Handoff in mobile communication:-
Handoff is the process of changing the channel associated with current connection while a call is in progress. Handoff is often initiated either by crossing a cell boundary or by a deterioration in quality of signal in current channel.
Process of hand off:-
Handoff must be performed successfully and as infrequently as possible and be imperceptible to the users. So in order to meet these requirements, system designers must specify optimum signal level at which to initiate a hand off. Once a particular signal level is set standard as the minimum usable for proper voice quality at the base station receiver, a slightly stronger signal level is used as threshold at which handoff is made.
So the margin = Pr handoff – Pr minimum usable must be kept as optimum as possible. Because too large value of can burden the MSC by unnecessary handoffs or too small value may be insufficient time to complete a handoff before call is lost due to weak signal conditions.
The time over which a call may be maintained within a cell, without handoff, is called dwell time.
Handoff in first generation:-
Signal strength measurements are made by base stations and supervised by MSC.
Handoff in second generation:-
In second generation handoff decision are mobile assisted. In mobile assisted handoff every mobile station measures the received power from surrounding base stations and continually reports the results of the measurement for base station.