一种新的自适应OFDM算法的探讨

在具有多径干扰的无线信道中仅应用传统OFDM既影响通信速率,也浪费资源.由于信道的频率选择性衰落,OFDM系统的每个子信道具有不同的传输能力.文中提出一种计算量较小、简单实用的自适应OFDM算法,在保证通信质量所需BER的前提下,按照各个子信道衰落程度动态的分配比特和功率,使所需要的发射总功率最小.仿真结果表明,采用该自适应OFDM算法可以提高OFDM系统的性能.     

一种TR-UWB系统的改进型自相关接收机性能分析

TR-UWB系统采用自相关接收检测技术作为一种非最优接收机,其结构简单、性能优良。对TR-UWB系统的自相关接收检测技术进行改进,通过合并有限数目多径信号以提高接收信号能量,同时对接收信号做平均处理抑制噪声,从而提高系统性能。采用高斯近似法得到系统的误码率,最后在多径信道环境下进行仿真,验证了接收机性能的改进和误码率分析的正确。     

UHF频段陆地卫星移动通信业务多径效应测量

UHF测段陆地卫星移动业务多径实验于1999年6月至8月间利用日本GMS140E气象卫星为信标,分别在河南郑州至开封高速公路、林州至上党方向公路以及石家庄至阳泉高速公路段进行。地面接收系统和数据处理设备安置于汽车上。此项实验的目的是为地面卫星移动通信系统的设计提供重要的信道参数。本文给出了不同环境下多径效应的累计分布特性以及相应的预测模型。     

ATM‐based wireless broadband access in the local loop

Broadband networks using wireless transmission techniques are a quick and flexible means of implementing subscriber access. Unoccupied frequency bands with sufficient bandwidth to allow the transmission of digital signals at very high bit rates are found only in the microwave bands. Because the path loss is fairly high at these frequencies, the diameter of radio cells is limited to a maximum of a few kilometres. This results in a microcellular system, which is best implemented in the form of a point‐to‐multipoint system, where one radio‐base station serves all subscribers registered in that radio cell. An interactive, broadband, ATM‐based radio local loop has undergone successful trials in Munich. Copyright © 2001 John Wiley & Sons, Ltd.     

空时联合均衡水声数据检测仿真研究

水声信道的衰落特性对单传感器数据检测性能影响较大。本文采用空间分集技术，结合判决反馈均衡器，即进行空时联合均衡，实现了水声多径衰落信道的数据检测仿真，分析了检测性能，并给出了均衡算法参数的选取方法。仿真结果表明，当信道出现衰落时，单通道数据检测效果较差，而通过空时联合均衡可以使检测误码率显著降低，提高了水声传输系统的可靠性。     

Performance Improvement by Microdiversity for Wideband Signals in Frequency Selective Fading Indoor Channels with Co-Channel Interference

A comprehensive analytical bit-error-rate (BER) model is presented to analyse the performance of antenna-microdiversity for wideband BPSK modulated signals in the frequency selective fading multipath channel, specified by its complex impulse response. The model includes the disturbance by intersymbol interference (ISI) and co-channel interference (CCI), as well as the channels' impact on the carrier phase- and clock recovery in the receiver. The channel impulse responses at the antenna elements are determined by taking into account the direction of arrival of the individual paths. Computational BER- and SNIR-gain results (SNIR = signal-to-noise+interference-ratio) show that a substantial performance improvement is achieved with antenna combining for wideband signals which suffer ISI and/or CCI. For the indoor multipath channel with exponentially decaying power delay profile, the performance enhancement is compared for several antenna combining schemes. Quasi-coherent equal gain combining (QCEGC) is proposed as an novel EGC scheme based on a less accurate phase estimation technique. For wideband signals, QCEGC shows a slight performance degradation when compared to maximal ratio combining or minimum mean square error combining (MMSEC), but has a much lower implementation complexity. In the channel with CCI, where the best performance is achieved with MMSEC, QCEGC performs very poor.     

一种能量有效的多径Ad Hoc网路由算法

这里研究了一种能满足服务质量(QoS,Quality of Service)需求的能量有效的多路径多速率路由算法EAMM,该算法能结合节点地理位置、延迟时间、丢包率和剩余能量信息,选择符合要求的若干条路径,满足数据传输的可靠性和实时性要求,为不同应用的数据提供不同等级的可靠性和实时性传输质量。仿真结果显示,该算法不仅能保证各等级可靠性和实时性的数据传输,还能均衡网络的能量消耗,延长了网络的生存时间。     

An Extended Dynamic Source Routing Scheme in Ad Hoc Wireless Networks

In this paper we consider a multipath extension to the dynamic source routing (DSR) protocol proposed by Johnson and Maltz, an on-demand routing protocol for ad hoc wireless networks. This extension keeps two node-disjoint paths between the source and destination of a routing process without introducing extra overhead. Unlike other multipath extensions where node-disjoint paths are selected at the destination or at the reply phase, our approach generates two node-disjoint paths during the query phase of the route discovery process by restricting the way the query packet is flooded. Several optimization options are also considered. Simulation is conducted to determine the success rate of finding node-disjoint paths.     

一种监测站多径检测和校正的新技术研究

监测站是卫星导航系统的核心部分,提供给主控站的原始测量数据精度决定着整个导航系统的定轨与时间同步精度,影响着系统的服务性能。多径和天线相位中心的变化是监测站高精度测距不可忽略的影响因素。采用一套基于高增益、抗多径面天线的多径检测和校正系统,定量地评估监测站的多径环境,并对接收机天线的相位中心和多径进行校正。通过多径检测与校正原型设施,开展阵列天线相心标校、多径检测与标校等试验,为监测站的天线相心与多径环境检测、抑制和校正提供一个完整的解决方案。     

改进的构造函数盲均衡算法研究

以提高通信信号质量和降低其受多径效应的影响为背景,介绍了恒模算法(CMA)及构造函数算法(CF算法),并在此基础上针对其不足作了相应的改进,提出分数间隔修正构造函数盲均衡算法(FSE-MCF)。对改进算法的均衡性能进行了仿真,仿真结果分析可知,新算法与CF算法相比较,在相同信噪比条件下可以进一步减小稳态误差,加快收敛速度,有较好的均衡性能。