This paper investigates a hybrid radio frequency (RF)/visible light communication (VLC) ultra-small cell network consisting of multiple optical angle-diversity transmitters, one multi-antenna RF access point (AP) and multiple terminal devices. In the network, the optical transmitters play the primary role and are responsible for delivering information and power over the visible light while the RF AP acts as a complementary power transfer system. Thus, we propose a novel collaborative RF and lightwave resource allocation scheme for hybrid RF/VLC ultra-small cell networks. The proposed scheme aims to maximize the communication quality-of-service provided by the VLC under a constraint of total RF and light energy harvesting performance while keeping illumination constant and ensuring health safety. This scheme leads to the formulation of two optimization problems that correspond to the resource allocation at the optical transmitters and the RF AP. Both problems are optimally solved by appropriate algorithms. Moreover, we propose a closed-form suboptimal solution with high accuracy to tackle the optical transmitters' resource allocation problem, as well as an efficient semi-decentralized method. Finally, simulation results illustrate the achievable performance of the investigated system and the effectiveness of the proposed solutions.

In this paper, we consider a wireless energy harvesting network consisting of one hybrid access point (HAP) having multiple antennas, and multiple sensor nodes each equipped with a single antenna. In contrast to conventional uplink wireless networks, the sensor nodes in the considered network have no embedded energy supply. They need to recharge the energy from the wireless signals broadcasted by the HAP in order to communicate. Based on the point-to-point and multipoints-to-point model, we propose two medium access control protocols, namely harvesting at the header of timeslot (HHT) and harvesting at the dedicated timeslot (HDT), in which the sensor nodes harvest energy from the HAP in the downlink, and then transform its stored packet into bit streams to send to the HAP in the uplink. Considering a deadline for each packet, the cumulative distribution functions of packet transmission time of the proposed protocols are derived for the selection combining and maximal ratio combining (MRC) techniques at the HAP. Subsequently, analytical expressions for the packet timeout probability and system reliability are obtained to analyze the performance of proposed protocols. Analytical results are validated by numerical simulations. The impacts of the system parameters, such as energy harvesting efficiency coefficient, sensor positions, transmit signal-to-noise ratio, and the length of energy harvesting time on the packet timeout probability and the system reliability are extensively investigated. Our results show that the performance of the HDT protocol outperforms the one using the HHT protocol, and the HDT protocol with the MRC technique has the best performance and it can be a potential solution to enhance the reliability for wireless sensor networks.

This paper studies a new concept so-called green cell-less radio frequency (RF) wireless power transfer (WPT) networks. We consider a scenario in which multiple indoor access points (APs) equipped with outdoor energy harvesters are connected with a central control unit via backhaul links. Further, such APs exploit the harnessed green energy to recharge wirelessly indoor devices under the coordination of the control unit. Considering the network, we focus on AP selection and beamforming optimization to maximize the total energy harvesting (EH) rate. The resulting mathematical problem has the form of mixed-integer optimization that is intractable to solve. Thus, we propose an algorithm to tackle this difficulty. Through numerical results, we show the advantages of the cell-less design over the conventional small-cell one to validate our ideas. In particular, the issue on safety requirements of human exposure to RF radiation is discussed. Finally, potential future research is provided.

This paper proposes a new communication protocol for a cooperative non-orthogonal multiple access (NOMA) system. In this system, based on users' channel conditions, each two NOMA users are paired to reduce system complexity. In this concern, the user with a better channel condition decodes and then forwards messages received from the source to the user with a worse channel condition. In particular, the direct link between the paired users is assumed to be unavailable due to the weak transmission conditions. To overcome this issue, we propose a new cooperative NOMA protocol in which an amplify-and-forward (AF) relay is employed to help the user-to-user communications. To evaluate the proposed protocol, the exact closed-form expressions of outage probability (OP) at the two paired users are derived. Based on the analysis of the OP, we further examine the system throughput in a delay-sensitive transmission mode. Finally, our analytical results verified by Monte-Carlo simulation show that the proposed protocol is efficient in enhancing the performance of NOMA system when the user-to-user communications is limited.

In this paper, we study energy harvesting cognitive radio networks (CRNs) in the presence of multiple eavesdroppers (EAVs) and multiple primary users (PUs). In particular, the secondary user (SU) harvests energy from multiple primary user transmitters (P-Tx), and then uses this harvested energy to deliver packets to the secondary access point (SAP). The SU communication faces multiple EAVs intending to steal its confidential information. In order to protect itself against multiple EAVs and also to protect the PUs communication from interference generated by the SU signals, the SU should be equipped with a suitable power allocation strategy which is derived from channel state information, harvested energy, security constraints given by the SU, and interference constraint given by the PU. Accordingly, an energy harvesting and communication protocol is proposed. Further, the optimal energy harvesting time, a power allocation policy, and a channel selection strategy for the SU are derived and analyzed. To this end, closed-form expressions for the packet error probability and the average packet delay including retransmissions are obtained. Interestingly, the numerical results obtained in this paper show that the proposed power allocation and channel selection strategy does not only improve the spectrum and energy utilization, but also protect the confidential information of the SU from the EAVs.

Recently, a short reference differential chaos shift keying system (SR-DCSK) has been proposed to overcome the dominant drawbacks related to low data rate and energy efficiency fondness of conventional DCSK systems. The fact that terminals on a network have a limited battery capacity and are in desperate need to high energy efficiency transmission schemes compels us to tackle these crucial challenges. In this paper, we propose an SR-DCSK system that performs simultaneous wireless information and power transfer (SWIPT). This promising design exploits the saved time gained from the fact that reference signal duration of SR-DCSK scheme occupies less than half of the bit duration to transmit a signal. The aim of this system is to allow receivers to perform without being equipped with any external power supply. Furthermore, at the receiver side, an RF-to-dc conversion is first performed, followed by data recovery without the need to any channel estimator. Closed-form expressions of multiple-input single-output SR-DCSK SWIPT system, such as ergodic rate, harvesting time, energy shortage, and data outage as well as exact and approximate bit error rate probabilities are derived under Rayleigh fading channel and are validated via simulation. Our results show that the proposed solution saves energy without sacrificing the non-coherent fashion of the system or reducing the rate compared to conventional DCSK, while keeping the design simple.

This paper analyzes a novel multiple-input single- output (MISO) simultaneous wireless information and power transfer (SWIPT) system model in the presence of an active eavesdropper over the frequency-selective fading channel. In this model, a transmitter applies the time reversal (TR) beamforming technique to combat the fading effects whereas a legitimate user employs a power splitter to jointly receive information and energy, and the active eavesdropper jams the user. Given the system model, the system performance in terms of symbol error rate (SER) and energy harvesting (EH) is analyzed. In particular, we devise a SER-energy region, instead of the conventional rate-energy region, to evaluate system performance of the SWIPT model. A moment generating function (MGF)-based method is presented to exactly derive the average SER analysis. Moreover, the closed-form expression of average effective harvested energy is then provided to complete SERenergy region analysis. Finally, analytical results confirmed by numerical simulations show that the TR technique can support the SWIPT system to notably improve the SER performance whereas the jamming signal can enhance the EH performance.

In this paper, we investigate the performance of an amplify-and-forward two-way relay network, in which the relay can harvest the energy from the radio frequency and all channels are subject to Nakagami-m fading. In particular, we assume that the relay has a single antenna, while two sources are equipped with multiple antennas. Also, two sources use the maximal ratio transmission (MRT) and maximal ratio combining (MRC) techniques to process the transmit and received signals. Moreover, the multiple access broadcast (MABC) protocol, which can improve the spectrum efficiency, is employed to coordinate the bidirectional communication of the two-way relay network. Given these settings, we derive analytical expressions for the throughput under the delay-limited and delay-tolerant transmission modes and the outage probability. Finally, Monte-Carlo simulations are provided to verify our calculation.

Based on the capability of harvesting the energy of all paths in the multipath environment, time-reversal (TR) transmission technique offers a great potential of low-complexity energy-efficient communications for future wireless network. The TR-employed systems benefit from a significantly reduced leakage of message-bearing signal to unintended users or eavesdroppers. In this paper, we propose a term so-called average effective secrecy signal-to-interference-plus-noise ratio (SINR) which represents the secrecy performance of TR-employed systems. Furthermore, we also consider: (i) the channel correlation between transmit antennas, and (ii) the channel correlation between a legitimate user and an eavesdropper. Accordingly, we derive the average effective secrecy-SINR in a closed-form expression of TR-employed systems. The obtained expression is based on the exact power-averaged expressions of the desired signal and the inter-symbol interference (ISI) components at both the legitimate user and eavesdropper side. The analytical results confirmed by numerical simulations show that the average effective secrecy-SINR metric is preferred to the average secrecy-SINR term in the perspective of measuring secrecy performance over correlated multi-path channel.