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With the development of satellite communication technology, the application of satellites in the Internet of Vehicles (IoV) system can effectively solve the limitations and deficiencies of ground communication networks. In this article, we investigate the security outage performance of a satellite–vehicle communication system consisting of a satellite ($S$), a legitimate receiving vehicle ($C$), and an eavesdropping vehicle ($E$), where $C$ and $E$ are randomly located on two different roads within the coverage area of $S$ and randomly distributed on their respective roads. The downlink communication links between $S$ and these terrestrial vehicles are assumed to suffer the shadowed-Rician fading. Then, the secrecy outage probability (SOP) is studied under the most straightforward case that $ C$ and $E$ are equipped with a single antenna. Next, we extend to the more common scenario where both $C$ and $E$ adopt multiple antennas by deriving the analytical expression for the SOP. Finally, numerical results are presented to verify our proposed analytical models.

Underwater exploration, inspection, and surveillance have become more popular thanks to recent advancements in underwater wireless communication technologies, of which underwater wireless optical communication (UWOC) boasts increased bandwidth, reduced latency, and heightened security. Normally, once underwater sensors collect the data, it is transmitted to remote offices through a relay node stationed on the sea surface. In this study, our focus is on establishing and analyzing the performance of secrecy outage in an uplink hybrid radio frequency (RF)-UWOC space-ocean system that comprises a collection of underwater sensors, a relay floating on the ocean surface, a legitimate satellite receiver, and an eavesdropping satellite. In the considered system, the transmission performance from end-to-end is influenced by several factors. These include path loss, small-scale fading, position randomness of the satellites in RF links, propagation loss, turbulence-induced fading, and random location distribution of the underwater sensors in UWOC links. To enhance our understanding of system design, geometric probability theory is employed to investigate the end-to-end secrecy outage performance of the dual-hop RF-UWOC space-ocean uplink transmission while comprehensively considering the impacts of these factors. Finally, the accuracy of the proposed analysis models is verified through numerical results.

Millimeter wave (mmWave) signals are sensitive to blockages in wireless channels. Traditional mmWave transceiver designs intend to harvest both beamsteering and spatial multiplexing gains, but without considering the potential change in the channel state incurred by sudden blockages. In this paper, we propose a blockage-resilient hybrid transceiver design for supporting robust data transmissions in the face of dynamic blockages. Upon exploiting the spatial structure of mmWave channels, we formulate a weighted spectral efficiency maximization problem by utilizing the statistical information concerning the potential future blockages of different path clusters, which uniquely distinguishes this work from existing transceiver optimization problems. On the basis of alternating optimization, we propose a two-stage algorithm to deal with the resultant non-convex problem riddled with highly coupled variables. First, we alternatively optimize the fully digital transmit precoder and receive equalizer by transforming the optimization problem into a quadratic form. Based on the Block Successive Upper-bound Minimization (BSUM) framework, the optimal fully digital precoder and equalizer can be found by exploiting the Karush-Kuhn-Tucker (KKT) conditions and the matrix monotonic method. Then, inspired by the sparse signal recovery philosophy, the hybrid analog/digital transceiver structure is designed for approximating the fully digital solution. Our numerical results show that the proposed design strikes an improved throughput vs. blockage-resilience trade-off compared to existing schemes, which demonstrates its superiority.

Channel estimation and data detection constitute a pair of pivotal modules in multiple-input multiple-output (MIMO) communication systems, where achieving accurate channel estimation is particularly important for large-scale MIMO communications. However, more accurate channel estimation requires more resources. Hence, we investigate the joint optimization of the channel estimator, transmit precoder and receiver in large-scale MIMO systems. In contrast to the classic signal processing philosophy, the joint optimization aims for solving two equations in the face of realistic channel estimation and data transmission imperfections. Closed-form solutions are derived for a pair of schemes. For the first one, the joint optimization consists of the three procedures of channel estimation, data estimation and channel refinement. In this method, the estimated data symbols are also harnessed as pilots, based on which the channel estimation performance is improved. As for the second scheme, since data estimation is our final goal and channel estimation is only an intermediate step, the channel estimation procedure is substituted into the data estimation regime without deriving an explicit solution for the estimated channel. Given our objective of optimizing the data estimation performance, the channel estimator and data transceiver are jointly optimized, and the intricate linkages between these two methods are discussed. Finally, several numerical results are provided for demonstrating the performance advantages over the traditional designs.

This letter investigates the secure delivery performance of the rate-splitting multiple access scheme in land mobile satellite (LMS) systems, considering that the private messages intended by a terminal can be eavesdropped by any others from the broadcast signals. Specifically, the considered system has an $N$ -antenna satellite and numerous single-antenna land users. Maximum ratio transmission (MRT) and matched-filtering (MF) precoding techniques are adopted at the satellite separately for the common messages (CMs) and for the private messages (PMs), which are both implemented based on the estimated LMS channels suffering from the Shadowed-Rician fading. Then, closed-form expressions are derived for the ergodic rates for decoding the CM, and for decoding the PM at the intended user respectively, and more importantly, we also derive the ergodic secrecy rate against eavesdropping. Finally, numerical results are provided to validate the correctness of the proposed analysis models, as well as to show some interesting comparisons.

Coherent fast frequency hopping (CFFH) is attracting growing attention owing to its good antijamming performance and the coherent combining ability. However, compared with the conventional non-coherent fast frequency hopping, CFFH requires a more precise system synchronization. In this paper, we propose a new fine synchronization algorithm for CFFH. This algorithm consists two stages, namely, open-loop stage and closed-loop stage. In the open-loop stage, a grid-based search parameter estimation method is proposed. In the closed-loop stage, we construct a fully coherent phase-locked loop (PLL) and a delay-locked loop (DLL) with decoding feedback structure to perform further fine estimation of the system clock skew and time delay, respectively. Moreover, we analyze the effect of the search parameter settings on the estimation error and derive the root mean squared error (RMSE) of estimates in the steady state of the closed-loop stage. Finally, through simulation, the RMSE performance are compared with the corresponding Cramer-Rao low bound (CRLB) and conventional code loop estimation to show the effectiveness of proposed algorithm.