无线城域网标准802.16的探讨

文章对802.16和802.16e网络结构进行了分析和比较,并对802.16标准的MAC层和物理层进行了详细的描述。     

一种新的基于跨层的Ad Hoc网络的MAC协议设计

为了提高Ad Hoc网络的性能,提出一种新的基于跨层的MAC协议,它能自适应的选择802.11b物理层规范中的两种不同的物理层数据单元格式进行传输。由于具有短导频的物理层数据单元格式比具有长导频的物理层数据格式占用更少的信道时间,基于跨层的MAC协议在一定条件下,采用具有短导频的物理层数据单元进行传输以减少物理层的开销,提高网络性能。其基本思想是如果需要通信的两个节点都支持具有短导频的物理层数据格式,则采用具有短导频的物理层数据格式进行传输,否则,采用具有长导频的物理层数据格式进行传输。同时提出一种自适应的网络分配向量计算算法,该算法能够根据MAC数据包的持续时间值判断节点是否支持具有短导频的物理层数据格式,不需要修改802.11b的帧格式。通过NS仿真证明,基于跨层的MAC协议能够提高网络的性能,如端到端的时延、吞吐量和传包率。     

IEEE802.16标准中的关键技术

文章介绍了无线城域网空中接口规范IEEE802．16标准,重点分析了媒体访问控制(MAC)层和物理层中的关键技术,以及标准中的QoS保证机制。     

一种新的增加Ad hoc 网络吞吐量的MAC协议设计

该文提出一种新的MAC协议,其目的是增加802.11b的网络容量。虽然IEEE的802.11b协议提供了较高的原始速率,但是物理层和MAC层随速率提高而引入的额外开销也不断增大。此外,物理层规范定义了两种物理层数据单元格式,但是研究者没有研究如何利用开销小的物理层数据单元来提高802.11b的容量。该文提出一种物理层自适应的算法,它能自适应地选择802.11b物理层规范中的两种不同物理层数据单元格式进行传输,并计算相应的网络分配向量。通过NS仿真证明,该协议能够提高网络的性能,如端到端的时延,有效吞吐量和传包率,特别是在高负载,高速率情况下。     

无线传感器网络的功率控制技术

文章介绍了功率控制技术在无线传感器网络中所起的作用,分析了功率控制对网络层、媒体访问控制(MAC)层和物理层性能的影响,在此基础上归纳出一种以提高网络能量效率为目的,同时能够减少物理层信号间的干扰、保障网络层网络的连通性、减少MAC层数据包竞争冲突率的跨层功率控制机制.     

一种新型的基于GSM1900标准的1.9GHz CMOS混频器

介绍了一种0.18μm CMOS工艺基于GSM1900(PCS1900)标准低中频接收机中的混频器.该混频器采用了一种新型的折叠式吉尔伯特单元结构.在3.3V电源电压、中频频率为100kHz的情况下,该混频器达到了6dB的转换增益,18.5dB的噪声系数(1MHz中频)和11.5dBm IIP3的高线性度,同时仅消耗7mA电流.     

IEEE 802．16的关键技术

介绍了IEEE 802.16(WiMAX)系列标准的发展并对其MAC层和物理层结构及关键技术进行了详细的阐述.概述了无线城域网中应用的其他先进技术,WiMAX的发展趋势.     

一种基于IEEE 802．11a的PHY—MAC跨层设计

文章基于IEEE802．11a协议,从理论上分析了物理层的编码速率、调制方式,以及MAC层的数据帧长度对吞吐率的影响,提出一种基于PHY和MAC层的跨层算法。仿真结果表明,文章提出的PHY-MAC跨层传输方案能显著提高系统的数据吞吐率。     

基于IEEE 802.16e的跨层上行调度架构设计

对IEEE 802.16标准的上行链路调度架构进行了研究,并联合MAC层和物理层,设计了一种跨层的上行调度结构,在满足移动性要求的同时增强了系统的QoS保障能力,使频谱利用率和吞吐量得到提高.     

HIPERLAN/2与IEEE802.11a物理层比较

目前,支持宽带多媒体通信的无线局域网(WLAN)正在发展和标准化,其中两个标准是由ESTI BRAN定义的HIPERLAN／2和由IEEE定义的802.11a。它们都可以提供54Mbps的数据速率。其主要不同在于它们的媒体控制层(MAC)层,很多文章都时此进行了详细介绍。对两个标准的物理层进行比较,得出它们的异同之处。     

Modeling and performance evaluation of the IEEE 802.15.4e LLDN mechanism designed for industrial applications in WSNs

The IEEE 802.15.4 standard has been introduced for low latency and low energy consumption in wireless sensor networks. To better support the requirements of industrial applications, where the use of this standard is limited, the low latency deterministic network (LLDN) mechanism of the IEEE 802.15.4e amendment has been proposed. In this paper, we develop a three dimensional Markov chain model for the IEEE 802.15.4e LLDN mechanism. Then, we estimate the stationary probability distribution of this chain in order to derive theoretical expressions of some performance metrics, as the reliability, energy consumption, throughput, delay and jitter. After that, we conduct a comparative study between the IEEE 802.15.4e LLDN and the IEEE 802.15.4 slotted carrier sense multiple access with collision avoidance (CSMA/CA). Numerical results show that the deterministic behavior of the LLDN mechanism significantly reduces the collision probability providing best performances in terms of reliability, energy consumption, throughput and delay compared to the IEEE 802.15.4 slotted CSMA/CA. Finally, the accuracy of our theoretical analysis is validated by Monte Carlo simulations.     

Cross-layer network formation for energy-efficient IEEE 802.15.4/ZigBee Wireless Sensor Networks

In IEEE 802.15.4/ZigBee Wireless Sensor Networks (WSNs) a specific node (called the PAN coordinator or sink) controls the whole network. When the network operates in a multi-hop fashion, the position of the PAN coordinator has a significant impact on the performance: it strongly affects network energy consumption for both topology formation and data routing. The development of efficient self-managing, self-configuring and self-regulating protocols for the election of the node that coordinates and manages the IEEE 802.15.4/ZigBee WSN is still an open research issue. In this paper we present a cross-layer approach to address the problem of PAN coordinator election on topologies formed in accordance with the IEEE 802.15.4. Our solution combines the network formation procedure defined at the MAC layer by the IEEE 802.15.4 standard with a topology reconfiguration algorithm operating at the network layer. We propose a standard-compliant procedure (named PAN coordinator ELection – PANEL) to self-configure a IEEE 802.15.4/ZigBee WSN by electing, in a distributed way, a suitable PAN coordinator. A protocol implementing this solution in IEEE 802.15.4 is also provided. Performance results show that our cross-layer approach minimizes the average number of hops between the nodes of the network and the PAN coordinator allowing to reduce the data transfer delay and determining significant energy savings compared with the performance of the IEEE 802.15.4 standard.     

An overview of the IEEE 802.15.4a Standard

This article presents the IEEE 802.15.4a standard, the first international standard that specifies a wireless physical layer to enable precision ranging. As an amendment to the popular IEEE 802.15.4-2006, the IEEE 802.15.4a-2007 standard introduces new options for the physical layer in order to support higher data rates, extended range, improved robustness against interference, and mobility, while enabling new applications based on distance information of the devices in a low-rate wireless personal area network.     

Efficient topology construction and routing for IEEE 802.15.4m-based smart grid networks

IEEE 802.15.4m TVWS Multi-Channel Tree PAN (TMCTP) standard that uses the vacant TV frequency of a region is the key to provide a flexible, scalable and cost-effective AMI smart grid networks. However, the performance of the IEEE 802.15.4m based AMI network can suffer from network interruption, varying transmission reliability and energy consumption problems due to the excessive number of channels and periodic channel scanning. To resolve these issues, we presented an enhanced IEEE 802.15.4m TMCTP called TVWS Orphan channel scanning with Multi-Channel Tree PAN Routing (TOMTPR). The proposed TOMTPR framework includes pilot-channel based Multi-Channel beaconing and interleaving-based TVWS orphan channel scanning. Furthermore, a capacity-aware routing tree is constructed during the neighbor discovery procedure. The proposed protocol suite is designed to provide compatibility with the IEEE 802.15.4 family standards with lower architecture complexity. The simulation results in presence of realistic AMI traffic and AMI network model show that TOMTPR can not only satisfy delay requirements of the AMI traffic, but also outperforms IEEE 802.15.4m TMCTP with IEEE 802.15.5 layer 2 mesh routing in terms of topology construction delay, end-to-end transmission reliability, and energy efficiency.     

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.     

An adaptive CSMA/TDMA hybrid MAC for energy and throughput improvement of wireless sensor networks

IEEE 802.15.4 as a standard for low rate wireless personal area networks (LR-WPAN) is an applicative choice for implementation of wireless sensor networks. Due to the advantages of this standard and its capabilities for more specification to wireless sensor networks, we were persuaded to resolve some of its proven weaknesses in such environments. The slotted CSMA/CA method utilized in beacon-enabled mode of 802.15.4 causes unacceptable level of energy consumption and throughput in conditions like high loads. To overcome these issues, we proposed an adaptable CSMA/TDMA hybrid channel access method by applying some modifications to the 802.15.4 standard. The energy and throughput improvement is achieved by dedicating a part of the contention access period to a time division medium access protocol (TDMA). To evaluate our proposed method in comparison with 802.15.4, we developed a simulation in OMNeT++. Analysis of the simulation results indicates general improvement of energy consumption and throughput. As a sensor network grows more populated or the load increases, the proposed method shows a better performance in comparison with IEEE 802.15.4 standard.     

Throughput and delay limits of chirp spread spectrum‐based IEEE 802.15.4a

The IEEE 802.15.4 standard is designed to provide a low‐power, low data rate protocol offering a high reliability. As an amendment to this standard, IEEE 802.15.4a introduces new options for physical layer to enable precision ranging. In this work, we analyzed the theoretical throughput and delay bounds of the unslotted version of chirp spread spectrum PHY‐based 802.15.4a. The formulae for transmission between one sender and one receiver for an ideal channel with no transmission errors are given. The throughput and delay bounds are derived for different frequency bands and data rates. Additionally, to measure spectral utilization, we measured the bandwidth efficiency for both the standards. We also compared our results with IEEE 802.15.4. The comparative analysis concludes that the performance of 802.15.4a exceeds 802.15.4 in terms of throughput and delay. The analytical results of throughput are verified by computer simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

On Analysis of the Contention Access Period of IEEE 802.15.4 MAC and its Improvement

The release of IEEE 802.15.4 medium access control (MAC) and physical layer specifications represents a significant milestone in promoting deployment of wireless sensor networks. This paper first analyzes the performance of the contention access period (CAP) specified in the IEEE 802.15.4 standard by integrating the discrete-time Markov chain models of the node states and the channel states. Then a modified CAP is analyzed, which could significantly improve the performance of the system. Based on the theoretical analysis of the CAP and the effect of the modification, we have that in the saturated network of IEEE 802.15.4, the collision probability is large, and the throughput is small. The main reasons are the employment of slotted carrier sense multiple access-collision avoidance and the mechanism that if a frame transmission cannot be completed before the end of the CAP, it has to wait until the start of the next CAP. Thus an enhanced collision-avoidance MAC protocol, which achieves a better performance and is compatible with the IEEE 802.15.4 standard, is proposed to improve the performance of the system. Extensive simulations validate our conclusions.     

A Subthreshold Low-Noise Amplifier Optimized for Ultra-Low-Power Applications in the ISM Band

The IEEE 802.15.4 standard relaxes the requirements on the receiver front-end making subthreshold operation a viable solution. The specification is discussed and guidelines are presented for a small area ultra-low-power design. A subthreshold biased low-noise amplifier (LNA) has been designed and fabricated for the 2.4-GHz IEEE 802.15.4 standard using a standard low-cost 0.18-mum RF CMOS process. The single-stage LNA saves on chip area by using only one inductor. The measured gain is more than 20 dB with an S₁₁ of -19 dB while using 630 muA of dc current. The measured noise figure is 5.2 dB.     

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.