Multiple Access -3.Channel Assignment and Control
For mobile communications based on the cellular system, the assignment of communications channels is conducted from each cell's base station in accordance with traffic requirements. The methods used include the Fixed Channel Assignment (FCA) system that assigns the channels to be used to each cell on a fixed basis in advance, and the Dynamic Channel Assignment (DCA) system that adaptively determines the channels to be assigned for each call by monitoring the actual situation.
In FDMA and TDMA, these systems use these methods either individually or in combination, according to the situation. As CDMA can flexibly deal with traffic fluctuations by code processing only, the FCA system is normally used in CDMA.
Because of limits on the bandwidth that can be used for mobile communications, the basic approach is to assign an idle channel from among those available in accordance with the occurrence of a call. The technology used is called multi-channel access. However, as mobile stations' transmission usage is normally random, there are cases in which signals from multiple mobile stations collide. This leads to the need for random access control. While various methods have been proposed for controlling random access, busy-tone control or the combination of busy tones and a divided channel reservation system is widely used.
Signal configuration for an idle line control random access scheme with partial echo