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Handover -The Process of Changing cells during a call is called handover PowerPoint PPT Presentation


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Handover -The Process of Changing cells during a call is called handover -MS & BTS perform measurements -MS measures signal strength and quality on its cell and signal strength on the BCCH carries of neighbouring cells. -Measurement are made on down link when MS is in active mode.

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Handover -The Process of Changing cells during a call is called handover

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Handover the process of changing cells during a call is called handover

Handover

-The Process of Changing cells during a call is called handover

-MS & BTS perform measurements

-MS measures signal strength and quality on its cell and signal strength on the BCCH carries of neighbouring cells.

-Measurement are made on down link when MS is in active mode.

-Measurement result are sent to the BTS at regular intervals.

-Measurement from BTS & MS are sent to BSC in form of measurement reports.

-Based on reports received BSC decides if a handover is necessary and to which cell. This is called Locating.

-As soon as a neighbouring cell is considered to be better than the serving cell, a handover is attempted.

-Other reason for handover is TA. When MS exceeds TA than a threshold value set by the operator. This happens when MS is moving over the cell border to another cell.


Handover the process of changing cells during a call is called handover

-When the MS has changed cells the new BTS informs the MS about new BCCH carrier so measurement can be taken again.

-If the MS has switched to a new LA, a location updating type normal takes place after the call has finished.

-Handover can be used for load balancing between cells.

-During a call setup in a congested cell, MS can be transferred to a cell with less traffic, if the quality of new connection is acceptable.

-Handover is also used during maintenance. Channel can be released for BTS maintenance. This is called forced handover.


Handover the process of changing cells during a call is called handover

Types of Handover:-

1.Intra - cell handover

2.Handover between cells controlled by the same BSC.

3.Handover between cells controlled by different BSC but same MSC-/VLR.

4.Handover between cells controlled by different MSC/VLRs.

For each handover, the decision to perform a handover has already been made and a target cell has been identified

Intra cell - Handover:- It is when BSC considers the quality of connection is too low but receives no indication from the measurements that another cell would be better, BSC identifies another channel in the same cell which may offer better qualify, and MS is ordered to re-tune to it.


Handover the process of changing cells during a call is called handover

Um

A

MS

BSC

INTRA-BSS INTER BTS HANDOVER

BSS

Signal Strength Measurement

SACCH

1.MS listen to BCCHs, (Current) and neighbouring channels and reporting results to BSS

2.BSC allocates a new radio channel and instructs the MS to re-tune to it.

3.MS tunes to new radio channel.

4.MS sends a handover complete message to BSS.

5.BSS informs the MSC about new location of the MS.

1

Handover Command

SACCH

2

Handover Access

SACCH

3

Handover Complete

SACCH

4

Handover Performed

5


Handover the process of changing cells during a call is called handover

INTRA-MSC HANDOVER

Um

A

OLD

BSS

A

MS

MSC

New BSS

Signal Strength

Measurement

SACCH

1.MS listen is own BCCH & neighbouring BCCH.

2.Old BSS determines that the MS requires to be handed over, it will send a Handover Required message with a list of cells to which the MS can be handed over to MSC.

3.MSC send a handover Request Message to new BSS.

4.New BSS sends Handover Request-ACK message to MSC.(It contains Handover Reference Number - hrn.)

5.MSC informs Old BSS for Handover.

6.Old BSS send command to MS, to take to new radio channel.

1

Handover Required

2

Handover Requested

3

Handover Requested

Acknowledge (hrn.)

4

Handover command (hrn)

5

Handover command (hrn)

SACCH

6


Handover the process of changing cells during a call is called handover

INTRA-MSC HANDOVER

Um

A

OLD

BSS

A

MS

MSC

New BSS

Handover Access

7.MS across the new radio resourse by sending the message Handover Access containing the (hrn.) The (hrn.) is checked by new BSS to ensure that MS captured is correct.

8.If correct new BSS sends Handover detect message to MSC

9.When MS communicating with new BSS, it (MS) sends a Handover Complete Message .

10.New BSS forwards this message to MSC.

11.Trunk between MSC & Old BSS is released.

12.Radio Traffic Channel is released.

7

Handover Detected

8

Handover Complete

SACCH

9

10

Handover Complete

Release Radio

Channel

11

Release Channel

Released

12


Handover the process of changing cells during a call is called handover

  • BASIC HAND-OVER

    • CALL IS HANDED OVER FROM HOME MSC

    • (MSC-A) TO A 2nd MSC (MSC-B)

  • SUBSEQUENT HAND-OVER

    • 1.CALLS IS HANDED OVER FROM THE 2nd MSC BACK TO THE HOME MSC.

    • 2.CALL IS HANDED OVER FROM THE 2nd MSC TO ANOTHER MSC (3rd MSC)


  • Handover the process of changing cells during a call is called handover

    BSS

    A

    MSC

    A

    MSC

    B

    BSS

    B

    VLR

    B

    Um

    A

    E

    A

    MS

    Signalling Strength

    Measurement

    SACCH

    1.MS is listening to it own BCCH & neighbouring BCCH.

    2.Old BSS (BSS-A) determines that MS requires to be handover it will send a Handover Required message to MSC-A, with a list of cells to which the MS can be handed over.

    3.MSC-A send message to MSC-B for handover, this message contain information to allocate radio channel and identity of cell, to which the call to be handed over.

    4.MSC-B ask its VLR to allocate a (hrn.)

    5.MSC-B retrieves the (hrn.) which will be used for routing the connection of the call to MSC-A.

    1

    Handover

    Required

    2

    Perform

    Handover

    3

    Allocate

    Handover

    Number

    4

    Handover

    Number

    Allocated (hrn)

    5


    Handover the process of changing cells during a call is called handover

    BSS

    A

    MSC

    A

    MSC

    B

    BSS

    B

    VLR

    B

    Um

    A

    E

    A

    MS

    Handover

    Request

    6.If no traffic channel is available in MSC-B, it ask the BSS-B to allocates one

    7.BSS-B return the allocated traffic channel (TN).

    8.An ACK-message containing the new radio resources definition sent by MSC-B to MSC-A.

    9.MSC-A asks MSC-B to establish a communication circuit.

    10.MSC-B establishes a circuit with MSC-A using the signalling procedures supported by the N/W.

    6

    HO Request

    Acknowledge (TN)

    7

    Perform HO Acknowledge

    8

    Network

    Setup

    9

    Setup

    Complete

    10


    Handover the process of changing cells during a call is called handover

    BSS

    A

    MSC

    A

    BSS

    A

    BSS

    B

    VLR

    B

    MS

    10A

    Handover

    Command

    10AMSC-A send handover command to Old BSS-A.

    10BOld BSS-A send handover command to MS.

    10CMS access the new radio resources by sending the message. Handover access containing hrn. The hrn is checked by new BSS to ensure it, as expected and the correct MS has been captured.

    10DIf this is correct the new BSS sends a handover detect message to MSC-B

    10EWhen the MS is successfully communicating with BSS-B,it (MS) sends a handover complete message to BSS-B.

    10FBSS-B forward the message to MSC-B.

    10GMS is now served by BSS-B the trunk between MSC-A & BSS-A can be released.

    10HConsequently the radio channel (between MS & BSS-A is released).

    Handover

    Command

    10B

    MS send handover access message (hrn)

    10C

    BSS sends

    Handover Detect message

    10D

    10E

    MS sent handover complete

    Message to BSS-B

    Handover

    Complete message

    to MSC-B

    10E

    Release TRK

    & Radio channel

    10F

    10H


    Handover the process of changing cells during a call is called handover

    BSS

    A

    MSC

    A

    MSC

    B

    BSS

    B

    VLR

    B

    A

    E

    A

    MS

    Handover

    Command

    11

    Handover

    Command

    SACCH

    12


    Handover the process of changing cells during a call is called handover

    BSS

    A

    MSC

    A

    MSC

    B

    BSS

    B

    Um A

    E

    A

    MS

    Handover Access

    SACCH

    13

    Handover

    Delected

    14

    Handover Complete

    SACCH

    15

    Handover

    Complete

    16


    Handover the process of changing cells during a call is called handover

    BSS

    A

    MSC

    A

    MSC

    B

    BSS

    B

    Um A

    E

    A

    MS

    Send END

    Signal

    17

    17.MSC-B inform , MSC-A that connection can be ended.

    18.MSC-A acknowledge the receipt of this message.

    19.Link between MSC-A & BSS-A is released.

    20.Radio Channel between BSS-A to MS is released.

    Answer

    18

    Release Radio

    Released

    19

    Radio Channel

    Released

    20


    Handover the process of changing cells during a call is called handover

    E

    B

    MSC

    B

    MSC

    A

    VLR

    B

    End Signal

    SACCH

    21.MSC-A inform MSC-B that the old resources used by the MS are released.

    22.Network connection between MSC-A & MSC-B to released.

    23.hrn between MSC-A & MSC-B is now needed and can be de-allocated.

    21

    Network Release

    SACCH

    22

    Release Handover

    Number

    23


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