Answer:

Handoff:

• The act of transferring support of a mobile from one base station to another is termed handoff. Handoff occurs when a call has to be handed off from one cell to another as the user moves between cells.

​There are various categories of handoffs which are encapsulated below:

Soft handoff:

• In soft handoff, a moving user can receive and combine signals from two or more base stations at the same time. During this handoff, a mobile station is in the overlapping cell coverage area of two sectors belonging to two different base stations. The communications between mobile station and base station occur simultaneously through two air interface channels from each base station separately. Both signals are received at the mobile station by maximal combining Rake processing. It occurs in about 20–40% of calls. This handoff is an integral part of CDMA design. Soft handoff needs less power which reduces intrusion and increases capacity.

Softer handoff:

• In this process, the base station transmits through one sector but receives from more than one sector. In this case, the mobile station has active uplink radio connections with the network through more than one sector belonging to the same base station.

Soft Softer handoff:

• When soft and softer handoffs occur simultaneously, then this soft-softer handoff process is usually used.

Hard handoff:

• A process if the old connection is terminated before making the new connection, it is called a hard handoff. The hard handoff can be further divided into intra frequency and inter frequency hard handoffs.

Inter-frequency hard handoff:

• In this process, the carrier frequency of the new radio access is different from the old carrier frequency to which the mobile station was connected.

Intra-frequency handoff:

• In this process, the new carrier frequency to which the mobile station is accessed after handoff process is the same as the original carrier.

Intra-BTS handover:

• This form of GSM handover occurs if it is needed to change the frequency or slot being used by a mobile because of intrusion or other reasons. In this form of GSM handover, the mobile remains attached to the same base station transceiver, but change the channel or slot.

Inter-BTS Intra BSC handover: 

• This form of GSM handover or GSM handoff occurs when the mobile moves out of the coverage area of one BTS but into another controlled by the same BSC. In this instance the BSC is able to perform the handover and it assigns a new channel and slot to the mobile before releasing the old BTS from communicating with the mobile.

Inter-BSC handover:

• When the mobile moves out of the range of cells controlled by one BSC, a more involved form of handover has to be performed handing over not only from one BTS to another but one BSC to another. For this the handover is controlled by the MSC.

Inter-MSC handover: 

• This form of handover occurs when changing between networks. The two MSCs involved negotiate to control the handover.