handoff management :detection and assignment :radio link transfer

DIMADIMA

Handoff ManagementHandoff Management:Detection and Assignment:Detection and Assignment

:Radio Link Transfer:Radio Link Transfer

Song HyokSong Hyok

Digital Media Lab.Digital Media Lab.

2003. 3 . 11 .2003. 3 . 11 .

http://www.gwu.ac.kr/

DIMADIMA

ContentsContents

● Handoff Detection (1st class)Handoff Detection (1st class) Mobile controlled handoff (MCHO) Network controlled handoff (NCHO) Mobile assisted handoff (MAHO)

● Channel assignment (1st class)Channel assignment (1st class) Nonprioritized scheme and reserved channel scheme Queuing priority scheme Subrating scheme

● Radio link transferRadio link transfer (2 (2ndnd class) class)


DIMADIMA

Mobile controlled handoffMobile controlled handoff

● The most popular technique for low-tier radio systemsThe most popular technique for low-tier radio systems European DECT, North American PACS air interface protocol

Link-qualityAcceptable?

Select newChannel ortime slot

ExecuteALT or TST

Measurementsprocess

Yes No

Monitoring the signal strength and quality from BSs Checks the best candidate BS

Automatic link transfer controlTime slot transfer control

Make quality measurementsof channels


DIMADIMA

Network controlled handoffNetwork controlled handoff

● low-tier CT-2 plus, high-tier AMPS low-tier CT-2 plus, high-tier AMPS (advanced mobile phone service)(advanced mobile phone service)

● Heavy network signaling traffic happensHeavy network signaling traffic happens Long interval handoff execution

Threshold

Monitor signal strengthand quality

Arranges for a handoffto another BS

Choose new BSInforms both the MS

and the new BS Ask to monitor the signal from the MS

Network

BS

MS

BS

BS

Report the measurement result

RSSI

RSSI

RSSI


DIMADIMA

Mobile assisted handoffMobile assisted handoff

● GSM, IS-95 CDMA, IS-136 TDMAGSM, IS-95 CDMA, IS-136 TDMA● Decentralized processDecentralized process

Both MS and BS supervise

● GSM 1sec handoffGSM 1sec handoff

Network

BS

MS

BS

Report the measurement back

RSSIRSSI

Measure signals from surrounding BSs

WEIWEI Select


DIMADIMA

Handoff failuresHandoff failures

● No channel is available on selected BSNo channel is available on selected BS● Handoff is denied by the networkHandoff is denied by the network

Lack of resources

● Too long time setting up the handoffToo long time setting up the handoff● Target link failureTarget link failure


DIMADIMA

Channel assignmentChannel assignment

● StrategyStrategy To achieve a high degree of spectrum utilization To reduce forced terminations

● Trade off factors for channel assignment methodTrade off factors for channel assignment method Service quality Implementation complexity Number of database lookups Spectrum utilization

● Channel assignment process for the successful Channel assignment process for the successful handoff handoff DCA-Dynamic channel assignment FCA-Fixed channel assignment QSAFA-Quasi-static autonomous frequency assignment


DIMADIMA

Nonprioritized schemeNonprioritized schemeThe reserved channel schemeThe reserved channel scheme● NPSNPS

BS handles a handoff call in exactly the same with a new call

● RCSRCS A number of channels or transceivers in each BS are reserved

Channels are divided into two groups The normal channels The reserved channels

Channelavailable?

Channelassigned

New orhandoff call

arrival

Ongoingcall

Channelreleased

Call blockedno

yes

Normalchannel

available?

Channelassigned

New call

arrival

Ongoingcall

Channelreleased

Call blocked

no

yes

Normalchannel

available?

Handoff call

arrival

Reservedchannelavailable

yes

nono

yes


DIMADIMA

Queuing priority schemeQueuing priority scheme

● Based on the network overlapping conditionBased on the network overlapping condition● Two scheduling policies for the QPSTwo scheduling policies for the QPS

FIFO scheme, measured based priority scheme

Normalchannel

available?

Channelassigned

New call

channelreleased

Ongoingcall

Channelreleased

Call blocked

no

yes

Handoff call

arrival

yes

no

no yes

Isa channel

available beforethe callexpires

?

Isthe waiting

queueempty?

The cahnnel is idle

Insert thecall into the

waiting queue

MS entering a handoff area

MS checking available channel

Queuing the handoff call

Old BS useduntil new channel available

Process in MCHO


DIMADIMA

Subrating shemeSubrating sheme

● Subrating an existing call for creating a new channelSubrating an existing call for creating a new channel Dividing an occupied full rate channel into two channels at half

● PCS system ( using priority based scheme )PCS system ( using priority based scheme ) A traffic channel needed

● Two ways in SRSTwo ways in SRS Two mode ADPCM

No impact on the channel delay No cost increasing

Switchable ADPCM Higher delay High cost in MS Increasing the power draining

Channelavailable?

Channelassigned

New call

channelreleased

Ongoingcall

Channelreleased

Callblocked

no

yesHandoff call

arrival

yes

no

yes

Isthere a

subratedchannel

pair?

Isthe release

channelsubrated?

Thechannelis idle

Each channelof the subratedpair is upgraded

to full-rate channel

Channelavailable for

subrating

The other channelof the subratedpair is upgraded

yes

no


DIMADIMA

Radio link transferRadio link transfer

● Hard handoff procedureHard handoff procedure MS connects with only one BS Interruption during the link transition TDMA, FDMA

● Soft handoff procedure Soft handoff procedure Soft handoff, Softer handoff Receives/transmits from/to multiple BSs simultaneously Complicated than hard handoff CDMA, TDMA with macro diversity


DIMADIMA

Link transfer casesLink transfer cases

● Intracell handoffIntracell handoff Between two time slots or channels in the same BS

● Intercell handoff (Inter-BS handoff)Intercell handoff (Inter-BS handoff) Between two BSs attached to the same BSC

● Inter-BSC handoffInter-BSC handoff Between two BSs connected to different BSCs

● Intersystem handoff (Inter-MSC handoff)Intersystem handoff (Inter-MSC handoff) Between two BSs connected to different BSCs on different MSCs

● Intersystem handoff between two PCS networksIntersystem handoff between two PCS networks Between two BSs connected to different MSCs homing to different PCS


DIMADIMA

Hard handoff (1/4)Hard handoff (1/4)

● MCHO link transferMCHO link transfer1. link suspend message

2. handoff request message

8. handoff execution message

4. link resume message

9. access release message

10. handoff execution message

11. handoff complete message

12. voice is resumed on new link

3. handoff acknowledgment message

5. voice is resumed on old link

The MS initializes the synchronization with the new BS. The MS returns to the old BS, then comes back to the new BS. Cipher starts at this point

MS Old BS New BS

6. New BS acquirescipher key7. Network bridgesthe new and old BSs

Voice isinterrupted

Voice isinterrupted


DIMADIMA


Old BSNew BS

MS

1.Link suspend message2.Handoff request message

3.Handoff acknowledgement message

5.Link resume message

MSC

Cipher key

Bridge

8.Handoff execution message9.Access release message

10.Handoff execution message

11.Handoff complete message


DIMADIMA


● MAHO/NCHOMAHO/NCHO1. measurementreport

2. handoffrequired message

6. handoffcommand message

3. handoffrequest message

New BS acquirescipher key

4. handoff requestacknowledgment

5. handoffcommand message


8. handoffcomplete message

9. clear commandmessage

10. clear completeacknowledgment

Voice is resumed on new link

MS Old BS MSC New BS

Voice isinterrupted


DIMADIMA

Hard handoff(4/4)Hard handoff(4/4)

● Subrating MCHOSubrating MCHO

MS handoffNetworkMS existing

MSleaving

Requesting ALT

Assigning full-rate channelsto the subrated calls

Subrating an existing call

Assigning a channelfor the ALT request

Releasing atraffic channel

1. priority access request message *

2. priority access request acknowledgment*

3. time slot transfer message

4. transfer complete message

5.priority channel assignment*

6. handoff request message

8. access release message

9. time slot transfer message


11. timeslot transfer message



*These messages are conveyed in the CSC. All other messages are in the traffic channel.


DIMADIMA

Soft handoff (1/3)Soft handoff (1/3)

● Used in CDMAUsed in CDMA Transmit/receive the same information to/from several BSs Signaling from multiple BSs combined at the MSC


DIMADIMA


● Adding a new BSAdding a new BS1. pilot strengthmeasurement 2. handoff request

message

6. joinacknowledgment

4. null trafficmessage

5. join requestmessage

7. handoffacknowledgment

10 handoff completemessage

8. handoffacknowledgment9. handoff command

message


3. handoff requestmessage

11. handoff informationacknowledgment

13. pilot measurementrequest message


14. pilot strengthmeasurement


DIMADIMA


● Dropping a BSDropping a BS1. pilot strengthmeasurement

6. handoffinformation message

4. interface primarytransfer message

3. handoff completemessage

2. handoff commandmessage



8. pilot measurementrequest message

10 remove linkrequest message

9. pilot strengthmeasurement

5. interface primarytransferacknowledgment

11. remove linkacknowledgment


handoff management :detection and assignment :radio link transfer

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