Adaptive decorrelating detectors for CDMA channels

Multi-user detection allows for the efficient use of band-width in code-division multiple-access (CDMA) channels through mitigation of near-far effects and multiple-access noise limitations. Due to its inherent noise and multi-path immunity, CDMA multi-access is being considered as a platform for personal communication systems (PCS). As CDMA based digital communication networks proliferate, the need to determine the presence of a new user and integrate knowledge of this new user into the detection scheme becomes more important. The decorrelating detector is a linear multi-user detector that is asymptotically optimal in terms of near far resistance; however, in the presence of a new unknown user, performance of the decorrelator is severely degraded. Adaptive decorrelators are constructed which adaptively augment an existing conventional decorrelator to demodulate a new active user in addition to existing risers. Several likelihood ratio based schemes are proposed.