The disclosed subject matter is directed towards a clear channel assessment procedure based on a common preamble, such as for use with 3GPP and IEEE 802.11 technologies, or any other radio technology, including for use in the 6 GHz band. Detection of the common preamble is based on detecting known sequences in signal part, which can be detected without decoding the preamble's payload (channel) part to determine an ongoing transmission's duration. If an ongoing transmission is detected, subsequent energy detection monitoring is performed to determine when transmission ends, which can use a different energy detection threshold from what is used in the initial clear channel assessment's energy detection. The technology facilitates the usage of different sampling rates by different radio technologies that work concurrently in the same unlicensed band, by correlating a received preamble with a stored preamble that accounts for deterministic distortions arising from the different sampling rates.