The umbrella cell concept in cellular system is the system, where the same radio system is used for microcells and overlaying macro-cells. It is the most promising strategy for deploying microcell service to cope with increased portable radio subscribers. Although the cellular concept clearly provides additional capacity through the addition of cell sites, in practice it is difficult for cellular device providers to obtain new physical cell site locations in urban areas. Ordinances and other non-technical barriers often make it more attractive for a cellular provider to install additional channels and base stations at the same physical location of an existing cell, rather than find new site locations.
By using different antenna heights and power levels, it is possible to provide “large” and “small” cells which are co-located at a single location. This technique is called the Umbrella cell approach. It is used to provide large area coverage to high speed users while providing small area coverage to users travelling at low speeds. Fig illustrates an umbrella cell which is co-located with some smaller microcells. It also ensures that the number of handoffs is minimized for high speed users and provides additional microcell channels for pedestrian users.
Umbrella cell approach
If a 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 co-located microcell, without MSC invention.