CN108988911B

CN108988911B - Cooperative relay method of mobile ad hoc network

Info

Publication number: CN108988911B
Application number: CN201810987204.7A
Authority: CN
Inventors: 冯敏; 张晶; 孙健兴; 苏郢; 董冉; 汪洋; 郑文超; 赵佳; 李谦; 李翔; 代荣; 刘亨立
Original assignee: Wuhan Zhongyuan Mobilcom Engineering Co Ltd
Current assignee: Wuhan Zhongyuan Mobilcom Engineering Co Ltd
Priority date: 2018-08-28
Filing date: 2018-08-28
Publication date: 2021-09-07
Anticipated expiration: 2038-08-28
Also published as: CN108988911A

Abstract

The invention discloses a cooperative relay method of a mobile ad hoc network, which comprises the following steps: step S1, copying the baseband signal to a plurality of cooperative transmitting terminals; step S2, the cooperative transmitting terminal modulates the corresponding baseband signal to obtain a baseband modulation signal; step S3, each cooperative transmitting terminal respectively performs phase jitter, amplitude jitter and time jitter on the corresponding baseband modulation signal, and sends the baseband modulation signal to a receiving terminal through a multipath channel; step S4, the receiving end receives the complex baseband modulation signal and demodulates it. The invention can realize cooperative diversity without the need of known channel state signal of transmitting terminal or user adjustment.

Description

Cooperative relay method of mobile ad hoc network

Technical Field

The invention relates to the technical field of diversity and anti-fading of a mobile ad hoc network, in particular to a cooperative relay method of the mobile ad hoc network.

Background

The mobile ad hoc network wireless channel usually causes various fading of the signal, and one effective method for eliminating the fading is diversity anti-fading technology, and the existing diversity anti-fading technology has space diversity, time diversity and frequency diversity. Recently, a new diversity method called cooperative diversity technology has attracted great attention by adopting a cooperative communication method, and compared with the traditional spatial diversity method of single-user communication, cooperative communication is based on a typical relay channel, and different users or nodes are allowed to actively share the antenna and other resources in a wireless network, so that a virtual antenna array is obtained to obtain spatial diversity.

The cooperative diversity technology adopts a distributed space-time coding or a distributed beam forming technology, but both the technologies have significant challenges in the implementation process. When distributed beamforming is employed. Not only does the transmitter need to know the channel characteristics, but the transmitter's oscillator must be very stable and controlled to maintain this coherence, which is a challenge even for transmitters in coherent arrays, but for transmitters in non-coherent arrays. This problem is further exacerbated by the conflicting presence of mobility between the transmitter and receiver, mobility in the propagation environment, and the desire to acquire inexpensive, highly stable radio frequency circuit components, among other things. When the distributed space-time coding is adopted, several coordination situations are needed, and in the first situation, a transmitter and a receiver must acquire the number information of the transmitter; second, the ordering concept of the transmitter needs to be established, either of which presents implementation challenges.

Disclosure of Invention

The present invention aims to overcome the technical deficiencies, and provide a cooperative relay method for a mobile ad hoc network, which solves the technical problem that in the prior art, an emitter needs to know channel state information or perform user adjustment to realize cooperative diversity.

In order to achieve the technical purpose, the technical scheme of the invention provides a cooperative relay method of a mobile ad hoc network, which comprises the following steps:

step S1, copying the baseband signal to a plurality of cooperative transmitting terminals;

step S2, the cooperative transmitting terminal modulates the corresponding baseband signal to obtain a baseband modulation signal;

step S3, each cooperative transmitting terminal respectively performs phase jitter, amplitude jitter and time jitter on the corresponding baseband modulation signal, and sends the baseband modulation signal to a receiving terminal through a multipath channel;

step S4, the receiving end receives the complex baseband modulation signal and demodulates it.

Compared with the prior art, the invention has the beneficial effects that: through the jitter of each cooperative node to the baseband modulation signal, each cooperative transmitting end is associated and distinguished and marked by adopting a distinguishable initial seed value, and cooperative diversity can be realized without the known channel state signal of the transmitting end or the adjustment of a user; meanwhile, in the aspect of statistical probability, the system presents a static and destructive interference mode, a receiving end cannot meet the interference mode, and higher diversity gain can be obtained.

Drawings

Fig. 1 is a flowchart of a cooperative relaying method of a mobile ad hoc network provided by the present invention;

fig. 2 is a block diagram of phase jitter and time jitter of a cooperative relaying method of a mobile ad hoc network provided by the present invention;

fig. 3 is a flowchart of an algorithm implementation of a cooperative relaying method of a mobile ad hoc network provided by the present invention;

FIG. 4 is a graph of time jitter simulation for a first amplitude case;

FIG. 5 is a graph of time jitter simulation for a second amplitude case;

FIG. 6 is a simulation of phase jitter for a first amplitude case;

fig. 7 is a simulation diagram of phase jitter in the case of a second amplitude.

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.

Example 1:

as shown in fig. 1, embodiment 1 of the present invention provides a cooperative relay method for a mobile ad hoc network, including the following steps:

The invention utilizes the dithering technology, each cooperative transmitting terminal obtains different dithering values, different channels and different cooperative transmitting terminals are distinguished through different dithering values, and signals of all the cooperative transmitting terminals are combined at a receiving terminal, thereby improving the reliability of the system, namely the capability of resisting multipath channels. Because different channels and the cooperative transmitting end are distinguished through dithering, the invention does not need the transmitter to know the channel state information area to complete distributed beam forming or user adjustment required by distributed space-time codes. Also, the receiving end does not need to know the number of packet transmitting ends or evaluate their respective channel information, which is done by the dithering technique.

In the invention, the jitter sequences of phase jitter, amplitude jitter and time jitter can be randomly generated or directly stored in the corresponding cooperative transmitting terminal. In a cooperative uncorrelated array, independently distinguishable dither patterns are assigned to each transmit side. The dithering modes of phase dithering, amplitude dithering and time dithering can be generated by a pseudo-random PN sequence or pseudo-random noise generator at the transmitting end, and each transmitter has an independently distinguishable dithered initial seed value; the jitter values may be stored in RAM, registers, ROM, EPROM and EEPROM or flash memory. The time dithering technology delays or advances different time domain segments based on one hop or one time slot, thereby obtaining stronger anti-multipath channel capability. The phase dithering technique is that the dithering value before each sub-packet is a unique and distinguishable time-invariant dithering value, and the phase dithering is a discrete value of phase, which can be generated by a pseudo-random number generator, which is placed at each cooperative transmitting end, and uses distinguishable initial seed values to associate and distinguish and mark each cooperative transmitting end. The receiving end receives a composite signal that is the sum of the jittered signals transmitted from each of the cooperating transmitting ends. The receiving end does not need to know the number of the non-relevant radio transceivers; the receiver uses the training sequence or a portion thereof to estimate the channel response and adjust the timing synchronization for the demodulator; the demodulated signal is then rearranged and used to decode the forward error correction decoding module.

Specifically, as shown in fig. 2, user m receives a version of the transmission signal of the cooperative user and converts the data of this transmission signal to construct a baseband modulated signal s k. The nth cooperative transmitting end adopts phase jitter, time jitter and amplitude jitter. The receiving end noiseless composite baseband signal z k can be expressed by the following equivalent formula

In the above formula, θ_n[k]Representing phase jitter, A_n[k]Representing amplitude jitter, k₀Represents the time jitter value, s [ k ]]Representing the kth symbol.

We take as an example the limitation of AWGN white gaussian noise channels, each channel being modeled using the following formula:

where D is the size of the dimension used by each channel. The information-bearing signal x is a complex vector signal and the distributed probability characteristic fits a finite set

And a distribution probability factor P_m＝P_r{x＝S_m}. A denotes the complex channel gain for the symbol information carrying signal x. Thus, when we use phase/time dithering, α explains the signal C [ k ] in equation (1)]I.e. experience any additional added channel gain, such as a rayleigh fading channel. The noise omega is an implementation of complex gaussian baseband processing, traversing the entire channel and the information-bearing signal x independently of each other. Further, the real part and imaginary part of ω are also independent and equal probability distributions with 0 mean and N₀The variance of/2, and in addition, the information-bearing signal x, the gain α, and the noise ω are normalized such that the overall signal energy E_SAnd the noise variance of each dimension is N₀/2, in particular, as shown in the following equation:

E|α|²＝1 (4)

the diversity and interleaving techniques generated by the phase-jittered and time-jittered patterns together experience that the channel is captured by modern error correction coding through LLR maximum likelihood ratios. The LLRs represent the diversity information (channel gain) and the alpha and noise variance in equation (2) are entered into the decoder by appropriately scaling the identifiable metric values. The following LLR formula definition is preferably used here for the channel model:

the present invention is applicable to a variety of wired or wireless networks including, but not limited to, the types described herein, such as powerline, WLAN, WiMAX, cellular GSM, CDMA, WCDMA and TD-SCDMA, TDD _ LTE, FDD _ LTE, data audio broadcast and data video broadcast networks. For example, in a cellular environment, including composite users (transceivers), a transmitting end user can communicate with other transceiver users via an omni-directional antenna to achieve spatial diversity and time diversity for uplink communications. This is particularly advantageous when the transmitting end user is behind a building and cannot have a direct communication path to the base station, while other users of the radio transceiver participating in cooperative communication and having line-of-sight communication with the base station are able to relay the signal relayed to the transmitting end user. Also for example, in a digital signal broadcasting system, a multiplex broadcasting tower is included. The transmitting end can cooperatively communicate with other transmitting towers to achieve coverage of a single frequency network over a region, even nationwide. The invention is suitable for MANET, namely mobile Ad-Hoc network of SRW soldier radio waveform in the same way, can support the framework of mobile Ad-Hoc network 'mobility' flexible networking of MANET, and the invention can expand the communication range and save time delay, and can convert space diversity into time diversity on the basis of the cooperative communication anti-multipath interference, thereby further improving the reliability of the system.

Preferably, as shown in fig. 3, the step S2 specifically includes:

step S21, performing forward error correction coding on the baseband signal;

step S22, interleaving the baseband signal after forward error correction coding;

step S23, performing spread spectrum processing on the baseband signal after the interleaving processing to obtain a plurality of packet signals, and adding the same training sequence before each packet signal;

step S24, performing modulation mapping on each of the packetized signals to obtain the baseband modulation signal.

Each cooperative transmitting end receives a common transmission channel at the receiving end and can further ensure that the error correction receiving end adopts an error detection method, such as Cyclic Redundancy Check (CRC) coding. This helps to confirm that the composite baseband signal s k is equivalent for all cooperating transmitting ends. Additional diversity is obtained by the interleaving process and is denoted by I in fig. 2.

Preferably, step S21 is preceded by: and checking the baseband signal by adopting a cyclic redundancy check method.

In order to ensure that the synthesized signal after each branch acquires the baseband signal is equivalent, the embodiment adopts Cyclic Redundancy Check (CRC) to check the baseband signal.

Preferably, the step S21 specifically includes: and carrying out forward error correction coding on the baseband signal by adopting a 3GPP coding technology.

The 3GPP coding technology has better error correction performance.

Preferably, the step S22 specifically includes: and 3GPP interleaving technology is adopted to realize the interleaving processing.

The interleaving process can also be realized by random interleaving, but the performance of the 3GPP interleaving technology is better. Additional diversity is obtained by interleaving.

Preferably, the training sequence is selected from PN sequences or obtained by multiplexing the PN sequences.

Preferably, the step S24 specifically includes: and modulating and mapping the sub-packet signals by adopting a PSK (phase Shift keying) modulation mode or a QAM (Quadrature amplitude modulation) modulation mode.

Preferably, the phase jitter value of each of the cooperative transmitting ends is a discrete value.

The jitter values preceding each sub-packet signal are unique distinguishable time-invariant values, and the phase jitter values are discrete values of phase that can be generated by a pseudo-random number generator placed at each transmitter and using distinguishable initial jitter values to correlate the baseband signal with the corresponding cooperating transmitter that transmitted the baseband signal.

Preferably, the step S4 specifically includes:

step S41, performing spread spectrum timing synchronization on the composite baseband modulation signal, and then performing multipath merging processing;

step S42, the composite baseband modulation signal after the multipath merging processing is processed with the de-spread spectrum processing;

step S43, de-interleaving the composite baseband modulation signal after de-spreading;

step S44, forward error correction decoding is performed on the composite baseband modulation signal subjected to the deinterleaving processing, so as to obtain a demodulation signal.

The receiving end receives the composite signal of the coordinated sending end through the multipath channel, carries out spread spectrum timing synchronization processing, the PN sequence in the existing spread spectrum scheme can basically and accurately find the synchronization head for timing synchronization, then the receiving end adopts the multipath combination technology, and if the channel estimation needs to be realized, the common channel estimation method in the industry can be directly used. And then, performing despreading processing, frequency offset estimation or frequency offset compensation, wherein a common frequency offset estimation method is adopted, and frequency offset can be added during simulation and then deviation rectification processing is performed. And demodulating each sub-packet, wherein the demodulation is carried out according to a modulation method of the corresponding cooperative sending end. And (3) de-interleaving, namely performing corresponding de-interleaving treatment on an interleaving method corresponding to a sending end, wherein the de-interleaving technology is a blue transmission random de-interleaving technology or a 3GPP de-interleaving technology with stronger performance. And performing FEC forward error correction decoding on all the packet numbers, wherein a corresponding transmitting end can directly adopt a 3GPP decoding algorithm which can be realized by adopting the LLR definition algorithm. And after the decoding is finished, recovering the transmission information data of the sending end to obtain a demodulated signal, and then comparing FER/BER/PER performance with the data source of the original sending end.

In order to verify the technical effect of the cooperative relaying method of the mobile ad hoc network provided by the invention, simulation demonstration is carried out on the method.

The simulation verification simulates time jitter and phase jitter, the channel types comprise urban multi-path channels and suburban multi-path channels, the total number of the multi-path channels is four, the simulation times simNums is 2000, and the number of the radio stations at the sending end is as follows: 4, the receiving ends are uniformly combined for receiving, AWGN white noise only uses the white noise of the first path, and other paths are superposed upwards for combination. The signal amplitude is divided into two conditions for simulation, wherein the amplitudes of the four paths are all fixed to be 1; the other is that the amplitude of the first path is fixed to be 1, and the amplitudes of other paths are random. Radio ID number range of sending end radio station: 0-31, 32 total radio stations participate in cooperative relay, and the maximum number of users of mobile Ad-Hoc networking access nodes accords with SRW waveform MANET.

Time jitter mode: differfmod ═ 0 denotes no time jitter; differfmod ═ 1 denotes time-slot jitter; differfmod ═ 2 denotes time jitter. The time jitter is in the range of 0-7 chips.

Phase jitter pattern: differfmod ═ 0 indicates no phase jitter; differfmod 4 indicates that the phase is jittered by slot; differmmod-8 denotes phase jitter by jump. And if the phase jitter range is-pi- + pi, and the requirement of the phase jitter value is a phase discrete value, the simulation is set to be eight equally divided discrete phase values in the phase jitter range.

And (3) simulation results:

fig. 4 is a simulation result when the time jitter is constant and the amplitudes of the four paths are all fixed to 1, three solid lines in fig. 4 are performance simulation results in three time jitter modes, respectively, and the multi-path channel frame error rate FER is 10-2. From the simulation result of fig. 4, the performance effect of time jitter according to hops is the best when the amplitudes of the four paths are all fixed to 1.

Fig. 5 shows simulation results when the amplitude of the first path is fixed to 1 and the amplitudes of other paths are random, three solid lines in fig. 5 respectively show performance simulation results of three time jitter modes, and the multi-path channel frame error rate FER is 10-2. From the simulation result of fig. 5, the amplitude of the first path is fixed to 1, and the performance effect of time jitter according to hops is the best when the amplitudes of other paths are random.

Fig. 6 shows simulation results when the amplitudes of the four paths are all fixed to 1, and three solid lines in fig. 6 respectively show performance simulation results of three phase jitter modes, and the multi-path channel frame error rate FER is 10-2. From the simulation result of fig. 6, the performance effect of the phase dithering according to the jump is the best when the amplitudes of the four paths are all fixed to 1.

Fig. 7 shows simulation results of phase jitter when the amplitude of the first path is fixed to 1 and the amplitudes of other paths are random, and three solid lines in fig. 7 respectively show performance simulation results of three phase jitter modes, and the multi-path channel frame error rate FER is 10-2. From the simulation result of fig. 7, the amplitude of the first path is fixed to 1, and the performance effect of phase dithering according to the time slot is the best when the amplitudes of other paths are random.

Compared with distributed beam forming and distributed space-time coding, the mobile ad hoc network cooperative relay method provided by the invention does not need to share CSI among team radio members, and does not need any user to adjust (such as sequencing). The present invention is based on modern error correction coding, interleaving, direct sequence spreading, multipath combining, CRC checking and phase/time dithering techniques, which ensures that a static, destructive interference is not encountered at the target receiver by allowing each user to dither its own signal. Modern error correction coding techniques, such as the 3GPP coding techniques, typically achieve large diversity gains in time-varying interference patterns generated via channel and jitter patterns. Further, by adopting the phase jitter and time jitter techniques, for the cooperative relay mode in cooperative communication, the space diversity is converted into the time diversity, so as to obtain a more reliable multipath interference resistant mode, and because of the introduction of the jitter techniques, the requirements on the implementation of the transmitting end and the receiving end of the cooperative communication are obviously reduced, and the loss of an ideal cooperative communication scheme is minimal. The method is particularly suitable for the 'mobile' flexible networking mode of the SRW waveform MANET mobile Ad-hoc Ad-hoc network.

The above-described embodiments of the present invention should not be construed as limiting the scope of the present invention. Any other corresponding changes and modifications made according to the technical idea of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A cooperative relay method of a mobile ad hoc network is characterized by comprising the following steps:

step S4, the receiving end receives the composite baseband modulation signal and demodulates the signal;

the jitter sequences of the phase jitter, the amplitude jitter and the time jitter are randomly generated or stored in corresponding cooperative transmitting terminals, and the jitter modes of the phase jitter, the amplitude jitter and the time jitter are generated by pseudo-random PN sequences or pseudo-random noise generators of the cooperative transmitting terminals;

the receiving end noiseless composite baseband signal is expressed by the following equivalent formula:

θ_n[k]representing phase jitter, A_n[k]Representing amplitude jitter, k₀Represents the time jitter value, s [ k ]]Denotes the kth symbol, z [ k]Representing the complex baseband signal, Ck]Representing the channel gain for a channel experiencing rayleigh fading.

2. The cooperative relaying method of a mobile ad hoc network according to claim 1, wherein said step S2 specifically comprises:

step S21, performing forward error correction coding on the baseband signal;

3. The cooperative relaying method of mobile ad hoc network according to claim 2, wherein said step S21 is preceded by the step of: and checking the baseband signal by adopting a cyclic redundancy check method.

4. The cooperative relaying method of a mobile ad hoc network according to claim 2, wherein the step S21 is specifically: and carrying out forward error correction coding on the baseband signal by adopting a 3GPP coding technology.

5. The cooperative relaying method of a mobile ad hoc network according to claim 2, wherein the step S22 is specifically: and 3GPP interleaving technology is adopted to realize the interleaving processing.

6. The cooperative relaying method of mobile ad hoc network as claimed in claim 2, wherein said training sequence is selected from PN sequences or obtained by multiplexing said PN sequences.

7. The cooperative relaying method of a mobile ad hoc network according to claim 2, wherein the step S24 is specifically: and modulating and mapping the sub-packet signals by adopting a PSK (phase Shift keying) modulation mode or a QAM (Quadrature amplitude modulation) modulation mode.

8. The cooperative relaying method of mobile ad hoc network as claimed in claim 1, wherein the phase jitter value of each said cooperative transmitting end is a discrete value.

9. The cooperative relaying method of a mobile ad hoc network according to claim 2, wherein the step S4 is specifically: