In this paper, we develop a novel framework to analyze the successful content delivery performance of device-to-device (D2D) networks with cache-enabled and self-sustained mobile helpers (MHs). Particularly, to facilitate the access of multimedia services for user equipments (UEs) under intermittent energy arrivals, an energy-based content delivery strategy, namely the energy-dependent nearest MH transmission (ED-NMT) strategy is considered. Under the proposed ED-NMT strategy, an MH is capable of delivering the content to the requesting UE if sufficient energy is harvested in its battery and it is the nearest MH of the tagged UE. Assuming infinite battery capacity, with ED-NMT strategy, we characterize the energy availability, and thereby, the transmission probability of MHs which cache the f-th file at the local storage. Then, we derive the cache-hit probability and the coverage probability of the f-th file. Finally, with the obtained results, we evaluate the successful content delivery probability (SCDP) of the D2D network with cache-enabled and self-sustained MHs. It is shown through both analytical and numerical results that under certain conditions, there is no performance loss due to stochastic and intermittent energy arrivals. INDEX TERMS D2D networks, self-sustained and cache-enabled mobile helpers, energy harvesting, stochastic energy arrivals, successful content delivery probability.

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We analyse the coverage performance of cognitive radio networks powered by renewable energy. Particularly, with an energy harvesting module and energy storage module, the primary transmitters (PTs) and the secondary transmitters (STs) are assumed to be able to collect ambient renewables, and store them in batteries for future use. Upon harvesting sufficient energy, the corresponding PTs and STs (denoted by eligible PTs and STs) are then allowed to access the spectrum according to their respective medium access control (MAC) protocols. For the primary network, an Aloha-type MAC protocol is considered, under which the eligible PTs make independent decisions to access the spectrum with probability $\unicode[STIX]{x1D70C}_{p}$. By applying tools from stochastic geometry, we characterize the transmission probability of the STs. Then, with the obtained results of transmission probability, we evaluate the coverage (transmission nonoutage) performance of the overlay CR network powered by renewable energy. Simulations are also provided to validate our analysis.

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The development of personalized medical systems should be supported by a fast and stable network system. The FAST TCP network system is the appropriate support system for this purpose. However, when the FAST TCP is deployed, the static mapping selection method for protocol parameters is unable to guarantee the small queuing delay and fast convergence of the network simultaneously. By conducting theoretical analysis and simulation experiments, the relationships among FAST TCP protocol slow start condition, control law gain parameters, and FAST TCP system convergence rate were examined. To ensure the stability of the FAST TCP system and to select the smallest protocol parameters, an improved method to effectively accelerate the convergence velocity of the FAST TCP system is proposed in this study. In this method, the number of packets for staying in the buffer for FAST TCP connections was taken as the criterion of the slow start, and the gain parameter of the control law was dynamically adjusted according to the local information of each FAST TCP connection. Using this improved method, the FAST TCP system can achieve a stable and small queuing delay, whilst the FAST TCP system could converge quickly to the equilibrium point simultaneously.