Degradation of Service Modelling and Investigation in WCDMA Mobile Communications

Erlang capacity is the average traffic tolerated by the network that is hard limited by a certain number of servers, the active user capacity, at a certain acceptable blocking percentage. In WCDMA, contrary to GSM or analogue AMPS, interference limits the active user capacity which means that we don’t have a hard limit on the number of users and therefore obtaining the Erlang traffic capacity is not a direct problem. However, a model for WCDMA active user capacity boundaries, on the uplink, is obtained which relates the maximum capacity of any service class to the number of users in other service classes. This enables the usage of Erlang B formula to calculate the blocking on a service by service basis. In this work, an overall performance parameter, Degradation of Service, DoS, is defined as a linear combination of all blocking percentages for the different services and is studied for the points on the flexible active capacity boundary. It is shown that this parameter can be useful for selecting asuitable operating point on the boundary for a given traffic as well as in the case of relaxed WCDMA cell operating below the boundary.