Agner Krarup Erlang was born in Denmark in 1878. He
was a pioneer in the theory of telecommunications traffic and he proposed a formula to
calculate the percentages of users served by a telephone exchange that would have to wait
when attempting to place a call. He could calculate how many lines were needed to service a
specific number of users, with a specific availability of lines for the users.
A. K. Erlang published the result of his study in 1909: The Theory of Probabilities and Telephone Conversations. Erlang is now recognized worldwide for this work, and his formula is accepted as the standard reference for calculating telecommunication traffic load. The unit we use for telephony traffic load is ‘Erlang’ or E. Erlang worked for the Copenhagen Telephone Company (KTAS) for many years, until his death in 1929.
An Erlang is a unit of telecommunications traffic measurement. One Erlang is the continuous use of one voice channel. In call minutes, one Erlang is 60 min/h, 1440 call min/24 h. In practice, when doing mobile capacity calculations, an Erlang is used to describe the total traffic volume of 1 h, for a specific cell.
Here is Erlang Example:
If a group of 20 users makes 60 calls in 1 h, and each call had an average duration of 3 min, then we can calculate the traffic in Erlangs:
Knowing the number of users (20), we can calculate the load per user:
Then, if we have the same type of users inside a building with 350 mobile users, we can calculate what capacity we need:
Yet what do these 52.5 Erlangs mean in terms of number of voice channels needed? Do we then need 53 channels in order to service the users? Not exactly. It depends on the user behavior: how the calls are distributed and how many calls are allowed to be rejected in the cell. In theory – if you do not want any rejected calls due to lack of capacity, you should provide 350 channels for the 350 users, and then you would have 100% capacity for all users at any given time. However, it is not likely that all users will call at the same time, and users will accept a certain level of call rejection due to lack of capacity. To estimate the number of channels needed, we need to look at maximum call blocking we allow in the busiest hour during the day.
A. K. Erlang published the result of his study in 1909: The Theory of Probabilities and Telephone Conversations. Erlang is now recognized worldwide for this work, and his formula is accepted as the standard reference for calculating telecommunication traffic load. The unit we use for telephony traffic load is ‘Erlang’ or E. Erlang worked for the Copenhagen Telephone Company (KTAS) for many years, until his death in 1929.
What is One Erlang?
An Erlang is a unit of telecommunications traffic measurement. One Erlang is the continuous use of one voice channel. In call minutes, one Erlang is 60 min/h, 1440 call min/24 h. In practice, when doing mobile capacity calculations, an Erlang is used to describe the total traffic volume of 1 h, for a specific cell.
How to calculate GSM Capacity Station in Radio Network Planning?
Here is Erlang Example:
If a group of 20 users makes 60 calls in 1 h, and each call had an average duration of 3 min, then we can calculate the traffic in Erlangs:
- total minutes of traffic in 1 h = duration x number of calls
- total minutes of traffic in 1 h = 3 x 60
- total minutes of traffic in 1 h = 180 min
- Erlangs = 180/60 = 3E
Knowing the number of users (20), we can calculate the load per user:
- user load = total load/number of users
- user load = 3/20 = 0.115 E = 150mE per user
Then, if we have the same type of users inside a building with 350 mobile users, we can calculate what capacity we need:
- total load = number of users x load per user
- total load = 350 x 0.150 = 52.5E
Yet what do these 52.5 Erlangs mean in terms of number of voice channels needed? Do we then need 53 channels in order to service the users? Not exactly. It depends on the user behavior: how the calls are distributed and how many calls are allowed to be rejected in the cell. In theory – if you do not want any rejected calls due to lack of capacity, you should provide 350 channels for the 350 users, and then you would have 100% capacity for all users at any given time. However, it is not likely that all users will call at the same time, and users will accept a certain level of call rejection due to lack of capacity. To estimate the number of channels needed, we need to look at maximum call blocking we allow in the busiest hour during the day.
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