<p>This paper analyzes the physical layer security performance of cache-enabled hybrid satellite-terrestrial networks with intelligent reflecting surfaces (IRS). Content caches are deployed at both satellite and ground station to help fast content delivery to users. The IRS assists in securing communications from the ground station and satellite to the user against an eavesdropper. The connection probability and the secrecy probability are derived in asymptotic and closed-form expressions for both ground station-IRS-user and satellite-IRS-user links under practical channel models. From the obtained results, the secure transmission probability of the system is evaluated, and then maximized by designing the caching probabilities and the transmission rates. Numerical results verify the accuracy of the analysis and demonstrate the performance gains of having IRS support secure content delivery.</p>

Enabling global Internet access is challenging for cellular-based Internet of Things (IoT) due to the limited range of terrestrial network services. One viable solution is to deploy IoT over satellite systems for coverage extension. However, operating a hybrid satellite-terrestrial network (STN) might incur high satellite bandwidth consumption and excessive service latency. Aiming to reduce the content delivery latency from the Internet-connected gateway to the users, this work proposes a two-tier cache-enabled model with full-duplex transmissions where content caches are deployed at the satellite and ground station. A closed-form solution for the successful delivery probability (SDP) of the files is derived considering the requested content distributions and channel statistics. Then, the SDP performance under common caching policies can be evaluated. The results are also used to optimize cache placement under caching capacity constraints. Numerical results demonstrate the performance improvements of the proposed system over those of single-tier cache-aided and half-duplex transmission systems.

Enabling global Internet access is challenging for cellular-based Internet of Things (IoT) due to the limited range of terrestrial network services. One viable solution is to deploy IoT over satellite systems for coverage extension. However, operating a hybrid satellite-terrestrial network (STN) might incur high satellite bandwidth consumption and excessive service latency. Aiming to reduce the content delivery latency from the Internet-connected gateway to the users, this work proposes a wireless two-tier cache-enabled model with full-duplex transmissions where content caches are deployed at the satellite and ground station. A closed-form solution for the successful delivery probability (SDP) of the files is derived considering the requested content distributions and channel statistics. Then, the SDP performance under common caching policies can be conveniently evaluated. The results are also used to optimize cache placement under caching capacity constraints. Numerical results demonstrate the performance improvements of the proposed system over those of single-tier cache-aided and half-duplex transmission systems.

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In this study, a novel directional medium access control scheme with an extreme power saving mechanism is developed for traffic indication map stations in the IEEE 802.11ah networks. To improve the aggregate throughput, stations are managed based on their geographical locations in combination with the employment of directional operation mode on the access point. In addition to the restricted access window mechanism used in the IEEE 802.11ah standard for power saving, an adaptive transmission power scheme is proposed for uplink transmission to leverage the power-saving efficiency. With the proposed access scheme, the network performance is significantly enhanced compared to the IEEE 802.11ah standard. The analytical models for throughput and energy consumption are formulated using Markov Chains under unsaturated conditions. The simulation results indicate the effectiveness of the proposed directional access scheme under various network scenarios.