CN101860873A - Distributed relay selection method based on cross-layer information exchange - Google Patents

Abstract

The invention relates to a distributed relay selection method based on cross-layer information exchange, which comprises the following steps: firstly, obtaining the distributed selection protocol of the best cooperative relay according to the best selection criteria of the cooperative relay in the dynamic network environment, and providing a self-adaptive cooperative transmission scheme according to the wireless channel quality between the cooperative relay and a source node. Therefore, the method mainly comprises two parts: one part provides the best selection criteria of the cooperative relay in the dynamic network environment and the distributed selection protocol of the best cooperative relay, and the second part provides the self-adaptive cooperative transmission scheme according to the wireless channel quality between the cooperative relay and the source node, thereby effectively resisting against the wireless fading in the multi-user network environment.

Description

A kind of distributed relay system of selection based on cross-layer information exchange

Technical field

The present invention relates to new generation of wireless network (Adhoc, WSN and MESH) in opportunistic cooperation communicate by letter, especially a kind of distributed relay system of selection based on cross-layer information exchange (cross-layer information interaction) belongs to the technical field that wireless network signal is handled.

Background technology

Make a general survey of the whole development course of cordless communication network, promptly from analog to digital, mobile from being fixed to, from centralized to distributed, the multipath fading characteristic that wireless channel has all is to hinder that channel capacity increases and the one of the main reasons of service quality improvement all the time.MIMO technology based on space diversity thought has remarkable advantages aspect the anti-channel multi-path decline, and can under the prerequisite that does not increase power and frequency spectrum, increase substantially channel capacity, the popular protocol of being communicated by letter by new generation of wireless is adopted gradually, but still existing problems.Specifically, existing many antennas mostly are arranged on the base station end, yet portable terminal is difficult to settle many antennas usually owing to the harsh requirement to volume, quality and power consumption.For this reason, people such as Sendonaris have proposed the conceptual model of collaboration communication, its basic thought is the formal construction " virtual multi-antenna array " by shared antenna each other and other Internet resources between a plurality of users, and in conjunction with the cooperation of distributed treatment generation definitely, thereby can obtain further performance gain, improve network capacity.

Collaboration communication is as a kind of emerging radio network technique, its current most of work all are the concrete cooperation schemes of research, as: the cooperation scheme that Barbarossa proposes, and the coding cooperative (Coded Cooperation) of Hunter proposition based on distributed space time packet (Distributed Space-Time Block Code).About " who and who cooperation ", promptly the selection problem of cooperating relay fails effectively to be solved so far, and this is to concern one of key issue that can the collaboration communication technology practicability.In addition, because the time-varying characteristics of wireless communications environment, whom selects cooperate with source node belong to probability event, in other words, all nodes in the network all have an opportunity to be chosen as best cooperating relay, and its key depends on current state information of channel between network node and the source node (Channel State Information).Based on this 2 point, the present invention proposes a kind of distributed relay selection scheme, and be applied to the technology realization of opportunistic cooperation communication.

Summary of the invention

The purpose of this invention is to provide a kind of distributed relay system of selection, from all candidate relay, select best cooperating relay, in order to realize opportunistic cooperation communication by distributed earth based on cross-layer information exchange.This just requires data source nodes can know in real time which node is the optimal candidate relaying in the current network, and can only utilize local information (local information) to satisfy the requirement of distributed realization in whole relay selection process.In addition, after knowing best cooperating relay, how to realize very effectively that the cooperation transmission of source node and best relay also will be the problem that the present invention need consider to obtain big as far as possible performance gain.

A kind of distributed relay system of selection of the present invention based on cross-layer information exchange, at first according to the optimal selection criterion of cooperating relay in the dynamic network environment, obtain the distributed selection agreement of best cooperating relay, then according to the quality of wireless channel between cooperating relay and source node, provide the adaptive cooperation transmission plan, mainly comprise two parts, the optimal selection criterion of cooperating relay in the dynamic network environment has at first been proposed, and provided the distributed selection agreement of best cooperating relay, secondly according to the quality of wireless channel between cooperating relay and source node, a kind of adaptive cooperation transmission plan has further been proposed, with the wireless fading channel in effective opposing multiple-user network environment, the job step of its entire method is as follows:

(1) distributed selection algorithm of best cooperating relay

Distributed collaborative relay selection algorithm mainly comprises timer setting and relay selection design of protocol two parts:

1) timer setting

According to best cooperating relay selection criterion, can adopt channel condition information to weigh parameter based on amplifying the cooperating relay that retransmits and retransmit, promptly as its performance based on decoding

${\mathrm{BalaPara}}_{\mathrm{AF}}\left(i\right)=\frac{{\left|{\mathrm{\α}}_{p_{i}d}(k+1)\right|}^2{\left|{\mathrm{\α}}_{{\mathrm{sp}}_i}\left(k\right)\right|}^2}{{\left|{\mathrm{\α}}_{{\mathrm{sp}}_i}\left(k\right)\right|}^2+{\left|{\mathrm{\α}}_{p_{i}d}(k+1)\right|}^2};$

${\mathrm{BalaPara}}_{\mathrm{DF}}\left(i\right)={\left|{\mathrm{\α}}_{p_{i}d}(k+1)\right|}^2;$

In order to realize that distributed earth selects best cooperating relay, respectively the relaying timer initial value based on AF and DF strategy is done as giving a definition here

$\left\{\begin{array}{c}{T}_{\mathrm{AF}}\left(i\right)=\frac{{\mathrm{\λ}}_{\mathrm{AF}}}{{\mathrm{BalaPara}}_{\mathrm{AF}}\left(i\right)}\\ T_{\mathrm{DF}}\left(i\right)=\frac{{\mathrm{\λ}}_{\mathrm{DF}}}{\log {\mathrm{BalaPara}}_{\mathrm{DF}}\left(i\right)}\end{array}\right.;$

In the formula, λ _AFAnd λ _DFAll represent the normalization time constant, unit is generally millisecond or microsecond.Obviously, the T that defines in the formula _AF(i) and T _DF(i) all be greater than zero positive number, so can be used as the timer initial value all the time.Simultaneously, corresponding to the timer initial value T of best cooperating relay _AF(best) and T _DF(best) all be minimum in all candidate relay, in other words, the timer of best cooperating relay will make zero at first.Therefore, the initial value of best relay timer is

T _AF(best)＝min{T _AF(i)}，T _DF(best)＝min{T _DF(i)}；

2) distributed collaborative relay selection agreement

According to timer method to set up set forth above, the specific implementation process that we provide distributed collaborative relay selection agreement is as follows:

At first, source node is intercepted channel status.If channel is busy, source node then begins to wait for, is in the free time until channel.If wireless network adopts to amplify and retransmits as trunk protocol, source node broadcasting RTS frame; If adopt decoding to retransmit, source node is then broadcasted the V-RTS frame.In case receive RTS or V-RTS bag, destination node will be broadcasted CTS (Clear to Send) frame.

Case I (adopt amplify retransmit as trunk protocol): all candidate relay will be carried out channel estimating according to the RTS and the CTS that successively receive from source node and destination node, to obtain source node to relaying be relayed to channel condition information between the destination node.Estimating to obtain source node to relaying and after being relayed to channel condition information between the destination node, via node is according to the relay selection criterion, according to following formula calculating timer initial value separately,

$T_{\mathrm{AF}}\left(i\right)=\frac{{\mathrm{\λ}}_{\mathrm{AF}}}{{\left|{\mathrm{\α}}_{{\mathrm{sp}}_i}\left(k\right)\right|}^2}+\frac{{\mathrm{\λ}}_{\mathrm{AF}}}{{\left|{\mathrm{\α}}_{p_{i}d}(k+1)\right|}^2};$

Wherein, λ _AFExpression normalization time constant, unit is generally millisecond or microsecond.

Case II (adopting decoding to retransmit as trunk protocol): all candidate relay are wrapped the channel condition information of estimating to be relayed between destination node according to the CTS that receives, and solve pilot frequency sequence to carry out CRC check from the V-RTS bag.If the CRC check success then is labeled as this candidate relay " better " relaying (preferable candidate), corresponding timer initial value is set to

$T_{\mathrm{DF}}\left(i\right)=\frac{{\mathrm{\λ}}_{\mathrm{DF}}}{{\left|{\mathrm{\α}}_{\mathrm{id}}\left(k\right)\right|}^2};$

Otherwise the timer initial value is arranged to infinity, generally only need be set to bigger number in the reality certainly and get final product.Wherein, λ _DFExpression normalization time constant, unit is generally millisecond or microsecond.Simultaneously, corresponding to the timer initial value T of best cooperating relay _AF(best) and T _DF(best) all be minimum in all candidate relay, in other words, the timer of best cooperating relay will make zero at first.Therefore, the timer of best cooperating relay will take the lead in reducing to zero, afterwards with broadcast transmission HTS.

All candidate relay with timer zero clearing separately, and begin to keep out of the way in order to avoid cause conflict after receiving the HTS bag.If source node is received the HTS controlling packet, source node will solve the MAC Address territory in the HTS bag, and beginning is to best cooperating relay transfer data packets.If source node is not received the HTS bag yet in a HTS time out period, then adopt the pattern that direct transfers, promptly directly send packet to destination node.

Destination node is received after the packet, will send an ACK and reply.If source node can not receive the ACK of destination node and replys always, think behind a time out period that then this sends failure, and start exponential backoff algorithm.

(2) adaptive cooperation transmission plan

According to the quality of wireless channel from the source node to the cooperating relay, we propose a kind of new adaptive cooperation transmission plan, as shown in Figure 2.At first, source node successively through constellation modulation and power division, obtains launching symbol s with bit stream b to be sent ₁, and it is broadcast to cooperating relay and destination node with power Es/2.Then, cooperating relay will be carried out coherent reception to the broadcast singal of source node, according to its received signal

Come the detection signal-to-noise ratio value, judge with this whether source node produces interruption to the wireless channel between cooperating relay.If received signal to noise ratio is greater than interrupting judging threshold (meaning that source node does not interrupt to the wireless channel of cooperating relay), cooperating relay is with its received signal

After carrying out the relaying amplification, Es/2 sends to destination node with power; Otherwise remaining Es/2 power will be transmitted to destination node by source node oneself.At last, destination node will be carried out high specific to the two paths of signals of receiving and be merged, and finally obtain the estimated sequence of bit stream b by the maximum likelihood decision device

Whether obviously, interrupt to the wireless channel between cooperating relay according to source node, the adaptive cooperation scheme that is proposed comprises two kinds of transmission policys that may adopt.

Advantage of the present invention and beneficial effect:

1. propose the selection criterion of two kinds of best cooperating relay based on amplifying re-transmission reconciliation code weight biography, and provided the distributed selection agreement of cooperating relay, thereby realized the optimal selection of cooperating relay under the multiple-user network environment.Error performance at the cooperating relay selection criterion has carried out system emulation, and the result shows that the cooperating relay selection criterion that is proposed obviously is better than traditional relay selection criterion, and system's average error bit rate significantly descends.

2. according to the quality of wireless channel of source node, proposed a kind of adaptive cooperation transmission plan, can effectively resist the wireless fading channel in the multiple-user network environment to cooperating relay.The numerical simulation experiment shows that the adaptive cooperation transmission plan that we propose has obtained further performance gain, and bit error rate significantly descends.

Description of drawings:

Fig. 1 is the distributed selection course of best cooperating relay;

Fig. 2 is the realization block diagram of adaptive cooperation transmission plan;

Fig. 3 retransmits following impact of performance figure that puies forward the relay selection criterion for amplification;

Fig. 4 retransmits following impact of performance figure that puies forward the relay selection criterion for decoding;

Fig. 5 is the characteristic curve of error code of adaptive cooperation transmission plan.

Embodiment

The distributed relay system of selection that the present invention is based on cross-layer information exchange is mainly used in multi-user's collaboration communication of realizing in the wireless network, have advantages such as implementation complexity is low, distributed treatment, be fit to very much novel wireless communication network of future generation, as wireless sensor network, Ad hoc network and MESH network etc.Specific embodiments is as follows:

As Fig. 1, distributed collaborative relay selection algorithm need additionally increase the HTS controlling packet on the basis of conventional I EEE802.11MAC, comprises the MAC Address territory in the packet format definition of HTS.The effect of HTS mainly contains two aspects: the one, be convenient to the MAC Address that source node obtains best cooperating relay; The 2nd, obtain to other relayings statement best relay, other relaying receives behind the HTS bag will be with the timer zero clearing of oneself, and begins to keep out of the way.Implementation procedure mainly comprises three steps: at first, all candidate relay nodes carry out channel estimating by RTS/CTS, secondly, candidate relay is estimating to obtain source node calculating timer initial value and start timer to relaying and after being relayed to the channel condition information of destination, the timer of final best relay will take the lead in making zero, and broadcasting HTS controlling packet; At last, source node demodulation HTS packet header begins to send packet afterwards to obtain the MAC Address of best relay.Detailed process is seen Fig. 2.

1) at first, source node begins to intercept channel status, if channel is in idle condition at a DIFS in the time period, and source node finished backoff procedure, then broadcasts a RTS bag.If channel busy, source node then must be waited for until DIFS cycle of channel idle, and then send RTS.Meanwhile, destination will send the CTS bag after receiving the RTS bag.

2) all candidate relay will be carried out channel estimating according to the RTS and the CTS that successively receive from source node and destination node, with the acquisition source to relaying be relayed to channel condition information between the destination node.Estimating to obtain source node to relaying and after being relayed to channel condition information between the destination node, via node will begin to calculate timer initial value separately, and the startup timer.Obviously, the timer of best cooperating relay will take the lead in reducing to zero, afterwards with broadcast transmission HTS.

3) all candidate relay with timer zero clearing separately, and begin to keep out of the way in order to avoid cause conflict after receiving the HTS bag.If source node is received the HTS controlling packet, with the MAC Address territory that solves in the HTS bag, beginning is to best cooperating relay transfer data packets.If source node is not received the HTS bag yet in a HTS time out period, then adopt the pattern that direct transfers, promptly directly send packet to destination node.

4) destination node is received after the packet, will send an ACK and reply.If source node can not receive the ACK of destination and replys always, think behind a time out period that then this sends failure, and start exponential backoff algorithm.

To the cooperating relay selection algorithm that the present invention proposes, we have carried out Matlab emulation, and the 8PSK modulation is adopted in system emulation, and all wireless channels all adopt the Jakes model to carry out modeling, and normalization Doppler frequency shift fdTs=0.0113.The scale of wireless network is set to five network nodes, comprising a source node, and a purpose terminal and three candidate relay.In addition, need carry out energy normalized when carrying out signal forwarding based on the cooperating relay of amplifying re-transmission policy and handle, female sign indicating number of RCPC coding is that a kind of speed is 1/3 simultaneously, and generator polynomial is G (D)=[11+D 1+D+D ²] convolution code, receiving terminal adopts the viterbi decoder based on hard decision.

Fig. 3 compares with the error performance that Fig. 4 has provided cooperative diversity system under the different relay selection criterions respectively, Fig. 3 provides is based on to amplify and retransmits the decoding that is based on of adopting system's error performance of relay selection, minimum criteria and best cooperating relay selection criterion at random, Fig. 4 then to provide down respectively and retransmit the system's error performance that adopts minimum criteria, harmonic average criterion and best cooperating relay selection criterion down respectively.Find out easily that from figure the cooperating relay criterion that this paper proposes obviously is better than other criterion, has improved systematic function greatly, this has also illustrated the validity and the optimality of the best cooperating relay selection criterion that this paper proposed.

When Fig. 5 has provided message transmission rate R=2bit/s/Hz the BER performance of adaptive cooperation transmission plan and coding cooperative transmission plan relatively, the error code curve among the figure correspond respectively to (η, μ)=(3,-3), (η, μ)=(3,3) and (η, μ)=(10,10).From Fig. 5, find out easily, when (η, μ)=(3 ,-3) and (η, in the time of μ)=(3,3), during respectively less than 20dB and 10dB, corresponding error performance is inferior to non-cooperation transmission to coding cooperative in the signal to noise ratio of source node between destination node.Yet the adaptive cooperation transmission plan that we propose all is better than non-cooperation transmission in whole signal to noise ratio zone, this also side light the adaptive cooperation transmission be better than the coding cooperative transmission.In addition, compare coding cooperative, adaptive cooperation can obtain the more property gain, further illustrates the superiority of adaptive cooperation transmission plan.What deserves to be mentioned is that compare with the coding cooperative scheme, system's implementation complexity of adaptive cooperation transmission plan is lower, this mainly is because the coding cooperative transmission plan has used the higher Viterbi decoder of complexity.

Claims (1)

1. distributed relay system of selection based on cross-layer information exchange, it is characterized in that at first optimal selection criterion according to cooperating relay in the dynamic network environment, obtain the distributed selection agreement of best cooperating relay, then according to the quality of wireless channel between cooperating relay and source node, provide the adaptive cooperation transmission plan, comprise

(1) distributed selection algorithm of best cooperating relay contains timer setting and relay selection design of protocol two parts:

1) timer setting

According to best cooperating relay selection criterion, adopt channel condition information to weigh parameter based on amplifying the cooperating relay that retransmits and retransmit, promptly as its performance based on decoding

$\mathrm{BalaPar}{a}_{\mathrm{AF}}\left(i\right)=\frac{{\left|{\mathrm{\α}}_{p_{i}d}(k+1)\right|}^2{\left|{\mathrm{\α}}_{{\mathrm{sp}}_i}\left(k\right)\right|}^2}{{\left|{\mathrm{\α}}_{{\mathrm{sp}}_i}\left(k\right)\right|}^2+{\left|{\mathrm{\α}}_{p_{i}d}(k+1)\right|}^2};$

$\mathrm{BalaP}{\mathrm{ara}}_{\mathrm{DF}}\left(i\right)={\left|{\mathrm{\α}}_{p_{i}d}(k+1)\right|}^2;$

In order to realize that distributed earth selects best cooperating relay, respectively the relaying timer initial value based on AF and DF strategy is done as giving a definition

$\left\{\begin{array}{c}{T}_{\mathrm{AF}}\left(i\right)=\frac{{\mathrm{\λ}}_{\mathrm{AF}}}{\mathrm{BalaPar}{a}_{\mathrm{AF}}\left(i\right)}\\ T_{\mathrm{DF}}\left(i\right)=\frac{{\mathrm{\λ}}_{\mathrm{DF}}}{\log {\mathrm{BalaPara}}_{\mathrm{DF}}\left(i\right)}\end{array}\right.;$

In the formula, λ _AFAnd λ _DFAll represent the normalization time constant, be used as the timer initial value; Timer initial value T corresponding to best cooperating relay _AF(best) and T _DF(best) all be minimum in all candidate relay, the timer of best cooperating relay will make zero at first, and therefore, the initial value of best relay timer is

T _AF(best)＝min{T _AF(i)}，T _DF(best)＝min{T _DF(i)}；

2) distributed collaborative relay selection agreement

According to timer setting set forth above, the specific implementation process that provides distributed collaborative relay selection agreement is as follows:

At first, source node is intercepted channel status, if channel is busy, source node then begins to wait for, is in the free time until channel; If wireless network adopts to amplify and retransmits as trunk protocol, source node broadcasting RTS frame; If adopt decoding to retransmit, source node is then broadcasted the V-RTS frame, in case receive RTS or V-RTS bag, destination node will be broadcasted the CTS frame;

Adopt to amplify retransmit as trunk protocol: all candidate relay will be carried out channel estimating according to the RTS and the CTS that successively receive from source node and destination node, to obtain source node to relaying be relayed to channel condition information between the destination node, estimating to obtain source node to relaying and after being relayed to channel condition information between the destination node, via node is according to the relay selection criterion, according to following formula calculating timer initial value separately

$T_{\mathrm{AF}}\left(i\right)=\frac{{\mathrm{\λ}}_{\mathrm{AF}}}{{\left|{\mathrm{\α}}_{{\mathrm{sp}}_i}\left(k\right)\right|}^2}+\frac{{\mathrm{\λ}}_{\mathrm{AF}}}{{\left|{\mathrm{\α}}_{p_{i}d}(k+1)\right|}^2};$

Wherein, λ _AFExpression normalization time constant;

Adopt decoding to retransmit as trunk protocol, all candidate relay are wrapped the channel condition information of estimating to be relayed between destination node according to the CTS that receives, and from the V-RTS bag, solve pilot frequency sequence to carry out CRC check, if CRC check success, then this candidate relay is labeled as " better " relaying, corresponding timer initial value is set to

$T_{\mathrm{DF}}\left(i\right)=\frac{{\mathrm{\λ}}_{\mathrm{DF}}}{{\left|{\mathrm{\α}}_{\mathrm{id}}\left(k\right)\right|}^2};$

Otherwise the timer initial value is arranged to infinity, wherein, and λ _DFExpression normalization time constant is corresponding to the timer initial value T of best cooperating relay _AF(best) and T _DF(best) all be minimum in all candidate relay, the timer of best cooperating relay will make zero at first, and therefore, the timer of best cooperating relay will take the lead in reducing to zero, afterwards with broadcast transmission HTS;

All candidate relay with timer zero clearing separately, and begin to keep out of the way in order to avoid cause conflict after receiving the HTS bag, if source node is received the HTS controlling packet, source node will solve the MAC Address territory in the HTS bag, and beginning is to best cooperating relay transfer data packets; If source node is not received the HTS bag yet in a HTS time out period, then adopt the pattern that direct transfers, promptly directly send packet to destination node;

Destination node is received after the packet, will send an ACK and reply, and replys if source node can not receive the ACK of destination node always, thinks behind a time out period that then this sends failure, and starts exponential backoff algorithm;

(2) adaptive cooperation transmission plan

According to the quality of wireless channel from the source node to the cooperating relay, at first, source node successively through constellation modulation and power division, obtains launching symbol s with bit stream b to be sent ₁, and it is broadcast to cooperating relay and destination node with power Es/2, then, cooperating relay will be carried out coherent reception to the broadcast singal of source node, according to its received signal

Come the detection signal-to-noise ratio value, judge with this whether source node produces interruption to the wireless channel between cooperating relay, if received signal to noise ratio is greater than interrupting judging threshold, promptly source node does not interrupt to the wireless channel of cooperating relay, and cooperating relay is with its received signal

After carrying out the relaying amplification, Es/2 sends to destination node with power; Otherwise remaining Es/2 power will be transmitted to destination node by source node oneself; At last, destination node will be carried out high specific to the two paths of signals of receiving and be merged, and finally obtain the estimated sequence of bit stream b by the maximum likelihood decision device

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