Wireless relay networks

Two network architectures for connecting fixed wireless nodes to a central concentrator-relay and star-are combined into a structured network architecture called a relay star network. A relay star network is characterized by the property that there is a unique communication path between any two nodes; that is, the graph of the network is a rooted tree. In this article we present a tutorial discussion of relay star networks using examples and an extended discussion of a protocol for wireless data collection on relay star networks. The target application for this work is data collection on networks of fixed low-cost, low-data-rate environmental monitors such as urban terminals (parking meters, pay telephones, fire alarm boxes, distress call stations, etc.) and utility meters (water, electricity, gas, steam, etc.)     

Frame relay and ATM interworking

Frame relay has proven to be a very successful wide area networking service, and ATM is gaining momentum in the industry to become the preferred common backbone technology for supporting a wide variety of network services, including native ATM cell relay service and frame relay service. In the years ahead, ATM is poised to become the dominant networking technology. Since frame relay and cell relay services will coexist for a long time to come, it is imperative that the network and service interworking specifications be defined and implemented. This article focuses on the topic of frame relay and ATM cell relay service and network interworking. The authors provide the rationale, the standards-based methodology, the major open issues, and a likely evolution scenario for the interworking of frame relay and ATM cell relay networks and services     

Collision resolving relay selection in large-scale blind relay networks

Optimal relay selection in large-scale networks is a difficult task since the network is usually considered as blind due to the high volume and collection difficulty of the relays’ information. In this paper, we develop a collision resolving relay selection (CReS) scheme that achieves the optimal relay from a random set of candidates without the previous knowledge of any individual relay. By introducing stochastic geometry based quality-of-service region, the relation between the distribution of the available relay number and the transmission request is established. Furthermore, the selection phase of the CReS scheme is divided into two sub-phases according to different distributions of the relay number in boundless and bounded regions. A switch rule is proposed when several relays collide in the first sub-phase, followed by the second sub-phase to resolve the collision with the splitting algorithm. The optimal solution that requires minimum selection slots for all sub-phases is derived. In addition, a sub-optimal solution is also explored to reduce the computational complexity. The scheme shows a better applicability than conventional information-based schemes in view of its little information requirement when dealing with large-scale relay allocation problems.     

帧中继技术及其应用

帧中继技术是在分组技术、数字与光纤传输技术、计算机技术日益成熟的条件下发展起来的,它是一种用于连接计算机系统的面向分组的通信方法。它完成了开放系统互连(OSI)物理层、链路层的功能;流量控制、纠错等功能改由智能终端去完成,这大大简化了节点机之间的协议,提高了线路带宽的利用率。帧中继主要应用在局域网(LAN)互联、高清晰度图像业务、宽带可视电话业务和Internet连接业务等。本文首先简要介绍了数据通信技术的发展;然后详细阐述了帧中继技术特点、接入方式的实现;最后对帧中继电路的一般故障进行了诊断分析。     

Optimal relay functionality for SNR maximization in memoryless relay networks

We explore the SNR-optimal relay functionality in a mernoryless relay network, i.e. a network where, during each channel use, the signal transmitted by a relay depends only on the last received symbol at that relay. We develop a generalized notion of SNR for the class of memoryless relay functions. The solution to the generalized SNR optimization problem leads to the novel concept of minimum mean squared uncorrelated error (MMSUE) estimation. For the elemental case of a single relay, we show that MMSUE estimate is a scaled version of the MMSE estimate. This scheme, that we call estimate and forward (EF), performs better than the best of amplify and forward (AF) and demodulate and forward (DF) in both parallel and serial relay networks. We determine that AF is near-optimal at low transmit power in a parallel network, while DF is near-optimal at high transmit power in a serial network. For hybrid networks that contain both serial and parallel elements, the advantage of EF over the best of AF and DF is found to be significant. Error probabilities are provided to substantiate the performance gain obtained through SNR optimality. We also show that, for Gaussian inputs, AF, DF and EF are identical     

Outage analysis of opportunistic multi-antenna relay selection in decode-and-forward relay networks

This article studies the closed-form expressions of outage performance for opportunistic relay under aggregate power constraint in decode-and-forward(DF)relay networks over Rayleigh fading channels,assuming that multiple antennas are available at the relay node.According to whether instantaneous signal-to-noise ratio(SNR)or average SNR can be utilized for relay selection,two opportunistic relay schemes,opportunistic multi-antenna relay selection(OMRS)and average best relay selection(ABRS)are proposed.The performances of both two schemes are evaluated by means of theoretical analysis and simulation.It is observed that OMRS is outage-optimal among multi-antenna relay selection schemes and closely approaches the beamforming(BF)scheme known as theoretical outage-optimal.Compared with previous single-antenna opportunistic relaying(OR)scheme,OMRS brings remarkable performance improvement,which is obtained from maximum ratio combining(MRC)and beamforming techniques.It is also shown that the performance of ABRS in asymmetric channels is close to OMRS in the low and median SNR range.     

Linear beamformer schemes with simple relay selection in MIMO relay networks

This article considers a wireless multi-hop/mesh network where single multi-antenna source-destination pair communicates through a selected relay subset using simple relay selection under the constraint of fixed relay＇s number. Compared with random selection, the simple relay selection can yield certain capacity advantages while linear zero-forcing （ZF） receiver and linear beamformer are considered at the relay. For match-filter （MF） beamformer and amplified-and-forward （AF） beamformer with a fixed number of relays, the capacities are given. Furthermore, we extend the simple selection methods to the relaying scheme with orthogonal-triangular （QR） beamformer and investigate these linear beamformer schemes over spatially correlated multi-input multi-output （MIMO） links for both the backward and forward channel over the two-bop MIMO relay networks.     

On-demand diversity wireless relay networks

There has been much recent attention on using wireless relay networks to forward data from mobile nodes to a base station. This network architecture is motivated by performance improvements obtained by leveraging the highest quality links to a base station for data transfer. With the advent of agile radios it is possible to improve the performance of relay networks through intelligent frequency assignments. First, it is beneficial if the links of the relay network are orthogonal with respect to each other so that simultaneous transmission on all links is possible. Second, diversity can be added to hops in the relay network to reduce error rates. In this paper we present algorithms for forming such relay networks dynamically. The formation algorithms support intelligent frequency assignments and diversity setup. Our results show that algorithms that order the sequence in which nodes join a relay network carefully, achieve the highest amount of diversity and hence best performance. This research is supported in part by NSF grant CNS-0508114. JaeSheung Shin received the B.S. and M.S. degree in Computer Science and Engineering from DongGuk University, Korea, in 1991 and 1993, respectively. He is currently working toward the Ph.D. degree in Computer Science and Engineering at the Pennsylvania State University, University Park. He is a research assistant at the Networking and Security Research Center (NSRC). Prior to joining Pennsylvania State University, he was with Electronics and Telecommunications Research Institute (ETRI), Korea, since 1993. He worked on development of 2G and 3G wireless cellular core network elements. His research interests include mobility management and signaling for wireless cellular and routing and resource allocation for multi-radio multi-hop wireless cellular networks. Kyounghwan Lee received the B.S. degree in Electrical and Electronics Engineering from University of Seoul, Seoul, Korea, in 2000, and the M.S. degree in Information and Communication Engineering from Gwangju Institute of Science and Technology, Gwangju, Korea, in 2002. He is currently a Ph.D candidate at the Electrical Engineering department at the Pennsylvania State University and a research assistant at the Wireless Communications and Networking Laboratory (WCAN@PSU). His research interests include wireless communication theory and relay networks. E-mail: kxl251@psu.edu Aylin Yener received the B.S. degrees in Electrical and Electronics Engineering, and in Physics, from Bogazici University, Istanbul, Turkey, in 1991, and the M.S. and Ph.D. degrees in Electrical and Computer Engineering from Rutgers University, NJ, in 1994 and 2000, respectively. During her Ph.D. studies, she was with Wireless Information Network Laboratory (WINLAB) in the Department of Electrical and Computer Engineering at Rutgers University, NJ. Between fall 2000 and fall 2001, she was with the Electrical Engineering and Computer Science Department at Lehigh University, PA, where she was a P.C. Rossin assistant professor. Currently, she is with the Electrical Engineering department at the Pennsylvania State University, University Park, PA, as an assistant professor. Dr. Yener is a recipient of the NSF CAREER award in 2003. She is an associate editor of the IEEE Transactions on Wireless Communications. Dr. Yener’s research interests include performance enhancement of multiuser systems, wireless communication theory and wireless networking. Thomas F. La Porta received his B.S.E.E. and M.S.E.E. degrees from The Cooper Union, New York, NY, and his Ph.D. degree in Electrical Engineering from Columbia University, New York, NY. He joined the Computer Science and Engineering Department at Penn State in 2002 as a Full Professor. He is the Director of the Networking Research Center at Penn State. Prior to joining Penn State, Dr. La Porta was with Bell Laboratories since 1986. He was the Director of the Mobile Networking Research Department in Bell Laboratories, Lucent Technologies. He is an IEEE Fellow and Bell Labs Fellow. Dr. La Porta was the founding Editor-in-Chief of the IEEE Transactions on Mobile Computing. He has published over 50 technical papers and holds 25 patents.     

Cooperative relaying in multi-antenna fixed relay networks

Space, cost, and signal processing constraints, among others, often preclude the use of multiple antennas at wireless terminals. This paper investigates distributed decode-and-forward fixed relays (infrastructure-based relaying) which are engaged in cooperation in a two-hop wireless network as a means of removing the burden of multiple antennas on wireless terminals. In contrast to mobile terminals, the deployment of a small number of antennas on infrastructure-based fixed relays is feasible, thus, the paper examines the impact of multiple antennas on the performance of the distributed cooperative fixed relays. Threshold-based maximal ratio combining (MRC) and threshold-based selection combining (SC) of these multiple antenna signals are studied and analyzed. It is found that the end-to-end (E2E) error performance of a network which has few relays with many antennas is not significantly worse than that which has many relays each with a fewer antennas. Obviously, the former network has a tremendous deployment cost advantage over the latter. It is also observed that the E2E error performance of a network in which the multiple antennas at relays are configured in SC fashion is not significantly worse than that in which MRC is used. For implementation, SC presents a significantly lower complexity and cost than a full-blown MRC. The analysis in this paper uses the versatile Nakagami fading channels in contrast to the Rayleigh model used in most previous works     

一种中继选择与分布式空时码相结合方案

针对一个发送端、接收端及每个中继都配置单根天线的无线中继网络,在假设中继不知道任何信道信息的条件下,为了提高系统性能,本文提出中继选择与分布式空时码相结合的方案.证明了选择2个中继与Alamouti正交空时码的结合方案成对错误概率的Chernoff上界要比对应的只选择2个中继参加协作不使用Alamouti正交空时码的情...     

Energy-efficient relay selection and optimal relay location in cooperative cellular networks with asymmetric traffic

Energy-efficient communication is an important requirement for mobile relay networks due to the limited battery power of user terminals. This paper considers energy-efficient relaying schemes through selection of mobile relays in cooperative cellular systems with asymmetric traffic. The total energy consumption per information bit of the battery-powered terminals, i. e. , the mobile station(MS)and the relay, is derived in theory. In the joint uplink and downlink relay selection(JUDRS)scheme we proposed, the relay which minimizes the total energy consumption is selected. Additionally, the energy-efficient cooperation regions are investigated, and the optimal relay location is found for cooperative cellular systems with asymmetric traffic. The results reveal that the MS-relay and the relay-base station(BS)channels have different influence over relay selection decisions for optimal energy-efficiency. Information theoretic analysis of the diversity-multiplexing tradeoff(DMT)demonstrates that the proposed scheme achieves full spatial diversity in the quantity of cooperating terminals in this network. Finally, numerical results further confirm a significant energy efficiency gain of the proposed algorithm comparing to the previous best worse channel selection and best harmonic mean selection algorithms.     

Optimized distributed MIMO for cooperative relay networks

This paper presents an optimized distributed multiple-inputmultiple-output (OD-MIMO) for cooperative communication in wireless relay networks. The set of cooperating nodes is a priori unknown. In order to avoid the centralized stream and pilot allocation procedure, a fixed signature vector (SV) is assigned for each node in the network. We analyze the constraints of the proposed scheme, and derive an optimization criterion for the decision of the SVs. A gradient-based algorithm for SV design is provided. Simulation results show that the performance loss of OD-MIMO compared to centralized distributed MIMO is small for large number of cooperative relay nodes.     

Packet scheduling for OFDMA based relay networks

The combination of relay networks with orthogonal frequency division multiple access （OFDMA） has been proposed as a promising solution for the next generation wireless system. Considering different traffic classes and user quality of service （QoS）, three efficient scheduling algorithms are introduced in such networks. The round-robin （RR） algorithm in relay networks serves as a performance benchmark. Numerical results show that the proposed algorithms achieve significant improvement on system throughput and decrease system packet loss rate, compared with the RR and absence of relaying system （traditional network）. Furthermore, comparisons have been carried out among the three proposed algorithms.     

Joint relay selection and power allocation algorithm in two-way relay networks with proportional fair constraint

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 pro...     

Location-quality-aware policy optimisation for relay selection in mobile networks

Relaying can improve the coverage and performance of wireless access networks. In presence of a localisation system at the mobile nodes, the use of such location estimates for relay node selection can be advantageous as such information can be collected by access points in linear effort with respect to number of mobile nodes (while the number of links grows quadratically). However, the localisation error and the chosen update rate of location information in conjunction with the mobility model affect the performance of such location-based relay schemes; these parameters also need to be taken into account in the design of optimal policies. This paper develops a Markov model that can capture the joint impact of localisation errors and inaccuracies of location information due to forwarding delays and mobility; the Markov model is used to develop algorithms to determine optimal location-based relay policies that take the aforementioned factors into account. The model is subsequently used to analyse the impact of deployment parameter choices on the performance of location-based relaying in WLAN scenarios with free-space propagation conditions and in an measurement-based indoor office scenario.     

Bit error rate performance analysis in amplify-and-forward relay networks

Wireless Networks - Two methods are proposed in this paper to estimate asymptotic and exact bit error rate (BER) in two-hop amplify-and-forward (AF) relay networks . Rayleigh-fading channels are...     

Robust cross layer optimization in relay aided cellular networks

A robust optimization framework for cross layer optimization is proposed to deal with time varying channels, reducing the required channel state feedback overhead and giving strong QoS guarantees. Lower bounds for the achieved goodput when robust scheduling is used are derived and through simulation we study the impact in terms of blocked calls and QoS achieved by the robust solution for two different cell topology layouts: when 2-hop relaying is allowed and when only direct base station to user transmissions are allowed. The results reveal that the price of robustness is lower for the 2-hop case than the single hop case.     

中继网中基于QoS保证和比例公平的资源分配

中继系统下的众多资源分配策略很少同时考虑多用户情形下的子载波配对和不同用户需求。针对这一问题,提出了一种基于QoS(服务质量)保证和比例公平的多用户子载波配对和功率分配算法,该算法既能保证QoS用户的最小速率要求,又能满足BE(尽力而为)用户之间速率比例公平的准则。该算法首先根据不同用户需求分配第二跳的子载波,然后利用匈牙利配对算法得到两跳子载波的最佳配对,最后用类似注水算法进行功率分配。仿真结果表明,所提算法在满足用户QoS保证和比例公平准则的同时有效提升了系统的吞吐量。     

Optimal throughput performance in full-duplex relay assisted cognitive networks

Wireless Networks - In this paper, we study a full-duplex cooperative cognitive radio network with multiple full-duplex secondary users acting as potential relays for transmitting the packets of a...     

Cooperative relay to improve diversity in cognitive radio networks

Recent studies demonstrated that dynamic spectrum access can improve spectrum utilization significantly by allowing secondary unlicensed users to dynamically share the spectrum that is not used by the primary licensed users. Cognitive radio was proposed to promote the spectrum utilization by opportunistically exploiting the existence of spectrum ?holes.? Meanwhile, cooperative relay technology is regarded widely as a key technology for increasing transmission diversity gain in various types of wireless networks, including cognitive radio networks. In this article, we first give a brief overview of the envisioned applications of: cooperative relay technology to CRNs, cooperative transmission of primary traffic by secondary users, cooperative transmission between secondary nodes to improve spatial diversity, and cooperative relay between secondary nodes to improve spectrum diversity. As the latter is a new direction, in this article we focus on this scenario and investigate a simple wireless network, where a spectrum-rich node is selected as the relay node to improve the performance between the source and the destination. With the introduction of cooperative relay, many unique problems should be considered, especially the issue for relay selection and spectrum allocation. To demonstrate the feasibility and performance of cooperative relay for cognitive radio, a new MAC protocol was proposed and implemented in a universal software radio peripheral-based testbed. Experimental results show that the throughput of the whole system is greatly increased by exploiting the benefit of cooperative relay.