Joint channel tracking and intercarrier-interference equalisation for vertical Bell Labs layered space time-orthogonal frequency division multiplexing in vehicle ad hoc network

Vertical Bell Labs layered space time-orthogonal frequency division multiplexing (VBLAST-OFDM) systems can achieve high spectral efficiency in quasi-stationary links and with channel state information (CSI) matrix knowledge. Owing to the high speeds of nodes in vehicle ad hoc network (VANET), the channel is fast fading thus raising the need for channel tracking. Furthermore, inter-carrier interference (ICI) causes an error floor at high signal-to-noise ratio (SNR) even with perfect CSI knowledge. In this paper we investigate channel tracking and ICI mitigation for VBLAST-OFDM. The analysis of ICI shows that it increases with speed, number of subcarriers and/or number of transmit antennas. The authors then introduce a simple channel tracking algorithm for VBLAST-OFDM. Simulation results show that our algorithm reduces the bit error rate (BER) of a 2 times 4 VBLAST system by 10^-2 at 40 dB SNR and 100 km/h speed compared to obtaining a channel estimate from a training sequence only. The change in the channel response is estimated using the channel tracking algorithm and then passed to an ICI equaliser to enhance performance and reduce the error floor caused by ICI at high SNR. Equalising five pairs of subcarriers gives 4 dB improvement for 2times4 VBLAST at 180 km/h relative speed. The performance is enhanced as more subcarriers are included in the ICI equaliser at the expense of increased receiver complexity.