IQ Imbalance Correction for OFDMA Uplink Systems

Direct conversion receivers are attractive for low cost systems as they avoid intermediate frequency (IF) filters. However, the direct conversion from radio frequencies (RF) to complex inphase (I) and quadrature (Q) baseband signals in one mixing step introduces additional front-end distortions. These IQ distortions lead to a degradation in the system performance. The problem becomes more significant in orthogonal frequency division multiple access (OFDMA) systems where multiple user signals with different IQ impairments are combined in the uplink (UL) signal. In this paper, detection methods for OFDMA-UL signals corrupted by IQ distortions are investigated. The received signal as a function of transmitted signals, IQ parameters, and communication channels is mathematically formulated. We designed a novel pilot pattern that is used by two proposed estimation and compensation methods of IQ impairments to the signal. Proposed methods were shown to significantly improve the system performance.