Virtual quadrature phase shift keying with low-complexity equalization for performance enhancement of OFDM systems

The Zero-Forcing (ZF) equalizer suffers from two main problems; the noise enhancement and the high complexity due to direct matrix inversion, especially with a large number of sub-carriers. On the other hand, the Minimum Mean Square Error (MMSE) equalizer has a high complexity and requires estimation of the Signal-to-Noise Ratio (SNR). In this paper, we modify the structure of the traditional Orthogonal Frequency Division Multiplexing (OFDM) system by adding a Virtual Quadrature Phase Shift Keying (VQPSK) block with power allocation that reduces the computational complexity of the equalization process using banded-matrix approximation, and duplicates the transmitted symbols compared to the corresponding QPSK mapping algorithm.