Integrated sensing and symbiotic backscatter communication (ISSBC) enables a cooperative receiver (CRX) to communicate with and locate a low-cost backscatter device (BD), thus is recognized as a promising technology for future low-power Internet of Things. This paper focuses on the BD location sensing and data detection for an ISSBC system with blocked BD-to-CRX line-of-sight path. In such non-line-of-sight (NLOS) scenario, the existing localization algorithms are not applicable, and the detection algorithms suffer from poor performance due to extremely weak backscatter signal. As such, utilizing the designed frame structure, we propose a two-stage three-dimensional (3D) localization method based on the forward–backward spatial-smoothing multiple signal classification (SSMUSIC) and specular reflection geometry (SRG). The CRX estimates the angles of arrival (AOAs) via the SSMUSIC-SRG algorithm to obtain the environmental reflector locations in the first stage with silent BD and utilizes the reflector locations and the estimated backscatter-link AOAs to obtain the BD’s 3D coordinates in the second stage with backscattering BD. Moreover, we propose a maximum likelihood detector for the BD signal. The strong direct-link interference (DLI) from the RF source is first canceled via successive interference cancelation, and the residual DLI is further mitigated by the obtained optimal receive beamformer in closed form. Numerical results verify that the proposed method outperforms the RSSI-based localization and conventional beamforming baselines. The proposed method achieves a localization root mean squared error of 3 centimeters at a signal-to-noise ratio (SNR) of 15 dB, and 7.6 dB SNR gain for backscatter detection at a bit error rate of 0.001.
Li et al. (Mon,) studied this question.