Low Complexity User Scheduling Schemes In Two-way Relay Systems

Recently,two-way relay network has attracted much attention because it has been suggested to improve the spectral efficiency,and it has been applied in a variety of fields such as ad-hoc networks and cellular.However,the research on user scheduling schemes in two-way relay network is not much.In order to figure out how the user scheduling algorithms benefit the two-way relay sys-tem,some user scheduling schemes are studied in this paper,and the system perfoamance is analyzied in multiple scenes.The main innovations and contributions of the paper are as follows.1)we develop a new scheme called opportunistic signal space alignment which combines beam-forming design with user selection based on singular value decomposition.Opportunistic alignment is realized by taking take ad-vantage of multi-user diversity.Then,its performance is analyzed in terms of user scaling law required to achieve the degrees of freedom of N per channel use when the number of user pairs grow faster than the system signal ratio.Exten-sive simulations are conducted,and the results show that the proposed scheme provides significant improvement in terms of sum rates.2)we consider low-complexity user scheduling schemes for the multi-pair two-way relay channel,where L pairs of single antenna users are selected from K pairs to perform pair-wise information exchange via an Nr-antenna amplify-and-forward relay(Nr ? 2L-1)with analogue network coding.We first pro-pose a simple channel norm(CN)based scheme,which enables low-complexity implementation.Then,we propose a user scheduling by jointly considering the pair-wise channels norms and orthogonality among all the users(CNO-A),which requires global channel state information(CSI)and centralized compu-tation at the relay.It is noted that CNO-A scheme can achieve comparable per-formance as the optimal scheduling with reduced computational complexity.Finally,we propose a two-step selective CNO scheme(CNO-S),which strikes a flexible balance between complexity/CSI overhead and performance.CNO-S significantly reduces CSI overhead and computational complexity at the relay,while achieving comparable performance as the CNO-A scheme.Numerical results and complexity analysis not only show that the proposed schemes are feasible and effective,but also demonstrate their advantages over the existing schemes.3)a source-destination pair nodes communicate with each other via a relay selected from the candidate relays,while the rest of the relays harvest energy in each time slot.The aim of this paper is to design an optimal relay scheduling scheme that maximizes the long term average system throughput subjecting to a minimum required average harvested energy.Through some mathematical operations,the original problem can be translated into a convex optimization problem.In order to reduce the computation complexity,a low-complexity suboptimal with partial optimal scheme is proposed.The proposed optimization algorithm maximizes the average sum-rate of the system while harvests energy from the relays as much as possible.Numerical simulation results corroborate the conjecture and provide insight on the theoretical findings.