Integrated sensing and communication (ISAC) has emerged as a pivotal technology for next-generation wireless communication and radar systems, enabling high-resolution sensing and high-throughput communication with shared spectrum and hardware. However, achieving a fine radar resolution often requires high-rate analog-to-digital converters (ADCs) and substantial storage, making it both expensive and impractical for many commercial applications. To address these challenges, this paper proposes an orthogonal time frequency space (OTFS)-based ISAC architecture that operates at reduced ADC sampling rates, yet preserves accurate radar estimation and supports simultaneous communication. The proposed architecture introduces pilot symbols directly in the delay-Doppler (DD) domain to leverage the transformation mapping between the DD and time-frequency (TF) domains to keep selected subcarriers active while others are inactive, allowing the radar receiver to exploit under-sampling aliasing and recover the original DD signal at much lower sampling rates. To further enhance the radar accuracy, we develop an iterative interference estimation and cancellation algorithm that mitigates data symbol interference. We propose a code-based spreading technique that distributes data across the DD domain to preserve the maximum unambiguous radar sensing range. For communication, we implement a complete transceiver pipeline optimized for reduced sampling rate system, including synchronization, channel estimation, and iterative data detection. Experimental results from a software-defined radio (SDR)-based testbed confirm that our method substantially lowers the required sampling rate without sacrificing radar sensing performance and ensures reliable communication.

Numerous anti-jamming techniques are available for wireless communication systems in the literature. However, no work offers a spectrum-efficient anti-jamming technique for orthogonal time frequency space (OTFS) systems under delay Doppler domain jamming attacks, despite it being the most promising waveform for future wireless communication. In this work, we propose two novel and robust anti-jammers based on the maximum correntropy criterion (MCC) and maximum Versoria criterion (MVC). The proposed anti-jamming receivers can withstand most practical jammers, such as shot jammers, chirp jammers, and others. This is because the MCC and MVC-based cost functions are robust under impulsive interference (jamming signals are also high-power impulses that interfere with the intended signals). The theoretical mean deviation of error is computed for proposed anti-jammers to demonstrate their ability to withstand the impacts of jamming. The bit-error rates of the proposed anti-jamming detectors are simulated and compared with the existing detectors for OTFS systems.

This paper proposes index modulation (IM) based on pilot location for an Orthogonal time frequency space (OTFS)based dual function radar communication (DFRC) system to circumvent the complexity involved in conventional IM schemes. A joint channel and indexing of the pilot estimation algorithm is proposed at the communication receiver. A joint target range and precise channel prediction algorithm is proposed at the joint transmitter and radar (JTR). The precise channel information predicted by the JTR is utilized to perform zero-forcing beamforming for providing physical layer security to the proposed autonomous vehicle network (AVN) over limited feedback and high mobility scenario. A closed-form expression of ergodic secrecy capacity over an outdated and generalized Norton channel is derived to provide the analytical guarantees of the proposed algorithms. Simulations of different performance metrics for the proposed schemes are provided and corroborated with existing works.

Underlay device-to-device (D2D) communication network is becoming a promising solution for the fifth generation (5G) and beyond wireless technology. It exploits the proximity of the D2D pairs and improves the overall network’s latency, capacity, and spectral efficiency by sharing/reusing the existing cellular resources. However, due to the frequency-sharing/reusing, the security of the device users (DUs) and the cellular users (CUs) becomes vulnerable. This paper presents a novel physical-layer security (PLS) scheme for the underlay multiple-input multiple-output (MIMO) D2D communications in the presence of multiple eavesdroppers. The proposed new PLS scheme can significantly reduce the information leakage for both CUs and DUs by adopting a null steering scheme at the transmitter. A signal alignment technique is also employed to eradicate the stringent requirement of a larger number of transmitter antennas than that of the receiver antennas. A generalized nonlinear optimization problem has been formulated to improve the PLS performance for MIMO-D2D communications. A closed-form and generalized analytical expression of the secrecy outage probability for CUs and DUs is derived over the imperfect Nakagami-$m$and Norton fading channels. Theoretical and simulation results of our proposed new PLS scheme have shown significant improvement in the secrecy capacity and secrecy outage probability for both CUs and DUs in comparison with the existing methods.