High doppler MIMO OFDM capacity maximizing spatial transceivers exploiting excess cyclic prefix

Performance of OFDM systems is limited by inter carrier interference (ICI) under high Doppler scenarios such as that encountered in high speed trains such as TGV. Several publications have addressed the receiver design for SISO (single input single output) and SIMO (single input multiple output) to combat ICI. Notably, the use of multiple receive antennas is a known to be a very effective way to combat ICI. In a recent publication, the authors explored the use of transmit (Tx) antennas for ICI mitigation. It considered a MIMO (multiple input multiple output) scenario and iteratively designed a transmit beamformer to maximize the sum capacity across all the subcarriers in the presence of ICI. Another important tool in the mitigation of ICI is the exploitation of excess CP (cyclic prefix). With an appropriate window function, the excess CP at the receiver may be exploited to reduce the ICI. In this work, we extend the transmit beamformer design to include the excess CP exploitation at the receiver. We jointly optimize both the receive window coefficients and the transmit beamformer using alternating minimization. The optimal window is determined using gradient descent algorithm. The convergence of the iterative approach is proved and the theory is validated via numerical simulations.