基于中继抑制蜂窝网络同频干扰的方案

在传统蜂窝网络中,同频干扰问题极大地制约着通信网络数据传输速率以及通信质量的提高。针对这一问题,提出了在蜂窝小区中部署中继的办法,并根据用户的不同服务等级要求规定了3种中继使用方式。分析了加入中继后,蜂窝网络中对同频干扰的来源并进行了计算。对比了传统蜂窝网与中继蜂窝网的中断概率和信干比(SIR)。通过对比得出,与传统蜂窝网络相比,在蜂窝小区边缘使用中继站能在小区边缘显著提升移动接收端的SIR,降低中断概率。而在整个蜂窝小区内使用中继站能显著提升移动接收端在整个小区内的SIR,降低中断概率。     

基于固定中继的盲区覆盖的研究

如何减小蜂窝小区的盲区覆盖一直是多跳蜂窝网络研究的热点问题。这里提出了一种新的在传统蜂窝小区中划分扇区并加入固定中继的系统模型。该系统模型通过数学模型解析了节点移动到盲区边缘或未完全进入盲区时的距离,并通过算法描述了盲区附近节点需要选择跳板节点的条件以及通过跳板节点连接到固定中继后再同基站通信的过程。该方法设计降低了掉话率,维持了正常通信,仿真证明了该方法的可行性。     

B3G中的多跳蜂窝小区的结构分析

基于多跳通信及蜂窝通信的特点,提出了一种由中心基站及其周围的固定多跳中继节点共同实现小区覆盖范围的多跳小区结构。在此结构中,基站附近的移动台以一跳方式直接接入基站,而距离基站较远的移动台通过其与基站之间的多跳中继节点的中继以多跳通信方式接入基站。该结构提供了在低成本及低发射功率条件下完成区域覆盖的方法。并对多跳小区结构的覆盖特性进行了分析,通过仿真计算给出了多跳节点数目与小区覆盖范围的关系。     

IEEE 802.16j中的协作中继机制

蜂窝网络中配置中继节点可以提高系统容量和小区覆盖范围.IEEE成立802.16j工作组研究移动多跳中继.首先介绍了协作中继的基本概念,然后讨论了802.16j中定义的三种协作分集机制:协作源端分集、协作发送分集和协作混合分集.最后,给出了实现协作中继的四个步骤.     

两跳中继OFDMA蜂窝网络下行链路呼叫阻塞率分析

本文首先提出了一种分析OFDMA蜂窝网络下行链路呼叫阻塞率的方法,在此基础上进一步分析了加入两跳中继的OFDMA蜂窝网络呼叫阻塞率.OFDMA蜂窝网络的每个呼叫接入都需要随机数量的子载波来满足用户传输速率的需求,传统GSM及CDMA网络的容量分析方法不能应用到OFDMA网络系统中.本文根据用户对子载波的需求量,把接入用户分成不同的服务类型,以多维马尔可夫链为数学模型分别分析传统和两跳中继OFDMA蜂窝网络下行链路呼叫阻塞率,最终通过数值计算分析各种参数对系统性能的影响,数值分析结果表明加入中继后的两跳中继OFDMA蜂窝网络下行链路容量比传统网络有显著的提升.     

中继蜂窝网络中小区间和小区内的资源分割

文章提出了一种应用于固定中继蜂窝网络中基于复用分割的小区间频谱分配框架,通过引入有效复用因子这一指标来优化小区内基站和中继之间的资源分割,并比较了不同的链路带宽分配方案对系统性能的影响。理论分析和仿真结果显示,该方案可以在保证小区边缘用户的吞吐量的同时提高小区容量。     

两跳蜂窝移动系统中继信道分配策略

在频率复用因子为1的两跳固定中继节点的蜂窝移动通信系统中,基于现实移动业务分布的时变性和非均匀性,提出了新的中继信道分配策略。与传统的中继信道分配策略相比,该策略不需要BS之间的协作,也能严格控制相邻小区之间同频RS的干扰距离,降低同信道干扰,在较低的系统复杂度下,实现了无线资源的有效利用。     

两跳中继CDMA蜂窝系统的上行链路容量分析

首先在两跳中继CDMA蜂窝系统的基础上,提出了2种使用带外信道提高传统CDMA蜂窝系统上行链路容量的中继方法;然后通过分析传统无中继CDMA蜂窝系统的干扰功率,分别得到这2种中继方法对当前小区和邻居小区总的干扰功率;最后在一种对称小区模型的基础上,通过数值计算对两跳中继CDMA蜂窝系统的上行链路容量进行分析,并讨论了2种中继方法对系统性能所产生的影响.     

LTE-A多小区中继网络两跳速率匹配资源分配算法

针对中继网络的两跳特性,提出一种多小区中继网络两跳速率匹配资源分配算法。首先,在第一个子时隙内各小区独立地为小区中所有用户分配子载波,并根据子载波分配结果,建立基于非合作博弈的功率分配模型;然后,由第一跳资源分配结果对第二跳速率匹配,自适应地为中继分配资源以满足边缘用户的速率需求。仿真结果表明,该算法在满足边缘用户速率需求的前提下,进一步提高了中心用户的吞吐量,同时降低了系统的发射功率,从而提升了系统性能。     

基于智能固定中继的两跳蜂窝网络

提出一种新的CDMA方式下的两跳蜂窝结构模型。这种新的结构在特定区域使用多个非再生固定中继，并在固定中继使用智能天线和波束成型技术，通过移动台在多个固定节点的信号功率的最大比合并和移动台平均发射功率的调整，有效地增加了系统的上行容量（25％左右）。研究结果还表明，这种新的网络结构可以有效降低小区间干扰，在发射功率和固定中继拓扑上都有较大的灵活性，并可根据实际的网络需求进行合理调整。     

Semi-analytic Performance of a Multiaccess MIMO Scheme Using Precoding Vectors

This paper addresses the problem of transmitting data to multiple mobile stations using a decode-and-forward strategy. Precoding vectors are used in relays to cancel out multiple access interference at the mobile stations. The diversity gain of the system has been analytically calculated for the case of two mobile stations. The system performance for arbitrary number of mobile stations is calculated using a semi analytic approach. In this approach the distribution of signal to noise ratio is approximated by a mixture of Nakagami laws using an Expectation-Maximization algorithm. Then the symbol error probability of this mixture is analytically calculated. Simulations confirm the theoretical results showing that the full diversity advantage can be obtained, which is the product of the number of antennas at each relay by the number of relays minus the total number of system constraints.     

多中继协作通信系统容量分析及中继选择协作分集策略

本文针对多中继辅助通信系统,将系统建模为一个两跳通信链路,并进行了系统容量分析。针对两种特殊情况:用户端接收噪声方差远小于中继端接收噪声方差和中继端接收噪声方差远小于用户端接收噪声方差的情况,本文具体给出了系统传输容量上限与协作中继个数之间的关系。基于容量的分析,本文设计了两种中继选择策略。在第一种情况下,根据中继与用户间的信道特征值对多路数据流分别选取不同的中继子信道进行传输;在第二种情况下,选择一个信道条件最好的中继完成多路数据流的并行传输。仿真分析表明,不同的信道环境需要选择不同的中继选择策略。      

Simple precoding algorithms using Gram–Schmidt orthonormalization process for multiuser relay communications with optimized power allocation

This paper proposes a new simple precoding solution based on the Gram–Schmidt orthonormalization to be used at the relay station of a multirelay wireless networks where the different mobile stations belong to the same network, in order to mitigate the multiuser interference at each mobile station. The strength of this method is that it only requires the knowledge of all channel impulse responses from a given relay to all the mobile stations. In other words, to compute its precoding vectors, each relay does not need to know the channel impulse responses of the channels of other relays. Unlike the centralized reference method where each mobile station benefits from the same diversity gain, using this algorithm, some mobile stations will improve their diversity gain at the cost of a loss in the diversity gain of other users. This constitutes a simple solution to supply different qualities of service in the case of a multiservices network. Furthermore, this work proposes an optimized power allocation between the relays. Analytical and accurate performance analyses for the different studied contexts are provided.     

A hierarchical framework of dynamic relay selection for mobile users and profit maximization for service providers in wireless relay networks

Although extensive research has been carried out on the issue of how to optimally select relays in wireless relay networks, relay selection for mobile users is still a challenging problem because of the requirement that the dynamic selection should adapt to user mobility. Moreover, because the selected relays consume their energy on relaying data for the users, it is required that the users have to pay for this relay service. The price of selecting relays will affect the users' decisions. Assuming that different relays can belong to different service providers, we consider the situation that the service providers can strategically set the prices of their relays to maximize their profits. In this paper, we jointly study the dynamic relay selection for mobile users and profit maximization for service providers. Also, we design a Stackelberg‐game hierarchical framework to obtain the solution. At the lower level, we investigate the relay selection problem for the mobile users under given prices of selecting the relays. It is formulated as a Markov decision process problem with the objective to minimize the mobile user's long‐term average cost (which consists of the payment to the relay service and the cost due to packet loss), and solved by applying the linear programming technique. At the upper level, we study the game of setting relay prices for the service providers, with the knowledge that the mobile users will make relay selections based on their given prices. Nash equilibrium is obtained as the solution. Our results can help to provide a guidance for service providers to compete for providing relay services. Copyright © 2012 John Wiley & Sons, Ltd.     

Radio resources allocation for decentrally controlled relay stations

To enhance throughput and to extend coverage of wireless networks based on IEEE 802.16 standards, relay stations can be implemented. The crucial point influencing the overall system performance is allocation of appropriate amount of resources to individual relay stations depending on their current needs. If resources are not allocated properly, relay stations can experience congestion situations resulting in system throughput decrease and packet delays increase. If the base station is enhanced purely by centrally controlled relay stations, the base station itself is able to dynamically schedule data transmissions of its relays. Nevertheless, decentrally controlled relays schedule data for its users on its own and the base station is no longer capable to allocate the right amount of radio resources for them. The decentrally controlled relays have to ask for radio resources by means of existing scheduling services defined in IEEE 802.16 standard. While utilization of the conventional unsolicited grant service decreases the system capacity, the use of real-time polling or extended real-time polling services results in higher signaling overhead and longer packet delays. In order to maximize system throughput and to minimize packet delays and signaling overhead, we suggest a mechanism that pre-allocates to decentrally controlled relay stations a certain amount of default radio resources while the remaining resources are dynamically shared. The obtained results show that for low traffic load, overhead and packet delays are significantly smaller as relays do not have to ask base stations for resources. On the other hand, at heavy traffic load the system throughput slightly decreases whereas packet delays and signaling overhead are still significantly smaller.     

A coalitional game‐based relay load balancing and power allocation scheme in decode‐and‐forward cellular relay networks

In this paper, a game theoretic relay load balancing and power allocation scheme is proposed for downlink transmission in a decode‐and‐forward orthogonal frequency division multiple access‐based cellular relay network. A system with a base station communicating with multiple users via multiple relays is considered. The relays have limited power, which must be divided among the users they support. In traditional scheme, each relay simply divides its transmit power equally among all its users. Moreover, each user selects the relay with the highest channel gain. In this work, we do not apply the traditional relay scheme. It is because the users are distributed randomly, and by applying the traditional relay selection scheme, it may happen that some relays have more users connected to them than other relays, which results in having unbalanced load among the relays. In order to avoid performance degradation, achieve relay load balancing, and maximize the total data rate of the network, a game theoretic approach is proposed, which efficiently assigns the users to relays. The power of each relay is wisely distributed among users by the efficient power allocation scheme. Simulation results indicate that the proposed game‐based scheme can considerably improve the average sum‐spectral efficiency. Moreover, it shows that by applying the game, users who can connect to uncongested relays join them as opposed to connecting to congested relays. Copyright © 2015 John Wiley & Sons, Ltd.     

An evolved cellular system architecture incorporating relay stations - [WiMAX update]

Shrinking cell sizes, primarily a result of keeping up with the increasing demand for higher data rates, are stretching thin the notion of our traditional cellular system architecture. More and more base stations are serving smaller and smaller areas (cells) which in effect is driving up deployment costs. The option of deploying relay stations is increasingly beginning to look like a solution to the problem of providing a cost-effective way to extend the coverage and capacity in a cellular network. A relay station can be used to extend the point-to-multipoint link between the base station and mobile stations. Relay stations connect to the base stations without wires and are expected to be deployed to cover smaller geographic areas. Primarily the deployment costs but also the equipment costs are expected to be substantially lower than those of base stations. In this article we first introduce the relay station and discuss the place it is likely to carve out for itself in the traditional cellular architecture. We highlight the important economic and performance benefits relay stations could potentially offer, and outline a few scenarios where relays are likely to be deployed in the beginning. The multihop relay standard developed by the IEEE 802.16 working group is then used as a basis to provide an overview of the relay-enhanced cellular architecture and the key choices that can be made in developing relay support within a cellular system ? a precursor to what can be expected in later releases of the Mobile WiMAX system. Finally, we discuss some future directions in the development of relay systems.     

Bandwidth allocation and distributed relay selection for multiple‐user and multiple‐relay cooperative systems using Stackelberg game

Cooperative communication is an ongoing research area which lies on the basic idea of transmission of information from the transmitter to the receiver with the assistance of a virtual array of relay nodes in between, which will eventually provide the spatial diversity. This paper deals with the resource allocation (bandwidth in this case) among multiple users (source‐ destination pairs) in a cooperative communication environment along with the relay selection when there are multiple relay nodes to assist the transmitting nodes to pass on their data signal to respective receivers. A multi‐user, multi‐relay system model is considered here on which Amplify‐and‐Forward relaying scheme is applied. The bandwidth allocation and relay selection are done based on the Stackelberg game according to which transmitting nodes are treated as purchasers and relaying nodes are treated as vendors. By this planned approach, the transmitting nodes can discover the relays at comparatively better positions and can purchase the optimal bandwidth from those helping relays. By this approach, the relays which are competing with each other can increase their own utilities by demanding the optimal prices and the multiple users which are competing with each other can maximize their own utilities by demanding the optimal bandwidths. Distributed relay selection scheme is applied here which does not require precise information of channel state information as opposed to Centralized scheme and it gives comparable results, too.     

Performance analysis of multiuser diversity in cooperative multi-relay networks under rayleigh-fading channels

In multiuser cooperative relay networks, cooperative diversity can be obtained with the help of relays, while multiuser diversity is an inherent diversity in multiuser systems. In this letter, the performance analysis of multiuser diversity in cooperative multi-relay networks is presented. Both the case of all relay participating and the case of relay selection are considered. We first derive asymptotic expressions of outage probability and symbol error probability for amplify-and-forward (AF) and decode-and-forward (DF) protocols with joint multiuser and cooperative diversity. Then, the theoretical analysis are validated by Monte Carlo simulations. Both the theoretical analysis and simulations show that a multiuser diversity order of K and a cooperative diversity order of M+ 1 can be achieved simultaneously for both AF and DF protocols (where K is the number of accessing users and M is the number of available relays). These demonstrate that the multiuser diversity can be readily combined with the cooperative diversity in multiuser cooperative relay networks.     

一种多用户多中继MIMO通信系统迭代预编码方案

该文针对多中继MIMO通信系统多用户传输时的用户间干扰问题,提出了一种可以有效抑制多用户干扰的发射端与中继端迭代预编码的方案。该方案首先在中继端进行多中继联合的迫零预编码,然后将基站与多用户之间等效为一个点到多点的MIMO信道,采用最大化信漏噪比的预编码方法,在发射端进一步消除用户间的干扰,同时避免了噪声放大的影响,进而通过中继端预编码与发射端预编码的多次迭代,更好地保持了多中继并行传输引入空间分集所带来的性能优势,有效地抑制了用户间干扰,获得了更高的系统和容量。