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Abstract

Variable-rate data transmission is one of the key techniques to effectively reduce the mutual interference and as a result increase the link capacity in direct sequence code division multiple access (DS-CDMA) systems. To avoid frame overhead, a blind rate detection scheme that does not explicitly transmit any rate information of transmitted data has been proposed for use in the third-generation DS-CDMA cellular communication systems. In this thesis, a novel joint rate detection and data decoding algorithm (JRDDDA) for variable-rate data transmission in DS-CDMA systems is proposed. Its performance in terms of frame error rate and false rate detection rate is investigated by means of computer simulation in three different, standard channels; namely, the additive white Gaussian noise channel, the frequency-flat Rayleigh fading channel, and the frequency-selective Rayleigh fading channel. The effect of channel estimation error on the system performance is also investigated in the considered channels. Moreover, a novel joint source and channel coding based rate detection algorithm (JSCCRDA) is proposed, which exploits rate sequence redundancy for combating the effect of the noisy channels. A first-order Markov process is used to model the rate sequence from the vocoder's output in the case of voice transmission. An instantaneous Maximum a posteriori algorithm is employed in our joint source and channel decoder due to the delay constraint on real-time cellular communication systems. The proposed JSCC-RDA is applied to two well-known rate detection algorithms and the JRDDDA as well for performance improvement in terms of false rate detection rate.