7 - Indira Gandhi Centre for Atomic Research

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3. Cellular System Architecture
Figure 1: Basic Mobile Telephone Service Network
Because the amount of frequency spectrum available for mobile cellular use was limited,
efficient use of required frequencies was needed. Provisioning for each region is planned
accordingly that includes cell, clusters, frequency reuse, cell
splitting and handoff.
3.1 Cells and Clusters
A cell is the basic geographical unit covered by cellular radio antennas. This
is represented in the form of simple hexagon. A cluster is a group of cells. No
channels are reused within a cluster. Cluster is usually seven.
3.2 Frequency Reuse
Because only a small number of radio channel frequencies were
available, the solution industry adopted was called frequency
planning or frequency reuse. The concept of frequency reuse is
based on assigning to each cell a group of radio channels used
within a small geographical area. Cells are assigned a group of
channels that is completely different from neighbouring cells.
105 Figure 3: Cell Splitting
Fig. 2: Frequency Reuse
The coverage area of cells are called footprint. This footprint is limited by a boundary so
that the same group of channels can be used in different cell that are far enough away from
each other so that their frequencies do not interfere. Cells with the same number have set
of frequencies. Here the number of available frequencies is seven, the frequency reuse
factor is 1/7. Each cell is using 1/7 of available cellular channels.
3.3 Cell Splitting
Economic considerations made the
concept of creating full systems with
many small areas impractical. To
overcome this difficulty, the idea of cell
splitting was developed. As a service
area becomes full of users, a single area
is split into smaller ones. Urban centers