Explanation-Capacity of cellular system can be increased using additional cell sites but it is practically difficult to get new physical site in urban areas. Thus instead of new cell sites additional channels and base stations can be installed to increase the capacity.

Different antenna heights and different power levels can be used to provide small and large cells located at single site. This technique is called as umbrella cell approach. This approach is used to provide large area coverage to high speed users while small area coverage to low speed users.

It also ensures additional microcell channels for pedestrian users. The speed of each user is estimated by base station or MSC by evaluating how rapidly the short term average signal strength on RVC changes over time or with sophisticated algorithms.

If high speed user in the large umbrella cell is approaching the base station, and its velocity is rapidly decreasing, the base station may decide to hand the user into the co-located microcell without MSC permission.

This approach is basically used to reduce number of hand off for high speed users.