Presented By: Nouman Ali, Mohsin Ehsan, Mohsin Ashraf

RF Department

Internee

Handover Types

What is Handover? As the MS1 moves, it is quite possible that it reaches to

the edge of the cell, this is a point at which the Radio signals are too weak to continue the call.

There is probably another cell neighboring onto this cell, but this cell uses different frequency and knows nothing about MS1.

The mechanism which allows mobile to move from current cell to neighboring cell is called handovers.

Why we need Handover?

To keep a continuous communication with a moving MS.

‡To reduce the call drop rate.

Intra BSC HO Process First current MS send the measurement reports to BTS

in uplink, RX Quality, RX Level, BSIC, DTX used or not in serving cell.

BTS (original cell) will forward this measurement report to BSC.

BSC will send the Channel activation command to the BTS (Target cell).

BTS (Target cell) will send the channel activation acknowledgment message to the BSC.

BSC sends the HO command to the BTS (original cell). BTS (Target Cell) will forward this message to the MS on

FACCH. MS will send the HO Access Command to the BTS

(Original Cell) on FACCH.

Intra BSC HO Process BTS (Original cell) forwards the HO complete message

to the BSC. BSC will release the connection from BTS (Original cell)

and connect BTS (Target Cell)

Network Elements Involved in HO Process

MS Responsible for measurement report of the serving cell and neighboring cells.

BTS Responsible for monitoring of uplink received level and quality of each served MS.

BSC Processing the measurement report and making handover judgment.

MSC Participating in the confirmation of target cell in inter-BSC handover.

Handover Types

PBGT Handover Rx Level Handover (UL and DL) Rx Quality Handover (UL and DL) TA Handover Direct Retry Handover

PBGT Handover PBGT handover algorithm is based on path loss. It seeks

a cell with lower path loss and meeting certain system requirements, and judges whether it’s necessary to perform handover.

When there is a difference of 4dBm between serving and neighboring cells, then serving cell gives handover to the neighboring cell, it means that the PBGT HO threshold is set to 68 and the reference point is 64.

The reference value for Urban Ares is 68 & for the Rural areas is 70 to 72.

Reducing PBGT HO Threshold makes the PBGT handover more accessible. If the PBGT HO Threshold is set to an excessively smaller value, ping-pong handover may easily occur.

Rx Level of Cell A is 60 dBm Rx Level of Cell B is 56 dBm

Cell ACell B

RX Level HO If downlink level is worse then HO Thresholds

Lev DL parameter, then an immediate level handover takes place. This parameter is set to –95dBm as default.

If uplink level is worse then HO Thresholds Lev UL parameter, then an immediate level handover takes place. This parameter is set to –105dBm as default.

RX Quality HO

If downlink quality is worse then HO Thresholds Quality DL parameter, then an immediate quality handover takes place.

If uplink quality is worse then HO Thresholds Quality UL parameter, then an immediate quality handover takes place.

Default RX Quality threshold value is 3.2%-6.4% for both UL and DL.

Directed Retry HO

When no TCH is available in the serving cell, TCH can be allocated in an adjacent cell.

It is basically handover from SDCCH to TCH.

TA HO

This is performed on the basis of a distance of a mobile from BTS.

This parameter is set to 63 as default TA=63