Optimization and Quantization of Multibeam Beamforming Vector for Joint Communication and Radio Sensing

Abstract

Joint communication and radio sensing (JCAS) in millimeter wave (mmWave) systems requires the use of steerable beam. For analog antenna arrays, a single beam is typically used, which limits the sensing area to within the direction of the communication. Multibeam technology can overcome this limitation by separately generating package-level directionvarying sensing subbeams and fixed communication subbeams and then combing them coherently. In this paper, we investigate the optimal combination of the two subbeams and the quantization of the beamforming (BF) vector that generates the combined beam. When either full channel matrix or only the angle of departure (AoD) of the dominating line-of-sight (LOS) path is known at the transmitter, we derive closed-form expressions for the optimal combining coefficients that maximize the received communication signal power. For quantization of the BF vector, we focus on the two-phase-shifter array where two phase shifters are used to represent each BF weight. We propose novel joint quantization methods by combining the codebooks of the two phase shifters. The mean squared quantization error is derived for various quantization methods. Extensive simulation results validate the accuracy of the analytical results and the effectiveness of the proposed multibeam optimization and joint quantization methods.

An Overview of Signal Processing Techniques for Joint Communication and Radar Sensing

“…A good solution is the multibeam technology [23], [75], [76]. The multibeam consists of a fixed subbeam dedicated to communication and a scanning subbeam with directions varying over different communication packets.…”

“…Two classes of methods have been proposed for the multibeam optimization: the subbeam-combination method [23], [75], [76] via constructively combining two pre-generated subbeams according to given criteria, and the global optimization [76] by jointly considering the C&R BF requirements and optimizing a single BF vector directly. These methods can also be extended to full digital arrays.…”

“…where w T,F and w T,S are the BF vectors that are predetermined, corresponding to the fixed subbeam and scanning subbeam, respectively. The value of ρ can typically be determined via balancing C&R distances [75], and the optimization is conducted mainly with respect to ϕ, which can ensure the pregenerated subbeams are coherently combined when generating the multibeam.…”

Beamformer Design and Optimization for Full-Duplex Joint Communication and Sensing at mm-Waves

“…In this case, the JCAS system transmits a sum of independent communication and sensing waveforms, forming multiple beams. The effects of beamforming weight quantization in multibeam JCAS systems are analyzed in [27], focusing purely on the TX side and thus neglecting joint TX-RX optimization.…”

“…Then, similar to [24], [27], [39], the communication and sensing weights are combined coherently. Considering the U communication beams and a single sensing beam, all coexisting simultaneously, the combined TX weights can be expressed as…”