Explain different handoff strategies in Details including hard, soft, delayed forced handoff

• Handoff is the technique which enables a call to proceed uninterrupted when the user moves from one cell to another

• There are two basic types of Handoffs.

  1) Hard Handoff

  2) Soft Handoff

• Handoff process involves 3 main stages a. Handoff Initiation b. Establishing a new connection c. Data transfer to new handoffs.

1) Hard Handoff:

• It is also known as “Break before make” connection.

• In this type of handoff the link to the old base station is terminated before the mobile station establishes a link with the new base station.

• It is used in FDMA and TDMA based mobile system. Figure shows the mechanism of hard handoff.

• Hard handoff is classified as

  a) Intra cell handoff:

  • In Intra cell Handoff, the handover occurs within the same cell.

  • Intra cell handover switches a cell in progress from one physical channel of a cell to another physical channel of the same cell.

  b) Inter cell handoff:

  • In Inter cell Handoff, the handover occurs between two cells.

  • The inter cell handover switches a cell in progress from one cell to another cell.

  • It can be of two types

    1. Inter BSC: Here the MS moves from one cell to another cell controlled by the different BSCs.

    2. Inter MSC: Here the MS moves from one cell to another cell controlled by the different MSCs.

  c) Inter System Handoff:

  • In inter system handoff; the handover occurs between two systems.

  • This type of handoff occurs when the mobile unit moves from one cellular system to a different cellular system.

  • Example from GSM to UMTS.

2) Soft Handoff:

• It is also called as Mobile Directed handoff or make before Break Connection.

• In these types of handoff the link to the old base station is not terminated before the mobile station established a link with the new base station.

• Once the link is established the connection to old BS is terminated.

• It is used in UMTS to improve the signal quality

• It is more seamless handover.

• Figure shows the mechanisms of soft handoff.