A practical precoding approach for radar/communications spectrum sharing

In this paper, we consider spectrum sharing between multiple-input multiple-output (MIMO) radar system and a communication system modeled as MIMO interference channel. We derive a zero-forcing precoder for radar transmitter which completely eliminates the radar interference to communication users. Obtaining the precoder requires the knowledge of an effective interference channel matrix composed of the channel matrices to all of the communication receivers and the postprocessing matrices employed by them. We propose a channel estimation phase in which all of the communication receivers coordinate in their choice of training symbols and power transmission and the radar transmitter can estimate the effective interference channel. We investigate the effect of radar precoder and channel estimation error on the performance of radar and interference to communication receivers. Our results indicate that while the precoder null steers the radar interference to communication users it degrades the radar performance by introducing correlation to the probing signals. We show that this performance loss can be compensated for by increasing the number of radar antennas.