Research On Cooperative Transmission Mechanism And Application Of Multi-relay Spatial Information Networks

Currently,spatial information network has become the research hot spot due to advantages of coverage area,networking speed and so on.But there are still some shortcomings,such as high bit error ration(BER),limited bandwidth and power,and so on.Therefore,cooperative communication and physical-layer network coding(PNC)are studied in this dissertation to alleviate the above problems.First,the background,significance and current status of spatial information networks are briefly introduced.Second,basic wireless cooperative communication model with common relaying strategies are investigated briefly,and the decision threshold-aided fast Z-forward(DT-FZF)scheme is also introduced.Then,the concept of network coding is introduced,and an efficient PNC with a selective soft-message-forward(SSMF)cooperation is presented.Finally,two adaptive power allocation schemes are proposed for the PNC with the SSMF cooperation.The main content and contributions are concluded and listed as follows:1.To solve the problems of high BER and poor reliability in spatial information network,a DT-FZF sheme is firstly proposed based on the existing Z-forward scheme.When the absolute value of the log-likelihood ratio(LLR)of a source-relay reception is less than the decision threshold,the relay remains silient.Otherwise,it directly sends the truncated LLR metrics to the destination.In addition,the DT-FZF scheme incorporates the amplify-and-forward(AF),decode-and-forward(DF),piecewise-and-forward(PF)and ZF schemes,all of which can be the special case of the proposed scheme.Then,the approximately expressions of the decision threshold and outage probability are derived in the DT-FZF scheme.Finally,simulation results indicated that the DT-FZF scheme outperforms the ZF scheme by approximately 0.6 d B in a three-relay system at BER of 10^-3.In addition,with the increase in relay number,the proposed scheme obtains further better BER performance.2.To overcome the limitation of spectrum resources in satellite links of spatial information networks,a joint PNC and threshold decision decoding algorithm with the SSMF scheme are proposed and derived from the existing PNC scheme.The signals least affected by noises after zero forcing detection are mapped into LLR metrics for most reservation of the soft messages.The complexity of the proposed SSMF scheme is reduced from O(M⁴+M)of current soft-message-forward(SMF)schemes to O(M³+M²+1)(where M represents the number of antennas at relays).Simulation results indicate that the SSMF-based PNC surpasses the existing PNC.At BER of 10^-3,the SSMF-based PNC scheme outperforms the selective decode-and-forward(SDF),SMF and DF schemes by approximately 0.6 d B,1.0 d B and 1.7 d B,respectively.3.To solve the problem of limited power caused by the size of satellite nodes in spatial information networks,two adaptive power allocation(APA)schemes with SSMF scheme are proposed for the multiple access(MA)and broadcast(BC)stages,respectively.In the MA stage,it aims to maximize the Euclidean distance of network coding symbols received by relay nodes.In the BC stage,the relay node takes the maximization of the minimum mutual information of two source nodes as objective function.Then it uses the narrow range method(NRM)to select the optimal antenna set and equally allocates power to them.To further reduce the systematic complexity,an antenna set pre-selection is proposed.It minimizes the antenna number in the initial antenna set of the NRM based on the deletion standard which does not reduce the mutual information in the BC stage.Therotical analyses and simulation results indicate that our APA schemes surpass the existing equal power allocation(EPA)scheme with a binary phase-shift keying modulation.Compared with the current EPA scheme,the proposed APA schemes for the BC,MA and global stages obtain about1 d B,2 d B and 3.5 d B performance gains at BER of 10^-3with two antennas in a relay node,respectively.By optimization and improvement of the relaying strategies and physical-layer network coding,this thesis contributes to solve existing problems of multi-relay spatial information networks,such as high BER,the limitation of spectrum and power,and so on.Furthermore,those innovations all can help improve the performance of the spatial information network.