城市微区角度色散移动信道特性的建模与仿真

城市微蜂窝数字移动通信网无线电信道的一个非常重要的传播特征就是多径传播环境结构所造成的电波入射角度色散。这种现象是移动台在随机游走过程中，由于周围随机分布的复杂建筑结构和随机变化的人为及自然环境使得经过等效反射路径到达接收机的电波入射角度随着移动速度而产生的其分布不断变化的任意扩散结果。因此角度色散信道是在多普勒效应的作用下伴随着频率色散而出现的，而对其信道特性进行研究的关键就是了解各种传播环境下的电波入射角分布结构。本文在研究角度色散信道传播特性理论模型的基础上，构造了一种用代表其信道物理量的特征参数表示任意传播信道电波入射角分布的一般结构模型，并根据这种入射角分布模型来研究和分析在不同城市环境中移动无线电多径色散信道的信号传播特性，最后通过计算机模拟仿真进一步分析了不同的电波入射角角度分布对信道传播特性的影响。     

A versatile wave propagation model for the VHF/UHF rangeconsidering three-dimensional terrain

A polarimetric wave propagation model for field strength forecasting and coverage prediction in the VHF/UHF frequency range is presented. The model uses a digital terrain data bank and considers multipath propagation. Based on the uniform geometrical theory of diffraction (UTD) and physical optics an approach is described for calculating the propagation effects in natural 3-D terrain, given by topological and morphographical data. The method for field strength forecasting is described and methods for the analysis of the predicted multipath signal are discussed. It is shown how the complex probability density function (PDF) for the receiver field strength and the field strength delay spectrum can be derived. Methods for further evaluation of the transmitting channel characteristics are discussed     

Digital audio broadcasting in the FM band based on continuous phase modulation

A method for broadcasting digital audio signals simultaneously with existing analog frequency modulation radio (88-108 MHz) in adjacent channels is presented. The digital transmission is based on continuous phase modulation (CPM) and a proper reduced-state sequence estimator. With the proposed method, the power level and the symbol rate of the transmitter signal is determined in a manner that the interference the CPM signal poses for the analog FM signal in adjacent channels remains below a level according to the radio frequency emission mask defined by international rules. Due to the multipath propagation of the transmitted signal, the transmission behavior of the radio channel is determined by high dispersion up to 85 /spl mu/s. With the selected bit rate, the receiver has to cope with a channel memory of up to 17 bits. Since Viterbi detection is not feasible due to the number of channel states, detection is performed by a reduced-state sequence estimator that is able to eliminate the complete channel interference by decision feedback. Simulation results show that the detector almost achieves the detection quality of the optimum receiver. CPM achieves data rates of up to 200 kb/s inside a 200 kHz FM channel, which is sufficient for transmission of digital compressed audio signals at compact disc quality. The encouraging results of field tests will be published in another paper.     

Theoretical and experimental investigation of feedforward signal regeneration as a means of combating multipath propagation effects in pilot-based SSB mobile radio systems

A technique is described, feedforward signal regeneration (FFSR), to combat the effects of multipath propagation on VHF and UHF pilot tone single sideband (SSB) mobile radio systems. Unlike feedforward automatic gain control (FFAGC), FFSR suppresses both the random amplitude and phase fluctuations in the received signal. Extensive laboratory and field tests have shown that the operation of SSB at UHF frequencies is a viable proposition for both speech and data communication.     

Les dispositifs de lutte contre les effets des évanouissements sélectifs dans les faisceaux hertziens numériques

An overview of the countermeasure techniques used in digital radio systems for combatting the effects of selective fading due to multipath propagation is presented. Basic principles are analyzed. Their performances, based upon experimental measurements carried out throughout the world are compared. Frequency diversity techniques and channel interference cancellation techniques specific to a multichannel environment are not investigated. Future trends in the field are finally discussed.     

A general statistical channel model for mobile satellite systems

In order to guarantee the service quality and reliability for mobile satellite communication systems, we have to take into account outages due to obstruction of the line-of-sight path between a satellite and a mobile terminal as well as the signal fluctuation caused by interference from multipath radio waves. Thus, we need a good characterization for the satellite propagation channel. In this paper, we derive a general statistical model for mobile communication systems based on propagation scattering theory. Both the probability density function (PDF) of the received signal envelope and that of received signal power are given. This model is shown to be more general than previously known statistical models and can provide a better fit to the experimental data. This new model will play a significant role in the design of mobile satellite communication systems     

Noise immunity of the wireless communications scheme based on ultrawideband chaotic radio pulses in multipath channels

The problem of determining the noise immunity of wireless data transmission based on ultrawide-band (UWB) chaotic radio pulses in the multipath channel with white noise is substantiated. The results have been calculated via numerical simulation using the multipath channel models describing UWB signal propagation in rooms of different classes at distances as long as several tens of meters. The direct chaotic communications method is shown to have the noise immunity high enough to employ this scheme in practical wireless applications where information is transmitted under severe conditions of multipath propagation. In this case, the ultimate data transfer rates are found to 25 Mb/s.     

Separation of cochannel GSM signals using an adaptive array

The Global System for Mobile communications (GSM) is a digital cellular radio network that employs time division multiple access (TDMA). In such a cellular system, frequencies are reused in different regions for spectral efficiency, and thus, the transmissions in a given cell can interfere with those in distant cells. This cochannel interference can be a major impairment to the signal of interest. In this paper, we describe a beamformer and equalizer system that is capable of separating and demodulating several cochannel GSM signals. The signal model includes intersymbol interference (ISI) induced by the Gaussian transmit filter, and the channel model incorporates multipath propagation and additive white Gaussian noise. The GSM synchronization sequences are used to compute the beamformer weights and achieve frame synchronization simultaneously. Decision-feedback equalization is employed to compensate for the transmit filter ISI and to demodulate the data     

A UHF channel simulator for digital mobile radio

A device to simulate the channel propagation characteristics of the ground mobile environment at UHF has been designed, built, and characterized. This device provides a flexible, easily changed set of simulated channel characteristics, which allows the performance of a mobile radio unit to be evaluated in the laboratory under controlled conditions. The channel simulator was designed to simulate mobile platform speeds up to 675 mi/h and multipath components having differential delays approaching 10 µs. The channel simulator can provide up to four easily selectable, independently fading, multipath components, having calculated time delay spreads of up to 3.5 µs. The adjustable fading bandwidths and the exceptional long delays were implemented using the relative new signal processing technologies of charged-coupled devices and surface wave devices. Envelope statistics such as fading distributions and level crossing rates produced by the channel simulator show excellent agreement with theoretical prediction and documented experimental data.     

Measurement, modeling, and simulation of digital LOS microwavechannels with applications to outage prediction

A summary of prior work in the field of microwave line-of-sight (LOS) channel propagation measurements, channel models, and channel simulators is presented. The objective of these efforts is the reliable prediction of digital microwave radio performance on any specified link. Many digital radio outage prediction techniques are predicted upon the use of m-curves, which characterize a digital radio's performance in a simulated fading environment. These m-curves are generated by subjecting the radio under test to simulated multipath fading. This requires the use of a channel simulator that accurately emulates the fading conditions found on real LOS links. All parameters of an ideal channel simulator should be based on a model that has been validated through propagation measurements on a number of different paths. Although much progress has been made, some issues remain for further investigation. New channel propagation measurement, modeling, and simulation results that are directly applicable to these issues are given     

多径分量噪声干扰下无线电扩频通信优化技术

无线电扩频通信受到多径分量噪声的干扰,导致通信信道均衡性不好,抗干扰能力不强,误码率较高。需要进行噪声干扰抑制,改善无线电扩频通信质量。提出一种基于自适应级联陷波和码间干扰抑制的无线电扩频通信优化技术。构建无线电扩频通信系统传输结构模型,采用自适应陷波器对无线电扩频通信中的多径分量噪声进行有效抑制,降低了进入信号通频带内的干扰功率,提高解调器的输出信噪比和信干比。采用扩展后的序列去调制载波,将信号搬移到载频上,实现信道均衡,提高抗干扰能力。仿真结果表明,该算法能有效降低无线电扩频通信的误比特率,抗干扰性较强,提高通信质量。     

Propagation Properties of Radio Wave in Multipath Scattering Mobile Channel

1IntroductionAgoodunderstandingofthepropagationPropellesoftheurbanndcrocellularradiotransmissionchannelisveryimpo~tforthedesignofmobileradioandcordlesstelephonesystems.ThechannelbehaviorinurbanndcrocellsisdetenninedbyPropagationofrwhowavesinthetransmissionenvirolllnent.Typicalwavephenomenalikescattering,difhachon,andabsorphonbyPhysicalstIUctUresintheenvironmentSleadtoadiffusionofa~saltteddigitalsignalwaveintoacontinuousdistribuhonofpnalwaves.Obviously,theseeffeCtSdependonthegeometricalande…     

Wide-band packet radio for multipath environments

A direct-sequence spread-spectrum packet radio is described that has versatile signal-processing and local-control capabilities designed to support the functions required of a robust mobile communications network. Noteworthy capabilities include eleven selectable data rates with accurate range measurements in a fading multipath channel. The radio uses a hybrid analog/digital signal processor and nonrepeating spreading codes for suppression of intersymbol interference and jamming. It incorporates two sets of monolithic surface-acoustic-wave convolvers as programmable matched filters with time-bandwidth products of 64 and 2000. The analog matched filters are coupled with binary postprocessing for the functions of detection, RAKE demodulations and ranging measurements over a wide multipath spread. The data rate can be varied in response to channel conditions from 1.45 Mb/s down to 44 b/s with an almost ideal tradeoff in signal-processing gain from 18 dB up to 61 dB prior to multipath combining     

Mobile teletext reception using signal processing in frequencydomain

An experimental study of mobile teletext reception is described. Teletext in Japan is a broadband signal with 5.73 Mb/s; therefore, multipath interference is a serious problem in mobile reception, and it is impossible to obtain the teletext correctly by conventional methods. A multipath reduction technique using signal processing in the frequency domain is developed. In this technique, an original chirp signal is used for reference to identify the radio propagation path. In field trials, the delay profile was precisely obtained, and the bit error rate was reduced. The error correction capability was tested in a computer simulation     

A comparison of multipath distortion characteristics among digital modulation techniques

In a digital mobile radio transmission, long-delayed multi-path propagation causes frequency selective fading, resulting in signal waveform distortion and hence bit error rate (BER) degradation. Comparison of multipath distortion among various digital modulation techniques (binary, quaternary, offset quaternary, and minimum phase shift keying (BPSK, QPSK, OQPSK and MSK)) is made using a two-ray propagation model, which is a fundamental model to evaluate multipath tolerant capability. The analysis clarified the multipath conditions causing severe distortions and also the mechanisms of eye pattern degradation, showing the superiority of BPSK in multipath tolerance.     

Millimetric wavelengths radiowave propagation for line-of-sightindoor microcellular mobile communications

Discusses millimeter waves for indoor microcellular communications. The results of propagation experiments conducted at 60.4 GHz (the oxygen absorption band) and 38.25 GHz to determine multipath characteristics in a number of indoor microcell channels employing omnidirectional antennas are presented. Cumulative distribution functions for received signal envelope, as well as corresponding power spectra are given. In addition, a comparison between the fading statistics measured at 60.4 GHz and 38.25 GHz under similar conditions is made. The change in multipath characteristics due to the presence of different building materials is also illustrated. A ray model is developed to represent indoor microcell propagation by considering a direct ray plus rays which have undergone single and double reflections from the walls. Specular floor-reflected and ceiling-reflected rays are included when the antennas radiation pattern does not preclude them. Using this simple model, the signal variations and the amplitude of reflected rays with respect to the line of sight (LOS) ray as functions of mobile receiver position are predicted and used to assist in interpreting experimental results. Theoretical results are found to be in good agreement with measured ones, with the model also being used to predict structure-induced root mean square (rms) delay spread along receiver routes in an indoor microcell environment. This parameter is a measure of multipath conditions in a mobile radio channel and is inversely proportional to the maximum usable data signalling rate of a channel     

Effects of Multipath Propagation on Digital Radio

This paper summarizes experimental work at Bell Laboratories in the field of multipath propagation as it affects digital radio. Field and laboratory measurements are presented on commercial-quality high-speed digital radio systems working in the 4, 6, and 11 GHz common carrier bands. Circuits and equipment used in these systems are all state of the art, but no attempt has been made to describe them in any detail. Modulation types are offset-4 PSK, conventional 8 PSK, and 16 QAM. Outages(BER > 10^{-3})vastly exceeding accepted objectives are measured on unprotected radio hops. A very effective method for reducing outages has been the use of a space diversity combiner followed by an amplitude slope equalizer. Results from single, as well as dual-polarized digital radio relay systems, are presented. The paper also describes the laboratory measurement of an equipment "signature" as a means to compare different digital radio designs in their sensitivity to multipath fading.     

Observations and Conclusions from a Three Year Digital Radio Field Experiment in Australia

For the purpose of investigating the performance of digital radio systems, Telecom Australia established and conducted over a three year period (1982-1984), a 140 Mbit/s 16 QAM digital radio field experiment. In parallel with this experiment, analytical work was undertaken to develop an "outage prediction method" to assist with route design. This paper presents the observations and conclusions drawn from this work. Emphasis is placed on the aspects which relate to system design. We show that for digital radio outage prediction, a radio path can be characterized for multipath fading by the probability of occurrence of multipath fading and the mean echo delay, while the radio equipment can be characterized by a set of normalized parameters. The performance improvements achieved through the use of adaptive equalization and space-diversity are highlighted. Finally, we present a methodology for considering the performance of digital radio systems in the presence of interference and thermal noise, and present results for system performance with adjacent channel interference.     

军用无线电通信的码间干扰抑制算法仿真研究

军用无线电通信对通信质量和码元的保真性要求较高,军用无线电通信信道受到多径向量的影响产生码间干扰,需要进行码间干扰抑制,降低通信误码率。传统的码间干扰抑制方法采用波特间隔信道均衡算法,当通信信道受到电磁扰动的强度较大时,信道均衡性和码间干扰抑制能力不好。提出一种基于时间反转镜技术的军用无线电通信的码间干扰抑制算法,首先构建了军用无线电通信的信道模型,进行军用无线电通信的信道多径特性测量,采用自适应级联滤波器进行干扰滤波,结合时间反转镜技术实现码间干扰抑制算法改进。仿真结果表明,采用该算法进行军用无线电通信的码间干扰抑制,能有效提高通信传输的保真率,信道均衡性能较好,提高了通信输出的信噪比,降低通信误码率,提高了通信质量。     

Hybrid DS/SFH spread-spectrum multiple access with predetectiondiversity and coding for indoor radio

The authors derive close upper and lower bounds on the average bit error probability for hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access (DS/SFH-SSMA) systems with noncoherent DPSK demodulation, using predetection diversity (selection combining and equal gain combining) in conjunction with interleaved channel coding (Hamming (7,4) code and BCH (15,7) code) operating through indoor radio channels. A multipath Rayleigh fading model is assumed for the indoor radio channel. The results show that the DS portion of the modulation combats the multipath interference, whereas the FH portion is a protection against large multiaccess interference. It is shown that, for the considered types of channel coding, the use of predetection diversity is still essential for obtaining satisfactory error performance