Abstract :
Using a transmit antenna array (TAA), the downlink beamforming is able to improve the performance of wireless communication systems. We propose a semiblind downlink beamforming method based on channel reciprocity of the wireless channels for code-division multiple-access (CDMA) systems equipped with TAA. In the proposed semiblind method, it is shown that the feedback delay can result in performance degradation under a time-varying fading channel environment. Hence, the performance of the semiblind method is satisfactory only when the maximum Doppler frequency is low or the feedback delay is not significant. To overcome this difficulty, the channel prediction is considered. Using the channel predictor, the semiblind method can provide a reasonable performance for a moderate maximum Doppler frequency (about a few hundred hertz). For theoretical performance analysis, upper, and lower bounds of the bit error probability under a fading channel environment are derived
Keywords :
adaptive antenna arrays; array signal processing; code division multiple access; delays; error statistics; fading; feedback; land mobile radio; multiuser channels; radio links; time-varying channels; transmitting antennas; CDMA systems; adaptive antenna arrays; bit error probability; channel prediction; channel reciprocity; code-division multiple-access; feedback delay; lower bounds; maximum Doppler frequency; mobile station; performance analysis; semiblind downlink beamforming method; time-varying fading channel; transmit antenna arrays; upper bounds; wireless channels; wireless communication systems; Antenna arrays; Array signal processing; Delay; Downlink; Fading; Feedback; Frequency; Multiaccess communication; Transmitting antennas; Wireless communication;
