A method and a device in communication nodes used for wireless communications. A communication node receives first information, transmits a first radio signal, and monitors a first-type signaling in a first time window. Wherein an end time for a transmission of the first radio signal is used for determining a start of the first time window, and a time-domain resource occupied by the first radio signal is used for determining a first characteristic identity. The first characteristic identity is one of M characteristic identities, M being a positive integer greater than 1, and the first information is used for determining the M characteristic identities. The first-type signaling carries one of the M characteristic identities, and the communication node determines a characteristic identity carried by the first-type signaling out of the M characteristic identities through blind detection. The random access performance is therefore improved.