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Handoff strategies in details

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

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  • 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. enter image description here

  • 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. enter image description here

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