Handoff:

When a mobile moves into a different cell while a conversation is in progress, the MSC automatically transfers the call to a new channel belonging to the new base station. This process of transferring call to a new base station is called as Hand off.

Types of Hand off

1. Mobile Assisted Hand off
2. Intersystem Hand off
3. Delayed Handoff (Two level Hand off)
4. Queued Handoff
5. Hard hand off
6. Soft hand off
7. Inter system handoff

Hand off Process:

• The term hand-off does not mean a physical change in the assigned channel but rather than a different base station handles the radio communication task.
• Hand-off is a process of automatically transferring the call to a new frequency channel belonging to a new base station, when the cellular mobile phone moves into a different frequency zone so that the conversation can be continued in a new frequency zone without dialing.
• The processing of hand-off is an important task in a cellular telephone system.
• In the hand-off strategies higher priority is given to the hand-off request than the call initiation request in the cellular system.
• The procedure of hand-off should be performed successfully and it should not be repeated frequently.
• The system designers must specify the optimum signal level at which the hand-off is to be initiated.
• The minimum signal level $ Pr_{minimum}$ is first decided for maintaining the call. Then the slightly stronger signal levels used as a hand-off $ Pr_{threshold}$ threshold for maintaining the call.

• The difference between these two levels of the signal is denoted by a symbol delta, $\Delta$ and it is given by,

• $\Delta$= $Pr, _{threshold}- Pr,_{minimum}$

• As the value of delta is very critical, it should not be too small or too large.

• If the value of delta is too small, then the call may lost due to weak signal and if the value of delta is too large ,then unnecessary hand-off may take place at any time.
• Before initiating the hand-off, it is always necessary to ensure that the reduction in the measured signal level is not due to the momentary signal fading and that the mobile is actually moving