DIMA Handoff Management Handoff Management :Detection and Assignment :Detection and Assignment :Radio Link Transfer :Radio Link Transfer Song Hyok Song Hyok Digital Media Lab. Digital Media Lab. 2003. 3 . 11 . 2003. 3 . 11 .
Jan 14, 2016
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 .
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
Hard handoff (2/4)Hard handoff (2/4)
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
Hard handoff (3/4)Hard handoff (3/4)
● MAHO/NCHOMAHO/NCHO1. measurementreport
2. handoffrequired message
6. handoffcommand message
3. handoffrequest message
New BS acquirescipher key
4. handoff requestacknowledgment
5. handoffcommand message
7. handoff complete 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
10. transfer complete message
11. timeslot transfer message
12. transfer complete message
7. handoff complete 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
Soft handoff (2/3)Soft handoff (2/3)
● 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
MS Old BS MSC New BS
3. handoff requestmessage
11. handoff informationacknowledgment
13. pilot measurementrequest message
12. handoff informationacknowledgment
14. pilot strengthmeasurement
DIMADIMA
Soft handoff (3/3)Soft handoff (3/3)
● Dropping a BSDropping a BS1. pilot strengthmeasurement
6. handoffinformation message
4. interface primarytransfer message
3. handoff completemessage
2. handoff commandmessage
MS Old BS MSC New BS
7. handoff informationacknowledgment
8. pilot measurementrequest message
10 remove linkrequest message
9. pilot strengthmeasurement
5. interface primarytransferacknowledgment
11. remove linkacknowledgment