双向AF中继系统中继选择及功率分配策略

为了提高双向中继系统的系统可达总速率,提出一种Two-way AF中继系统的最大化瞬时信噪比乘积（MISP）的中继选择策略,该策略联合考虑了两条链路的链路质量,实现了最优中继选择。在此基础上,运用信噪比平衡技术进行瞬时功率分配（SNR-Balancing-IPA）,推导出了最优功率分配方案的表达式。理论分析和仿真结果都表明,建议的最大瞬时信噪比乘积中继选择及SNR-Balancing-IPA的策略有效提高了系统的可达总速率,降低了系统的中断概率,改善了系统的性能。     

Two way中继系统中的双向中继选择及功率分配策略*

通过中继选择和功率分配,可以达到提高two-way中继系统总速率的目的。综合考虑中继节点处的接收信噪比和中继节点到目的节点间的信道增益,提出了two-way AF中继系统中的双向中继选择策略(BRS);同时,在总功率受限的条件下,建立了two-way AF中继系统中的优化功率分配模型,通过对模型进行数学分析求解,提出了一种自适应的最优功率分配策略(OPA)。仿真结果证明两种策略均能提高系统总速率。     

Optimal power allocation for cognitive relay networks: amplify-and-forward versus selection relay

We consider a cognitive relay network which is defined by a source,a destination,and cognitive relay nodes and primary user nodes.In this network,a source is assisted by cognitive relay nodes which allow coexisting with primary user nodes by imposing severe constraints on the transmission power so that they operate below the noise floor of primary user nodes.In this paper,we mainly study the power allocation strategies of this system to minimize the outage probability subject to total and individual power c...     

在认知中继网络中基于放大转发与最佳中继的最优功率分配算法

由于受认知无线电与中继通信技术的启发,提出了一种认知中继网络模型.该模型由源节点、目的节点、认知中继节点及主用户(primary user,PU)构成.认知中继节点以与PU共存的方式为源节点辅助传输信息到目的节点,只要保证其对PU通信造成的干扰在PU干扰门限值以下.假设源节点、目的节点和认知中继节点之间的瞬时信道边信息(channel side information,CSI)和认知中继节点到主用户之间的均值信道增益已知的前提下,研究该模型中的认知中继节点分别采用放大转发(amplify-and-forward,AF)和基于AF的中继选择(selection AF,S-AF)下的功率分配策略,该策略以最小化系统中断概率为目标,同时也满足认知中继节点的发射功率约束(包括总发射功率和个体发射功率约束)和对主用户的干扰功率约束.最后,通过数值仿真来验证推导出的功率分配策略.仿真结果表明:本文提出的最优功率分配策略,无论在AF,还是S-AF下,均能明显的改善系统的中断性能和平均吞吐量;同时在S-AF下最优分配策略可以得到更高的平均吞吐量,因此中断概率更小.     

Two-path中继系统中基于最小化中断概率的功率分配方法

为了降低two-path中继系统的通信中断概率,针对DF协议中继,推导了two-path中继系统在存在中继间干扰情况下的中断概率闭式解,并在总功率受限的情况下,提出了一种最小化中断概率的最优功率分配算法。仿真验证结果表明该算法能够有效地降低系统的中断概率,提高系统的性能。     

门限决策的AF中继选择协作网络性能分析

中继选择能有效地克服信道衰弱影响,提高分集效果,但全天候协作降低了系统的带宽效率。研究了Rayleigh信道条件下一种新的基于门限决策的多中继选择系统并分析了系统性能,推导了M-PSK信号多中继选择系统的SER闭式表达式和系统带宽效率表达式。实验结果显示,在低信噪比和较少候选中继场景,提高协作门限,可提高系统带宽利用率;高信噪比和较多候选中继场景,适度降低协作门限,可有效提高系统平均SER性能。     

面向安全的轮流中继选择方案

针对多中继轮流中继系统被窃听的问题,提出面向安全的轮流中继选择方案。首先提出了遍历的最优中继选择方案,并推导得到了保密速率的理论值;之后为降低复杂度,分别从降低计算复杂度和信道估计开销的角度设计了两种两阶段的次优中继选择方案,先缩小中继选择范围再进行搜索。仿真结果表明K-最大主信道中继选择方案能够以较低的复杂度实现最优保密速率。     

ICRN功率分配与中继选择联合优化

针对工业认知无线电网络中出现的无线干扰和冲突严重,特别是工业现场的金属环境和移动特性造成多径与阴影衰落,从而使得传输可靠性难以保证的问题,引入感知信道概率及信道可用度概念,提出一种联合优化中继选择与功率分配的算法。该算法给出3种认知中继选择方案,分别是信道增益最大准则、最近准则及调和平均准则,并在源节点和所选中继节点之间进行最优功率分配,以最小化网络中断概率。仿真结果表明,与平均功率分配算法相比,所提算法能更好地降低系统中断概率,提高传输可靠性。     

Superimposed training for channel estimation of OFDM modulated amplify-and-forward relay networks

This paper is concerned with the problem of channel estimation for amplify-and-forward （AF） cooperative relay networks with orthogonal frequency division multiplexing （OFDM） modulation. The algorithm is based on both the least square （LS） and minimum mean square error （MMSE） technique with a superimposed training strategy. Specifically, both the source and relay superimpose their own training signal onto data stream prior to transmission so as to estimate the separate channel state information of the source to relay link and the relay to destination link. We also present the performance analysis and derive the approximated closed-form expressions for the MSE of separate channel estimation of source to relay link and the relay to destination link, respectively, from which we compute the optimal training signal as well as the relay power-amplification factor. To further improve the performance of channel estimation, we adopt a weighted average process to enhance the estimation performance over multiple OFDM blocks, from which we compute the optimal tracking factor. Simulation results are provided to corroborate the proposed scheme.     

Joint optimal sensing time and power allocation for multi-channel cognitive radio networks considering sensing-channel selection

In this paper,we consider a multi-channel cognitive radio network(CRN)where each secondary user(SU)can only choose to sense a subset of channels.We formulate a joint optimization problem of sensingchannel selection,sensing time and power allocation under the constraints of average transmit power budget and average interference power budget,which maximizes the CRN’s total throughput.We propose a greedy algorithm to solve the joint optimization problem,which has much less computational complexity.Moreover,it is shown that the search space of the greedy algorithm can be further pruned.Finally,numerical results demonstrate that the greedy algorithm has comparable performance to the exhaustive search algorithm.     

A simple amplify-and-forward opportunistic relaying based on outdated channel state information

Opportunistic relay selection(ORS)is a promising approach for cooperative communications owing to its low complexity by activating only the best relay.However,in mobile scenarios,the channel state information(CSI)estimated in relay selection may be different from the actual CSI employed in data transmission due to relatively fast varying channels,i.e.,CSI is outdated,which may lead to incorrect relay selection,and hence system performance deteriorates.To address the problem,this paper designs a relay selection strategy with instaneous and statistical CSIs in amplify-and-forward(AF)cooperative networks whose instantaneous CSIs of two hops employed in relay selection are both outdated.Based on high signal-to-noise ratio(SNR)analysis,we propose a distinctive relay selection strategy which can be described as selecting the relay with the asymptotic optimum average symbol error probability(SEP)and outage probability at high SNR.The corresponding asymptotic outage probability and SEP performance analysis are also provided.Finally,simulation results not only validate our theoretical analysis,but also show that in asymmetrical outdated CSI scenarios,the proposed strategy achieves better performance than existing relay selection strategies at medium and high SNR values.     

基于多用户QoS的中继系统功率分配算法

研究了非再生中继满足不同用户速率需求的公平性功率分配问题。提出了基于用户期望速率比例公平性功率分配算法,由于源端无法预先接收用户期望速率信息,该算法在实际操作中存在一定的不可操作性。进一步提出了预均分公平性功率分配算法,可弥补基于用户期望速率比例公平性功率分配算法的不足。仿真结果表明,两种算法都实现了保证用户服务质量(QoS)的最优功率分配以最小化用户速率与期望速率差值,节约网络资源的优化目标。     

Low-complexity distributed differential spacetime coding scheme for amplify-and-forward cooperative networks

By introducing a space-time coding scheme based on amicable orthogonality, we develop a distributed differential space-time coding scheme with the amplify-and-forward (AF) method for wireless cooperative networks. The scheme requires no knowledge of the channel state information at both transmitters and receivers, and effectively decreases the realization complexity due to no channel estimation. Moreover, it has lower decoding complexity and higher coding advantage than the existing scheme, thus avoiding the shortcoming of exponential decoding complexity of some existing schemes. According tothe pairwise error probability (PEP) analysis of the system, the power allocations of source and relay terminals are jointly optimized, and as a result, the PEP is minimized, which will provide a helpful guideline for system design. Numerical calculation and simulation results show that the developed scheme is superior to the existing scheme. Moreover, the scheme with optimal power allocation yields obvious performance improvement over that with equal power allocation. Supported partially by the China Postdoctoral Science Foundation (Grant No. 2005038242) and the startup fund of Nanjing University of Aeronautics and Astronautics (Grant No. S0855-041)     

Tensor-based blind signal recovery for multi-carrier amplify-and-forward relay networks

Cooperative communications have great potentials in performance enhancement via deploying relay nodes. However, these kinds of benefits usually come at the cost of more system parameters to be estimated. This fact definitely reduces the efficiency of wireless systems and then it motivates the research on the blind algorithms for cooperative communications that need fewer parameters. In this paper, we investigate the parallel factors （PARAFAC） decomposition-based blind signal recovery algorithm design for two-hop amplify-and-forward （AF） multi-carrier cooperative networks. In particular, the uniqueness of the PARAFAC decomposition used in the proposed algorithm is first investigated in detail, and then the performance of signal recovery is analyzed. Finally, the simulation results assess the performance of our proposed algorithm.     

AF型中继辅助OFDM系统中的功率优化

讨论了AF型中继辅助OFDM通信系统中的功率优化方案,并针对最优的功率优化方案很难得到闭合解的问题,提出了一种迭代的功率优化算法。这种迭代算法将AF型中继辅助OFDM通信系统中,单个子载波上源节点与中继节点间的功率分配问题以及各个子载波之间的功率优化问题分开,首先计算给定某个子载波上发送总功率下源节点与中继节点间的功率分配,然后在此基础上进一步优化子载波间的功率分配,并迭代逼近最优解。实验证明,在给定传输总功率的情况下,与传统的等功率分配相比这种迭代的优化方案可以获得较高的系统性能优势。     

基于MABC的中继系统资源分配策略

针对MABC的中继系统,对资源配置策略的优化问题进行研究,并将功率分配问题和中继选择问题相结合。基于此,提出了一种存在干扰情况MABC模型的多中继系统资源分配策略（IS-MABC-OPOR）。考虑双向中继系统干扰信号对其传输性能的影响,以通信链路信道容量最大化为优化目标,利用拉格朗日方法,对通信链路上的各节点进行了最优功率分配和最佳中继选择,给出了通信链路信道容量最大意义下的资源分配数学表达式。仿真结果表明,该链路的信道容量受中继节点位置以及链路总功率的制约,相比于等功率分配方案（EPA）、随机功率分配方案（RPA）和在所提方案的基础上加大干扰信号的信道增益,IS-MABC-OPOR方案有效提高了系统的信道容量,从而实现资源能够满足更高速率的业务传输需求。     

中继OFDMA系统用户公平性的资源分配算法的研究

在OFDMA解码—转发中继系统中,为了公平地进行资源分配,提出了在两个用户模型下,在保证每个用户最小速率需求的前提下,先按照用户预定速率比进行子载波分配,再根据实际速率比对用户的子载波进行调整的分配算法,最后使整个系统的吞吐量达到最大。提出了三种方案。方案一通过对Lagrange对偶函数问题的求解,根据所得代价函数值的大小对用户的子载波做重新调整。这样不仅考虑到了公平性,也减少了用户的速率损失。方案二、方案三分别从子载波端和用户端出发考虑子载波的分配问题,且从不同的分配角度分析了公平性问题。研究结果表明,三种方案获得的公平性均有所提高。     

无线协作网络中的能量有效性中继选择算法

研究了无线协作网络中的中继选择问题,允许中继具有缓存数据的能力,提出了一种带有buffer的能量有效性中继选择算法,以延长网络生命周期并提高系统吞吐量。该算法综合考虑链路信息,中继的队列状态以及节点的剩余能量信息,通过加权效用公式选择最优接收数据中继与最优发送数据中继。考虑源节点与中继节点间的功率分配,以降低因源节点到中继节点以及中继节点到目的节点间的信道速率不一致所引起的系统丢包率。仿真实验结果表明,该算法有效地延长了网络的生命周期,随着中继个数的增加网络吞吐量有明显的提高,考虑功率分配后,有效降低了系统丢包率。