无线多址信道中的协作模型研究

在无线多址信道环境下,为了充分利用协作分集技术提高系统的传输速率和通信质量,引入了多址接入中继信道（MARC）模型。通过加入一个专门的中继节点,MARC模型中的发送节点类似操作在普通的多址信道下,从而使得现有的系统可平滑过渡到协作系统,实用性强。把MARC模型应用在直序扩频CDMA系统中,在Rayleigh信道下对其误码率进行仿真,结果表明,采用MARC模型的协作网络能获得显著的性能增益。     

一种在宽带无线网络环境下的协作分集方法

协作通信可以使单天线的移动终端共享它们的天线而产生虚拟多发射天线阵列以获得发射分集。提出了一种在频率选择性衰落信道条件下的协作分集方法,信宿不仅利用转接节点转发的信号而且还利用了信源直接传来的信号来进行解码。通过计算机仿真,比较了考虑信源到信宿的直接传输的协作方法和未考虑信源到信宿的直接传输的协作方法的误比特率性能。结果表明,考虑信源到信宿的直接传输可提高系统的协作分集增益。     

一种基于分布式空时码的协作MIMO分集复用折衷新方案

协作MIMO通过多个单天线节点的相互协作构造多发射天线,以此形成一种虚拟MIMO多天线阵列获得空间分集增益。考虑到协作MIMO特点,天线间采用分布式空时编码进行编码协作。文章研究了协作MIMO中基于分布式空时码(DSTC)的分集复用折衷(DMT)新方案,该方案通过推导两种DSTC的中断概率与分集增益表达式,结合两类DSTC的DMT策略,根据改变复用增益阈值自适应获得最佳DMT与中断性能。数值仿真表明,所提的DMT策略可以逼近协作MIMO的DMT上限,协作节点采用该策略的中断性能仅次于上限的中断性能。在多节点构成协作MIMO网络分布式空时编码协作中,提出的DMT新方案可使系统高效地获得协作分集增益与中断性能。     

相关瑞利信道下的分集与复用折衷

多天线可以用来增加通信系统的分集增益或者复用增益，二者之间存在着基本的折衷关系。相关瑞利信道的折衷性能差于i．i．d瑞利衰落信道，并且相关矩阵降秩时，折衷性能进一步下降。本文给出了相关瑞利信道下分集增益和复用增益的最优折衷关系。     

基于任一随机选择转接节点的协作分集方法及其中断概率分析

 转接节点的选择是协作通信中的一个比较重要的问题.在许多实际情况中并不是所有节点都参与转接,本文研究了在所有潜在的转接节点中任选一个节点作为转接节点的协作分集方法,推导了这种协作分集方法中断概率的上界和下界.理论计算和仿真结果表明该协作分集的 中断概率的上界基本不随潜在的转接节点的数目的增加而变化,而下界却随潜在的转接节点的数目的增加而显著降低.     

基于LDDMA的多用户分集性能分析

针对线性离散多址复用（LDDMA）系统,文章研究在线性迫零（Zero-Force）接收机条件下的多用户选择分集与调度算法。对于用户子集选择算法,遍历搜索是最优的,但它所引起的繁重的计算复杂度,很难在实际中应用。基于此考虑,本文提出三种次优的贪婪选择准则：最大信道增益选择,最大信道容量选择与最大最小后验SNR选择。数值仿真结果表明：最大最小后验SNR准则可以提供较好的BER性能。     

无线通信中的协作分集技术

协作分集技术是在多用户环境下,具有单天线的多个终端可以共享彼此的天线,形成一个虚拟的多天线系统,来实现上行链路的发送分集。协作分集技术能够提高系统的吞吐量,减少发送功率,并能降低系统的误码率,因此受到了广泛的关注。     

协作分集在Wimax中的应用研究

采用空间分集技术可以有效的对抗无线信道中的衰落。协作分集是一种新的空间分集技术，其原理是单天线的无线用户通过协作，811227共享他们的天线和资源从而形成一个虚拟的多天线系统。OFDM是Wimax中的关键技术，其将数据调制到各个子载波上发送。将协作分集引入到Wimax系统中，利用OFDM技术，可以有效地抵抗信道频率选择衰落的影响，使系统性能得到显著提高。     

一种选择最大多用户分集MIMO信道调度方法及性能分析

提出了一种选择最大多用户分集MIMO信道调度方法,能在不降低性能的基础上减少反馈负载：每个用户将最大的信干噪比值与设定的门限比较,只有大于门限的值及对应的发射天线序号返回给基站,基站分配独立的信道给最大信干噪比用户。给出了所提方案的系统平均容量和反馈负载量的分析,仿真结果与分析一致。     

一种改进的基于网络路径选择的协同分集方法

天线协同视为用来形成虚拟天线阵列,从而能在慢衰落无线环境中显著提高分集增益的一种新方法.然而,已经提出的解决方案中大部分都需要分布式空时编码,这就带来实现复杂度太高的问题.A.Bletsas提出了一种新颖的方法,能够解决以上问题,并能提供等于候选节点数的分集阶.该方法需要在多个候选节点中选择一个最佳节点,但最佳节点选择冲突概率较大,在此基础上引入了CSMA协议,仿真结果表明该改进使冲突概率降低了两个数量级,大大提高了通信可靠性.理论分析表明我们提出的改进方法也能达到与不发生冲突时相同的分集增益.     

Diversity-multiplexing tradeoff in multiple-access channels

In a point-to-point wireless fading channel, multiple transmit and receive antennas can be used to improve the reliability of reception (diversity gain) or increase the rate of communication for a fixed reliability level (multiplexing gain). In a multiple-access situation, multiple receive antennas can also be used to spatially separate signals from different users (multiple-access gain). Recent work has characterized the fundamental tradeoff between diversity and multiplexing gains in the point-to-point scenario. In this paper, we extend the results to a multiple-access fading channel. Our results characterize the fundamental tradeoff between the three types of gain and provide insights on the capabilities of multiple antennas in a network context.     

Capacity region of the linear four-node half-duplex wireless relay network

A three-phase transmission scheme for the linear four-node half-duplex wireless relay network is proposed. In each of its two cooperative phases, the setting is equivalent to the broadcast channel with cognitive receiver, whose capacity region is determined. Based on that result, the three-phase scheme is shown to be capacity achieving. Its performance is compared with two suboptimal schemes.     

Throughput-range tradeoff of wireless mesh backhaul networks

Wireless backhaul communication is expected to play a significant role in providing the necessary backhaul resources for future high-rate wireless networks. Mesh networking, in which information is routed from source to destination over multiple wireless links, has potential advantages over traditional single-hop networking, especially for backhaul communication. We develop a linear programming framework for determining optimum routing and scheduling of flows that maximizes throughput in a wireless mesh network and accounts for the effect of interference and variable-rate transmission. We then apply this framework to examine the throughput and range capabilities for providing wireless backhaul to a hexagonal grid of base stations, for both single-hop and multihop transmissions for various network scenarios. We then discuss the application of mesh networking for load balancing of wired backhaul traffic under unequal access traffic conditions. Numerical results show a significant benefit for mesh networking under unbalanced loading.     

A cross-layer framework for optimal delay-margin,network lifetime and utility tradeoff in wireless visual sensor networks

For wireless multimedia sensor networks a distributed cross-layer framework is proposed, which not only achieves an optimal tradeoff between network lifetime and its utility but also provides end-to-end delay-margin. The delay-margin, defined as the gap between maximum end-to-end delay threshold and the actual end-to-end delay incurred by the network, is exploited by the application layer to achieve any desired level of delay quality-of-service. For optimal performance tradeoff an appropriate objective function for delay-margin is required, which is obtained by employing sensitivity analysis. Sensitivity analysis is performed by incorporating delay-margin in the end-to-end delay constraints while penalizing its price in the objective function. For distributed realization of proposed cross-layer framework, the optimal tradeoff problem is decomposed into network lifetime, utility and delay-margin subproblems coupled through dual variables. The numerical results for performance evaluation show that compromising network utility does not guarantee both lifetime and delay-margin improvement, simultaneously, for the set of operating points. Performance evaluation results also reveal that the fairness among different delay-margins, corresponding to different source–destination node pairs, can be improved by relaxing the end-to-end delay threshold.     

Energy spectral efficiency tradeoff in downlink OFDMA network

Spectral efficiency (SE) is an important metric in traditional wireless network design. However, as the development of high‐data rate services and rapidly increase of energy consumption, energy efficiency (EE) has received more and more attention. In this paper, we investigate the EE–SE tradeoff in downlink OFDMA network. Different from previous researches, we try to optimize EE and SE simultaneously. First, the problem is formulated as a multiobjective optimization problem (MOP), and its Pareto optimal set is characterized. Then, we convert the MOP to a single‐objective optimization problem (SOP) by the weighted linear sum method and show that it is neither quasi‐convex nor quasi‐concave. After that, a novel algorithm using particle swarm optimization is proposed to solve the SOP. Simulation results validate that the proposed algorithm can efficiently reduce total transmit power and improve EE, although the cost is sacrificing some SE, which could be used to design an flexible energy efficient network in the future.Copyright © 2014 John Wiley & Sons, Ltd.     

Energy–delay tradeoff in wireless multihop networks with unreliable links

Energy efficiency and transmission delay are very important parameters for wireless multihop networks. Numerous works that study energy efficiency and delay are based on the assumption of reliable links. However, the unreliability of channels is inevitable in wireless multihop networks. In addition, most of works focus on self-organization protocol design while keeping non-protocol system parameters fixed. While, very few works reveal the relationship between the network performance and these physical parameters, in other words, the best networks performance could be obtained by the physical parameters. This paper investigates the tradeoff between the energy consumption and the latency of communications in a wireless multihop network using a realistic unreliable link model. It provides a closed-form expression of the lower bound of the energy–delay tradeoff and of energy efficiency for different channel models (additive white Gaussian noise, Rayleigh fast fading and Rayleigh block-fading) in a linear network. These analytical results are also verified in 2-dimensional Poisson networks using simulations. The closed-form expression provides a framework to evaluate the energy–delay performance and to optimize the parameters in physical layer, MAC layer and routing layer from the viewpoint of cross-layer design during the planning phase of a network.     

Diversity-multiplexing trade-off for mobile urban environments

Measured data from an urban microcell has been used to determine typical operational diversity-multiplexing trade-offs provided by MIMO channels at finite SNRs. It is seen that the optimal relationship obtained using theoretical channel models is overly optimistic     

On the optimal power-distortion tradeoff in asymmetric gaussian sensor network

We present necessary and sufficient conditions, similar to the recent results of Gastpar [1], for the achievability of all power-distortion tuples (P,D) = (P_{1, P2, · · · , PL,D) in an asymmetric Gaussian sensor network where L distributed sensors transmit noisy observations of a Gaussian source through a Gaussian multiple access channel to a fusion center. We show numerically that in general the gap between the provided upper bound and the lower bound of the distortion D is small. We also provide an optimal power allocation that minimizes the total power consumption, P = L i=1 Pi, for uncoded transmission scheme while satisfying a given distortion constraint D. Numerical evaluations show that by applying the optimal power allocation uncoded transmission can perform nearly optimal in an asymmetric sensor network subject to a sum-power constraint. In the symmetric case both bounds agree and provide the optimal power-distortion tradeoff (P,D); this agrees with result of [1]. Thus, in the sense of achieving the optimal (P,D) tradeoff, uncoded transmission is optimal in the symmetric case and can be nearly-optimal in the asymmetric case.}     

一起无线网络干扰的查找与思考

随着无线网络的发展和广泛应用,家庭或单位通过组建无线网络来访问互联网已经越来越普遍,无线网络在给用户带来更加方便快捷的网络服务的同时,也隐藏着许多网络安全方面的问题。事实上,无线网络比有线网络更容易受到入侵,因为被攻击端的电脑与攻击端的电脑并不需要网线连接,只要能连接目标网络的无线路由器或中继器,