Effect of frequency division duplex on open loop downlink beamforming in WCDMA systems

We investigate the effect of the frequency division duplex (FDD) gap - the separation of the uplink and downlink carrier frequencies - on the performance of open loop adaptive beamforming antenna arrays for wideband code division multiple access (WCDMA) communication systems. We show that the system performance worsens with increasing FDD gap. Also, a simple technique that mitigates the FDD effect is presented. It is easily implemented and compensates for most of the performance loss even for relatively large FDD gap values. Finally, we compare this technique with a more complex one and show that the two compensation techniques yield very similar results in the studied channel environment.