In each cell it must be ensured that the connection between one base station and a higher number of mobile stations in each period of time might be established and realized. For this purpose the methods of the multiple access are used.
A dedicated frequency band for a given radio system can be accessed by one of the following methods:
Above mentioned basic access methods are very often combined in practical applications (for example FDMA and TDMA).
The assigned frequency bands can be accessed in either Time Division Duplex (TDD) or Frequency Division Duplex (FDD) way. In case of TDD, the transmission in downlink (transmission to user) and in uplink (transmission from user) directions are separated in time domain but, the same frequency is assigned to both transmission direction. This means that the frequency is better utilized. On the other hand, the issue here is the high requirements on synchronization. In case of FDD, both transmission directions are separated in frequency, but the transmission/reception is simultaneous. The main disadvantage of this approach is that two antennas, one for receiving and one for transmitting, are necessary to be used. In most of countries, FDD duplex is utilized for its less complex implementation