signal, the noise power and the noise signal;
(5) initializing a message from a random signal to a code symbol according to the sparsity of the code element of the random signal;
(6) updating a probability quality function PMF of the RCM coding symbols according to the message from the random signal to the coding symbols;
(7) calculating a message from the code symbol to a random signal according to the maximum posterior probability of the RCM code symbol output by the a-th external iteration and a probability quality function PMF of the RCM code symbol;
(8) outputting the probability that the b +1 th internal iteration random signal is 1 and 0 according to the message from the coding symbol to the random signal, normalizing the probability and updating the message from the random signal to the coding symbol;
(9) judging whether the internal iteration frequency B is the maximum internal iteration frequency B, if so, turning to the step (10); otherwise, if B is B +1, returning to the step (6) until the internal iteration number B is the maximum internal iteration number B, and turning to the step (10);
(10) judging whether the external iteration times a are the maximum external iteration times A or not, if so, judging the random signal according to the probability that the normalized random signal is 1 and 0; otherwise, updating the prior probability of the code symbol according to the message from the random signal to the code symbol, wherein a is a +1, turning to the step (4), and judging the value of the random signal until the external iteration frequency a is the maximum external iteration frequency A;
the CPM-based RCM coding method comprises the following steps:
(1) mapping the random signal into an RCM coding symbol through a sparse measurement matrix;
(2) modulating the RCM coding symbol by a CPM modulator to obtain a constant envelope signal with a peak-to-average ratio of 0 dB;
wherein, RCM is rate compatible modulation of blind rate adaptive transmission; CPM is continuous phase modulation;
the step (4) is specifically as follows:
according to the formula
Figure FDA0002845585930000021
Calculating the maximum posterior probability of the RCM coding symbol;
wherein,
Figure FDA0002845585930000022
for the a-th external iteration, the symbol y is encoded while the noisy signal r (t) is obtainedjMaximum a posteriori probability of; p(a)(θj,θj+1L r (t)) is the phase state of the constant envelope signal from theta when the noise signal is obtained as r (t) in the a-th external iterationjTo thetaj+1The probability of (d); thetajTo code symbols yjThe accumulated phase of the corresponding constant envelope signal; (theta)j,θj+1) Is from thetajTo thetaj+1The phase state of the constant envelope signal of (a);
phase state of constant envelope signal from thetajTo thetaj+1Probability P of(a)(θj,θj+1L r (t)) is:
Figure FDA0002845585930000023
wherein,
Figure FDA0002845585930000024
from theta for the phase state of the constant envelope signal for the a-th iterationjTo thetaj+1A corresponding branch metric;
Figure FDA0002845585930000025
the phase state of the constant envelope signal at the a-th iteration is thetajCorresponding forward directionMeasuring;
Figure FDA0002845585930000026
the phase state of the constant envelope signal at the a-th iteration is thetaj+1A corresponding backward metric;
Figure FDA0002845585930000027
and
Figure FDA0002845585930000028
respectively as follows:
Figure FDA0002845585930000031
wherein,
Figure FDA0002845585930000032
the phase state of the constant envelope signal at the a-th iteration is thetajA corresponding forward metric;
Figure FDA0002845585930000033
the phase state of the constant envelope signal at the a-th iteration is thetaj-1A corresponding forward metric;
Figure FDA0002845585930000034
from theta for the phase state of the constant envelope signal for the a-th iterationjTo thetaj+1A corresponding branch metric;
Figure FDA0002845585930000035
from theta for the phase state of the constant envelope signal for the a-th iterationj-1To thetajA corresponding branch metric;
Figure FDA0002845585930000036
is constant at the a-th iterationThe phase state of the envelope signal being thetaj+1A corresponding backward metric;
Figure FDA0002845585930000037
the phase state of the constant envelope signal at the a-th iteration is thetajA corresponding backward metric;
in the case of a gaussian channel, the channel,
Figure FDA0002845585930000038
comprises the following steps:
Figure FDA0002845585930000039
wherein, r (t) is a noise adding signal; s*(t) is the conjugate of the constant envelope signal;
Figure FDA00028455859300000310
a priori probabilities of the RCM encoded symbols for the a-1 st external iteration; n is a radical of0Is the noise power;
Figure FDA00028455859300000311
branch metrics for the a-th external iteration; t is the code symbol duration; jT is the symbol interval corresponding to the jth coded symbol.
2. The decoding method according to claim 1, wherein when b ≧ 1, the probability that the random signal is 0 or 1 is:
Figure FDA00028455859300000312
wherein,
Figure FDA00028455859300000313
and
Figure FDA00028455859300000314
in the case of the a-th external iteration and the b + 1-th internal iteration, respectively, according to the exclusion of the coding symbol yjThe message updated random signal x of the coded symbol outputiProbabilities of 0 and 1;
Figure FDA0002845585930000041
and
Figure FDA0002845585930000042
encoding the symbol y at the a-th external iteration and the b-th internal iteration, respectivelyj'To a random signal xiThe probability of the message of (1) being 0 and 1; p is a radical of0Is the symbol sparsity of the random signal; miW is a symbol which does not include a code symbol yjM of (A)i；MiRepresenting a random code xiOf adjacent coded symbols.
3. The decoding method according to claim 1 or 2, wherein the criterion method for the random signal value is as follows: comparing the probability that the random signal is 0 with the probability that the random signal is 1, and if the probability that the random signal is 0 is greater than the probability that the random signal is 1, judging the random signal to be 0; otherwise, the random signal criterion is 1.
4. The coding method according to claim 1, wherein the constant envelope signal is:
Figure FDA0002845585930000043
wherein,
Figure FDA0002845585930000044
e is the average signal energy of the constant envelope signal; t is the duration of the code symbol;
Figure FDA0002845585930000045
is the phase of the constant envelope signal; h is the modulation index of the CPM modulator; y isjEncoding a symbol for the jth RCM; g (t) is a frequency pulse function of the constant envelope signal; l is the memory length of the constant envelope signal.
5. A CPM-based RCM system, comprising: the device comprises an RCM coder, a CPM modulator, an AWGN channel, a CPM demodulator and an RCM decoder which are connected in sequence;
the RCM encoder is used for mapping the random signal vector into RCM encoding symbols through a sparse measurement matrix; the CPM modulator is used for modulating the RCM coded symbols into constant envelope signals with peak-to-average ratio of 0 dB; the AWGN channel is used for connecting the CPM modulator and the CPM demodulator to acquire a noise-added signal; the CPM demodulator is used for calculating the maximum posterior probability of the RCM code symbols by adopting a BCJR method according to the prior probability of the code symbols transmitted by the RCM decoder and the received noise-added signals; the RCM decoder is used for calculating the probability of the random signal value being 0 and 1 by adopting a BP method according to the maximum posterior probability of the RCM coding symbol, and realizing the judgment of the random signal value;
wherein, RCM is rate compatible modulation of blind rate adaptive transmission; CPM is continuous phase modulation; the BP method is a belief propagation algorithm;
the method for calculating the maximum posterior probability of the RCM coding symbol by adopting the BCJR method comprises the following steps:
according to the formula
Figure FDA0002845585930000051
Calculating the maximum posterior probability of the RCM coding symbol;
wherein,
Figure FDA0002845585930000052
for the a-th external iteration, the symbol y is encoded while the noisy signal r (t) is obtainedjMaximum a posteriori probability of; p(a)(θj,θj+1L r (t)) is constant envelope signal obtained at the time of the a-th external iteration when the noise signal is obtained as r (t)Phase state of the signal from thetajTo thetaj+1The probability of (d); thetajTo code symbols yjThe accumulated phase of the corresponding constant envelope signal; (theta)j,θj+1) Is from thetajTo thetaj+1The phase state of the constant envelope signal of (a);
phase state of constant envelope signal from thetajTo thetaj+1Probability P of(a)(θj,θj+1L r (t)) is:
Figure FDA0002845585930000053
wherein, P(a)(θj,θj+1L r (t)) is the phase state of the constant envelope signal from theta when the noise signal is obtained as r (t) in the a-th external iterationjTo thetaj+1The probability of (d);
Figure FDA0002845585930000054
from theta for the phase state of the constant envelope signal for the a-th iterationjTo thetaj+1A corresponding branch metric;
Figure FDA0002845585930000055
the phase state of the constant envelope signal at the a-th iteration is thetajA corresponding forward metric;
Figure FDA0002845585930000056
the phase state of the constant envelope signal at the a-th iteration is thetaj+1A corresponding backward metric;
Figure FDA0002845585930000057
and
Figure FDA0002845585930000058
respectively as follows:
Figure FDA0002845585930000061
wherein,
Figure FDA0002845585930000062
the phase state of the constant envelope signal at the a-th iteration is thetajA corresponding forward metric;
Figure FDA0002845585930000063
the phase state of the constant envelope signal at the a-th iteration is thetaj-1A corresponding forward metric;
Figure FDA0002845585930000064
from theta for the phase state of the constant envelope signal for the a-th iterationjTo thetaj+1A corresponding branch metric;
Figure FDA0002845585930000065
from theta for the phase state of the constant envelope signal for the a-th iterationj-1To thetajA corresponding branch metric;
Figure FDA0002845585930000066
the phase state of the constant envelope signal at the a-th iteration is thetaj+1A corresponding backward metric;
Figure FDA0002845585930000067
the phase state of the constant envelope signal at the a-th iteration is thetajA corresponding backward metric;
in the case of a gaussian channel, the channel,
Figure FDA0002845585930000068
comprises the following steps:
Figure FDA0002845585930000069
wherein, r (t) is a noise adding signal; s*(t) is the conjugate of the constant envelope signal;
Figure FDA00028455859300000610
a priori probabilities of the RCM encoded symbols for the a-1 st external iteration; n is a radical of0Is the noise power;
Figure FDA00028455859300000611
branch metrics for the a-th external iteration; t is the code symbol duration; jT is the symbol interval corresponding to the jth coded symbol.
6. The RCM system of claim 5, wherein the criterion method for the random signal value is as follows:
and comparing the probability that the random signal is 0 with the probability that the random signal is 1, if the probability that the random signal is 0 is greater than the probability that the random signal is 1, judging the random signal to be 0, otherwise, judging the random signal to be 1.
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