Discrete Codebook Synthesis for Self-interference Suppression based on Fractional Programming and Spherical Search

This work presents an efficient codebook synthesis method with self-interference (SI) suppression for mmWave integrated sensing and communication (ISAC) devices employing RF beamforming. We formulate a signal-to-interference-and-noise ratio (SINR) maximization problem which aims to suppress the near-field SI signal while maintaining the beamforming gain in the far-field sensing directions. In particular, we consider the practical constraints of discrete codebooks with quantized phase settings. To solve such a discrete optimization problem, we propose to use a fractional programming (FP) technique to decouple the numerator and the denominator of the optimization target, which is followed by a spherical search (SS). Simulations show that the proposed method significantly outperforms the existing methods, which are based on continuous optimization algorithms. The results also demonstrate that the proposed method can reach the same performance as the exhaustive search method, but with a lower complexity.