Multi-user detection in multicarrier-CDMA systemsMehrnutzerdetektion in Mehrträger-Codemultiplex-Systemen

The upcoming third generation mobile radio system in Europe is based on UMTS (Universal Mobile Telecommunications Standard). In order to supply access to a common transmission channel for several users, UMTS incorporates Code Division Multiple Access (CDMA). Besides a lot of practical advantages, CDMA suffers from multi-user interference limiting spectral efficiency dramatically. However, bandwidth is a very valuable resource and should be used as efficiently as possible. One appropriate mean to increase spectral efficiency of CDMA systems is multi-user detection. This paper gives an overview of different multi-user detection techniques and compares them with the conventional single-user detection including channel coding. Specifically, linear as well as nonlinear multi-user detectors are considered. Efficient realizations of linear detectors are presented and extended to improved nonlinear techniques. It is shown that nonlinear MUD including channel decoding can achieve a spectral efficiency twice as high as that of the well-known GSM standard (Global System for Mobile Communications) employing TDMA and FDMA.