Optimal Time Allocation for Wireless Powered Relay Systems with Joint S-D Energy Transfer

Wireless energy transfer (WET) is a promising technique to prolong the lifetime of an energy-constrained wireless network. In this paper, we consider a two-hop communication system with multiple relay nodes powered by WET. To minimize the transmission time, we propose an optimal transmission scheme, in which the relay nodes adopt a “harvest-then-decode and forward” policy. The optimal transmission time allocation of the source and each relay node is calculated by a linear program under causality constraints on both data and energy arrivals. The analytical and simulation results reveal the relationship between the optimal time allocation and system parameters.

In this paper, we consider a full duplex wireless powered communication network where multiple users with RF energy harvesting capabilities communicate to a hybrid energy and information access point. An optimization framework is proposed with the objective of maximizing the sum throughput of the users subject to energy causality and maximum transmit power constraints considering a realistic energy harvesting model incorporating initial battery levels of the users. The joint optimization of power control, time allocation and scheduling is mathematically formulated as a mixed integer non linear programming problem which is hard to solve for a global optimum. The optimal power and time allocation and scheduling decisions are investigated separately based on the optimality analysis on the optimization variables. Optimal power and time allocation problem is proven to be convex for a given transmission order. Based on the derived optimality conditions, we propose a fast polynomial-time complexity heuristic algorithm. We illustrate that the proposed algorithm performs very close-to-optimal while significantly outperforming an equal time allocation based scheduling scheme.

In this paper, we characterize optimal resource allocation for the uplink and downlink of wireless powered cellular networks (WPCNs). In particular, we investigate a time-slotted WPCN, where a hybrid access point (HAP) is in charge of energy replenishing of M cellular users (CUs), along with transmission/reception of information to/from them. Unlike prior works, which give attention to information transmission in only one direction (either uplink or downlink), our work incorporates information transmission in both directions, along with energy transfer over the downlink. Besides harvesting energy explicitly from the HAP, each user opportunistically harvests the RF energy borne by the information sent by the HAP over the downlink to the remaining M−1 users, in order to boost its uplink throughput. Towards this objective, we formulate the total (uplink and downlink) sum throughput maximization problem to characterize the optimal time allocation for energy, downlink information, and uplink information slots, subject to time allocation constraints. Furthermore, we establish the convexity of the problem, and an efficient algorithm based on the gradient projection method is proposed. The obtained numerical results reveal valuable insights about the fairness-throughput trade-offs. Moreover, and among others, the network dynamics are introduced, which clarify how the optimal time allocation pattern is changed in accordance with the change of the users' placement, and the HAP's transmission power, in both energy and information slots.

In this paper, we propose an optimal time and power allocation scheme in a wireless power supply full-duplex (FD) relay system, where we consider the number of relay antennas in the energy harvesting stage. At the same time, the energy efficiency optimization problem of the system is structured, where optimization issues related to time allocation factors and power allocation are established. For the FD dual-antenna and the FD single-antenna energy harvesting system, energy efficiency function is proven to be a concave function over the time-switch factor, and the optimal time-switching factor is theoretically obtained using the Lambert function. Then, according to the given value range of the optimal time switching factor, the optimal power distribution scheme is obtained by analyzing the derivative function of the system energy efficiency and using the properties of the Lambert function. The time-switching factor and transmission power are optimally selected at the wireless power supply FD relay. Results reveal that the performance of energy efficiency of the dual-antenna energy harvesting at the FD relay outperforms that of the single-antenna. Moreover, our results demonstrate that FD relay systems always substantially boost the energy efficiency compared with half-duplex (HD) relay systems.

Optimal Time Allocation for Process Improvement and Growth for Entrepreneurs

SummaryIn this paper, we propose a general model to study the full‐duplex non‐coherent (NC) decode‐and‐forward Gaussian relay channel (RC) with energy harvesting (EH) nodes, called NC‐EH‐ , in three cases: (i) no energy transfer (ET), (ii) one‐way ET from the source (S) to the relay (R), and (iii) two‐way ET. We consider the problem of optimal power allocation in NC‐EH‐ in order to maximize the total transmitted bits from S to the destination in a given time duration. General stochastic energy arrivals at S and R with known EH times and values are assumed. In NC‐EH‐ with no ET, the complicated min‐max optimization form along with its constraints make the problem intractable. It is shown that this problem can be transformed to a solvable convex form; however, convex optimization solution does not provide the structural properties of the optimal solution. Therefore, following an alternative perspective, we investigate conditions on harvesting process of S and R where we find optimal algorithmic solution. Further, we propose some suboptimal algorithms and provide some examples, in which the algorithms are optimal. Moreover, we find a class of problems for NC‐EH‐ with one‐way ET from S to R, where the optimal algorithmic solution is devised. For NC‐EH‐ with two‐way ET, we propose general optimal algorithmic solution. Furthermore, the performance of the proposed algorithms are evaluated numerically and compared with optimal numerical convex optimization tools. Copyright © 2014 John Wiley & Sons, Ltd.

Generation and characterization of entanglement are crucial tasks in quantum information processing. A hypothesis testing scheme for entanglement has been formulated. Three designs were proposed to test the entangled photon states created by the spontaneous parametric down conversion. The time allocations between the measurement vectors were designed to consider the anisotropic deviation of the generated photon states from the maximally entangled states. The designs were evaluated in terms of the p-value based on the observed data. It has been experimentally demonstrated that the optimal time allocation between the coincidence and anti-coincidence measurement vectors improves the entanglement test. A further improvement is also experimentally demonstrated by optimizing the time allocation between the anti-coincidence vectors. Analysis on the data obtained in the experiment verified the advantage of the entanglement test designed by the optimal time allocation.

In this paper, we investigate the optimal power and time allocation for a wireless relay network, called BCFR (Broadcasting Channel with Fixed Relay), where the relay node is limited by the half-duplex operation. Introducing a relay in two-node broadcasting channel for a node which has a link of bad quality or requires higher transmission rate enlarges the rate region with well-designed power and time allocation. Also, BCFR is a common component of many relay networks, in which either orthogonal or non-orthogonal transmission can be adopted at the information source node. In particular, for the non-orthogonal transmission, the layered transmission with superposition coding is applied at the source node. By deriving the optimal power and time-fraction allocation at each node of BCFR, we show that the non-orthogonal structure enhances the capacity region and achieves higher log-sum capacity than the orthogonal transmission.

In this paper, we proposed an optimal time allocation to maximize the total average transmission data of two-way relay system. First, we derived the average transmission data rate of two-way relay system by the probability of successful transmission and the target data rate. Next, based on the derived the average transmission data rate of two-way relay system, we proposed an optimal time allocation of each link as a closed form. The simulation result verifies that the proposed time allocation is optimal.

This study proposes an optimal time allocation scheme for two‐way relay channel (TWRC) using the physical‐layer network coding (PNC). In other words, this study analytically determines the optimal transmit time durations for the first and the second time slot, which maximise the achievable sum rate under a sum time constraint for a given squared magnitude of the channel coefficients and transmit power values. Numerical results show that the achievable sum rate for the proposed optimal time allocation is greater than or equal to that for equal time allocation.

The unbalanced traffic distribution is a severe problem in cellular networks, which leads to congestion and reduces spectrum efficiency. To tackle this problem, we propose an unmanned aerial vehicle (UAV)-assisted wireless network architecture in which UAV acts as relay to divert the traffic from the overloaded cell to its neighbor underloaded cell. Considering that UAV communications are easily eavesdropped, we use the secrecy capacity to evaluate the performance of the network. To fully exploit the advantages of the proposed architecture, we formulate a joint UAV position optimization, user association, and time allocation problem to maximize the sum-log-rate of all users in two adjacent cells. To tackle the complicated joint optimization problem, we first design a genetic-based algorithm to optimize the UAV position, and then use the branch-and-bound method to devise a low-complexity algorithm to get the optimal user association and time allocation schemes. The simulation results indicate that the proposed UAV-assisted wireless network architecture is superior to the terrestrial network, and the proposed algorithms can further improve the network performance in comparison with the other schemes.

A Dynamic decode-and-forward (DDF) relaying protocol with partial Channel state information at the transmitter (CSIT) for a three-node half-duplex single-antenna network, which consists of a single source destination pair and a relay, is proposed. A Diversity multiplexing trade off (DMT) analysis is presented, in which the DMT of the proposed protocol is derived in a closed form and an adaptive time allocation strategy is also developed to achieve the optimal performance. It is shown that time allocation with partial CSIT significantly improves the achievable DMT for DDF relaying. Moreover, unlike the existing DDF protocol with CSIT, which is performed with the assumption of long-term power constraint, the proposed protocol can be generalized to the practical scenarios where a strict short-term power constraint is often imposed on, due to the environmental safety and interference prevention.

1. Animals foraging for resources are under a variety of selective pressures, and separate optimality models have been developed predicting the optimal reproductive strategies they should adopt. 2. In most cases, the proximate behavioural mechanisms adopted to achieve such optimality goals have been identified. This is the case, for example, for optimal patch time and sex allocation in insect parasitoids. However, behaviours modelled within this framework have mainly been studied separately, even though real animals have to optimize some behaviours simultaneously. 3. For this reason, it would be better if proximate behavioural rules were designed to attain several goals simultaneously. Despite their importance, such multi-objective proximate rules remain to be discovered. 4. Based on experiments on insect parasitoids that simultaneously examine their optimal patch time and sex allocation strategies, it is shown here that animals can adopt multi-objective behavioural mechanisms that appear consistent with the two optimal goals simultaneously. 5. Results of computer simulations demonstrate that these behavioural mechanisms are indeed consistent with optimal reproductive strategies and have thus been most likely selected over the course of the evolutionary time.

In this paper, the buffer-constrained throughput performance of a multi-user wireless-powered communication (WPC) system is investigated, where energy harvesting follows a non-linear model. The investigation focuses on the buffer overflow performance of sending data in the downlink (DL) from the access point (AP) node to each user equipment (UE) node and that in the uplink from each UE node to the AP node, based on which the throughput performance on both directions when a buffer constraint is enforced is studied. Specifically, the buffer overflow probability at each node is analyzed, based on which the buffer-constrained throughput is studied. In addition, to ensure the throughput performance under the buffer constraint, the DL transmission power allocation policy and the required energy storage capacity at each UE are investigated. Also, the optimal channel time allocation policy is studied with the objective of maximizing the minimum buffer-constrained throughput guaranteed to each UE at the same time. To this aim, an optimization problem is first formulated and then a dichotomy-based time allocation algorithm combined with a one-dimensional search is proposed to solve this problem. The analysis and results, explicitly relating the throughput to the buffer constraint in addition to WPC characteristics, shed new light on the design and performance analysis of WPC systems.

© 2017 University of Western Australia. In this paper, we study a two-hop amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay system, where the relay node has no self-power supply, and relies on harvesting the radio frequency energy transferred from the source node to forward information from source to destination. We apply the time switching (TS) protocol between wireless information and energy transfer. As a novel contribution of this paper, we propose a more general energy consumption constraint at the source node during the information and energy transfer, which includes the constant power constraints used in existing works as special cases. We study the joint optimization of the source precoding matrices, the relay amplifying matrix, and the TS factor to maximize the source-destination mutual information (MI). The optimal structure of the source and relay matrices is derived, which reduces the original transceiver optimization problem to a simpler power allocation problem. Numerical simulations show that the proposed algorithm yield higher system MI and better rate-energy tradeoff than an existing approach.