MU-MIMO Communications with MIMO Radar: From Co-existence to Joint Transmission

Beamforming techniques are proposed for a joint multi-input-multi-output (MIMO) radar-communication (RadCom) system, where a single device acts both as a radar and a communication base station (BS) by simultaneously communicating with downlink users and detecting radar targets. Two operational options are considered, where we first split the antennas into two groups, one for radar and the other for communication. Under this deployment, the radar signal is designed to fall into the null-space of the downlink channel. The communication beamformer is optimized such that the beampattern obtained matches the radar's beampattern while satisfying the communication performance requirements. To reduce the optimizations' constraints, we consider a second operational option, where all the antennas transmit a joint waveform that is shared by both radar and communications. In this case, we formulate an appropriate probing beampattern, while guaranteeing the performance of the downlink communications. By incorporating the SINR constraints into objective functions as penalty terms, we further simplify the original beamforming designs to weighted optimizations, and solve them by efficient manifold algorithms. Numerical results show that the shared deployment outperforms the separated case significantly, and the proposed weighted optimizations achieve a similar performance to the original optimizations, despite their significantly lower computational complexity.Comment: 15 pages, 15 figures. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Utilizing sidelobe ASK based joint radar-communication system under fading

© 2017 IEEE. A joint radar-communication (JRC) system can provide cost-effective and spectrum-efficient platform solution with simultaneous operation, while accomplishing important tasks, sensing via radar processing and allocation of communication links. Existing modulation techniques where information embedding is achieved using sidelobe Amplitude-Shift Keying (ASK) for the JRC system are not investigated so far under fading channels and an optimum threshold estimation algorithm is yet to be developed. Specifying an optimum threshold level under fading can become a comprehensive problem, especially for mobile communication systems. In this paper, a novel non-data aided (NDA) threshold estimation technique and a receiver design are introduced. Furthermore, a new sidelobe ASK modulation technique is proposed for utilizing JRC system for mobile platforms under fading. Proposed modulation technique implements dual Sidelobe Level (SLL) ASK with waveform diversity by exploiting multiple orthogonal waveforms. One pair is modulated with dual SLL in amplitude rotational manner and initiates NDA threshold estimation process at the receiver. This method utilizes K bits of information using only K + 1 orthogonal waveform. The performance of the proposed technique is investigated in terms of the bit error rate (BER) and data rate. Simulations reveal that the operation of proposed method coupled with NDA threshold estimation process can reach more data rate, since it exhibits almost the same BER performance as existing methods under fading channel without requiring more orthogonal waveform

Physical Layer Security in Integrated Sensing and Communication Systems

The development of integrated sensing and communication (ISAC) systems has been spurred by the growing congestion of the wireless spectrum. The ISAC system detects targets and communicates with downlink cellular users simultaneously. Uniquely for such scenarios, radar targets are regarded as potential eavesdroppers which might surveil the information sent from the base station (BS) to communication users (CUs) via the radar probing signal. To address this issue, we propose security solutions for ISAC systems to prevent confidential information from being intercepted by radar targets. In this thesis, we firstly present a beamformer design algorithm assisted by artificial noise (AN), which aims to minimize the signal-to-noise ratio (SNR) at the target while ensuring the quality of service (QoS) of legitimate receivers. Furthermore, to reduce the power consumed by AN, we apply the directional modulation (DM) approach to exploit constructive interference (CI). In this case, the optimization problem is designed to maximize the SINR of the target reflected echoes with CI constraints for each CU, while constraining the received symbols at the target in the destructive region. Apart from the separate functionalities of radar and communication systems above, we investigate sensing-aided physical layer security (PLS), where the ISAC BS first emits an omnidirectional waveform to search for and estimate target directions. Then, we formulate a weighted optimization problem to simultaneously maximize the secrecy rate and minimize the Cram\'er-Rao bound (CRB) with the aid of the AN, designing a beampattern with a wide main beam covering all possible angles of targets. The main beam width of the next iteration depends on the optimal CRB. In this way, the sensing and security functionalities provide mutual benefits, resulting in the improvement of mutual performances with every iteration of the optimization, until convergence. Overall, numerical results show the effectiveness of the ISAC security designs through the deployment of AN-aided secrecy rate maximization and CI techniques. The sensing-assisted PLS scheme offers a new approach for obtaining channel information of eavesdroppers, which is treated as a limitation of conventional PLS studies. This design gains mutual benefits in both single and multi-target scenarios

Toward Multi-Functional 6G Wireless Networks: Integrating Sensing, Communication, and Security

Integrated sensing and communication (ISAC) has recently emerged as a candidate 6G technology, aiming to unify the two key operations of the future network in a spectrum/energy/cost-efficient way. ISAC systems communicate and sense for targets using a common waveform, a common hardware platform, and ultimately the same network infrastructure. Nevertheless, the inclusion of information signaling in the probing waveform for target sensing raises challenges from the perspective of information security. At the same time, the sensing capability incorporated in ISAC transmission offers unique opportunities to design secure ISAC techniques. This overview article discusses these unique challenges and opportunities for the next generation of ISAC networks. We first briefly discuss the fundamentals of waveform design for sensing and communication. Then we detail the challenges and contradictory objectives involved in securing ISAC transmission, along with state-of-the-art approaches to ensure security. We then identify the new opportunity of using the sensing capability to obtain knowledge target information as an enabling approach against the known weak-nesses of PHY security. Finally, we illustrate some low-cost secure ISAC architectures, followed by a series of open research topics. This family of sensing-aided secure ISAC techniques brings new insight on providing information security, with an eye on robust and hardware-constrained designs tailored for low-cost ISAC devices

Toward Multi-Functional 6G Wireless Networks: Integrating Sensing, Communication, and Security

Integrated sensing and communication (ISAC) has recently emerged as a candidate 6G technology, aiming to unify the two key operations of the future network in a spectrum/energy/cost-efficient way. ISAC systems communicate and sense for targets using a common waveform, a common hardware platform, and ultimately the same network infrastructure. Nevertheless, the inclusion of information signaling in the probing waveform for target sensing raises challenges from the perspective of information security. At the same time, the sensing capability incorporated in ISAC transmission offers unique opportunities to design secure ISAC techniques. This overview article discusses these unique challenges and opportunities for the next generation of ISAC networks. We first briefly discuss the fundamentals of waveform design for sensing and communication. Then we detail the challenges and contradictory objectives involved in securing ISAC transmission, along with state-of-the-art approaches to ensure security. We then identify the new opportunity of using the sensing capability to obtain knowledge target information as an enabling approach against the known weak-nesses of PHY security. Finally, we illustrate some low-cost secure ISAC architectures, followed by a series of open research topics. This family of sensing-aided secure ISAC techniques brings new insight on providing information security, with an eye on robust and hardware-constrained designs tailored for low-cost ISAC devices

Low-Complexity Reduced-Rank Beamforming Algorithms

A reduced-rank framework with set-membership filtering (SMF) techniques is presented for adaptive beamforming problems encountered in radar systems. We develop and analyze stochastic gradient (SG) and recursive least squares (RLS)-type adaptive algorithms, which achieve an enhanced convergence and tracking performance with low computational cost as compared to existing techniques. Simulations show that the proposed algorithms have a superior performance to prior methods, while the complexity is lower.Comment: 7 figure