Adaptive Transmission Policy for Energy Harvesting Relaying systems

In this paper, we consider an energy harvesting (EH)-based relaying system where an EH-source node equipped with a rechargeable battery to store the energy harvested from the environment, communicates with a destination with the help of a relay node. The relay and destination both have an unlimited power supply, while the source relies solely on the harvested energy. A delay-limited transmission mode is assumed in this paper, in which if the source data cannot be transmitted within a delay deadline, it will be lost. Based on this model, an efficient adaptive source transmission policy is proposed. Markov chain analysis is considered to model the levels of the stored energy at the source node and the system performance is evaluated in terms of the transmission and success probabilities. The results reveal that the benefit of the proposed transmission strategy in delay-limited applications is highly dependent on the proper choice of the system design parameters and the harvested energy per packet

Secrecy Capacity for Multi-Antenna Wireless-Powered AF Relaying Systems

This paper analyzes the ergodic secrecy capacity of an energy-constrained multiple-antennas amplify-and-forward (AF) relaying system in the presence of a passive eavesdropper. In the first phase, the source broadcasts information signal, while the destination sends an artificial jamming signal. The jamming signal has two main purposes: 1) enhancing the system security; 2) increasing the energy harvesting (EH) at the relay node. In the second phase, the relay uses the harvested energy to amplify and forward the received signal to the destination. For this system model, explicit mathematical expressions for the ergodic secrecy capacity are derived for three different common EH-relaying protocols, namely, power splitting relaying (PSR), antenna selection and power splitting (ASPS) receiver, and ideal relaying receiver (IRR). Monte-Carlo simulations are included to validate the analysis and the effect of different parameters on the system security are investigated. The results show that, the ASPS receiver outperforms PSR in terms of secrecy capacity

Statistical Delay QoS Driven Energy Efficiency and Effective Capacity Tradeoff for Uplink Multi-User Multi-Carrier Systems

In this paper, the total system effective capacity (EC) maximization problem for the uplink transmission, in a multi-user multi-carrier OFDMA system, is formulated as a combinatorial integer programming problem, subject to each user?s link-layer energy efficiency (EE) requirement as well as the individual?s average transmission power limit. To solve this challenging problem, we first decouple it into a frequency provisioning problem and an independent multi-carrier linklayer EE-EC tradeoff problem for each user. In order to obtain the subcarrier assignment solution, a low-complexity heuristic algorithm is proposed, which not only offers close-to-optimal solutions, while serving as many users as possible, but also has a complexity linearly relating to the size of the problem. After obtaining the subcarrier assignment matrix, the multi-carrier link-layer EE-EC tradeoff problem for each user is formulated and solved by using Karush-Kuhn-Tucker (KKT) conditions. The per-user optimal power allocation strategy, which is across both frequency and time domains, is then derived. Further, we theoretically investigate the impact of the circuit power and the EE requirement factor on each user?s EE level and optimal average power value. The low-complexity heuristic algorithm is then simulated to compare with the traditional exhaustive algorithm and a fair-exhaustive algorithm. Simulation results confirm our proofs and design intentions, and further show the effects of delay quality-of-service (QoS) exponent, the total number of users and the number of subcarriers on the system tradeoff performance

Energy efficient resource allocation in 5G hybrid heterogeneous networks: A game theoretic approach

Millimeter wave (mmWave) technology integrated with heterogeneous networks (HetNets) has emerged as a new wave to overcome the thirst for higher data rates and severe shortage of spectrum. In this paper, we consider the uplink of a hybrid HetNet with femtocells overlaid on a macrocell, and formulate a two layer game theoretic framework to maximise the energy efficiency (EE) while optimising the network resources. The outer layer allows each femtocell access point (FAP) to maximise the data rate of its users by selecting the frequency band either from the sub-6 GHz and the mmWave. The solution to this non-cooperative game can be obtained by using pure strategy Nash equilibrium. The inner layer ensures the energy efficient user association method subject to the minimum rate and maximum transmission power constraints by using dual decomposition approach. Simulation results show that the proposed hybrid HetNet scheme exploiting the mmWave frequency band improves the sum-rate and EE in comparison to the scenario where all the networks operate at sub-6 GHz frequency band. The performance can further be enhanced by incorporating the power control mechanism

Weighted Tradeoff between Spectral Efficiency and Energy Efficiency in Energy Harvesting Systems

This paper proposes a new power allocation scheme to jointly optimize energy efficiency (EE) and spectral efficiency (SE) of a point-to-point communication system in which the transmitter is equipped with fixed as well as energy harvesting batteries. Time switching protocol is used such that in each time frame the node either harvests energy or transmits information. Firstly, a multi-objective optimization problem which jointly optimizes EE and SE is formulated. An importance weight parameter is introduced to control the priority level between EE and SE. Secondly, the multi-objective problem is transformed into a single-objective optimization problem by using importance weight, and then solved through fractional programming. Using the Karush-Kuhn-Tucker conditions, the optimum power allocation scheme without input power constraint is developed. The ensuing solution is then generalized for system operation with average input power constraint. Closed-form expressions are derived and tested through simulations. Numerical results results are provided, and show the impact of the harvested power in improving the overall rate of the system. Also investigation is done to analyze the effect of system parameters on the achievable trade-off performance of the energy-harvesting based syste

Novel Mathematical Framework for Performance Analysis of Energy Harvesting-Based Point-to-Point Communications

This paper presents a novel performance evaluation framework for energy harvesting communications. As the harvested energy may not always be at the required levels in the transmitter’s battery, possible energy outage may hinder the transmission, especially in weak channel conditions. Herein, we analyze the performance of an energy harvesting communication link by allowing a certain level of energy outage to occur. Such operation is challenging, given that the energy coming into the battery from an uncontrollable source, e.g., solar energy, does not relate to the channel conditions and quality-of-service (QoS) requirement, whereas energy going out of the battery is directly dependent on both. Hence, the incoming energy and outgoing energy become independent of each other. Knowing the exact level of energy that is accumulated in the battery is therefore challenging. To deal with these challenges, a probabilistic energy-outage approach and a virtual battery queuing model are proposed and used to develop the target performance evaluation framework while leveraging the large deviation principle theorem. The derived energy-outage probability of the communication system relates the system parameters, namely, QoS component, channel conditions, and harvested energy. Numerical results are presented to confirm the analytical findings and discuss the performance of energy harvesting based communication with tolerable energy-outage as a function of the system parameters

Computationally Intelligent Techniques for Resource Management in MmWave Small Cell Networks

Ultra densification in HetNets and the advent of mmWave technology for 5G networks have led researchers to redesign the existing resource management techniques. A salient feature of this activity is to accentuate the importance of CI resource allocation schemes offering less complexity and overhead. This article overviews the existing literature on resource management in mmWave-based Het- Nets with a special emphasis on CI techniques and further proposes frameworks that ensure quality of service requirements for all network entities. More specifically, HetNets with mmWave-based small cells pose different challenges compared to an all-microwave- based system. Similarly, various modes of small cell access policies and operations of base stations in dual mode, that is, operating both mmWave and microwave links simultaneously, offer unique challenges to resource allocation. Furthermore, the use of multi-slope path loss models becomes inevitable for analysis due to irregular cell patterns and blocking characteristics of mmWave communications. This article amalgamates the unique challenges posed because of the aforementioned recent developments and proposes various CI-based techniques, including game theory and optimization routines, to perform efficient resource management

Effective Capacity in Broadcast Channels with Arbitrary Inputs

We consider a broadcast scenario where one transmitter communicates with two receivers under quality-of-service constraints. The transmitter initially employs superposition coding strategies with arbitrarily distributed signals and sends data to both receivers. Regarding the channel state conditions, the receivers perform successive interference cancellation to decode their own data. We express the effective capacity region that provides the maximum allowable sustainable data arrival rate region at the transmitter buffer or buffers. Given an average transmission power limit, we provide a two-step approach to obtain the optimal power allocation policies that maximize the effective capacity region. Then, we characterize the optimal decoding regions at the receivers in the space spanned by the channel fading power values. We finally substantiate our results with numerical presentations.Comment: This paper will appear in 14th International Conference on Wired&Wireless Internet Communications (WWIC

Low Latency Driven Effective Capacity Analysis for Non-Orthogonal and Orthogonal Spectrum Access

In this paper, we theoretically investigate the performance of non-orthogonal and orthogonal spectrum access protocols (more generically known as NOMA) in supporting ultra-reliable low-latency communications (URLLC). The theory of effective capacity (EC) is adopted as a suitable delay-guaranteed capacity metric to flexibly represent the users' delay requirements. Then, the total EC difference between a downlink user-paired NOMA network and a downlink orthogonal multiple access (OMA) network is analytically studied. Exact closed-form expressions and the approximated closed-forms at high signal-to-noise ratios (SNRs) are derived for both networks and validated through simulation results. It is shown that for a user pair in which two users with the most distinct channel conditions are paired together, NOMA still achieves higher total EC (compared to OMA) in high SNR regime as the user group size becomes larger, although the EC performance of both NOMA and OMA reduces with the increase in group size. It is expected that the derived analytical framework can serve as a useful reference and practical guideline for designing favourable orthogonal and nonorthogonal spectrum access schemes in supporting low-latency services

Impact of antenna correlation on the performance of partial relay selection

Antenna correlation is generally viewed as an obstacle to realize the desired performance of a wireless system. In this article, we investigate the performance of partial relay selection in the presence of antenna correlation. We consider both channel state information (csi)-assisted and fixed gain amplify-and-forward (AF) relay schemes. The source and the destination are equipped with multiple antennas communicating via the best first hop signal-to-noise ratio (SNR) relay. We derived the closed form expression for outage probability, average symbol error rate (SER) for both schemes. Further, an exact expression is derived for the ergodic capacity in the csi-assisted relay case and an approximated expression is considered for the fixed gain case. Moreover, we provide simple asymptotic results and show that the diversity order of the system remains unchanged with the effect of antenna correlation for both types of relay schemes