Wireless Powered Mobile Edge Computing Research Articles

Computation Energy Efficiency Maximization for NOMA-Based and Wireless-Powered Mobile Edge Computing With Backscatter Communication

Computation Energy Efficiency Maximization for NOMA-Based and Wireless-Powered Mobile Edge Computing With Backscatter Communication

Energy-Efficiency Maximization for Relay-Aided Wireless-Powered Mobile Edge Computing

Energy-Efficiency Maximization for Relay-Aided Wireless-Powered Mobile Edge Computing

Intelligent Reflecting Surface Assisted Secure Computation of Wireless Powered MEC System

The integration of mobile edge computing (MEC) and wireless power transfer (WPT) can effectively improve the computing ability and energy sustainability of energy-constrained wireless devices in the Internet of Things (IoT) networks. Intelligent reflecting surface (IRS) has recently emerged as an effective technique to improve the performance of wireless systems by intelligently reconfiguring wireless environments. This paper studies the exploitation of IRS to improve the secure computation performance of WPT-MEC systems with a passive eavesdropper. A wireless access point (AP) first charge multiple users with the emitted energy signals, and then the users perform local computing and partial offloading to complete their computation tasks with the harvested energy in the presence of an eavesdropper, where the local computing can be executed during the whole process of WPT and offloading. Meanwhile, deploying IRS can improve the energy capture and secure offloading performance of the users. We maximize the secure computation task bits of users by jointly optimizing the AP energy transmit beamforming, the IRS phase shifts, the transmit power, users' offloading time, and the local computation frequency of users, which are tangled with each other. An iterative optimal algorithm is developed to solve this non-convex problem by combining Taylor expansion method, semidefinite relaxation (SDR) algorithm, the Lagrange duality theory and Karush-Kuhn-Tucker (KKT) conditions. The numerical results show that the proposed scheme can effectively increase the secure computation task bits compared with other benchmark schemes, especially for the maximum transmit power of AP, the improvement is above 45 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> .

Energy Minimization in Reconfigurable Intelligent Surface-Assisted Unmanned Aerial Vehicle-Enabled Wireless Powered Mobile Edge Computing Systems with Rate-Splitting Multiple Access

In this study, a reconfigurable intelligent surface (RIS)-assisted wireless-powered mobile edge computing (WP-MEC) system is proposed, where a single-antenna unmanned aerial vehicle (UAV)-mounted cloudlet provides offloading opportunities to K user equipments (UEs) with a single antenna, and the K UEs can harvest the energy from the broadcast radio-frequency signals of the UAV. In addition, rate-splitting multiple access is used to provide offloading opportunities to multiple UEs for effective power control and high spectral efficiency. The aim of this paper is to minimize the total energy consumption by jointly optimizing the resource allocation in terms of time, power, computing frequency, and task load, along with the UAV trajectory and RIS phase-shift matrix. Since coupling issues between optimization variable designs are caused, however, an alternating optimization-based algorithm is developed. The performance of the proposed algorithm is verified via simulations and compared with the benchmark schemes of partial optimizations of resource allocation, path planning, and RIS phase design. The proposed algorithm exhibits high performance in WP-MEC systems with insufficient resources, e.g., achieving up to 40% energy reduction for a UAV with eight elements of RIS.

Decomposition-based learning in drone-assisted wireless-powered mobile edge computing networks

This paper investigates the multi-Unmanned Aerial Vehicle (UAV)-assisted wireless-powered Mobile Edge Computing (MEC) system, where UAVs provide computation and powering services to mobile terminals. We aim to maximize the number of completed computation tasks by jointly optimizing the offloading decisions of all terminals and the trajectory planning of all UAVs. The action space of the system is extremely large and grows exponentially with the number of UAVs. In this case, single-agent learning will require an overlarge neural network, resulting in insufficient exploration. However, the offloading decisions and trajectory planning are two subproblems performed by different executants, providing an opportunity for problem-solving. We thus adopt the idea of decomposition and propose a 2-Tiered Multi-agent Soft Actor-Critic (2T-MSAC) algorithm, decomposing a single neural network into multiple small-scale networks. In the first tier, a single agent is used for offloading decisions, and an online pretrained model based on imitation learning is specially designed to accelerate the training process of this agent. In the second tier, UAVs utilize multiple agents to plan their trajectories. Each agent exerts its influence on the parameter update of other agents through actions and rewards, thereby achieving joint optimization. Simulation results demonstrate that the proposed algorithm can be applied to scenarios with various location distributions of terminals, outperforming existing benchmarks that perform well only in specific scenarios. In particular, 2T-MSAC increases the number of completed tasks by 45.5% in the scenario with uneven terminal distributions. Moreover, the pretrained model based on imitation learning reduces the convergence time of 2T-MSAC by 58.2%.

Deep Reinforcement Learning Empowers Wireless Powered Mobile Edge Computing: Towards Energy-Aware Online Offloading

Deep integration of wireless power transmission and mobile edge computing (MEC) promotes wireless powered MEC to become a new research hotspot in the field of Internet of Things. In this paper, we focus on the joint optimization problem of online offloading decision and charging resource allocation for minimizing task accomplishing time in dynamic time-varying wireless channel scenarios. The optimal solution involves addressing a mixed integer programming problem in real time, which is proved to be NP-hard, and imposes nontrivial challenges to design with conventional optimization methods. To efficiently address this problem, we leverage the deep reinforcement learning (DRL) technology to propose an energy-aware online offloading algorithm called EAOO. EAOO algorithm learns empirically the online offloading decision policies via a well-designed DRL framework, and adopts the feasible solution region analysis method to implement the charging resource allocation. We further propose a novel feasible decision vector generation method, and incorporate the crossover and mutation technology to expand the offloading vector search space with the provable feasibility guarantee. Extensive experimental results show that, our EAOO algorithm outperforms existing baseline algorithms, and achieves near-optimal performance with low CPU execution latency, which well satisfies the practical requirements of real-time and efficiency.

Minimizing the computation latency of FDMA‐based wireless powered edge computing network

AbstractThe 0–1 mixed integer programming problem of binary offloading on wireless powered mobile edge computing (WP‐MEC) networks requires joint optimization of binary and continuous variables, which is computationally expensive for traditional techniques and difficult to solve within the channel coherence time under time‐varying condition. Using machine learning models to output variable values is also challenging. Hence, designing efficient and low‐complexity algorithms is crucial for optimal network performance. This paper focuses on the computation latency of the FDMA‐based WP‐MEC network and proposes a task‐offloading algorithm to minimize the total completion delay (TCD). The TCD minimization is modelled as a 0–1 MIP problem and is decomposed into a master problem of optimizing the offloading decision and the sub‐problem of optimizing other parameters under a given offloading decision. The sub‐problem is solved using optimization method, while the master problem is solved using a deep reinforcement learning algorithm. Simulation results show that the proposed algorithm can achieve almost minimal TCD with low complexity.

DRL based binary computation offloading in wireless powered mobile edge computing

AbstractThis paper considers the wireless powered mobile edge computing combining wireless power transmission (WPT) and mobile edge computing, where the hybrid access point (HAP) uses multiple radio beams to charge multiple wireless devices (WDs) and WD adopts the binary offloading mode to offload computation workload to HAP via FDMA. It is aimed to maximize the sum computation rate (SCR) of WDs by jointly optimizing the binary offloading decision, transmit power of each radio beam, and WPT duration. Due to the strong coupling between the offloading decision and other optimization variables, the SCR maximization is formulated as a mixed integer nonlinear programming problem. To address this challenging problem, an online DRL‐based decoupling optimization algorithm is proposed. Specifically, the original problem is first split into a top‐problem of optimizing binary offloading decision and a sub‐problem of optimizing transmit powers and WPT duration under given offloading decision. Then a self‐learning DRL framework is designed to output the near‐optimal offloading decisions. Finally, for the sub‐problem, based on the Lagrangian dual theory, an efficient approach to fast obtain the closed‐form expression of the optimal solution is proposed. The simulation results show that the proposed DRL‐based algorithm can achieve the near‐maximal SCR with low computational complexity.

Wireless Powered Mobile Edge Computing Networks: A Survey

Wireless Powered Mobile Edge Computing (WPMEC) is an integration of Mobile Edge Computing (MEC) and Wireless Power Transfer (WPT) technologies, to both improve computing capabilities of mobile devices and energy compensation for their limited battery capabilities. Generally, energy transmitters, mobile devices, and edge servers form a WPMEC system that realizes a closed loop of sending and collecting energy as well as offloading and receiving task data. Due to constraints of time-varying network environments, time-coupled battery levels, and the half-duplex character of mobile devices, the joint design of computation offloading and resource allocation solutions in WPMEC systems has become extremely challenging, and a great number of studies have been devoted to it in recent years. In this article, we first introduce the basic model of the WPMEC system. Then, we present key issues and techniques related to WPMEC. In addition, we summarize solutions for computation offloading and resource allocation to solve critical issues in WPMEC networks. Finally, we discuss some research challenges and open issues.

Energy-Efficient Resource Allocation for Backscatter-Assisted Wireless Powered MEC

In this paper, we study the energy-efficient resource allocation for a backscatter-assisted wireless powered mobile edge computing (MEC) network. Considering the binary offloading mode and the limited computation capacity of the MEC server, we propose to minimize the MEC server's energy consumption by jointly optimizing the binary offloading decision of each IoT node, the computing frequencies and time at the MEC server and IoT nodes, the backscatter time and reflection coefficients of IoT nodes, as well as the MEC server's transmit power and time. It is formulated into a non-convex mixed integer programming problem. To solve this problem, we first obtain the optimal computing time and frequency for the MEC server and the optimal computing time of each IoT node based on the proof by contradiction and the monotonicity of the objective function, then we decouple the resulting simplified problem into two subproblems and transform each subproblem into a convex one. On this basis, we propose a low-complexity iterative algorithm to solve the simplified problem by solving the two convex subproblems alternately. Simulation results verify the fast convergence of the proposed iterative algorithm and its superiority over the baseline schemes in terms of the MEC server's energy consumption.

Game-Combined Multi-Agent DRL for Tasks Offloading in Wireless Powered MEC Networks

Wireless powered mobile edge computing (MEC) networks, where wireless devices (WDs) are allowed to offload parts of computation-intensive tasks to remote servers and charge the built-in batteries over the air, have been envisaged as a promising technology to ensure the ultra-low-power requirement and enhance the continuous work capacity of WDs. However, when multiple WDs coexist in the network, it is non-trivial to minimize the total tasks delay since the optimization variables are intrinsically coupled. Even more, channels are dynamically varying from time to time and the tasks are unpredictable, which aggravates the difficulty to obtain the closed-form solution. Although reinforcement learning (RL) has been proved to be effective for such complex optimization problems, there is still the challenge that the training of neural networks is time-consuming. This paper considers a challenging hybrid tasks offloading scenario, where offloading tasks can be partially executed locally and remotely in parallel, and each WD is endowed to take both the active RF-transmission and passive backscatter communication (BackCom) for remote tasks offloading. Furthermore, a game-combined multi-agent deep deterministic policy gradient (MADDPG) algorithm is proposed to minimize the total tasks delay with the fairness consideration of multiple WDs, i.e., potential game for offloading decision and MADDPG for time scheduling and harvested energy splitting. The introduction of potential game which can be proved to converge with finite iterations, helps to accelerate the training and reduce the computation complexity. Equipped with the feature of ‘centralized training with decentralized execution,’ once well trained, each agent in MADDPG can figure out the proper time scheduling and harvested energy splitting independently without sharing information with others. Besides the unilateral contention among WDs for the offloading decision by potential game, a fully decentralized framework is finally designed for the proposed algorithm. Numerical results demonstrate that the game-combined MADDPG algorithm can achieve the near-optimal performance compared with existing centralized approaches, and reduce the convergence time compared with other no-game learning approaches.

Energy-Efficient Task Offloading for Three-Tier Wireless-Powered Mobile-Edge Computing

Mobile edge computing (MEC) is envisioned to address the computation demands of Internet of Things (IoT) devices. However, it is crucial for the MEC to operate in coordination with the cloud tier to achieve a highly scalable IoT system. In addition, IoT devices require regular maintenance to either recharge or replace their batteries which may not always be feasible. Wireless energy transfer (WET) can provide IoT devices with a stable source of energy. Nonetheless, proper scheduling of energy harvesting and efficient allocation of computing resources are the key to the sustainable operation of these devices. In this paper, we introduce a three-tier wireless powered mobile edge computing (WPMEC) consisting of cloud, MEC servers, and IoT devices. We first formulate a combinatorial optimization problem that aims to minimize the wireless energy transmission. To tackle the complexity of the problem, we use bipartite graph matching and propose a harvest-then-offload mechanism for IoT devices. We also exploit parallel processing to increase the performance of the proposed algorithm. Through numerical experiments, we evaluate the performance of our proposed mechanism. Our results show that the proposed mechanism significantly reduces the required energy for the operation of IoT devices comparing to different offloading policies. We further show that WiEnTM results in up to 34% less wireless energy transmission in comparison to an existing work in the literature.

Joint Communication and Computation Cooperation in Wireless-Powered Mobile-Edge Computing Networks With NOMA

Incorporating wireless power transfer (WPT) into mobile edge computing (MEC) is an effective way to enhance the self-sustainability of the MEC network. However, it is susceptible to the effect of double-far-near. Meanwhile, inspired by the fact that non-orthogonal multiple access (NOMA) has shown its great potential in improving the spectral efficiency of the network over OMA, this paper investigates a cooperative computation offloading scheme for a basic three-node wireless powered MEC scenario with NOMA, where users overcome the effect of double-far-near through joint communication and computation cooperation. Specifically, we consider a “harvest-then-offload” protocol composed of three stages. In the first stage, users harvest wireless energy signals from the access point (AP). In the second and third stages, based on NOMA, users offload their partial computing tasks on the same time-frequency resource block by using the harvested energy, in which the near user can cooperatively compute and forward the computing task of the far user. We formulate an optimization problem to minimize the transmission energy consumption of the AP by jointly optimizing the transmission power, the offloading coefficient and the duration of each stage. Due to the non-convexity of the formulated problem, we first transform it into an equivalent one by using the variable substitution method. Then, we propose an efficient iterative algorithm based on the successive convex approximation (SCA) and Lagrangian duality method to solve this transformed problem. Simulation results show that the proposed algorithm has good convergence and the proposed scheme can achieve the best performance compared with several baseline schemes, which highlights the superiority of the proposed scheme.

Augmented Deep Reinforcement Learning for Online Energy Minimization of Wireless Powered Mobile Edge Computing

Mobile edge computing (MEC) offers an opportunity for devices relying on wireless power transfer (WPT), to accomplish computationally demanding tasks. Such WPT-powered MEC systems have yet to be optimized for long-term efficiency, due to random and changing task demands and wireless channel states of the devices. This paper presents an augmented two-staged deep Q-network (DQN), referred to as “TS-DQN”, for online optimization of WPT-powered MEC systems, where the WPT, offloading schedule, channel allocation, and the CPU configurations of the edge server and devices are jointly optimized to minimize the long-term average energy requirement of the systems. The key idea is to design a DQN for learning the channel allocation and task admission, while the WPT, offloading time and CPU configurations are efficiently optimized to precisely evaluate the reward of the DQN and substantially reduce its action space. Another important aspect is that a new action generation method is developed to expand and diversify the actions of the DQN, further accelerating its convergence. As validated by simulations, the proposed TS-DQN is much more energy efficient and converges much faster, than its potential alternative directly using the state-of-the-art Deep Deterministic Policy Gradient algorithm to learn all decision variables.

Joint Resource Allocation and Configuration Design for STAR-RIS-Enhanced Wireless-Powered MEC

In this paper, a novel concept called simultaneously transmitting and reflecting RIS (STAR-RIS) is introduced into the wireless-powered mobile edge computing (MEC) systems to improve the efficiency of energy transfer and task offloading. Compared with traditional reflecting-only RIS, STAR-RIS extends the half-space coverage to full-space coverage by simultaneously transmitting and reflecting incident signals, and also provides new degrees-of-freedom (DoFs) for manipulating signal propagation. We aim to maximize the total computation rate of all users, where the energy transfer time, transmit power and CPU frequencies of users, and the configuration design of STAR-RIS are jointly optimized. Considering the characteristics of STAR-RIS, three operating protocols, namely energy splitting (ES), mode switching (MS), and time splitting (TS) are studied, respectively. For the ES protocol, based on the penalty method, successive convex approximation (SCA), and the linear search method, an iterative algorithm is proposed to solve the formulated non-convex problem. Then, the proposed algorithm for ES protocol is extended to solve the MS and TS problems. Simulation results illustrate that the STAR-RIS outperforms traditional reflecting/transmitting-only RIS. More importantly, the TS protocol can achieve the largest computation rate among the three operating protocols of STAR-RIS.

Multi-IRS Assisted Wireless-Powered Mobile Edge Computing for Internet of Things

This paper proposes a multiple intelligent reflecting surfaces (IRSs) assisted wireless-powered mobile edge computing (MEC) system, where the IRSs are deployed to assist both the downlink wireless power transfer (WPT) from the multi-antenna hybrid access point (HAP) to the wireless devices (WDs) and the uplink computation offloading from the WDs to the MEC server. To further improve the system performance, the energy beamforming and multiple-user detection (MUD) technologies are exploited. We consider both partial and binary offloading schemes and formulate the sum computation rate (SCR) maximization problems for them, respectively. To tackle the non-convexity of each problem, we propose an efficient alternating optimization (AO) method. Specifically, the Lagrange duality method is used to optimize the energy beamforming vector and the MUD matrix at the HAP, and the CPU frequencies and transmit power of the WDs. Then, we optimize the discrete phase shifts via the successive convex appropriation (SCA) method, the rank-one equivalents, and rounding method. Finally, the optimal time scheduling can be obtained via the one-dimensional search method. In addition, we propose a greedy algorithm with low complexity to optimize the computing modes for the binary offloading scheme. Numerical results show that our proposed schemes outperform the benchmarks.

IRS-Aided Wireless Powered MEC Systems: TDMA or NOMA for Computation Offloading?

Anintelligent reflecting surface (IRS)-aided wireless-powered mobile edge computing (WP-MEC) system is conceived, where each device’s computational task can be divided into two parts for local computing and offloading to mobile edge computing (MEC) servers, respectively. Both time division multiple access (TDMA) and non-orthogonal multiple access (NOMA) schemes are considered for uplink (UL) offloading. To fully unleash the potential benefits of the IRS, employing multiple IRS beamforming (BF) patterns/vectors in the considered operating frame to create time-selectivity channels, i.e., dynamic IRS BF (DIBF), is in principle possible at the cost of additional signaling overhead. To strike a balance between the system performance and associated signalling overhead, we propose three cases of DIBF configurations based on the maximum number of IRS reconfiguration times. The degree-of-freedom provided by the IRS may introduce different impacts on the TDMA and NOMA-based UL offloading schemes. Thus, it is still fundamentally unknown which multiple access scheme is superior for MEC UL offloading by considering the impact of the IRS. To answer this question, we provide a comprehensively theoretical performance comparison for the TDMA and NOMA-based offloading schemes under the three cases of DIBF configurations by characterizing their achievable computation rate. Analytical results demonstrate that offloading adopting TDMA can achieve the same computation rate as that of NOMA, when all the devices share the same IRS BF vector during the UL offloading. By contrast, computation offloading exploiting TDMA outperforms NOMA, when the IRS BF vector can be flexibly adapted for UL offloading. Then, we propose computationally efficient algorithms by invoking alternating optimization for solving their associated computation rate maximization problems. Our numerical results demonstrate the significant performance gains achieved by the proposed designs over various benchmark schemes and also unveil that the optimal time allocated to downlink wireless power transfer can be effectively reduced with the aid of IRSs, which is beneficial for both the system’s spectral efficiency and its energy efficiency.

Resource Allocation in UAV-Enabled Wireless-Powered MEC Networks With Hybrid Passive and Active Communications

This article proposes a novel unmanned aerial vehicle (UAV)-enabled wireless-powered mobile edge computing (WP-MEC) network, where several Internet of Things (IoT) nodes use the energy harvested from the UAV’s radio frequency signals to support the local computation and the hybrid active–passive communications-based task offloading. Two weighted sum computation bits (WSCB) maximization problems are formulated under the partial and binary offloading, respectively, by jointly optimizing the local computing frequencies and time, the IoT nodes’ reflection coefficients, the IoT nodes’ transmit powers, the UAV’s trajectory, etc., subject to the quality-of-service and energy-causality constraints per IoT node, the speed constraint of the UAV, etc. Since the formulated problems are highly nonconvex, two iterative algorithms are proposed to solve the formulated problems under two modes. Simulation results demonstrate that the proposed iterative algorithms have a fast convergence rate, and the proposed schemes achieve higher WSCB than several baseline schemes.

Joint task processing/offloading mode selection and resource-allocation for backscatter-aided and wireless-powered MEC

We propose to develop the joint task processing/offloading mode selection and system resource-allocation schemes for a backscatter-aided and wireless-powered mobile edge computing (MEC), where multiple edge users (EUs), a hybrid access point (H-AP) working as a dedicated energy source and an information receiver, and several carrier emitters (CEs) coexist. We aim to maximize the residual energy of all energy harvesting based EUs while ensuring that EUs can complete their tasks, by jointly optimizing EUs’ task processing mode (local computing mode or edge computing mode), task offloading mode, and system resource-allocation. For the task offloading mode, each EU can select the bistatic backscatter (BB) communication mode or the harvest-then-transmit (HTT) mode to directly offload its task to the MEC server co-located with the H-AP. Also, each EU can select the ambient backscatter (AB)＋BB communication mode or the AB＋HTT communication mode to backscatter its data to nearby EUs through AB communication and then offload data to the MEC server with the help of nearby EUs through HTT or BB communication. First, we formulate a residual energy maximization problem for the considered system. Since the formulated optimization problem is non-convex with multiple coupled variables, we adopt the block coordinate descent (BCD) method to decompose it into several subproblems. Then, we utilize the alternating directions method of multipliers (ADMM) to transform the non-convex subproblems into convex subproblems, and propose the distributed joint task processing/offloading mode selection and system resource-allocation schemes. Finally, we verify and evaluate the performance of our proposed scheme through numerical analyses, which show that our proposed scheme outperforms the other benchmark schemes in terms of the residual energy and the task completion rate of EUs by jointly selecting the task processing mode and the task offloading mode for each EU.

Utility Maximization for IRS Assisted Wireless Powered Mobile Edge Computing and Caching (WP-MECC) Networks

This paper exploits an intelligent reflecting surface (IRS) assisted wireless powered mobile edge computing and caching (WP-MECC) network. In particular, an IRS is utilized to reflect energy signals from a power station (PS) to various IoT devices for energy harvesting during uplink wireless energy transfer (WET). These devices collect energy to support their own partially local computing for computational tasks and their offloading capabilities to an access point (AP), with the help of IRS via time or frequency division multiple access (TDMA or FDMA). The AP is equipped with a local cache connected with a MEC server via a backhaul link, which prefetches the data to facilitate edge computing capabilities. The maximization of a utility function is formulated to evaluate the overall network performance, which is defined as the difference between the sum of computational bits (offloading bits and local computing bits) and total backhaul cost. Due to multiple coupled variables, we first design the optimal caching strategy. Then, an auxiliary vector is introduced to coordinate the energy consumption of local computing and offloading, where its optimal solution can be achieved by an exhaustive search. Moreover, we utilize the Lagrange dual method and the Karush-Kuhn-Tucker (KKT) conditions to derive the optimal time scheduling for the TDMA scheme or the optimal bandwidth allocation for the FDMA counterpart in closed form. The IRS phase shifts are iteratively designed by employing the quadratic transformation (QT) and the Riemannian Manifold Optimization (RMO). Finally, simulation results are demonstrated to validate the network utility performance and confirm the advantage of the employment of IRS, the optimal IRS phase shift design and caching strategy, in comparison to the benchmark schemes.