Channel Inversion Power Control Research Articles

Jamming Signal Cancellation by Channel Inversion Power Control for Preserving Covert Communications

Uninformed jammers are used to facilitate covert communications between a transmitter and an intended receiver under the surveillance of a warden. In reality, the signals the uniformed jammer emits to make the warden’s decision uncertain have inadvertently interfered with the detection of the intended receiver. In this paper, we apply truncated channel inversion power control (TCIPC) to both the transmitter and the uninformed jammer. The TCIPC scheme used on the uninformed jammer may help the intended receiver remove jamming signals using the successive interference cancellation (SIC) technique. Under the assumption that the warden knows the channel coefficient between two intended transceivers and achieves the optimal detection power threshold, we form the optimization problem to maximize the effective transmission rate (ETR) under covertness and decoding constraints. With the aim of enhancing covertness-related performance, we achieve the optimal power control parameters and determine system parameter-related constraints required for the existence of these solutions. According to the simulations, the use of the TCIPC scheme on the uninformed jammer significantly improves covertness-related performance in comparison to that of random power control (RPC) and constant power control (CPC) schemes. In addition, simulation results show that, for the TCIPC scheme: 1) the maximum ETR tends to converge as the transmitter’s or the uninformed jammer’s maximum transmit power increases, and 2) there exists an optimal value of the transmitter’s predetermined transmission rate to achieve the optimal performance.

Achieving Near Ideal Covertness in NOMA Systems With Channel Inversion Power Control

In this letter, we propose two resource allocation schemes for covert communication in a downlink NOMA system, where the transmitter can send information simultaneously both to the public and the covert receiver, while maintaining ideal (or near-ideal) covertness with respect to the warden. The covert transmission is concealed by combining NOMA and channel inversion power control, acting as a random source of uncertainty at the warden. The transmission scheme supports zero outage transmission to the public user and non-zero outage transmission to the covert user, while guaranteeing an ideal or near-ideal covertness at the warden, depending on whether the covert user employs single-user decoding or successive interference cancellation (SIC) decoding. In the latter case, we determine the optimal power sharing factor between the public and covert signals that maximizes the average covert throughput, given a predefined fixed transmission rate to the public user. If the channel between the transmitter and the covert receiver is moderate or strong, the SIC decoding, compared to the single-user decoding, leads to much higher covert throughput at the cost of minor degradation of covertness.

Truncated Channel Inversion Power Control to Enable One-Way URLLC With Imperfect Channel Reciprocity

We propose to use channel inversion power control (CIPC) to achieve one-way ultra-reliable and lowlatency communications (URLLC), where only the transmission in one direction requires ultra reliability and low latency. Based on channel reciprocity, our proposed CIPC schemes guarantee the power of received signal that is used to decode the information to be a constant value <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> , by varying the transmit signal and power, which relaxes the assumption of knowing channel state information (CSI) at the user. Thus, the CIPC schemes eliminate the overhead of CSI feedback, reduce communication latency, and explore the benefits of multiple antennas to significantly improve transmission reliability. We derive analytical expressions for the packet loss probability of the proposed CIPC schemes, based on which we determine a closed interval and a convex set for optimizing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> in CIPC with imperfect and perfect channel reciprocity, respectively. Our results show that CIPC is an effective means to achieve one-way URLLC. The tradeoff among reliability, latency, and required resources (e.g., transmit antennas) is further revealed, which provides novel principles for designing one-way URLLC systems.

Multiple Antennas-Based Secure Communications With Channel Inversion Power Control

In this letter, a multiple antennas-based truncated channel inversion power control (CIPC) secure transmission scheme with artificial noise (AN) is proposed. Specifically, the transmitter with multiple antennas varies the transmit power as per channel to ensure the received signal power equals a certain constant value <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> , and uses the residual power to transmit AN for interfering the eavesdropper. We first derive the expression for the probability of secure transmission. Relying on this, we then study the optimization problem in terms of the achieved effective secrecy throughput (EST), which quantifies the amount of information that the transmitter can securely send to the receiver, subject to the constraints that the probability of secure transmission is no less than a predetermined value. The numerical results show that increasing the transmission power will not continuously decrease the probability of secure transmission. Furthermore, we find that there exists an optimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> to maximize the EST performance, and the optimal value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> increases with the number of antennas.

Channel Inversion Power Control Aided Covert Communications in Uplink NOMA Systems

In this letter, we investigate covert communications in uplink non-orthogonal multiple access (NOMA) systems, where a covert user tries to transmit private information to a legitimate receiver without being detected by a warden. Specifically, the covert user is shielded by a public user with truncated channel inversion power control, which works as a random transmit power jammer to interfere the warden’s detection. To this end, we derive the closed-form expressions of the detection error probability and optimal detection threshold at the warden. Furthermore, we present the optimal choice of the power control parameter to achieve the maximum effective covert throughput (ECT). Our analysis and numerical results indicate that boosting the maximum transmit power of public user both increases the covertness and prior transmission probability, which leads to a larger ECT.

Covert Communication With Truncated Channel Inversion Power Control in D2D Underlaid Cellular Networks

Device-to-device (D2D) underlaid cellular networks are regarded as an emerging network structure in the 5G systems. We study the covert communication of such networks consisting of a base station BS, a cellular user Alice, a D2D pair with a transmitter Dt and a receiver Dr , and a warden W illie. To conduct the covert communication, Alice adopts the truncated channel inversion power control (CIPC) to hide itself from W illie, where the received signal power at BS is fixed avoiding channel estimation for decoding Alice’s signal. Meanwhile, the interference generated by the D2D pair reusing the spectrum of Alice is exploited to confuse W illie. To understand the fundamental covert rate performance in the considered network, we first provide a theoretical model for characterizing the detection error probability of W illie as well as the effective covert rate at BS under the truncated CIPC scheme. Based on the main results, we then explore the effective covert rate maximization under the constraint of the detection error probability to identify the optimal truncated CIPC scheme designing and interference management. Finally, extensive numerical results are presented to illustrate the impacts of the truncated CIPC and interference from Dt on the covert performance.

Covert communications with channel inversion power control in uplink NOMA systems

Covert communications with channel inversion power control in uplink NOMA systems

Covert Communications With Channel Inversion Power Control in the Finite Blocklength Regime

In this letter, we investigate covert communications with finite blocklength under the channel inversion power control (CIPC) scheme, where a transmitter is allowed to communicate with a receiver without transmitting the pilot signals, which facilitates the hidden of the transmitter from the warden. Considering both the conventional and truncated CIPC schemes, we provide the novel expressions of the optimal detection threshold and the minimum total error probability at the warden. Furthermore, the optimization of the power control parameter at the transmitter is presented to maximize the effective covert throughput, which quantifies the amount of the information bits transmitted from the transmitter to the receiver subject to the covert constraint, under two kinds of CIPC schemes.

On the Performance of LTE/Wi-Fi Dual-Mode Uplink Transmission: Connection Probability Versus Energy Efficiency

This paper evaluates the performance of uplink transmission in an LTE/Wi-Fi coexisting heterogeneous network (HetNet), where user equipments (UEs) capable of jointly performing LTE/Wi-Fi dual access and dual power control have a higher preference in connecting the Wi-Fi access points (WAPs) than the LTE base stations (LBSs). Thereby, each UE competes for Wi-Fi connection using carrier-sense multiple access with collision avoidance (CSMA/CA) and, only if unsuccessful, employs cellular communication. During uplink transmission, the UEs employ truncated channel inversion power control with receiving thresholds adjusted according to the occupied communication modes. Based on the stochastic geometry theory, we derive the analytical expressions for the successful connection probability and the average energy efficiency (EE) of Wi-Fi communications. We show that there exists a maximal successful connection probability for Wi-Fi communications, where the optimal receiving signal and energy thresholds of WAPs depend critically on the density of WAPs. Moreover, the average EE of UEs successfully accessing WAPs saturates in the large receiving signal threshold regime, independent of the density of WAPs. These findings significantly differ from those in cellular communications, where maintaining stable service connection is more emphasized than other operation goals, and reveal that deploying Wi-Fi communication has a potential for improving the EE of the considered HetNet. Both simulation and experiment results validate the analytical derivations. These results together show that, compared with single-mode uplink transmission, the considered dual-mode transmission can achieve higher connection probability and EE simultaneously in LTE/Wi-Fi coexisting HetNets.

Optimization of base station density and user transmission power in multi-tier heterogeneous cellular systems

In this paper, a loss minimization issue is proposed, which includes both cost of user power consumption and base station (BS) deployment. A multi-tier heterogeneous network (HetNet) is considered and modeled with random geometry of Poisson point process (PPP). BSs and users are distributed randomly following PPP with the specific densities. Cutoff threshold (ρk) as the average received power at the kth tier BS is proposed to model uplink channels. The kth tier user transmission power is formulated through a channel inversion power control. Tier Selection Probability indicating the possibility of a user accessing a certain tier is derived. Bias (Bk) is proposed to change the kth tier Tier Selection Probability. Thus, an operator is able to change bias based on nearby environment and communication status. Also, Truncated Outage Probability and signal-to-interference ratio (SINR) Outage Probability are derived, which represents a connection failure status. Truncated outage results from insufficient power supply at users and SINR outage results from poor communication environment. Genetic algorithm (GA) is introduced to determine the trade off between outage constraints and the loss minimization issue. Simulation shows that, when equipped with equal bias, multi-tier network has smaller Truncated Outage Probability but larger SINR Outage Probability than single-tier network. On the contrary, with different bias, Truncated Outage Probability in multi-tier is larger than the single-tier case and SINR Outage Probability in multi-tier is less than that in single-tier. A considerable loss reduction can be witnessed in both cases.

Optimized Power Control for Over-the-Air Computation in Fading Channels

Over-the-air computation (AirComp) of a function (e.g., averaging) has recently emerged as an efficient multiple-access scheme for fast aggregation of distributed data at mobile devices (e.g., sensors) at a fusion center (FC) over wireless channels. To realize reliable AirComp in practice, it is crucial to adaptively control the devices' transmit power for coping with channel distortion to achieve the desired magnitude alignment of simultaneous signals. In this paper, we solve the power control problem. Our objective is to minimize the computation error by jointly optimizing the transmit power at devices and a signal scaling factor (called denoising factor) at the FC, subject to individual average power constraints at devices. The problem is generally non-convex due to the coupling of the transmit powers at devices and denoising factor at the FC. To tackle the challenge, we first consider the special case with static channels, for which we derive the optimal solution in closed form. The derived power control exhibits a threshold-based structure: if the product of the channel quality and power budget for each device, called quality indicator, exceeds an optimized threshold, this device applies channel-inversion power control; otherwise, it performs full power transmission. We proceed to consider the general case with time-varying channels. To solve the more challenging non-convex power control problem, we use the Lagrange-duality method via exploiting its “time-sharing” property. The derived power control exhibits a regularized channel inversion structure, where the regularization balances the tradeoff between the signal-magnitude alignment and noise suppression. Moreover, for the special case with only one device being power limited, we show that the power control for the power-limited device has an interesting channel-inversion water-filling structure, while those for other devices (with sufficiently large power budgets) reduce to channel-inversion power control. Numerical results show that the derived power control significantly reduces the computation error as compared with the conventional designs.

Outage Probability in the Uplink of Multitier Millimeter Wave Cellular Networks

In this article, using the stochastic geometry, we develop a tractable uplink modeling framework for the outage probability of the multitier millimeter wave (mmWave) cellular networks. Each tier’s mmWave base stations (BSs) are randomly located and they have particular spatial density, antenna gain, receiver sensitivity, blockage parameter, and pathloss exponents. Our model takes account of the maximum power limitation and the per-user power control. More specifically, each user, which could be in line-of-sight (LOS) or non-LOS to its serving mmWave BS, controls its transmit power such that the received signal power at its serving BS is equal to a predefined threshold. Hence, a truncated channel inversion power control scheme is implemented for the uplink of mmWave cellular networks. We derive closed-form expressions for the signal-to-interference-plus-noise-ratio (SINR) outage probability for the uplink of the multitier mmWave cellular networks, which we later degrade to the single-tier network. Furthermore, we analyze the case with a dense network by utilizing the simplified model, where the LOS region is approximated as a fixed LOS disk. The results show that imposing a maximum power constraint on the user significantly affects the SINR outage probability in the uplink of mmWave cellular networks.

Covert Communications Without Channel State Information at Receiver in IoT systems

Covert communications can hide the very existence of wireless transmissions and thus are able to address privacy issues in numerous applications of the emerging Internet of Things (IoT). In this article, we adopt channel inversion power control (CIPC) to achieve covert communications in Rayleigh fading wireless networks, where a transmitter can possibly hide itself from a warden while transmitting information to a receiver. The CIPC can guarantee a constant signal power at the receiver, which removes the requirement that the receiver has to know the channel state information in order to coherently decode the transmitter's signal. Specifically, we examine the performance of the achieved covert communications in terms of the effective covert rate (ECR), which quantifies the amount of information that the transmitter can reliably convey to the receiver subject to the warden's total error probability being no less than some specific value. The noise uncertainty at the warden serves as the enabler of covert communications. For fairness, we also consider noise uncertainty at the legitimate receiver. Our examination shows that increasing the noise uncertainty at the warden and the receiver simultaneously may not continuously improve the ECR achieved in the considered system model.

Uplink Performance of NOMA-Based Combined HTC and MTC in Ultradense Networks

In this article, we study the uplink coverage and the uplink network throughput of an ultradense network (UDN) where human-type communication (HTC) users and machine-type communication (MTC) devices coexist. We employ non-orthogonal multiple access (NOMA) radio access to address the massive connectivity requirements of MTC while satisfying the high data rate requirements of HTC. To this end, stochastic geometry is utilized to model the network exploiting the inherent randomness of the proposed scenario. The enormous number of small cells in UDN along with NOMA can provide a common ground to satisfy the diverse requirements of both MTC and HTC. The distinguishing features of both UDNs and MTC are considered in modeling the network where stretched exponential path-loss (SEPL) is used to capture short-link distances. Moreover, the truncated channel inversion power control is employed in both HTC users (HTCUs) and MTC devices (MTCDs) to mitigate the uplink intercell interference. The results show the significant impact of various system parameters on the network performance. Closed-form and easy-computable expressions are derived for the considered performance metrics, and are assessed by Monte Carlo simulations.

Covert Wireless Communications With Channel Inversion Power Control in Rayleigh Fading

In this work, we adopt channel inversion power control (CIPC) to achieve covert communications aided by a full-duplex receiver. Specifically, the transmitter varies the power and phase of transmitted signals as per the channel to the receiver, such that the receiver can decode these signals without knowing the channel state information. This eliminates the required feedback from the transmitter to the receiver, which aids hiding the transmitter from a warden. The truncated CIPC and conventional CIPC schemes are proposed and examined, where for truncated CIPC covert transmission ceases when the channel quality from the transmitter to the receiver is low, while for conventional CIPC covert transmission always occurs regardless of this channel quality. We examine their performance in terms of the achieved effective covert throughput (ECT), which quantifies the amount of information that the transmitter can reliably convey to the receiver, subject to the constraint that the warden's detection error probability is no less than some specific value. Our examination shows that the truncated CIPC scheme can outperform the conventional CIPC scheme due to this constraint.

Evolutionary Game for Hybrid Uplink NOMA With Truncated Channel Inversion Power Control

In this paper, we consider hybrid uplink non-orthogonal multiple access (NOMA) that can support more users by exploiting the notion of power-domain NOMA. In hybrid uplink NOMA, we do not consider centralized power control as a base station (BS) needs instantaneous channel state information (CSI) of all users which leads to a high signaling overhead. Rather, each user is allowed to perform power control under fading in accordance with a truncated channel inversion power control policy. Due to the lack of coordination of centralized power control, users in the same resource block compete for access. To analyze users' behavior, evolutionary game can be considered so that each user can choose transmission strategies to maximize payoff in hybrid uplink NOMA with power control. Evolutionarily stable strategy (ESS) is characterized with fixed costs as well as costs that depend on channel realizations, and it is also shown that hybrid uplink NOMA can provide a higher throughput than orthogonal multiple access (OMA). To update the state in evolutionary game for hybrid uplink NOMA, the replicator dynamic equation is considered with two possible implementation methods.

On Coverage Probability With Type-II HARQ in Large-Scale Uplink Cellular Networks

This letter studies uplink transmission in large-scale cellular networks with a Type-II hybrid automatic repeat request (HARQ) retransmission scheme, under which an unsuccessful transmission (if occurs) is combined with the corresponding retransmission through maximal-ratio combining (MRC). Based on stochastic geometry analysis, the uplink coverage probabilities are characterized under a generalized power control scheme in the scenarios with quasi-static interference (QSI) and fast-varying interference (FVI), where the same and different interfering users, respectively, are present during the transmission and retransmission phase. Our analytical expressions reveal some scaling properties of the coverage probabilities and can be used to evaluate the diversity gain of MRC (i.e., the ratio of the required signal-to-interference ratio (SIR) for achieving a target coverage probability with MRC to that without MRC). We show that the diversity gain of MRC is more remarkable in the scenario with QSI compared to that with FVI. Moreover, the diversity gain of MRC can be mostly exploited by adopting full channel-inversion power control.

2-to-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$M$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Coordinated Multipoint-Based Uplink Transmission in Ultra-Dense Cellular Networks

The ongoing densification of small cells, i.e., ultimately evolving toward ultra-dense networks (UDNs), yields an unprecedented paradigm shift in network design by bringing the base stations (BSs) and users to approximate the spatial scale and number magnitude. To address the super-frequent handovers of mobile users in such UDNs, the coordinated multipoint (CoMP) then becomes a feasible solution by effectively improving communication reliability. In this paper, we consider CoMP-based uplink transmission in heterogeneous UDNs. As our first step, a CoMP uplink transmission scheme is proposed for each user to transmit to multiple (2 to $M$ ) cooperating BSs with channel inversion power control in a multi-channel scenario. The performance of the proposed uplink CoMP is analyzed in the context of UDNs using stochastic geometry, in terms of outage probability and ergodic capacity, considering the effects of BS intensity, power control, number of cooperating nodes, and network tiers, first in a single-tier network, and later extended to a $K$ -tier heterogeneous network. Performance evaluation through extensive simulations is conducted and it is shown that the simulation results fit well with the analytical ones. The performance of the proposed scheme is then compared with that of the non-CoMP scheme, and it is found that the proposed scheme can significantly improve outage probability and ergodic capacity of mobile users.

Performance Analysis of RF‐Powered Cognitive Radio Networks with Integrated Ambient Backscatter Communications

Integrating ambient backscatter communications into RF‐powered cognitive radio networks has been shown to be a promising method for achieving energy and spectrum efficient communications, which is very attractive for low‐power or no‐power communications. In such scenarios, a secondary user (SU) can operate in either transmission mode or backscatter mode. Specifically, an SU can directly transmit data if sufficient energy has been harvested (i.e., transmission mode). Or an SU can backscatter ambient signals to transmit data (i.e., backscatter mode). In this paper, we investigate the performance of such systems. Specifically, channel inversion power control and an energy store‐and‐reuse mechanism for secondary users are adopted for efficient use of harvested energy. We apply stochastic geometry to analyze coverage probability and achievable rates for both primary and secondary users considering both communication modes. Analytical tractable expressions are obtained. Extensive simulations are performed and the numerical results show the validity of our analysis. Furthermore, the results indicate that the performance of secondary systems can be improved with the integration of both communication modes with only limited impact on the performance of primary systems.

Uplink Area Spectral Efficiency Analysis for Multichannel Heterogeneous Cellular Networks With Interference Coordination

The deployment of small cells (SCs) in heterogeneous cellular networks (HCNs) has been shown to be a promising approach to increase the system capacities of wireless communications. However, the bandwidth sharing and densification of the SCs cause co-tier and cross-tier interferences that limit the system spectral efficiency. In this paper, a framework of an uplink area spectral efficiency (ASE) analysis for multichannel HCNs using a proposed biased cell association scheme with coordinated subchannel allocation and channel inversion power control for mitigating the interferences is developed. The coordinated subchannel allocation is proposed to alleviate the severe cross-tier interference caused by macrocell users around the edges of the SCs. By incorporating the coordinated subchannel allocation into the biased cell association scheme with a bias factor, the proposed scheme is able to design the bias factor to reshape the coverage areas of the SCs providing an effective tradeoff between user offloading and cross-tier interference avoidance. By applying the tools of stochastic geometry, the uplink ASE is analytically derived as a function of the bias factor for the multichannel HCNs. The optimal bias factor can be obtained numerically by maximizing the system ASE. It is shown that the ASE performance analysis agrees with computer simulation very well. The results demonstrate that the proposed scheme can substantially improve the ASE performance of the multichannel HCNs for different small cell densities and outperform upon an existing biased cell association scheme.