Cellular CDMA capacity with out-of-band multihop relaying

In this paper, we consider the capacity of cellular code division multiple access (CDMA) when there is out-of-band ad hoc traffic relaying. The mobile stations (MSs) are dual-mode, having both ad hoc and cellular CDMA radios. An active MS is free to choose any available relay station (RS) within its ad hoc radio coverage area for dual-hop communication with the CDMA base station (BS). Communications between the RSs and the MSs use bandwidth which is available to the ad hoc radio and does not consume the CDMA capacity. Using this mechanism, CDIVIA interference can be reduced by dynamically selecting RSs which have more favorable CDMA link characteristics. Several relay station selection criteria are considered, namely, ad hoc relaying with low relative interference (ARRI), with best link gain (ARLG), and with shortest distance (ARSD). The relay station selection protocols are compatible with existing wireless local area network (WLAN) standards such as IEEE 802.11. An analytic model is used to compute the effects on uplink and downlink CDMA capacities when out-of-band relaying is added. The results show that very significant capacity improvements are possible by using these criteria compared with conventional CDMA with hard or soft handoff. Ad hoc relaying which dynamically tracks CDMA link quality can achieve greater capacity improvements than that using a distance-based relay station selection. Relaying, which considers both signal and interference conditions, achieves better capacity than that based on signal link quality alone.     

Average SNR and Ergodic Capacity Analysis for Opportunistic DF Relaying with Outage over Rayleigh Fading Channels

In the paper, we deal with a single-selection opportunistic relaying with the decode-and-forward (DF) protocol over Rayleigh fading channels. The exact end-to-end average signalto- noise ratios (SNR) and ergodic capacities of both proactive and reactive opportunistic relaying are derived as a closed-form for arbitrary link SNR. In addition, the effective ergodic capacity satisfying the minimum required data rate without outage is also identified for both relaying schemes. The analysis results are used to demonstrate which relaying scheme outperforms the other for given system parameters.     

Probability Analysis of Capacity Gain by Cooperative Relaying Over Single-Hop OSTBC Transmission in Low SNR Regime

In this paper, we investigate the capacity gain obtained by putting a multiple-antenna relay in an original single-hop multiple-input multiple-output system using an orthogonal space-time block code over uncorrelated Rayleigh fading channels. As relaying techniques, we consider decode-and-forward relaying as well as decouple-and-forward relaying in which no decoding is performed at the relay. Focusing on the low signal-to-noise ratio regime, closed-form expressions of the probability of the capacity gain are provided for the respective relaying schemes. The probability results in an explicit function of an average power ratio of the per-hop channel in dual-hop relaying to the single-hop channel. Numerical examples show the impact of the power ratio, the relaying strategy, the number of antennas and the relay location on the capacity gain, respectively.     

基于RBF神经网络的超高压继电保护的算法研究

提出一种基于RBF神经网络的超高压继电保护的算法。是由于径向基神经网络（RBFN）具有学习性,可以根据已有的继电保护参数样本集进行训练,从中分析出故障检测、故障定位,自适应自动重合闸技术、差动保护以及距离保护的内在联系,实现对以后的继电保护数据样本进行自适应控制。该算法的优点就是在构造过程考虑了径向基神经网络（RBFN）的预测精度和训练时间,采用了线性最小二乘法（LLS）和梯度下降法的方法,运用Matlab做了仿真实验,获得了较为准确的预测结果。     

Joint improvements for capacity and power‐efficiency of mobile WiMAX by relaying schemes

The mobile WiMAX standard promises to enable low‐cost mobile Internet applications over extensive areas and to meet the capacity requirements by combining advanced multiple input multiple output (MIMO) and relay transmission techniques. In this paper, we propose a solution to increase the channel capacity between wireless links and to conserve the average required uplink transmission power consumption simultaneously through deploying relay stations' (RSs) locations judiciously. Two relaying schemes, analogue (amplify and forward) relaying and digital (decode and forward) relaying from a mobile device to the base station (BS) through a relay node, are adopted with weighting filters to increase the channel capacity. Based on the enhanced channel capacity, a new manipulation way to save power is introduced by deploying RSs strategically where the branch‐and‐bound (BB) algorithm is applied to determine the placements of RSs. Our simulation results demonstrate the significant improvement of network capacity by applying the weighting filter techniques and the great power saving of the average total network power by utilizing the BB algorithm to arrange RSs locations. Copyright © 2011 John Wiley & Sons, Ltd.     

On the Capacity of Underlay Multihop Cognitive Relaying Over Generalized-K Composite Fading Channels

Cognitive radio (CR) is one of the candidate enabling technologies for future wireless communication systems. This paper is devoted to analyze the capacity of underlay cognitive multihop relaying over independent and non-identically distributed generalized-K fading channels. In doing so, we derive upper and lower-bounded expressions for the ergodic capacity and the outage probability of the secondary user (SU), respectively. By using these expressions, new insights in the performance of the cognitive multihop amplify-and-forward relaying are revealed. The obtained results provide interesting details on the joint effect of shadowing and multipath fading on the capacity of the SU in relay-assisted underlay CR networks. The analytical results are verified by Monte-Carlo simulations for different fading conditions.     

两跳高斯线性中继信道：可达码率与最优设计

The relay node with linear relaying transmits the linear combination of its past received signals. The optimization of two-hop relay channel with linear relaying is discussed in this paper. The capacity for the two-hop Gaussian relay channel with linear relaying is derived, which can be formulated as an optimization problem over the relaying matrix and the covariance matrix of the signals transmitted at the source. It is proved that the solution to this optimization problem is equivalent to a “single-letter ”optimization problem. We also show that the solution to this “single-letter ”optimization problem has the same form as the expression of the rate achieved by Time-Sharing Amplify and Forward ( TSAF ). In order to solve this equivalent problem, we proposed an iterative algorithm. Simulation results show that if channel gain of one hop is relatively smaller, the achievable rate with TSAF is closer to the max-flow min-cut capacity bound, but at a lower complexity.     

Closed-Form Solution of Outage Capacity for Cooperative DF and AF Relay Network

Cooperative relaying permits one or more relays to transmit a signal from the source to the destination, thereby increasing network coverage and spectral efficiency. The performance of cooperative relaying is often measured as outage probability. However, appropriate measure for the channel quality is outage capacity. Although the outage probability for cooperative relaying protocol has been analyzed before, very little research has been addressed for the outage capacity. This paper is the first of its kind to derive a closed-form analytical solution of outage capacity using fixed decode and forward relaying and amplify and forward relaying in independent but non identically distributed (i.n.i.d.) Rayleigh fading channels, considering channel coefficients known to the receiver side. The analytical results show a tradeoff between the SNR and the number of relays for a specific outage capacity. A comparison between decode and forward relaying and amplify and forward relaying shows that decode and forward relaying outperforms amplify and forward relaying for a large number of relays.     

Joint resource allocation,routing and CAC for uplink OFDMA networks with cooperative relaying

In this paper, we propose a joint resource allocation, routing, and connection admission control (CAC) scheme for uplink transmission in orthogonal frequency division multiple access (OFDMA) relay networks with cooperative relaying. For cooperative relaying, relay station can relay uplink data from mobile station (MS) to base station with cooperation of the MS using transmit diversity. Transmit diversity can be achieved by virtual MISO via distributed space–time coding. The proposed scheme jointly allocates OFDMA resources and selects path for each user with CAC to maximize the upink throughput of cooperative OFDMA relay networks. The basic OFDMA resource unit is considered as a resource element which is one subcarrier over one OFDMA symbol. An efficient multi-choice multi-dimensional knapsack (MMKP) algorithm is presented for the proposed scheme. The proposed MMKP algorithm provides a unified framework which is applicable to OFDMA networks with and without cooperative relaying. We evaluate the performance of the proposed scheme with and without cooperative relaying in a hilly terrain with heavy tree density by using OPNET-based simulation. We show that the cooperative relaying improve the uplink system throughput compared with non-cooperative relaying, and the proposed scheme outperforms the conventional link quality-based scheme in both cooperative and non-cooperative relay networks.     

硬件损伤条件下的中继网络性能分析

物理层的损伤会造成系统性能的降低.主要分析基于机会中继选择策略下的中继网络.机会中继选择策略是中继节点的选择依靠所有信道的即时信息,选择其中最大的进行传输.得到了系统端到端中断概率的准确表达式以及遍历容量的近似表达式.公式的给出提供了快速计算具有硬件损伤的系统性能的方法.重点讨论了具有硬件损伤的中继系统和理想硬件系统的性能对比.给出了仿真的结果和必要的讨论来证明理论分析的正确性.     

Performance analysis for relay networks with hierarchical support vector machines

In this paper, we consider a cooperative relay scheme for a mobile network with MIMO technology. The channel capacity for two well‐known relaying schemes are investigated: analogue relaying (amplify and forward) and digital relaying (decode and forward) from a mobile device to the base station through a relay node. In order to further increase the channel capacity, we propose an efficient hierarchical procedure based on support vector machine, namely hierarchical support vector machines (HSVM), to estimate the wireless networks condition approximately and design two ways (matched filter and minimum mean square error filter) of increasing the channel capacity according to the estimated wireless network condition. The proposed HSVM can estimate the wireless networks condition in much shorter time compared with the traditional minimum mean square error scheme without incurring much estimation error, which is spatial, useful for delay sensitive communication. For digital relaying, the effect of imperfect channel decode is also addressed. Our numerical results demonstrate the reduction of estimation complexity by adopting HSVM and the significant improvement of network capacity by applying the matched filter weight at relay nodes according to the network estimation. Copyright © 2011 John Wiley & Sons, Ltd.     

预编码技术在协同中继系统中的应用

协同中继系统中的多个通信实体问通过协作协议共享有限资源,使得系统具有较高的容量.本文提出了将预编码技术应用到协同中继系统来有效地提高频谱效率.首先,简要介绍了协同中继通信的发展,并指出半双工协同中继系统蕴含着较大的容量潜力;然后分析和总结了各类现有的预编码技术;最后,给出了预编码技术在协同中继系统中的几种应用方式.     

On the energy efficiency of MIMO cooperative relaying networks

Cooperative relaying techniques can greatly improve the capacity of the multiple input and multiple output (MIMO) wireless system. The transmit power allocation (TPA) strategies for various relaying protocols have become very important for improving the energy efficiency. This article proposes novel TPA schemes in the MIMO cooperative relaying system. Two different scenarios are considered. One is the hybrid decode-and-forward (HDF) protocol in which the zero-forcing (ZF) process is operated on relays, and the other is the decode-and-forward (DF) protocol with relay node and antenna selection strategies. The simulation results indicate that the proposed schemes can bring about significant capacity gain by exploiting the nature of the relay link. Additionally, the proposed TPA scheme in the HDF system can achieve the same capacity as the equal TPA with fewer relay nodes used. Finally, the capacity gain with the proposed schemes increases when the distribution range of relay nodes expands.     

Power allocation and effective capacity of AF successive relays

In the relay based telecommunications with K relays between the source and destination, \(K+1\) time or frequency slots are required for a single frame transmission. However, without the relays, only one time or frequency slot is used for a single frame transmission. Therefore, despite the benefits of relaying systems, this type of communications is not efficient from the spectral efficiency viewpoint. One solution to reduce this issue might be the full-duplex (FD) relays. An old technique which is reconsidered recently to improve the spectral efficiency of telecommunication systems. However, FD relays have a certain complexity, so, some similar techniques such as successive relays with nearly the same performance but less complexity is taken into account now. In successive relaying systems, two relays between the source and destination are employed which receive the transmitted frames from the source and relay it to the destination successively. This structure generally acts like an FD relays. In this paper, the effective capacity performance of an amplify and forward successive relaying systems with power allocation strategy at the relays are studied perfectly. However, while the inter-rely interference (IRI) between two successive relays has to be managed well, the power allocation and the effective capacity is derived under different assumptions about the IRI. In this way, we assume weak or strong, short or long-term constraints on the IRI. Then we extract the optimal transmitted power at the relay to maximize the effective capacity under these constraints.     

Relay assisted F/TDMA ad hoc networks: node classification, power allocation and relaying strategies

This paper considers the design of relay assisted F/TDMA ad hoc networks with multiple relay nodes each of which assists the transmission of a predefined subset of source nodes to their respective destinations. Considering the sum capacity as the performance metric, we solve the problem of optimally allocating the total power of each relay node between the transmissions it is assisting. We consider four different relay transmission strategies, namely regenerative decode-and-forward (RDF), nonregenerative decode-and-forward (NDF), amplify- and-forward (AF) and compress-and-forward (CF). We first obtain the optimum power allocation policies for the relay nodes that employ a uniform relaying strategy for all nodes. We show that the optimum power allocation for the RDF and NDF cases are modified water-filling solutions. Weobserve that for a given relay transmit power, NDF always outperforms RDF whereas CF always provides higher sum capacity than AF. When CF and NDF are compared, it is observed that either of CF or NDF may outperform the other in different scenarios. This observation suggests that the sum capacity can be further improved by having each relay adopt its relaying strategy in helping different source nodes. We investigate this problem next and determine the optimum power allocation and relaying strategy for each source node that relay nodes assist. We observe that optimum power allocation for relay nodes with hybrid relaying strategies provides higher sum capacity than pure RDF, NDF, AF or CF relaying strategies.     

On the ergodic capacity of multi-hop wireless relaying systems

The ergodic capacity in Rayleigh fading of multihop wireless transmission systems employing either amplifyand- forward relaying or decode-and-forward relaying is studied, assuming channel state information is only known at the receiving terminals. Two upper bounds based on Jensen?s inequality and the harmonic-geometric means inequality as well as an infinite series representation for the ergodic capacity of an amplify-andforward multi-hop transmission system are derived. Numerical results are provided to examine the tightness of the upper bounds as well as to show the high accuracy of the infinite series approach. In addition, the ergodic capacity of a decodeand- forward multi-hop transmission system is obtained. It is shown that multi-hop transmission systems employing a decodeand- forward relaying scheme achieve higher ergodic capacities than multi-hop transmission systems with amplify-and-forward relaying schemes.     

Secrecy Analysis of Cooperative Vehicular Relaying Networks over Double-Rayleigh Fading Channels

In this paper, we investigate physical-layer security performance of the cooperative vehicular relaying networks, wherein the communication from a source vehicle to the destination vehicle is assisted by an amplify-and-forward (AF) relay vehicle in the presence of a passive eavesdropper vehicle. We assume that the communication links between the vehicles experience double-Rayleigh fading. We also consider two AF relaying protocols: (1) fixed gain relaying which requires partial channel state information (CSI), and (2) variable gain relaying which requires full CSI. Specifically, we derive the novel intercept probability and ergodic secrecy capacity expressions for both fixed and variable gain relaying in the presence of double-Rayleigh fading channels. The numerical and simulation results verify our theoretical and analytical findings, and show the impacts of channel conditions and relay and eavesdropper locations on the system secrecy performance.

     

MGF based performance analysis of dual-hop regenerative relaying IR-UWB systems

In this paper, a dual-hop regenerative cooperative relaying UWB communication system with detect-and-forward (DTF) and decode-and-forward (DF) in multipath channels is studied. The average system bit error rate (BER) and the system performance with DTF and DF relaying schemes are provided. The DF relaying with convolutional coding is employed in this cooperative relaying UWB system. Gaussian quadrature numerical method is used to obtain the moment-generating function (MGF) of the received energy. Our simulation results show the advantages of the DF based cooperative IR-UWB system over IEEE 802.15.3a channels.     

Optimal Relay Station Placement in Broadband Wireless Access Networks

To satisfy the stringent requirement of capacity enhancement in wireless networks, cooperative relaying is envisioned as one of the most effective solutions. In this paper, we study the capacity enhancement problem by way of Relay Stations (RSs) placement to achieve an efficient and scalable design in broadband wireless access networks. To fully exploit the performance benefits of cooperative relaying, we develop an optimization framework to maximize the capacity as well as to meet the minimal traffic demand by each Subscriber Station (SS). In specific, the problem of joint RS placement and bandwidth allocation is formulated into a mixed-integer nonlinear program. We reformulate it into an integer linear program which is solvable by CPLEX. To avoid exponential computation time, a heuristic algorithm is proposed to efficiently solve the formulated problem. Numerical analysis is conducted through case studies to demonstrate the performance gain of cooperative relaying and the comparison between the proposed heuristic algorithm against the optimal solutions.     

On the Intercept Probability of DF Relaying Wireless Communication

Wireless Personal Communications - In this work, we determine the probability of intercept for relaying wireless communication over Nakagami-m faded environment. An eavesdropper attempts to...