CN108880629B - Cooperative communication method based on space-time coding and physical layer network coding - Google Patents

Cooperative communication method based on space-time coding and physical layer network coding Download PDF

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CN108880629B
CN108880629B CN201810575826.9A CN201810575826A CN108880629B CN 108880629 B CN108880629 B CN 108880629B CN 201810575826 A CN201810575826 A CN 201810575826A CN 108880629 B CN108880629 B CN 108880629B
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CN108880629A (en
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张佳岩
刘春刚
李怀彬
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Harbin Institute of Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/026—Co-operative diversity, e.g. using fixed or mobile stations as relays
    • 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
    • H04L1/0054—Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H04L27/22—Demodulator circuits; Receiver circuits

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Abstract

The invention discloses a cooperative communication method based on space-time coding and physical layer network coding, and relates to a cooperative communication method based on space-time coding and physical layer network coding. The invention aims to solve the problems of low network throughput and high error rate of the existing communication system. In the broadcasting stage of the multi-user cooperative network model, the communication method of the invention respectively adopts orthogonal carrier modulation to the information of two user nodes, and broadcasts the information from two respective transmitting antennas through Alamouti space-time coding. And the relay node R and the destination node D both adopt maximum likelihood decoding to complete the mapping of the physical layer network coding. Compared with the traditional physical layer network coding, when the bit error rate BER is 10‑3The cooperative communication method of the present invention can provide approximately 7dB bit error rate gain. Accordingly, the throughput of the system network is greatly improved due to the reduction of the bit error rate. The invention is used in the field of wireless communication.

Description

Cooperative communication method based on space-time coding and physical layer network coding
Technical Field
The invention relates to the field of wireless communication, in particular to a cooperative communication method based on Alamouti space-time coding and physical layer network coding.
Background
Compared with wired communication, a significant characteristic of wireless communication is the multipath effect of a wireless channel, that is, a plurality of propagation paths with different time delays exist between a transmitting node and a receiving node, and when the maximum time delay of multipath is greater than the duration of a code word, frequency selective fading is caused. The MIMO technology is to effectively utilize wireless space resources by using characteristics of multipath propagation of a wireless communication channel and advanced signal processing techniques, thereby counteracting the negative effects of a wireless fading channel. The cooperative diversity technology is presented to solve the problem that the MIMO technology cannot be applied to an actual wireless communication system, but because a user needs to transmit information of a cooperative partner thereof, additional system energy is consumed, resulting in a decrease in system throughput. Furthermore, due to the broadcast nature of the wireless channel, electromagnetic waves transmitted by one transmitting node may be received simultaneously by multiple nodes. Similarly, a receiving node may receive transmitted signals from multiple transmitting nodes simultaneously. This broadcast characteristic causes interference between signals, which negatively affects the overall communication process.
The concept of Physical-Layer Network Coding (PNC) was first proposed in 2006 by Shengli Zhang et al. The basic idea is to use a proper mapping mechanism at the relay node to map the electromagnetic signals superimposed on each other as an exclusive or of the response digital bit stream, so that the interference becomes part of the operation of the network coding algorithm. The method can greatly improve the system throughput, for example, in a bidirectional relay channel, the system throughput of the PNC can be improved by 100% compared with the traditional routing scheme. Since then, research on cooperative communication systems based on physical layer network coding has been a research hotspot in the field of wireless communication.
The cooperative communication system based on the physical layer network coding well solves the problem that the traditional cooperative communication needs to consume extra system resources to cause the reduction of throughput. However, in the face of increasing user demands for high-speed and high-quality communication, the terminal multi-antenna is becoming a necessary trend for the development of wireless communication. Under the wireless communication environment of the multi-antenna terminal, the research on a cooperative communication system combining space-time coding and physical layer network coding has strong theoretical value. However, currently, there is not much research on the performance of a cooperative system based on physical layer network coding for multiple antennas of a terminal.
Disclosure of Invention
The invention aims to solve the defects of low network throughput of the existing communication system and high error rate of the communication system, and provides a cooperative communication method based on Alamouti space-time coding and physical layer network coding.
A cooperative communication method based on space-time coding and physical layer network coding comprises the following steps:
the method comprises the following steps: respectively generating user nodes S in a broadcasting stage in a multi-user cooperative network model1And a subscriber node S2Using orthogonal carrier pairs to generate the user node S1And a subscriber node S2Modulating the two-bit information to obtain the user node S1And a subscriber node S2The modulation signal of (a);
step two: for the user node S obtained in the step one1And a subscriber node S2The modulation signal is subjected to Alamouti space-time coding to obtain a sending signal, and the sending signal is broadcasted to the relay node R and the destination node D by the transmitting antenna;
step three: the relay node R and the destination node D respectively receive the user node S sent by the transmitting antenna in the step two1And a subscriber node S2Mixed signal of
Figure GDA0002951832940000021
And
Figure GDA0002951832940000022
the above-mentioned
Figure GDA0002951832940000023
And
Figure GDA0002951832940000024
signals received by jth antennas of the relay node R and the destination node D in a kth time slot are respectively represented, and k is 1 and 2; each antenna of the relay node R and the destination node D demodulates the received mixed signal by using the relevant demodulator shown in fig. 2 to obtain the demodulated mixed signal
Figure GDA0002951832940000025
And
Figure GDA0002951832940000026
used for the next step of processing; the above-mentioned
Figure GDA0002951832940000027
And
Figure GDA0002951832940000028
receiving an in-phase part and an orthogonal part of a signal at a k time slot by a j antenna of the relay node R respectively;
Figure GDA0002951832940000029
and
Figure GDA00029518329400000210
respectively receiving an in-phase part and a quadrature part of a signal at a k time slot by a jth antenna of the destination node D;
step four: the relay node R demodulates the correlation to obtain a signal according to Alamouti space-time coding
Figure GDA00029518329400000211
And
Figure GDA00029518329400000212
after linear combination, maximum likelihood detection is carried out, namely the user node S is obtained1And a subscriber node S2Is estimated from
Figure GDA00029518329400000213
The above-mentioned
Figure GDA00029518329400000214
Indicating the user S decoded by the relay node RiJ-th estimation information of (1);
step five: the relay node R sends the user node S obtained in the step four1And a subscriber node S2Is estimated from
Figure GDA00029518329400000215
QPSK modulation is carried out firstly, then Alamouti space-time coding is carried out, and the coded signals are sent to a target node D through a relay node R in a relay stage;
step six: after receiving the encoded signal sent by the relay node R, the destination node D performs coherent demodulation as shown in fig. 2 to obtain a signal
Figure GDA00029518329400000216
Figure GDA00029518329400000217
Respectively representing an in-phase part and a quadrature part of a signal received by a j-th antenna of the destination node D in a k-th time slot in a relay stage, wherein k is 3, 4; the target node D transmits the signals received in the four time slots according to Alamouti space-time coding
Figure GDA00029518329400000218
Linear combination is carried out to obtain user node S1And a subscriber node S2The obtained combined information is subjected to maximum likelihood detection, namely, the user node S in the step one is decoded1And a subscriber node S2Namely, the cooperative communication based on the space-time coding and the physical layer network coding is completed.
The invention has the beneficial effects that:
compared with the prior art, the invention has the most prominent characteristics and remarkable beneficial effects that: in the broadcasting stage of the multi-user cooperative network model, the communication method of the invention respectively adopts orthogonal carrier modulation to the information of two user nodes, and broadcasts the information from two respective transmitting antennas through Alamouti space-time coding. And the relay node R and the destination node D both adopt maximum likelihood decoding to complete the mapping of the physical layer network coding. The invention not only reduces the error rate of the communication system, but also improves the network throughput of the communication system.
The invention aims to further improve the performance of a wireless communication system, improve the network throughput of the communication system and reduce the bit error rate of the communication system. The invention not only improves the network throughput of the communication system, but also reduces the bit error rate of the communication system. Compared with the traditional physical layer network coding, when the bit error rate BER is 10-3The cooperative communication method of the present invention can provide approximately 7dB bit error rate gain. Accordingly, the throughput of the system network is greatly improved due to the reduction of the bit error rate.
Drawings
FIG. 1 is a schematic diagram of a communication model of the present invention;
FIG. 2 is a schematic block diagram of a coherent demodulator;
fig. 3 is a signal processing flow at the relay node R;
FIG. 4 is a graph of bit error rate versus signal to noise ratio for a communication system;
fig. 5 is a graph of throughput versus signal-to-noise ratio for a communication system.
Detailed Description
The first embodiment is as follows: a cooperative communication method based on space-time coding and physical layer network coding comprises the following steps:
the method comprises the following steps: respectively generating user nodes S in a broadcasting stage in a multi-user cooperative network model1And a subscriber node S2Using orthogonal carrier pairs to generate the user node S1And a subscriber node S2Modulating the two-bit information to obtain the user node S1And a subscriber node S2The modulation signal of (a);
step two: for the user node S obtained in the step one1And a subscriber node S2The modulation signal is subjected to Alamouti space-time coding to obtain a sending signal, and the sending signal is broadcasted to the relay node R and the destination node D by the transmitting antenna;
step three: the relay node R and the destination node D respectively receive the user node S sent by the transmitting antenna in the step two1And a subscriber node S2Mixed signal of
Figure GDA0002951832940000031
And
Figure GDA0002951832940000032
the above-mentioned
Figure GDA0002951832940000033
And
Figure GDA0002951832940000034
representing relay node R and destination node D, respectivelyA signal received by the jth antenna in the kth time slot, wherein k is 1, 2; each antenna of the relay node R and the destination node D demodulates the received mixed signal by using the relevant demodulator shown in fig. 2 to obtain the demodulated mixed signal
Figure GDA0002951832940000041
And
Figure GDA0002951832940000042
used for the next step of processing; the above-mentioned
Figure GDA0002951832940000043
And
Figure GDA0002951832940000044
receiving an in-phase part and an orthogonal part of a signal at a k time slot by a j antenna of the relay node R respectively;
Figure GDA0002951832940000045
and
Figure GDA0002951832940000046
respectively receiving an in-phase part and a quadrature part of a signal at a k time slot by a jth antenna of the destination node D;
step four: the relay node R demodulates the correlation to obtain a signal according to Alamouti space-time coding
Figure GDA0002951832940000047
And
Figure GDA0002951832940000048
after linear combination, maximum likelihood detection is carried out, namely the user node S is obtained1And a subscriber node S2Is estimated from
Figure GDA0002951832940000049
The above-mentioned
Figure GDA00029518329400000410
Indicating decoded use of the relay node RHousehold SiJ-th estimation information of (1);
step five: the relay node R sends the user node S obtained in the step four1And a subscriber node S2Is estimated from
Figure GDA00029518329400000411
QPSK modulation is carried out firstly, then Alamouti space-time coding is carried out, and the coded signals are sent to a target node D through a relay node R in a relay stage;
step six: after receiving the encoded signal sent by the relay node R, the destination node D performs coherent demodulation as shown in fig. 2 to obtain a signal
Figure GDA00029518329400000412
Figure GDA00029518329400000413
Respectively representing an in-phase part and a quadrature part of a signal received by a j-th antenna of the destination node D in a k-th time slot in a relay stage, wherein k is 3, 4; the target node D transmits the signals received in the four time slots according to Alamouti space-time coding
Figure GDA00029518329400000414
Linear combination is carried out to obtain user node S1And a subscriber node S2The obtained combined information is subjected to maximum likelihood detection, namely, the user node S in the step one is decoded1And a subscriber node S2Namely, the cooperative communication of the space-time coding and the physical layer network coding is completed.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the multi-user cooperative network model in the step one comprises a user node S1User node S2Each node is provided with a double antenna, the transmitting power of each node is the same, and each node adopts a half-duplex working mode.
The channel between each node in the multi-user cooperative network model is quasi-static and subject to rayleigh flat fading, and the receiver can obtain accurate channel state information CSI.
And the two user nodes adopt orthogonal carriers to broadcast information to the relay node and the destination node simultaneously.
Other steps and parameters are the same as those in the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: respectively generating user nodes S in the step one1And a subscriber node S2Using orthogonal carrier pairs to generate the user node S1And a subscriber node S2Modulating the two-bit information to obtain the user node S1And a subscriber node S2The specific process of modulating the signal is as follows:
broadcast phase, generating subscriber node S1Two bits of information (x)11，x12) Generating a user node S2Two bits of information (x)21，x22) Wherein x isijRepresenting a user node SiThe j-th transmitting antenna needs to send bit information, i is 1,2 is the user node serial number, j is 1,2 is the transmitting antenna serial number;
generation of user node S using orthogonal carrier pairs1And a subscriber node S2Are modulated to obtain (x) respectively11(t)＝x11cos2πfct，x12(t)＝x12cos2πfct) and (x)21(t)＝x21sin2πfct，x22(t)＝x22sin2πfct), where t is the time, fcIs the carrier frequency.
Other steps and parameters are the same as those in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: in the second step, the user node S obtained in the first step1And a subscriber node S2The modulation signal is subjected to Alamouti space-time coding to obtain a sending signal, and the specific process that the sending antenna broadcasts the sending signal to the relay node R and the target node D is as follows:
obtaining a user node S1Sending a signal of
Figure GDA0002951832940000051
And
Figure GDA0002951832940000052
obtaining a user node S2Sending a signal of
Figure GDA0002951832940000053
And
Figure GDA0002951832940000054
wherein
Figure GDA0002951832940000055
Is x12(t) the conjugation of the (t),
Figure GDA0002951832940000056
is x11(t) the conjugation of the (t),
Figure GDA0002951832940000057
is x22(t) the conjugation of the (t),
Figure GDA0002951832940000058
is x21(t) conjugation;
in the first time slot of the broadcast phase, the subscriber node S1And a subscriber node S2Separately transmitting signals
Figure GDA0002951832940000059
And
Figure GDA00029518329400000510
in the second time slot of the broadcast phase, the subscriber node S1And a subscriber node S2Separately transmitting signals
Figure GDA00029518329400000511
And
Figure GDA00029518329400000512
other steps and parameters are the same as those in one of the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: the mixed signal in the third step
Figure GDA00029518329400000513
And
Figure GDA00029518329400000514
the method specifically comprises the following steps:
Figure GDA0002951832940000061
Figure GDA0002951832940000062
Figure GDA0002951832940000063
Figure GDA0002951832940000064
wherein h isSiRmn、hSiDmnRespectively representing user nodes SiWith the channel fading coefficients between the nth antenna of (a) and the mth antenna of the relay node R and the destination node D (m, n is 1, 2);
Figure GDA0002951832940000065
noise signals received by jth antennas of the relay node R and the destination node D in a kth time slot are respectively represented (j, k is 1, 2);
Figure GDA0002951832940000066
is xijConjugation of (1);
other steps and parameters are the same as in one of the first to fourth embodiments.
The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: in the fourth step, the signal obtained after the correlation demodulation is obtained
Figure GDA0002951832940000067
And
Figure GDA0002951832940000068
after linear combination, maximum likelihood detection is carried out, namely the user node S is obtained1And a subscriber node S2Is estimated from
Figure GDA0002951832940000069
The specific process comprises the following steps:
the merging information of the two user nodes obtained by linear merging is as follows:
Figure GDA00029518329400000610
Figure GDA00029518329400000611
Figure GDA0002951832940000071
Figure GDA0002951832940000072
wherein the content of the first and second substances,
Figure GDA0002951832940000073
is hSiRmnConjugation of (1);
Figure GDA0002951832940000074
in-phase and quadrature parts of the noise signal received at the j-th antenna of the relay node R in the k-th time slot, respectively, j, k being 1, 2;
Figure GDA0002951832940000075
is that
Figure GDA0002951832940000076
Conjugation of (1);
Figure GDA0002951832940000077
is that
Figure GDA0002951832940000078
Conjugation of (1);
Figure GDA0002951832940000079
is that
Figure GDA00029518329400000710
Conjugation of (1);
Figure GDA00029518329400000711
is that
Figure GDA00029518329400000712
Conjugation of (1);
other steps and parameters are the same as those in one of the first to fifth embodiments.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: in the step five, the relay node R sends the user node S obtained in the step four1And a subscriber node S2Is estimated from
Figure GDA00029518329400000713
Firstly, QPSK modulation is carried out, then Alamouti space-time coding is carried out, and the specific process of sending the coded signal to the destination node D through the relay node R in the relay stage is as follows:
the relay node R decodes the obtained estimated information
Figure GDA00029518329400000714
Firstly, QPSK modulation is carried out to obtain:
Figure GDA00029518329400000715
Figure GDA00029518329400000716
for xR1(t) and xR2(t) performing Alamouti space-time coding, namely, transmitting a signal to a destination node D by a relay node R in a third time slot
Figure GDA00029518329400000717
Transmitting signal in the fourth time slot
Figure GDA00029518329400000718
The whole signal processing flow at the relay node R is shown in fig. 3.
Other steps and parameters are the same as those in one of the first to sixth embodiments.
The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: in the sixth step, the signals received in four time slots are processed
Figure GDA00029518329400000719
Linear combination is carried out to obtain user node S1And a subscriber node S2The merging information is specifically:
Figure GDA0002951832940000081
Figure GDA0002951832940000082
Figure GDA0002951832940000083
Figure GDA0002951832940000084
wherein h isSiDmn，hRDmnRespectively represent Si-complex channel fading coefficients of the n-th transmitting antenna to the m-th receiving antenna of the D-link and the R-D link (m, n is 1, 2);
Figure GDA0002951832940000085
is that
Figure GDA0002951832940000086
Conjugation of (1);
Figure GDA0002951832940000087
is that
Figure GDA0002951832940000088
Conjugation of (1);
Figure GDA0002951832940000089
is that
Figure GDA00029518329400000810
Conjugation of (1);
Figure GDA00029518329400000811
is that
Figure GDA00029518329400000812
Conjugation of (1);
Figure GDA00029518329400000813
user node S obtained by representing destination node DiAnd j is the combined information of the transmitted information on the j-th transmitting antenna, i, j is 1, 2.
Other steps and parameters are the same as those in one of the first to seventh embodiments.
The first embodiment is as follows:
in this embodiment, each node adopts a half-duplex working mode, and the transmission power is the same, and 4 time slots are required for completing transmission of 2-bit information sent by each user.
This implementationIn the example, each user node randomly transmits 1024 bits of 0,1 information, the channel in each step is a quasi-static rayleigh flat fading channel, and the channel fading coefficient obeys a mean value of 0 and a variance of σ2Complex gaussian random variables. The two-user cooperative network shown in FIG. 1 is a symmetric network, and from the aspect of signal-to-noise ratio, the signal-to-noise ratio of the S1-R link and the S2-R link are equal, namely, the SNRS1R＝SNRS2R＝SNRSR(ii) a The S1-D link and S2-D link also have equal signal-to-noise ratios, i.e., SNRS1D＝SNRS2D＝SNRSD. In addition, the signal-to-noise ratio of each link in the two-user cooperative network model shown in fig. 1 is the same, i.e., the SNRSR＝SNRSD＝SNRRD。
After 1000 Monte Carlo simulation experiments, compared with the conventional cooperative communication method based on physical layer network coding, the cooperative communication method of the present invention has the change curve of the bit error rate of the system along with the SNR of the link as shown in FIG. 4. In FIG. 4, the abscissa represents the SNR of each link, which ranges from 0 to 20]dB; the ordinate represents the bit error rate of the system, which is in the range [10 ]-7,10-1]. As can be seen from fig. 4, the bit error rate of the cooperative communication method of the present invention is lower than that of the conventional cooperative communication system based on physical layer network coding. Compared with the traditional physical layer network coding, when the bit error rate BER is 10-3The cooperative communication method of the present invention can provide approximately 7dB bit error rate gain.
After 1000 monte carlo simulation experiments, compared with the traditional cooperative communication method based on physical layer network coding, the cooperative communication method of the invention has the advantage that the change curve of the network throughput along with the signal-to-noise ratio (SNR) is shown in fig. 5. In FIG. 5, the abscissa represents the SNR for each link, which ranges from [0,20] dB; the ordinate represents the normalized throughput of the system, which ranges from 0, 1.1. As can be seen from fig. 5, the network throughput of the cooperative communication method of the present invention is higher than that of the conventional cooperative communication system based on physical layer network coding due to the reduction of the bit error rate of the system.
The present invention is capable of other embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and scope of the present invention.

Claims (8)

1. A cooperative communication method based on space-time coding and physical layer network coding is characterized in that: the cooperative communication method based on the space-time coding and the physical layer network coding comprises the following steps:
the method comprises the following steps: respectively generating user nodes S in a broadcasting stage in a multi-user cooperative network model1And a subscriber node S2Using orthogonal carrier pairs to generate the user node S1And a subscriber node S2Modulating the two-bit information to obtain the user node S1And a subscriber node S2The modulation signal of (a);
step two: for the user node S obtained in the step one1And a subscriber node S2The modulation signal is subjected to Alamouti space-time coding to obtain a sending signal, and the sending signal is broadcasted to the relay node R and the destination node D by the transmitting antenna;
step three: the relay node R and the destination node D respectively receive the user node S sent by the transmitting antenna in the step two1And a subscriber node S2Mixed signal of
Figure FDA0002971008990000011
And
Figure FDA0002971008990000012
the above-mentioned
Figure FDA0002971008990000013
And
Figure FDA0002971008990000014
signals received by jth antennas of the relay node R and the destination node D in a kth time slot are respectively represented, and k is 1 and 2; each antenna of the relay node R and the destination node D respectively adopts related demodulationThe device demodulates the received mixed signal to obtain
Figure FDA0002971008990000015
And
Figure FDA0002971008990000016
the above-mentioned
Figure FDA0002971008990000017
And
Figure FDA0002971008990000018
receiving an in-phase part and an orthogonal part of a signal at a kth time slot by a jth antenna of the relay node R respectively;
Figure FDA0002971008990000019
and
Figure FDA00029710089900000110
respectively receiving an in-phase part and a quadrature part of a signal at a kth time slot by a jth antenna of a destination node D;
step four: the relay node R demodulates the correlation to obtain a signal according to Alamouti space-time coding
Figure FDA00029710089900000111
And
Figure FDA00029710089900000112
after linear combination, maximum likelihood detection is carried out, namely the user node S is obtained1And a subscriber node S2Is estimated from
Figure FDA00029710089900000113
The above-mentioned
Figure FDA00029710089900000114
Indicating the user S decoded by the relay node RiThe j-th estimation information of (1),wherein, i is 1,2 is the serial number of the user node, j is 1,2 is the serial number of the transmitting antenna;
step five: the relay node R sends the user node S obtained in the step four1And a subscriber node S2Is estimated from
Figure FDA00029710089900000115
QPSK modulation is carried out firstly, then Alamouti space-time coding is carried out, and the coded signals are sent to a target node D through a relay node R in a relay stage;
step six: after receiving the encoded signal sent by the relay node R, the destination node D obtains a signal through relevant demodulation
Figure FDA00029710089900000116
Respectively representing an in-phase part and a quadrature part of a signal received by a j-th antenna of the destination node D in a k-th time slot in a relay stage, wherein k is 3, 4; the destination node D demodulates the demodulation signals received in the four time slots according to Alamouti space-time coding
Figure FDA0002971008990000021
Linear combination is carried out to obtain user node S1And a subscriber node S2The obtained combined information is subjected to maximum likelihood detection, namely, the user node S in the step one is decoded1And a subscriber node S2Namely, the cooperative communication of the space-time coding and the physical layer network coding is completed.
2. A cooperative communication method based on space-time coding and physical layer network coding according to claim 1, characterized in that: the multi-user cooperative network model in the step one comprises a user node S1User node S2Each node is provided with a double antenna, the transmitting power of each node is the same, and each node adopts a half-duplex working mode.
3. Space-time based according to claim 1 or 2The cooperative communication method of coding and physical layer network coding is characterized in that: respectively generating user nodes S in the step one1And a subscriber node S2Using orthogonal carrier pairs to generate the user node S1And a subscriber node S2Modulating the two-bit information to obtain the user node S1And a subscriber node S2The specific process of modulating the signal is as follows:
broadcast phase, generating subscriber node S1Two bits of information (x)11，x12) Generating a user node S2Two bits of information (x)21，x22) Wherein x isijRepresenting a user node SiThe j-th transmitting antenna needs to send bit information, i is 1,2 is the user node serial number, j is 1,2 is the transmitting antenna serial number;
generation of user node S using orthogonal carrier pairs1And a subscriber node S2Are modulated to obtain (x) respectively11(t)＝x11cos 2πfct，x12(t)＝x12cos 2πfct) and (x)21(t)＝x21sin 2πfct，x22(t)＝x22sin 2πfct), where t is the time, fcIs the carrier frequency.
4. A cooperative communication method based on space-time coding and physical layer network coding according to claim 3, characterized in that: in the second step, the user node S obtained in the first step1And a subscriber node S2The modulation signal is subjected to Alamouti space-time coding to obtain a sending signal, and the specific process that the sending antenna broadcasts the sending signal to the relay node R and the target node D is as follows:
obtaining a user node S1Sending a signal of
Figure FDA0002971008990000022
And
Figure FDA0002971008990000023
obtaining user nodesS2Sending a signal of
Figure FDA0002971008990000024
And
Figure FDA0002971008990000025
wherein
Figure FDA0002971008990000026
Is x12(t) the conjugation of the (t),
Figure FDA0002971008990000027
is x11(t) the conjugation of the (t),
Figure FDA0002971008990000028
is x22(t) the conjugation of the (t),
Figure FDA0002971008990000031
is x21(t) conjugation;
in the first time slot of the broadcast phase, the subscriber node S1And a subscriber node S2Separately transmitting signals
Figure FDA0002971008990000032
And
Figure FDA0002971008990000033
in the second time slot of the broadcast phase, the subscriber node S1And a subscriber node S2Separately transmitting signals
Figure FDA0002971008990000034
And
Figure FDA0002971008990000035
5. cooperation based on space-time coding and physical layer network coding according to claim 4A communication method, characterized by: the mixed signal in the third step
Figure FDA0002971008990000036
And
Figure FDA0002971008990000037
the method specifically comprises the following steps:
Figure FDA0002971008990000038
Figure FDA0002971008990000039
Figure FDA00029710089900000310
Figure FDA00029710089900000311
wherein h isSiRmn、hSiDmnRespectively representing user nodes SiThe channel fading coefficient between the nth antenna and the mth antenna of the relay node R and the destination node D, m, n being 1, 2;
Figure FDA00029710089900000312
j, k is 1,2, which represents noise signals received by jth antennas of the relay node R and the destination node D in the kth time slot respectively;
Figure FDA00029710089900000313
is xijT is the time, fcIs the carrier frequency.
6. Space-time coding and physical layer based on according to claim 5The cooperative communication method of the network coding is characterized in that: in the fourth step, the signal obtained after the correlation demodulation is obtained
Figure FDA00029710089900000314
And
Figure FDA00029710089900000315
after linear combination, maximum likelihood detection is carried out, namely the user node S is obtained1And a subscriber node S2Is estimated from
Figure FDA00029710089900000316
The specific process comprises the following steps:
the merging information of the two user nodes obtained by linear merging is as follows:
Figure FDA0002971008990000041
Figure FDA0002971008990000042
Figure FDA0002971008990000043
Figure FDA0002971008990000044
wherein the content of the first and second substances,
Figure FDA0002971008990000045
is hSiRmnConjugation of (1);
Figure FDA0002971008990000046
respectively represents the noise received by the j antenna of the relay node R in the k time slotThe in-phase and quadrature parts of the acoustic signal, j, k being 1, 2;
Figure FDA0002971008990000047
is that
Figure FDA0002971008990000048
Conjugation of (1);
Figure FDA0002971008990000049
is that
Figure FDA00029710089900000410
Conjugation of (1);
Figure FDA00029710089900000411
is that
Figure FDA00029710089900000412
Conjugation of (1);
Figure FDA00029710089900000413
is that
Figure FDA00029710089900000414
Conjugation of (1).
7. A cooperative communication method based on space-time coding and physical layer network coding according to claim 6, characterized in that: in the step five, the relay node R sends the user node S obtained in the step four1And a subscriber node S2Is estimated from
Figure FDA00029710089900000415
Firstly, QPSK modulation is carried out, then Alamouti space-time coding is carried out, and the specific process of sending the coded signal to the destination node D through the relay node R in the relay stage is as follows:
the relay node R decodes the obtained estimated information
Figure FDA00029710089900000416
Firstly, QPSK modulation is carried out to obtain:
Figure FDA00029710089900000417
Figure FDA00029710089900000418
for xR1(t) and xR2(t) performing Alamouti space-time coding, namely, transmitting a signal to a destination node D by a relay node R in a third time slot
Figure FDA00029710089900000419
Transmitting signal in the fourth time slot
Figure FDA00029710089900000420
8. A cooperative communication method based on space-time coding and physical layer network coding according to claim 7, characterized in that: in the sixth step, the signals received in four time slots are processed
Figure FDA00029710089900000421
Wherein k represents time slot, linear combination is carried out to obtain user node S1And a subscriber node S2The merging information is specifically:
Figure FDA0002971008990000051
Figure FDA0002971008990000052
Figure FDA0002971008990000053
Figure FDA0002971008990000054
wherein h isSiDmn，hRDmnRespectively represent Si-complex channel fading coefficients of the n-th transmitting antenna to the m-th receiving antenna of the D-link and the R-D link, m, n being 1, 2;
Figure FDA0002971008990000055
is that
Figure FDA0002971008990000056
Conjugation of (1);
Figure FDA0002971008990000057
is that
Figure FDA0002971008990000058
Conjugation of (1);
Figure FDA0002971008990000059
is that
Figure FDA00029710089900000510
Conjugation of (1);
Figure FDA00029710089900000511
is that
Figure FDA00029710089900000512
The conjugate of (a) to (b),
Figure FDA00029710089900000513
user node S obtained by representing destination node DiAnd j is the combined information of the transmitted information on the j-th transmitting antenna, i, j is 1, 2.
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