On Performance of SWIPT Enabled PPP Distributed Cooperative NOMA Networks Using Stochastic Geometry

This book chapter investigates the advances of energy harvesting (EH) and multiple accesses protocols for smart city applications. In particular, a novel communication scheme that combines EH and a cooperative non-orthogonal multiple access (NOMA) system is introduced. In the proposed scheme, the relay harvests energy from the base station to serve some user groups including the near and far users. Later, simultaneous wireless information and power transfer (SWIPT) technique is exploited to determine performance improvement at least amount of harvested energy. The other parameters need to investigate the impact of imperfect power allocation factors on system performance. It is proved that introducing SWIPT does not harm system performance. Furthermore, the outage probability of both near and far users is derived and indicated in closed-form expressions. Numerical simulations are conducted to examine the outage probability of the proposed scheme and to verify the derived formulas. The proposed scheme has the potential to solve the problem of EH in the context of smart city.KeywordsSimultaneous wireless information and power transfer (SWIPT)Non-orthogonal multiple access (NOMA)Outage probabilitySmart cities

This paper investigates the solution to an optimisation problem to minimise the total transmission power at the transmitter in a cooperative non-orthogonal multiple access (NOMA) system with simultaneous wireless information and power transfer (SWIPT) and an energy-harvesting user. First, we formulate the optimisation problem to obtain the minimum transmission power at the transmitter under the constraints of minimum signal-to-interference-plus-noise ratio and minimum energy harvesting. Since the problem is not convex, we transform it into a bi-level optimisation problem. Then, conditions to guarantee the feasibility of the problem are provided, and we derive the analytical optimal solution via the Lagrange method meeting Karush–Kuhn–Tucker optimality conditions to solve the lower-level variables of the inner convex problem. Second, we use particle swarm optimisation to find the approximately optimal values of the upper-level variables. Next, we present two baseline schemes based on orthogonal multiple access (OMA) and equal power splitting for performance comparison with the proposed cooperative NOMA system with SWIPT. Finally, simulation results show that cooperative NOMA with SWIPT can reduce the transmit power at the transmitter, compared to two baseline schemes: OMA and EPS.

In this paper, a novel communication scheme that combines beamforming, energy harvesting, and cooperative non-orthogonal multiple access (NOMA) system is introduced. In the proposed scheme, NOMA is first combined with beamforming to serve more than one user in each beamforming vector. Later, simultaneous wireless information and power transfer (SWIPT) technique is exploited to encourage the strong user to relay the weak user's information messages in full-duplex (FD) manner. However, one major drawback of FD communications is the self-interference (SI) signal due to signal leakage from terminal's output to the input. Three different cases are adopted. In the first case, the SI signal is assumed to be fully cancelled at the strong user using SI cancellation techniques. In the second case, SI is only cancelled at the information decoding circuits, while being harvested in the energy harvester to provide extra energy. The third case investigates the impact of imperfect SI cancellation on system performance is investigated. It is proved that introducing SWIPT doesn't only motivate users to collaborate, but also mitigates the impact of the SI signal. In addition, the problem of total sum rate maximisation is formulated and solved locally by means of two-step difference of convex functions (DC)-based procedure. Furthermore, the outage probability of both weak and strong user is derived and provided in closed-form expressions. Numerical simulations are presented to illustrate the sum rate gain of the proposed scheme if compared with existing schemes, and to verify the derived formulas.

Rate-splitting multiple access (RSMA) and the intelligent reflecting surface (IRS) are novel technologies to improve spectrum and energy efficiencies in multi-antenna networks. In this paper, we investigate a multi-user multiple-input single-output (MISO) simultaneous wireless information and power transfer (SWIPT) system assisted with an IRS and using RSMA. In particular, the IRS assists with data and energy transmission from the base station (BS) to power-splitting (PS) users under a non-linear energy harvesting (EH) model. Our objective is to minimize the transmission power subject to rate and EH requirements at the users. To solve the non-convex problem, we propose a bilevel programming problem in which a genetic algorithm is used to solve the outer optimization problem, and the inner optimization problem is addressed with the semidefinite relaxation (SDR) method. In addition, to study a practical scenario of imperfect channel state information (CSI), we consider a robust beamforming design based on imperfect cascade channels at the BS. Then, we propose a solution based on the S-procedure with the SDR technique. Simulation results show that our proposed RSMA-based scheme provides a significant reduction in transmission power compared to the space-division multiple access (SDMA) and non-orthogonal multiple access (NOMA) methods under perfect and imperfect CSI.

In this paper, a bidirectional relaying (BR) non-orthogonal multiple access (NOMA) with simultaneous wireless information and power transfer (SWIPT) termed as BR NOMA-SWIPT is proposed and investigated for the Internet of Things (IoT) relay networks. Here, multiple NOMA users in one group can communicate or exchange information with multiple NOMA users in another group through a common energy harvesting (EH) based relay. The EH based relay exploits the radio frequency (RF) energy supplied by the two NOMA user groups to recharge itself, and then it exchanges the information between them. Specifically, the two groups of NOMA users transmit the information intended for the exchange to the relay node using the uplink NOMA protocol. The relay node first harvests the RF energy through the signals of the two group of NOMA users, and then it carries out the exchange of information between two NOMA user groups by using the downlink NOMA protocol. To the best of our knowledge, there is no existing study or research on BR NOMA with SWIPT. Therefore, in this paper, we examine in detail, the performance of BR NOMA-SWIPT enabled IoT relay networks. Specifically, we study a popular EH time switching (TS) relaying architecture with BR and NOMA. We also study the effect of both perfect successive interference cancellation (pSIC) and imperfect SIC (ipSIC) on the proposed BR NOMA-SWIPT system. Analytical expressions for the outage probability and ergodic capacity are mathematically derived. The analytical results of our proposed system model are validated by the simulation results, and representative performance comparisons are presented thoroughly, which not only provides practical insights into the effect of different system parameters on the overall network performance, but it also demonstrates that our proposed BR NOMA-SWIPT can attain significant throughput and capacity gains as compared to conventional BR multiple access schemes.

This paper investigates the physical layer security issue in an amplify-and-forward (AF) multi-input multi-output (MIMO) two-way relay assisted cognitive radio (CR) nonorthogonal multiple access (NOMA) network, where the simultaneous wireless information and power transfer (SWIPT) technology is employed to improve network energy efficiency. We consider the scenario that a pair of primary users and two pairs of secondary users (SUs) exchange information via a MIMO two-way relay, where the edge SU of each SU pair is untrusted and tries to wiretap the central SU’s information. For ensuring security, we aim to maximize the sum achievable secrecy rate (SASR) by jointly optimizing the power allocation at all users, power splitting factor and relay beamforming subject to the quality of service (QoS), energy harvesting and transmit power constraints. The formulated optimization problem is highly nonconvex due to coupling variables, thus it is challenging to solve. An effective path-following (PF)-based algorithm is proposed, which is proven to converge to a stationary point. Theoretical and simulation results show that the proposed PF-based algorithm has lower complexity than the state-of-art algorithm. To further reduce complexity, we proposed a zero-forcing (ZF)-based scheme. Numerical simulations show that the proposed PF-based algorithm achieves the same SASR as the state-of-art algorithm with moderate complexity, while the proposed ZF-based scheme strikes a good balance between performance and complexity.

In this article, a cooperative non-orthogonal multiple access (NOMA) mobile edge computing (MEC) network aided by reconfigurable intelligent surfaces (RIS) and simultaneous wireless information and power transfer (SWIPT) is considered, where the transmitters offload parts of their computing tasks to the MEC server via a relay and an RIS for enhancing the transmission environment. The goal is to minimize the task delay and energy consumption for the considered networks by jointly designing the RIS's reflection beamforming vector, the power splitting (PS) ratio, the power allocation factors of the relay, as well as the offloading transmit power and the offloading task ratio. To solve the proposed problems, an iterative optimization algorithm based on the successive convex approximation (SCA) method and the penalty method is proposed to decompose the formulated problems into two sub-problems. In particular, we jointly optimize the PS ratio, the power allocation coefficients and the edge computing resource based on the SCA technology, and then the penalty method is used to optimize the RIS's reflecting beamforming vector. Simulation results illustrate that the proposed NOMA-MEC networks aided by RIS and SWIPT are superior to the conventional orthogonal multiple access MEC networks with SWIPT aided by RIS in terms of task delay and energy consumption.

Non-orthogonal multiple access (NOMA) is one of the most significant technologies to meet the demand of high spectral efficiency (SE) in the fifth generation (5G) cellular networks. The utilization of simultaneous wireless information and power transfer (SWIPT) contributes to prolonging the battery life of the mobile users (MUs) and enhancing the system energy efficiency (EE), especially in the NOMA scenario where the inter-user interference can be reused for energy harvesting (EH). In this paper, we study the achievable data rate maximization problem for the downlink multi-carrier NOMA (MC-NOMA) network with power splitting (PS)-based SWIPT, in which power allocation and PS control are jointly optimized with the limitation of available power budget as well as the requirement for EH. The considered non-convex optimization problem is arduous to tackle, resulting from the presence of the coupled variables and the inter-user interference. To cope with the problem, a decoupled approach is developed, in which the power allocation and PS control are separated and the corresponding sub-problems are respectively solved through Lagrangian duality method. Furthermore, an alternative approach based on deep learning is proposed, which is capable of effectively obtaining the approximate optimal solution according to the empirical data. Simulation results confirm the effectiveness of the proposed schemes, and demonstrate the superiority of the combination of PS-based SWIPT with MC-NOMA over SWIPT-aided single-carrier NOMA (SC-NOMA) and SWIPT-aided orthogonal multiple access (OMA).

The increase in number of cellular users had lead to the evolution from the traditional cellular networks to the more efficient heterogeneous cellular networks (HetNet) to handle the traffic. Offloading plays a vital role in handling the traffic from the congested macro base station by handing users to the less congested femto base stations (FBS). Further, non-orthogonal multiple access (NOMA) has proved to be efficient for the future generation networks. In this work, we study the offloading in HetNets, where the FBS tier serves the users using NOMA. Imperfect channel state information (CSI) is considered to analyze the outage probability of offloaded user, since, in practice CSI estimation requires significant system overhead, especially when the number of users are large. Hence, for practical systems, the analyses with imperfect CSI is more relevant. Some important observations regarding offloading to FBS tier with NOMA based on imperfect CSI are drawn. The analytical results are validated using Monte Carlo simulations.

This paper investigates the application of simultaneous wireless information and power transfer (SWIPT) to cooperative non-orthogonal multiple access (NOMA). A new cooperative multiple-input single-output (MISO) SWIPT NOMA protocol is proposed, where a user with a strong channel condition acts as an energy-harvesting (EH) relay to help a user with a poor channel condition. The power splitting (PS) scheme is adopted at the EH relay. By jointly optimizing the PS ratio and the beamforming vectors, the design objective is to maximize the data rate of the "strong user" while satisfying the QoS requirement of the "weak user". It boils down to a challenging nonconvex problem. To resolve this issue, the semidefinite relaxation (SDR) technique is applied to relax the quadratic terms related with the beamformers, and then it is solved to its global optimality by two-dimensional exhaustive search. We prove the rank-one optimality, which establishes the equivalence between the relaxed problem and the original one. To further reduce the high complexity due to the exhaustive search, an iterative algorithm based on successive convex approximation (SCA) is proposed, which can at least attain its stationary point efficiently. In view of the potential application scenarios, e.g., IoT, the single-input single-output (SISO) case of the cooperative SWIPT NOMA system is also studied. The formulated problem is proved to be strictly unimodal with respect to the PS ratio. Hence, a golden section search (GSS) based algorithm with closed-form solution at each step is proposed to find the unique global optimal solution. It is worth pointing out that the SCA method can also converge to the optimal solution in SISO cases. In the numerical simulation, the proposed algorithm is numerically shown to converge within a few iterations, and the SWIPT-aided NOMA protocol outperforms the existing transmission protocols.

The acoustic signal transmission over the underwater channel has a limited sum rate and it consumes high power due to the properties of the underwater environment. This study attempts to use the non‐orthogonal multiple access (NOMA) technologies for underwater communications. NOMA can be an attractive candidate for underwater communication due to its high spectral efficiency, resistance for carrier frequency offset, and efficient energy consumption. To cope with the hard‐recharging capability of the underwater wireless sensor nodes caused by the ocean environment, this study proposes a novel transmission scheme called time‐reversed NOMA (TR‐NOMA) for underwater communication. In the proposed TR‐NOMA, a single‐input multiple‐output NOMA scheme with a passive‐time reversal technique is proposed to reduce the time–frequency dispersion of the underwater acoustic channels. Consequently, simultaneous wireless information and power transfer (SWIPT) can be applied for underwater TR‐NOMA. In this study, a SWIPT‐NOMA is postposed to harvest energy in downlink transmission from the transmitted signal. The bit error rate (BER) and the outage probability are used to characterise the performance of the proposed TR‐NOMA scheme and simulation results show how the proposed TR‐NOMA significantly outperforms the conventional NOMA schemes. Additionally, a mathematical framework for the average BER of TR‐NOMA is delineated.

This paper investigates a relay assisted simultaneous wireless information and power transfer (SWIPT) for downlink in cellular systems. Cooperative non-orthogonal multiple access (C-NOMA) is employed along with power splitting protocol to enable both energy harvesting (EH) and information processing (IP). A downlink model consists of a base station (BS) and two users is considered, in which the near user (NU) is selected as a relay to forward the received signal from the BS to the far user (FU). Maximum ratio combining is then employed at the FU to combine both the signals received from the BS and NU. Closed form expressions of outage propability, throughput, ergodic rate and energy efficiency (EE) are firstly derived for the SWIPT based C-NOMA considering both scenarios of with and without direct link between the BS and FU. The impacts of EH time, EH efficiency, power-splitting ratio, source data rate and distance between different nodes on the performance are then investigated. The simulation results show that the C-NOMA with direct link achieves an outperformed performance over C-NOMA without direct link. Moreover, the performance of C-NOMA with direct link is also higher than that for OMA. Specifically, (1) the outage probability for C-NOMA in both direct and relaying link cases is always lower than that for OMA. (2) the outage probability, throughput and ergodic rate vary according to beta, (3) the EE of both users can obtain in SNR range of from -10 to 5 dB and it decreases linearly as SNR increases. Numerical results are provided to verify the findings.

SummaryThe 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.

Realising both wireless information transfer (WIT) and wireless power transfer (WPT) in the same RF spectral band has imposed great challenges on the system design but the spectral efficiency can be substantially improved, which triggers the significant research interest in the simultaneous wireless information and power transfer (SWIPT). In order to fully exploit the limited spectral resources, a non-orthogonal-multiple-access (NOMA) technique aided SWIPT system is considered for simultaneously realising both of WIT and WPT, which consists of a single access point (AP), a single WPT user and a pair of WIT users. The AP delivers the requested information to the pair of WIT users by adopting the NOMA technique. In order to maximise the amount of energy received by the WPT user, a novel constellation rotation based modulation scheme is proposed for constructively combining the symbols requested by the pair of the WIT users by optimising the constellation rotation angle. By considering the sensitivity of the energy harvester, the simulation results demonstrate that our modulation scheme is capable of efficiently increasing the energy harvested by the WPT user without incurring additional symbol detection errors.

In this paper, simultaneous wireless information and power transfer (SWIPT) concept is introduced for multi group multicast beamforming. Each user has a single antenna and a power splitter which divides the radio frequency (RF) signal into two for both information decoding and energy harvesting. The aim is to minimize the total transmission power at the base station while satisfying both signal-to-interference-plus-noise-ratio (SINR) and harvested power constraints at each user. Unlike unicast and certain broadcast scenarios, semidefinite relaxation (SDR) is not tight and global optimum solution cannot be found for this problem. We propose an iterative algorithm where a convex optimization problem is solved at each iteration. Both perfect and imperfect channel state information (CSI) at the base station are considered. Simulation results show that the proposed solution is very close to the SDR lower bound and a few number of iterations are enough for the algorithm convergence.