The purpose of wireless networks is to provide wireless access to the fixed network (PSTN)

The most common model used for wireless networks is uniform hexagonal shape areas

A base station with omni-directional antenna is placed in the middle of the cell

The design is done in two steps Area coverage planning Channel (Frequency) allocation

An efficient way of managing the radio spectrum is by reusing the same frequency, within the service area, as often as possible

This frequency reuse is possible thanks to the propagation properties of radio waves

For hexagonal cells, the number of cells in the cluster is given by

NRD

NJIJIJIN

3

,...}21,19,16,12,9,7,4,3,1{...4,3,2,1,),(22

Frequency reuse pattern for N=3

Frequency reuse pattern for N=7

Frequency reuse only with a certain distance between the base stations

Standard model using 7 frequencies:

Note pattern for repeating the same color: one north, two east-north

Fixed Channel Allocation

Fixed Channel Allocation (FCA) systems allocate specific channels to specific cells

This allocation is static and can not be changed For efficient operation, FCA systems typically

allocate channels in a manner that maximizes frequency reuse

The distance between cells using the same channel is the minimum reuse distance for that system

Disadvantage: The available channels are not being used efficiently

Dynamic Channel Allocation

Dynamic Channel Allocation (DCA) attempts to alleviate the problem mentioned for FCA systems when offered traffic is non-uniform

In DCA systems, no set relationship exists between channels and cells

Problems: First, DCA methods typically have a degree of randomness

Secondly, DCA methods often involve complex algorithms for deciding which available channel is most efficient

CDM systems: cell size depends on current load Additional traffic appears as noise to other users If the noise level is too high users drop out of cells