Wideband Mobile Radio Channels Research Articles

Use of Hidden Markov Model Technique to Characterize and Classify the Wideband Mobile Radio Channel in Different Environments

Use of Hidden Markov Model Technique to Characterize and Classify the Wideband Mobile Radio Channel in Different Environments

Doppler Shift Characterization of Wideband Mobile Radio Channels

The prevailing approach for characterizing the Doppler shift (DS) of mobile radio channels assumes the transmission of an unmodulated carrier. This consideration is valid for the analysis of narrowband channels, but its pertinence is questionable in regards to the modeling of wideband channels. In this correspondence, we redefine the DS from a time-frequency analysis perspective that does not depend on the aforementioned assumption. We systematically demonstrate that the DS can be characterized by the instantaneous frequency of the channel transfer function. This generic definition makes evident a fundamental aspect of the DS that is seldom acknowledged, namely, the DS is a frequency-varying quantity. We show that the second-order statistics of wideband mobile radio channels are non-stationary due to the DS's frequency variations. In addition, we present numerical results of a case study showing that such non-stationarities can cause significant system performance degradations.

Phase Noise Effects on Wideband Mobile Radio Channel Sounding

In this work three wideband mobile radio channel sounding methods are simulated and compared using computational tools. The considered sounders include the traditional STDCC and two other proposed sounding methods that are based on OFDM digital transmission and detection procedures and on matched filtering. The impact of the phase noise introduced by the receiver local oscillator in the precision of the examined sounders is analyzed by comparing the estimated channel results with the simulated reference channel. Other impairments factors like thermal noise or nonlinear distortion affecting the system are not considered.

An Improved Iterative Nonlinear Least Square Approximation Method for the Design of SISO Wideband Mobile Radio Channel Simulators

In this paper, we present an improved version of the iterative nonlinear least square approximation (INLSA) method for designing measurement-based single-input single-output (SISO) wideband channel simulators. The proposed method aims to fit the time-frequency correlation function (TFCF) of the simulation model to that of a measured channel. The parameters of the simulation model are determined iteratively by minimizing the Frobenius norm, which serves as a measure for the fitting error. In contrast to the original INLSA method, the proposed approach provides a unique optimized set of model parameters, which guarantees a quasi-perfect fitting with respect to the TFCF. We analyze the performance of the proposed method in terms of the goodness of fit to the measured data. The investigations will be carried out with respect to the TFCF and the scattering function. We demonstrate that the proposed approach is a powerful tool for the design of measurement-based wideband channel simulators, which are important for the performance evaluation of mobile communication systems under real-world propagation conditions.

Analysis and simulation of received signal level distribution in wide‐band mobile radio channels

AbstractThis paper considers the propagation model in which the amplitude of the direct wave is kept constant and that of the indirect wave exhibits Rayleigh fluctuations in the line‐of‐sight and non‐line‐of‐sight channels. The instantaneous received signal level distribution is examined by computer simulation and a fading simululator, with the equivalent received bandwidth (product of received bandwidth 2Δf and maximum path length difference ΔLmax) as the propagation parameter. It is seen that the equivalent received bandwidth is suited as a parameter to represent the instantaneous received signal level distribution. The instantaneous received signal level distributions derived by the computer simulation and the fading simulator agree well. Conventional narrow‐band transmission corresponds to the case in which 2ΔfΔLmax is less than 10 MHz‐m. Then, the fading depth is determined by the power ratio a between the direct wave and the indirect wave. Wide‐band transmission corresponds to the case in which 2ΔfΔLmax is larger than 10‐MHz‐m. Then, the fading depth is determined by a and 2ΔfΔLmax, becoming less when those quantities are increased. When 2ΔfΔLmax is very large, the fading depth also depends on the number of arriving waves. These properties are derived theoretically and are verified by the simulation and the fading simulator. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(2): 94–105, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1157

Calibration scheme for synthesizer phase fluctuations in virtual antenna array measurements

A calibration scheme is presented for synthesizer phase fluctuations in virtual antenna array measurements for wideband mobile radio channel sounding. The standard deviation of the direction-of-arrival error is calculated from the Allan variance of frequency synthesizers. Estimated errors for a 5.3 GHz channel sounder are less than 1°. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 183–187, 2000.

Autocorrelation characteristics for received signal level in a wide-band mobile radio channel

Autocorrelation characteristics for received signal level in a wide-band mobile radio channel

Wideband mobile radio channel characterization

La caracterisation a large bande des canaux radioelectriques est realisee a partir de sondeurs. Ces systemes emettent soit une impulsion, soit une suite pseudo-aleatoire dit prbs (pseudo random binary sequences) et utilisent en reception une technique de compression s’appuyant sur unfiltre adapte ou sur un correlateur. Recemment une technique de modulation de frequence (fmcw ou chirp) a ete mise en ozuvre dans ces sondeurs. Cet article presente une breve revue de la theorie liee a la caracterisation des canaux a large bande et relie les expressions analytiques connues aux traitements necessaires pour obtenir les parametres caracteristiques de ces canaux. Les differents types d’architectures de sondeurs chirp sont compares et les avantages d’une technique heterodyne du sondeur chirp sont soulignes. Ceci est illustre par la presentation de mesures a large bande a l’interieur ou a l’exterieur des bâtiments.

Condensed Parameters for Characterizing Wideband Mobile Radio Channels

Condensed parameters are used for a concisedescription of wideband mobile radio channelmeasurements. The most popular are the delay spread, thecoherence bandwidth, and the delay window. In thispaper, we analyze their definitions, interrelations,and applicability under various circumstances.Similarily, we analyze condensed parameters in theDoppler frequency domain. There are importantdifferences between instantaneous and averaged parameters,and we discuss the meaning of them. We show thatergodicity and WSSUS (wide-sense stationary uncorrelatedscattering) are required so that averageparameters can be defined. For overspread channels, delayspread and coherence bandwidth can be defined, but theyare not meaningful. We demonstrate that the“classical” descriptions, namely delayspread and coherence bandwidth, do not allow a system independentcharacterization of the channel, and we propose a set ofwindow parameters instead. Their meaning for channelcharacterization and system simulation isinvestigated.

Soft-decision feedback equalizer for continuous phase modulated signals in wideband mobile radio channels

A combination of a decision feedback equalizer (DFE) and a Viterbi processor for the equalization of continuous phase modulated (CPM) signals transmitted over wideband mobile radio channels is described. The equalizer structure allows soft-decision to be made and incorrect decisions to be changed in the feedback filter of the DFE. The provision of soft decisions significantly alleviates the catastrophic effect of error propagation due to error bursts caused by the fading channel. Simulation results show that the proposed equalizer approaches the performance of the more complicated maximum likelihood sequence estimation (MLSE) detector to within 2.0 dB and 2.5 dB at bit error rates (BERs) of 10/sup -2/ and 10/sup -3/ in a two-path Rayleigh fading channel while the complexity is reduced to half of that of the MLSE detector.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Received signal-level characteristics in a wide-band mobile radio channel

A mobile propagation model aimed at clarifying fundamental propagation characteristics in received signal-level variation for wide-band transmission is proposed. On the basis of this model, the author derives an expression for a received signal level in wide-band transmission and examines the fundamental signal-level characteristics by computer simulation and experiment. Both simulation and measurement results agree well and the results follow. For a received signal-level variation in wide-band transmission: first, received signal-level depth becomes shallower with increasing receiver bandwidth 2/spl Delta/f, and the level has no Rayleigh distribution. In an urban area when 2/spl Delta/f is 3 MHz, the level difference between the cumulative probability 50% and 1% values is about 5 dB. Second, received signal-level distribution depends on the number of arriving waves N and path length difference |/spl Delta/L/sub ij/|. The level depth becomes shallower with increasing N and |/spl Delta/L/sub ij/|. Third, received signal-level distribution is almost independent of radio frequency f/sub c/. The author also derives expressions for the autocorrelation coefficient /spl rho/(z) and frequency coefficient /spl rho/(s) of the received signal level. /spl rho/(z) is independent of 2/spl Delta/f, and is about J/sub 0/(Z//spl lambda//sub c/)/sup 2/, which is known as narrow-band reception. The /spl rho/(s) becomes higher with increasing 2/spl Delta/f. >

Sounding techniques for wideband mobile radio channels: a review

A major prerequisite to the specification and design of any wideband digital mobile radio system is a thorough knowledge of the propagation characteristics of the mobile radio channel. The various methods of channel sounding are reviewed, with both narrowband and wideband techniques being discussed. The advantages and limitations of each method are highlighted and the swept time-delay crosscorrelator (STDCC) technique is presented as the optimum choice. The main features of an experimental STDCC sounder are identified, factors that are considered essential to good system performance are discussed, and the interrelationships between the sounder parameters are emphasised. It is shown that extension of the power-delay profile prior to calculation of the frequency correlation function leads to the achievement of substantially improved frequency resolution. This is particularly relevant when the average power delay profile contains significant echoes at large excess time delays.

Measurement and modelling of wideband mobile radio channels at 900 MHz

The complex bandpass impulse response of urban mobile radio channels is measured at 900 MHz using a swept time-delay cross-correlator channel sounder, having a time resolution capability of 0.1 μs. The receiver has a slightly different configuration than those described in previous studies and gives superior performance. The propagation data are analysed with particular relevance to the development of a representative channel simulation and production of parameters useful to systems engineers. In both cases, a two-stage characterisation of the data is used. A moving average normalisation method is applied to the processing of the simulation data. The wideband propagation path is shown to be well modelled by a tapped-delay line, with each tap comprising an uncorrelated Rayleigh modulator, a partially correlated log-normal modulator and a weighting factor. These results lend support to the Gaussian wide-sense stationary uncorrelated scattering model which has been proposed for small-scale mobile radio channels. The simplicity of using this model is highlighted by way of an example. Gross non-stationarity in the channel impulse responses identifies the need for formulating cumulative distributions of the small-scale systems parameters. It is shown how these results may be used in assessing the performance of existing and future mobile radio systems.

Wide-band Measurements on Mobile Radio Channels by SAW Convolvers

After the explanation of the wide-band mobile radio channel with its linear, time-variant transmission characteristics, a measuring system is described. The experimental set-up is demonstrated, where a SAW convolver acts a correlator. The measurement results taken from the urban areas of Kassel are interpreted clearly