Erlang B Chart

Erlang B ExampleGiven :

- Total number of channels in a cellular cluster = 112

- GOS = 2 %

- Average call duration = 2 minutes

Calculate

- the traffic intensity and

- the number of calls per hour

that can be serviced in a cluster, when :

a) The cluster size is 7 cells [Ans. 9.83 x 7, 2064]

b) The cluster size is 4 cells [Ans. 20.2 x 4, 2424]

Note : 4-cell cluster has higher Trunking Efficiency than 7-cell cluster,

i.e. it can support more calls/hr for same GOS and number of channels.

Erlang C Formula (Blocked Calls Delayed)

With C trunked radio channels, blocked calls queued:

Pr( )>Delay 0 DC

AC

AC ..!C 1

A

C= 0

C 1

k

Ak

!k

Recursive Evaluation :

DC

.C BC

.BC

C A

Average Delay for All Calls :

TAv.DC

H

C A

Pr ( )>wait t .Dc exp .C A

Ht

A

Erlang C Chart

Erlang C Example

Given :

- Total number of channels in a cell = 15

- GOS = Prob (delay > 0) = 5 %

- Traffic Intensity per User = 0.029 Erlangs

- Call requests per user = 1 call/hr

Calculate

a) The traffic intensity for the cell [ 8.8 ]

b) The number of users [303]

c) The average holding time [104.4 s]

d) The average delay time for all calls [0.84 s]

e) Prob(wait > 10s) [2.76%]