“Make-It-Real” precoders for MIMO OFDM/OQAM without inter carrier interference

Low complexity Multiple Input Multiple Output (MIMO) precoders for Orthogonal Frequency Division Multiplex (OFDM), such as Maximum Ratio Transmission (MRT) and Minimum Mean Square Error (MMSE) precoders enable to multiplex data streams in the spatial domain, without breaking OFDM orthogonality in the frequency domain, and therefore achieve a high spectral efficiency. OFDM using Offset Quadrature Amplitude Modulation (OFDM/OQAM) is an alternate modulation which is more spectrally efficient than OFDM. Unfortunately, when applied to OFDM/OQAM, traditional low complexity precoders introduce an inter-carrier interference (ICI) which is complex to cancel at the receiver side. This paper proposes a new family of low complexity precoders, called “Make-It-Real” (MIR) precoders. These precoders are designed so that the equivalent channel including precoding and propagation is “made real” and does not break the orthogonality of OFDM/OQAM in the frequency domain. At the receiver side, a simple extraction of the real part of the demodulated signal is necessary. Simulations show that OFDM/OQAM with MIR MMSE precoder outperforms all studied MIMO OFDM solutions, without requiring a complex ICI cancellation at the receiver.