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UBC Theses and Dissertations

Performance of concatenated walsh/PN spreading sequences for CDMA systems Sebeni, Johnson Oghenevwareh


The Bit Error Rate (BER) performance on the forward link of a Code Division Multiple Access (CDMA) system using the concatenated orthogonal Walsh/m-sequence scheme for bandwidth spreading is studied. Expressions are derived for the BER for single cell systems using the Gaussian approximation and the characteristic function method. Performance results obtained using these expressions are compared to those obtained by Monte Carlo simulation. It was found that BER estimates using the Gaussian approximation are inaccurate because of statistical dependence among the interference terms. To take advantage of multipath diversity, the performance of the Rake receiver is compared to that of the correlation receiver for such systems. A modified Rake receiver is suggested whose BER performance is shown to be better than that of the Rake and correlation receiver especially for Rician fading multipath channels with Rice factor greater than 2dB. The area-averaged BER on the forward link of a multiple cell CDMA system is evaluated. A lognormal probability density function (pdf) is suggested to approximate the distribution of the ratio of the sum of average power of the received signals from other base stations to that of the received signal from the controlling base station which is assumed to be the one with the lowest attenuation to the mobile. A comparison of areaaveraged BER's obtained using this approximate pdf and the Gaussian approximation to those obtained by Monte Carlo simulation shows a reasonable agreement.

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