Linear multi-user detectors for TDD mode of UMTS (IMT-TC)

We have examined the effect of multi-user detectors for the TDD mode of wideband CDMA, particularly the downlink. It is shown that under dispersive conditions a RAKE receiver suffers from a high mean square error at its output when all the codes are used in parallel and is not particularly suitable for high levels of QAM. Generally it is not possible to use the CDMA channel at a user bit rate which approaches the Shannon capacity. A MUD demodulator on the other hand restores the output MSE to within 1 dB of what would occur in an ideal channel and can offer a much higher bit rate. The average DSP load for downlink MUD detectors is modest and it is reasonable to consider their use in nomadic and portable instruments such as hand held portables or lap-tops computers with wireless modems