In-phase And Quadrature Imbalance Research Articles

Estimation of IQI for AF Cooperative Single-Carrier Frequency Domain Equalization Systems Using Channel Decoder Feedback

The process of amplify-and-forward (AF) relaying is essential to the improvement of both current and future wireless communication standards. Nevertheless, significant performance loss may be posed by in-phase and quadrature imbalance (IQI) caused by defects in radio frequency components. Prior studies into this research problem were restricted to uncoded broadcasts, even though error-correcting codes are frequently used in real applications. To this purpose, we develop a novel approach applicable to the destination terminal for estimating and compensating for IQI that occurs at the source, relay, and destination terminals. The proposed approach is explored in the context of coded emissions of AF single-carrier frequency domain equalization (SC-FDE) systems. In contrast to other methods for mitigating this radio frequency deflection at each node, the proposed system estimates and compensates for all IQI parameters and channel impulse responses simultaneously. With the use of an iterative expectation–maximization (EM) process, a maximum-likelihood (ML) solution to the problem is computed. At each round, the soft information supplied by the channel decoder is employed to create the a posteriori expectations of the sent data symbols, which are then fed into the estimation process as if they were training symbols. In addition, we address how to use the estimated parameters to perform the task of data detection. The offered predictor and detector exchange soft information in a sequential process, boosting the overall system effectiveness. The simulation results show that the proposed method is not only practicable but superior to the established methods.

Secrecy Analysis of Uplink IM-OFDMA Systems in the Presence of IQ Imbalance

This paper introduces the secrecy analysis of the index modulation-based orthogonal frequency division multiple access (IM-OFDMA) schemes by considering the in-phase and quadrature imbalance (IQI) presence at the users' RF front ends. In particular, by assuming the existence of an eavesdropper, the secrecy performance of the considered uplink multiple-access system is investigated through the strictly positive secrecy capacity and secrecy outage probability, and closed-form expressions are derived for both quantities. Moreover, the secrecy performance is conducted regarding IQI compensation based on a preamble-based estimation method. Further, analysis of the impact of the different parameters of IM-OFDMA, IQI, and estimation method is included via analytical and simulation-based results. The results reveal that IM-OFDMA is more reliable in secrecy performance than OFDMA, regardless of whether IQI is present. Also, IQI compensation can lead to a better secrecy performance compared to the case of no IQI.

Impact of carrier frequency offset and in-phase and quadrature imbalance on the performance of wireless precoded orthogonal frequency division multiplexing

<p>Precoding in orthogonal frequency division multiplexing (OFDM) system proved to reduce the peak-to-average power ratio (PAPR), so that it improves BER. However, from the existing literature, the effect of carrier frequency offset (CFO), in-phase and quadrature (IQ) imbalance on precoded wireless OFDM systems has not been carried out. Therefore, this study evaluated the precoded OFDM (P-OFDM) system performance by considering the impact of CFO and IQ imbalance. P-OFDM performance evaluation is expressed in signal-to-interference noise ratio (SINR) and bit error rates (BER). The communication channels used are the additive white Gaussian noise (AWGN) channel and the frequency-selective Rayleigh fading (FSRF) channel, while the channel equalization process is considered perfect. The results of the analysis and simulation show that P-OFDM is greater affected by the presence of CFO and IQ imbalance than conventional OFDM system. In AWGN channel, P-OFDM experiences different SINR for each subcarrier. This is different from conventional OFDM system, where all SINRs are the same for all subcarriers. In the FSRF channel, both the POFDM system and the OFDM system experience different SINR for each subcarrier, where the SINRs fluctuation in the P-OFDM system is much larger than in the OFDM system.</p>

Estimation and Compensation of IQ Imbalance for OTSM Systems

Recently, orthogonal time sequency multiplexing (OTSM) waveform was proposed using Walsh Hadamard transform (WHT) for doubly-dispersive channels at a lower modulation/demodulation complexity than orthogonal time frequency space (OTFS) waveform. At high frequencies, hardware imperfections such as in-phase and quadrature (IQ) imbalance is prominent at the transceiver. In this letter, the input-output (I/O) relation in the delay-sequency domain is derived under these impairments at the receiver. The impairment parameters are estimated in the delay-time domain and are compensated in the time domain using proposed dual pilot approach. The normalized mean square error (NMSE) of the estimated imbalance parameters is evaluated and it is observed that NMSE reduces with increase in SNR and with reduction in mobility. The results are evaluated with OTFS system and it is observed that the NMSE performance of OTSM is similar to OTFS under high pilot power and high SNR at no excess pilot power. The bit error rate performance of the compensated system is evaluated and its performance is close to the ideal system.

Analysis, Estimation and Compensation of Hardware Impairments for CP-OTFS Systems

Orthogonal time frequency space (OTFS) waveform, which is robust to doubly-selective fading channels is a strong contender for the Fifth generation (5G) communications. At high frequencies, hardware imperfections are prominent in practice at the transceivers. In this letter, we consider impairments such as carrier frequency offset (CFO), direct current (DC) offset and in-phase and quadrature (IQ) imbalance at the transmitter (Tx) and receiver (Rx) for cyclic prefix (CP) OTFS system. We derive the input-output (I/O) relation in the delay-Doppler (DD) domain under these impairments and show that due to the DC offset and IQ imbalance, image Doppler interference (IDI) appears along the Doppler domain and the CFO becomes part of the channel parameters. We estimate impairment parameters in the DD domain and compensate these at Tx and Rx in the time domain. The normalized mean square error (NMSE) of the estimated imbalance parameters are evaluated and it is observed that NMSE reduces with increase in, pilot power, number of Doppler bins and with windowing techniques applied in time-frequency (TF) domain.

Multipath Canceled RF Fingerprinting for Wireless OFDM Devices Based on Hammerstein System Parameter Separation

Radio frequency fingerprint (RFF) based authentication of wireless devices can be used in the fields of the access security at the physical-layer of wireless networks and radio spectrum management. However, the stability of RFF is easily damaged by the wireless multipath fading channel in mobile communications. An RFF fingerprinting method with the nonlinearity and in-phase and quadrature (IQ) imbalance of the transmitter is proposed for chunk-based wireless orthogonal frequency division multiplexing (OFDM) devices based on a Hammerstein system parameter separation technique, which cancels the adverse influence of the time-varying multipath channel. First, the parameters of the nonlinear model of the transmitter and finite impulse response (FIR) of the wireless multipath channel are estimated with the Hammerstein system parameter separation technique. Second, the best IQ imbalance parameter combination is obtained with the FIR estimation of the channel. Finally, the estimated parameters of the nonlinear model and IQ imbalance are used as RFFs to classify the transmitters. Theoretical analyses and numerical experiments demonstrate that the obtained RFFs are stable and the fusion authentication of transmitters with subtle differences from the same model and same series is feasible using the novel method.

Widely linear equalization for IQ imbalance contaminated multicarrier systems

In a multicarrier modulated (MCM) wireless communication system, the received bandpass signal is downconverted to the baseband signal for ease of receive processing. During downconversion, a slight mismatch in the amplitude and phase of locally generated sinusoidal signal in the In-Phase and Quadrature (IQ) branches of downconverter results in IQ imbalance of the baseband signal. The IQ imbalance leads to mirror interference between subcarriers of an MCM system and degrades the performance. To compensate for the effects of IQ imbalance, this paper presents widely linear minimum mean square error (WL-MMSE) based equalization technique and compares it with the traditionally used linear minimum mean square error (L-MMSE) based equalization technique. A performance comparison between WL-MMSE and L-MMSE based estimation techniques in terms of mean square error (MSE) and bit error rate (BER) suggests that the former outperforms the latter in the presence of IQ imbalance.

Secrecy Performance of Full-Duplex Jamming and Reception Under I/Q Imbalance

Investigating the physical layer security performance of full-duplex (FD) radio transceivers has been the subject of numerous research studies. However, self-interference cancellation that enables full exploitation of FD communications is a crucial aspect that deserves special attention. Hence, in this paper, we analyze the effect of a FD transceiver's in-phase and quadrature imbalance (IQI) on simultaneously jamming the receiver of an eavesdropper and detecting a signal of interest by deriving an expression for the secrecy outage probability (SOP) metric. Through further analysis for some special and limiting cases, performance insights are drawn by showing that the SOP is dependent on the image rejection capability of the FD transceiver and is approximately equal to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\frac{3}{\text{IRR}}(\ln {(\text{IRR})} - 1.83)$</tex-math></inline-formula> , where the IRR is the image-rejection ratio. The accuracy of the derived SOP expression is verified through Monte-Carlo simulations.

Joint estimation and compensation of transceiver IQ imbalance for PDM CO-OFDM system

In this paper, a frequency-domain mathematical model is deduced for polarization-division multiplexing (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) system with transceiver in-phase and quadrature (IQ) imbalances. A novel training symbol structure is designed in which the mirror-subcarriers of pilot subcarriers were modulated with zero signal so that the channel distortion with transceiver IQ imbalances can be estimated. It proves that the channel distortion and transmitter IQ imbalances cannot be separated using the training symbols; therefore, the channel equalization method was used to recover the signals. Simulation results show that at 2 dB transmitter amplitude imbalances, 15° transmitter phase imbalances, 100 Gbit/s transmission rate, 1 040 km standard signal-mode fiber link, and 1×10−3 bit error rate, 23.5 dB optical signal-to-noise ratio (OSNR) is necessary for the proposed method. However, the compared schemes cannot achieve effective transmission.

Compensation of Phase Noise and IQ Imbalance in Multi-Carrier Systems

Compensation for the impacts of phase noise (PN) and in-phase and quadrature (IQ) imbalance on cyclic-prefix (CP) based multi-carrier modulation systems in the presence of imperfect channel estimation is considered in this paper. A unified two-stage algorithm is proposed. In the first stage, IQ imbalance parameters and channel impulse response are estimated based on the transmission of a preamble which is designed in such a way that the estimation of IQ imbalance does not require any knowledge about the channel and PN. Given the estimates from the first stage, the impacts of IQ imbalance and PN are subsequently compensated in the second stage based on the transmission of pilot symbols. The proposed algorithm is further extended to a MIMO system that employs a diversity technique. Simulation results are presented for a wide range of PN and IQ imbalance scenarios to corroborate the effectiveness of the proposed algorithm.

Spectrum Sensing in SIMO Cognitive Radios Under Primary User Transmitter IQ Imbalance

In this paper, we model the received signal of a single-input-multiple-output (SIMO) cognitive radio with in-phase and quadrature imbalance (IQI) in the transmitter. Then, the spectrum sensing problem is formulated as a composite hypothesis testing problem. We propose two new eigenvalue-based detectors based on the likelihood ratio test (LRT), Rao and Wald frameworks, i.e., the resultant LRT leads us to the Wald test. For the proposed Rao test, we find closed-form expressions for false alarm and detection probabilities under noise variance uncertainty in order to get the level of desired false alarm probability $p_{\text{fa}}$ , i.e., it is called a level $p_{\text{fa}}$ test. This is required for nonconstant false alarm rate (non-CFAR) such as the Rao test to guarantee that the obtained false alarm rate is always below a required level $p_{\text{fa}}$ . Additionally, an analytical formula for the probability of false alarm of Wald test is presented to confirm our simulation results. In this case, the proposed Wald detector is a size $p_{\text{fa}}$ test, called a CFAR detector. Detection performances of the proposed detectors are compared in different scenarios by extensive Monte Carlo simulations. It is shown that the Wald detector outperforms the proposed Rao one. Also, we show that the effects of transmitting IQI can be considered as a signal-to-noise ratio factor, just affecting the detection performance. Also, our performance results show that the proposed Wald detector is fairly robust to the receiver IQI when direct down-conversion receivers are exploited.

A 16-QAM 100-Gb/s 1-M Wireless Link With an EVM of 17% at 230 GHz in an SiGe Technology

This letter presents a 1-m wireless link established with a set of fundamentally operated Tx/Rx direct-conversion in-phase and quadrature (IQ) radio frequency (RF) front-end modules in a 0.13- $\mu \text{m}$ SiGe HBT technology featuring full chip-on-board packaging. Using a 16-quadrature amplitude modulation, data rates from 20 to 100 Gb/s with an error vector magnitude from 7% to 17% were achieved at a 1-m distance. Thanks to the new mixer-first Rx, the maximum data rate improved from 90 to 100 Gb/s compared with our previous work using the amplifier-first Rx. The peak performance was reached at 230 GHz. The Tx operates at a 3.5 dB backoff from $\text{P}_{\textbf {sat}}$ showing a 3-dB RF bandwidth (BW) of 28 GHz, a $\text{P}_{\textbf {out}}$ of 5 dBm, and an IQ imbalance below 0.7 dB. The Rx features a peak conversion gain of 8 dB, a single-sideband noise figure of 14 dB, a 3-dB RF BW of 26 GHz, and an IQ imbalance below 1 dB. This letter also provides an analysis of the RF front-end imperfections related to the large link BW.

An 802.11ax 4 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\times$ &lt;/tex-math&gt; &lt;/inline-formula&gt; 4 High-Efficiency WLAN AP Transceiver SoC Supporting 1024-QAM With Frequency-Dependent IQ Calibration and Integrated Interference Analyzer

A fully integrated 4 $\times $ 4 802.11abgn/ac/ax transceiver system-on-chip (SoC) with integrated interference analyzer and frequency-dependent in-phase and quadrature (IQ) (FD-IQ) calibration is presented. The FD-IQ technique helps meeting the extremely strict IQ imbalance requirement for 1-K quadratic-amplitude modulation (QAM). The pure current-mode TX baseband (BB) improves SNR to better than 50 dB, and a multi-mode local oscillator (LO) distribution circuit provides non-contiguous operation with the error vector magnitude (EVM) of less than −37 dB. The integrated interference analyzer achieves the highly reliable connection in the presence of the undesired signal and hence improves the frequency usage efficiency by identifying the wireless LAN (WLAN) and other signals in the 2G/5G band.

Robust and Blind Eigenvalue-Based Multiantenna Spectrum Sensing Under IQ Imbalance

We investigate the spectrum sensing problem in a single-input-multiple-output cognitive radio system under in-phase and quadrature imbalance (IQI). To do this, the received signal model is obtained in the presence of IQI at the analog front-ends of both the primary and secondary users. We first use a preprocessing stage to mitigate the effect of receiver IQI (RX-IQI). It is found that the received matrix signal is composed of an unknown rank-2 matrix contaminated by the receiver noise matrix. Then, we apply the likelihood ratio test principle to develop three eigenvalue-based detectors. Analytical expressions for the false alarm probabilities of the proposed detectors are derived to adjust their detection thresholds, especially under noise variance uncertainty. Simulation results are provided to illustrate the spectrum sensing performance of the proposed detectors in comparison with existing detectors in the literature also to verify the analytical expressions derived for the false alarm probability. Our simulation results show that the proposed spectrum sensing algorithms are not susceptible to the RX-IQI effects. In addition, we analytically show that one of the proposed spectrum sensing algorithms has constant false alarm rate property with respect to the noise variance uncertainty.

Calibration of transmitter IQ imbalance with 1-bit feedback

Modern wireless technology calls for high throughput, which can be achieved by large spectral bandwidth, and/or high-order modulation. The in-phase and quadrature (IQ) imbalance is an important factor degrading the transmitter error vector magnitude (EVM), thus limiting the transmitter performance. In order to compensate for the IQ imbalance, a feedback path at the transmitter output is needed to estimate the mismatch. The analog-to-digital converter (ADC) in the feedback path can be power hungry when the signal bandwidth is large. In this paper, we propose a digital IQ imbalance estimator and compensator with 1-bit quantization in the feedback path. We show that the proposed algorithm is valid in terms of estimation convergence and accuracy. Numerical results show that the proposed algorithm achieves comparable estimation accuracy as that using the conventional least mean squares (LMS) method at a much lower cost.

IQI Mitigation for Narrowband IoT Systems With OFDM-IM

The crucial aim for 5G narrowband Internet of Things (NB-IoT) is to support massive connectivity with wide coverage area, low power consumption, low hardware complexity, and low data rate. Direct conversion receiver (DCR) has a simple structure to fulfill NB-IoT requirements. However, a significant degradation has been observed on the performance of orthogonal frequency division multiplexing (OFDM) systems with the DCR due to in-phase and quadrature imbalance (IQI) at RF front-end. Estimation and mitigation of IQI in OFDM systems require an iterative receiver at the expense of high complexity and power consumption. In this paper, OFDM with index modulation (OFDM-IM) is proposed as a promising candidate in order to meet the demands of NB-IoT use cases. OFDM-IM-based systems carry data information not only by modulated subcarriers but also by indices of fractionally used subcarriers. A non-iterative and efficient receiver that exploits inactive subcarriers is introduced to mitigate the effect of IQI for NB-IoT with OFDM-IM. Cyclic redundancy check algorithm is used to investigate the accuracy of the receiver under IQI. Theoretical analysis and computer-based simulations show that the proposed non-iterative receiver for OFDM-IM in NB-IoT under IQI works very well in various scenarios. Moreover, our findings show that the OFDM-IM under IQI provides higher signal-to-interference ratio in comparison with classical OFDM.

Channel Compensation for Reciprocal TDD Massive MIMO-OFDM With IQ Imbalance

Massive multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems are sensitive to in-phase and quadrature (IQ) imbalances, which destroys the reciprocity of time-division duplex (TDD) uplink/downlink channels with potentially large performance degradation. In this letter, we investigate the compensation of channel reciprocity for TDD massive MIMO-OFDM systems in the presence of IQ imbalances at both the transmitter and receiver. A frequency-domain compensation scheme is proposed, which uses compensation matrices to precode uplink and downlink transmissions. By disassembling the effective channel model into pairs of mirror subcarriers and utilizing block matrix inversion, the compensation matrices can be calculated with a complexity that is linear in the number of antennas at the base station and mobile station. Simulations verify the effectiveness of the proposed scheme.

IQ Imbalance Compensation for Generalized Frequency Division Multiplexing Systems

Generalized frequency division multiplexing (GFDM) with a flexible structure is one of the promising candidates for the fifth generation wireless communication system. This letter presents a compensation scheme of in-phase and quadrature (IQ) imbalance caused by radio frequency front-end for GFDM. The motivation behind this letter is to relax the requirement on time-invariant channel in the process of estimating IQ imbalance parameters. A low computational complexity approach is proposed to directly estimate IQ imbalance parameters without any prior knowledge of channel. Meanwhile, the structure of training sequences that avoid channel estimation is derived. Simulation results confirm that the proposed method can reduce the effects of IQ imbalance and provide reliable performance even over severe IQ imbalance environment.

Massive MIMO Systems With IQ Imbalance: Channel Estimation and Sum Rate Limits

In this paper, we study the impact of in-phase and quadrature imbalance (IQI) on single-cell multiuser multiple-input multiple-output systems with large antenna arrays. Moreover, we consider a time-division duplex system, where we assume uplink/downlink channel reciprocity in the downlink precoding design. First, we investigate the effect of transceiver IQI on the uplink channel estimation by deriving the linear minimum-mean-square-error estimator for the IQ-impaired model and prove that only the receiver IQI at the base station (BS) limits the estimation accuracy. Then, we study the impact of uplink/downlink channel mismatch on the downlink rate caused by different IQI at the BS and user equipments (UEs). We prove that the achievable downlink rate of each UE is limited either by the receiver IQI at the UEs or jointly by the transmit and receive IQI at the BS, when there is mismatch between the uplink and downlink channels.

Impact of IQ imbalance on the performance of QSM multiple‐input–multiple‐output system

Quadrature spatial modulation (QSM) is proposed recently as an efficient multiple-input–multiple-output wireless communication technique. In QSM, spatial multiplexing gain is achieved through modulating a two-dimensional spatial constellation diagram in addition to conventional signal modulation. It was demonstrated that QSM can be designed with single in-phase and quadrature (IQ) transmitter. However, the impact of IQ modulator imperfections, which degrade signal fidelity and overall system performance, has not been studied in the literature. In this study, typical IQ modulator/demodulator is considered for QSM system and the performance of the system is analysed and discussed. In particular, IQ imbalance channel modelling, pair-wise error probability, and average bit error ratio are discussed. Results reveal that IQ imbalance can lead to significant performance degradation of QSM system and should be carefully addressed for any future deployment.