A high-performance MIMO OFDM wireless LAN

Tremendous consumer interest in multimedia applications is fueling the need for successively higher data rates in wireless networks. Data rates in wireless wide area networks are limited by the need to address wide coverage, vehicular mobility, and the limitations of licensed spectrum. Thus, data rates in WWANs continue to lag advances in wireless local area networks by orders of magnitude. There are valuable lessons to be learned from the design of WLANs that provide data rates in excess of hundreds of megabits per second. Several technologies are instrumental in enabling the future of high-performance WWANs, including multiple transmit and receive antennas, OFDM, closed loop transmission control, and low-latency MAC operation. We describe a MIMO WLAN design and prototype that exploits these attributes to provide data rates in excess of 200 Mb/s above the MAC     

Turbo processing for an OFDM-based MIMO system

We consider improving the overall system performance of an orthogonal frequency-division multiplexing-based multiple-input multiple-output (MIMO) wireless local area network system. We use a combined iterative detection/decoding and channel updating method, referred to herein as turbo processing, to improve performance. First, we improve a recently proposed list sphere decoder-based iterative MIMO soft-detector by constraining the value of the a priori information from a soft-in soft-out channel decoder. Second, we propose a channel updating scheme using the decoded packet data to improve the channel estimation accuracy. Simulation results show that turbo processing can be used to significantly improve the performance of the system considered.     

Reducing feedback load for OFDM-based wireless system

In this paper, the feedback load reduction problem in wireless systems based on orthogonal frequency division multiplexing (OFDM) is investigated and an opportunistic feedback scheme (OFS) is proposed. The key idea behind OFS is that only the key channel gains which can significantly affect the system throughput are fed back to the BS. Firstly, the key channel gains are proved to belong to a channel gain interval. Secondly, a statistical method is proposed to estimate the channel gain interval. Thirdly, the opportunistic feedback scheme is formulated and the feedback load of OFS is analyzed. The advantage of OFS is threefold: the first is OFS can work in both OFDM-based multicast system and OFDM-based unicast system. The second is the channel fading type of the BS-user link is not required, which is more realistic. The third is OFS can get better feedback load performance compared with other schemes, while achieving almost the same throughput performance compared with that of full feedback scheme.     

基于OFDM的宽带MIMO信道容量研究

研究在发射端和接收端两端都分布有散射体的情况下基于OFDM的MIMO信道容量,推导了归一化信道功率情形下信道容量的上限,分析了各种参数对容量的影响,仿真结果表明:MIMO-OFDM信道容量不仅受到天线数目的限制,同时还受到延时扩展、簇角度扩展、相邻天线间距等因素的影响。     

无线MIMO系统中天线选择技术的算法

针对多天线需要多射频链路带来的高硬件成本,分析了低复杂度的MIMO天线选择的必要性,介绍了递增天线选择算法、递减天线选择算法和改进的递增递减天线选择算法.链路仿真结果表明:递增递减算法可以快速选择出使系统容量最大的天线子集,该算法简单易于实现,计算速度快,获得的结果非常接近穷尽搜索方法得到的结果.     

一种便携式无线监控的实现

为了实现一种价格低廉、便携式无线监控系统来满足智能家居的应用要求。采用一种无线路由作为终端,在手机上开发APK作为客户端接收显示视频数据,在终端上编译安装SDK包,配置内核USB摄像头的驱动,并改写内核的USB摄像头驱动程序使其支持摄像头的使用。实验结果表明,可以在安卓系统手机上运行APK自动连接路由器发出的Wi Fi信号,实现视频数据的清晰监控。     

一种应用于无线通信系统的MIMO天线

MIMO系统是通过不同的分集技术,以实现在相同带宽和发射功率的条件下大幅改善系统容量和可靠性,减小信道失真。作为系统关键模块之一的天线,则要求有着好的分集特性,并接收较多的这波。这里提出的MIMO天线工作在2．4GHz,天线单元是等边三角形贴片天线。三角形天线的宽波瓣可以使MIMO天线接收更丰富的多径这波,与天线单元的高增益相结合能较好改善MIMO系统的SNR和抗干扰能力。通过对天线端口间的互耦和相关性分析,该系统能实现好的极化和方向图分集,获得高的分集增益。     

Fair Radio Resource Allocation for MIMO OFDM-based Multicast Systems

This paper investigates the problem of resource allocation in a multiple-input multiple-output (MIMO) OFDM-based system, wherein multiple multicast groups exist. Multicasting is a transmission technique which enables a transmitter to communicate via a single wireless link with multiple receivers simultaneously. Moreover, the presence of multiple antennas in both transmitter and receiver enhances significantly the system spectral efficiency. MIMO technology along with multicasting offers major advantages to wireless systems. However, optimum exploitation of these technologies adds significant complexity to the system which makes very difficult any possible practical implementation. Another important issue of such systems is their capacity to ensure to all users a certain level of QoS. To that end, we propose a low complexity fair resource allocation algorithm aiming at ensuring a certain amount of resources to all users when multicasting is applied. Validation of the proposed solution is achieved through extensive simulation and it is compared to other multicast schemes for MIMO systems which exist in literature. Numerical results and complexity analysis show the feasibility of the proposed algorithm.     

Performance of the 19-GHz high-speed wireless LAN system

This paper describes a new high-speed wireless LAN system in the 19-GHz band. This system features a maximum throughput of 15.2 Mbit/s, which is faster than Ethernet's. To achieve high speed wireless data transmission, we propose the new global scheduling multiple access (GSMA). This system consists of a control module (CM) and some user modules (UMS). One CM can communicate with up to ten UMs. This GSMA, in which all data transmission is managed in the CM, has both short-length and long-length frames, and concatenates multiple packets, so that it performs well with light traffic and heavy traffic: with minimal delay. For high-speed transmission and easy construction, DQPSK/differential detection is used as a modulation/demodulation scheme, and both FEC and ARQ are adopted as the error control method. In addition, as a countermeasure to shadowing and multipath fading, the CM has an omnibeam antenna, and each UM uses a 12-sector antenna, and sector selection diversity is carried out at the UM. This wireless LAN system is based on the RCR STD-34A Japanese radio system standard     

PAPR effect remedy in OFDM-based wireless systems

An enhancement proposition for a Terrestrial Digital Video Broadcasting (DVB-T) systems is discussed in this work. DVB-T physical layer uses a powerful technique namely Orthogonal Frequency Division Multiplexing (OFDM) technique, which has been used to combat the channel’s effect. However, it has a major drawback that degrades its efficiency; namely Peak-to-Average Power Ratio (PAPR). Two criteria have been used for this purpose; BER curves and CCDF curves in order to distinguish the powerfulness of those propositions in reducing the PAPR effect. In fact, a powerful special averaging technique results are compared to previously published propositions, namely based on wavelet transformations and the one that is based on the pulse width modulation. A mathematical model has been drawn in order to check both of the CCDF and the BER curves, and simulated at same channel limitations and specifications. The proposition gives extra 35% noise immunity over our previously published work that is based on entropy wavelet, and an enhancement of over 25% from the CCDF point of view in combatting the PAPR. Furthermore, a complexity reduction has been attained by decreasing the side information transmission in compared with the work in the literature.     

一种基ARM7的无线局域网 MAC片上系统架构

提出了一种ARM7TDMI核和先进微控制器总线架构的无线局域网MAC控制器片上系统方案,对各个组成模块进行了详细描述,并从设计复杂度、功耗、性能等方面对其该方案和其他方案进行了分析和比较.     

Distributed fair scheduling in a wireless LAN

Fairness is an important issue when accessing a shared wireless channel. With fair scheduling, it is possible to allocate bandwidth in proportion to weights of the packet flows sharing the channel. This paper presents a fully distributed algorithm for fair scheduling in a wireless LAN. The algorithm can be implemented without using a centralized coordinator to arbitrate medium access. The proposed protocol is derived from the Distributed Coordination Function in the IEEE 802.11 standard. Simulation results show that the proposed algorithm is able to schedule transmissions such that the bandwidth allocated to different flows is proportional to their weights. An attractive feature of the proposed approach is that it can be implemented with simple modifications to the IEEE 802.11 standard.     

设计和仿真无线局域网设备天线

对带有开关电路的2.4 GHz极化分集印刷天线进行电磁场及电磁场与电路协同仿真 通过采用极化分集技术,可以用低成本PCB基片制造具有良好接收机性能的无线局域网设备(WLAN)天线.本文将描述如何使用最新的三维电磁场(EM)仿真工具来设计和仿真一对2.4GHz正交极化的印刷偶极子天线,同时预测表面电流和相关的远场辐射图.     

Low-latency handover in a wireless ATM LAN

The micro- and picocellular architectures proposed for wireless ATM LANs lead to wireless terminals frequently changing their point of attachment to the network. Because ATM connections have quality of service (QoS) guarantees which must be maintained, handover must be as seamless as possible. We present a novel architecture and protocol which primarily aims to keep the interruption period due to handover low, rather than seeking to keep the process entirely lossless. We compare the tradeoffs made, with those in other schemes from the literature, and give quantitative results from an implementation of our scheme on a 10 Mbits/s^-1 prototype wireless ATM LAN     

Large-scale wireless LAN design

The design of a large-scale wireless LAN poses a number of interesting questions. Building the Wireless Andrew network at Carnegie Mellon University has given us the opportunity to deal with these questions. This article describes the approaches we have developed for the design of similar networks. A large-scale wireless LAN must be designed so that all of the target space has radio coverage (i.e., there are no coverage gaps). It must also be designed so that its capacity is adequate to carry the expected load. These requirements generally can be met by using the proper combination of access point locations, frequency assignments, and receiver threshold settings     

基于分布式MIMO矿井无线通信系统的研究

针对矿井巷道的特殊环境以及无线通信问题,通过MIMO系统和分布式天线系统,建立了井下分布式MIMO信道模型。仿真结果表明,分布式MIMO系统具有更高的信道容量。基于分布式天线的灵活设置,分布式MIMO系统既提高了频谱利用率又减少了信号盲区,最终扩大了井下信号覆盖范围,提高了整个系统的信道容量。     

基于分布式MIMO矿井无线通信系统的研究

针对矿井巷道的特殊环境以及无线通信问题,通过MIMO系统和分布式天线系统,建立了井下分布式MIMO信道模型。仿真结果表明,分布式MIMO系统具有更高的信道容量。基于分布式天线的灵活设置,分布式MIMO系统既提高了频谱利用率又减少了信号盲区,最终扩大了井下信号覆盖范围,提高了整个系统的信道容量。     

瑞利衰落时MIMO无线通信系统分集性能分析

针对多输入多输出（MIMO）无线通信系统提高系统性能的同时增加了系统的复杂度，提出了基于最大特征值传输的分集解决方案，在天线数量一定的情况下最大可能的提高系统的分集增益。对单输入多输出和多输入多输出的情况进行了数学分析，推导出了系统性能的变化范围，并且对分析的结果进行了数值仿真。     

MIMO水下无线光通信系统性能解析研究

为了消除海洋湍流引起的信号衰落和衰减,在基 于BPSK调制的水下无线光通信(underwater wireless optical communication,UWOC)系统中引入了MIMO(multi-input multi-outpu t)技术。在 假设海洋湍流模型为log-normal分布基础上,得出了球面波光束在弱海洋湍流传输的闪烁 指数计算公 式。借助于Gauss-Hermite正交积分近似公式,推导了UWOC系统分别采用SISO(single-in put single-output)、SIMO(single-input multi-output)、MIMO三种技术,且接收端 采用等增益合并法时, 系统误码率(bit error rate,BER)的解析公式。应用此解析公式,数值仿真观察了系统 误码率在不同 的信噪比下受三种海洋参数(即均方温度耗散率,单位质量液体中的湍流动能耗散率,温度 和盐度波 动的相对强度)以及系统通信距离的影响。仿真结果表明,UWOC系统采用MIMO技术,在较小 的 均方温度耗散率、较小的温度和盐度波动的相对强度、较大的湍流动能耗散率的海洋中,以 及通过较 短的通信链路都可以得到更优的误码率性能。