A two stage decorrelator for a dual rate synchronous DS/CDMA system

This paper proposes a signature assignment technique for a dual rate DS/CDMA system that serves both low bit rate and high bit rate users. In an interval of duration T₀, a low rate user transmits one bit while a high rate user transmits M bits. Under the new signature sequence assignment technique, M low rate users share the signature of a single high rate user without wasting bandwidth. Based on the signature assignment technique, we propose a decorrelator that generates bit decisions for each high rate user in every subinterval of duration T₀/M. In order to decode a low rate user, an orthogonal projection is applied to M separate decorrelated outputs of each low rate user. It is observed that applying a standard decorrelator to the interval of duration T₀ yields a computational complexity that grows with M. The proposed decorrelator significantly reduces the computational complexity of the standard decorrelator. Due to the structural simplicity, the proposed receiver slightly suffers in terms of bit error rate. However, it is observed that in several cases, the proposed receiver achieves the standard decorrelator performance