IQ Imbalance Research Articles

ADAPTIVE COMPLEX FILTERS BASED TRANSMITTER IQ IMBALANCE REJECTION

This paper presents an efficient method for compensation of frequency-dependent (FD) transmitter In-phase Quadrature (IQ) imbalance. Proposed method compensates imbalance by exploiting indirect learning architecture (ILA) and complex filters whose coefficients are determined in an iterative process. Compensation performance is assessed after the method has been implemented in a Software Defined Radio (SDR) platform, capable of transmitting modulations at different central frequencies. Measured results demonstrate that the imbalance related images are reduced down to the noise floor. After applying the proposed IQ imbalance correction method, the transmitter image rejection ratio (IRR) is increased by 15dB in the case of an SDR transmitter operating at central frequency of 1.7 GHz. The ADC/DAC sampling rate is 61.44MS/s, while the signal bandwidth, for which the compensation is performed, is 30.72MHz. The advantage of the proposed method is low complexity in terms of a reduced number of coefficients. The method is generic and can be utilized for IQ imbalance compensation when wideband signals are transmitted.

Improved PHY-layer authentication utilizing multi-modal features for mmWave MIMO UAV-enabled systems

This paper exploits multi-modal Physical (PHY)-layer features in terms of artificial fingerprint, In-phase/Quadrature (IQ) imbalance and Angle of Arrival (AoA) to propose a novel PHY-layer authentication framework for a Millimeter Wave (mmWave) Multiple-Input Multiple-Output (MIMO) Unmanned Aerial Vehicle (UAV)-enabled communication system. First, we resort to the AoA-based spatial fingerprint to effectively address the challenge of channel fingerprint instability induced by high-speed UAV mobility. To further enhance the low discriminability of hardware fingerprints caused by refined manufacturing techniques, artificial Gaussian noise is injected into the transmission signals to assist the receiver in better distinguishing between legitimate and illegitimate UAVs. Then, we jointly combine with inherent IQ imbalance and AoA features to design a hybrid authentication scheme and thus construct a multi-dimensional fingerprint space for a comprehensive characterization of UAV identities. To theoretically evaluate the effectiveness of the proposed authentication framework, the analytical closed-form expressions of performance metrics like false alarm and detection probabilities are also exactly derived based on the statistical signal processing technology and composite hypothesis testing. Finally, we provide large simulation results to validate the correctness and feasibility of the proposed theoretical models, and also discuss the relation between system security and communication service quality under different artificial fingerprint level.

Joint carrier phase tracking and IQ imbalance tolerance with the dynamic adaption of reference constellation for probabilistic shaped signals

Joint carrier phase tracking and IQ imbalance tolerance with the dynamic adaption of reference constellation for probabilistic shaped signals

Sofware-Defined Radio Testbed for I/Q Imbalanced Single-Carrier Communication Systems

An end-to-end testbed for In-phase and Quadrature (I/Q) Imbalance (IQI) communication systems based on Software-Defined Radio (SDR) is presented. The scenario under consideration is a Single-Input–Single-Output (SISO) single-carrier communication where the transmitter is heavily affected by IQI, whose effects are mitigated through digital signal processing at the receiver. The presented testbed is highly configurable, enabling the testing of different communication and IQI parameters. Crucial insights into the practical implementation of IQI mitigation techniques, specifically through the use of asymmetric signaling at the receiver, are provided. Initially, a detailed description of the mathematical framework is given. This framework serves as the foundation for the subsequent discussion on system implementation, effectively bridging the gap between research on IQI mitigation and its practical application in single-carrier architectures. Over-The-Air (OTA) Symbol Error Rate (SER) measurements for different constellations validate the receiver design and implementation. The source code of the presented testbed is publicly available.

OFDM Modulation Classification Using Cross-SKNet With Blind IQ Imbalance and Carrier Frequency Offset Compensation

OFDM Modulation Classification Using Cross-SKNet With Blind IQ Imbalance and Carrier Frequency Offset Compensation

Multi-gigabit X-band transmitter for satellite communication using the optical phase-locked loop.

Optical generation of microwave signals using photonic techniques offers benefits of frequency agility, ease of frequency scaling, and reduced hardware complexity. We demonstrate the generation and detection of QPSK modulated with symbol rates up to 5 GBaud at carrier frequencies of 8-12 GHz through optical heterodyning of two-phase-locked lasers. The received data is demodulated through appropriate post-processing to correct for the phase noise and IQ imbalance. The approach is scalable to mmWave and THz communication.

Joint Channel and IQ Imbalance Compensation Method for MIMO-OFDM Using in Coastal Railway

Joint Channel and IQ Imbalance Compensation Method for MIMO-OFDM Using in Coastal Railway

Coherent optical transmitter IQ imbalance mitigation with embedded carrier phase and frequency offset estimation.

We present a 4×4 real-valued channel equalizer with embedded phase estimator, designed for carrier phase and frequency offset estimation and compensation in coherent optical communications with in-phase/quadrature (IQ) impairments. These impairments include IQ timing skew, gain imbalance, and quadrature phase errors at the transmitter side. To achieve adaptive control of the equalizer's filter coefficients, we employ the decision-directed least mean square (DD-LMS) algorithm. This algorithm minimizes the error between the filter outputs and the desired signals in a symbol-by-symbol manner, resulting in faster channel coefficients adaptation speed. Simulation results for a 60 GBaud polarization-multiplexing 16 quadrature amplitude modulation (PM-16QAM) signal demonstrate that our proposed equalizer outperforms a 2×2 cascaded multi modulus algorithm-based (CMMA-based) equalizer, a 2×2 complex-valued method based on the DD-LMS algorithm, and the 4×4 real-valued equalizer without embedded frequency offset estimation (FOE), when the transmitter IQ impairments exist. Experimental validation is also conducted for the 60 GBaud PM-16QAM and 45 GBaud PM-64QAM signals. Similar to the simulation results, our experiments show that the proposed 4×4 real-valued equalizer with embedded FOE can achieve effective SNR penalties of less than 0.41 dB at 7 ps skew, 1.33 dB at 3.5 dB gain imbalance, and 1.64 dB at the bias voltage shift of 0.5 V for the 60 GBaud PM-16QAM signal. Finally, our experimental results confirm the effectiveness of our proposed method in carrier phase estimation as well as the frequency offset compensation, when compared with 4×4 real-valued equalizer without embedded FOE.

Study of signal separation and demodulation techniques considering IQ imbalance by stored data batch signal processing

Study of signal separation and demodulation techniques considering IQ imbalance by stored data batch signal processing

Background Receiver IQ Imbalance Correction for In-Field Testing

Background Receiver IQ Imbalance Correction for In-Field Testing

A Novel Radio Frequency Fingerprint Concealment Method Based on IQ Imbalance Compensation and Digital Pre-Distortion

A Novel Radio Frequency Fingerprint Concealment Method Based on IQ Imbalance Compensation and Digital Pre-Distortion

OFDM-Based Waveforms for Joint Sensing and Communications Robust to Frequency Selective IQ Imbalance

OFDM-Based Waveforms for Joint Sensing and Communications Robust to Frequency Selective IQ Imbalance

Low-complexity Coherent Optical Transceiver IQ Imbalances Calibration Enabled by Cross-power Spectrum Method

Low-complexity Coherent Optical Transceiver IQ Imbalances Calibration Enabled by Cross-power Spectrum Method

IQ Imbalance Correction in Wideband Software Defined Radio Transceivers

IQ Imbalance Correction in Wideband Software Defined Radio Transceivers

Joint Estimation and Compensation of CFO, IQ Imbalance and Channel Parameters for Zero Padded OTSM Systems

Joint Estimation and Compensation of CFO, IQ Imbalance and Channel Parameters for Zero Padded OTSM Systems

Hardware-Efficient and Robust DSP Scheme for Coherent DSCM System in Presence of Transmitter IQ Impairments

In this paper, a hardware-efficient and robust DSP scheme for the coherent digital subcarrier multiplexing (DSCM) system in presence of transmitter (Tx) in-phase/quadrature (IQ) impairments is introduced and demonstrated. An analytic complex model is given to describe the effects of IQ skew, IQ amplitude and phase imbalance (referred to as IQ mixing) on the DSCM signal. Based on the model, residual frequency offset, polarization and carrier phase noise are jointly recovered using frequency pilot tones (FPT) in presence of IQ mixing. This process avoids the coupling effect of phase noise and Tx IQ mixing in conventional schemes, which allows the Tx IQ mixing to be compensated for by the following joint equalization of conjugate symmetric subcarriers. Compared to the conventional scheme based on widely linear equalizer, the polarization and carrier phase tracking capability of the proposed scheme is robust to IQ mixing. Meanwhile, the proposed scheme can tolerate a wide range of Tx IQ mixing in the presence of residual frequency offset and carrier phase noise. Since polarization crosstalk is eliminated, the signals of the two polarizations can be equalized separately in the proposed scheme, thus reducing the computational complexity by half. For a 4-subcarrier DSCM system with baud rate of 32 Gbaud, experimental results show that the Q-factor degradation of the proposed scheme is less than 0.5dB in the presence of Tx IQ time skew within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 15 ps, IQ phase imbalance within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 20 degrees or IQ amplitude imbalance within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 3 dB. With 1dB Q-factor degradation, the proposed scheme can track polarization variation up to 10 Mrad/s, residual frequency offset of 10 MHz or carrier phase noise with 3dB linewidth of 200 kHz in the presence of Tx IQ mixing. Therefore, the proposed scheme provides a hardware-efficient and robust DSP solution for coherent DSCM targeting access network applications.

Multi-domain blind source separation in-band full-duplex technique considering RF impairments

In-band full-duplex (IBFD) technology can potentially improve spectrum efficiency compared to half-duplex technology. The cancellation of the self-interference (SI) signal is the key to implementing the IBFD system to achieve accurate detection of the signal of interest. In this work, we fully account for the effect of IQ imbalance, phase noise (PN), additional Gaussian white noise (AWGN), and the nonlinear caused by the RF impairments of power amplifier, and adopt the method of canceling SI signal combined with the propagation, analog, and digital domain to cancel the SI signal, but the residual SI signal is still mixed with the signal of interest in the same time and frequency domain. In addition, a novel multi-domain blind source separation (MDBSS) self-interference cancellation method implemented by using the off-the-shelf components is proposed in this paper, which can realize the separation of residual self-interference signals from the signal of interest (SOI). Additionally, the multi-domain blind source separation (MDBSS) self-interference cancellation technique is used to achieve 75 dB of self-interference cancellation performance, which is proven through numerical simulation analysis, and the SOI is successfully separated in the receiver. Moreover, the multi-domain blind source separation (MDBSS) method in this paper can be applied to radar, jammer, and communication systems in the future.

An Efficient Transmitter Feature Extraction Scheme with IQ Imbalance and Nonlinearity in TDD OFDM Systems

Radio frequency (RF) fingerprints have been an emerging research topic for the last decade. Numerous algorithms for recognition have been proposed. However, very few algorithms for the accurate extraction of IQI and PA nonlinearity are available, especially when multiple paths are considered. In this study, we present a scheme that uses the transmitter in-phase/quadrature-phase imbalance (IQI) and the power amplifier (PA) nonlinearity as RF fingerprint features in time-division duplexing (TDD) OFDM systems, which are always considered to be harmful to data transmission. The scheme consists of two round trips with four steps for two cases: in the first, the IQI and PA nonlinearity are unknown at the terminal; in the second, they are known at the terminal. A channel state information (CSI)-tracking algorithm based on the sliding-window least squares method is first adopted at the terminal. In case A, the obtained CSI is sent to the base station (BS) to remove its impact there; in case B, this removal is conducted directly by using pre-equalization at the terminal. Then, by following a sequential iterative approach, the IQI and nonlinearity are individually calculated. Theoretical analyses reveal how CSI estimation errors influence subsequent estimates at the BS in these two cases. Furthermore, the approximate unbiasedness is verified. The theoretical variance and Cramer–Rao lower bound (CRLB) are also given. It is indicated that the theoretical minimum variance in case B is lower than that in case A from the perspective of the CRLB. The numerical results demonstrate the efficiency of the scheme in comparison with existing techniques in the literature.

Low-complexity algorithms for coherent optical systems with transceiver IQ imbalance.

The next-generation coherent optical communication relies on higher symbol transmission rates with higher modulation cardinality. The imbalance between the in-phase (I) and the quadrature (Q) arms in such systems leads to deteriorated performance if not corrected. In this work, we propose a reference constellation adaptation-based single-tap, novel carrier phase recovery algorithm, tolerant to the transmitter IQ imbalance and a pilot-free geometric parameter extraction-based receiver IQ imbalance correction method for MQAM signals. The proposed scheme is numerically investigated through extensive simulations for 32 GBaud polarization multiplexed (PM)-16QAM, and 64QAM modulation formats and experimentally verified for 32 GBaud PM-16QAM signal. The proposed pilot-free scheme is applicable to any modulation format and offers lower computational complexity than traditional algorithms.

Experimental Comparison of Single-Carrier and Digital Subcarrier Multiplexing Transmissions in a W-Band 200 Gb/s Fiber-Wireless System Considering Transmitter IQ Imbalance and Skew Mitigation

Experimental Comparison of Single-Carrier and Digital Subcarrier Multiplexing Transmissions in a W-Band 200 Gb/s Fiber-Wireless System Considering Transmitter IQ Imbalance and Skew Mitigation