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Soft Handoff

Soft Handoff. Soft handoff for MC 1X and DS works as in IS-95-B Soft handoff for MC 3X is a straightforward extension of that in MC 1X E c /I 0 used is the sum of the E c /I 0 on all three carriers. Inter-Frequency Hard Handoff.

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Soft Handoff

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  1. Soft Handoff • Soft handoff for MC 1X and DS works as in IS-95-B • Soft handoff for MC 3X is a straightforward extension of that in MC 1X • Ec/I0 used is the sum of the Ec/I0 on all three carriers

  2. Inter-Frequency Hard Handoff • Inter-Frequency Hard Handoff (HHO) required in following situations • Handoff between operators in different bands • Handoff between different CDMA RF carriers for congestion control • Handoff from a (private) micro-cell to a macro-cell • Handoff between different radio technologies (CDMA to AMPS, GSM, …, OHG DS)

  3. Messages for HHO • CFSRQM (Candidate Frequency Search Request Message) • BS informs MS about • Candidate Freq. Neighbor List (CFNL) • Candidate Freq Search Set (CFSS), a subset of CFNL • Freq. band and channel number • Search Period (for Periodic Search) • Thresholds (MS Rx power and total pilot Ec/I0, etc.) • Can specify a search for AMPS (other formats can be added) -MS support is optional • Optionally, can synchronize timing between MS and BS • Can also start search • CFSRSM (Candidate Frequency Search Response Message) • MS replies to CFSRQM • Dead time to search entire CFSS (fwd and rev) • Dead time per visit to candidate frequency (fwd and rev) • Dead time can be specified in frames or in 1.25 ms slots

  4. Messages for HHO (cont.) • CFSCNM (Candidate Frequency Search Control Message) • To start and stop searches (periodic or single) • GHDM (General Handoff Direction Msg) • Contains flags to specify • Use of this procedure upon HHO failure • CFRSPM (Candidate Frequency Search Report Message): • MS reports to BS on the serving freq • MS rx power on candidate freq. • Pilots above T_ADD • Sent in periodic search only if total Ec/I0 of Candidate Freq. Search Set is above threshold • All pilot measurements have to be made within 0.8 sec. of the report

  5. CRSRQM(Search Parameters) GHDM(HHO) CRSCNM(Search Order) CFSRSM (Acceptance) CFSRPM (Report) F2 (candidate) F1 (serving) Inter-Frequency Hard Handoff

  6. Candidate Frequency Search

  7. Inter-freq. Handoff Failure Recovery 1. On Traffic Ch. on F 1 , w/o Search Set Reports on SS + intended Active Set CFSReqM, CFSReqM, CF=F , Search Set 2 on F CF=F , Search 2 2 = {P ,...,P }, start periodic 1 n EHDM to F , periodic Set = {P ,...,P } 2 1 n off, HHO fails Send s Send s CFSRspM CFSRspM 2. On F , Search Set on F , no 1 2 periodic search EHDM to F , 2 Reports on SS + periodic on, intended Active HHO fails CFSC M, F , 2 CFSCM , F , 2 Set on F 2 Reports on periodic on periodic off SS + intended EHDM to F , 2 Active Set on F periodic off, 2 HHO fails 3. Periodically searches for Search Set on F from F 2 1 Reports on SS + intended EHDM to F , 2 Active Set periodic on, on F 2 HHO fails Notes: - CF: Candidate Freq. - SS: Search Set - CFSReqM: CF Search Request Msg -CFSRspM: CF Search Response Msg - SS update by CFSReqM not shown -Not all EHDM shown HHO Fig. 2 IS-95-B Inter-freq. Hard Handoff Example (All hard handoffs fail)

  8. cdma2000 Inter-Frequency HHO Improvements • To minimize interruptions during search excursions: • MS can store pilot samples while on target frequency and process them offline (when returning to originating frequency) • Forward link target Eb/Nt theshold is increased before search excursion; Viterbi decoder uses additional symbol energy to decode frame successfully • Reverse link traffic to pilot ratio for code channel increased • If synthesizer can be tuned fast enough, no frames are lost • No complex BS-MS coordination required for search • As RF phone technologyimproves, performance increases

  9. cdma2000 Forward Link HHO Searching • Method can be used when excursion is less than 10 ms Forward Link Transmitted Power

  10. IF HHO Performance Example on RL

  11. IF HHO Performance Example on RL

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