Hardware Impairments Research Articles

Uavnoma: A UAV-NOMA Network Model under Non-Ideal Conditions

Uavnoma is a set of Python functions and a front-end script for modeling, studying, and analyzing the communication system composed by an unmanned aerial vehicle (UAV) and two ground users. We assume that the UAV acts as an aerial base station to serve the users according to non-orthogonal multiple access (NOMA) principles. For more practical insights, residual hardware impairments (RHI) and imperfect successive interference cancellation (ipSIC) are considered. More specifically, <strong>uavnoma</strong> allows the modelers to study and visualize the system performance in terms of achievable rate and outage probability. Additionally, the package produces figures and tables showcasing results from the specified performance metrics.

Two‐timescale design for RIS‐aided full‐duplex MIMO systems with transceiver hardware impairments

This paper focuses on a reconfigurable intelligent surface (RIS)-aided full-duplex multi-user massive multiple-input multiple-output system with transceiver hardware impairments (THWIs). Different from the existing works, the two-timescale design scheme is considered. The phase shift at the RIS is designed only based on the statistical channel state information. Firstly, the closed-form expression of the uplink and downlink achievable rate is derived. Then, the power scaling laws are revealed. Finally, the impact of THWIs on the system performance is analysed and genetic algorithm to maximize the achievable rate is used.

Performance of Spectrum Sharing in Hybrid Satellite Terrestrial Network with Opportunistic Relay Selection

In this paper, we consider the uplink of a hybrid satellite-terrestrial spectrum sharing system, in which satellite terminal communicates with satellite through terrestrial relay-assisted transmission. To accommodate expanding networks within limited spectrum, spectrum sharing is considered a promising candidate. For the system in which satellite terminals and terrestrial terminals share spectrum, we propose opportunistic relay selected spectrum sharing method based on decoding and forwarding protocol. Selecting the optimal relay station is aimed at minimizing the outage probability of the satellite terminal and maximizing the throughput of the system. Due to spectrum sharing policy and imperfections in the RF front end, we also consider the effects of cochannel interference (CCI) and hardware impairments (HIs). The satellite link is modeled as Shadowed-Rician fading, and the terrestrial link uses Nakagami-m fading. In addition, we deduce the closed-form analytical expressions of the satellite terminal outage probability, deduce the asymptotic expressions under the condition of high signal-to-noise ratio, and analyze their achievable diversity orders. Numerical and simulation results validate the performance gain of opportunistic relay selection compared to partial relay selection. Monte Carlo simulations confirm the correctness of the theoretical analysis and illustrate the effects of CCI and HIs on the system.

Robust Beamforming and Power Allocation for Secure Communication in Systems With Imperfect Channel and Hardware Impairments

In practice, hardware impairments (HIs) of communication systems are inevitable. In addition, perfect channel state information (CSI) is difficult to get due to channel estimation errors. In this letter, we design the power allocation strategy (PAS) at transmitters to optimize the worst-case secrecy rate for the wireless communication system with both norm-bounded channel uncertainty and HIs. The proposed problem is non-convex and difficult to solve. To solve this thorny problem, we use S-procedure, conservative approximation (CA), robust beamforming, and sequential convex approximation (SCA) to effectively convert the non-convex problem into a series of convex problems that are easy to solve. The numerical results demonstrate that the proposed PAS and robust beamforming method can offset the performance loss caused by HIs to a large extent.

Digital Compensation of IQ Imbalance, DC Offset for Zero-Padded OTFS Systems

Next generation communication systems (e.g., 6G) foresee higher mobility, higher data rates with higher constellations and with high levels of integration in a small form factor. Direct conversion orthogonal time frequency space modulation (OTFS) systems suffer from hardware impairments such as in-phase and quadrature (IQ) imbalance, direct current (DC) offset causing image Doppler interference (IDI) among the sub-carriers in the delay Doppler (DD) domain. In this letter, we propose a novel method of estimation and compensation of hardware impairments for zero padded (ZP) OTFS systems in the delay time (DT) domain. A dual pilot approach with a phase difference of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\frac {\pi }{2}}$ </tex-math></inline-formula> between these symbols is followed in DD domain with which hardware impairments are estimated with less computational complexity in DT domain. It is found that the compensated system performs close to ideal system. The mean square error (MSE) of the estimated channel is computed and MSE reduces with increase in signal to noise ratio (SNR), pilot power ratio (PPR) and with reduction in mobility.

On the Impacts of I/Q Imbalance in Analog Least Mean Square Adaptive Filter for Self-Interference Cancellation in Full-Duplex Radios

Frequency-dependent in-phase/quadrature-phase imbalance (IQI) is a critical hardware impairment, which affects the performance of the self-interference (SI) cancellation structure in full-duplex systems. A novel frequency-dependent IQI model is proposed in this paper, providing a theoretical tool to evaluate the impacts of this impairment in the analog domain. The model is then applied to investigate the performance of the analog least mean square (ALMS) loop under both frequency-selective and frequency-independent IQI. The degradation in the SI cancellation performance of the ALMS loop is revealed and its upper bound is derived. Numerical results show that the ALMS loop is resilient to both types of IQI with the maximum level of only 3.5 dB performance degradation even when the image rejection ratio is just 15 dB.

Joint Impact of Phase Error, Transceiver Hardware Impairments, and Mobile Interferers on RIS-Aided Wireless System Over κ-μ Fading Channels

Reconfigurable intelligent surface (RIS) has recently emerged as a promising technology that can potentially benefit the existing wireless communication technologies in addition to being able to fulfill the more stringent requirements of beyond- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5^{th}$ </tex-math></inline-formula> generation/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6^{th}$ </tex-math></inline-formula> generation wireless networks. Motivated by the numerous benefits of RIS technology for improving the performance of wireless communication systems, in this letter, a RIS-aided wireless system is considered in which the destination node is surrounded by the mobile co-channel interferers (CCIs). Each mobile CCI follows the random waypoint (RWP) mobility pattern within a circular region centered around the destination node. Source-destination, source-RIS, RIS-destination, and each interferer-destination links follow the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa - \mu $ </tex-math></inline-formula> distribution. Additionally, a more realistic system model is considered that also incorporates the impact of transceiver (transmitter as well as receiver) hardware distortions. The system’s performance is evaluated by deriving novel closed-form expressions for the coverage probability (CP) and ergodic capacity (EC) based on the cumulative distribution function and probability density function (PDF) of the received signal-to-interference-plus-distortion-plus-noise ratio (SIDNR).

Optimizing the Focusing Performance of Non-Ideal Cell-Free mMIMO Using Genetic Algorithm for Indoor Scenario

This paper proposes a genetic algorithm (GA) combined with ray tracer to generate a cell-free topology of massive MIMO (mMIMO) for the optimal focusing performance serving multiple users. The realistic hardware impairment, for instance the non-ideal power amplifier, is taken into account of the system modeling and topology optimization. To the best of our knowledge, this is the first attempt to apply GA in optimizing the hardware-impaired multi-user cell-free mMIMO. Although the demonstrated numerical analysis is for indoor scenario, the proposed approach is transferable for generic scenarios. In GA, the base station (BS) antennas’ placement is encoded with an adjusted binary matrix representation, which is straightforward for the subsequent genetic operations. The explored candidates by GA can evolve beyond the parents, where the fitness of individuals is evaluated dynamically via a ray tracer radio channel simulator. Compared to the traditional GA, our proposed GA can find better solutions with a faster convergence speed. The algorithm provides near-optimal results in experiments, applicable to generic environment with multiple mobile users and different signal-to-interference-plus-noise ratios.

Double relay selection for combating the impact of interference and hardware impairments in mixed RF/FSO two way relay networks

Double relay selection for combating the impact of interference and hardware impairments in mixed RF/FSO two way relay networks

NOMA-Based Cognitive Satellite Terrestrial Relay Network: Secrecy Performance Under Channel Estimation Errors and Hardware Impairments

Nonorthogonal multiple access (NOMA) and cognitive integrated satellite terrestrial relay networks are the promising and key part for the next-generation wireless networks. This article researches the joint effects of channel estimation errors (CEEs) and hardware impairments on the secrecy performance of cognitive integrated satellite terrestrial relay networks. The noncolluding eavesdropping scheme is applied in the multiple eavesdroppers, where the eavesdropper with the highest eavesdropping capacity is selected to overhear the legitimate transmission signal. Moreover, the detailed analysis for the secrecy outage probability (SOP) is obtained based on the utilized partial terrestrial relay selection strategy. To obtain the insightful conclusions, the asymptotic analysis along with the secrecy coding gain and secrecy diversity order for the SOP are further derived, which gives the effective methods to valuate the impacts of CEEs and hardware impairments on the considered system with the NOMA scheme in high signal-to-noise ratio regime. Moreover, simulations are derived for the secrecy energy efficiency. Finally, Monte Carlo simulations are given to prove the correctness of the theoretical SOP analysis.

Error Bounds for 3D Localization and Maximum Likelihood Estimation of mm-Wave MISO OFDM Systems in the Presence of Hardware Impairments

Millimeter-wave ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$mm$ </tex-math></inline-formula> -wave) multiple-input single-output (MISO) systems are expected to be extremely advantageous for the fifth generation (5G) cellular systems. In fact, these systems are considered key enablers of centimeter-level localization accuracy, even in the case of a single base station (BS). However, there are still fundamental issues that need to be addressed when applying <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$mm$ </tex-math></inline-formula> -wave MISO systems to practical scenarios, namely the effects of hardware impairments (HWIs). In this study, the 3D localization accuracy of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$mm$ </tex-math></inline-formula> -wave MISO OFDM systems is investigated when there are HWIs at both the BS and the mobile station (MS). The localization is performed by estimating the downlink channel parameters of the line-of-sight (LOS) path using only a maximum likelihood (ML) estimator at the MS. We then transform these channel parameters into ones for localization. The Fisher information matrix (FIM) is employed to assess the accuracy of the estimation processes, considering also any non-LOS (NLOS) paths. The limit of localization is calculated in terms of the position error bound (PEB). Computer simulations demonstrate the destructive impacts of HWIs on the localization process. Moreover, it was proven that the effect of NLOS paths from unknown scatters on the localization process is related to the ratio between LOS and NLOS path gains.

On the Performance of RIS-Assisted Space Shift Keying: Ideal and Non-Ideal Transceivers

In this study, we present a unifying framework for future reconfigurable intelligent surface (RIS)-assisted space shift keying (SSK) systems; we additionally propose two novel transmission schemes. The key strategies surrounding this concept, namely power-sensing RIS-SSK and partitioned RIS-SSK, grant knowledge of the activated transmitter (Tx) antenna index at the RIS, which, when using SSK, allows us to adjust the reflection phases. The performance of the proposed scheme is investigated in terms of the theoretical average bit error rate (ABER), and the effect of non-ideal transceivers. The performance is then compared to that of a reference RIS-SSK scheme, and a complexity analysis is provided. The obtained results, verified by extensive computer simulations, demonstrate that the partitioned and power-sensing RIS-SSK schemes achieve a higher ABER than the reference one. Moreover, hardware impairments clearly have a critically degrading impact on the system performance for all schemes, and should be carefully taken into account in future communication systems.

Hardware Impaired RIS Assisted Multipair FD Communication With Spatial Correlation

We investigate a multi-pair full-duplex (FD) two-way communication system assisted by a reconfigurable intelligent surface (RIS), where each user-pair exchanges information via RIS. Unlike most existing works related to FD systems with RIS, we take into account an inevitable electromagnetic interference (EMI) and also consider a practical Rician channel between RIS and users, and spatial correlation owing to size constraint at the RIS. In addition we consider low-cost hardware at RIS and users resulting in impairments. We first derive an approximate expression for the achievable sum-rate of the system. We then optimize RIS phases to achieve the optimum sum-rate using particle swarm optimization (PSO) algorithm. We, through the simulation results, show the optimality of PSO algorithm and the impact of EMI and hardware impairments on the sum-rate.

Physical Layer Security for Cognitive Multiuser Networks With Hardware Impairments and Channel Estimation Errors

In this paper, we investigate the physical layer security for a cognitive multiuser network which is composed of multiple cognitive sources, a cognitive destination and an eavesdropper under the joint impact of hardware impairments (HIs) and channel estimation errors (CEEs). We consider a practical scenario where mutual interference exists between the primary users and cognitive users. To achieve high physical layer security with low implementation complexity, we propose three pure user scheduling schemes, namely, selection combining (SC) scheme, threshold-based switched diversity (tSD) scheme and switch-and-examine combining with post-selection (SECps) scheme. To further improve physical layer security, we present an extension of our SC framework to a jammer aided multiuser network and propose a jammer aided SC (JSC) scheme. We derive the closed-form intercept probability (IP), outage probability (OP) and effective secrecy throughput (EST) expressions for SC, tSD, SECps and JSC schemes over Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> channels to analyze the system performance. Numerical results show that among the three pure multiuser scheduling schemes, the SC scheme achieves the best secrecy performance with the highest complexity, the SECps scheme obtains the worst secrecy performance with the lowest complexity. In addition, the secrecy performance of JSC scheme is better than that of SC scheme in the high SNR region.

Performance analysis of communications systems with radar interference and hardware impairment

The development of future wireless communications systems faces a big challenge of spectrum scarcity. Co-existence of radar and communications systems is thus of great interest. In this work, the performance of a communications system with hardware impairment (HWI) as well as interference from radar systems will be studied. The impact of radar interference, I/Q imbalance coefficients as well as channel state information (CSI) will be evaluated in terms of outage probability and symbol error rate. Simulation results prove that the proposed detectors provide explicit and conducive insights for further exploration of joint radar-communications designs.

Wireless powered cognitive radio networks with multiple antenna sources and hardware impairments

In this paper, a radio-frequency (RF) energy harvesting enabled cognitive radio network (CRN) is considered in the presence of transceiver hardware impairments (HIs). Herein, one of the secondary nodes (SNs) exploits simultaneous wireless information and power transfer (SWIPT) technology to harvest energy from the primary signal and provides relay assistance for the primary transmission. We consider multiple antennas at the primary nodes (PNs) to ensure better link reliability and spectrum sharing to mitigate the spectrum scarcity. In the first phase, relaying SN uses non-linear energy harvester circuit to harvest energy from the RF signals received from PN using the power splitting approach. In the second phase, the same SN adds its own signal intended for the other SN along with the primary signal and broadcasts the combined signal. Assuming the network to operate in a Nakagami-m fading environment, the performance of the considered CRN is evaluated in terms of outage probability and system throughput. Also, we formulate two optimization problems to minimize the OP and maximize the system throughput. The Karush–Kuhn–Tucker conditions are used to obtain the closed-form solution of the constrained convex optimization. Numerical results are provided to examine the performance impact concerning different system and channel parameters.

Performance analysis and optimization of energy harvesting cognitive multi-hop relay network over mixed Rayleigh and double-Rayleigh fading channels

In this paper, we investigate the outage performance of an energy harvesting underlay cognitive multi-hop relay network. In the network, energy-constrained secondary network (SN) nodes harvest energy from radio frequency signal of a power beacon (PB) node. The source node transmits information to destination node via multiple intermediate relay nodes by using a time division broadcast protocol, and the hardware impairments of SN nodes’ transceiver are modeled. The outage performance of SN is analyzed and evaluated by accurately approximate and asymptotic closed-form expressions of outage probability (OP) over quasi-static mixed Rayleigh and double-Rayleigh fading channels. Additionally, due to the complexity of OP expression, a chaotic dragonfly algorithm (CDA) is proposed to jointly optimize energy harvesting ratio and PB node’s abscissa, which can achieve OP minimization of SN. Extensive simulations demonstrate the correctness of theoretical analysis and the effectiveness of the proposed CDA.

Performance analysis of ABCom NOMA systems for 6G with generalized hardware impairments

With the continuous emergence of new smart applications, the number of smart devices is increasing exponentially. Therefore, it is a great challenge to meet the rising network demands for the sixth generation (6G) communication. To solve the above problem, non-orthogonal multiple access (NOMA) and ambient backscatter communication (AmBC) technologies are introduced. However, deploying a large number of low cost components, all nodes are prone to hardware non-ideal, and the system performance is limited by the imperfect factors of in-phase and quadrature-phase imbalance (IQI) and residual hardware impairments (RHIs). Motivated by this, this paper considers an AmBC-NOMA communication system with both IQI and RHIs. In particular, we derive the analytic expressions for outage probability (OP) and ergodic rate (ER) of each node for the cases of ideal and non-ideal conditions. In order to get further insights, we analyze the asymptotic behavior of OPs and ERs at high signal-to-noise ratios (SNRs). The comparison of theoretical analysis and Monte Carlo simulation show that: (1) IQI and RHIs have negative impacts on the effectiveness and reliability of the system; (2) As the transmit SNR increases, the OP of each node converges to a non-zero constant, resulting in the diversity order approaches zero; (3) The ER of Uf is less affected by these two non-ideal factors; (4) RHIs have a greater impact on the ER of Un than Uf.

MSE-Based Transceiver Designs for RIS-Aided Communications With Hardware Impairments

It is challenging to precisely configure the phase shifts of the reflecting elements at the reconfigurable intelligent surface (RIS) due to inherent hardware impairments (HIs). In this letter, the mean square error (MSE) performance is investigated in an RIS-aided single-user multiple-input multiple-output (MIMO) communication system with transceiver HIs and RIS phase noise. We aim to jointly optimize the transmit precoder, linear received equalizer, and RIS reflecting matrices to minimize the MSE. To tackle this problem, an iterative algorithm is proposed, wherein the beamforming matrices are alternately optimized. Specifically, for the beamforming optimization subproblem, we derive the closed-form expression of the optimal precoder and equalizer matrices. Then, for the phase shift optimization subproblem, an efficient algorithm based on the majorization-minimization (MM) method is proposed. Simulation results show that the proposed MSE-based RIS-aided transceiver scheme dramatically outperforms the conventional system algorithms that do not consider HIs at both the transceiver and the RIS.

Exploiting Multiple RISs and Direct Link for Performance Enhancement of Wireless Systems With Hardware Impairments

In this paper, the performance of a wireless system, which is beneficial from utilization of multiple reconfigurable intelligent surfaces (RISs) and the direct link between the source node and the mobile user, is analyzed. Especially, the effect of transceiver hardware impairments (HIs) are taken into consideration. We successfully derive the outage probability (OP), throughput, achievable data rate (ADR), and symbol error probability (SEP) expressions of this multiple-RIS assisted wireless systems with and without HIs (referred as RIS-HI and RIS-ID system, respectively) over Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> fading channels. The above performance factors are also benchmarked with the case that only a point-to-point (P2P) link without RIS is considered (denotes as as P2P-HI and P2P-ID systems for HI and ideal hardware conditions, respectively). All obtained formulas are verified by Monte-Carlo simulations. It is observed that the RIS-HI system significantly outperforms the P2P-HI system at low transmit power regime, while the performance of the RIS-ID system is always better than that of P2P-ID system. On the other hand, HIs show more severe effect for higher data transmission rates or high modulation orders.