Practical Waveform Design for ISAC Systems: An Instrumental Variable Approach

With the advancement of hardware and signal processing technologies, next-generation wireless networks are expected to be multi-functional, offering various radio-based services such as communications and sensing. In this context, integrated sensing and communications (ISAC) is a promising solution for improving spectral efficiency, but its implementation is challenging because of practical constraints such as complexity. In this paper, we propose a novel waveform design principle for ISAC systems, which can decompose a complex ISAC waveform design problem into more tractable subproblems. The proposed method enables superimposing a sensing signal onto the communication signal without affecting the communication channel via the instrumental variable (IV) method. We apply the proposed waveform structure to a beampattern matching problem and develop the corresponding solution. We provide an in-depth analysis with respect to degrees of freedom (DoF), channel mismatch, and so forth. We evaluate the performance of the proposed waveform design algorithm through simulations.