Pilot Designs for Channel Estimation of OFDM Systems with Frequency-Dependent I/Q Imbalances

The advances in semiconductor downscaling have empowered communication devices with significantly enhanced signal processing capability, but with the side effect of larger device impairments. Among those impairments, the I/Q imbalance is a critical one as it causes intercarrier interferences in orthogonal frequency division multiplexing (OFDM) systems. The I/Q imbalances in general exist at both transmitter and receiver, and they can be frequency-dependent. They may vary over time (e.g. due to sudden changes in temperature or the dynamics of the cooperating/relaying users). Under such scenarios, estimation and compensation of the combined effect of the channel and I/Q imbalances are crucial. This paper presents efficient pilot designs for such tasks. The advantages of the proposed designs over the existing ones in terms of estimation performance and overhead efficiency are corroborated by analysis and simulation results.