All multiple access techniques depend on the adoption of digital technology. Digital technology is now the standard for the public telephone system where all analog calls are converted to digital form for transmission over the backbone. Digital has a number of advantages over analog transmission:
- It economizes on bandwidth.
- It allows easy integration with personal communication systems (PCS) devices.
- It maintains superior quality of voice transmission over long distances.
- It is difficult to decode.
- It can use lower average transmitter power.
- It enables smaller and less expensive individual receivers and transmitters.
- It offers voice privacy.
Frequency Division Multiple Access (FDMA)
TDMA is basically analog’s FDMA with a time-sharing component built into the system. FDMA allocates a single channel to one user at a time (see Figure 1). If the transmission path deteriorates, the controller switches the system to another channel. Although technically simple to implement, FDMA is wasteful of bandwidth: the channel is assigned to a single conversation whether or not somebody is speaking. Moreover, it cannot handle alternate forms of data, only voice transmissions.
Figure 1. FDMA
