Waveform Design for Integrated Sensing and Communication Systems Based on Interference Exploitation

Integrated sensing and communication (ISAC) is a spectrum and energy efficient approach to realizing dual functions by a unified hardware platform. In this paper, we consider a multiple-input multiple-output (MIMO) ISAC system, where the transmitted waveform consisting of communication signals and dedicated sensing signal is optimized for dual purposes of estimating targets and serving downlink single-antenna users. Specifically, the sensing interference and multi-user interference are exploited, rather than suppressed, by the waveform design scheme. The joint waveform design problem is formulated by maximizing the constructive interference (CI) while ensuring the power budget and waveform similarity error with the benchmark signal, which limits the sensing estimation accuracy. To obtain the benchmark signal which achieves the optimal estimation performance, we propose a semidefinite relaxation based algorithm to solve the optimization problem. For clarity, we derive the real representation of the complex joint waveform design problem and prove its convexity. Numerical results verify the superiority of the proposed CI-based waveform design when the interference was efficiently exploited as a useful signal source achieving favorable symbol error ratio performance. Moreover, the dedicated sensing signal provides more degree of freedom for waveform design.