# Handoff If a user is moving from one cell, they will move from one [base station](Base%20station.md) to another. It is a switching from one cell/base-station to another cell/base-station. Talking on the phone while moving, you will trigger the handover process.  ## How often do you perform handoff? Depends on cell size, mobile speed and others. If you are moving too fast, might not work ## Types of handoff ### Hard handoff Break before make. Break the previous connection before starting a new connection  For [GSM](Global%20System%20for%20Mobile.md) and other switching-frequency type systems. Break the connection between the frequencies. ### Soft Handoff Make before break. Gradual switching of [base station](Base%20station.md) (or sectors) but not frequency channel (only in [CDMA](Code%20division%20multiple%20access.md)). You might be talking to two [base stations](Base%20station.md) at once. The likelihood that both drop your call is much lower. You can calculate the probability of improving on error - it's alot! ## How to decide when to hand over? ### Ping-Pong effect #### In the middle? This will cause ping-ponging if the user is exactly in between (due to wireless fluctuation). Better to have a buffer. #### When P(new cell) - P(old cell) is large enough ensure the difference in power is substantial. #### Only when P(new cell) > P(current cell) for long enough may avoid the fluctuating effects #### A combination Get the best of both. ## Who decides the handoff? The [base station](Base%20station.md) makes the call. The [base station](Base%20station.md) has the network level information. Need to know if the other [base station](Base%20station.md) has available channels. ### Analogue system [BS](Base%20station.md) only by measuring reverse link signal strength ### Digital (New) [Mobile assisted handoff](Mobile%20assisted%20handoff.md) ## What if the new cell has no frequency channel available? [Guard channel](Guard%20channel.md) [^1] # References [^1]: