Spread-spectrum based low-cost provision of downlink channel state information to the access points of FDD OFDM mobile radio systems

We present a low-cost scheme for the provision of downlink channel state information to the access points of FDD OFDM mobile radio systems. In the mobile terminals the channel transfer function values of the downlink subcarriers are mapped on the complex amplitudes of certain uplink subcarriers and then retransmitted to the access points. For retransmission we utilize for each downlink transfer function value more than one uplink subcarrier, that is we resort to a spread spectrum approach. The resulting frequency diversity mitigates the adverse impact of the frequency selectivity of the uplink channel when performing retransmission