# The process of transferring a cell from one best station to another when our users radio signal becomes weaker at the first and strongest at the second best station."Weaker" & "Stronger" is a certified by a single threshold level, which is above the minimum signal level for acceptable voice communication.
- Selecting the threshold level is critical to ensure:
• unnecessary handoffs do not occur
•call dropping does not occur
- minimum acceptable signal level is between 90dbm &100dbm, Delta which is 0 to 6dbm.
- delta cannot be too small or too large, unnecessary handoff which burden the MSC
may occur,&if Delta to small there may be insufficient time to complete the the handoff before a cell is loss due to weak signal conditions. 
- in diagram of improper handoff it is shown that handoff is not made and the signal drops below the minimum acceptable level to keep the channel active. This dropped events happens when excessive time is taken by MSC to assign handoff or when Delta is very small.
- to decide when to handoff it is important to ensure that the drop in signal level is not due to the momentary fading but it is due to mobile moving away from best station.
- in order to ensure that bese station monitors the signal level for a certain period of time before handoff is made.
 


# there are four types of handoff
1-hard handoff
2-soft handoff
3-mobile assisted handoff
4-inter system handoff

1- hard handoff:
-frequency channels are taken back by the order base station before new connection is established.
-this is break before make type of handoff.in this frequency channels are utilised properly but chances of drops are more.

2-soft handoff:
-frequency channels are taken back by the order bese station after new connection is established.
-this is break after make type of handoff. This is reliable but frequency channels are not utilised properly.

3-mobile assisted handoff:
-in this a mobile scan signal strength of all base station near to it.
-and continuously report the results of this measurement the serving bese station.
-whenever signal strength of it is Karan best station decreases and become less than the power received from the neighbour cells it initiate handoff.

4-intersystem handoff: 
-this hand off occurs when the user moves from one MSC to another MSc.
-i.e. from one cellular system to another cellular system while on a voice call.
-when mobile signal become weak in a given cell and the MSc cannot find another cell with in its system to which it can transfer the call in progress intersystem handoff is implemented.