Mitigation of mutual interference in IEEE 802.15.4-based wireless body sensor networks deployed in e-health monitoring systems

Wireless Networks - One of the main issues experienced in wireless body sensor networks (WBSNs) is the destructive impacts of “mutual interference” caused by neighboring WBSNs on each...     

Performance evaluation of IEEE 802.15.4 sensor networks in industrial applications

Wireless sensor networks have been widely applied in industrial applications especially since the release of IEEE 802.15.4 standard. By participating in an automobile project in which an IEEE 802.15.4 based sensor and actuator network is deployed to measure and control the vibrations of an automotive system, we need to study many metrics of IEEE 802.15.4 sensor networks (e.g., packet delivery rate, latency, and energy consumption) under various sampling rates. In order to provide detailed modeling of hardware and software as well as network behaviors on each sensor node, we conduct plenty of experiments on a SystemC‐based wireless sensor networks simulator IDEA1, which supports the hardware and software co‐simulation of sensor nodes with certain flexibility of abstraction level. Compared with the existing works on performance evaluation of IEEE 802.15.4 protocols, the main contributions of this paper are the comprehensive studies of both beacon‐enabled and nonbeacon‐enabled modes under various parameter settings and the beacon tracking synchronization mechanism in the IEEE 802.15.4 standard, which is ignored in most previous works. Additionally, the in‐depth analysis of simulation results enables us to find the best parameter configurations to different traffic loads and application requirements, which can be used as general experiences for other applications.Copyright © 2014 John Wiley & Sons, Ltd.     

IEEE802.15.4标准的无线传感器网络自组网方案

无线传感器网络需要低功耗短距离的无线通信技术,IEEE 802.15.4标准就是针对低速无线个人区域网络的无线通信标准,把低功耗、低成本作为设计的主要目标,由于IEEE 802.15.4标准定义的LR-WPAN网和无线传感器网络存在很多相似之处.所以把它作为无线传感器的无线通信平台.在分析LR-WPAN网的网络拓扑及形成过程的基础上,实现无线传感器网络的自组网方案.     

Emergency access mechanism in IEEE 802.15.4 for wireless body area sensor networks

IEEE 802.15.4 protocol has attracted much attention in research and industrial communities as candidate technology for wireless body area sensor networks (WBASNs). IEEE 802.15.4 supports the exclusive use of a wireless channel through guaranteed time slot (GTS). However, on one hand, bandwidth underutilization rate may be lower because of the variance between the guaranteed bandwidth and the arrival rate. On the other hand, the waiting time for transmitting emergency notification is getting longer when the GTSs assigned to the nodes increase in WBASNs. To solve these problems, in this article, a new scheme is proposed to reduce transmission delay for the alarm notification in emergent situations. Simulation results are presented to validate the efficiency of the proposed scheme by comparing it with the medium access control (MAC) protocol of IEEE 802.15.4.     

A survey of IEEE 802.15.4 effective system parameters for wireless body sensor networks

Wireless body sensor networks are offered to meet the requirements of a diverse set of applications such as health‐related and well‐being applications. For instance, they are deployed to measure, fetch and collect human body vital signs. Such information could be further used for diagnosis and monitoring of medical conditions. IEEE 802.15.4 is arguably considered as a well‐designed standard protocol to address the need for low‐rate, low‐power and low‐cost wireless body sensor networks. Apart from the vast deployment of this technology, there are still some challenges and issues related to the performance of the medium access control (MAC) protocol of this standard that are required to be addressed. This paper comprises two main parts. In the first part, the survey has provided a thorough assessment of IEEE 802.15.4 MAC protocol performance where its functionality is evaluated considering a range of effective system parameters, that is, some of the MAC and application parameters and the impact of mutual interference. The second part of this paper is about conducting a simulation study to determine the influence of varying values of the system parameters on IEEE 802.15.4 performance gains. More specifically, we explore the dependability level of IEEE 802.5.4 performance gains on a candidate set of system parameters. Finally, this paper highlights the tangible needs to conduct more investigations on particular aspect(s) of IEEE 802.15.4 MAC protocol. Copyright © 2015 John Wiley & Sons, Ltd.     

基于IEEE802．15．4实现无线语音通信

提出一种基于IEEE802.15.4的无线语音通信技术方案,该方案采用TI公司的CC2430芯片进行设计,充分利用CC2430 SoC的性能特点,使用的外围器件很少,很好地实现了短距离无线语音传输,具有成本低,音质较好的优点.     

移动Sink传感网中基于IEEE 802.15.4的拓扑控制与路由

针对查询驱动的移动Sink无线传感器网络,基于IEEE 802.15.4标准,提出了一个联合簇树组网和移动路由的跨层协议设计方案。以能耗、网络连通度、负载均衡和子树深度等指标为评价因子,在多目标优化模型下定义了一个拓扑综合评价函数,构建稳定的最优簇树网络结构;改进了IEEE 802.15.4 MAC中基于信标帧调度的分布式睡眠同步算法,维护较低占空比下的网络同步与拓扑修正;利用拓扑形成过程中依"最早信标帧"、"最好链路"、"最小层次"3种准则确立的父子关系,建立移动Sink与N-Hop范围内节点的双向路由路径。最终将上述MAC层的拓扑控制方案与网络层的查询路由方法完整实现于TinyOS协议栈中。实验结果表明,评价函数能够有效地反映组网质量,N-Hop后验式路由结合睡眠同步机制,在"最好链路"拓扑下表现出较高的能量效率。     

Accurate time synchronization of ultrasonic TOF measurements in IEEE 802.15.4 based wireless sensor networks

This paper discusses the problem of accurate time synchronization of wireless sensor networks (WSNs) used in applications in which a physical phenomenon must be monitored through periodical sampling. In some applications incorrect time synchronization can significantly degrade the system precision. This is for example the case of local positioning systems (LPSs) using ultrasonic time of flight (TOF) measurements for pseudorange estimation. The nodes clock drifts and the random variations of the start time used in each measurement are the two main error sources. In this work a Time Division Multiple Access (TDMA) synchronization algorithm is presented to overcome these problems for WSN using the IEEE 802.15.4 standard. The algorithm is able to compensate for the mentioned error sources in an easy and effective way. Experimental results for an implementation of an ultrasonic pseudorange measurement system between wireless nodes show the effectiveness of the proposed algorithm.     

Duty cycle learning algorithm (DCLA) for IEEE 802.15.4 beacon-enabled wireless sensor networks

The current specification of the IEEE 802.15.4 standard for beacon-enabled wireless sensor networks does not define how the fraction of the time that wireless nodes are active, known as the duty cycle, needs to be configured in order to achieve the optimal network performance in all traffic conditions. The work presented here proposes a duty cycle learning algorithm (DCLA) that adapts the duty cycle during run time without the need of human intervention in order to minimise power consumption while balancing probability of successful data delivery and delay constraints of the application. Running on coordinator devices, DCLA collects network statistics during each active duration to estimate the incoming traffic. Then, at each beacon interval uses the reinforcement learning (RL) framework as the method for learning the best duty cycle. Our approach eliminates the necessity for manually (re-)configuring the nodes duty cycle for the specific requirements of each network deployment. This presents the advantage of greatly reducing the time and cost of the wireless sensor network deployment, operation and management phases. DCLA has low memory and processing requirements making it suitable for typical wireless sensor platforms. Simulations show that DCLA achieves the best overall performance for either constant and event-based traffic when compared with existing IEEE 802.15.4 duty cycle adaptation schemes.     

Performance evaluation of an IEEE 802.15.4 sensor network with a star topology

One class of applications envisaged for the IEEE 802.15.4 LR-WPAN (low data rate—wireless personal area network) standard is wireless sensor networks for monitoring and control applications. In this paper we provide an analytical performance model for a network in which the sensors are at the tips of a star topology, and the sensors need to transmit their measurements to the hub node so that certain objectives for packet delay and packet discard are met. We first carry out a saturation throughput analysis of the system; i.e., it is assumed that each sensor has an infinite backlog of packets and the throughput of the system is sought. After a careful analysis of the CSMA/CA MAC that is employed in the standard, and after making a certain decoupling approximation, we identify an embedded Markov renewal process, whose analysis yields a fixed point equation, from whose solution the saturation throughput can be calculated. We validate our model against ns2 simulations (using an IEEE 802.15.4 module developed by Zheng [14]). We find that with the default back-off parameters the saturation throughput decreases sharply with increasing number of nodes. We use our analytical model to study the problem and we propose alternative back-off parameters that prevent the drop in throughput. We then show how the saturation analysis can be used to obtain an analytical model for the finite arrival rate case. This finite load model captures very well the qualitative behavior of the system, and also provides a good approximation to the packet discard probability, and the throughput. For the default parameters, the finite load throughput is found to first increase and then decrease with increasing load. We find that for typical performance objectives (mean delay and packet discard) the packet discard probability would constrain the system capacity. Finally, we show how to derive a node lifetime analysis using various rates and probabilities obtained from our performance analysis model.

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.     

Priority-based service differentiation scheme for IEEE 802.15.4 sensor networks

In sensor networks, data packets transmitted by different devices in home networking and industrial applications maintain different levels of importance. In this paper, we propose two mechanisms for IEEE 802.15.4 sensor networks to provide multi-level differentiated services which are required by each and every device. Mathematical model based on the discrete-time Markov chain is presented and is analyzed to measure the performance of the proposed mechanisms. Numerical results show the effects of the variation of contention window size and backoff exponent for service differentiation on 802.15.4 sensor networks. From the results, we derive that contention window size is more affective than backoff exponent on the saturation throughput while backoff exponent is more affective than contention window size on the average delay of every device. Simulation results are given to verify the accuracy of the numerical model.     

Performance evaluation of IEEE 802.11-based wireless LANs under finite-load conditions

Since its release in 1999, IEEE 802.11 became the defacto standard for Wireless Local Area Networks (WLANs). Despite its widespread deployment, analytical modeling efforts of the IEEE 802.11 standard have been focusing on the performance under saturated load conditions. This paper aims at analytically modeling and analyzing the performance of the IEEE 802.11-based networks. The model proposed in this paper follows exactly the real implementation of the DCF method. Extensive NS2 simulations are conducted to verify the results of the analytical model. Our model gives a new interpretation for the saturation behavior reported in the literature, relates the critical point (inflection point) to the various system and traffic parameters and analytically explains why the RTS/CTS mechanism is favorable for certain offered loads.     

On enabling cooperative communication and diversity combination in IEEE 802.15.4 wireless networks using off-the-shelf sensor motes

This paper presents the ‘Generalized Poor Man’s SIMO System’ (gPMSS) which combines two approaches, cooperative communication and diversity combination, to reduce packet losses over links in wireless sensor networks. The proposed gPMSS is distinct from previous cooperative communication architectures in wireless sensor networks which rely on a relay channel, and also distinct from implementations in 802.11 networks that require a wired infrastructure or hardware changes for cooperation. gPMSS foregoes the need for any changes to mote hardware and it works within the current IEEE 802.15.4 standard. We describe the gPMSS protocol that governs the cooperation between receivers. Three variants are evaluated including selection diversity, equal gain and maximal ratio combining. First, we demonstrate gPMSS on bit error traces in a fully reproducible manner. This is followed by an implementation of gPMSS in C# on the .NET Micro Framework edition of the recently released Imote2 mote platform. We demonstrate by means of experiments an increase in the packet reception rate from 22–30% to 73–76%, a relative increase of 150–245%. We also analyzed the power consumed by the transmitter per delivered packet and observe a reduction of up to 68%. We also take into account the retry limit of the IEEE 802.15.4 protocol and demonstrate that gPMSS is able to provide 99% packet delivery at the protocol’s default retry parameters against 65–75% without it.     

Optimal designs for IEEE 802.15.4 wireless sensor networks

This paper investigates the maximum achievable channel throughput in a single‐channel and single‐hop wireless sensor network using IEEE 802.15.4 Medium Access Control (MAC) protocol. We introduce a simple mean‐field approach to model the Carrier Sense Multiple Access with Collision Avoidance mechanism of the 802.15.4 MAC protocol under unsaturated conditions. We derive a set of expressions such as optimal sensing rate of a sensor node, its corresponding failure probability, and the channel throughput for both saturated and unsaturated networks. With those expressions, we propose several network designs to achieve the optimal throughput by choosing the appropriate MAC parameters. We validate the proposed optimal designs using ns‐2 simulations. Furthermore, we evaluate the network lifetime expectancy of the optimal designs and compare it with the lifetime of network settings under saturated conditions that use the default MAC parameters of IEEE 802.15.4. Copyright © 2011 John Wiley & Sons, Ltd.     

Analyzing and improving the energy efficiency of IEEE 802.15.4 wireless sensor networks using retransmissions and custom coding

This paper analyzes the performance of error control strategies in IEEE 802.15.4 wireless sensor networks. ARQ schemes of the IEEE 802.15.4 are used and also we propose custom coding using BCH codes. The performance is analyzed through simulation using the energy efficiency parameter. Performance results are obtained for multi-hop networks with different channel conditions and packet sizes. The results have shown that the ARQ scheme and BCH codes are energy efficient for networks with high number of hops and low values of signal-to-noise ratio.     

Traffic-aware stateless multipath routing for fault-tolerance in IEEE 802.15.4 wireless mesh networks

Wireless Networks - Single-path routing is widely used in wireless networks due to low resource consumption. However, it is vulnerable to link failure because such a failure may adversely affect an...     

On energy‐efficient aggregation routing and scheduling in IEEE 802.15.4‐based wireless sensor networks

In wireless sensor networks, continued operation of battery‐powered devices plays a crucial role particularly in remote deployment. The lifetime of a wireless sensor is primarily dependent upon battery capacity and energy efficiency. In this paper, reduction of the energy consumption of heterogeneous devices with different power and range characteristics is introduced in the context of duty scheduling, dynamic adjustment of transmission ranges, and the effects of IEEE 802.15.4‐based data aggregation routing. Energy consumption in cluster‐based networks is modeled as a mixed‐integer linear and nonlinear programming problem, an NP‐hard problem. The objective function provides a basis by which total energy consumption is reduced. Heuristics are proposed for cluster construction (Average Energy Consumption and the Maximum Number of Source Nodes) and data aggregation routing (Cluster‐based Data Aggregation Routing) such that total energy consumption is minimized. The simulation results demonstrate the effectiveness of balancing cluster size with dynamic transmission range. The heuristics outperform other modified existing algorithms by an average of 15.65% for cluster head assignment, by an average of 22.1% for duty cycle scheduling, and by up to 18.6% for data aggregation routing heuristics. A comparison of dynamic and fixed transmission ranges for IEEE 802.15.4‐based wireless sensor networks is also provided. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamic bandwidth management in IEEE 802.11-based multihop wireless networks

In this paper, we propose a new protocol named dynamic regulation of best-effort traffic (DRBT) which supports quality of service (QoS) throughput guarantees and provides a distributed regulation mechanism for best-effort traffic in multihop wireless networks. By adapting dynamically the rate of best-effort traffic at the link layer, DRBT increases the acceptance ratio of QoS flows and provides a good use of the remaining resources through the network. Our protocol also provides an accurate method to evaluate the available bandwidth in IEEE 802.11-based ad hoc networks which is able to differentiate QoS applications from best-effort traffic. Through extensive simulations, we compare the performance of our proposal scheme with some others protocols like QoS protocol for ad hoc real-time traffic for instance.     

Robust power control for IEEE 802.15.4 wireless sensor networks with round‐trip time‐delay uncertainty

This paper presents a novel, practically implementable robust Power Control (PC) technique that is generally applicable to a variety of IEEE 802.15.4 infrastructure and peer‐to‐peer wireless sensor networks (WSNs) where there is a round‐trip time‐delay uncertainty. In this methodology, robust stability and performance constraints are cast as a set of exclusion regions on the Nichols chart. The desired PC strategy is achieved through an iterative shaping of the system frequency response until these constraints are satisfied. A Smith Predictor (SP) is also adopted to mitigate the effects of time delay that occurs quite naturally in this type of problem. Such an approach is shown to be entirely appropriate for the discrete time controller design problem at hand. The designs are validated experimentally using a fully compliant 802.15.4 testbed where mobility is introduced using autonomous robots. This testbed provides a good basis for a formal comparison of the new approach against a number of existing strategies. Copyright © 2009 John Wiley & Sons, Ltd.