Signal design to mitigate the impact of RF impairment in OFDM communication systems

Orthogonal frequency division multiplexing (OFDM) signals are sensitive to the mismatching errors between the in-phase (I) and quadrature (Q) branches in the up and down-conversions. These mismatching errors including phase and amplitude mismatches make the signal constellation expand and rotate, which severely degrades the performance of OFDM systems. In this paper, a method of signal design for OFDM communication system is proposed in order to mitigate the impact of IQ mismatching errors. A simple quasi-symmetric conjugate (QSC) structure of signal in frequency domain designed at the transmitter side can completely remove the self-interference caused by IQ mismatching errors. At the receiver, the estimation and the compensation for IQ mismatch are not necessary. Analytic and simulation results can show the efficiency of QSC method in IQ mismatch mitigation compared to other techniques such as Adjacent Symbol Repetition (ASR), Adjacent Conjugate Symbol Repetition (ACSR), Symmetric Symbol Repetition (SSR), or Symmetric Conjugate Symbol Repetition (SCSR), respectively.