In this paper, we investigate physical-layer security of the uplink millimeter wave communications for a cellular vehicle-to-everything (C-V2X) network comprised of a large number of base stations (BSs) and different categories of V2X nodes, including vehicles, pedestrians, and road side units. Considering the dynamic change and randomness of the topology of the C-V2X network, we model the roadways, the V2X nodes on each roadway, and the BSs by a Poisson line process, a 1D Poisson point process (PPP), and a 2D PPP, respectively. We propose two uplink association schemes for a typical vehicle, namely, the smallest-distance association (SDA) scheme and the largest-power association (LPA) scheme, and we establish a tractable analytical framework to comprehensively assess the security performance of the uplink transmission, by leveraging the stochastic geometry theory. Specifically, for each association scheme, we first obtain new expressions for the association probability of the typical vehicle, and then derive the overall connection outage probability and secrecy outage probability by calculating the Laplace transform of the aggregate interference power. Numerical results are presented to validate our theoretical analysis, and we also provide interesting insights into how the security performance is influenced by various system parameters, including the densities of V2X nodes and BSs. Moreover, we show that the LPA scheme outperforms the SDA scheme in terms of secrecy throughput.

This paper studies covert communications between a pair of legitimate transmitter-receiver against a watchful warden over fading channels. There coexist multiple friendly helper nodes who are willing to protect the covert communication from being detected by the warden. An uncoordinated jammer selection scheme is proposed where those helpers whose instantaneous channel gains to the legitimate receiver fall below a pre-established selection threshold will be chosen as jammers radiating jamming signals to defeat the warden. Afterwards, we jointly design the optimal selection threshold and transmission rate for maximizing covert throughput under the premise that the detection error of the warden exceeds a certain level. Numerical results demonstrate that the maximal covert throughput improves significantly as the total number of helpers increases.

In this paper, we investigate secure content delivery in a two-tier cache-enabled millimeter wave (mmWave) heterogeneous network composed of a macro base station (MBS) and K small base stations (SBSs) with caching capabilities. We allocate finite cache units at the SBSs and MBS to pre-store files with high popularities, where the SBSs store the most popular files, and the MBS stores the less popular ones. To deliver the file requested by a legitimate user securely, two secure transmission schemes, namely, distributed beamforming and direct transmission, are employed at the SBSs and MBS, respectively. Moreover, artificial noise (AN) is combined with the above two transmission schemes to further improve transmission security. The connection outage probability, secrecy outage probability, and secrecy throughput for the proposed mmWave transmission schemes are obtained. Based on these results, we jointly design the transmission rates and the cache resource allocation between the SBSs and MBS to maximize the overall secrecy throughput. We also provide insights into how the overall secrecy throughput is influenced by various parameters, including transmission rates, power allocation ratio of the AN scheme, and cache allocation factor. Numerical results are eventually presented to validate our theoretical analysis and demonstrate the effectiveness of the proposed transmission schemes and cache resource allocation strategy.

In this paper, we study millimeter wave (mmWave) communications of an uplink cellular vehicle-to-everything (C-V2X) network consisting of vehicles, pedestrians, road side units (RSUs), and cellular base stations (BSs). We propose an association scheme that a vehicle delivers messages to either the V2X nodes, including vehicles, pedestrians, and RSUs, or the BSs, based on the distance and the bias factor. Subsequently, we provide a tractable analytical framework to comprehensively assess the reliability performance of the considered uplink transmission, in terms of success probability. By leveraging the stochastic geometry theory, we model the locations of vehicles, pedestrians, and RSUs as independent cox process and model the locations of BSs as a Poisson point process (PPP), and derive new expressions for the association probability, the success probability of different associating types, and the overall success probability of the C-V2X network. Numerical results are presented to validate the theoretical analyses and provide interesting insights into how the success probability is influenced by various parameters, including the signal-to-interference-plus-noise ratio (SINR) threshold, the densities of V2X nodes and BSs, the blockage density, and the bias factor.

This paper studies multi-antenna covert communications coexisting with randomly located wardens and interferers. We analyze and optimize the covert throughput under a stochastic geometry framework. We first introduce covert outage probability and connectivity probability to respectively characterize covertness and reliability, and derive analytically tractable expressions for them. We then consider a worst-case covert communication, where the wardens can invariably maximize the covert outage probability by adjusting the detection thresholds of their detectors. Afterwards, we jointly design the optimal transmit power and transmission rate to maximize the covert throughput while satisfying the covertness requirement. Interestingly, it is found that the maximal covert throughput is invariant to either the density of interferers or the interfering power, regardless of the number of transmit antennas.