In-phase And Quadrature-phase Imbalance Research Articles

Secrecy analysis of collaborative NOMA networks with IQI

This paper studies the secrecy performance of collaborative non-orthogonal multiple access (NOMA) systems over κ–μ shadowed distribution with in-phase and quadrature-phase imbalance (IQI). The analytical expressions for outage probability (OP), intercept probability (IP), secure outage probability (SOP), and strictly positive secrecy capacity (SPSC) are derived relying on the NOMA eavesdropping model. Moreover, the Monte Carlo simulation perfectly coincides with the theoretical derivation, which confirms the accuracy of academic results. The numerical analysis indicates that IQI reduces reliability but enhances the secrecy of relaying NOMA networks. Additionally, the increase of kN or the decrease of μS can weaken the antijamming capability, whereas reducing mS or mE will strengthen the confidentiality. Furthermore, to realize real-time secrecy analysis, we investigate the anti-interference ability of the relaying system by the Elman neural network. Compared to other algorithms, the prediction accuracy is improved by 56.4% on average, and the runtime is decreased.

Improper Gaussian Signaling for IRS Assisted Multiuser SWIPT Systems With Hardware Impairments

In this paper, we focus on intelligent reflecting surface (IRS) assisted multiuser simultaneous wireless information and power transfer (SWIPT) systems with hardware impairments (HWIs), which result from the aggregate effect of in-phase and quadrature-phase imbalance (IQI), power amplifier non-linearity, quantization distortion, phase noise, etc. Improper Gaussian signaling (IGS) is employed to combat the signal distortion incurred by HWIs and the interference from other users. We aim to maximize the minimum achievable information rate among all users by jointly optimizing the active beamforming vectors, passive reflecting coefficients, and power splitting coefficients, subject to the minimum harvested energy requirements of these users and the total power budget at the transmitter. Due to the intricate coupling between the reflecting coefficients and beamforming vectors, we propose a two-level iterative optimization algorithm to solve this non-convex problem. Based on the above, we also study the weighted rate-energy region maximization problem. Numerical results show that the use of IGS significantly outperforms traditional proper Gaussian signaling (PGS) in the considered systems and also affirm the effectiveness of the proposed optimization algorithm.

Throughput performance optimization of NOMA-assisted cooperative relay system with realistic impairments

Abstract This work aims to investigate the outage and throughput performance of non-orthogonal multiple access assisted cooperative relay system (CRS-NOMA) considering the realistic impairments caused due to in-phase and quadrature-phase imbalance (IQI), channel estimation errors (CEE), and successive interference cancellation (SIC) errors. More specifically, we investigate a model in which two-phase downlink transmission is carried out in two different modes: (i) CRS-NOMA without direct links and (ii) CRS-NOMA with direct links (CRS-DLNOMA). In CRS-NOMA mode, the source broadcasts a composite NOMA signal to destination users with the assistance of a decode-and-forward (DF) relay. In contrast, in CRS-DLNOMA, direct and cooperative links are available for transmission. We derive the analytical expressions of outage probability and throughput for both the NOMA destinations to evaluate the system performance of both CRS-NOMA and CRS-DLNOMA modes of transmission. Furthermore, numerical simulations also study and validate the influence of IQI, CEE, and SIC errors on the outage and throughput performance. The simulation results verify that realistic impairments degrade the system performance, but the presence of direct link has a positive impact on outage and throughput. Additionally, we use the golden search method to optimize the power allocation factor (PAF) and transmission rate to maximize the throughput at the near user while ensuring the throughput constraint at the far user.

Cell-Free Massive MIMO With Mixed-Resolution ADCs and I/Q Imbalance Over Rician Spatially Correlated Channels

The practical deployment of cell-free massive multiple-input multiple-output (CF mMIMO), a promising technology empowering the sixth-generation with multitudinous access points (APs). This paper considers a CF mMIMO system over Rician spatially correlated fading channels with the single-antenna user equipments (UEs) and multi-antenna APs, where the phase-shift induced by the UEs' movement exists at the line-of-sight path. Though the low-resolution analog-to-digital converters (ADCs) can effectively address the expensive hardware cost and power-hungry problems, complicated data processing algorithms are of vital importance to be well designed to compensate for the performance gap compared with the real scenarios since the hardware impairments. However, the novel mixed-ADC architecture could solve the above challenges with better performance. So, we investigate the effect of mixed-resolution ADCs deploying at APs and the in-phase and quadrature-phase imbalance (IQI) on the CF mMIMO systems. Furthermore, the achievable uplink spectral efficiency (SE) is analyzed considering IQI and quantization loss based on a two-layer decoding scheme. Moreover, the novel closed-form SE expression with the maximum ratio (MR) combining is derived. And we find the relationship between the SE performance and different combining schemes, quantization bits, and IQI parameters. Finally, the numerical results reveal the mixed-resolution ADCs show a great advantage in boosting the SE performance, and increasing the number of APs is an effective means to promote the system performance.

Performance Analysis of Polar Codes Over Fox’s H-Fading Channels With RHI and IQI Impairments

This study examined the error probability performance of polar codes across Fox’s <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -fading (FHF) channels while taking into account in-phase and quadrature-phase imbalance (IQI), as well as residual hardware impairments (RHI). This fading model generalizes most of the commonly used fading and turbulence models where Málaga- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {M}$ </tex-math></inline-formula> turbulence is taken into account as a specific case of FHF in this paper. Specifically, an upper bound on block error probability (BLER) for the successive cancellation (SC) decoding method of polar codes is derived in terms of the Fox’s <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -function. According to numerical results, by lengthening polar codes and changing the properties of fading channels, it is possible to decrease the impact of system impairments on the error probability performance.

Performance Analysis of I/Q Imbalance With Hardware Impairments Over Hyper Fox’s H-Fading Channels

Impairments baseband model in-phase and quadrature-phase Imbalance (IQI) and Residual hardware impairments (RHI) are two key factors degrading the performance of wireless communication systems (WCSs), particularly when high-frequency bands are employed, as in 5G systems and beyond. The impact of either IQI or RHI on the performance of various WCSs has been investigated exclusively in a separate way. To fill this gap, in this paper, the joint effect of both IQI and RHI on the performance of a WCS subject to Hyper Fox’s H-fading (HFHF) channel, is investigated. Such a fading model generalizes most, if not all, of well-known fading and turbulence models. To this end, closed-form expressions for the outage probability (OP), Average channel capacity (ACC) under constant power with optimum rate adaptation (ORA) policy, and average symbol error probability (ASEP) for both coherent and non-coherent modulation schemes are derived. Specifically, all the analytical expressions are derived for three different scenarios: (i) ideal Tx and Rx impaired, (ii) Tx impaired and ideal Rx, and (iii) both Tx and Rx are impaired. Further, asymptotic expressions for OP, ACC under ORA policy, and ASEP are obtained, based on which, insightful discussions on the IQI and RHI impacts are made. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha -\mu $ </tex-math></inline-formula> and Málaga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {M}$ </tex-math></inline-formula> turbulence with pointing error distribution models have been considered as particular cases of the HFHF distribution. The analytical derivations, endorsed by simulation results, demonstrate that the RF impairments’ effects should be seriously taken into account in the design of next-generation wireless technologies.

Security analysis of relaying NOMA systems over Beaulieu–Xie fading channels with I/Q imbalance

The paper studies the impact of in-phase and quadrature-phase imbalance (IQI) on the performance of cooperative non-orthogonal multiple access (NOMA) systems over Beaulieu–Xie fading channels. In the presence of an eavesdropper, the information is decoded-and-forward to the legitimate users at the relay, and the successful interference cancellation technology is utilized at the receiving end to eliminate the interference between the far and the near users. The closed-form expressions of outage probability (OP) and intercept probability (IP) are deduced to investigate the reliability and security. Moreover, the asymptotic expressions of OP for high signal-to-noise ratio are obtained. Finally, Monte Carlo simulations coincide perfectly with the results of theoretical derivation, which verifies the correctness of the analysis. The interesting results are that the presence of IQI reduces reliability but increases security. In addition, the increase of the target rate and the decrease of the channel parameter m can weaken the reliability.

NOMA-based cognitive radio network with hybrid FD/HD relay in industry 5.0

The continued growth of the industrial Internet of Things (IoT) paves the way for the fifth industrial revolution (Industry 5.0), which is expected to further enhance the wireless connectivity and human machine collaboration. Nonetheless, Industry 5.0 will inevitably face the great challenges such as large scale connectivity and explosive data traffic because of the proliferation of IoT devices. To meet these challenges, we propose a novel non-orthogonal multiple access (NOMA)-based overlay cognitive radio (OCR) network for Industry 5.0. Specifically, the hybrid full-duplex (FD)/ half-duplex (HD) mode at the secondary user (SR) is adopted and in-phase and quadrature phase imbalance (IQI) is introduced to better comply with the practical scenarios. We investigate the outage probability (OP) and ergodic sum rate (ESR) of the considered network with the Nakagami-m channels. Extensive simulation experiments are performed to verify the accuracy of the analysis. From the simulation results, we can conclude: i) Increasing the signal-to-noise ratio (SNR), OP decreases but ESR increases and tends to a fixed value at high SNR regimes, indicating that the existence of IQI leads to a ceiling for the ESR; ii) The primary system has higher reliable performance at low SNR regions when SR is in FD mode, and for ergodicity, the system with FD relay is superior to HD relay; iii) The reliable performance of OMA system for primary users will be better since there is no interference at the relay.

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.

Intelligent Reflecting Surface Aided Wireless Systems with Imperfect Hardware

In this article, we investigate the design of reconfigurable intelligent surface (RIS)-aided transmission as a smart method to reflect signals received from access points to users and, hence, improving users’ performance. To implement smart Internet of Things (IoT) networks, massive connectivity and low-cost deployment are essential in designing such systems. In particular, we consider two practical scenarios (dual-hop and single-hop transmissions). These scenarios highlight the potential of RIS in enhancing the system’s outage probability performance. Furthermore, to characterize channel conditions in practice, we pay particular attention to two-channel distributions that are non-central chi-square (NCCS) distributions that approximate the channel distribution of the RIS-aided wireless system and the squared KG distribution. In addition, the RIS-aided system may face imperfect hardware-related issues in practice. Therefore, we need to consider the degraded performance of practical RIS-aided systems by considering the detrimental impact of in-phase and quadrature-phase imbalance (IQI). To characterize the main system performance metric, we provide closed-form formulas of outage probability and ergodic capacity. We then evaluate system performance under the impacts of signal-to-noise ratio (SNR), the number of meta-surfaces, and channel parameters. All closed-form outage expressions are validated via Monte Carlo simulations. Simulation results indicate that the considered RIS scheme at dual-hop and single hop under the impact of IQI and RIS hardware impairment achieves significant improvements in terms of outage probability at high SNR and high meta-surface number N. Additionally, the simulation results demonstrate that the impact of IQI on the proposed system is limited. It is worth noting that, in terms of ergodic capacity, ergodic capacity faces an upper limit. Despite this limitation, the proposed system can still work well once some parameters are controlled well, such as the transmit SNR, levels of IQI, and the number of RIS components.

Cognitive AmBC-NOMA IoV-MTS Networks With IQI: Reliability and Security Analysis

Internet-of-Vehicle (IoV) enabled Maritime Transportation Systems (MTS) communication is anticipated to support ultra-reliable and low latency, diverse quality-of-service (QoS) and large-scale connectivities. To meet such stringent demands, a cognitive ambient backscatter non-orthogonal multiple access (C-AmBC-NOMA) IoV-MTS network is proposed. We explore the reliable and secure performance of the proposed C-AmBC-NOMA IoV-MTS network with in-phase and quadrature phase imbalance (IQI) at radio-frequency (RF) front-ends and the existence of an eavesdropper. In particular, the analytical expressions on the outage probability (OP) and intercept probability (IP) are obtained after a series of calculations. For a deeper understanding, we discuss the asymptotic behavior of OPs in the high signal-to-noise ratio (SNR) region, the diversity orders of OPs, and IPs in the high main-to-eavesdropper ratio (MER) regime. The results of Monte-Carlo simulation and a series of corresponding theoretical analysis show that: i) As the SNR approaches infinity, the OPs tend to be fixed non-negative values, indicating that the diversity orders of the OPs have error floors; ii) When the MER approaches infinity, the IPs of legitimate users decrease continuously, while the IP of backscatter device (BD) increases; iii) Compared with the system performance under ideal condition, the system performance is less reliable under IQI condition, but the security performance is enhanced; iv) By carefully selecting the system parameters, a trade-off can be achieved between reliability and security.

Channel Estimation and Robust Detection for IQ Imbalanced Uplink Massive MIMO-OFDM With Adjustable Phase Shift Pilots

In this paper, we investigate channel estimation and robust detection for uplink massive multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with in-phase and quadrature-phase imbalances (IQI). We represent the received signal with a real-valued model, where the combination of the IQI and the wireless channel is treated as the effective channel. Based on the real-valued model, we then perform the minimum mean square error (MMSE) criterion based estimation for the effective channel. We use adjustable phase shift pilots (APSPs) to reduce the pilot overhead and verify that the MSE of the effective channel estimation can be minimized by scheduling the pilot phase shifts properly. We propose a pilot phase shift scheduling algorithm based on the covariance matrices of the effective channels. Since the channel estimation performance might be degraded due to using APSPs, we develop an MMSE criterion based data detection scheme which is robust to the channel estimation error. Using operator-valued free probability theory, we derive an asymptotic deterministic equivalent for the ergodic achievable sum rate of the proposed detection scheme. The performance of the channel estimation with APSPs and the robust data detection is demonstrated via extensive numerical results.

Secrecy Analysis of Ambient Backscatter NOMA Systems Under I/Q Imbalance

We investigate the reliability and security of the ambient backscatter (AmBC) non-orthogonal multiple access (NOMA) systems, where the source aims to communication with two NOMA users in the presence of an eavesdropper. We consider a more practical case that nodes and backscatter device (BD) suffer from in-phase and quadrature-phase imbalance (IQI). More specifically, exact analytical expressions for the outage probability (OP) and the intercept probability (IP) are derived in closedform. Moreover, the asymptotic behaviors and corresponding diversity orders for the OP are discussed. Numerical results show that: 1) Although IQI reduces the reliability, it can enhance the security. 2) Compared with the traditional orthogonal multiple access (OMA) system, the AmBC-NOMA system can obtain better reliability when the signal-to-noise (SNR) ratio is low; 3) There are error floors for the OP because of the reflection coefficient \b{eta} .

I/Q Imbalance Aware Nonlinear Wireless-Powered Relaying of B5G Networks: Security and Reliability Analysis

Physical layer security is known as a promising paradigm to ensure secure performance for the future beyond 5G (B5G) networks. In light of this fact, this paper elaborates on a tractable analysis framework to evaluate the reliability and the security of wireless-powered decode-and-forward (DF) multi-relay networks. More practical, the nonlinear energy harvesters, in-phase and quadrature-phase imbalance (IQI) and channel estimation errors (CEEs) are taken into account. To further enhance the secure performance, two relay selection strategies are presented: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1) suboptimal relay selection (SRS); 2) optimal relay selection (ORS)</i> . Specifically, exact analytical expressions for the outage probability (OP) and the intercept probability (IP) are derived in closed-form. For the IP, we consider that the eavesdropper can wiretap the signal from the source or the relay. In order to obtain more deep insights, we carry out the asymptotic analysis as well as the diversity orders for the OP in the high signal-to-noise ratio (SNR) regimes. Numerical results show that: 1) Although the mismatches of amplitude/phase of transmitter (TX)/receiver (RX) limit the OP performance, it can enhance IP performance; 2) Large number of relays yields better OP performance; 3) There are error floors for the OP due to the CEEs; 4) There is a trade-off for the OP and IP to obtain the balance between reliability and security.

A low complexity iterative equalization technique for OFDMA and SC-FDMA uplink systems with Tx-Rx IQ imbalance and CFO under doubly selective channels

The next-generation wireless communication systems must address the compensation of in-phase and quadrature phase imbalance (IQI), carrier frequency offset (CFO), and doubly selective channel (DSC) to provide a high quality of service for high mobility users with low-cost radio . None of the existing works consider all these RF impairments under DSC for multi-user scenario. To address this gap, in this paper, we propose an iterative equalization technique to compensate the multi-user interference (MUI) and self inter-carrier interference (S-ICI) induced by the joint effect of transmitter IQI, receiver IQI, CFO and DSC for single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) uplink systems. In each iteration of the proposed equalization technique, the extrinsic information from the decoder is used to cancel the MUI and S-ICI from the received signal. After interference cancellation, each mirror subcarriers pairs are equalized simultaneously. Additionally, unlike existing works, our proposed technique does not put any restriction on the carrier assignment scheme (CAS) used with OFDMA/SC-FDMA systems. Further, to validate the performance of the proposed compensation scheme analytically, we derive an upper bound on the bit error rate (BER) of coded OFDMA and SC-FDMA system without MUI and S-ICI. It is established that the system BER with the proposed technique satisfies the derived upper bound as the iteration converges, demonstrating the effective cancellation of MUI and S-ICI due to all the impairments.

Performance Analysis of IQI Impaired Cooperative NOMA for 5G-Enabled Internet of Things

This paper investigates the joint effects of in-phase and quadrature-phase imbalance (IQI) and imperfect successive interference cancellation (ipSIC) on the cooperative Internet of Things (IoT) nonorthogonal multiple access (NOMA) networks where the Nakagami-m fading channel is taken into account. The closed-form expressions of outage probability for the far and near IoT devices are derived to evaluate the outage behaviors. For deeper insights of the performance of the considered system, the approximate outage probability and diversity order in high signal-to-noise ratio (SNR) regime are obtained. In addition, we also analyze the throughput and energy efficiency to characterize the performance of the considered system. The simulation results demonstrate that, compared with IQI, ipSIC has a greater impact on the outage performance for the near-IoT-device of the considered system. Furthermore, we also find that the outage probabilities of IoT devices can be minimized by selecting a specific power allocation scheme.

IQ imbalance analysis and compensation in multiple antenna systems

This study analyses in-phase and quadrature-phase imbalance (IQI) in large-scale multiple antenna systems and Rayleigh fading channel. Specifically, the authors compare between different approaches (using pilot-based or blind channel estimation processes) to remove the IQI effect at a base station equipped with massive number of antennas. They obtain closed-form expression for the asymptotic achievable rate when using IQI removal algorithm and zero-forcing data detection. They also provide complexity analysis for the proposed solutions and show, by means of Monte Carlo simulations, that the proposed algorithm improves the system performance even for small number of antennas.

I/Q Imbalance and Imperfect SIC on Two-Way Relay NOMA Systems

Non-orthogonal multiple access (NOMA) system can meet the demands of ultra-high data rate, ultra-low latency, ultra-high reliability and massive connectivity of user devices (UE). However, the performance of the NOMA system may be deteriorated by the hardware impairments. In this paper, the joint effects of in-phase and quadrature-phase imbalance (IQI) and imperfect successive interference cancellation (ipSIC) on the performance of two-way relay cooperative NOMA (TWR C-NOMA) networks over the Rician fading channels are studied, where two users exchange information via a decode-and-forward (DF) relay. In order to evaluate the performance of the considered network, analytical expressions for the outage probability of the two users, as well as the overall system throughput are derived. To obtain more insights, the asymptotic outage performance in the high signal-to-noise ratio (SNR) region and the diversity order are analysed and discussed. Throughout the paper, Monte Carlo simulations are provided to verify the accuracy of our analysis. The results show that IQI and ipSIC have significant deleterious effects on the outage performance. It is also demonstrated that the outage behaviours of the conventional OMA approach are worse than those of NOMA. In addition, it is found that residual interference signals (IS) can result in error floors for the outage probability and zero diversity orders. Finally, the system throughput can be limited by IQI and ipSIC, and the system throughput converges to a fixed constant in the high SNR region.

Channel Estimation With Pilot Reuse in IQ Imbalanced Massive MIMO

In this paper, we investigate channel estimation with pilot reuse for massive MIMO with in-phase and quadrature-phase imbalances (IQI). Firstly, we obtain an augmented real-valued representation for the received signal by processing the real and imaginary parts individually with relative compensation. Then based on the obtained augmented real-valued representation, we perform minimum mean square error (MMSE) estimation for the effective channel which comprises the IQI matrix and wireless channel coefficients. Pilots are reused to reduce the pilot overhead. A lower bound of the effective channel estimation MSE is obtained. Motivated by the optimal conditions under which the lower bound can be achieved, we propose a pilot schedule algorithm. Finally, a least square based method to obtain the relative IQI compensation coefficients is provided. Numerical results verify the performance of the proposed effective channel estimation with pilot reuse.

Physical Layer Security of Cooperative NOMA for IoT Networks Under I/Q Imbalance

In this paper, we investigate the reliability and security of cooperative dual-hop non-orthogonal multiple access (NOMA) for internet-of-thing (IoT) networks, in which the transceivers consider a detrimental factor of in-phase and quadrature-phase imbalance (IQI). The communication between the source and destination is accomplished through a decode-and-forward (DF) relay in the presence of an eavesdropper. In order to characterize the performance of the considered system, exact analytical expressions for the outage probability (OP) and intercept probability (IP) are derived in closed-form. Furthermore, to better understanding the performance of the considered system, we further derive the asymptotic expressions of OP in the high signal-to-noise ratio (SNR) regime and IP at the high main eavesdropping ratio (MER) region. A large number of analysis and Monte Carlo simulation results show that the existence of IQI usually increases the corresponding OP and reduces the IP, which means that reduces the reliability of the system and improves the security. In addition, the provided results provide useful insights into the trade-off between reliability and security of secure cooperative communication systems.