Doppler spread analysis for suppressing channel time variation in high-mobility massive MIMO V2V communications

Here, fast time-varying channels of high-mobility vehicle-to-vehicle communications for massive multiple-input multiple-output orthogonal frequency division multiplexing systems are considered. Large-scale uniform linear arrays are configured at the transmitter and receiver to separate multiple angle domain Doppler frequency offsets based on transmit and receive beamforming with high spatial resolution. Then, each beamforming branch comprises only one dominant Doppler frequency offset. Next, the conventional channel estimation method is performed for each beamforming branch, and carry out maximum-ratio-combining for data detection. Power spectrum density and Doppler spread of the equivalent link between the transmitter and receiver are derived and regarded as the criterion for assessing the residual channel time variation caused by limited antennas in practice. Interestingly, a scaling law between the asymptotic Doppler spread and the number of transceiver antennas shows that asymptotic Doppler spread is proportional to the maximum Doppler frequency offset and decreases at the rate of $\sqrt{\frac{1}{{N_T}^2}+\frac{1}{{N_R}^2}}$, where $N_T$ and $N_R$ are the number of transmit and receive antennas, respectively. Simulation results confirm the validity of the proposed Doppler suppression framework in high-mobility vehicle-to-vehicle communications.