Outage Performance of Energy Harvesting DF Relaying NOMA Networks

In this paper, we investigate energy harvesting decode-and-forward relaying non-orthogonal multiple access (NOMA) networks. We study two cases of single relay and multiple relays with partial relay selection strategy. Specifically, one source node wishes to transmit two symbols to two respective destinations directly and via the help of one selected intermediate energy constraint relay node, and the NOMA technique is applied in the transmission of both hops (from source to relay and from relay to destinations). For performance evaluation, we derive the closed-form expressions for the outage probability (OP) at D ₁ and D ₂ with both cases of single and multiple relays. Our analysis is substantiated via Monte Carlo simulation. The effect of several parameters, such as power allocation factors in both transmissions in two hops, power splitting ratio, energy harvesting efficiency, and the location of relay nodes to the outage performances at the two destinations is investigated.     

Secrecy analysis of a cooperative NOMA network using an EH untrusted relay

In this paper, a down-link non-orthogonal multiple access (NOMA) system with imperfect successive interference cancellation (SIC) using Energy-Harvesting untrusted relays is investigated. These relaying nodes use in this study use a power-switching architecture to harvest energy from the sources signals and apply an amplify-and-forward protocol to forward the signals. In addition, transmit jamming or artificial noise, is generated by a source node to improve the security of the system and protect confidential source information from untrusted relays. Likewise, three relaying selection strategies are employed to examine the secrecy performance of the proposed system. In order to evaluate the performance evaluation of the proposed system, closed-form expressions of the Secrecy Outage Probability (SOP) are studied over Rayleigh fading channels and a Monte Carlo simulation is used to confirm the analytical results. Furthermore, we study the effects of various parameters, such as power allocation factors, relay node selection, the number of relays, energy harvesting efficiency and the location of relay nodes on the secure outage performances for two users of NOMA system and conventional orthogonal multiple access (OMA). These results show that NOMA offers the better security performance with multiple users.     

硬件损伤条件下的中继网络性能分析

物理层的损伤会造成系统性能的降低.主要分析基于机会中继选择策略下的中继网络.机会中继选择策略是中继节点的选择依靠所有信道的即时信息,选择其中最大的进行传输.得到了系统端到端中断概率的准确表达式以及遍历容量的近似表达式.公式的给出提供了快速计算具有硬件损伤的系统性能的方法.重点讨论了具有硬件损伤的中继系统和理想硬件系统的性能对比.给出了仿真的结果和必要的讨论来证明理论分析的正确性.     

Power allocation schemes for wireless powered NOMA systems with imperfect CSI: An application in multiple antenna–based relay

The simultaneous wireless information and power transfer or energy harvesting (EH) can be combined in nonorthogonal multiple access (NOMA) as green applications towards 5G. This paper investigates a new cooperative EH‐NOMA protocol, where the intermediate relay has not equipped the fixed power source and acts as a wireless powered relay to help signal transmission to representative weak user and strong user in NOMA. However, impacts of imperfect channel estimation contribute to outage system performance evaluations. We formulate the power resource assignment paradigms as two schemes, namely, fixed power allocation and dynamic power allocation, by considering imperfect channel state information (CSI). To solve this problem, we derive the closed‐form expressions of outage probability under imperfect CSI and the power allocation constraints. The expected numerical results related to the derived expressions for the outage probability are examined that numerical and the Monte Carlo simulations are strictly matching lines.     

On outage minimization in RF energy harvesting relay assisted bidirectional communication

This paper explores an end-to-end outage probability experienced in a bidirectional relay assisted communication where the relay is assumed to be equipped with an RF energy harvesting circuit. First, the closed-form expression for the outage of the system is derived. This is followed by the formulation of an unconstrained optimization problem to achieve minimum outage probability with respect to the relay placement and consequent time allocation for energy harvesting. The system model is further extended in an underlay cognitive radio framework to study the impact of a primary user outage constraint on the end-to-end outage performance of the two-way communications. The accuracy of analytical results is validated through simulation results. The impact of various system parameters like relay position, time allocation factor, target rate of transmission on the outage probability is also observed. In addition, it is also shown that spectral efficiency of the communication system using hybrid power-time switching relaying protocol is much superior to similar one-way and two-way relay assisted communication system with power splitting relaying protocol.

     

Performance analysis of SWIPT-assisted adaptive NOMA/OMA system with hardware impairments and imperfect CSI

This paper investigates the effect of hardware impairments (HIs) and imperfect channel state information (ICSI) on a SWIPT-assisted adaptive nonorthogonal multiple access (NOMA)/orthogonal multiple access (OMA) system over independent and nonidentical Rayleigh fading channels. In the NOMA mode, the energy-constrained near users act as a relay to improve the performance for the far users. The OMA transmission mode is adopted to avoid a complete outage when NOMA is infeasible. The best user selection scheme is considered to maximize the energy harvested and avoid error propagation. To characterize the performance of the proposed systems, closed-form and asymptotic expressions of the outage probability for both near and far users are studied. Moreover, exact and approximate expressions of the ergodic rate for near and far users are investigated. Simulation results are provided to verify our theoretical analysis and confirm the superiority of the proposed NOMA/OMA scheme in comparison with the conventional NOMA and OMA protocol with/without HIs and ICSI.     

Performance Evaluation of Relay Assisted Wireless Powered Network over Fluctuating Two Ray Fading Channel with Diversity Reception

Recently wireless powered networks have emerged as cutting-edge technology for addressing the power constraint issue of wireless devices (WD’s). This technology enables wireless nodes to harness power from the ambient radio frequency (RF) signal thus enhances the energy efficiency of the communication network and also improves the network longevity. The underlying principle of energy harvesting (EH) by wireless power transfer (WPT) has implications on system performance due to link distance and channel fading. To address the impact of channel fading on energy constraints WD’s this work explores the maximal ratio combining (MRC) diversity at the receiver node for the presented simultaneous wireless information and power transfer (SWIPT) model considering the energy constraint unmanned aerial vehicle (UAV) mounted amplify and forward (AF) relay. Assuming fluctuating two ray (FTR) fading scenario a novel analytical expression for the outage probability (OP) and symbol error rate (SER) for the presented system has been derived. As the FTR fading channel provides a generalized fading model and can significantly model millimeter wave band signals. Based on derived performance metrics this paper investigates the impact of variation on node positioning and EH time allocation factor on system outage probability (OP) and symbol error rate (SER) performance. Finally, the derived expression has been validated by comparing the results obtained from the Monte Carlo simulation.

     

Physical Layer Security for Wireless Powered Massive MIMO Decode and Forward Relay Systems with Hardware Impairments: Performance Analysis

In this paper, the issue of secrecy capacity of wireless powered massive MIMO dual hop relay system with a single antenna eavesdropper having non ideal hardware is addressed. The relay harvests energy in a proportionate manner and passes it to destination through beamforming with classical decode and forward relaying protocol. The relay has no channel state information (CSI) of passive eavesdropper but has CSI of the legitimate channel. The work presented in this paper focuses on the analysis of the difference in system performance with ideal and non ideal hardware, bounded by strict outage probability. The performance (in terms of secrecy outage capacity) is studied with hardware impairments (HWIs) defined for all network elements, i.e., source, relay, destination and passive eavesdropper. It is also observed that compared to ideal hardware, there is significant degradation in performance due to HWIs.

     

Performance of cognitive relay network with energy harvesting relay under imperfect CSI

This paper evaluates the performance of an underlay cognitive relay network under imperfect channel state information (CSI) where a secondary user (SU) transmits using a secondary relay (SR) based on decode and forward scheme. The outage probability (OP) of SU is investigated in a scenario where the decode and forward relay harvests energy from radio frequency signal of SU. The relay uses a fraction of time for harvesting in time switching–based relaying (TSR) while a fraction of received power is used for harvesting in power splitting–based relaying (PSR) scheme. The SU and relay control their transmit power using a scaling factor, based on CSI of the interfering links (ie, links from SU transmitter and SR to the primary user [PU] receiver) to protect the quality of service of PU. The available CSI at the SU and SR are imperfect due to practical limitation. Analytical expressions of the OP are derived for TSR‐ and PSR‐based schemes. The impact of harvesting time, power splitting ratio, imperfect CSI, PU outage constraint and interference threshold on the OP of the SU network, and average transmit power of SR is indicated. Further, the impact of multiple SRs is also shown.     

Impact of fixed power allocation in wireless energy harvesting NOMA networks

The time switching‐based relaying (TSR) scheme is considered in energy harvesting protocol to implement with its advantage to nonorthogonal multiple access (NOMA) system. In particular, decode‐and‐forward (DF) mode is proposed to employ in relay to forward signal to serve two far NOMA users. There are two main metrics including outage probability and ergodic rate, which are derived in exact expressions with respect to varying performance under impacts of energy harvesting fractions. To evaluate system performance, outage event and related capacity are illustrated, and we tailor performance gap among two NOMA users and such gap can be controlled by selecting of appropriate power allocation factors assigned for each user to obtain optimal performance. By examining node arrangement, target rates and varying transmit signal to noise ratio (SNR), it can be further achieved performance in several situations of such NOMA. As important result, the considered NOMA system outperforms than the conventional multiple access scheme, and this expected result is confirmed in numerical result and theoretical results. We also explore impacts of transmit power at source, noise power, the other key parameters of energy harvesting scheme to exhibit outage, and ergodic performance. Simulation results are presented to corroborate the proposed methodology.     

直达链路下的全双工能量采集中继系统的吞吐量分析

针对三节点传输系统,研究了基于时间切换能量采集的全双工放大转发协作中继方案。考虑源和目的地之间存在直达链路,全双工中继节点采用天线选择技术以最小化中继自干扰,目的节点采用最大比合并技术以最大化目的地接收信噪比。在延迟受限传输模式下,推出了自干扰信道增益为常数时系统吞吐量近似闭合表达式。运用最佳目的地选择策略和自适应中继选择策略讨论了系统吞吐量性能。如图4所示,在源发送功率为30 dB时,就系统吞吐量而言,本文算法比其他两种算法分别提高了0.22 bits/s/Hz和0.68 bits/s/Hz。数值分析和蒙特卡洛仿真表明,增加中继个数,增加目的地个数或者增大能量采集效率均能够提升系统吞吐量性能。      

Diversity achieving full-duplex DF relaying with joint relay-antenna selection under Nakagami-m fading environment

One of the main imperfections degrading the performance of full-duplex (FD) relaying systems is the outage floor. In this work, a power scaling method is proposed, which overcomes this effect even when there does not exist a direct channel between source and destination nodes. The system is composed of $K$ decode-and-forward (DF) FD relays over the Nakagami-m fading environment. To promote system performance, joint antenna and relay selection methods are employed in the FD relaying systems. Each FD relay is equipped with multiple antennas for receiving and the other for transmitting the information. The transmitting and receiving antennas are chosen based on the instantaneous channel variations, and one relay is selected to improve the signal-to-interference and noise ratio (SINR) of the FD relaying system. The performance of the proposed design is investigated. Moreover, the closed-form equations of the ergodic capacity and outage probability are attained. The analytical results are confirmed by different simulations. Results indicate that the proposed design achieves an additional spatial diversity gain because of using the antenna selection at the relay nodes. Moreover, by power scaling (PS) method, the system performance is effectively improved compared to the conventional FD relaying structures.     

广东工业大学信息工程学院

广东工业大学信息工程学院成立于2000年4月，其前身为原电子与信息工程系和原机械电子工程二系的测量与控制专业。现设有“信息工程”和“测控技术与仪器”两个本科专业，拥有“电子电力与电力传动”与“测试计量技术与仪器”两个学科的硕士学位授予点。     

SWIPT in multi-hop amplify-and-forward wireless sensor networks

ABSTRACT

Energy harvesting (EH) is an eminent solution to perpetuate the lifetime of energy-constrained relay nodes in wireless sensor networks (WSNs). This paper considers a multi-hop amplify-and-forward (AF) network in which relay nodes with EH capability harvest energy inherent in the source transmitted radio frequency (RF) signal and use the harvested energy for signal transmission. Based on the time switching and power splitting EH receiver designs, we have examined the performance of, (i) time switching based relaying (TSR) and (ii) power splitting based relaying (PSR) protocols in multi-hop AF network, with throughput as the figure of merit. The numerical analysis reveals that, PSR outperforms TSR at high signal-to-noise ratio (SNR) whereas TSR outperforms PSR at low SNR, in multi-hop AF-WSNs with energy harvesting.     

Outage performance of relay selection with spatially random relays using RF energy harvesting

To enable green wireless networks, one appealing approach is to deploy energy harvesting (EH) relays to assist the source transmission. Unlike conventional relays relying on fixed power supplies, EH relays make use of the energy collected from the RF radiation of the source node, and thus, they do not introduce extra energy cost to the network. This paper presents an analytical study to assess the efficacy of EH relays when the one with the maximal end‐to‐end signal‐to‐noise ratio is selected to perform data relaying while others perform EH. Because the action (either harvesting energy or forwarding data) of one EH relay affects those of others, exact performance analysis is not tractable. Additionally, relay density and positions may be random, which further complicates the analysis. Our analysis is conducted based on the hypothesis that each EH relay has an equal chance to be selected. This hypothesis allows for analytical tractability and is of importance to EH relays because otherwise some may drain their batteries fast. We identify the conditions under which the aforementioned hypothesis is valid. Our analysis also considers two variants of amplify‐and‐forward relays with and without using channel state information. Numerical results are presented to validate the analysis accuracy along with extensive discussions on the impact of numerous system parameters. Copyright © 2015 John Wiley & Sons, Ltd.     

Wireless powered underlay cognitive radio network with multiple primary transceivers: Energy constraint,node arrangement,and performance analysis

This paper considers a cognitive radio–assisted wireless information and power transfer system consisting of multipair of transceiver in primary network and 2‐hop relaying link in secondary network. In this investigation, a decoded‐and‐forward–assisted relay node and power splitting protocol are deployed to obtain ability of wireless energy transfer. The relay node harvests energy from the radio frequency signals of the secondary transmitter and primary transmitters in data transmission to the destination by reusing the licensed spectrum resource. We propose 2 policies for wireless power transfer at the relay, namely, (1) multisource power transfer and (2) single‐source power transfer. To evaluate performance under energy harvesting regime, we derive the closed‐form outage probability expressions and achievable throughput of the secondary network in delay‐limited transmission mode. In addition, we investigate the impact of various system parameters including number of primary transceivers, primary outage threshold, and position arrangement of nodes in primary transceivers on the outage performance of the proposed scheme. Furthermore, we evaluate the system energy efficiency to show trade‐off metric of energy consumption and throughput. Performance results are presented to validate our theoretical derivation and illustrate the impacts of various system parameters. An important result is that the secondary network is more beneficial than harmful from the primary interference under power constraint and reasonable node location arrangement.     

Simultaneous energy harvesting and information processing in wireless multiple relays with multiple antennas

Wireless networks suffer from battery discharging specially in cooperative communications when multiple relays have an important role but they are energy constrained. To overcome this problem, energy harvesting from radio frequency signals is applied to charge the node battery. These intermediate nodes have the ability to harvest energy from the source signal and use the energy harvested to transmit information to the destination. In fact, the node tries to harvest energy and then transmit the data to destination. Division of energy harvesting and data transmission can be done in two algorithms: time-switching-based relaying protocol and power-splitting-based relaying protocol. These two algorithms also can be applied in delay-limited and delay-tolerant transmission systems. The previous works have assumed a single relay for energy harvesting, but in this article, the proposed method is concentrated on improving the outage probability and throughput by using multiple antennas in each relay node instead of using single antenna. According to our simulation results, when using multi-antenna relays, ability of energy harvesting is increased and thus system performance will be improved to great extent. Maximum ratio combining scheme has been used when the destination chooses the best signal of relays and antennas satisfying the required signal-to-noise ratio.     

Alternate energy harvesting and information relaying in cooperative AF networks

This paper studies an energy harvesting (EH) based cooperative relaying system, where two half-duplex relays operate with EH and alternately amplify and forward source data to the destination. When one relay joins in the cooperative data transmission, the other relay will harvest wireless energy by overhearing the transmissions from both the source and the transmitting relay. Both the time-switching and power-splitting architectures are considered for the EH and data reception at relays. Since the EH can be implicitly performed by each relay through listening the ongoing transmissions, more energy can be harvested for the cooperative data transmission. The outage probability and throughput of the proposed scheme are derived. Simulation results are provided to verify the correctness of our theoretical analysis and show that our scheme can significantly outperform the single-relay system in terms of throughput.     

Secure Energy Harvesting Communications with Relay Selection over Nakagami-m Fading Channels

In this paper, an energy harvesting relay network over Nakagami-m fading is investigated. In the considered system, the power beacon can provide wireless energy for the source and relays which deploy time-switching-based radio frequency energy harvesting technique. Two relay selection schemes, namely partial relay selection and optimal relay selection, are proposed in order to enhance the system performance. In the former, the source only has the channel state information of the first hop, while in the latter it has the full knowledge of the channel state information. The eavesdropper is able to wiretap to the signal transmitted from the source and the relays. The exact closed-form expressions of secrecy outage probability are derived. The results show that optimal relay selection performs better than partial relay selection. With increasing number of relays, the considered system shows better performance. In addition, the energy harvesting duration has a significant effect on the secrecy outage probability.     

Spatial modulation and physical layer network coding based bidirectional relay network with transmit antenna selection over Nakagami‐m fading channels

In this paper, a high data rate bidirectional relay network is proposed by combining the merits of spatial modulation (SM) and physical layer network coding. All nodes in the network are equipped with multiple antennas. Spatial modulation technique is used to reduce hardware complexity and interchannel interference by activating only one antenna at any time during transmission. In the proposed bidirectional relay network, transmit antennas are selected at the source nodes and relay node on the basis of the order statistics of channel power. It increases received signal power and provides a significant improvement in the outage performance. Also, the data rate of the proposed network is improved by physical layer network coding at the relay node. A closed form analytical expression for the outage probability of the network over Nakagami‐m fading channel is derived and validated by Monte Carlo simulations. In addition, asymptotic analysis is investigated at high signal‐to‐noise ratio region.The outage performance of the proposed network is compared with SM and physical layer network coding bidirectional relay network without transmit antenna selection and point‐to‐point SM. With approximate SNR≈1 dB difference between the two networks, the same data rate is achieved.