By using  different antenna heights [often in the same building or tower] And different power levels, it is possible to provide large and small cells which are co located at a single location. This technique is called umbrella cell approach.

The fig above illustrates an umbrella cell which is co located with some smaller micro cells. Here a separate set of channels are reserved for large umbrella cell. The umbrella cell approach is used to provide large area coverage to high speed users while providing small area coverage to users travelling at low speeds. This ensures that the number of handoffs are minimized for high speed users while at same time additional micro cell channels are provided for pedestrian users.

The speed of each user may be estimated by the base station or MSC by evaluating how rapidly  the short term average signal strength on the RVC changes over time or more sophisticated algorithms may be used to evaluate and partition users.

If a high speed user in large umbrella cell is approaching the base station, and its velocity is rapidly decreasing, the base station may decide to handthe user to the co located micro cell, without MSC intervention.

Umbrella cell approach:

The cell with low traffic speed is called as micro-cells and large high-speed traffic called macro-cells.

A hexagonal cell method is one of the closest approximation of a circle device. It is being typically used for the system.

The smaller cell is grouped and assumed to be under a large cell. This method called as an umbrella cell concept.

It can be used to provide a large area to high-speed users while small area coverage to users that travel at low speeds.

Some advantages of using an umbrella cell concept in cellular technology:

1.Umbrella cell provides a large coverage area to high-speed users.

2.Minimize the number of handoff for high-speed users.

3.Speed estimation can be performed by slop of short term average calculation of receive power.

4.If a high-speed user in large umbrella cell is near the base station and if its velocity is decreasing then the BS stands for can decide whether to hand the user into the co-located micro-cell without the intervention of the mobile switching center (MSC stands for).

5.Provide additional micro-cell channel for pedestrian user.