Performance of analog feedback in closed-loop transmit diversity systems

Knowledge of channel state information (CSI) at the transmitter can be used for transmit beamforming. However, providing the transmitter with CSI typically requires feedback from the receiver, and this is complicated by low feedback rates. This thesis is concerned with the efficient transmission of CSI in the uplink, and data in the downlink, of a closed-loop transmit diversity system. Two main ideas are explored. First, we consider the employment of analog CSI feedback whereby downlink gain estimates are fed back periodically to the base station at a rate of only one analog symbol per estimate per data frame. Second, we consider the use of position dependent modulation (PDM) to counter the signal to noise ratio variation across a downlink data frame. Simulation results indicated that analog feedback can achieve better bit error rate (BER) than digital feedback, and PDM can attain higher throughput than fixed modulation at a target BER.