Performance of time-frequency coded spread spectrum systems operating over noisy fading channels

The performance of time-frequency coded spread spectrum systems (TFCSSS) is considered when the systems are operating over noisy fading channels. Systems employing the random addressing technique of Viterbi [1] and the addressing scheme developed more recently by Einarsson [3] are examined. An exact expression is derived for the word-error probability associated with the Viterbi scheme. This expression provides the tightest known upper bound to the performance of the Einarsson addressing scheme. Also in the paper the question of the most appropriate way of using power is considered, and it is shown that if the possibility of using an increased transmitter power exists, it is better to increase the power per transmission chip to a higher level and keep it constant, irrespective of the number of users occupying the chip, rather than to use a power level that increases with the number of users occupying the chip.