Dissertation > Industrial Technology > Radio electronics, telecommunications technology > Wireless communications > Radio relay communications,microwave communications

Research on Wireless Two-Way Relay Networks

Author ChenZhiYong
Tutor WangWenBo
School Beijing University of Posts and Telecommunications
Course Signal and Information Processing
Keywords two-way relay network physical layer network coding coded modulation design capacity analysis resource allocation software defined radio side information
Type PhD thesis
Year 2011
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The invention and development of network coding bring about a revolution in the wireless communications networks. One of the application scenario of wireless network coding is the two-way relay channel. Based on the application of network coding in the relay node, two-way relay network not only can enlarge the cell coverage, but also can improve the spectrum efficiency by taking advange of the side information. As result, the concept of two-way relay network has been obtained great attention in the academic and industry. This dissertation focuses on the two-relay network in wireless communications. Towards this end, the dissertation gives a deep survey and study of the transmission scheme based network coding, the analyzes of capacity, the wireless resource allocation and the realization of two-way relay network based software defined radio. The major work and contributions of this dissertation consist in:1. Research on the Phyiscal layer network coding in the two-way relay networkFirst, according the analysis of the structure of two-way relay network, the disseration points out some problems of existing phyiscal layer network coding, and then proposes a novel transmission scheme based phyiscal layer network coding, termed the decode-and-forward with joint modulaiton (DF-JM). Based on the DF-JM scheme, the end-to-end bit error ratio (e2e BER) has beeb analyzed in the disseration and the labeling design criterion and approach of optimal constellation labeling map in the relay node have been proposed in order to minimize the e2e BER.Secondly, the disseration presents and analyzes joint coded modulation schemes for two-way asymmetric relay channels at the relay node based on the DF-JM scheme. Depending on how the side information is utilized, two relay-to-destination decode-and-forward approaches are investigated. The first one jointly modulates the two source messages in which the side information is applied to the modulator and the dempper, whereas the second one is a joint coded modulation relay scheme in which the side information is directly used in the low-density parity-check (LDPC) encoder and decoder. By formulating the capacity with side information, the disseration establishs an optimal constellation labeling criterion for the joint modulation scheme. The encoding and decoding methods are derived for the second scheme.2. An capacity analysis of two-way relay networkAccording to the a deep survey and study of the analysis for capacity in two-way relay network with one relay node, the disseration considers a two-way relay system where two sources exchange information with the assistance of multiple, non-cooperative, relay nodes. Specificially, the disseration proposes a capacity upper bound for the two-way relay channel and derive the achievable regions for different relay strategies, such as the amplify-and-forward (AF), the decode-and-forward (DF) and the compress-and-forward (CF). Furthermore, the upper bound and the achievable regions for the additive white Gaussian noise channel are presented. For the DF strategy, the achievable regions based on bit-level and symbol-level relay forward schemes are provided.3. On the resource allocation for two-way relay networkConsidering a two-way relay network with one relay node, the disseration first proposes a optimal resource allocation model for the two-way asymmetric relaying channel with unmatched traffics from two sources under a QoS minimum rate constraint. Aiming at maximizing the sum rate, we address the optimization problem (in terms of time and power allocation) for two decode-and-forward (DF) strategies, namely, the decode-and-forward with joint modulation (DF-JM) and the decode-and-forward with network-superposition coding (DF-NSC). Closed-form solutions under different relay settings are presented. The disseration proves that the DF-JM protocol performs better than the DF-NSC in terms of the end-to-end relay rates.Considering a two-way relay network with multi-relay nodes, the disseration gives a deep survey and study of the relay selection scheme in the two-way relay network with multiple relay nodes. Then, two effective relay selection schemes based on the DF scheme have been proposed in this disseration, termed best relay selection based on the maximum of the end-to-end rates with the optimal time slot allocation (BRC) and best relay pair selection based on the maximum of the end-to-end rates with the optimal time slot allocation (BRPC). In order to reduce the complexity of proposed scheme, the disseration also provides two correponding suboptimal relay selection algorithms. Numerical results illustrate that when the transmit power of relay node is large than that of both sources, the BRC outperforms BRPC, whereas the BRPC is the best choice when the transmit power of relay node is lower than that of both sources.4. The realization of two-way relay network based software defined radioIn order to realize the two-way relay network, the disseration builds the platform of the two-way relay network based on a new type of software defined radio (Sora). Based on the platform, some results are provided to illustrate the performance of independent LDPC scheme based on DF-JM in the disseration. Some approachs built the phyical layer in the Sora have been provided in the disseration, and the flow of transmitter and receiver of the platform based the Sora also have been illustrated. Numerical results illustrate that comparing with Gray mapping based DF-JM, the DF-JM scheme based optimal constellation labeling has 28.73% gain in terms of throughput. The simulation results also show that when the channel gain is low (SNR<7 dB), the performance of DF-JM scheme based Gray mapping is worse than that of the 4 time slot two-way relay network.

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