Iterative IQ Imbalance Compensation Receiver for Single Carrier Transmission

In low-intermediate-frequency (low-IF) receivers, I/Q imbalance (IQI) causes interference on the desired signal from the blocker signal transmitted over the image frequencies. Conventional approaches for pilot-aided IQI estimation in zero-IF receivers are not applicable to low-IF receivers, where the image interference is unknown at the receiver. We propose a low-complexity subspace method for the estimation of IQI parameters in low-IF receivers in the presence of unknown fading, where we utilize knowledge of the pilots to null out the signal part. This reduces the variance of the sample mean estimate and leads to faster convergence. The proposed nulling method offers significantly better image rejection at low input signal-to-interference power ratio (SIR) than existing methods. Performance analysis of the output SIR as well as computer simulations are also provided. 1 INTRODUCTION One of the common impairments of the radio frequency (RF) frontend is the inphase and quadrature imbalance (IQI) embodied in the gain and phase mismatches between the inphase and quadrature mixers due to inherent manufacturing inaccuracies. 1 In the frequency-domain, the impact of IQI appears as interference between the positive and negative frequency components known as the image leakage problem. 1,2 Consequently, the IQI causes degradation in the signal-to-interference (SIR) power ratio and, hence, in the overall receiver performance and throughput. 3-5 The IQI problem is very important in 5G/6G systems where higher SINR (high IQI rejection ratio) is needed to support high QAM orders and/or high MIMO ranks. 6-9 In low-IF receivers, neighboring signals (blockers) appear as the image of the desired signal after down conversion as shown in Figure 1. 10 If these blockers leak into the desired signal due to IQI, they will severely impact the receiver performance, especially if they are stronger than the desired signal. Hence, IQI estimation and compensation is vital for low-IF receivers. The IQI in Zero-IF transmitters and receivers were studied in Reference 11, investigating the ergodic capacity in a cognitive radio system. In zero-IF receivers, both the desired signal and IQI-induced interference (image leakage) originate from the transmitted desired signal, see section 4.1.4 of Reference 1. Hence, pilots are transmitted at both the subcarrier and its image for pilot-aided IQI estimation as in References 12-16. Blind estimation algorithms were also proposed in the literature for direct conversion architecture.

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“…Dividing (15) by (16) and substituting for the expectation operators by sample mean measurements, we obtain the following estimate for̂=…”

Section: Low-complexity Pilot-aided Iqi Estimationmentioning

confidence: 99%

Low‐complexity subspace method for I/Q imbalance estimation in low‐IF receivers with unknown fading

Gomaa

Elezabi

Eissa

2020

Trans Emerging Tel Tech

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“…They serve as the long‐term evolution advanced (LTE‐A) standards used in base stations with benefits from higher‐order modulation such as 256‐QAM. It offers capabilities to exploit the available bandwidth . However, the main disadvantage is the presence of high peak‐to‐average‐power ratio (PAPR) levels, which appear in multilevel signals at transmitters (TXs) when the signals are amplified and sent through an RF high power amplifier (PA), and which also are inherent power‐hungry devices that exhibit a strong nonlinear behavior .…”

Section: Introductionmentioning

confidence: 99%

“…It offers capabilities to exploit the available bandwidth. 3 However, the main disadvantage is the presence of high peak-to-average-power ratio (PAPR) levels, 4 which appear in multilevel signals at transmitters (TXs) when the signals are amplified and sent through an RF high power amplifier (PA), and which also are inherent power-hungry devices that exhibit a strong nonlinear behavior. 5 This leads to undesirable effects from nonideal imperfections, such as in-band distortion, harmonics, and intermodulation distortion (IMD) products that tend to degrade the transmitted signal.…”

mentioning

confidence: 99%

FPGA‐based system for effective IQ imbalance mitigation of RF power amplifiers

Pérez¹,

Cazares²,

Galaviz-Aguilar

et al. 2020

Circuit Theory & Apps

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Summary To provide an adequate signal integrity to a power amplifier (PA), we propose a digital system for the degradation at the transmitter path, and it is implemented on a field‐programmable gate array (FPGA) board. The proposed system offers the following features: A M‐ary quadrature amplitude modulation (QAM) digital signal generation and in‐phase/quadrature (IQ) imbalance mitigation, and by default, it performs as a predistortion model extraction from PA‐measured data. The simulations and tests provided are performed to effectively verify the PA linearity by using 256‐QAM signals. The nonlinearities are predicted as a reliable solution for linearizing the PA from measurements of AM/AM and AM/PM conversion curves. The performance is evaluated in terms of linearity, computation complexity, and FPGA hardware synthesis according to a dependability compliance of digital signal processing. Finally, the model is validated with input/output data observations to linearize the model with a fitting normalized mean squared error (NMSE) of around −35 dB, a spurious free dynamic range of 40 dBm, and an adjacent channel power ratio reduction by −20 dBm, for a class‐AB broadband radio frequency PA GaN HEMT of 10 W working at 2.34 GHz.

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“…The compensation methods of IQI in OFDM systems are initially proposed in [4 ], and then used in mmWave single carrier (SC) systems in [5 ]. Moreover, other IQI compensation methods have also been put forward on basis of trained sequences [6 ], feedback receiver [7 ], precoding [8 ] and filter optimisation [9 ]. For GFDM systems with IQI, although compensation methods have been investigated in [10, 11 ], there is no solid theoretical analyses for BER performances before and after IQI compensation, nor rigorous proof for usefulness of IQI compensation.…”

Section: Introductionmentioning

confidence: 99%

BER analysis of IQ imbalance compensation for GFDM systems

2020

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As one of the 5G waveform candidates, generalised frequency division multiplexing (GFDM) systems have been proposed to achieve lower out of band radiation and stronger robustness against synchronisation errors. However, theoretical BER performances of GFDM systems with in‐phase/quadrature (IQ) imbalance, as well as compensation strategies, have not been widely investigated. In this Letter, the authors evaluate theoretical BER performances of GFDM systems with transmitter IQ imbalance (IQI) before and after a proposed compensation method. Basically, they give approximated BER expressions for different modulations through considering introduced IQI completely as useless interference, and then derive a more precise BER expression for QPSK modulation. Additionally, they put forward a compensation method to remove IQI interference in GFDM systems at the cost of enlarged noise. Furthermore, analytical BER expressions with IQI compensation are derived, and then the effectiveness of the proposed compensation strategy is proven by theoretical and simulation results.

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Iterative IQ Imbalance Compensation Receiver for Single Carrier Transmission

Cited by 24 publications

References 31 publications

Low‐complexity subspace method for I/Q imbalance estimation in low‐IF receivers with unknown fading

Low‐complexity subspace method for I/Q imbalance estimation in low‐IF receivers with unknown fading

FPGA‐based system for effective IQ imbalance mitigation of RF power amplifiers

BER analysis of IQ imbalance compensation for GFDM systems

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