A new VSL scheme for multi-rate DS-CDMA systems

This paper considers multiuser detection in variable-spreading-length (VSL) multi-rate direct-sequence code division multiple access (DS-CDMA) systems. In such systems, linear multiuser receivers for users transmitting at data rates higher than the basic rate in general need to be time-varying. This makes the adaptive implementation of these receivers difficult. Here, a two-layer spreading code scheme is proposed which facilitates the low complexity adaptive implementation of linear MMSE multiuser receivers in a dual-rate system. Extension of this scheme to more general multi-rate systems is straightforward. It is demonstrated via analysis and simulation results that this scheme achieves good performance.