Dynamic half-rate connections in GSM

Dynamic half-rate is an optional feature that allows a Global System for Mobile communication (GSM) cell to switch new incoming half-rate capable calls to half-rate speech coding, when the cell is nearly congested. Since two half-rate speech calls can be put together in one single-time slot, dynamic half-rate has the potential to double the radio capacity of the cell. We develop a new queueing model to analyze the performance of this feature. This model is based on a reduction of the state space, which makes an efficient approximation possible. The developed approximation is a modification of the well-known Kaufman–Roberts recursion. It turns out to be extremely accurate, computationally efficient and approximately insensitive with respect to the holding time distribution. Finally, with the help of this approximation the benefits of dynamic half-rate are shown both by theoretical cases and by data from a field study in the Vodafone-Netherlands network.