Automotive radars at the Terahertz (THz) frequency band have the potential to be compact and lightweight while providing high (nearly-optical) angular resolution. In this paper, we propose a bistatic THz automotive radar that employs the recently proposed orthogonal chirp division multiplexing (OCDM) multi-carrier waveform. As a standalone communications waveform, OCDM has been investigated for robustness against interference in time-frequency selective channels. The THz-band path loss, and, hence, radar signal bandwidth, are range-dependent. We address this unique feature through a multicarrier wideband OCDM sensing transceiver that exploits the coherence bandwidth of the THz channel. We develop an optimal scheme to combine the returns at different ranges/bandwidths by assigning weights based on the Cramér-Rao lower bound on the range and velocity estimates. Numerical experiments demonstrate improved target estimates that can be obtained using our proposed combined estimation from measurements with varied attenuation at THz bands.

We consider a bistatic vehicular integrated sensing and communications (ISAC) system that employs the recently proposed orthogonal chirp division multiplexing (OCDM) multicarrier waveform. As a stand-alone communications waveform, OCDM has been shown to be robust against the interference in time-frequency selective channels. In a bistatic ISAC, we exploit this property to develop efficient receive processing algorithms that achieve high target resolution as well as high communications rate. We derive statistical bounds for our proposed Sequential symbol decoding and radar parameter estimation (SUNDAE) algorithm and compare its competitive performance with other multicarrier waveforms through numerical experiments.

We study the performance of a cognitive small cell network, catering multicast services to multiple groups of secondary users, using a pre-assigned set of orthogonal channels of primary users present in the corresponding macrocell. We consider the hybrid mode of cognitive radio operation for efficient spectrum access, where cooperative spectrum sensing is performed by the collocated secondary users of each group to ensure better protection to primary users' communication. Considering delay-sensitive application for each multicast group and availability of a rate adaptive application layer and a power adaptive link layer, we aim to maximize the energy efficiency of the small cell base station using a cross-layer approach. More precisely, a joint optimization problem involving sensing time, rate and power allocation is formulated to maximize the energy efficiency of the small cell network under the probabilistic interference constraint of each primary user and heterogeneous quality of service constraints of each SU multicast group. The problem is found to be generally non-convex and an iterative algorithm is proposed to find either an optimal or a near-optimal solution. Simulation results are presented to analyze the performance of our proposed scheme in terms of energy efficiency concerning some key system parameters. The results confirm that our solution is much more energy-efficient than the conventional approach with only transmit power adaptation.

This study outlines a non‐orthogonal multiple access (NOMA) scheme for cooperative multicasting in a cognitive radio network. The network consists of a common base station (BS), which serves a primary user multicast group (PU‐MG) and a secondary user MG (SU‐MG). The SU‐MG is located in between the BS and the PU‐MG. Their proposed spectrum sharing protocol comprises of three transmission phases. The first phase is utilised by the BS for multicasting both PUs' and SUs' signals, using NOMA transmission. In the second phase, to overcome fading impairments, the BS exploits spatial diversity among SUs, by seeking their cooperation to relay PUs' message signal. The BS, as an incentive, leases a time slot in the third phase, exclusively for supporting multicast to SU‐MG over PUs' licenced spectrum. Analytical expressions for outage probabilities of both PU‐MG and SU‐MG are derived and validated using simulations. Furthermore, outage performance of PUs and ergodic capacity of SUs are compared with a prominent recent scheme.