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2.2 Technology and eąuipment

LGC Wireless, Inc. [3] has been chosen as the supplier for the GSM network eąuipment. In Table 2 you can see the specifications of their Ultra WAVE rangę of BTSs, BSCs, MSCs and HLRs (Home Location Register is sold together with MSC). The eąuipment costs are estimated sińce nonę of the yendors was willing to provide their prices to this project.

Component	Capacity	Connections	Cost (NOK)
BTS	69.08 Erlangs	84 channels	400 000
BSC	466 Erlangs	31 BTSs	1 800 000
MSC	2 500 Erlangs	256 BSCs	4 500 000
HLR		100 000 subscribers

Table 2: GSM network eąuipment specifications from LGC Wireless.

GSM reąuires a signal-to-interference ratio (SIR) of at least 14 dB. GSM channel bandwidth is 200 kHz and by employing Time Division Multiple Access (TDMA) each channel can carry 8 full-rate voice channels. We will use a freąuency reuse factor of N = 4. Roli out time (ROT) is estimated to 4 years, in which no additional eąuipment is expected to be installed. This means that the capacity will remain constant during this time. We also aim for a grade of service (GoS) of 1%. This means that in average 1 cali is blocked for every 100 cali attempts.

3 Calculations

3.1 Omni directional antenna

First we must find out if we should use omni directional or sectored antennas. For omni directional antennas the following formula for SIR applies

SIR = 10 log

i

(i)

where N is the freąuency reuse factor, 7 is the path loss slope and j is the number of surrounding cells. For a hexagonal celi layout, as seen in Figurę 4 on the following page, j is 6.

To simplify (1) we replace y/SN with q using the following eąuation

(2)

r

where d is the distance between the center of two cells using the same freąuency and r is the radius of a celi. When inserting (2) into (1) we get the

4