RF Power Amplifier, 2nd Edition

1.16 Multiple-Access Techniques

In multiple-access communications systems, information signals are sent simultaneously over the same channel. Cellular wireless mobile communications use the following multiple-access techniques to allow simultaneous communication among multiple transceivers:

• Time-division multiple access (TDMA).
• Frequency-division multiple access (FDMA).
• Code-division multiple access (CDMA).

In the TDMA, the same frequency band is used by all the users but at different time intervals. Each digitally coded signal is transmitted only during preselected time intervals, called the time slots . During every time frame , each user has access to the channel for a time slot . The signals transmitted from different users do not interfere with each other in the time domain.

In the FDMA, a frequency band is divided into many channels. The carrier frequency determines the channel frequency. Each baseband signal is transmitted at a different carrier frequency. One channel is assigned to each user for a connection period. After the connection is completed, the channel becomes available ...