IQ Compensation for OFDM in the Presence of IBI and Carrier Frequency-Offset

In this paper we propose a frequency-domain equalization technique for OFDM transmission over frequency-selective channels. We consider the case where the analog front-end suffers from an IQ imbalance and the local oscillator suffers from carrier frequency-offset (CFO). Besides we consider the channel delay spread is larger than the cyclic prefix (CP). This means that interlock interference is present. While the IQ imbalance results into mirroring effect, the CFO induces intercarrier interference (ICI). CFO in conjunction with IBI results into sever intercarrier interference. The frequency-domain equalizer is proposed to combat these effects. It is obtained by transferring a timedomain equalizer (TEQ) to the frequency-domain resulting into per-tone equalizer (PTEQ). Due to the presence of IQ imbalance conventional TEQ (where only one TEQ is applied to the received sequence) is not sufficient to cope with the mirroring effect. A sufficient TEQ consists of tow time-domain filters; one applied to the received sequence and the other is applied to a conjugated version of the received sequence. The TEQs are designed according the basis expansion model (BEM) which showed to be able to cope with the ICI problem. We also propose an RLS initialization scheme for direct equalization.