Performance evaluation of the S(2) short scrambling code based multiuser detection in asynchronous WCDMA systems

Abstract

Scrambling is one of the key processes in the asynchronous wideband code division multiple access (WCDMA) systems. It overcomes the problem that the number of orthogonal variable spreading factor (OVSF) codes is relatively small and system capacity is consequently constrained. In this paper, the characteristics of S(2) short codes and their impacts on the performance of multiuser detection (MUD) are investigated. We demonstrate that for the same MUD, S(2) short code scrambling can complicate the multiple access interference (MAI) and increase the difficulty of signal detection. However, when more users are served, MUDs in the scrambled system will outperform those in the non-scrambled one. Compared with the conventional single user detection, the adaptive linear minimum mean square error (MMSE) MUD algorithm dealing with the output of matched filter (MF) and the constant modulus (CM) blind MUD algorithm at chip rate can both suppress the MAI more effectively and enhance the bit error rate (BER) performance of the scrambled system more prominently.