Indoor Radio Planning: A Practical Guide for GSM, DCS, UMTS, HSPA and LTE, Second Edition

6.1 Erlang, the Traffic Measurement

Agner Krarup Erlang (Figure 6.1) was born in Denmark in 1878 (close to where I live). 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.

Figure 6.1 The Danish statistician Agner Krarup Erlang

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.

6.1.1 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.

Erlang Example

If a group of 20 users makes 60 calls in 1 h, and each call had an average duration of 3 ...