This paper presents the design of a Lifetime-Aware Centralized Q-routing Protocol (LACQRP) for Wireless Sensor Network (WSN) to maximize the network lifetime. This is achieved by implementing Q-learning on the sink of the WSN, which also acts as a controller that has global knowledge of the network topology as enabled by Software-Defined WSN (SDWSN). The controller generates all possible distance-based minimum spanning trees (MSTs), which form the set of routing tables (RTs). The maximization of the network lifetime is achieved by the controller learning the routing table that minimizes the maximum of the sensor nodes’ consumption energies using Reinforcement Learning (RL). The simulation results show that the LACQRP learns the best RT that maximizes the network lifetime and has a better network lifetime performance when compared with recent distributed RL routing protocols for lifetime optimization, which are Reinforcement Learning-Based Routing (RLBR) and Reinforcement Learning for Lifetime Optimization (R2LTO).

In this paper, a file popularity and size-aware (PSA) caching scheme is proposed for a hybrid heterogeneous network (HetNet) comprising a file server, macro base stations (BSs) operating in the microwave frequency bands, and pico BSs operating in the millimeter wave frequency wave bands. Different than the state-of-the-art size-weighted popularity (SWP) and popularity-based caching schemes that assume equal file size, the file PSA caching scheme utilizes knowledge of the file popularity and size distributions to maximize the network average cache hit probability and the network average success probability subject to the available cache capacity. Moreover, the maximization of the network average success probability is shown to be non-convex and dynamic programming and branch and bound algorithms are employed to circumvent its convexity. New expressions for the optimal file caching probabilities that maximize the network average success probability in noise-limited and interference-limited HetNet scenarios are provided which are evaluated using numerical techniques. The results demonstrate that the proposed file PSA caching scheme provides up to 7% gain in the network average success probability compared to the SWP-based scheme. Lastly, the combination of coded caching with cooperative transmission achieves up to 40% gain compared to a non-cooperative transmission scheme without coded caching.

Secure transmission of cached files in wireless networks is crucial to protect the transmitted files from interception by illegitimate nodes. This paper analyzes the secrecy rate performance of a cache-enabled millimeter wave (mmWave) cellular network in the presence of colluding eavesdroppers. The average cache hit probability is computed and the stochastic geometry framework is used to evaluate the average secrecy rate of the network, taking into consideration directional beamforming and Nakagami-m fading. Moreover, the size of the available files is modeled by a Pareto distribution based on existing studies, while a memory and file size-aware caching (MFC) scheme is proposed. The MFC scheme incorporates an optimized memory allocation algorithm that reserves memory blocks in the cache of a base station (BS) based on the frequency of the requested files, the parameters of the Pareto file size distribution, and the network design parameters. The numerical results show that the proposed MFC scheme achieves up to two-fold gain in the average secrecy rate compared to the state-of-the-art probabilistic and most-popular-content (MPC) caching schemes. Furthermore, the impact of the skew exponent and the colluding eavesdroppers' intensity on the average cache hit probability and secrecy rate, respectively, is investigated.

A memory and file size-aware caching (MFC) scheme is proposed and studied in a D2D-enabled small cell network operating in millimeter wave bands. The proposed MFC scheme is characterized by the parameters of the file size distribution which are assumed to be Pareto distributed based on existing studies. The MFC scheme incorporates a memory allocation protocol where memory blocks are reserved for files based on the user requests, the Pareto file size distribution, and the available memory capacity. Analytical expressions for the cache hit probability and the cache-layer throughput are derived under the proposed MFC scheme. The results show that the MFC scheme achieves up to 33% increase in the cache hit probability of the cellular tier when compared to the state-of-the-art geographic and popularity-based caching schemes. Lastly, insights are provided on the impact of concurrent D2D and cellular transmissions on the cache-layer throughput.

The downlink performance of a millimeter-wave cellular network comprising multiple-antenna-remote radio heads (RRHs) that service users under a hybrid Joint Transmission and Coordinated Beamforming (JT-CB) scheme is analyzed. Using the tools of stochastic geometry, the signal-to-interference-plus noise ratio (SINR) distribution at a typical user is derived and analytical expressions are provided for the coverage probability and network area spectral efficiency (ASE) under the proposed scheme. In addition, the average rate gain under the proposed scheme is characterized as a function of the network load, file request and caching distributions, and the spatial distribution of the RRHs. Numerical results reveal up to 68% coverage probability gain under the hybrid JT-CB scheme, compared to a CB-only scheme in the low coverage regime (>10 dB SINR threshold), while a CB-only scheme outperforms the hybrid JT-CB scheme by up to 5% in the high coverage regime (<;10 dB SINR threshold). Moreover, the hybrid scheme is shown to outperform a JT-only scheme in all coverage regimes, attaining 52% at 30 dB SINR threshold. In addition, up to 25%, 35%, and 120% gains in ASE are shown to be achieved, compared to the JT-only, CB-only, and non-coordinating schemes, respectively.

The spectral efficiency (SE) and energy efficiency (EE) performance of a millimeter-wave (mmWave) cellular network is studied where a user device can associate with a base station (BS) or another user for device-to-device (D2D) communication based on an interference-aware D2D distance threshold. Using the tools of stochastic geometry, the mean interference, coverage probability, area SE, and network EE are derived under the proposed association scheme. Performance of the proposed scheme is compared with that of the minimum path loss (Min PL)-based and maximum biased-received-power (Max BRP)-based association schemes. The proposed scheme is shown to give the best coverage probability performance in noise-limited networks, while the three schemes converge in performance in interference-limited networks in the high coverage threshold regime (>20 dB). Further, the proposed scheme achieves up to 60% increase in the area SE and EE, compared to the Min PL-based scheme that gives the next best performance. Lastly, the paper proposed a goal attainment algorithm that achieves up to a seven-fold decrease in the mean deviation from a preset SE objective and 50% savings in EE, compared to the achievable performance under a constant transmit power and bandwidth allocation scheme.

This paper presents an analytical framework to investigate the performance of full duplex (FD) device-to-device (D2D) networks where devices in a cluster are capable of caching popular content. Assuming spatially randomly distributed D2D users in the cluster where the users request for content according to the Zipf distribution, analytical expressions are derived for the device communication probability, coverage probability, cluster average spectral efficiency, and content average download latency of the system. The system performance metrics are derived for the three device operating modes of FD only mode, half duplex (HD) only mode, and mixed FD/HD mode. Numerical results show that the mixed FD/HD mode is the most appropriate communication mode for cache enabled FD D2D networks to achieve the highest cluster average spectral efficiency and low content average download latency.