On linear predistortion techniques for single-carrier and OFDM SD/CDMA systems

Instantaneous channel state information at a transmitting access point can be efficiently used by joint predistortion techniques (JP). The required channel state information can be obtained at the access point from a preceding reception time slot in time division duplex (TDD) systems. During the succeeding transmission time slot, transmit filters predistort data signals using multiple transmit antennas and spreading sequences in order to compensate for the channel influence. The separation of simultaneously transmitted users´ signals is based on combined space and code division multiple access (SD/CDMA). In this paper, linear predistortion techniques for single-carrier and orthogonal frequency division multiplexing (OFDM) transmission systems with frequency domain filtering are presented using either zero forcing or Wiener optimization. For OFDM transmission, different frequency and time domain spreading strategies are analyzed. In general, we focus on direct reuse of uplink filter coefficients for downlink transmission instead of just using uplink channel state information in order to avoid additional matrix inversions. The achievable uncoded and coded bit error ratio of the presented schemes is presented as well as peak-to-average power ratio (PAPR).