射频供能无线传感器网络高能效数据收集方案

在射频供能无线传感器网络中,提高网络能效和吞吐率是一个重要的研究问题.该文统筹考虑信道分配、节点的能量阈值以及MAC（Medium Access Control）帧分块重传机制,提出高能效和高吞吐率的数据收集方案;推导了节点的充电时间、节点传输一个MAC帧的平均能耗和平均时延、网络能效和吞吐率,定义了网络效用函数,形成了最大化网络效用的优化问题.通过调整效用系数并求解优化问题,可以获得使网络能效和吞吐率最大化的最优能量阈值和MAC帧最优分块个数.仿真结果表明,所提方案的能效和吞吐率高于已有方案.     

An Energy-Efficient and Collision-Avoidance MAC Protocol with Pre-scheduling for Wireless Sensor Networks

In this paper, we propose energy efficient MAC protocols for data gathering tree structure. The basic concept of the proposed protocol is that it reduces traffic overloads in low depth nodes by introducing full sleep state for one frame. To maximize network performance, we only control traffic from non-relay nodes which are leaf nodes in the tree. We introduce a new superframe structure for pre-scheduling to alleviate contentions and packet collisions between children nodes. In addition, leaf nodes go into a full sleep mode for one superframe in heavy traffic loads by using control packets, which results in a considerable reduction of energy consumption at low depth nodes. Simulation results show the proposed protocol saves more energy and achieves better packet delivery ratio compared to the DMAC with a moderate increase of a latency performance.     

A Channel Adaptive ACK Mechanism in High Rate Wireless Personal Area Networks

In IEEE 802.15.3 wireless personal area networks, the acknowledgement (ACK) mechanism has significant impact on the overall throughput. In this paper, we propose a channel adaptive ACK (CA-ACK) mechanism where an ACK is selectively transmitted depending on wireless channel conditions to maximize the data throughput. Specifically, an ACK is transmitted only when the frame error rate is greater than a pre-defined threshold; this threshold is derived for a given payload size and data rate using developed analytical models. Simulation results demonstrate that CA-ACK improves the throughput adaptively to varying channel conditions.     

分布式Alamouti空时码的信道容量及最优资源分配方案

该文针对基于译码转发协议的分布式Alamouti空时码(DF-DASTC)系统的信道容量以及最优资源分配策略问题。利用退化中继信道模型,推导得到了DF-DASTC系统在衰落信道下的信道容量闭式解。以DF-DASTC信道容量最大化为目标,对该系统在固定带宽分配时,中继及信源节点的最优功率分配方案进行了研究,推导得到了DF-DASTC系统的最优功率分配方案的闭式解。利用凸优化理论,将以DF-DASTC信道容量最大化为目标函数的多目标优化问题转换为非线性不等式约束的单目标凸优化问题,进一步得到了可变带宽分配时的DF-DASTC系统的最优带宽和功率分配策略。理论分析和系统仿真表明,该文所提出的资源分配策略,比平均分配的资源方案具有更大的信道容量。另外,该文的最优资源分配策略适用于具有多个中继节点的无线中继网络,具有普适性。     

EETP-MAC: energy efficient traffic prioritization for medium access control in wireless body area networks

Wireless body area network (WBAN) has witnessed significant attentions in the healthcare domain using biomedical sensor-based monitoring of heterogeneous nature of vital signs of a patient’s body. The design of frequency band, MAC superframe structure, and slots allocation to the heterogeneous nature of the patient’s packets have become the challenging problems in WBAN due to the diverse QoS requirements. In this context, this paper proposes an Energy Efficient Traffic Prioritization for Medium Access Control (EETP-MAC) protocol, which provides sufficient slots with higher bandwidth and guard bands to avoid channels interference causing longer delay. Specifically, the design of EETP-MAC is broadly divided in to four folds. Firstly, patient data traffic prioritization is presented with broad categorization including Non-Constrained Data (NCD), Delay-Constrained Data (DCD), Reliability-Constrained Data (RCD) and Critical Data (CD). Secondly, a modified superframe structure design is proposed for effectively handling the traffic prioritization. Thirdly, threshold based slot allocation technique is developed to reduce contention by effectively quantifying criticality on patient data. Forth, an energy efficient frame design is presented focusing on beacon interval, superframe duration, and packet size and inactive period. Simulations are performed to comparatively evaluate the performance of the proposed EETP-MAC with the state-of-the-art MAC protocols. The comparative evaluation attests the benefit of EETP-MAC in terms of efficient slot allocation resulting in lower delay and energy consumption.

     

无人机辅助车联网的网络传输链路优化

无人机(UAV)通信技术的快速发展与智能车联网应用需求的极速增长促进了无人机辅助车联网系统的产生与发展。在无人机辅助车联网系统中,如何节省能量的同时最大化系统性能对于能量有限的节点十分重要。基于此,本文主要考虑无人机辅助车联网通信过程中如何选择最优的通信网络链路,从而最大化能量效率的问题。首先建立通信网络链路选择问题为混合整数规划问题,然后提出基于能量效率最大化的网络传输链路优化算法获得最优的传输链路及对应的能量分配,最后通过数值实验仿真验证了所提算法的有效性。     

多带UWB优先级竞争接入饱和吞吐量优化方法

采用二维马尔可夫链模型,计入了超帧中的标记期和硬预留,对系统中的同一优先级竞争接入站点在差错信道下的饱和吞吐量进行研究。分析表明,信道质量较差时短帧比长帧的系统饱和吞吐量大。理论计算结果与NS2软件仿真结果在误差范围内相一致。差错信道条件下存在最优传输帧长,为优化链路控制,提高系统吞吐量提供了理论依据。     

Four-dimensional Markov chain model of single-hop data aggregation with IEEE 802.15.4 in wireless sensor networks

This paper introduces a new 4D Markov chain model for IEEE 802.15.4 wireless transmission, which corrects and extends an existing 3D model, providing more accurate and comprehensive results. It also introduces an analytical technique for calculating both the pdf and mean of the number of timeslots required to complete all transmissions, when a set of nodes contend for the channel at the beginning of a superframe. It is assumed that transmission takes place in beacon mode but without acknowledgement (NACK mode). The model can be used to determine the optimum value of the MAC attribute macSuperframeOrder (SO) required for saving energy, and the shortest delay required to receive all transmitted packets with a specified probability. It can also specify an upper threshold on the number of nodes and the packet length required, in order to achieve acceptable end-to-end delay. The potential creation of a traffic model for the aggregated data generated by the coordinating node is also discussed.     

Energy-efficient performance of cooperative relay network with joint sensing-transmission time duration and power allocation

A joint optimal sensing-transmission time duration and power allocation scheme has been proposed to maximize the energy efficiency for cooperative relay network.In particular,observing that the spectrum sensing and data transmission time duration lies within a strict interval,the joint optimal solutions of our proposed scheme are achieved by sequential optimization method.Numerical evaluation results reveal that the relay-assisted transmission using our proposed scheme significantly outperforms the non-relay transmission in terms of the network energy-efficiency.     

基于能量采集异构蜂窝网络的功率分配算法研究

针对能量采集异构蜂窝网络,由于能量到达和信道状态的随机性导致离线功率分配算法只能取得理论最优,本文提出了一种在线功率分配算法.算法在每个时隙开始时,基站控制器通过能量判别选出满足开启条件的小蜂窝基站,然后采用基于拉格朗日乘子的两层迭代算法对所选择的小蜂窝基站分配发射功率,能够实际最大化系统在每个时隙的能效.仿真表明在满足基站开启条件的情况下,所提算法可以为密集异构网络提供更高的能量效率.该算法适用于信道状态和能量状态不可预测的网络.     

Quasi‐optimal power allocation based on ergodic capacity for wireless relay networks

Half‐duplex amplify‐and‐forward (AF) transmissions may result in insufficient use of degrees of freedom if they always use the cooperative mode regardless of the fading states. In this paper, we investigate the conditions under which cooperation offers better performance and the corresponding optimal power allocation during cooperation. Specifically, we first derive an expression of ergodic capacity and its upper bound for an AF cooperative communication system with n relay nodes. Secondly, we propose a novel quasi‐optimal power allocation (QOPA) scheme to maximize the upper bound of the derived ergodic capacity. For the QOPA scheme, the cooperative mode is only adopted when the channel gain of source‐to‐destination is worse than that of relay‐to‐destination. Moreover, we analyze the performance of the system with QOPA scheme when the relay moves, which is based on the random direction model, in a single‐relay wireless network. For a multi‐relay AF network, we compare the ergodic capacity and symbol error rate, corresponding to the proposed QOPA and equal power allocation schemes, respectively. Extensive simulations were conducted to validate analytical results, showing that both ergodic capacity and symbol error rate of the system with QOPA scheme are better than those of the system with equal power allocation scheme in a multi‐relay AF network. Copyright © 2011 John Wiley & Sons, Ltd.     

Joint Channel Allocation and Power Control Optimal Algorithm Based on Non-cooperative Game in Wireless Sensor Networks

In order to reduce the wireless sensor network interference, and balance the network energy consumption, we have established a joint channel allocation and power control optimal game model. The model takes the network interference, and the residual energy of nodes as the parameters. What’s more, the model considers the independent and influencing relation between channel allocation and power control. In addition, we design a joint channel allocation and power control optimal algorithm based on non-cooperative game (JCAPGA), and then prove that JCAPGA converges to Nash equilibrium. Simulation results show that, JCAPGA has a good network performance of lower interference and uniform energy consumption.     

多标签无线供电反向散射通信网络能效优化算法

为了提高物联网(IoT)节点的运行周期和能量利用率,该文提出一种多标签无线供电反向散射通信网络能效最大化资源分配算法。考虑传输速率约束、能量收集约束以及发射功率约束,建立了基于系统能效最大化的资源分配模型。利用Dinkelbach理论、2次变换以及变量替换法,将原分式非凸问题转化为可求解的凸优化问题。通过拉格朗日对偶理论求得优化问题的全局最优解。仿真结果表明,该算法具有较好的收敛性和能效。     

Study of an adaptive frame size predictor to enhance energy conservation in wireless sensor networks

Technological advances in low-power digital signal processors, radio frequency (RF) circuits, and micromechanical systems (MEMS) have led to the emergence of wirelessly interconnected sensor nodes. The new technological possibilities emerge when a large number of tiny intelligent wireless sensor nodes are combined. The sensor nodes are typically battery operated and, therefore, energy constrained. Hence, energy conservation is one of the foremost priorities in design of wireless sensor networks (WSNs) protocols. Limited power resources and bursty nature of the wireless channel are the biggest challenges in WSNs. Link adaptation techniques improve the link quality by adjusting medium access control (MAC) parameters such as frame size, data rate, and sleep time, thereby improving energy efficiency. In This work, our study emphasizes optimizing WSNs by building a reliable and adaptive MAC without compromising fairness and performance. Here, we present link adaptation techniques at MAC layer to enhance energy efficiency of the sensor nodes. The proposed MAC uses a variable frame size instead of a fixed frame size for transmitting data. In order to get accurate estimations, as well as reducing the computation complexity, we utilize the extended Kalman filter to predict the optimal frame size for improving energy efficiency and goodput, while minimizing the sensor memory requirement. Next, we designed and verified different network models to evaluate and analyze the proposed link adaptation schemes. The correctness of the proposed theoretical models have been verified by conducting extensive simulations. We also prototype the proposed scheme with the MAC protocol on Berkeley Motes. Both prototype and simulation results show that the proposed algorithms improve the energy efficiency by up to 15%.     

Energy-efficient data sensing and routing in unreliable energy-harvesting wireless sensor network

Energy-harvesting wireless sensor network (WSN) is composed of unreliable wireless channels and resource-constrained nodes which are powered by solar panels and solar cells. Energy-harvesting WSNs can provide perpetual data service by harvesting energy from surrounding environments. Due to the random characteristics of harvested energy and unreliability of wireless channel, energy efficiency is one of the main challenging issues. In this paper, we are concerned with how to decide the energy used for data sensing and transmission adaptively to maximize network utility, and how to route all the collected data to the sink along energy-efficient paths to maximize the residual battery energy of nodes. To solve this problem, we first formulate a heuristic energy-efficient data sensing and routing problem. Then, unlike the most existing work that focuses on energy-efficient data sensing and energy-efficient routing respectively, energy-efficient data sensing and routing scheme (EEDSRS) in unreliable energy-harvesting wireless sensor network is developed. EEDSRS takes account of not only the energy-efficient data sensing but also the energy-efficient routing. EEDSRS is divided into three steps: (1) an adaptive exponentially weighted moving average algorithm to estimate link quality. (2) an distributed energetic-sustainable data sensing rate allocation algorithm to allocate the energy for data sensing and routing. According to the allocated energy, the optimal data sensing rate to maximize the network utility is obtained. (3) a geographic routing with unreliable link protocol to route all the collected data to the sink along energy-efficient paths. Finally, extensive simulations to evaluate the performance of the proposed EEDSRS are performed. The experimental results demonstrate that the proposed EEDSRS is very promising and efficient.     

Efficient Patient Care Through Wireless Body Area Networks—Enhanced Technique for Handling Emergency Situations with Better Quality of Service

Wireless body area networks (WBAN) is a wireless network of sensors placed in and around the human body for monitoring the patient conditions remotely. The goal of WBAN networks is to report the patient condition to the monitoring system with maximum reliability and minimum delay and deliver the life critical data in the emergency situation with utmost priority. The proposed MAC protocol is aimed at delivery of emergency packets with maximum reliability and minimum delay through the introduction of mini slots in the beacon enabled superframe for exclusive transmission of the same. To improve the packet delivery ratio of the normal packets and decrease the energy consumption of the low data rate nodes, a packet rate based scheduled slot allocation is added to this protocol. Extensive simulations show that the proposed protocol is able to achieve nearly 98% packet delivery ratio and less than 100 ms delay for emergency packets. By varying the number of allocated scheduled slots based on the packet rate of the nodes, the proposed protocol has shown improved performance in the packet delivery ratio (93%) of normal packets as compared to IEEE 802.15.6 (85%), also the energy consumption of low data rate nodes has decreased by 64%. The results show that the proposed protocol is successful in realizing much better delay and packet delivery values for emergency and normal packets.     

面向混合业务的无线传感器网络能量有效接入策略

研究了在实时业务和非实时业务同时存在的混合背景下,非实时业务的无线传感器节点自适应侦听和睡眠的动态接入机制。网络节点处于睡眠状态时所需的能量很低,节约了无线传感器网络节点的平均能量消耗;但是,过长的睡眠时间可能使得网络节点错失传输机会。因此,根据信道的使用情况,合理地设定无线传感器网络节点的睡眠时间,能够在网络能量消耗和传输效率之间进行调整,从而最大化无线传感器网络的能量传输效率。首先,利用连续时间 Markov 方法对问题进行建模,并利用基于摄动分析理论对系统模型进行分析,获得求解无线传感器网络能量效率最大化的最优睡眠时间梯度算法。最后通过理论结果和计算机仿真模拟的对比,验证了推荐方法的可行性。     

Optimal Resource Allocation for Data Service in CDMA Reverse Link

The optimal resource allocation policy is studied for non-real-time users in CDMA reverse link. The resource allocation policy of interest includes channel coding, spreading gain control and power allocation under the conventional receiver operation. The constraints in the optimization include peak transmit power of the mobile station, total received power at the base station and QoS in the form of minimum SINR for each user. The coding and spreading gain control can be separated from the power allocation strategy. Our results show that the optimal power allocation policy depends on the objective function: a greedy policy is optimal to maximize the sum of throughput from each user, whereas a fair policy is optimal to maximize the product of throughput from each user. A unified approach is taken to derive the optimal policies, and it can also be applied to other power allocation problems in CDMA reverse link. Numerical results of the channel capacity are presented for both objectives along with the effect of QoS constraints.     

TDMA scheduling design of multihop packet radio networks based onlatin squares

Many transmission scheduling algorithms have been proposed to maximize spatial reuse and minimize the time division multiple access (TDMA) frame length in multihop packet radio networks. Almost all existing algorithms assume exact network topology information and require recomputations when the network topology changes. In addition, existing work focuses on single channel TDMA systems. In this paper, we propose a multichannel topology-transparent algorithm based on latin squares. The proposed algorithm has the flexibility to allow the growth of the network, i.e., the network can add more mobile nodes without recomputation of transmission schedules for existing nodes. At the same time, a minimum throughput is guaranteed. We analyze the efficiency of this algorithm and examine the topology-transparent characteristics and the sensitivity on design parameters by analytical and simulation techniques     

A performance review of out-of-frame detection schemes for DS1signals

A basic framework is given for performance comparisons of several frame detection schemes used to identify individual channels within a DS1 digital transmission system in either the superframe (SF) or extended superframe (ESF) format. Key criteria include mean misframe times, out-of-frame detection times, reframe times, tolerance to error bursts and application considerations. Through the use of Markov chain models, analytical solutions for the mean misframe and out-of-frame detection times are derived in terms of the bit error ratio and frame period. Performance comparisons of several frame detection schemes in various error conditions are made