In this paper, we propose an ambient backscatter-enabled decode-and-forward (DF) cognitive relay network with wireless energy-harvesting capabilities. In our proposed scheme, a source node communicates with its destination node via a radio frequency-powered DF relay. It is assumed that the relay node is equipped with two different interfaces and can concurrently harvest/decode and backscatter the received source signals. A power-splitting-based approach is adopted for the information processing and the energy harvesting at the relay. The analytical expressions for the outage probability at all of the receiving nodes are derived. It has been shown that the analytical results match the simulation results. It has also been shown that using the ambient backscatter for secondary communications can significantly improve the overall network performance in terms of the achievable throughput and the energy efficiency.

We investigate self-energy recycling (S-ER)-based RF powered multi-antenna relay channels (RCs) for the coverage extension in sensor networks or small cells. In the S-ER-based RF powered RC, the power used at the relay station for data transmission depends only on the energy from the access point and the recycled energy from its own transmission. We propose an optimal beamforming scheme with associated protocols and study their behaviors for both cases of downlink only and joint up-down link. Strategies for the power allocation between data transmission and RF powering are provided and a comparison with the conventional RF powered RC is made. For the proposed power allocation strategies, the performance of the conventional RC is achieved by the proposed RF powered RC only when infinite RF power is available. A high value of S-ER helps the proposed systems to reach the performance of conventional relay systems. In the joint up-down link protocol, we show that the up-down rate region can simply be constructed with easy power allocation strategy.

This paper considers from the perspective of MAC layer, a throughput maximization problem of NOMA-ALOHA, ALOHA implemented over NOMA (non-orthogonal multiple access), that can decode simultaneously transmitted multiple packets via successive interference cancellation (SIC) if each of the multiple packets has a different power level from those of others. We start with a throughput optimization problem for two power levels and extend it to a problem for a general number of power levels. For the case of two power levels, we find upper and lower bounds of the maximum throughput and suggest a practical sub-optimal transmission probability whose throughput is close to the maximum. The maximum throughput of NOMA-ALOHA is at least 1.774 times higher than that of traditional slotted ALOHA in our numerical example. We extend the optimization problem into a general one with arbitrary number of power levels. We numerically analyze the performance through a relaxed problem of the original one with high complexity. Our numerical analysis shows that the maximum throughput of NOMA-ALOHA with three power levels is 2.33 times higher than simple ALOHA’s maximum throughput and that adding one power level to NOMA-ALOHA with two power levels enhances throughput at least by more than 28 percent.

In a Wireless Local Area Network (WLAN), devices have limited battery capacity. To improve the energy efficiency, we propose a new Medium Access Control (MAC) protocol to perform selective energy transfer request based on the amount of residual energy of a device in a WLAN with IEEE 802.11 Distributed Coordination Function (DCF). By supplying the energy only to the device requiring energy harvesting, the deterioration in network throughput during energy harvesting in a wireless network is minimized. We present a new energy Markov chain model to analyze the throughput and the energy efficiency of the proposed method. We confirm that the throughput and the energy efficiency of the proposed method is improved.

Power Beacons (PBs) can transfer energy wirelessly to devices in a Wireless Powered Communication Network (WPCN). When PBs are deployed in an IEEE 802.11 Wireless LAN (WLAN), the energy transfer of PBs may interfere with the WiFi stations if WiFi stations and PBs share the same frequency band. In this letter, to resolve this interference problem, we propose a new Medium Access Control (MAC) protocol for IEEE 802.11 WiFi stations to efficiently coexist with PBs. PBs contend just as WiFi stations to gain opportunity for transferring energy and determine its operation based on the average energy level of stations. It is demonstrated that the throughput of the proposed MAC protocol is superior to that of IEEE 802.11 WLAN without interference control.

The random access procedure in cellular networks suffers from a congestion problem caused by massive access requests from a large number of devices. Since this congestion problem causes inefficient energy consumption and increases the random access delay, an efficient random access procedure is required for various types of devices. In this paper, we propose a new access control scheme to reduce the access delay and the energy consumption by mining hidden random access resources. The proposed scheme consists of the random access procedure and the resource allocation algorithm. The proposed random access procedure utilizes the multiple access class barring (ACB) procedure to mine and utilize the hidden random access opportunities (RAOs) in order to increase the number of successfully admitted devices. The proposed algorithm optimizes the resource allocation parameters according to the estimated number of devices. We provide an analytical model for the proposed scheme by using an embedded Markov chain. The proposed scheme is shown to reduce the random access delay and the energy consumption for green communications by achieving 53 % maximum efficiency compared to 37 % in the conventional schemes with the ACB and random access procedure.