- As the mobile moves from one cell area to another, an active call must undergo a switch from one channel to another. This process is called a handover or handoff.
- Handoff can be categorized as hard handoff, soft handoff, and softer handoff.
- The hard handoff can be further divided into intra frequency handoff and inter frequency hard handoff.
- During the handoff process, if the old connection is terminated before making the new connection, it is called a hard handoff.
- In the case of an inter frequency hard handoff, the carrier frequency of the new radio access is different from the old carrier frequency to which the MS was connected.
- On the other hand, if the new carrier frequency, to which the MS is accessed after the handoff procedure is the same as the original carrier then it is referred to as an intra-frequency handoff.
- In the 2G TDMA systems, the majority of handoffs are intra frequency hard handoffs.
- Inter frequency handoffs may occur between two different radio access networks.
- For example, between GSM and Universal Mobile Telecommunications Services. In this case, it can also be called intersystem handoff.
- An intersystem handoff is always a type of inter frequency, since different frequencies are used in different systems.
- The handoff is referred to as soft handoff if the new connection is established before the old connection is released.
- In the 3G systems, the majority of handoffs are intra frequency soft handoffs. A soft handoff performed between two sectors belonging to different base stations but not necessarily to the same BSC is called a 2-way soft handoff.
- In softer handoff, the BS transmits through one sector but receives from more than one sector.
- In this case the MS has active uplink radio connections with the network through more than one sector belonging to the same BS.
- When soft and softer handoffs occur simultaneously, the term soft-softer handoff is usually used.
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