Study on efficient interference suppression for DS-CDMA systems

Abstract

Direct-sequence code-division multiple-access (DS-CDMA) systems have advantages such as the asynchronous multiple access, robustness to frequency selective fading and multipath combining. However, inequality in the power of the received signals and the inter-symbol interference (ISI) due to multipath degrade the performance of the DS-CDMA systems. The problem caused by the unequal power is called the near-far problem and many researches have been studied to solve the problem. The other users`` signals are considered as the interference (Multiple-access interference, MAI) from the point of the interested user. Among the methods to suppress interference, the adaptive receivers using the statistical property of the received signal, that is, the adaptive receivers have aroused interests for their simplicity to implement and good performance. Especially, the receivers requiring no training-sequence is called as the blind adaptive receivers. In this dissertation, the novel blind adaptive receivers are proposed to over-come the MAI and ISI. The previous adaptive receivers needs dimension equal to the length of the spreading code. Therefore, the dimension of the adaptive receiver may be a burden on. the computational complexity. The proposed receiver requires reduced dimension without great loss in the performance. In consequence, the MAI and ISI are suppressed effectively without knowledge of channels. The proposed receiver is construed with the three-stage. In the first stage, the length of the received signal is reduced to decrease the computational complexity. The second stage suppresses interference existing in each delay finger. Finally, the multipath effect is compensated in the third stage using the interference-free signals. To reduced the dimension of the adaptive receiver, the partial summation is proposed. The partial summation scheme is compared with the previously proposed partial decorrelation scheme. The partial decorrelation scheme out-performs the par...