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Handoff Management :Detection and Assignment :Radio Link Transfer

Handoff Management :Detection and Assignment :Radio Link Transfer. Song Hyok Digital Media Lab. 2003. 3 . 11. Contents. Handoff Detection (1st class) Mobile controlled handoff (MCHO) Network controlled handoff (NCHO) Mobile assisted handoff (MAHO) Channel assignment (1st class)

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Handoff Management :Detection and Assignment :Radio Link Transfer

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  1. Handoff Management:Detection and Assignment:Radio Link Transfer Song Hyok Digital Media Lab. 2003. 3 . 11 .

  2. Contents • Handoff Detection (1st class) • Mobile controlled handoff (MCHO) • Network controlled handoff (NCHO) • Mobile assisted handoff (MAHO) • Channel assignment (1st class) • Nonprioritized scheme and reserved channel scheme • Queuing priority scheme • Subrating scheme • Radio link transfer (2nd class)

  3. Mobile controlled handoff • The most popular technique for low-tier radio systems • European DECT, North American PACS air interface protocol Make quality measurements of channels Monitoring the signal strength and quality from BSs Checks the best candidate BS Automatic link transfer control Time slot transfer control Measurements process Link-quality Acceptable? Yes Select new Channel or time slot Execute ALT or TST No

  4. Network controlled handoff • low-tier CT-2 plus, high-tier AMPS (advanced mobile phone service) • Heavy network signaling traffic happens • Long interval handoff execution MS RSSI Monitor signal strength and quality RSSI BS BS RSSI Threshold BS Arranges for a handoff to another BS Network Choose new BS Informs both the MS and the new BS Report the measurement result Ask to monitor the signal from the MS

  5. Mobile assisted handoff • GSM, IS-95 CDMA, IS-136 TDMA • Decentralized process • Both MS and BS supervise • GSM 1sec handoff MS RSSI RSSI BS BS WEI Select WEI Network Report the measurement back Measure signals from surrounding BSs

  6. Handoff failures • No channel is available on selected BS • Handoff is denied by the network • Lack of resources • Too long time setting up the handoff • Target link failure

  7. Channel assignment • Strategy • To achieve a high degree of spectrum utilization • To reduce forced terminations • Trade off factors for channel assignment method • Service quality • Implementation complexity • Number of database lookups • Spectrum utilization • Channel assignment process for the successful handoff • DCA-Dynamic channel assignment • FCA-Fixed channel assignment • QSAFA-Quasi-static autonomous frequency assignment

  8. Nonprioritized schemeThe reserved channel scheme • NPS • BS handles a handoff call in exactly the same with a new call • RCS • A number of channels or transceivers in each BS are reserved • Channels are divided into two groups • The normal channels • The reserved channels

  9. Queuing priority scheme • Based on the network overlapping condition • Two scheduling policies for the QPS • FIFO scheme, measured based priority scheme MS entering a handoff area MS checking available channel Queuing the handoff call Old BS used until new channel available Process in MCHO

  10. Subrating sheme • Subrating 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 ) • A traffic channel needed • Two 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

  11. Radio link transfer • Hard handoff procedure • MS connects with only one BS • Interruption during the link transition • TDMA, FDMA • Soft handoff procedure • Soft handoff, Softer handoff • Receives/transmits from/to multiple BSs simultaneously • Complicated than hard handoff • CDMA, TDMA with macro diversity

  12. Link transfer cases • Intracell handoff • Between two time slots or channels in the same BS • Intercell handoff (Inter-BS handoff) • Between two BSs attached to the same BSC • Inter-BSC handoff • Between two BSs connected to different BSCs • Intersystem handoff (Inter-MSC handoff) • Between two BSs connected to different BSCs on different MSCs • Intersystem handoff between two PCS networks • Between two BSs connected to different MSCs homing to different PCS

  13. Hard handoff (1/4) • MCHO link transfer

  14. Hard handoff (2/4) MSC Bridge Cipher key New BS Old BS 11.Handoff complete message 1.Link suspend message 5.Link resume message 2.Handoff request message 8.Handoff execution message 3.Handoff acknowledgement message 9.Access release message 10.Handoff execution message MS

  15. Hard handoff (3/4) • MAHO/NCHO

  16. Hard handoff(4/4) • Subrating MCHO

  17. Soft handoff (1/3) • Used in CDMA • Transmit/receive the same information to/from several BSs • Signaling from multiple BSs combined at the MSC

  18. Soft handoff (2/3) • Adding a new BS

  19. Soft handoff (3/3) • Dropping a BS

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