In this paper, we consider a direct sequence spread spectrum (DS-SS) microphone system in 2.4 GHz ISM band under indoor environments. It can be modeled as the asynchronous DS-CDMA system in which multiple transmitters share a common channel to transmit information to a single receiver. However, this system has the two critical defects, one is that many burst errors are occurred because of the long-term deep fade in an indoor channel, and the other is that power control is impossible due to the unidirectional structure. Since the reliable performance of DS-CDMA systems can be guaranteed under a reliable bit error rate performance and perfect power control, the solution to these problems is imperative. Hence, in order to overcome these problems, we propose a zero forcing equalizer (ZFE) based multi-user detection (MUD) receiver for this system, since an MUD receiver doesn't require rigorous power control and is able to remove multiple access interference using linear equalization. We derive the modeling and the tap coefficients of the proposed ZFE, and also analyze the performance of the proposed receiver. Based on the performance comparison with the conventional receivers, such as single user detection and post-detection combining diversity receivers, it is shown that the proposed receiver can achieve a lower bit error rate performance.

In this paper, we propose a partial erasure decoding scheme with erasure-decision threshold for Reed-Solomon (RS) codes and analyze its performance in frequency-hopped multiple-access communications. RS code is used to correct erasures and errors caused by other-user interference. Binary FSK is employed to transmit the channel symbol. The proposed decoder decides whether to erase the received RS code symbol based on the ersure decsion threshold. The approximated formula for optimal erasure decision threshold is derived in such a way that packet error probability can be minimized. Numerical results show that the employment of adaptive erasure decision threshold attains the higher normalized throughput in the areas of high channel traffic cases.