Angle random forwarding (AnRaF) for wireless sensor networks: performances and realization

A novel random forwarding protocol for distributed wireless sensor networks (WSN_s) is reported in this paper. The proposed protocol features the utilization of azimuth angle of the nodes involved and opportunistic selection of the relaying node via contention among neighbors. First, the protocol with precise angle information is discussed and its multi‐hop performance is evaluated by means of both simulation and analysis in terms of average number of hops to the sink node. Simulation results show that it performs well especially in network connectivity. As a complement, node mobility is also introduced to evaluate multi‐hop performance in real environments. Then, a simple MAC scheme to ensure that the node with the highest angular advantage will be selected as a relay is proposed, and subsequently energy and latency performances based on it are evaluated. It is shown that our protocol can effectively deliver data with half number of active neighbors required in geographical random forwarding (G_eR_aF). Finally, a practical method is presented to estimate azimuth angle, combined with which, our forwarding protocol is shown to achieve the performance very close to the case with precise angle information. Copyright © 2008 John Wiley & Sons, Ltd.     

Hierarchical modulation-based cooperation utilizing relay-assistant full-duplex diversity

In this paper, we present a hierarchical modulation-based cooperation (HMC) scheme to overcome capacity degradation due to half-duplex transmissions in conventional cooperative relay systems. In the HMC scheme, two relay terminals are used for both transmit and receive operations, i.e., full-duplex transmission. This scheme reduces the required number of time slots for cooperation. Utilizing this cooperative mechanism, the HMC scheme achieves cooperative diversity at the destination node by combining the signals delivered from the source and relay nodes. In addition, we derive a closed form of the end-to-end bit error rate for the HMC scheme, which is utilized to determine an optimal power ratio for hierarchical signals at the source node. In concurrence with the HMC scheme, we develop the best relay selection scheme for a practical wireless communication networks.     

A matrix key-distribution scheme

A new key-distribution scheme is presented. It is based on the distinctive idea that lets each node have a set of keys of which it shares a distinct subset with every other node. This has the advantage that the numbers of keys that must be generated is proportional to the number of nodes. Moreover, two nodes can start a session with virtually no delay. The scheme suits an environment where there is a certain level of trust among the insiders. The security property to an outsider remains identical to that of other existing schemes. Two versions of the scheme are given. Analysis of security and performance shows it is a practical solution to some key-distribution problems.     

基于萤火虫算法的多中继功率分配

为了充分实现中继协作,降低多中继协作通信系统功率分配优化问题的计算复杂度,提出了基于萤火虫算法的多中继功率分配方案。在一定的总功率和节点功率约束下,以最大化平均信噪比为优化目标函数,建立了多中继协作系统的功率分配最优化模型。选取该目标函数作为萤火虫的适应度函数,用向量表示萤火虫的状态,该向量的维数为待分配源节点和中继节点的个数,通过萤火虫聚集得到种群中最好的萤火虫,即可获得渐进最优功率分配。仿真结果表明,与平均功率分配相比,基于萤火虫算法的功率分配方案能降低2.44%~6.17%的比特差错率,提高了系统性能。     

Improved online fountain codes based on shaping for left degree distribution

In this paper, an improved encoding scheme for online fountain codes is proposed with the joint optimization of variable node degree and check node degree is proposed. The coding scheme can be divided into the build-up phase and the completion phase. In the build-up phase, left degree distribution is exploited to guarantee optimal performance phase by modifying the traditional coding scheme of choosing input symbols uniformly at random. A memory-based selecting of the source symbols is employed to decrease the number of connected components, which can thus produce the dimension increasement of the linear subspace of a decoding graph constructed in the build-up phase. The upper bound on coding overhead is also derived from the analysis of random graph theory. Compared with conventional online fountain codes, it can be seen from the simulation results that the proposed scheme can provide significant performance improvement with respect to both coding overhead and feedback cost. Moreover, the lower encoding/decoding complexities may make the proposed scheme more practical in energy-constrained applications such as distributed storage.     

Fuzzy logic based route optimization in a multihomed mobile networks

The present work is a fuzzy logic based route optimization in multihomed mobile network. The mobile routers in the mobile network use best egress determination algorithm to identify its best egress interface for each service type supported by the mobile network dynamically and send the best egress interface per service type information to a local fixed node inside the mobile network. The mobile network node sends a request message to the local fixed node inside the mobile network to initiate a session. The local fixed node uses best route selection algorithm to select an optimal route from mobile network to Internet for the desired service type of the mobile network node. The performance of the proposed work is evaluated using NEMO_SIM simulator which is implemented using JAVA. Results based on a detailed performance evaluation study are also presented to demonstrate the efficacy of the proposed scheme.     

认知无线电中基于中继位置和主用户位置的功率分配

针对认知无线电网络,提出了一种基于组间协作的联合直接传输和协作传输的传输机制,在满足干扰约束和峰值功率约束的情况下,通过分析瑞利衰落环境下放大转发协作单中继系统的性能,研究了中继位置和主用户位置对于系统的最优功率分配和系统吞吐量的影响,并对最优功率分配方案和等功率分配方案的性能进行了比较。仿真结果表明,中继位置和主用户的位置对于系统性能起着关键的作用,最优功率分配方案取得相对于等功率分配方案更优的性能,采用最优功率分配方案时,中继节点位于源节点和目的节点连线的中点且靠近认知用户时的系统性能最优。     

PHY-layer Fairness in Amplify and Forward Cooperative Diversity Systems

We deal with the concept of physical-layer fairness in amplify and forward cooperative diversity systems, which reflects the need for equally allocating the consumed power among the relays. To this end, we propose a method which utilizes knowledge on both the instantaneous and average channel conditions in order to encompass this concept, by attributing a weight coefficient to each relay depending on its average channel state and then selecting the relay with the best instantaneous "weighted" channel conditions. We also provide a performance analysis of the proposed scheme that includes an analytical expression for the outage probability, together with a closed form one in the high signal-to-noise-ratio (SNR) regime. Through the latter expression, the average symbol error probability (ASEP) for high SNRs is also derived. Numerical results demonstrate that, for small number of available relays or for high SNRs, the performance of the proposed scheme resembles that of the "best relay selection" scheme, in terms of outage probability and ASEP, despite maintaining the average power consumptions equal.     

基于限定域-蜂群的光纤物联网节点定位算法研究

为了实现物联网光纤感知层中待测节点的快速精确定位,提出了基于限定域-蜂群的节点定位算法,建立了针对光纤传感网络数据特点的节点定位模型,采用矩形限定域简化约束条件,从而提高定位精度。实验结果显示,当参考节点数大于3时,对定位平均误差的影响基本不变;当种群数取18时,定位平均误差趋于稳定,3种算法的平均定位精度分别是2.3 m、3.1 m和3.4 m;而达到定位精度需要的迭代次数分别是12次、15次和41次。由此可见,本算法在稳定性、定位精度及收敛速度方面均具有更好的定位性能,其在大范围物联网光纤感知层节点定位领域具有一定的实际应用价值。     

A novel link adaptation scheme to enhance performance of IEEE 802.11g wireless LAN

A novel link adaptation scheme using linear Auto Regressive （AR） model channel estimation algorithm to enhance the performance of auto rate selection mechanism in IEEE 802.11g is proposed. This scheme can overcome the low efficiency caused by time interval between the time when Received Signal Strength （RSS） is measured and the time when rate is selected. The best rate is selected based on data payload length, frame retry count and the estimated RSS, which is estimated from recorded RSSs. Simulation results show that the proposed scheme enhances mean throughput performance up to 7%, in saturation state, and up to 24% in finite load state compared with those non-estimation schemes, performance enhancements in average drop rate and average number of transmission attempts per data frame delivery also validate the effectiveness of the proposed schelne.     

Bayesian Fusion Performance and System Optimization for Distributed Stochastic Gaussian Signal Detection Under Communication Constraints

The problem of decentralized detection and fusion of a Gaussian signal is considered under the assumption of analog relay-amplifier local processing. It is shown that under an average global (system) power constraint, there always exists an optimal number of nodes that achieves the best possible performance under both orthogonal and nonorthogonal sensor-to-fusion center communication. Any increase in the number of nodes beyond the optimal value leads to degraded performance. This implies that each node needs to maintain a certain minimum received power level at the fusion center in order to make a useful contribution to the final decision. This is contrasted with the monotonic performance improvement observed under individual node power constraints as well as in the case of deterministic signal detection under a global power constraint. Three communication scenarios are studied in detail: 1) orthogonal; 2) equicorrelated; and 3) random signaling waveforms. In each case, error exponents and resulting bounds for Bayesian fusion performance are derived. A sensor system optimization method based on Bhattacharya error exponent, that leads to simple rules for determining the optimal number of nodes under a global average power constraint is also proposed     

Progressive image transmission over space-time coded OFDM-based MIMO systems with adaptive modulation

This paper considers a progressive image transmission system over wireless channels by combining joint source-channel coding (JSCC), space-time coding, and orthogonal frequency division multiplexing (OFDM). The BER performance of the space-time coded OFDM-based MIMO system based on a newly built broadband MIMO fading model is first evaluated by assuming perfect channel state information at the receiver for coherent detection. Then, for a given average SNR (hence, BER), a fast local search algorithm is applied to optimize the unequal error protection design in JSCC, subjected to fixed total transmitted energy for various constellation sizes. This design allows the measurement of the expected reconstructed image quality. With this end-to-end system performance evaluation, an adaptive modulation scheme is proposed to pick the constellation size that offers the best reconstructed image quality for each average SNR. Simulation results of practical image transmissions confirm the effectiveness of our proposed adaptive modulation scheme.     

Multiuser detection for DS-CDMA systems using evolutionary programming

This article introduces a new multiuser detection scheme which uses evolutionary programming (EP) to detect the user bits based on the maximum-likelihood decision rule. The major advantage of the proposed detector is that it has a lower computational complexity compared to other popular evolutionary-algorithm-based detectors. The simulation results show that the EP has always converged to the optimum solution with a small number of generations. The simulated average computational time performance demonstrates that this approach achieves practical ML performance with polynomial complexity in the number of users.     

Practical and secure localization and key distribution for wireless sensor networks

In many applications of wireless sensor networks, sensor nodes are manually deployed in hostile environments where an attacker can disrupt the localization service and tamper with legitimate in-network communication. In this article, we introduce Secure Walking GPS, a practical and cost effective secure localization and key distribution solution for real, manual deployments of WSNs. Using the location information provided by the GPS and inertial guidance modules on a special master node, Secure Walking GPS achieves accurate node localization and location-based key distribution at the same time. We evaluate our localization solution in real deployments of MicaZ. Our experiments show that 100% of the deployed nodes localize (i.e., have a location position) and that the average localization errors are within 1–2 m, due mainly to the limitations of the existing commercial GPS devices. Our further analysis and simulation results indicate that the Secure Walking GPS scheme makes a deployed WSN resistant to the Dolev-Yao, the wormhole, and the GPS-denial attacks, the scheme is practical for large-scale deployments with resource-constrained sensor nodes and has good localization and key distribution performance.     

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.     

Space-time cooperative diversity scheme using full feedback

This article proposes a new space-time cooperative diversity scheme called full feedback-based cooperative diversity scheme (FFBCD). In contrast to the conventional adaptive space-time cooperative diversity schemes that utilize the feedback from only the destination node, the new scheme utilizes the feedback from both the destination node and the cooperation node. With the feedback from the destination node, the occasional successful reception of the destination node in the information distribution stage can be detected, thus avoiding unnecessary retransmissions in the information delivery stage. The feedback from the cooperation node indicates the receiving state of the cooperation node in the information distribution stage, and the source node and the cooperation node will not perform cooperative retransmission during the information delivery stage unless the cooperation node is received successfully in the information distribution stage. In this way the new scheme can reduce the number of transmission attempt and improve the channel utilization. The expressions of the average number of transmission attempt are given. Numerical approximations and simulation results both show that the new scheme performs better than the non-cooperative scheme and the conventional adaptive space-time cooperative diversity scheme.     

基于随机集模型的MIMO-OFDM信道估计算法

在多径分量数确定的前提下,MIMO-OFDM系统采用传统的基于导频辅助和盲信道估计算法能获得较好性能。实际无线环境中,多径分量数目与幅度都是时变的,则传统信道估计方法不再适用。该文采用随机集理论建模MIMO-OFDM系统信道多径分量数的变化和MIMO信道。基于此模型提出了集中粒子空间重采样方法(CRS),在保留大概率粒子抽样样本的同时主动抛弃小概率抽样样本,以获得更为准确的真实样本逼近。并提出了基于集中重采样Rao-Blackwellised粒子滤波的信道估计方法(RBPFC)。仿真结果表明：所提出的RBPFC方法信道估计性能最好,基本Rao-Blackwellised粒子滤波方法次之但优于基本粒子滤波算法,卡尔曼滤波的信道估计方法性能最差。     

DF模式协同通信的节点选择策略研究

在协同网络中,为了解决如何从所有候选协同节点中选择适当的协同节点进行协同通信的问题,提出了一种基于DF模式的协同节点选择策略,即根据即时信道信息来选择最优的协同节点。理论分析和仿真结果证明,该选择策略能够获得良好的性能,且候选节点在不同位置时采用路径取小准则是最优的方案。     

基于节点选择的Turbo编码协同ARQ协议

文中给出了一种基于节点选择的Turbo编码协同ARQ(TC-ARQ)协议方案,并从理论上证明了采用基于节点选择的TC-ARQ协议相比传统的Turbo ARQ协议(T-ARQ)能获得更高的分集增益以及比非节点选择的协同ARQ协议更低的误帧率.仿真结果证实了该方案相对T-ARQ的优异性能,并仿真分析了节点数对节点选择性能增益的影响.     

Faster Algorithms for Construction of Recovery Trees Enhancing QoP and QoS

Medard et al. proposed an elegant recovery scheme (known as the MFBG scheme) using red/blue recovery trees for multicast path protection against single link or node failures. Xue et al. extended the MFBG scheme and introduced the concept of quality of protection (QoP) as a metric for multifailure recovery capabilities of single failure recovery schemes. They also presented polynomial time algorithms to construct recovery trees with good QoP and quality of service (QoS). In this paper, we present faster algorithms for constructing recovery trees with good QoP and QoS performance. For QoP enhancement, our O(n + m) time algorithm has comparable performance with the previously best O(n²(n + m)) time algorithm, where n and m denote the number of nodes and the number of links in the network, respectively. For cost reduction, our O(n + m) time algorithms have comparable performance with the previously best O(n²(n + m)) time algorithms. For bottleneck bandwidth maximization, our O(m log n) time algorithms improve the previously best O(nm) time algorithms. Simulation results show that our algorithms significantly outperform previously known algorithms in terms of running time, with comparable QoP or QoS performance.