This article addresses the design problem of selecting an appropriate relay in amplify-and-forward(AF) cooperative diversity systems.In this regard,this article focuses on relay selection based on partial channel knowledge only across the source and relay links.In particular,the two fundamental questions will be answered,that is,whether to cooperate and whom to cooperate with.Through answering these two questions,an improved relay selection strategy based on partial relay link,which emphasizes that cooperation happens when necessary,is proposed to aim at maximizing the average mutual information.Then a joint optimization,in terms of power allocation and relay selection,is employed to guarantee a robust performance for relay selection based on partial relay link.Optimum power is allocated between the source and the selected relay to maximize the output signal-to-noise(SNR) at the destination.Simulation results turn out that the improved scheme can achieve better performance than previous work and the robust performance can be guaranteed by employing joint optimization.
In wireless multicast,network coding has recently attracted attentions as a substantial improvement to packet retransmission schemes.However,the problem of finding the optimal network code which minimizes the retransmissions is hard to solve or approximate.This paper presents two schemes to reduce the number of retransmissions for reliable multicast efficiently.One is retransmission using network coding based on improved Vandermonde matrix(VRNC),the other is retransmission using network coding based on adaptive improved Vandermonde matrix(AVRNC).Using VRNC scheme the sender selects the packets all receivers have lost and encodes them with improved Vandermonde matrix;when receivers receive enough encoded retransmission packets,all the lost packets can be recovered.With AVRNC scheme,the sender can obtain the recovery information from all the receivers after sending out per retransmission packet,and then the improved Vandermonde matrix can be updated,thus reducing the complexity of encoding and decoding.Our proposed schemes can achieve the theoretical lower bound assuming retransmission packets lossless,and approach the theoretical lower bound considering retransmission packets loss.Simulation results show that the proposed algorithms can efficiently reduce the number of retransmissions,thus improving transmission efficiency.
CAO ZhenTANG Bi-huaLIU Yuan-anXIE GangLIU FangDENG Pan-liang
In this paper,we investigate the power and subcarrier allocation issue in the case of partial side information for downlink orthogonal frequency division multiple access (OFDMA) system.Relaxation method is utilized to characterize the necessary conditions of the optimal solution and the uniqueness of the optimal solution is proved.The game theoretical concept,surplus function is also introduced to analyze the optimal solution.Based on the theoretical analysis,we propose iterative surplus balancing algorithm (ISBA) that can jointly assign the power and subcarriers in multiple rounds,and then the optimality of ISBA is proved.Simulation results are presented to show the characteristics of the theoretical analysis and ISBA.
ZENG Ling-kang LIU Yuan-an XIE Gang CHANG Ling-jun
In this paper,we consider the joint relay selection and power allocation problem for two-way relay systems with multiple relay nodes.Traditionally,relay selection schemes are primarily focused on selecting one relay node to maximize the transmission sum rate or minimize the outage probability.If so,it is possible to cause certain relay nodes overloaded.In addition,the joint relay selection and power allocation problem is a mixed integer program problem and prohibitive in terms of complexity.Therefore,we propose a novel low complexity joint relay selection and power allocation algorithm with proportional fair scheduling to get the load-balancing among potential relays.Simulation results turn out that,compared with round-robin schemes and max sum rate schemes,the proposed algorithm can achieve the tradeoff between system transmission sum rate and load-balancing.
A novel adaptive power loading algorithm with the constraint of target overall bit error rate (BER) for orthogonal frequency division multiplexing (OFDM) systems is proposed in this article. The proposed algorithm aims to minimize the required transmit power with fixed data rate and uniform (nonadaptive) bit allocation,while guaranteeing the target overall BER. The power loading is based on the unequal-BER (UBER) strategy that allows unequal mean BERs on different subcarriers. The closed-form expressions for optimal BER and power distributions are derived in this article. Simulation results indicate the superiority of the proposed algorithm in terms of BER performance and algorithmic complexity.
Two-hop relaying systems suffer spectral efficiency loss due to the half-duplex property of relays. This paper proposes an efficient relaying protocol which can recover the spectral efficiency loss but still work with half-duplex relays. However,there exists inter-relay interference which degrades the performance of the protocol. With this consideration,a power control policy is derived to suppress the interference using game theory,and then an algorithm is given to facilitate distributed implementation. Furthermore,impact of deploying more destination antennas on performance of the relaying protocol is investigated. Simulation results show that,with the power control policy,the proposed relaying protocol can achieve high spectral efficiency.
LI Xing-zheng,LIU Yuan-an,XIE Gang,CHANG Ling-jun,HAN Xiao Key Laboratory of Universal Wireless Communications,Ministry of Education,Beijing University of Posts and Telecommunications,Beijing 100876,China
