Q16Principle of Electronic Communication

Cellular Concept and Frequency Reuse

The cellular concept divides a large geographic coverage area into many small hexagonal cells, each served by its own low-power base station, rather than using one single high-power transmitter to cover the entire area. Since each cell only needs a modest transmit power to cover its own small area, the same set of frequency channels can be reused simultaneously in other cells located far enough away that their mutual co-channel interference remains acceptably low - this is the essence of frequency reuse, and it is what allows a cellular network to serve a very large number of simultaneous users within a limited total allocated spectrum, since the same limited pool of frequency channels is reused repeatedly across many geographically separated cells rather than being permanently and exclusively assigned to only one location. Cells are grouped into reuse clusters (commonly clusters of size 7), where all channels in the allocated spectrum are divided among the cells of one cluster, and this same channel allocation pattern is then repeated in every subsequent cluster across the coverage area, with cell splitting (subdividing cells into smaller cells as user density grows) allowing capacity to be further increased in high-demand areas without requiring additional spectrum.

As a mobile user moves from one cell toward the edge of its coverage area and into a neighboring cell, the network performs a handoff (handover), transferring the ongoing call or data session from the base station of the departing cell to the base station of the new cell without interrupting the connection - reliable handoff, together with frequency reuse itself, is what allows a cellular network to provide continuous, uninterrupted service to users moving across a wide geographic area while still gaining the enormous capacity benefit of reusing the same limited spectrum repeatedly throughout the coverage region.