Good and bad training sequences for zero IF sampling edge receivers

In the mobile communication standard GSM/EDGE, the base station can select one of eight training sequence codes as midamble of the downlink transmitted bursts. If the receiving mobile station uses zero intermediate frequency (IF) sampling the channel estimation is sensitive to the DC offset and IQ gain/phase imbalance of the RF transceiver. This note shows, for a common class of channel estimators, that the sensitivity depends on the selected training sequence code. This sensitivity can become significant for 8PSK modulation.