Handover

Handover:

Handoff or Handover is the process of transferring a mobile station from one channel or base station to another.

It is defined as a mechanism to hand over the control of a mobile device to the neighboring cell. The core network can perform handovers at various levels of the system architecture.

There are two main reasons for handover in cellular networks. They are:

(i) If the mobile device moves out of the range of one cell, a different base station provides it with a stronger signal.

(ii) If all channels of a base station are busy then the nearby base station can provide service to the device.

Must Read>> Base Station Subsystem (BSS)

Handover is important. It must be efficiently done using different strategies. Different mobile phones can use the same channel and the neighboring cells can use the same frequency bands. There are two types of handovers. They are:

(a) Hard Handover :

• In hard handover, the radio link must be dropped for a small amount of time before it can be taken over by another base station.

• A call that is in progress is redirected not only from a base station to another base station but from current transmit-receive frequency pair to another frequency pair. A break-in call transmission is called a call drop or call cut-off.

• The handover occurs in a few milliseconds. Handover to other cells is needed when the signal strength is low and the error rate is high.

• The GSM systems perform hard handovers.

(b) Soft Handover :

• The 3G CDMA systems support soft handover. The Soft handover indicates a mobile station (MS) at the boundary of two adjacent cells does not suffer call drops because of handover in the boundary region. A mobile can be connected to several base stations simultaneously.

Must Read>> Mobile Station