Decision directed methods of I/Q imbalance compensation in OFDM systems

Nonlinearities of analog hardware result in phase and amplitude imbalance in case of zero-IF receivers, which imply direct down-conversion of the RF signal. The compensation of undesirable effects must be performed in the digital baseband. Particularly OFDM based systems are likely to suffer from imbalances due to distortions introduced by the time-to-frequency transformation of the filtered signal in case of any I/Q imbalance. This paper introduces two decision directed compensation methods: a Hard Decision based and a Blind Source Separation based, operating in the time and frequency domain, respectively. Time and frequency domain compensation methods are compared, and corresponding analytical models analyzed. Special emphasis is placed on applicability of the compensation methods to OFDM communication systems. The theoretical study is accompanied by a presentation of simulation results involving an IEEE 802.11a system.