Hybrid Precoding and Combining for mmWave Full-Duplex Joint Radar and Communication Systems under Self-Interference

TL;DR

The paper tackles SI in mmWave full-duplex ISAC with a hybrid MIMO constraint by formulating a precoding problem that maximizes downlink rate while suppressing SI and guaranteeing radar gain. It solves a generalized eigenvalue problem $A_m F_m = C F_m \Lambda_m$ to optimize spectral efficiency, then coherently beams toward the radar direction using $B = a_{BS}(\theta_r) a_{BS}^H(\theta_r)$ and implements the solution via a hybrid decomposition ${F_m^{BS}} \approx F^{BS,RF} F_m^{BS,BB}$ under unit-modulus constraints. An analog combiner design via non-convex optimization and block-coordinate-descent further reduces residual SI while preserving radar performance. The system uses OFDM radar processing by constructing $Z$, applying DFTs to obtain $\bar{Z}$, and extracting range and velocity through $r = \frac{\bar{m}^* c}{2 \bar{M} \Delta f}$ and $v = \frac{\bar{n}^* \lambda}{\bar{N} T}$, achieving accurate target estimates. Numerical results show the architecture meets radar gain and SI mitigation with only small downlink spectral efficiency loss, and OFDM radar yields high-accuracy sensing, indicating practical viability for mmWave ISAC.

Abstract

In the context of integrated sensing and communication (ISAC), a full-duplex (FD) transceiver can operate as a monostatic radar while maintaining communication capabilities. This paper investigates the design of precoders and combiners for a joint radar and communication (JRC) system at mmWave frequencies. The primary goal of the design is to guarantee certain performance in terms of some sensing and communication metrics while minimizing the self-interference (SI) caused by FD operation and taking into account the hardware limitations coming from a hybrid MIMO architecture. Specifically, we introduce a generalized eigenvalue-based precoder design that considers the downlink user rate, the radar gain, and the SI suppression. Since the hybrid analog/digital architecture degrades the SI mitigation capability of the precoder, we further enhance SI suppression with the analog combiner. Our numerical results demonstrate that the proposed architecture achieves the required radar gain and SI mitigation while incurring a small loss in downlink spectral efficiency. Additionally, the numerical experiments also show that the use of orthogonal frequency division multiplexing (OFDM) radar with the proposed beamforming architecture results in highly accurate range and velocity estimates for the detected targets.

Figures (4)

• Figure 1: FD-JRC system with a downlink MS and target echoes.
• Figure 2: Downlink spectral efficiency vs $P_{\rm t}$ for different precoding methods.
• Figure 3: Radar SINR vs SI-to-noise ratio for different precoding and combining methods with $\tau_{\rm T}=0.35\sqrt{N_{\mathrm{BS}}}$ and $P_{\rm t}=20$dBm.
• Figure 4: Angle-range and range-velocity maps of the targets.