无线协作中继技术综述

无线协作中继技术具有低成本、扩大覆盖范围的作用,可以有效提高通信系统的可靠性和传输速率。对无线协作中继技术进行综述,讨论协作中继的基本协议和协作中继的选择方案,并且进行比较分析和仿真验证。     

浅议无线协作通信中继选择

无线协作通信技术的广泛使用成为一种趋势,但是在使用过程中,因为中继节点和中继策略方案的选择出现的问题越发的突出起来。本文针对这种情况进行了研究和论述。     

无线网状网与协作中继技术

无线网状网已经成为无线宽带通信领域的研究热点,但是基于交换技术的无线网状网因为其将整个网络看作是一个IP子网而无法适用于大范围的覆盖。在无线链路中采用协作中继,可以提高无线链路的传输速率及传输可靠性。同时采用基于网络层路由技术的无线网状网技术,可以实现整个无线网状网的频谱效率提升和厂域覆盖。不过,由于标准化、关键技术研究以及产业化推进方面还存在许多问题,使得协作中继技术在无线网状网中的应用面临着巨大挑战。     

协作通信中的中继技术研究

随着无线信道环境的复杂多样,本文引入了协作通信,并探讨了协作通信中的中继节点选择和功率分配两个重要的技术,最后提出了基于中继节点选择和功率分配的联合优化算法。     

移动中继通信技术综述

随着无线通信的发展,以中继为代表的协作通信技术被认为是未来无线通信系统中的关键技术之一。利用中继可以以较小的代价扩展小区覆盖范围和增加系统容量。目前,固定中继的研究已日趋成熟,移动中继正成为一个新的研究热点。由于移动中继本身的特性,它在带来诸多好处的同时也面临一些挑战。文中阐述了移动中继的研究现状,介绍了移动中继的应用场景,对其关键技术进行了综述与展望。     

无线局域网中接入中继业务的协作通信机制

在现有的文献中,协作通信机制都是通过建立协作链路,将源节点的业务通过中继节点转发到目的节点,而在目的节点将受到的源节点信号和目的节点信号进行合并处理。显然,协作通信机制可以提高数据传输的可靠性,但是,该机制并未考虑中继节点本身的业务。文章提出了一种新的MAC机制,称为接入中继业务的协作通信机制（RTACC）。该机制中,中继节点利用已经建立好的协作链路,待转发完成源节点的业务后,在SIFS时间间隔以后发送本身的业务到目的节点,从而提高网络的吞吐量。通过性能分析和仿真验证了本文中提出的机制有效提高了网络的吞吐量。     

协作通信网络中的中继节点选择技术

协作通信作为一种新型的通信模式越来越受到人们的关注,而中继节点选择技术是其关键技术之一,决定了协作能否带来性能增益。文章基于协同节点选择技术的性能评价标准给出了相应的分类方法,对近年来典型的协同节点选择算法并进行分析和比较,得出结论：只有根据系统需求合理地选择、配置中继节点才能更好地优化协同通信的性能。     

同频全双工中继协作通信关键技术综述

当前,线性增长的无线蜂窝网容量难以满足按指数规律增长的移动互联网业务量的需求。因此,学术界和工业界要求频谱效率进一步得到提升。与传统的半双工模式相比,同频全双工技术能使得频谱效率显著提高,同时,面临着自干扰的负面影响。文章对同频全双工技术进行了介绍,对相关技术特点进行分析,并对同频全双工所面临的技术挑战进行评述。     

协作通信中一种改进的最佳中继选择算法

已有研究结果表明,机会中继可以获得与更为复杂的空时编码协作通信相同的分集增益。但是,随着可选中继节点数的增多,发生冲突从而导致选择失败的概率也明显变大。本文提出了一种改进的最佳中继选择算法,源站收到最佳中继发出的标志分组后发送选择确认消息,中继节点在冲突发生后进行退避。分析结果证明,采用新算法可以大大降低选择失败的概率,而增加的开销却很小。     

基于跨层机制的最佳协作中继选择及其系统实现

为了获得最佳的协作中继用户,通过推导协作中继传输系统的误符号率,提出了基于放大重传和解码重传下最佳协作中继的选择准则,并结合跨层协作的思想给出了基于MAC层来实现最佳协作中继选择的分布式协议.与此同时,提出了协作分集系统的物理层传输方案,分析了瑞利衰落信道环境下所提方案的系统性能,得到了系统误比特率的闭式解.此外,针对协作中继选择准则和协作分集传输方案的误码性能进行了系统仿真和性能比较,结果表明,所提出的协作中继选择准则明显优于传统中继选择准则,且协作传输方案可以获得明显的分集增益,系统平均误比特率显著下降.     

Cooperative Relay Service in a Wireless LAN

As a family of wireless local area network (WLAN) protocols between physical layer and higher layer protocols, IEEE 802.11 has to accommodate the features and requirements of both ends. However, current practice has addressed the problems of these two layers separately and is far from satisfactory. On one end, due to varying channel conditions, WLANs have to provide multiple physical channel rates to support various signal qualities. A low channel rate station not only suffers low throughput, but also significantly degrades the throughput of other stations. On the other end, the power saving mechanism of 802.11 is ineffective in TCP-based communications, in which the wireless network interface (WNI) has to stay awake to quickly acknowledge senders, and hence, the energy is wasted on channel listening during idle awake time. In this paper, considering the needs of both ends, we utilize the idle communication power of the WNI to provide a Cooperative Relay Service (CRS) for WLANs with multiple channel rates. We characterize energy efficiency as energy per bit, instead of energy per second. In CRS, a high channel rate station relays data frames as a proxy between its neighboring stations with low channel rates and the Access Point, improving their throughput and energy efficiency. Different from traditional relaying approaches, CRS compensates a proxy for the energy consumed in data forwarding. The proxy obtains additional channel access time from its clients, leading to the increase of its own throughput without compromising its energy efficiency. Extensive experiments are conducted through a prototype implementation and ns-2 simulations to evaluate our proposed CRS. The experimental results show that CRS achieves significant performance improvements for both low and high channel rate stations     

Cooperative Connectivity Models for Wireless Relay Networks

This paper considers the ways that cooperating terminals can be connected to each other in wireless relay networks and the constraints imposed by the availability of different system resources. A framework is developed that exposes the relationship between constraints on available system resources and the achievable combinations of communication links between cooperating terminals. Cooperative connectivity models defined by the achievable combinations of links are derived, associated with their minimum cost constraint sets, and mapped to diversity techniques presented in the literature. The constraints considered are the available number of orthogonal relaying channels, the ability of terminals to diversity combine signals on a single common channel, the ability of terminals to diversity combine signals on orthogonal channels, the ability of terminals to transmit signals on multiple orthogonal channels, and the ability of terminals to cancel the effects of interhop interference.     

无线协作网络中一种高效的分布式安全中继选择方法

Cloud computing is always adopted to enhance the computing capability of mobile systems , especially when the mobile users prefer to use some computation intensive applications . Consequently, the distributed wireless relay infrastructure should be deployed to aid the traffic transmission. To further enhance the QoS provisioning goals of wireless cooperative network, this paper puts forward a multiobjective approach for distributed optimal relay selection, which takes Bit Error Rate (BER) and Secrecy Capacity (SC) into account simultaneously. Firstly, our proposal partitions the channel state into several levels according to the received signaltonoise ratio (SNR) and describes the timevarying Rayleigh fading channel characteristics by using first order finitestate Markov model. Secondly, we model the relay selection as Restless Multiarmed Bandit optimal solution problem with respect to the channel state and the state transition probability. Finally, simulation results demonstrate the efficiency of the proposed approach which outperforms the existing ones .     

BER-Constrained Incremental Relaying with Relay Selection in Cooperative Wireless Networks

One of the main drawbacks of cooperative communication systems with half-duplex relaying is inefficient use of spectrum. Incremental relaying is an effective technique that overcomes this limitation, particularly in the high-SNR regime. In this paper, for a multi-relay cooperative network with arbitrary number of relay nodes, we propose a spectrally-efficient incremental relaying scheme that eliminates redundant relay transmissions such that an average end-to-end bit error rate (BER) constraint is satisfied. For detect-and-forward relaying, under the assumption of error propagation from the relays to the destination, we analyze the performance of the system in terms of the end-to-end BER, the average spectral efficiency and the outage probability for Rayleigh fading environment. The performance of the system depends on a single threshold employed by the relays and the destination. We optimize this threshold such that the average spectral efficiency of the system is maximized under an average end-to-end BER constraint. This optimization criterion results in a constant-BER, variable-spectral efficiency relaying scheme. The proposed scheme makes use of spectrum as efficiently as possible, while providing the required quality of service at the destination.     

A Hybrid Adaptive Relay Technique for Cooperative Communication System

Cooperative communication will increase the channel capacity, when the communicating terminals exceed more than two. Therefore, a relay is termed, as three-terminal unit is a fundamental for user cooperation. The cooperation provides throughput enhancement, reliability, and coverage improvement for wireless communication. Relay technique plays a vital role in cooperative communication in terms of increasing coverage range as well as spectral efficiency. In existing techniques Amplify Forward increase the noise and Decode Forward increase the computational cost of the receiver. In order to overcome the above limitation, a hybrid adaptive relay technique is proposed for cooperative communication system, which will initially check the channel quality of the end user received SNR. When the receiver does not able to decode the message, then the user will choose relay signal. We derived a closed form expression to find the outage probability and channel capacity for the Rayleigh fading channel. Finally, simulation results show the performance of proposed adaptive relay technique in comparison with traditional relay technique by considering both perfect and imperfect CSI.     

Partner Selection Technique for Wireless Cooperative Communication

In wireless cooperative communication scheme, transmit diversity is achieved by coupling the distributed users. In this paper, a new partner selection algorithm is proposed. The selection scheme utilizes the basic work done by Almawgani on RS coded cooperation for wireless network. Users are classified into weak and strong ones based on the signal-to-Noise Ratio (SNR) uplink matrix. Users with good uplink channel SNR (strong users) are coupled with those experiencing weak uplink channel conditions (weak users). The proposed algorithm offers an improvement to the outage probability, \(P_{out}\) and power efficiency as compared to the established work. The algorithm shows a significant improvement of \(P_{out}\) at lower values of uplink SNR.     

Cooperative Wireless Medium Access Exploiting Multi-Beam Adaptive Arrays and Relay Selection

Cooperative transmission among wireless network nodes can be exploited to resolve collisions and thereby enhance the network throughput. Incorporation of multi-beam adaptive array (MBAA) at a base station/access point (destination) receiver has been shown to improve the network performance. In this paper, we propose an efficient cooperative wireless medium access scheme that exploits novel relay selection methods in a network equipped with MBAA at the destination receiver. Unlike existing techniques that require the estimation of angles-of-arrival (AoAs), the proposed scheme uses the spatial correlation among users for simpler but more effective collision detection and resolution. We present two useful relay selection methods based on channel gain and spatial correlation. It is shown that the joint use of an effective relay selection method and an MBAA in a wireless network can significantly improve the uplink throughput. The throughput of the proposed scheme and its upper bound are analytically derived. Numerical and simulation results have demonstrated significant performance enhancement achieved by the proposed cooperative wireless medium access scheme.     

A Contract-Based Model for Multiuser Cooperative Relay in Wireless Communication Networks

Cooperative communication utilizes multi-user spatial diversity to improve spectrum efficiency and channel capacity. However, due to the limited wireless network resource, the selfish relay nodes may be unwilling to offer their relay assistance without any extra incentive. In this paper, the incentive issue between multiple wireless nodes’ relay service and multiple sources’ relay selection is investigated. By modelling multi-user cooperative relay as a labour market, a contract model is proposed with the combination of relay power and basic wage. A relay factor is introduced to describe the contract-relay strategy in cooperative communication. To incentivize the relay nodes to participate in multiple sources’ relay efficiently and credibly, an optimization problem of multi-user relay incentive is formulated to obtain the sources’ maximum cooperative utility under the individually rational restraints. By exploiting the hidden convexity of the non-convex problems in both single-source and multi-source scenarios, the efficient iterative algorithms are developed. Numerical results show that the performance of our approach yields a significant enhancement compared with the equal relay-power and equal relay-factor strategies.     

非理想中继协作通信及其联合迭代译码技术

研究了基于非正规LDPC系统码的非理想中继协作通信系统.为了进一步提高编码系统性能,提出了有效的联合迭代译码技术和新颖的预译码技术.联合迭代译码技术是指目的节点借助一个联合校验矩阵对源节点和中继节点传送的信息同时进行译码,而预译码技术是指在联合迭代译码前首先对它们分别译码,然后对信息位初始化.理论分析和计算机模拟表明,通过译码-前向模式,中继协作通信系统性能得到了显著改善.