Polarization Diversity System for Mobile Radio

Conventional space diversity reception at typical elevated base locations requites separation of 30λ for broadside incidence and even more for in-line incidence and is therefore difficult to implement. A polarization diversity system for mobile radio is proposed. This is a two-branch receiver diversity system with the advantage that the base station antennas can be spaced as closely as desired. An experimental program has been carried out to obtain the statistical properties of vertically and horizontally polarized electromagnetic waves in a suburban environment at 836 MHz. It was observed that signals of both polarizations were Rayleigh plus log normal, where one is uncorrelated and other is correlated irrespective of base or mobile antenna spacings. The local means of the two signals were highly correlated and were with ± 3 dB for almost 90 percent of the time. Variation of base transmitter heights appeared to have little effect on the ratio of the local means of the two signals. The analysis and experiment demonstrated the feasibility of providing two diversity branches at UHF by polarization diversity.     

A Mobile Radio Single-Frequency "Two-Way" Diversity System Using Adaptive Retransmission from the Base

This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "twoway diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.     

Efficient Spectrum Utilization for Mobile Radio Systems Using Space Diversity

Space diversity combining is a well-known method of smoothing amplitude fluctuations of the received signal in Rayleigh fading environments, such as mobile radio. Perhaps less well known is that space diversity combining can also be an excellent method of combating cochannel interference. In this paper, it is shown that high spectrum efficiencies in mobile radio systems can be achieved with a modest number of space diversity branches. With a large number of diversity branches it is shown that frequency reuse is possible resulting in spectrum efficiencies, as defined herein, greater than 100 percent.     

移动通信中的分集接收技术和Rake接收机

由于移动环境的复杂性,无线信号在发送传输和接收过程中有很明显的衰落现象。通过分集接收技术在移动通信特别是第三代移动通信中的应用,介绍了传统Rake接收机和WCDMA中采用的典型Rake接收机的工作原理和结构框图。多径信号的每路信号都可能含有可以利用的信息,所以接收机可以通过接收多路信号来改善信噪比。Rake接收机算法就是通过多个相关接收器接收多径信号中各路信号,并把他们合并在一起,以此为原理基础的。     

移动通信系统中的软件无线电技术

软件无线电是在通用的、开放的硬件平台上采用软件技术来实现无线通信系统的各种功能的通信技术。本文介绍了软件无线电的基本概念、主要特点，分析了实现软件无线电的关键技术及其在第三代移动通信系统中的应用前景。     

HD Radio发射与接收系统

在世界范围内,主流的数字声音广播除了DAB和DRM外,近年来HD Radio技术在美国得到了快速发展,其他一些国家和地区也正在进行试验,做应用的准备.HD Radio技术是用在AM和FM中的IBOC(带内同频道)技术的发展与完善,尤其是应用在FM波段的FM HD Radio技术系统,可实现模拟与数字节目同播,可使模拟FM广播平滑过渡到数字广播,设备改造投资少.首先介绍了HD Radio技术的发展现状,着重阐述了发射与接收技术系统的构成与工作原理.     

Selection and MRC Diversity for a DS/CDMA Mobile Radio System through Nakagami Fading Channel

Spatial diversity is an attractive technology for coping with the fadingchannels encountered in mobile communications.In this paper, the bit error rate (BER) is analyzed theoretically fordiversity reception with a RAKE receiver in aNakagami fading environment using either selection or maximal ratio combining.A coherent binary phase-shiftkeying (CBPSK) direct sequence code division multiple access (DS/CDMA) systemis considered. An arbitrary branchcorrelation is also considered for any diversity order in the case ofidentical fading severity on the branches.     

未来移动通信系统中的无线资源管理

文章结合当前正在研究的后3代(B3G)、第4代(4G)移动通信系统的发展和处于运营及推广阶段的第3代移动通信系统,分析了未来移动通信系统中无线资源管理系统的关键技术,探讨了多体制标准下的无线通信网络和多种业务情况下的无线资源管理的研究方向。     

移动式12GHz DBS电视接收系统

在信息时代的今天,人们的活动尤为频繁,他们随时随地都想得到各种各样的信息,然而在乘坐汽车和火车等交通工具时,VHF和UHF广播电视的接收常常因建筑物等的遮挡而中断,同时VHF和UHF地面电波受传播距离的限制会影响正常接收。DBS电视接收则可克服上述缺点,而且没有因多径传输产生的重影失真。为了高质量地接收DBS广播电视信号,移动接收必须要有高性能的天线。这种天线要在全部接收时间内,始终精确地跟踪卫星波束。此外,这个接收系统从整体上来看,必须是坚固耐用,重量轻,特别是不能太高,以便在交通工具上安装。本文介绍的交通工具上装…     

Joint Detection and Diversity Techniques in CDMA Mobile Radio Systems

CDMA mobile radio systems suffer from intersymbol interference (ISI) and multiple access interference (MAI) which can be combated by using joint detection (JD) techniques. Furthermore, the time variation of the radio channels leads to degradations of the receiver performance due to fading. These degradations can be reduced by applying diversity techniques. Three suboptimum detection techniques based on matched filters (MF), zero forcing (ZF) and minimum mean square-error (MMSE) equalization are considered. For further improvements, switched and equal gain diversity techniques are employed to combat fading. The performance is depicted in terms of the average bit error probability versus the average SNR per bit in a single cell environment showing an appreciable improvement over the non diversity situation. Theoretical results for the SNR at the front end of the receiver and the BER for ideal channel are obtained and compared with the simulation results.     

A Multipath Fading Simulator for Mobile Radio

A simple device to simulate the Rayleigh distributed fast fading encountered in mobile radio is described and evaluated. The Rayleigh envelope statistics are obtained by adding two independent Gaussian noise source in quadrature. The theoretical spectrum of the received signal is approximated by shaping the spectrum of the noise sources with filters. A design is given whose performance is shown to agree very closely with theory.     

Frequency-Selective Fading Effects in Digital Mobile Radio with Diversity Combining

we analyze the effects of frequency-selective fading in a cellular mobile radio system that uses 1) phase-shift keying (PSK) with cosine rolloff pulses, and 2) space diversity with maximal-radio combining. The distorting phenomena with which we deal are multipath fading (which produces the frequency selectivity), shadow fading, and cochannel interference. The relevant quality measure is defined to be the bit error rate averaged over the multipath fading, denoted by (BER). The relevant system performance characteristic is defined to be the probability distribution for (BER), taken over the ensemble of shadow fadings and locations of the desired and interfering mobiles. To obtain numerical results, we use a combination of analysis and Monte Carlo simulation, invoke widely accepted models for the multipath and shadow fadings, and assume a cellular system with seven channel sets and centrally located base stations. The outcome is a set of performance curves that reveal the influences of various system and channel parameters. These include: the number of modulation levels (two or four), the diversity order, the shape of the multipath delay spectrum, and the standard deviation (or delay spread, τ0) of the multipath delay spectrum. Practical factors accounted for in these assessments include fading- and interference-related timing recovery errors and combiner imperfections. Our results highlight the importance of the ratiotau_{0}/T, whereTis the digital symbol period. They show that the delay spectrum shape is of no importance fortau_{0}/T leq 0.2, but can have a profound influence fortau_{0}/T geq 0.3. We also find that using 4-PSK leads to better detection performance, in certain cases, than using 2-PSK.     

移动终端的射频测试

测试是整个质量工程中的一个关键环节,发挥着越来越重要的作用.射频测试是终端测试的一项基本内容.本文描述了WCDMA射频电路的原理,阐述了移动终端射频测试的内容和方法.     

Outage Performance of QAM Digital Radio Using Adaptive Equalization and Switched Space Diversity Reception

Recently, the ability of anti-fading measures to reduce the outage which occurs on digital microwave radio links has been the subject of considerable study. Ideal and nonideal adaptive equalization in both the time and frequency domain have been evaluated for nondiversity reception using various performance criteria. Ideal adaptive equalization and space diversity reception have been considered using a recently published model of multipath fading on space diversity radio channels. In this paper, we determine the outage of 16-QAM and 64-QAM digital radio systems using adaptive slope equalization, finite-tap decision feedback equalization, and switched space diversity reception. The outage is evaluated by computing the probability of occurrence of those channel realizations which cause the bit error rate to exceed a critical value. The dependence of the outage prediction on the equalization method and the outage defining criterion is investigated by also considering ideal adaptive equalization and a signal-to-distortion ratio, respectively.     

一种基于集群计算的软件无线电接收系统实现

提出并实现了一种基于集群计算的实时软件无线电接收系统,对系统的硬件架构、软件组成和工作原理进行了详细描述.通过采用并行网络数据分发、高效负载均衡调度算法、两级并行计算等关键技术,系统数据流量最高可达200MB/s,最大处理信号带宽可达40MHz.实际运行表明,系统能够完成PSK、QPSK、8PSK、16PSK、mQAM等多种高速无线通信信号的实时接收和处理.     

DVB-T移动接收系统硬件设计

DVB-T移动接收系统硬件主要由DVB-T高频头、基于FPGA的TS码解复用模块和带USB2．0接口的51单片机3大部分组成。对基于MPEG-2的TS码结构以及程序特殊信息（PSI）中程序关联表（PAT）和程序映射表（PMT）的结构作了细致的分析，为FPGA中解复用模块的设计提供了理论基础。     

用于移动通信系统的发送分集技术

在分析接收分集技术最大比率接收合并(MRRC)方案的基础上，介绍了一种两分支发送分集方案。该方案采用2个发射天线、1个接收天线，可提供与1个发送天线、2个接收天线情况下的MRRC方案相同的分集增益。由于发送符号采用了正交性设计，该发送分集方案在接收端可以将不同的发送符号分离开来，分别进行最大似然检测。仿真结果表明，运用分集技术可大大改善无线通信系统的性能，且该方案和一发两收的MRRC方案性能相似、计算复杂性相同。该发送分集方案能更好地应用于移动通信系统。     

A Rectangular SRR Switched Slotted Microstrip Patch for Frequency Diversity Application

Planar antenna with a specific resonant mode is essential to meet the diversity demand for wireless communication. This paper presents modeling and experimental validation of a microstrip antenna design in which multiple resonant frequencies are excited based on different negative permeability response of the rectangular split ring resonator (SRR). The antenna geometry consists of a slotted patch with split ring resonator loaded between its two arms. The patch was fabricated on FR-substrate of relative permittivity ε_r?=?4.4, and has a size of 30.5 mm?×?34 mm. In the antenna desing, PIN diodes connect the outer ring and inner ring resonator of the SRR to the adjacent arms of the patch. Under various bias conditions, quad-band resonance was observed at 2.07 GHz, 2.11 GHz, 2.31 GHz, and 2.46 GHz. The measured S₁₁ results are found comparable to the simulated data, and demonstrate proper functioning of the proposed antenna with stable gain and radiation patterns.     

一种基于HARQ反馈的切换合并发送分集技术

本文提出了一种与HARQ相结合的天线选择发送分集方案,该方案利用HARQ的ACK/NAK信号作为天线选择指示,如果反馈ACK则继续使用当前天线,否则切换到下一个天线.仿真表明,在低速情况下,新方案相比单天线系统有显著的分级增益,与传统的选择分集相比,能节约反馈,简化系统,同时性能损失不大.     

一种分布式无线移动通信系统中远端天线单元动态选择模型

分布式无线移动通信系统中,远端天线单元的选择方案将影响移动通信系统的性能。该文基于软切换中激活集的思想,提出了一种远端天线单元动态选择模型,模型依据平均接收信号强度阈值以及延迟计数器确定激活集状态,而阈值由移动台运动速度决定。文章对模型作了详细的理论分析,并经过仿真证明了模型的合理性。