Spectral efficiency   =  (25 X 4 X 3) / (6)   X   (No of sites / sq. kms) 

=  50 X No of sites 

For a packing density range of 3 ~ 5, the spectral efficiency lies between 150 

to 250. If a loading factor of 0.8 is also taken into account, the effective 

efficiency achievable would be between 120 and 200. These levels are 

comparable with the best and highly loaded GSM networks practically in 

place.  However, it is important to note that on a single layer basis CDMA 

provides higher efficiency.  

CDMA networks are generally limited by inter site distances. Inter site 

distance of 500 metres

6

 (or nominal cell radius of 250 metres) is specified as 

the minimum inter site distance to be used in planning CDMA 2000 networks. 

The planning of CDMA networks is based on meeting a required value of 

E

B

/No to provide a required bit error rate.  E

B

/No is influenced by all the 

interferers in the same sector and from other sectors.   

3.2.2.2 

Estimating efficiencies of present day GSM and CDMA 

networks and their comparison with theoretical efficiencies. 

A questionnaire was sent to all operators requesting specific information on 

the network performance.  Cell traffic, installed capacity and cell blocking 

rates supplied by the operators were used in determining the spectrum 

utilisation.  For each network, the area of around 25 Sq. Km in the highest 

traffic demand location was identified.  Within this area a cluster of more than 

9 cells was selected for the evaluation.  For some networks, an area of 

around 8 Sq. Km within this cluster was also identified for evaluation.  The 

areas of 25 Kmsq and 8 Kmsq are representative average and peak traffic 

within the selected areas and were chosen after a sensitivity of cell traffic and 

cell dimensions. 

The following data for each cell was used: 

The radio spectrum allocation for the network 

Cell identity 

Carried traffic in cell 

Installed capacity of cell 

Blocking rate 

Nominal cell area   obtained from data supplied by operator or 

estimated from scale map of most likely server. 

From this data the following was calculated: 

6

 This figure comes from modelling, simulation and field measurements done by equipment 

vendors.  If smaller cells are deployed then the cost of the infrastructure increases and the 

gain in terms of additional capacity is small because of the need to balance transmission 

powers and minimise the impact of interference. 

27