Channel adaptive multiple access and intersymbol interference cancellation techniques for TDD-mode UMTS receivers

This paper presents a comparison of simulation results for various time division duplex (TDD) UMTS receiver architectures. Uplink and downlink simulations are performed over frequency-selective time varying channels. Results indicate that in practice, satisfactory performance cannot be obtained using fixed branch receiver architectures. To overcome this limitation, a reconfigurable blind adaptive linear minimum mean square error (LMMSE) receiver is proposed to simultaneously track channel variations and mitigate the effects of multiple access interference and intersymbol interference. This new method is compared with the standard correlator, RAKE receiver and chip level equalisation techniques. System performance is studied in terms of uncoded bit error rate for low and medium levels of RMS delay spread. Simulations demonstrate that adaptive branch and parameter selection greatly reduces the interference floor in multi-user CDMA systems. More specifically, the proposed reconfigurable blind adaptive LMMSE is shown to offer competitive results at low relative complexity. This approach can be used to improve the performance and capacity of TDD mode UMTS networks.