Cell Handover Process

Mobile stations are assigned a base station for service, hence a cell (or cluster of cells). This means that when a customer is using a mobile station it must be using a certain channel in a cell. The question that arise is, what happens when the mobile station leaves that particular cell while a call is in progress. Normally this will mean that the mobile station will lose the channel of that cell and one will expect the call to terminate, but this does not happen, that is the call is not terminated. Here is what happens when a mobile station changes cells: There is always a measurement of the field stregth of the received signal to ensure that a communicating mobile station is using the serving base station of that cell. When the mobile stations is around the boundary of cells, the strongest received signal is the one that the mobile station will pick, so the mobile station will be serviced by the base station provinding the stongest field. The call in progress will not terminate because when the mobile station changes base stations it does not lose the connection to the previous base station channel until it has fully established a connection to its new base station channel. Cellular systems are therefore capable of perfoming a change in radio channel as well as in base station during a call in progress. This process is called hand-over [3]

References

[1] J. E. Flood. Telecommunicattions Networks. Institution of Electrical Engineers, London, UK, 1997. chapter 12

[2] P. Key, D. Smith. Teletraffic Engineering in a competetive world. Elsevier Science B.V., Amsterdam Netherlands, 1999. Chapter 1 (Plenary) and 3 (mobile)

[3] Bernhard H. Walke. Mobile Radio Networks: Networking, protocols and traffic perfomance. John Wiley and Sons, LTD West Sussex England, 2002. Chapter 2