Digital Methods for Reduction of IQ Imbalance in OFDM Systems

Abstract: Orthogonal frequency division multiplexing (OFDM) based systems are susceptible to radio front end induced impairments. These impairments caused by as a consequence of imbalances in the In-phase (I) and Quadrature-phase (Q) branches. IQ imbalances are worries to be addressed for the Superhetrodyne and the zero IF architectures in analog domain. The zero-IF architecture is a prospective solution to include multiple RF standards while making straightforward the design and dropping overall costs. However in the practical implementation of the zero-IF receiver architecture IQ imbalance has been recognized as one of the most serious concerns. At the receiver the expected working signal to noise ratio (SNR) can be affected heavily by the presence of IQ imbalance. As a result of this imbalance the data rates and the supported constellation are also affected. In this thesis the effect of IQ imbalance on OFDM receivers is considered and digital methods are proposed to tackle the effect of IQ imbalance and enhance the operating signal to noise ratio (SNR). The methods are the least square (LS) and the least mean algorithm (LMS). With the help of computer simulation we are going to study the performance of both reduction techniques. The bit error rate (BER) Verses signal to noise ratio (SNR) result could indicate the proposed techniques provide sufficient improved performance.