In TDMA such as GSM, it is possible to transmit simultaneously by a common frequency to each base station. In this case, the frequency for a general communication is different in each base station while the frequency for the transmission simultaneously is a common frequency to the base station.

In TDMA such as GSM,  when cellular entrepreneurs transmit simultaneously by a common frequency to each base station, specific frequencies other than the frequency allocated in the two way communication are set to the transmission simultaneously. When cellular entrepreneurs transmit the frequency set to the transmission simultaneously, the means to take synchronization so as not to cause the mutual interference between each base station is needed.   It semi-synchronizes by the offset transmission as a means to take synchronization.  There are several synchronization methods using GPS.

Note 1.   What is one frequency for the transmission simultaneously? It is not meant that all information is sent by one frequency.   It means the number of frequencies used when certain information is transmitted in the band allocated to the cellular phone entrepreneur.

Note 2.   CDMA manual in English use word of "a frequency reuse factor of 1" in such a case.

Note 3.   When cellular entrepreneurs design the base station, engineers of the company was taught that the same wavelength shall not be used for the adjoining area. By the advance in technology, the various technologies that overcome the mutual interference are developed.   Using a separate frequency for the adjoining base station is not a basic condition anymore.