Effect of sequence selection on MAI suppression in limited spreading CDMA systems

Increasingly, spread spectrum systems are being proposed which support a range of data rates and traffic types in a band limited environment. One way to achieve a range of data rates with fixed bandwidth is to allow the use of different processing gains. If the range of data rates supported is large, the lower bound on the processing gain can become quite small. Receivers based on LMMSE algorithms offer high efficiency for CDMA systems through interference suppression, however at small processing gains, the sequence set correlation properties prove to be a significant limitation on the system efficiency. This paper provides examples of sets of short length spreading sequences which have good auto-correlation (AC) and cross-correlation (CC) properties which are essential to allow relatively high system efficiency. A CDMA system using an LMMSE receiver is examined with selected short length sets to demonstrate the application of the sequences. The sets proposed are compared to system performance when using well known sequence families. This revised version was published online in July 2006 with corrections to the Cover Date.