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Frequency Planning. The dilemma behind frequency planning is to provide needed capacity and coverage within a given frequency band Interference is caused when two network cells use the same channel too close to each other; more precisely this is a co-channel interference situation.
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The dilemma behind frequency planning is to provide needed capacity and coverage within a given frequency band • Interference is caused when two network cells use the same channel too closeto each other; more precisely this is a co-channelinterference situation
The frequency re-use rate is simplest to explain using a hexagonal model. • The cell shapes are different and cells do not have equal sizes. Therefore the frequency re-use rateis not a constant throughout the network, but varies from one place to another.
The available frequency band and the capacity plan give boundary conditionsfor the largest possible frequency re-use rate
The following is an example of the connection between frequency and capacity planning. If the operatorbandwidth is 6 MHz, the number of channels is 30 • the capacity of the network with 100 BTSs and 600 cells can be calculated as
The re-use pattern factor K can becalculated geometrically: • the re-use distance gives
To enable maximum capacity, the parameter K should be optimised to be as small as possible whenthe system is operational and fulfilling the planning requirements. • Parameter q is the co-channel interferencereduction factor
The co-channel interference can be calculated as the ratio of the carrier (C) to the sum of the interferers(In ):
where N is the number of interferers and the received carrier is • where d describes the distance between the transmitter and the receiver, α is a constant and γ is thepropagation path loss slope
Interference for the first tier is • and is simplified for the first tier, as all the interferers in the same tier are equally strong:
The C/I relation can be to improve the network using the following methods: decrease transmissionpower, fine tuning of the antenna azimuth and antenna down-tilting. • All the methods have an impacton the cell coverage area and therefore they need to be used carefully, keeping in mind the coverage targets.
The spectrum efficiency techniques, as indicated by their name, provide ways to utilise the frequenciesmore effectively. This is critical in network planning due to the limited resources, i.e. limited frequencies. • More effective usage of the frequency band is possible without increasing the interference level. In thisway the network capacity increases.
