COMM-5.1

Error Probabilities and Performance Comparisons of FFH/BFSK Receivers with Multitone Jamming and AWGN
Kah C Teh (Centre for Wireless Communications, National University of Singapore), Alex C Kot, Kwok H Li (Nanyang Technological University)

This paper studies the bit-error rate (BER) performance of a fast frequency-hopped (FFH) binary frequency-shift-keying (BFSK) clipper receiver in the presence of multitone jamming~(MTJ) and additive white Gaussian noise (AWGN). By using the Taylor-series expansion and the quantization approach, the BER expressions for higher diversity levels can be obtained without much extra computational complexity. The analytical BER results, validated by simulations, show that there is an optimum diversity level for the clipper receiver. Performance comparisons among various receivers demonstrate that the BER performance of the clipper receiver is significantly better than that of the linear-combining receiver. In addition, the clipper receiver also outperforms the product-combining receiver and the self-normalizing receiver provided that the clipping threshold is set at the desired signal power level.

COMM-5.2

Estimation in Cellular Radio Systems
Jonas Blom, Fredrik Gunnarsson, Fredrik Gustafsson (Link�pings universitet)

The problem to track time-varying parameters in cellular radio systems is studied, and the focus is on estimation based only on the signals that are readily available. Previous work have demonstrated very good performance, but were relying on analog measurement that are not available. Most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). For that matter a Maximum Likelihood estimator have been designed and exemplified in the case of GSM. Simulations indicate good performance, both when most parameters are varying slowly, and when subject to fast variations as in realistic cases. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

COMM-5.3

BER COMPUTATION OF AN MC-CDMA SYSTEM WITH CARRIER FREQUENCY OFFSET
YOUNSUN KIM, SOOYONG CHOI, CHULWOO YOU, DAESIK HONG (YONSEI UNIVERSITY, DEPT. OF ELECTRONIC ENGINEERING, YONSEI UNIVERSITY)

The effect of carrier frequency on the performance of an MC-CDMA (Multi-Carrier Code Division Multiple Access) system is considered. Bit error probability of the downlink of this system is analyzed taking into the effect of frequency offset. This paper will be focused on the derivation of the bit error probability mathematically. Derived results show that the performance of MC-CDMA is very sensitive even to a relatively minute degree of frequency offset. Parameters such as degree of carrier offset, number of subcarriers, number of users, method of combining, and type of channel will be varied so that the influence of each parameter can be assessed

COMM-5.4

FM Interference Suppression in Spread Spectrum Communications Using Time-Varying Autoregressive Model Based Instantaneous Frequency Estimation
Peijun Shan, A. A. (Louis) Beex (The Bradley Department of Electrical and Computer Engineering, VIRGINIA TECH, Blacksburg, Virginia 24061-0111, USA)

In case of a strong frequency modulated interference in a spread spectrum communication system, the interference can be effectively suppressed by applying a time-varying notch filter with its zero(s) placed at an instantaneous frequency (IF) estimate of the interference. In this paper, we present the use of a time-varying autoregressive model based IF estimator in such a scenario. We model the received signal with an autoregressive model whose coefficients are time-varying and modeled as a combination of a set of known functions of time. The IF of the interference is estimated from the model. It is demonstrated that this method provides superior performance compared to using a time-frequency distribution. The comparison reveals that the Wigner-Ville Distribution peak based IF estimator suffers drawbacks such that its filtering gain is limited.

COMM-5.5

Equalization of Satellite UMTS Channels Using Neural Network Devices
Steven Bouchired, Mohamed Ibnkahla, Daniel Roviras, Francis Castani� (INPT)

The presence of non-linear devices in several communication channels, such as satellite channels, causes distortions of the transmitted signal. These distortions are more severe for non-constant envelope modulations such as 16-QAM. Over the last years Neural Networks (NN) have emerged as competitive tools for linear and non-linear channel equalization. However, their main drawback is often slow convergence speed which results in poor tracking capabilities. The present paper combines simple NN structures with conventional equalizers. The NN techniques are shown to efficiently approximate the optimal decision boundaries which results in good symbol error rate (SER) performance. The paper gives simulation examples (in the context of satellite mobile channels) and compares neural network approaches to classical equalization techniques.

COMM-5.6

Hopped Linear Time-Varying Filters: Principles
Aawatif Hayar, Daniel Roviras, Bernard Lacaze, Alban Duverdier (INPT)

Privacy and security of radio communications becomes increasingly important. In this context, modulation techniques with embedded scrambling properties are suitable. The aim of this paper is to present a new transmitting technique using Linear Time Varying Filters with hopping in the frequency domain.

COMM-5.7

Low Complexity Source Controlled Channel Decoding in a GSM System
Paul Strauch, Carlo Luschi, Magnus Sandell, Ran Yan (Lucent Technologies, Bell Laboratories)

In this paper we investigate source controlled channel decoding with a hard output channel decoder. Various methods have been devised in the past for source controlled channel decoding, but most of them assume that a soft output channel decoder is used. Most receivers in mobile wireless communications have a standard Viterbi channel decoder which produces only hard outputs. It is shown that a simple sliding histogram is capable of improving the speech quality significantly. The ideas and methods in this paper are applied for the full-rate and enhanced full-rate speech codecs in the GSM system.

COMM-5.8

APPLYING GCMAC TO PREDISTORTION IN GSM BASE STATIONS
Juan Jose Murillo-Fuentes, Francisco J. Gonzalez-Serrano (Departamento de Teoria de la se�al y comunicaciones. Universidad Carlos III de Madrid.)

Predistortion in GSM has been introduced to deal with saturation in amplification at Base Transceiver Stations (BTS). This paper will focus on the elements and architectures in signal predistortion for mone carrier and multicarrier modulations. The GCMAC neural network has been introduced as predistorter to provide the design with adaptive, digital and practical features. Some results are included. These results show how the predistortion architectures proposed allows working in saturation regimen. This point is important since it gives flexibility in reassignment of cells by increasing the coverage when necessary. It also improves amplification characteristics avoiding co-channel interference, aging, intermodulation distortion, etc.

COMM-5.9

Burst Error Compensation for a Two-Dimensional Channel
J. Q Trelewicz (Arizona State University), Andrew J Siefker (Murray State University)

In an optical channel for a digital holographic data storage system, burst errors, in the form of severe amplitude compression, are experienced in the vicinity of dust and other optical aberrations in the channel. The locations of these burst errors are approximately fixed over a range of perturbations in magnification and vertical-horizontal position. In a calibrated channel, lower error rates can be realized by allocating energy in the modulation code based on a measurement of the approximate location of these effects. This paper discusses theoretical bounds on the energy inside the distortion region, and the modulation code which is used to approach this bound.

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Last Update: February 4, 1999 Ingo Höntsch