Peak Transmit Power Constraint Research Articles

Cooperative Resource Allocation for Hybrid NOMA-OMA-Based Wireless Powered MC-IoT Systems with Hybrid Relays

This paper considers an uplink wireless powered multichannel internet of things (MC-IoT) system with multiple hybrid relays, each serves a group of wireless-powered IoTDs. For coordinating radio frequency wireless power transfer (RF-WPT) and wireless information transfer (WIT), two cooperative protocols integrating non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA), namely hybrid NOMA-frequency division multiple access (FDMA) and hybrid NOMA-time division multiple access (TDMA), is proposed. For both protocols, we investigate cooperative resource allocation problems and aim to maximize the sum data delivered by all the IoTDs, subject to the peak transmit power constraint and the total consumable energy constraint of the hybrid relays. The problem with the hybrid NOMA-FDMA is first decomposed into two subproblems, one for time and power allocation of each hybrid relay and its associated IoTDs, and the other one for channel allocation among them. After some properties of the optimal solution are discovered and a series of transformations is performed, the former subproblem is solved by the bisection search and the Lagrange duality method, and the latter subproblem is solved by the Kuhn–Munkres algorithm. The problem with the hybrid NOMA-TDMA is first convexified by proper variable transformations and then solved by the Lagrange duality method. We provide extensive simulations to demonstrate the superiority of the proposed schemes. It is shown that various system parameters play key roles in the performance comparison of the two schemes.

Optimal Energy-Efficient Antenna Selection and Power Adaptation for Interference-Outage Constrained Underlay Spectrum Sharing

Underlay spectrum sharing addresses spectrum scarcity but imposes constraints on the interference the secondary system causes to the primary receiver. For a secondary transmitter that is subject to the stochastic and general interference-outage constraint and the peak transmit power constraint, we present a novel joint antenna selection and power adaptation rule. It addresses the twin goals of improving the spectral efficiency and reducing the power consumed of an underlay secondary system with low hardware complexity and cost. We prove that the rule maximizes the energy-efficiency (EE) of the secondary system. Its form differs from all other rules considered in the literature. We then present an insightful geometrical characterization of the optimal power of the selected antenna in terms of the channel gains within the secondary system and between the secondary and primary systems. Our approach leads to several special cases, which are themselves novel, and novel analytical insights about the performance and structure of the optimal rule. We also present an iterative subgradient-based algorithm and a simpler non-iterative bound-based algorithm to compute the rule’s parameters. The rule achieves a markedly higher EE compared to conventional approaches, and serves as a new fundamental benchmark for antenna selection in underlay spectrum sharing.

Fundamental Limits of Full-Duplex Spectrum Sharing Under Peak Interference Power Constraint

Cognitive radio (CR) and full-duplex (FD) have received extensive attention and research due to their high spectrum efficiency, which can effectively solve the problem of low spectrum efficiency in current communication systems. Based on CR and FD techniques, in this paper, a FD spectrum sharing CR networks is considered, in which both secondary users (SU1 and SU2) are each equipped with dual antennas, one antenna is used to transmit signals, and the other antenna is used to receive signals at the same time and frequency. Under peak interference power and peak transmit power constraints, we analysis the ergodic sum capacity and the outage probability based on the FD spectrum sharing CR networks and the conventional spectrum sharing CR networks. Furthermore, under no peak transmit power constrain and perfect self-interference cancellation (SIC), based on the FD spectrum sharing CR networks and the conventional spectrum sharing CR networks, the closed-form expressions of the theoretical performance upper bound of the ergodic sum capacity and the outage probability are derived by two lemmas and four propositions. Accurate mathematical analysis display, under the same bandwidth, the upper bound of ergodic sum capacity for the full-duplex spectrum sharing CR networks is twice as much as the traditional spectrum sharing CR networks, and the FD spectrum sharing CR networks based on SU1, also has better performance upper bound on the outage probability than the traditional spectrum sharing CR networks. Simulations results also validate that, the FD spectrum sharing CR networks obtains better communication performance than the conventional spectrum sharing CR networks, especially when the mean of self-interference channel power gain is small. Finally, we also can see that the simulation performance upper bound is completely consistent with the theoretical analysis performance upper bound, whether in the FD spectrum sharing CR networks or the conventional spectrum sharing CR networks. So also verifies the correctness of the theoretical performance upper bound derivation.

Joint Transceiver Optimization for DF Multicasting MIMO Relay Systems With Wireless Information and Power Transfer

In this article, we investigate a two-hop decode-and-forward (DF) multicasting multiple-input multiple-output (MIMO) wireless relay communication system. Different to conventional systems, the radio frequency (RF) energy from the source node is harvested at the relay node and used for forwarding signals to a group of receivers. Considering the structure of the energy harvesting (EH) relay node, we present a power splitting (PS) based protocol and a novel time switching (TS) based protocol by introducing two additional TS factors. For both protocols, we maximize the system mutual information (MI) of the multicasting MIMO relay system by jointly optimizing the source and relay covariance matrices under the constraints of the source energy and the relay harvested energy. In addition, a practical nonlinear EH model is adopted, where the energy harvested by the relay node is bounded as the incident RF signal power increases, and the harvested power is zero when the input power is below the minimum power for harvesting. For the TS based protocol, we also consider peak transmission power constraints at both the source and relay nodes. The performance of the proposed algorithms is verified via numerical simulations. The results demonstrate that the novel TS based protocol achieves a larger MI than the conventional TS protocol. The PS and TS based protocols achieve tradeoffs at different source power levels. In particular, compared with the PS based protocol, the proposed novel TS based protocol can reach a higher system MI when the EH bound is not reached, while the former protocol reaches a higher MI when the EH circuit is saturated. We show that the peak harvested energy constraint plays an important role in selecting the optimal location of the relay node.

Achievable Rate Region of Energy-Harvesting Based Secure Two-Way Buffer-Aided Relay Networks

This paper considered an energy-harvesting based secure two-way relay (EH-STWR) network, where two users exchanged information with the assistance of one buffer-aided relay that harvested energy from two users. To realize the confidential message exchange between two users in the presence of a potential eavesdropper, a secure bidirectional relaying scheme based on time division broadcast (TDBC) was proposed, where one user sent artificial noise to suppress the eavesdropper and another user transmitted data to the relay. A secure sum-rate maximization problem was formulated subject to average and peak transmit power constraints, data buffer and energy storage causality, and transmission mode constraints. By employing the Lyapunov optimization framework, a security-aware adaptive transmission scheme was proposed to jointly adapt transmission mode selection, power allocation, and security rate allocation according to channel/buffer/energy state information (CSI/BSI/ESI). Analysis results showed that the average achievable secrecy rate region can be significantly improved and there exists an inherent trade-off among transmission delay, requirement of transmit power consumption, and achievable secure sum-rate. Moreover, the channel condition between the energy-constrained relay and the potential eavesdropper is a critical factor on the achievable long-term average secrecy rate performance.

Ambient backscatter communications over NOMA downlink channels

In this paper, we investigate the performance of commensal ambient back-scatter communications (AmBC) that ride on a non-orthogonal multiple access (NOMA) downlink transmission, in which a backscatter device (BD) splits part of its received signals from the base station (BS) for energy harvesting, and backscatters the remaining received signals to transmit information to a cellular user. Specifically, under the power consumption constraint at BD and the peak transmit power constraint at BS, we derive the optimal reflection coefficient at BD, the optimal total transmit power at BS, and the optimal power allocation at BS for each transmission block to maximize the ergodic capacity of the ambient backscatter transmission on the premise of preserving the outage performance of the NOMA downlink transmission. Furthermore, we consider a scenario where the BS is restricted by a maximum allowed average transmit power and the reflection coefficient at BD is fixed due to BD's low-complexity nature. An algorithm is developed to determine the optimal total transmit power and power allocation at BS for this scenario. Also, a low-complexity algorithm is proposed for this scenario to reduce the computational complexity and the signaling overheads. Finally, the performance of the derived solutions are studied and compared via numerical simulations.

Performance Analysis of Cooperative Underlay Spectrum Sharing System in Co-channel Interference Limited Environment

In this paper, performance analysis of an asynchronous distributed space time block coded system with optimum combining at the cognitive radio receiver (CR-Rx) has been done in a cooperative underlay cognitive Internet of Things network under the influence of multiple co-channel primary users (PUs) interferers. The transmit power strategy being employed at the CR-Tx considers the PIP (peak interference power) at the PU-Rx and peak transmit power constraints at the CR-Tx, respectively. We have derived the probability density function of the signal-to-interference ratio (SIR) at the destination for the proposed system. The system is numerically and mathematically analyzed in terms of average post processed SIR (APPSIR), ergodic capacity ($${\text{C}}_{\text{erg}}$$), average bit error rate (ABER) and outage probability. All the numerical outcomes are in corroboration with its simulation counterpart.

Energy Efficient Buffer-Aided Transmission Scheme in Wireless Powered Cooperative NOMA Relay Network

In this paper, we consider a wireless powered cooperative non-orthogonal multiple access (NOMA) relay network, in which one source is supposed to send independent messages to two users with the assistance of one energy-constrained relay that harvests energy from the source. Firstly, we study the minimum power consumption at the source node to fulfill the least required transmission rates by two users in both time switching relaying (TSR) strategy and power splitting relaying (PSR) one. Secondly, when the relay is provisioned with data buffer and energy storage, the long-term average power consumption minimization problem is formulated to take into account of the data and energy queue causality, peak transmit power constraint, and transmission mode selection. By using Lyapunov optimization framework, a novel buffer-aided transmission scheme (BATS) is proposed to asymptotically approach the optimal solution. Our analysis shows that, the PSR outperforms the TSR in terms of the realized energy efficiency, and BATS can be utilized to further improve the energy efficiency. It is disclosed that, there is an inherent trade-off between the long-term power consumption and the average queuing delay. In addition, larger user rates or less power consumption can be realized if a larger delay can be tolerated.

Joint Resource Allocation for Frequency-Domain Artificial Noise Assisted Multiuser Wiretap OFDM Channels with Finite-Alphabet Inputs

The security issue on the physical layer is of significant challenge yet of paramount importance for 5G communications. In some previous works, transmit power allocation has already been studied for orthogonal frequency division multiplexing (OFDM) secure communication with Gaussian channel inputs for both a single user and multiple users. Faced with peak transmission power constraints, we adopt discrete channel inputs (e.g., equiprobable Quadrature Phase Shift Keying (QPSK) with symmetry) in a practical communication system, instead of Gaussian channel inputs. Finite-alphabet inputs impose a more significant challenge as compared with conventional Gaussian random inputs for the multiuser wiretap OFDM systems. This paper considers the joint resource allocation in frequency-domain artificial noise (AN) assisted multiuser wiretap OFDM channels with discrete channel inputs. This security problem is formulated as nonconvex sum secrecy rate optimization by jointly optimizing the subcarrier allocation, information-bearing power, and AN-bearing power. To this end, with a suboptimal subcarrier allocation scheme, we propose an efficient iterative algorithm to allocate the power between the information and the AN via the Lagrange duality method. Finally, we carry out some numerical simulations to demonstrate the performance of the proposed algorithm.

Reliability-Intercept Gap Analysis of Underlay Cognitive Networks Under Artificial Noise and Primary Interference

Underlay mode of cognitive radio networks (CRNs) permits secondary users (SUs) to simultaneously operate with primary users (PUs), inducing mutual interference between them. Nevertheless, primary interference (interference from PUs to SUs) is either neglected or treated as Gaussian noise in existing works. Moreover, artificial noise, which is deliberately introduced to harm signal reception of wire-tappers, can enhance information securing capability of CRNs. This paper analyzes a gap between reliability probability (successful decoding probability of legitimate receiver) and intercept probability (successful decoding probability of wire-tappers), which accounts for artificial noise, peak transmit power constraint, interference power constraint, and fading channels, and considers primary interference as non-Gaussian noise. Towards this end, exact closed-form expressions of reliability probability and intercept probability are first derived and then validated by computer simulations. Numerous results illustrate that both probabilities are saturated at either large peak interference power or large peak transmit power, the primary interference dramatically deteriorates them while the artificial noise creates a large gap between them, demonstrating its effectiveness in securing legitimate information.

Transceiver Optimization for DF MIMO Relay Systems With a Wireless Powered Relay Node

In this paper, a two-hop decode-and-forward (DF) multiple-input multiple-output (MIMO) relay system is investigated, where the relay node harvests the radio frequency energy transmitted by the source node and uses the harvested energy to forward information from source to destination. We consider both the time switching (TS) and power splitting (PS)-based protocols between wireless information and energy transfer. For each protocol, we study the optimal source and relay covariance matrices to maximize the source-destination mutual information (MI), under the source energy constraint and the harvested energy constraint at the relay node. For the TS protocol, the peak transmission power constraints are also considered at the source and relay nodes. The numerical results are presented to demonstrate the effectiveness of the proposed methods. It is shown that the proposed DF relay system achieves a higher MI than that of the amplify-and-forward relay system. Moreover, the PS-based protocol achieves a higher system MI than the TS-based protocol, but at a higher computational complexity.

Jammer-Assisted Legitimate Eavesdropping in Wireless Powered Suspicious Communication Networks

To enhance public safety, it is necessary to legitimately eavesdrop communication between suspicious users, such as terrorists and criminals. In this paper, we investigate legitimate eavesdropping in a wireless-powered suspicious communication network (WPSCN) with a wireless-powered suspicious transmitter and a suspicious receiver, who is legitimately eavesdropped by a legitimate monitor with the help from a wireless-powered friendly jammer. The “harvest-then-transmit” protocol is adopted by the suspicious communication to coordinate wireless energy transfer and information transfer. Both the suspicious receiver and the legitimate monitor can act as power sources for the suspicious transmitter and the jammer. The legitimate monitor can control the suspicious communication rate by broadcasting power signals, while the jammer can harvest energy and then interfere with the suspicious communication in collaboration with the legitimate monitor. Four different metrics are adopted to evaluate the eavesdropping performance based on different application requirements, and they are the successful eavesdropping probability, the average eavesdropping rate, the relative eavesdropping rate, and the eavesdropping energy efficiency. For each performance metric, we derive the optimal transmit power of the monitor for energy transfer and the optimal jamming transmit power of the jammer to maximize the performance metric under the peak transmit power constraint at the monitor and the energy causality constraint at the jammer. Some important insights are derived from these optimal power control policies. The simulations are conducted to verify the proposed optimal power control for legitimate eavesdropping in the WPSCN. It is shown that the proposed optimal power control policies greatly outperform other benchmark schemes.

Impact of Primary Interference on Secrecy Performance of Physical Layer Security in Cognitive Radio Networks

In cognitive radio networks (CRNs), primary interference is either neglected or considered as an additive white Gaussian random variable (r.v.). Current literature investigated such a case in evaluating their security capability. Generalizing this literature by considering primary interference power as exponentially-distributed r.v., we propose an analysis framework on impact of primary interference on security capability of CRNs under Rayleigh fading channels, peak transmit power constraint, and interference power constraint. The proposed framework is corroborated by Monte-Carlo simulations and illustrates that information securing performance in CRNs is saturated at either large values of peak transmit power or peak interference power, and can be enhanced by primary interference.

Resource Allocation for Green Cognitive Radios: Energy Efficiency Maximization

Green cognitive radios are promising in future wireless communications due to high energy efficiency. Energy efficiency maximization problems are formulated in delay‐insensitive green cognitive radio and delay‐sensitive green cognitive radio. The optimal resource allocation strategies for delay‐insensitive green cognitive radio and delay‐sensitive green cognitive radio are designed to maximize the energy efficiency of the secondary user. The peak interference power and the average/peak transmit power constraints are considered. Two algorithms based on the proposed resource allocation strategies are proposed to solve the formulated problems. Simulation results show that the maximum energy efficiency of the secondary user achieved under the average transmit power constraint is higher than that achieved under the peak transmit power constraint. It is shown that the design of green cognitive radio should take the tradeoff between its complexity and its achievable maximum energy efficiency into consideration.

Trajectory Optimization and Power Allocation for Multi-Hop UAV Relaying Communications

Unmanned aerial vehicles (UAVs) have found important applications in wireless communications due to their ability for on-demand and swift deployment, high mobility, and high probability of line-of-sight communication link with the ground. For UAV-enabled wireless communications, one of the main use cases is UAV relaying, where UAVs are deployed as flying relays in the sky to provide wireless connections between distant users that do not have reliable direct connectivity. This paper considers a general multiple UAV relaying system, where the information from a source node to a destination node is forwarded through multi-hop UAV relays. We aim to maximize the end-to-end throughput via joint UAV trajectory and transmit power optimization, subject to UAV mobility and collision avoidance constraints, the information-causality constraints, and the average and peak transmit power constraints of the source and UAV relays. The formulated problem is non-convex and challenging to solve, hence we propose an efficient iterative algorithm to obtain a suboptimal solution based on the alternating maximization and successive convex optimization techniques. Numerical results validate the effectiveness of the proposed algorithm as compared to three benchmark schemes with only transmit power allocation or trajectory optimization.

Secure EE maximisation in green CR: guaranteed SC

Physical-layer security from an energy-efficient perspective is of crucial importance in cognitive radio (CR). A CR network is considered where a secondary user (SU) coexists with a primary user in the presence of an eavesdropper and channel fading. Secure energy efficiency (EE) maximisation problems are formulated in secure green CR based on the condition that a minimum secrecy capacity (SC) of a SU is guaranteed. A peak interference power constraint and an average (ATP)/peak transmit power (PTP) constraint are imposed in the SU's Tx. Using fractional programming and the Lagrange dual method, energy-efficient optimal power allocation strategies are proposed to efficiently solve the secure EE maximisation problems. It is shown that the secure EE of the SU achieved under the ATP constraint is higher than that obtained under the PTP constraint. The tradeoff is elucidated between the secure EE and the SC of the SU.

On the Outage Performance of Reactive Relay Selection in Cooperative Cognitive Networks Over Nakagami-m Fading Channels

This paper evaluates outage performance of reactive relay selection in cognitive radio networks over Nakagami-m fading channels under consideration of imperfect channel information on both interference and transmission channels, peak transmit power constraint, long-term power constraint, interference from primary users (PUs), and direct channel between secondary source and destination. Toward this end, power allocation for secondary transmitters is first proposed to satisfy both power constraints and account for imperfect Nakagami-m channel information and interference from PUs. Then, exact closed-form outage probability representation for secondary destination is suggested to promptly assess system performance and provide useful insights into performance limits. Various results show validity of the proposed expressions, substantial system performance degradation due to imperfect channel information and interference from PUs, error floor in secondary network, performance trade-off between secondary and primary networks, and considerable performance enhancement with respect to the increase in the number of secondary relays and larger fading severity parameter.

Power Allocation for Energy-Harvesting-based Fading Cognitive Multiple Access Channels: with or without Successive Interference Cancellation

Abstract This paper considers a fading cognitive multiple access channel (CMAC), where multiple secondary users (SUs), who share the spectrum with a primary user (PU), transmit to a cognitive base station (CBS). A power station is assumed to harvest energy from the nature and then provide power to the SUs. We investigate the power allocation problems for such a CMAC to maximize the SU sum rate under the interference power constraint, the sum transmit power constraint and the peak transmit power constraint of each individual SU. In particular, two scenarios are considered: with successive interference cancellation (SIC) and without SIC. For the first scenario, the optimal power allocation algorithm is derived. For the second scenario, a heuristic algorithm is proposed. We show that the proposed algorithm with SIC outperforms the algorithm without SIC in terms of the SU sum rate, while the algorithm without SIC outperforms the algorithm with SIC in terms of the number of admitted SUs for a high sum transmit power limit and a low peak transmit power limit of each individual SU.

Packet-Size Optimization for Multiple-Input Multiple-Output Cognitive Radio Sensor Networks-Aided Internet of Things

The determination of optimal packet size (OPS) for a cognitive radio-assisted sensor networks (CRSNs) architecture is non-trivial. State of the art in this area describes various complex techniques to determine OPS for CRSNs. However, it is observed that under high interference from the surrounding users, it is not possible to determine a feasible OPS of data transmission under the simple point-to-point CRSN topology. This is contributed primarily to the peak transmit power constraint of the cognitive nodes. To address this specific challenge, this paper proposes a multiple-input multiple output-based CRSNs (MIMO-CRSNs) architecture for futuristic technologies, such as Internet of Things and machine-to-machine communications. A joint optimization problem is formulated, considering network constraints, such as the overall end-to-end latency, interference duration caused to the non-cognitive users, average BER, and transmit power. We propose our Algorithm 1 based on the generic exhaustive search technique to solve the optimization problem. Furthermore, a low complexity suboptimal Algorithm 2 based on solving classical Karush–Kuhn–Tucker conditions is proposed. These algorithms for MIMO-CRSNs are implemented in conjunction with two different channel access schemes. These channel access schemes are time-slotted distributed cognitive medium access control denoted as MIMO-DTS-CMAC and CSMA/CA-assisted centralized common control channel-based cognitive medium access control denoted as MIMO-CC-CMAC. Simulations reveal that the proposed MIMO-CRSN outperforms the conventional point-to-point CRSN in terms of overall energy consumption. Moreover, the proposed Algorithm 1 and Algorithm 2 show a perfect match, and the implementation complexity of Algorithm 2 is less than Algorithm 1 . Algorithm 1 takes almost 680 ms to execute and provides OPS value for a given number of users, whereas Algorithm 2 takes 4–5 ms on average to find the OPS for the proposed MIMO-CRSN framework.

Outage Analysis of Opportunistic Relay Selection in Underlay Cooperative Cognitive Networks Under General Operation Conditions

This paper investigates the impact of practical operation conditions such as channel information imperfection (CII), independent nonidentical (i.n.i) fading distributions, strict power constraints (i.e., peak transmit power constraint and primary outage constraint), and primary interference on outage performance of opportunistic relay selection (ORS) in underlay cooperative cognitive networks (UCCNs). Toward this end, the power of secondary transmitters is first established to meet strict power constraints and account for primary interference and CII. Then, exact closed-form outage probability expressions for the secondary destination employing the maximum ratio combining (MRC) and the selection combining (SC) are proposed to promptly evaluate the effect of these conditions and provide useful insights into performance limits. Numerous results illustrate significant system performance deterioration due to primary interference and CII, performance saturation phenomenon in the secondary network, performance compromise between the secondary network and the primary network, significant performance improvement with respect to the increase in the number of involved relays, a large gap between the lower outage bound (MRC's outage performance) and the upper outage bound (SC's outage performance), and the advantage of utilizing direct channel between the source and the destination.