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Using the following data for a GSM 1800 network calculate

(I) average busy hour traffic per subscriber. (2) Traffic capacity per BTS (3) required member of base stations per zone (4) The hexagonal cell radius for the zone. Subscriber usage per month = 150 minutes Days per month = 4 Busy hour per day = 06 Allocated spectrum = 4.8 MHz Frequency raise plan = 4/12 RF channel with = 200 KHZ (full rate) Present number of subscribers in the zone = 50,000 Subscriber growth = 5% per year Area of the zone = 5090 km2 Initial installation bused on a four year design capacity of a base station (transceiver) (BTS) = 30 Erlangs Traffic capacity of a GSM cell at 2% Gos (using Erlang B table = 8.2 Erlangs

Mumbai University > Electronics and Telecommunication > Sem8 > Wireless Networks

Marks: 10 M

Year: May 2016

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## Solution:

Erlangs per subscriber = ${\frac {150}{24 X 6 X 60}}$ = 0.0174

Total no. of RF carriers = ${\frac {4.8 X 1000}{200}}$ = 24

RF carriers per cell with a reuse factor of 4 = ${\frac{24}{4 X 3}}$ = 2 = (3 cells per BTS)

Traffic channels per cell (assuming two control channels per cell) = (2 X 8) - 2 = 14

Traffic capacity of a GSM cell at 2% GoS `(using Earlang-B table) = 8.2 Erlangs

Traffic per BTS = 8.2 X 3 = 24.6 < 30 Erlangs

Maximum number of subscriber per BTS = ${\frac{24.6}{0.0174}} \approx$ 1414

Number of Subscriber at initial installation = $50,000 (1+ 0.05)^4$ = 60,775

Number of BTSs in a zone = ${\frac {60,775}{1414}} \approx$ {43}

Average hexagonal cell radius = $\sqrt{\frac{500}{43 X 2.6}}$ = 2.1 Km

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Explain this in details : 1) RF carriers per cell with a reuse factor of 4 ...WHY ONLY 4 IS IT ASSUMPTION?? From where 24/4*3 =2 (3 cells per BTS) came?

2) TRAFFIC/BTS =8.2*3=24.6 ....WHERE 3 CAME FROM?

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