Dingcheng Yang

Energy cooperation in multi-user wireless-powered relay networks

In this study, energy cooperation schemes are considered in wireless cooperative networks; in these networks multiple pairs of users communicate with each other, assisted by an energy harvesting relay that gathers energy from the received signal by applying a power splitting scheme and forwards the received signal by using the harvested energy. This study is focused on the energy cooperation strategies for the relay to distribute the harvested energy between the multiple user pairs in amplify-and-forward and in decode-and-forward modes. Specifically, optimal solutions without energy cooperation at the relay node are first proposed and then the authors formulate the energy cooperation optimisation problem. This optimisation problem is non-convex. They propose an iterative energy cooperation solution to maximise the system throughput by assigning the proper harvested energy to each user pair for both types of forwarding models. They show that with the proposed method, the update in each iteration consists of a group of convex problems with a continuous parameter. Moreover, they derive the optimal solution to these convex problems in closed-form and it is shown that the solution can converge to a local optimum. Simulation results demonstrate that the proposed algorithm outperforms the traditional non-cooperation method.

User Cooperation in Wireless Powered Communication Networks With a Pricing Mechanism

This paper considers user cooperation and a pricing mechanism in a wireless-powered communication network (WPCN) in which two users harvest energy from a dedicated hybrid access point (H-AP), which has a constant power supply and acts as a power station during a downlink (DL). They also independently transmit their information to the H-AP [which acts as an information receiving station during an uplink (UL)] using the individually harvested energy. Based on the “doubly near-far” problem, this paper proposes a cooperative scheme among users in the WPCN. Compared with the source user (SU), the channel conditions for a helping user (HU), which is closer to the H-AP, is usually better for DL energy harvesting and for transmitting UL information. Thus, the HU can use its harvested energy to forward the SU’s information to the H-AP. Furthermore, energy is usually scarce for each user in a WPCN; therefore, the HU is under no obligation to accept the SU’s cooperative request and can choose to act selfishly to conserve resources. This paper presents a new pricing strategy to motivate the HU to sell its excess energy to help an SU complete a UL information transfer. Two transmission protocols are investigated: in the ideal case, the energy expenditure of the SU equals the energy used by the HU to relay information; in the normal case, the HU seeks additional profit. This paper formulates the SU’s expenditures and relay data in the ideal case as an optimization problem. An investigation of relay placement and the SU communication mode selection problem are also discussed. The numerical results show that the proposed pricing strategy can significantly reduce the expected costs to the SU and improve the reliability of user UL communications in a WPCN.

An Optimal Transmission Strategy for Joint Wireless Information and Energy Transfer in MIMO Relay Channels

An optimal resource allocation strategy for MIMO relay system is considered in simultaneous wireless information and energy transfer network, where two users with multiple antennas communicate with each other assisted by an energy harvesting MIMO relay that gathers energy from the received signal by applying time switching scheme and forwards the received signal by using the harvesting energy. It is focused on the precoder design and resource allocation strategies for the system to allocate the resources among the nodes in decode-and-forward (DF) mode. Specifically, optimal precoder design and energy transfer strategy in MIMO relay channel are firstly proposed. Then, we formulate the resource allocation optimization problem. The closed-form solutions for the time and power allocation are derived. It is revealed that the solution can flexibly allocate the resource for the MIMO relay channel to maximize the sum rate of the system. Simulation results demonstrated that the performance of the proposed algorithm outperforms the traditional fixed method.

An Energy-Efficient Scheme for Multirelay Cooperative Networks with Energy Harvesting

This study investigates an energy-efficient scheme in multirelay cooperative networks with energy harvesting where multiple sessions need to communicate with each other via the relay node. A two-step optimal method is proposed which maximizes the system energy efficiency, while taking into account the receiver circuit energy consumption. Firstly, the optimal power allocation for relay nodes is determined to maximize the system throughput; this is based on directional water-filling algorithm. Secondly, using quantum particle swarm optimization (QPSO), a joint relay node selection and session grouping optimization is proposed. With this algorithm, sessions can be classified into multiple groups that are assisted by the specific relay node with the maximum energy efficiency. This approach leads to a better global optimization in searching ability and efficiency. Simulation results show that the proposed scheme can improve the energy efficiency effectively compared with direct transmission and opportunistic relay-selected cooperative transmission.

Simultaneous Wireless Information and Power Transfer Mechanism in Interference Alignment Relay Networks

This paper considers a simultaneous wireless information and power transfer (SWIPT) mechanism in an interference alignment (IA) relay system, in which source nodes send wireless information and energy simultaneously to relay nodes, and relay nodes forward the received signal to destination nodes powered by harvested energy. To manage interference and utilize interference as energy source, two-SWIPT receiver is designed, namely, power splitting (PS), and antennas switching (AS) has been considered for relay system. The performance of AS- and PS-based IA relay systems is considered, as is a new energy cooperation (ECop) scheme that is proposed to improve system performance. Numerical results are provided to evaluate the performance of all schemes and it is shown from the simulations that the performance of proposed ECop outperformed both AS and PS.

Energy Efficient Wireless Sensor Network Modelling Based on Complex Networks

The power consumption and energy efficiency of wireless sensor network are the significant problems in Internet of Things network. In this paper, we consider the network topology optimization based on complex network theory to solve the energy efficiency problem of WSN. We propose the energy efficient model of WSN according to the basic principle of small world from complex networks. Small world network has clustering features that are similar to that of the rules of the network but also has similarity to random networks of small average path length. It can be utilized to optimize the energy efficiency of the whole network. Optimal number of multiple sink nodes of the WSN topology is proposed for optimizing energy efficiency. Then, the hierarchical clustering analysis is applied to implement this clustering of the sensor nodes and pick up the sink nodes from the sensor nodes as the clustering head. Meanwhile, the update method is proposed to determine the sink node when the death of certain sink node happened which can cause the paralysis of network. Simulation results verify the energy efficiency of the proposed model and validate the updating of the sink nodes to ensure the normal operation of the WSN.

A low-complexity block diagonalization algorithm for MU-MIMO two-way relay systems with complex lattice reduction

We design a scheme of precoding matrices for two-way multiuser relay systems, where a multiantenna relay station (RS) operating in an amplify-and-forward model simultaneously receives information from all multiple-antenna users. Considering the feasibility in mathematical analysis, users are distributed in two symmetrical groups. To reduce the complexity of proposed precoding scheme, we employ the QR decomposition and complex lattice reduction (CLR) transform to replace the two times singular value decomposition (SVD) of conventional BD-based precoding algorithm by introducing a combined channel inversion to eliminate the multiple users interference (MUI). Simulation and performance analysis demonstrate that the proposed LR-MMSE algorithm has not only a better bit error rate (BER) performance, a higher sum-rate, and simple architecture, but also 89.8% and 35.5% less complexity compared to BD- and MMSE-based scheme.

Transceiver Designs for Interference Alignment Based Cognitive Radio Networks with Energy Harvesting

Cognitive radio (CR) can improve the usage of spectrum resources, although the secondary users (SUs) will cause interference. Interference alignment (IA) is a prospective technique that can manage the interference effectively and has been applied to CR networks. However, interference can be used as an energy source by wireless energy harvesting techniques. In this paper, we consider an underlay CR network consisting of a primary user (PU) and SUs that are either energy harvesting users or information transmission users. The normal IA scheme neglects the priority of the PU, which leads to poor performance, particularly at low signal noise ratio (SNR) values. Three transceiver designs are proposed to improve the information rate of the PU and these benefit from the existence of energy harvesting users, by aligning the interference created by those energy harvesting users at information transmission users. Simulation results are presented to show the proposed designs can significantly improve the performance especially in low SNR situations.

Energy-Efficient UAV Communication with Multiple GTs Based on Trajectory Optimization

Wireless communications with unmanned aerial vehicles (UAVs) is a promising technology offering potential high mobility and low cost. This paper studies a UAV-enabled communication system, in which a fixed-wing UAV is deployed to collect information from a group of distributed ground terminals (GTs). Considering the requirements for quality of service (QoS) (i.e., the throughput of each GT is above a given threshold) and GT scheduling, we maximize the energy efficiency (EE) of the UAV in bits/Joule by optimizing the UAV’s flight trajectory. In this paper, a mixed integer nonconvex optimization problem is formulated. As that is difficult to solve, we divide the formulated problem into two subproblems and apply standard linear programming (LP) and successive convex optimization techniques. We further propose an efficient iterative algorithm that jointly optimizes GT scheduling and the UAV’s trajectory. Moreover, we set two special cases as benchmarks to measure the performance of the proposed design. The numerical results show that our proposed design achieves much better performance than the other two benchmark designs.

Optimal Pricing for MDS-Coded Caching in Wireless D2D Networks

In this paper, we investigate the caching of files in mobile devices in a wireless D2D network using maximum distance separable (MDS) codes. The coded symbols of each file are stored in the mobile devices. To regulate the D2D communications and reduce the transmission cost among mobile devices, a price mechanism is used for D2D communications so that they are allowed to choose whether to transmit the requested coded symbol to the other device or not. The mobile device can cooperate with others in terms of the battery level and the reward that is given from the other device. If the mobile device fails to retrieve enough coded symbols, the BS will respond with the missing coded symbols. We derived the optimal payment after taking the battery level of devices into consideration, and the problem was formulated as an optimization problem, subject to a range of payment. Numerical results demonstrate that using the MDS-coded scheme can significantly reduce the cost of transmitting a file, and there exist an optimal number of coded symbols cached in the mobile device, which consumes minimal cost of transmitting a requested file.