无线激光DH-PIM室内通信系统性能分析

研究了加性高斯白噪声和多径码间串扰下采用双头脉冲间隔调制(DH-PIM)的无线激光室内通信系统的性能,对DH-PIM系统的符号结构、带宽、差错率特性等方面进行了分析,并与OOK,PPM和DPIM调制方式做了比较。     

The Maritime Satellite Communication Channel--Channel Model, Performance of Modulation and Coding

Towards the year 2000, maritime satellite communications using the INMARSAT system will employ a second and third generation of satellites and new ship earth stations (SES). The new SES standards will use very small antennas with gains between 0 and 15 dBi. At the lower end of SES there will be no antenna stabilization. The communication channel for such small stations is described by a model including multipath fading, Doppler shift, and noise. The results of an extensive measurement program were used to determine the parameters of the channel model, which depend on antenna type and elevation angle. Analytical calculations as well as synthetic and stored channel hardware simulations have been used to determine the performance of several modulation schemes. A complete data link using PSK modems with AFC/Costas loop, interleaving, and FEC codecs at 1.2 kbits/s was built up around a hardware maritime channel simulator, to study the performance of data transmission on the small SES maritime channel. Theoretical and measured results are given for interleaved Viterbi decoding with channel state information and Reed-Solomon codes. The measurements show that with interleaved FEC schemes, the requiredE_{b}/N_{o}for a BER 10^-5is in the range of 9-15 dB and the effects of multipath fading are almost compensated for.     

Source coding, channel coding and modulation techniques used in theDigiCipher system

The DigiCipher high-definition television (HDTV) system, an all-digital approach that achieves full HDTV performance with error-free reception in a single 6-MHz television channel is described. The DigiCipher HDTV system is based on discrete cosine transform coding and uses motion prediction techniques to eliminate redundancy in the digital signal, channel equalization to defeat multipath, and error correction to defeat noise and interference. The source signal, source coding, channel coding, modulation, and performance of the system are discussed     

Application of coding and diversity to UHF satellite soundbroadcasting systems

Results are presented of a study of alternative means by which to reduce the required link margins in a satellite sound broadcasting system, thus improving the economic feasibility of the service and increasing the possibility of sharing a radio-frequency allocation with terrestrial services. Propagation models are presented that account for the effects of shadowing and multipath in the operating environments. Comparisons are made of the performance that results using time, frequency, and space diversity to moderate the effects of shadowing and multipath for vehicular and portable receivers. It is shown that space diversity has the broadest applicability in restoring the channel performance that would otherwise be degraded by Rayleigh fading channels and by quasistationary AWGN (additive white Gaussian noise) channels. Example link budgets are given for candidate satellite sound broadcasting system designs that use analog FM and digital modulation techniques     

Hybrid DS/SFH-SSMA with predetection diversity and coding overindoor radio multipath Rician-fading channels

The authors investigate the bit-error-rate (BER) performance of hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access (DS/SFH-SSMA) systems operating over a multipath Rician-fading channel (which models indoor radio propagation in factories). They consider both phase-shift-keying (PSK) modulation with coherent demodulation and differential phase-shift-keying (DPSK) modulation with noncoherent demodulation. Predetection multipath diversity (maximal ratio combining for coherent reception and equal gain combining for noncoherent reception) and simple interleaved channel coding are employed for improving the BER performance. The BER of both coherent and noncoherent hybrid systems is obtained using a Gaussian interference approximation     

一种新的短波数传调制体制

本文提出一种利用短波信道传输数据时能够抗衰落抗多径的新方案——多频相位组合编码结合跳频（ＭＦＰＣＣ／ＦＨ），讨论了ＭＦＰＣＣ／ＦＨ编码原理和性能，介绍了ＭＦＰＣＣ／ＦＨ调制解调器的实现方法。     

Diversity of modulation?a new concept in communication technology

A new concept called `diversity of modulation? has been presented. Its purpose is to reduce the fading range of the signals received through a time-varying multipath transmission medium. A digital-communication system with N-order diversity utilising this concept has also been described, and its performance is compared with the conventional diversity systems.     

Performance of a TDM/TDMA portable radio link for interference,noise, and delay spread impairments

Presents the measured/simulated performance of a time division multiplexing/time division multiple access (TDM/TDMA) portable radio link for noise, interference and delay spread impairments. The radio link transmits short TDMA bursts of 82 symbols at 450 kbits/sec using 4QAM. This modulation is also referred to 4PSK, but phase shift modulation is constant envelope. Nyquist filtering of quadrature signal components yields quadrature amplitude modulation which, of course, also contains π/2 phase variations at the sampling instants. Demodulation is performed by a low-overhead digital coherent demodulator with 2-branch selection diversity. The port or base has two receivers for diversity but the portable or handset uses only a single receiver to perform selection diversity. Signal-to-noise ratio and signal-to-interference ratio performance of the link was measured for a stationary channel and for a channel with different fading rates. In a Rayleigh fading environment, increasing the fading rate causes only a small performance degradation. The results also show that selection diversity is effective against interference in a slow Rayleigh fading environment. A separate set of experiments were performed to measure the effects of delay-spread on the link. Selection diversity is effective in reducing the word-error ratio floor caused by frequency-selective fading. As a result, relatively high data rates can be supported by a multipath fading channel without using adaptive equalization. Thus, a portable radio communications system using low complexity hardware design incorporating selection diversity can achieve good performance     

基于虚拟仪器的数据链测试模拟器研制

针对传统数据链测试设备功能单一且不易重构的问题,借鉴虚拟仪器模块化的设计思想,设计实现了一种基于美国国家仪器公司（National Instruments,NI）通用软件无线电平台的数据链测试模拟器。该模拟器采用线性调频信号叠加（Sum of Linear Frequency Modulation,SoLFM）的方法高效产生具备连续相位的时变信道衰落,包括瑞利衰落、莱斯衰落和对数正态衰落等,并结合多相滤波思想能够精确模拟数据链长时延的多径传播场景。利用矢量网络分析仪对硬件模拟器输出的信道传递函数和信道冲激响应进行实测验证,并对各支路的随机信道衰落包络分布进行统计验证。实测结果表明,该数据链测试模拟器输出的信道函数和统计分布均与理论值吻合,因而可用于数据链装备的系统优化、验证和性能评估。     

Angle diversity for nondirected wireless infrared communication

We outline the benefits and challenges of using angle diversity in nondirected wireless infrared (IR) communications systems. Multiple transmitter beams and multiple narrow field-of view receivers reduce the path loss, multipath distortion, and background noise of the channel, which leads to improved range. We also discuss practical considerations for multielement angle diversity systems, including channel characterization and suboptimal detection techniques. Maximal-ratio combining provides nearly optimal performance up to 100 Mb/s for the angle diversity systems considered. The design and performance of a prototype angle diversity IR communication system are discussed. The prototype can maintain 70 Mb/s at a P_e of 10^-9 over a 4-m range     

Transmission of high rate ATM packets over indoor radio channels

The design and performance of a high data rate modem that transmits asynchronous transfer mode (ATM) packets over indoor radio channels is discussed. A discrete Fourier transform (DFT)-based multicarrier modulation technique is used to mitigate intersymbol interface (ISI) caused by a multipath spread of up to 250 ns. A rate one-half channel code is used to combat fading. Computer simulation is performed to investigate the system performance for five different multipath intensity profiles. The system performance is compared using a differentially coherent scheme and a coherent scheme based on channel estimation. The effects of carrier frequency offset and some of the hardware nonlinearities are discussed. Using various channel codes, an signal-to-noise ratio (SNR) of 14-21 dB is required at an average bit error rate (BER) of 10^-5 to transmit a total of 155 Mb/s data over a bandwidth of 280 MHz     

高码率无线红外室内传输系统的通信性能

讨论仿真室内的红外漫射通信系统,并观测在提高系统传输码率情况下无线红外室内通信系统的性能。系统使用NRZ的OOK调制,在室内环境下,采用漫反射传输会导致多径效应,而多径传输又必然会带来码间干扰,因此采用均衡器来减弱码间干扰对系统性能的影响。仿真结果显示高码率无线红外室内通信的可行性。     

On Schemes for Multriate Support in DS-CDMA Systems

Different modulation schemes supporting multiple data rates in a Direct Sequence Code Division Multiple Access (DS-CDMA) system are studied. Both AWGN and multipath Rayleigh fading channels are considered. It is shown that the multi processing-gain scheme and the multi-channel scheme have almost the same performance. However, the multi-channel scheme may have some advantages due to easier code design and multiuser receiver construction. The drawback though, is the need for linear amplifiers also in mobile terminals. A multi-modulation scheme is also possible, but the performance for the users with the high data rates are significantly worse than for the other schemes. Furthermore multi chip-rate, parallel combinatory spread spectrum (PC/SS), pulse position modulation (PPM) and variable duty cycle schemes are discussed briefly.     

Performance analysis of a wireless multirate direct-sequence CDMAusing fast Walsh transform and decorrelating detection

We analyze the performance of a flexible multirate scheme for direct-sequence code division multiple-access (CDMA) mobile radio systems. The proposed scheme uses a variable processing gain serial pseudonoise modulation as a multirate strategy. To reduce the interference effects, the CDMA system utilizes the coherent fast Walsh transform transmission technique. The proposed scheme can be used in the reverse link (mobile-to-base station) of the upcoming third-generation wide-band CDMA system (has the feature of coherent reverse link). We analyze the system performance with and without using a decorrelating multiuser detector. The uncoded bit-error probability (BEP) with and without decorrelating detection on a multipath fading channel is derived analytically. In addition, the validity of the analysis results is demonstrated by computer simulations using the IMT-2000 vehicular multipath channel model. In order to make sure that the proposed processing techniques do not distort the soft values at the demodulator output, the proposed multirate scheme is also simulated in case of using turbo codes. The turbo-coded BEP is calculated for different user data rates and different number of decoding iterations     

Multicarrier transmission in a mobile radio channel

A multicarrier modulation system designed for communication in a multipath, mobile radio channel is described. The effect of introducing channel coding is investigated and the improvement in BER performance is shown. A comparison is made between the modulation schemes of DPSK and DQPSK     

Design considerations for broadband indoor infrared wireless communication systems

Recently there has been a growing interest in using infrared light for broadband indoor wireless communications. There are two major limitations for establishing a wideband infrared communications link. The first and most important limit is the power requirements of such a link. The second important impairment is the intersymbol interference caused by multipath dispersion. In this paper we address the issue of designing an optimized transmission system to provide the best power efficiency for an infrared link. Important parameters that should be considered for this design and some examples of efficient link designs are discussed. The suggested designs can improve the power efficiency of an indoor infrared link up to 4 to 8 dBo while providing a smaller rms delay spread, more robustness to shadowing and a more uniform distribution of power. Characteristics of the indoor infrared channel depends upon the directions of the receiver. This dependency can be used in designing a direction diversity receiver to decrease the rms delay spread of the received signal and to reduce the effects of noise by using proper combining techniques. We discuss the effects of receiver direction and field-of-view on the channel parameters and suggest a configuration for a direction diversity receiver.     

Performance evaluation of baseband OOK for wireless indoor infraredLAN's operating at 100 Mb/s

We investigate 100 Mb/s wireless nondirectional infrared communication in the indoor environment using baseband nonreturn-to-zero (NRZ) on-off keying (OOK) modulation. We show that intersymbol interference induced by multipath propagation impairs detection efficiency. Analytical and simulation results on specific channels demonstrate that an adaptive decision-feedback equalizer adapted according to the least-mean-squares algorithm recovers most of the performance degradation. We also evaluate the performance of a timing-recovery phase-locked loop operating independent of the adaptive equalizer; showing that it quickly and accurately determines the sampling phase with negligible performance degradation. We discuss effective methods of mitigating low-frequency noise induced by fluorescent lighting. We present a packet-based communication method and describe its features and performance. Our results support the feasibility of communication at 100 Mb/s over the infrared channel     

Gigabit/s indoor wireless systems with directional antennas

The design of a high speed (>150 Mb/s) wireless local area network (WLAN), requires that many factors be considered, including technical, economic, and regulatory. A major technical factor is the channel response behavior (multipath) in the indoor environment as a function of the frequency band, building type and radio system architecture. The consequences of designing indoor wireless systems with directional antennas at one or both ends of a line-of-sight (LOS) link are investigated. We determine how narrow the beamwidth must be so that the maximum data rate is not limited by multipath effects. For such beamwidths, simple unequalized two-level frequency shift keying (FSK) or phase shift keying (PSK) modems can be used in place of the more costly and complex “anti-multipath” modems, and data rates above 1 Gb/s may be achieved. The channel impulse response in an empty room is estimated using geometrical optics, observing that with directional antennas, multipath rays must arrive from the same direction as the LOS ray. The link outage probability is then estimated as a function of the antenna beamwidth, and guidelines are established for the selection of the frequency band and antenna placement. Experiments using a 19-GHz 622-Mb/s binary phase shift keying (BPSK) link and 15° beamwidth horn antennas in an office building with plaster walls and large metallized windows have demonstrated error-free performance on both LOS and non-LOS (NLOS) links     

Trellis-coded modulation on digital microwave radiosystems-simulations for multipath fading channels

The application of trellis-coded modulation to reducing the effects of residual interference levels encountered on multipath fading channels after adaptive equalization in high capacity digital microwave radio systems is investigated. Simulations used to derive error performance curves and outage probabilities are discussed. The results indicate that trellis-coded modulation offers performance improvements in addition to those offered by adaptive equalization     

High-Rate Direct-Sequence Spread Spectrum With Error-Control Coding

High-rate direct-sequence (DS) spread spectrum is a modulation technique in which most or all of the spreading is provided by nonbinary data modulation. For applications to mobile ad hoc wireless networks, the limited processing gain of high-rate DS spread spectrum gives only modest protection against multiple-access or multipath interference, which limits the applicability of the modulation technique to fairly benign channels. In this paper, we explore the increased interference-rejection capability that can be obtained from convolutional coding with Viterbi decoding, Reed–Solomon coding with errors-and-erasures decoding, and block product coding with iterative decoding. For channels with multiple-access or multipath interference, performance results are given for several soft-decision decoding metrics, the benefits of adaptive-rate coding are illustrated, and the accuracy and utility of the Gaussian approximation are described. We also show how to use the bit-error probability for a system without error-control coding to determine which modulation method will give the best packet-error probability in a system with error-control coding.