The Constant Tone Extension (CTE) is an unmodulated carrier consisting of unwhitened, modulated 1's where the receiver samples a waveform offset of 250 kHz from the channel center in 1 Mbps mode, and in 2 Mbps mode samples a waveform offset of 500 kHz from the channel center.
However, there is generally a frequency offset between the transmitter and receiver. This frequency offset can be calculated from the IQ samples in the reference period and be compensated by software for all IQ samples.
The frequency offset estimate can be refined by switching back to the reference antenna in one or several later switch slots.