number of interferers will be between 2 and 6, hence the minimum value k is 

taken for GSM to be 7, however three sectored sites are generally used to 

reduce the cost of radio sites (a cluster of three, three cell sites) so a re use 

factor of 9 is forced by this geometry. For omni directional cells a re use of 7 

is possible. 

Although Spectrum Efficiency calculations using a reuse pattern of 9 seems 

appropriate, it does not take into account the efficiencies achievable by 

deploying  

a) 

Advanced techniques such as Frequency Hopping (FH). The 

objective behind using these techniques is to achieve a reuse as 

close to 1 as possible. Using tighter reuse pattern such as 3 can 

simulate this factor.  

b) 

Multi layered architecture: The use of multi layered architecture 

helps in achieving much higher Spectral efficiency when compared 

with single layered macro architecture. A reuse of 3 has been used 

for micro layers in the methodology. The sensitivity of spectral 

efficiency with the percentage of area covered by micros has been 

carried out. 

A model was constructed in Excel that calculated the Spectrum Utilisation 

against radio frequency available. 

The model had two parts: 

Macro cell layer   input parameters nominal cell radius, 

frequency re use factor. 

Micro cell layer   input parameters, micro cell radius, frequency 

re use, % area of macro cell layer covered by micro cells, 

number of TRX per micro cell. 

The macro cell layer assumed a cluster of cells being equal to the re use 

factor. The model calculated the traffic capacity in Erlang at the macro cell 

layer for available radio spectrum, ranging from 1 MHz to 31 MHz.  The model 

calculated the TCH time slots available for each cell (sector) making an 

allowance for BCCH and SDCCH channels. 

The model assumed: 

Ideal plane earth 

Circular cells of equal radius 

full rate codecs. 

The micro cell layer calculated the traffic capacity of the micro cells based on 

the % area of the macro cells as specified by the input parameter.  The model 

carries out calculation on the assumptions that separate radio spectrum is 

available for the micro layer. 

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