Transmitter-Based Minimization of Error Rates in the Downlink of Wireless Systems

Using CDMA technology, one has to contend with interference in frequency-selective channels caused by multipath propagation and fading. Transmitter-based methods such as zero forcing joint transmission and transmit Wiener filter only reduce the bit error rate indirectly and do not exploit the knowledge of the transmit data symbols. Nonlinear optimization strategies, e.g., the Constrained Minimum BER MUT approach, outperform such methods while the computational complexity prevents their implementation. In this paper, a spread-spectrum TDD-CDMA downlink transmission system with 4-QAM modulation is considered, whereas perfect channel knowledge both in the transmitter and the receiver is assumed. Deriving a convex optimization problem, an alternative solution method with considerable decrease of the complexity is proposed.