Dual-function radar-communication system: when the radar also communicates
Creators: name: Xu, Zhaoyi
Publisher: name: No Publisher Supplied
Year: 2024

description: Dual-function radar-communication (DFRC) systems use the same hardware platform and the same waveform to achieve sensing and communication simultaneously. Due to their high spectral, hardware and power efficiency, DFRC systems are prime candidates for 6G wireless systems. The contribution of this dissertation is three-fold. First, we propose a novel DFRC system design, which, unlike existing methods that are communication- or sensing-centric can flexibly trade off communication rate for improved sensing performance. Second, we study a secure DFRC system for protecting communication information against unknown eavesdroppers. Third, we propose ways to improve the performance of DFRC systems via antenna selection and the use of double-phase shifters (DPS). The proposed DFRC system is a monostatic multiple-input multiple-output (MIMO) radar and transmits orthogonal frequency division multiplexing (OFDM) waveforms from its antennas. The system subcarriers are divided into two groups, i.e., shared and private. On a shared subcarrier, all antennas can transmit simultaneously thus efficiently exploiting the available bandwidth, while on a private one only one antenna can transmit at a time. The private subcarriers enable the construction of a virtual array with larger aperture than the physical receive array. The use of private subcarriers trades off communication rate for sensing performance. By controlling the number of private subcarriers, a flexible trade-off between communication and sensing is achieved. As DFRC systems use the same waveform for sensing and communication, the communication information is exposed to potential eavesdroppers. To mitigate this problem, we propose to leverage directional modulation (DM) enabled by a time-modulated array (TMA) that transmits OFDM waveforms. DM can scramble the signal in all directions except the directions of the legitimate users. However, the signal reflected by the targets is also scrambled, thus complicating the extraction of target parameters. We propose a novel method to estimate target parameters from the scrambled returns. The proposed DFRC system can securely communicate with users while having high-precision sensing functionality. A hybrid MIMO DFRC structure has fewer RF chains than antennas and can be designed to approximate the performance of a full MIMO structure at reduced hardware cost.However, such a structure may have a rank-deficient beamforming matrix, resulting in degraded sensing performance. We propose antenna selection as means to ensure a full-rank beamforming matrix, and also select the communication channels so that a high communication rate can be achieved. Phased array is the most widely used radar and has been employed in DFRC systems due to its low cost and simple structure. In a phased array, all the antenna elements are connected to a single radio-frequency (RF) chain through phase shifters. However, the phase shifters change only the phase of the signal coming from the RF chain, which results in limited beamforming capability. To tackle this issue, we propose to feed each antenna the output of two phase shifters. This enables the control of the signal magnitude as well as the phase, introducing more degrees of freedom in beampattern design. The advantages of the DPS-phase array are demonstrated via simulations and also via experiments with a self-fabricated prototype. The performance of the DPS-phase array in multi-target remote vital sign monitoring is demonstrated.