Interference suppression in TDD/CDMA cellular systems with asymmetric traffic using MVDR beamforming

The primary advantage of the TDD system is to accommodate asymmetric traffic by allocating different numbers of uplink and downlink time slots. However, in the TDD/CDMA cellular system, uplink signals may suffer strong interference from the downlink transmission of neighboring base stations. This kind of opposite direction interference has an adverse impact on the TDD/CDMA system performance. We propose the application of the MVDR (minimum variance distortionless response) beamforming technique to suppressing the opposite direction interference. We evaluate the uplink performance of the proposed technique by simulation. Moreover, by jointly employing transmit beamforming in all asynchronous cells, the TDD/CDMA cellular system can allow different rates of asymmetry in different cells. Thus, each cell can design its own pattern of slot allocation.