In-phase And Quadrature-phase Imbalance Research Articles

MMSE WL Equalizer in Presence of Receiver IQ Imbalance

In this correspondence, with reference to the transmission over a linear time-dispersive channel, we address the problem of the in-phase and quadrature-phase (IQ) imbalance compensation when a single-carrier modulation scheme is used. Low-cost fabrication technologies and high data-rate transmissions render the conventional receivers very sensitive to the imperfections of their analog stage and, hence, proper countermeasures need to be adopted. Since the IQ imbalance renders the received signal rotationally variant, we propose to resort to the widely linear (WL) filtering in the synthesis of the receiver. More specifically, the synthesis of the WL receiver is performed by assuming perfect knowledge of the IQ imbalance parameters, but a new blind algorithm for IQ imbalance compensation, which outperforms the existing blind technique, is also proposed.

Joint compensation of transmitter and receiver impairments in OFDM systems

The implementation of OFDM-based systems suffers from impairments such as in-phase and quadrature-phase (IQ) imbalances in the front-end analog processing. Such imbalances are caused by the analog processing of the radio frequency (RF) signal and can be present at both the transmitter and receiver. The resulting IQ distortion limits the achievable operating SNR at the receiver and the achievable data rates. In this paper, the effect of both the transmitter and receiver IQ imbalances in an OFDM system is studied and algorithms are developed to compensate for such distortions in the digital domain. The algorithms include post-FFT least-squares and adaptive equalization, as well as a pre-distortion scheme at the transmitter and a pre-FFT correction at the receiver

MIMO OFDM receivers for Systems with IQ imbalances

Orthogonal frequency division multiplexing (OFDM) is a widely recognized modulation scheme for high data rate communications. However, the implementation of OFDM-based systems suffers from in-phase and quadrature-phase (IQ) imbalances in the front-end analog processing. Such imbalances are caused by the analog processing of the received radio frequency (RF) signal, and they cannot be efficiently or entirely eliminated in the analog domain. The resulting IQ distortion limits the achievable operating SNR at the receiver and, consequently, the achievable data rates. The issue of IQ imbalances is even more severe at higher SNR and higher carrier frequencies. In this paper, the effect of IQ imbalances on multi-input multioutput (MIMO) OFDM systems is studied, and a framework for combating such distortions through digital signal processing is developed. An input-output relation governing MIMO OFDM systems is derived. The framework is used to design receiver algorithms with compensation for IQ imbalances. It is shown that the complexity of the system at the receiver grows from dimension (n/sub R//spl times/n/sub T/) for ideal IQ branches to (2n/sub R//spl times/2n/sub T/) in the presence of IQ imbalances. However, by exploiting the structure of space-time block codes along with the distortion models, one can obtain efficient receivers that are robust to IQ imbalances. Simulation results show significant improvement in the achievable BER of the proposed MIMO receivers for space-time block-coded OFDM systems in the presence of IQ imbalances.

Compensation schemes and performance analysis of IQ imbalances in OFDM receivers

The implementation of orthogonal frequency division multiplexing (OFDM)-based physical layers suffers from the effect of In-phase and Quadrature-phase (IQ) imbalances in the front-end analog processing. The IQ imbalances can severely limit the achievable operating signal-to-noise ratio (SNR) at the receiver and, consequently, the supported constellation sizes and data rates. In this paper, the effect of IQ imbalances on OFDM receivers is studied, and system-level algorithms to compensate for the distortions are proposed. The algorithms include post-fast Fourier transform (FFT) least-squares and least mean squares (LMS) equalization, as well as pre-FFT correction using adaptive channel/distortion estimation and special pilot tones to enable accurate and fast training. Bounds on the achievable performance of the compensation algorithms are derived and evaluated as a function of the physical distortion parameters. A motivation is included for the physical causes of IQ imbalances and for the implications of the approach presented in this paper on designing and implementing wireless transceivers.

Adaptive MIMO OFDM receivers: Implementation impairments and complexity issues

MIMO OFDM communications is a promising choice for future high data rate wireless systems. However, the commercial deployment of MIMO OFDM systems faces some challenges, including those arising from front-end analog implementation impairments and complex receiver structures. The impairments are caused by the analog processing of the received radio frequency (RF) signal and they cannot be e±ciently nor entirely eliminated in the analog domain. This paper illustrates the e®ect of In-phase and Quadrature-phase (IQ) imbalances on system performance. Receiver algorithms are described that compensate for IQ imbalances. The structure of space-time block codes, along with the assumed structure of the distortion models, are exploited to design reduced-complexity adaptive receivers that are robust to IQ imbalances.