Eigenvector precoding for FBMC modulations under strong channel frequency selectivity

The problem of eigenvector precoding for multi-stream MIMO transmission with filterbank multicarrier (FBMC) modulations is considered. The transmitter is assumed to use a different precoding matrix for each subcarrier, which is constructed by selecting some eigenvectors of the channel matrix. Surprisingly, the phase ambiguity that is inherent to the definition of the eigenvectors turns out to have a crucial effect on the system performance under strong channel frequency selectivity. This is due to the inherent lack of orthogonality of FBMC modulations in these situations. It is shown that by properly selecting the reference phase evolution of each eigenvector across the transmission bandwidth, the global performance of the system can be significantly improved. A phase reference construction strategy is presented that minimizes an upper bound on the total intersymbol/intercarrier interference (ISI/ICI) power.