Per-Subchannel Joint Equalizer and Receiver Filter Design in OFDM/OQAM Systems

Abstract

Orthogonal-frequency-division-multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) based multicarrier system achieves better spectral efficiency in comparison with the widely used multicarrier OFDM system. However, the OFDM/OQAM system suffers from intersubchannel interference and intersymbol interference in frequency-selective channels, which cause poor bit error rate (BER) performance. To overcome these challenging issues, in this paper, we propose a per-subchannel joint equalizer and receiver filter design method based on maximizing signal-to-interference-plus-noise ratio (SINR) of each subchannel. An iterative two-step algorithm is developed to design equalizer and receiver filter jointly. At the first step, by assuming that the receiver filter impulse response is identified, an equalizer is designed for each subchannel by maximizing its SINR. At the second step, by assuming that the channel and equalizer impulse responses are known, the SINR of each subchannel is derived based on the receiver filter impulse response coefficients. In this way, the receiver filter of each subchannel is designed independently by maximizing the SINR of that subchannel. The convergence of the proposed iterative design algorithm is proven and also the designing procedure is extended for multi-input-multi-output channels. Simulation results show that the proposed OFDM/OQAM system, in addition of its superior bandwidth efficiency, significantly achieves better performance in comparison with the OFDM system. Moreover, the convergence speed of the iterative SINR maximization algorithm is evaluated by numerical assessments under different scenarios.