 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

 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