Equalisation, despreading, and beamforming scenarios of complex spread-OFDM/OQAM in single-input multi-output channels

Orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) is a promising multicarrier system, which can achieve a better bandwidth efficiency than cyclic prefix (CP)-OFDM. However, OFDM/OQAM suffers from an inherent interference. Since in OFDM/OQAM, the data symbols are real-valued, the pure imaginary self-interference can be eliminated by removing the imaginary part of the received signal. On the other hand, in the literature, it is shown that even for complex-valued data symbols, the self-interference can be eliminated if a spreading code is employed. The resulted scheme is called spread-OFDM/OQAM. In this study, we extend spread-OFDM/OQAM for single-input multi-output channels. In case of multiple antennas, at the receiver after demodulation, the following processes must be performed: equalisation (to remove the channel effect), despreading of spreaded symbols, and beamforming of multiple antennas. We propose three scenarios to apply the mentioned processes. In the first scenario, despreading, equalisation, and beamforming are performed jointly in one step. In the second scenario, despreading and equalisation are accomplished jointly and then beamforming is performed. In the last scenario, each of those processes is applied separately. We compare the complexity of the proposed approaches. Also their performance is evaluated through simulations in terms of bit error rate.