DIMA Handoff Management :Detection and Assignment :Radio Link Transfer Song Hyok Digital Media Lab

DIMA 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 (2 nd class) Radio link transfer Radio link transfer

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

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

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

DIMA 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

DIMA 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

DIMA Nonprioritized scheme The 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

DIMA 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

DIMA 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

DIMA 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

DIMA 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

DIMA Hard handoff (1/4) ● MCHO link transfer

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

DIMA Hard handoff (3/4) ● MAHO/NCHO

DIMA Hard handoff(4/4) ● Subrating MCHO

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

DIMA Soft handoff (2/3) ● Adding a new BS

DIMA Soft handoff (3/3) ● Dropping a BS