Performance Trade-off in Joint Radar & Communications Transmit Beamforming

In this paper, we propose a joint multi-user communications and multi-direction radar beamforming design where the communications waveform is used for both communications and radar functions. The common-waveform design contrasts with traditional system designs, wherein separate waveforms are used to perform radar and communications operations. Employing a common waveform eliminates the notion of cross-system interference and, as demonstrated in this paper, provides improved performance for both operations. The proposed beamformer design, the SNR-maximizing common-waveform (SMCW) beamforming, maximizes total radar target signal-to-noise ratio while meeting communications rate constraints.The SMCW beamformer achieves higher radar target SNR, which translates to improved performance compared to stateof-the-art designs that we characterize by joint radar and communications achievable SINR regions. Numerical evaluation demonstrates that the common-waveform design allows smooth control over the radar-communications performance trade-off. It is demonstrated that not only does the SMCW design yield significant radar performance gains in exchange for a small sacrifice in communications performance, but it is also shown that this radar-communications trade-off is better for the SMCW design than for state-of-the-art designs.