Research On Wireless Resource Management For Two-way Relay Networks

Cooperative relaying is a practical technique to combat channel fading, enhance link stability, and extend cell coverage. Owing to these benefits, it is wildly used in wireless communication systems, eg:it has been under the latest broadband wireless communication standard specification:LTE-A to improve the system performance. Traditional one-way relaying has series advantages of cooperative relaying. However, One-way relaying reduces the spectral efficiency since it involves four phases when two users communicate with each other. This spectrum efficiency loss can be reduced with two-way relaying. Applying the network coding in the relay node and exploiting the users’own side information, Two-way relaying can maintain the large cell coverage and save half time resource to improve the system spectrum efficiency. Recently, two-way relaying is a hot topic in academia and industry.This dissertation focuses on the radio resource management in two-way relay networks. The thesis first discusses the transmission principle of the two-way relay networks, capacity region of the system, and other theory issues which reveal the direction of the optimization of radio resource management in two-way relay network, and then analyzed the main scenarios of the two-way relay network in wireless communication system. Through the analysis of existing results and a summary of the optimization problems, we proposed the innovative solutions for the unsolved resource allocation problems which are based on OFDM, MIMO, CR techniques in two-way relay networks. The major work and contributions of this dissertation are as follows:(1) Efficient resource allocation with user rate constraints in OFDM two-way relay networkGreen Radio with high energy efficiency has become a trend of future mobile communication. It is an important radio resource management issue to minimizing the total transmits power while maintaining all users’rate requirements in multi-user AF-OFDM two-way relay network. Through the analysis of optimization goal, this thesis proposed a hierarchical resource allocation scheme:(a) Optimal subcarrier allocation and sum power assignment among N parallel OFDM subcarriers.(b) Power optimization within user-pair and relay in each subcarrier. For the step (a), it is proposed to decompose each user-pair into two sub user-pairs:two-way relaying with same rates and one-way relaying with single rate, and modify the optimization goal to reduce the complexity of the original problem. Foe the step (b), using the convex optimization techniques, closed-form expressions of the power among user-pair and relay node is obtained. Based on these results, the proposed efficient resource allocation scheme can decrease the variable dimensionality of the objective function to reduce the complexity of the optimization problem which can provide a useful exploration for the real-time green radio.(2) Optimal power control for the OFDM two-way relay network with PNC For two-way relay network with physical network coding, it can obtain larger capacity region since the operator applies partial decoding to generate the new uplink PNC codes which can eliminate the multiple access capacity constraint of the sum rate. However, the capacity formula of the system is not-closed expression; the power optimization is still an open question. Through classifying the possible transmission cases of the system, optimizing the power allocation in each case, we obtained a closed-form solution for the resource allocation. This solution is then used to derive the optimal power allocation scheme which reduces the implementation complexity, improves the system capacity. Numerical and simulation results show that the approach achieves almost the optimal sum rate and outperforms the fixed power assignment method with less computational load in various scenarios.(3) Resource allocation in MIMO two-way relay networkFor MIMO two-way relay network, this thesis considers the spatial multiplexing gains of the system, proposes a low-complexity transmit and receive precode design that divide the complex MIMO channel into several parallel SISO subchannels. It can help users more easily to obtain spatial multiplexing gain by using network coding. Moreover, applying matrix calculation and transformation, this chapter proposed an optimal power allocation scheme for MIMO two-way relay network. This method can optimize each subchannel independently and dramatically decrease the complexity of the RRM in MIMO two-way relay network. Based on the above results, this chapter considers a RRM problem for multiuser MIMO two-way relay network with rate proportional fairness constraints. Applying optimal precode design, power control techniques, it is proposed a low-complexity resource allocation scheme that can comprehensively premeditate system capacity and users’fairness.(4) Joint relay selection and power control in CR two-way relay networkIn cognitive radio scenario, cooperative relay technique can expand the available bandwidth resource, and improve the rate performance of the cognitive user. This thesis proposed a joint relay selection and power control scheme in CR two-way relay network with multiple relay nodes. Using convex optimization technology, an optimal power allocation among three nodes is obtained. Furthermore, considering the power fallback issue which is caused by the interference threshold, we proposed a power compensation method for three nodes which consists of three cases. It can not only guarantee the authorized user quality of service, but also effectively maximize the transmission rate of cognitive system. Moreover, according to the characteristic of the cognitive system, we proposed two low-complexity suboptimal relay selection methods. Simulation results show the algorithms’effectiveness. Especially, the performance of low-complexity method can achieve it of the optimal method in high transmit power case.In summary, aimed at extending the cell coverage and improving the spectrum efficiency of the wireless communication system, this dissertation discussed the optimal resource allocation in OFDM two-way relay network with users’rate constraints for green radio, optimized the power control for the two-way relay network with PNC, investigated the optimal precode design for MIMO two-way relay network and analyze the optimal resource assignment when comprehensively considering users’fairness and energy-efficiency, at last, proposed a joint relay selection and power control scheme in CR two-way relay network. Our work has a positive academic value and is meaningful for application.