Telephones and Cell Phones with Radio - Channel Access Schemes

摘要

Time-division multiplexing (TDM) is one of the many applications of sampling in communication systems. TDM is often used to transmit several signals simultaneously over a single channel. Figure below describe the scheme of TDM. Each input message signal is first restricted in bandwidth by a low-pass filter, to remove frequencies that are not essential to an adequate signal operation. After that, the low-pass filter outputs are applied to a commutator that is usually implemented by using electronic switching circuit. Each signal is sampled at the Nyquist rate or higher. In reality, when the sampling rate is equal to 1.1 times the Nyquist rate, it is good enough to avoid aliasing. The samples are interleaved, and a single composite signal consisting of all interleaved pulses is transmitted over the channel.