Research On Cross-layer Power Allocation Schemes For Two-way Relaying System

Two-way relay systems,one of the cooperative relay technologies,have received significant attention because it can considerably improve the spectral efficiency in wireless communication networks.But most existing works has focused on resource optimization of the physical layer,and the cross-layer power allocation for statistical QoS guarantees only considers the one-way relay.The benefits of two-way relaying on datalink layer and upper layer are much less investigated,and delay quality of service requirements need to be achieved through the cross-layer optimization among different layers.To deal with these problems,this thesis uses the QoS(Quality of Service)index which can exchange information between the datalink layer and the physical layer to characterize the statistical delay constraint,we consider how to optimize the allocation of power to maximize the performance of two-way relay systems while guaranteeing the individual statistical delay-QoS requirement for each user in the datalink layer.The thesis firstly summarizes the basic model of two-way relay communication system and the basic concept of physical layer network coding.The two most widely used types of relay transfer protocols are Amplify-and-Forward and Decode-and-Forward.Based on the theory of effective capacity,this paper establishes a model of cross layer relaying system based on delay QoS guarantee,which the cross-layer optimization problem is equivalent to a weighted sum effective capacity maximization problem.And it can be proved that the problem is a convex optimization problem,there exists a unique optimal solution.The thesis then studies the optimal cross layer power allocation scheme on statistical QoS guarantees under the AF protocol.Firstly,the achievable rate regions of two-way relay in different phase are obtained respectively.Then,different rates are substituted into the weighted sum effective capacity and maximization problem.The Lagrange multiplier method is used to solve different optimization problems under different scenarios,and the optimal power allocation factor is given.The simulation results show that the proposed optimal power allocation scheme can significantly improve the performance of the system when compared with the equal power allocation scheme and the direct transmission scheme,and the scheme can efficiently provide QoS guarantees.The thesis finally studies the optimal cross layer power allocation scheme on statistical QoS guarantees under the DF protocol.Because of the problem of decoding the information of the user nodes in two-way relay,the optimal channel partition criterion of the MAC phase in two phase protocol is given based on the equal time allocation.And use this criterion to determine the order in which the user nodes are decoded and the maximum rate expression under different partitioned areas.By using the sub-gradient method to update the optimal value and the Lagrangian multiplier method to obtain the partial derivative,the optimal power allocation factor algorithm and the optimal power allocation scheme are obtained respectively.The simulation results show that the two phase protocols have the advantage in the case of low SNR,and the three phase protocol is more advantageous in the case of high SNR.