Cellular mobile systems were implemented to improve the utilization of spectrum efficiency. When traffic density starts to build up and frequency channels F_i in each cell C_i cannot provide enough mobile calls the original cell can be split into smaller cells. Normally the new radius is one half the original radius. Thus the new cell area becomes 1/4^th the old cell area. Thus each new cell carries the same maximum traffic load of the old cell. Thus the new traffic of the station becomes 4 times the old traffic. There are two kinds of cell-splitting techniques:

a.       Permanent splitting:  Each new split cell is planned ahead of time with consideration of the number of channels, transmitted power, assigned frequencies, selection of the cell-site and traffic load consideration. When the installation is ready the actual service cut-over is set at the lowest traffic point, usually at midnight on a weekend. The frequency assignment follows the rule based on frequency reuse distance ratio q.

b.     Dynamic splitting: This scheme is based on utilizing the allocated spectrum efficiency in real time. Cell splitting proceeds gradually over a cellular operating system to prevent dropped calls.  Suppose there exist a communication line between two stations 1A and 2A. If the area between two 2A sectors requires increased traffic capacity, then midpoint between two old 2A sectors is named as “new 2A”. The new 1A is found by rotating the old 1A-2A line clockwise by 120⁰. Then the orientation of new set of seven split cells is determined. To maintain service for the ongoing calls while doing the cell splitting, the channels assigned to the old 2A sector is separated into two groups: 2A= (2A)’+ (2A)”, where (2A)’ represents the frequency channels used in both new and old cells in small sectors, and (2A)” represents the frequency channels used only in the old cells. At the early splitting stage only a few channels are in (2A)’. Gradually more channels will be transferred from (2A)” to (2A)’. When no channel remains in (2A)” the cell-splitting procedure will be completed.

The size of splitting cells is dependent on two factors: 1) The radio aspect- The size of the cell is dependent on how well the coverage pattern can be controlled and how accurately vehicle location can be known and 2) The capacity of the switching processor- The smaller the cells the more hand offs will occur and more cell splitting process is required. Thus the capacity of the switching processor has larger role than the coverage area of small cells.

When cell splitting occurs to maintain the frequency reuse distance ratio q in a system the splitting takes into account the following considerations: a) Splitting of cells causes an unbalanced situation in power and frequency reuse distance. Hence it becomes necessary to split small cells in the neighboring cells. Thus cell splitting affects the neighboring cells. b) Certain channels are to be used as barriers. A group of frequencies are used only in cells located between the large cells on one side and the small cells on the other side. This eliminates the interference in transmission from large cells to small cells.