Homework SourseA cellular radio system using a cluster size of 4 have been
A cellular radio system using a cluster size of 4 have been allocated 160 channels. The average call duration is 180 seconds and there is one call in every 12 minutes. The system is designed to maintain a grade of service of GOS=2%. By stating your assumption, (i) calculate the theoretical maximum number of subscriber that can be served at one time by the system [124 users] (ii) calculate the maximum number of subscribers that can be supported by the system using FCA, DCA and HCA (30% of channel being shared) and [496 users, 586 users, 502 users] (iii) compare the maximum number of subscribers that can served by the system using channel sharing and channel borrowing if the two adjacent cells agree to share or borrow/lend 30% of their channels [531 users, 498 users]
Solution
Probability of blocking(GOS) = 2% = 0.02
Number of channels per cell used in the system C = 160/4 =40
Traffic intensity per user, Au = H = 3× (1/12) = 0.25 Erlangs (= avg call duration)
For GOS = 0.02 and C = 40, from the Erlang B chart,
the total offered traffic( A)= 30.997 Erlangs.
Therefore, the number of users that can be supported per cell is
U = A/ Au = 30.997/0.25 = 123.98124
Using FCA, maximum number of users = 124*4=496
using DCA, maximum number of users =124 + 0.3*(496-124) +124 +0.3*(496-248) +124 +0.3*(496-372) =595.2596
