Ultra-Low Complex Blind I/Q-Imbalance Compensation

Abstract

Direct-conversion transceivers are the predominating architecture in current mobile communication systems. Despite many advantages, this topology suffers from unavoidable mismatches in the analog part, which causes imbalance between the in-phase and quadrature (I/Q) component. In this paper, we present a novel fully digital, blind I/Q imbalance compensation algorithm that features extremely low computational complexity and high compensation performance for a wide range of input signal types. Different to many state-of-the-art compensation schemes, the approach is not based on a gradient descent optimization and does not require any global feedback. This simplifies the implementation at high data rates and reduces the configuration effort to a minimum. For comparison, we examine an existing method of moment-based estimator with similar properties, for which we also provide the detailed insights beyond available literature. For both algorithms, we provide a rigorous mathematical analysis, which is supported by simulations with a focus on various long-term evolution (LTE) signal types. In addition, hardware architectures, including field-programmable gate array (FPGA) verification, are presented for both algorithms.

Enhanced Propriety-Based I/Q Imbalance Compensation in LTE/NR Receivers

“…In this work, we employ a thorough mathematical analysis of the moment-based I/Q imbalance estimator to derive a powerful modification of this algorithm. Our investigations enable a deeper understanding of the allocation-dependent performance deviations presented in [8]. We provide two novel results compared to [8], [16], [17]: First, we show that a modified moment-based estimator features substantial performance improvements for improper LTE/NR sequences.…”

“…Our investigations enable a deeper understanding of the allocation-dependent performance deviations presented in [8]. We provide two novel results compared to [8], [16], [17]: First, we show that a modified moment-based estimator features substantial performance improvements for improper LTE/NR sequences. This modification requires an approximate knowledge of the LTE symbol boundaries (or, more generally, slot boundaries), which is usually available.…”

“…Further details on this aspect can be found in Section VI-D. Depending on the receiver design, for lower bandwidths, e. g. up to 20 MHz [8], a frequency-independent approximation of the form…”

“…It profits from technology scaling and avoids the need for factory calibration. The I/Q imbalance problem is extensively covered in literature, where various algorithms have been published ranging from very low [3]- [8] to comparably high hardware complexity [9]- [14]. Some of these approaches target a frequency-dependent I/Q imbalance, while others assume a frequency-independent effect.…”

“…In detail, this concept utilizes the variance and pseudo-covariance of the receive signal with I/Q imbalance. In [8] this moment-based algorithm is further analyzed and insights for the specific signal variants defined by the Long-Term Evolution (LTE) standard are provided. It is shown that the performance of the algorithm heavily depends on dynamic system parameters, such as the subcarrier allocation pattern and the modulation scheme.…”