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This page describes handoff or handover used in cellular communication and also mention different types of handoff/handover.

Handoff or Handover is the term most popular in cellular communication. It refers to transfer of mobile connection from one resource to another without disconnecting the voice or data call and falls in following categories. This happens when mobile device is moving at vehicular speed and using wireless cellular connection for voice/data call.

Factors causing handoff/handover in the wireless system:
1. Signal strength/power 2.speed of the device/mobile 3. weaker signal from serving Base station and strong signals from neighbour base stations 4. Bit Error Rate 5. Interference from adjacent channels

Let us understand types of handoff/handover with respect to GSM system below.

1. Handoff in the same BTS from one channel to the other

2. Handoff from one BTS to the other BTS (within one BSC)

3. Handoff from one BSC to the other BSC (within one MSC)

This is network initiated either in open loop or close loop mode when received power from mobile at Base station falls below particular level and will no longer provide strong RF link to deliver required BER or Eb/No. The estimation of power is either reported by mobile itself or base station will send signal to mobile to report the power level back to Base station.

There are two main types soft handoff and hard handoff based on connection with the target resource.
Hard handoff- break before make, in this type connection with the source channel/BTS/BSC is first broken before making connection with target channel/BTS/BSC.
soft handoff- make before break, in this type connection with the source channel/BTS/BSC is retained for sometime before connection with the target channel/BTS/BSC is established. In this type user of cellular network will not experience any glitch and will continue to receive better service.

HANDOVER or Handoff related links

IRAT basics and Inter-RAT handover with example of WCDMA RAT to GSM RAT handover, Refer IRAT Handover.
Femtocell Handover
Soft handover vs Softer Handover
LTE to WLAN and WLAN to LTE Handover
UMTS to WLAN and WLAN to UMTS handover
Mobile WiMAX Handover as per IEEE 802.16e standard

RF and Wireless Terminologies

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