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In the wireless telecom sector the given geography, of any place, is divided into cells. These cells are facilitated with a portion of the net frequency spectrum, which is allocated by respective countries. They are also known as channels for performing communication between users.
Channels can be allocated to cells through fixed channel allocation, dynamic channel allocation, and hybrid channel allocation. Hybrid channel allocation is a combination of both fixed and dynamic channel allocations.
Difference between fixed and dynamic channels
Fixed channel allocation (FCA)
As the name suggests, fixed channel allocation is a type of channel allocation in which static or fixed channels are allocated to cells, which cannot be changed. Due to its fixed feature, FCA assign channels to respective cells in a manner that maximize frequency reuse. One of the drawbacks of fixed channel allocation is the state of a cell when all channels are occupied. In that case, if the user is trying to make a call in that cell, he/she will be blocked from calling.
FCA is fixed, so there is no use of complex algorithms for allocation of the channels. FCA is not so complex, so it is less costly to deploy as compared to dynamic channel allocation. In FCA after the termination of the call by the user, the free frequency channel remains in the cell, the scenario is quite different in case of dynamic channel allocation. The role of MSC (Mobile Station Centre) in FCA is quite low, as there is no management of free channels due to its fixed nature.
Dynamic channel allocation (DCA)
DCA is another type of channel allocation technique in the wireless medium. In DCA the allocated channels to cells do not permanently belong to the respective cells, as the user call request first goes to BS (base station) which sends the request to MSC (mobile station centre) for the allocation of the voice channel, and the channel is then allocated by MSC. DCA also resolve the issue of blocking phone calls, as in case of more users in a cell, more channels are allocated to that cell, and vice versa.
As for dynamic allocation and the identification of effective channel, it uses a complex algorithm. DCA is quite costly, which is due to its complex nature and requirement for a lot of computation power in real-time. In DCA, after the termination of the call from a user, the free channel moves back to MSC for further allocation. In DCA, MSC has quite a bigger role as compared to FCA, as MSC is responsible for allocation of channels to cells, and it also bears more signalling load than FCA.