Section 3:cdma2000 Handoff

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

Section 3:cdma2000 Handoff

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)

Section 3:cdma2000 Handoff

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

Section 3:cdma2000 Handoff

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

Section 3:cdma2000 Handoff

5

Inter-Frequency Hard Handoff

CFSRPM(Report)

CRSCNM(Search Order)

F1 (serving)

F2 (candidate)

GHDM(HHO)

CRSRQM(Search Parameters)

CFSRSM(Acceptance)

Section 3:cdma2000 Handoff

6

Candidate Frequency Search

CFSCM, F2,

periodic off

Searches &reports F2

Reports on F2

Total Ec/Io of pilots in SSabove CF_T_Add

exceeds Threshold from CFNLM

3. Periodically searches forSearch Set on F2 from F1

2. On F1, Search Set on F2, no

periodic search

CFSCM, F2,

periodic on

HHO Fig. 1 IS-95B Inter-freq. Hard Handoff Mobile Example(All handoffs successful)

EHDM to F3,

periodic off

EHDM to F2,

periodic on/off

4. On F2, Search Set on F2, no

periodic search

EHDM to F2,

periodic on/off

Notes: -CF: Candidate Freq. -SS: Search Set -CFSReqM: CF Search Request Msg -CFSRspM: CF Search Response Msg -SS update by CFSRegM not shown -Hard handoff failure not shown -Not all EHDM shown -Handoff Completion Msg omitted

CFSReqM, CF=F2,

Search Set ={P1,...,Pn}

SendsCFSRspM

6. Periodically searches forSearch Set on F2 from F3

5. On F3, Search Set on F2, no

periodic search

EHDM, to F3,

periodic on

EHDM, to F3,

periodic off

EHDM to F3,

periodic on

CFSCM, F2,

periodic off

1. On Traffic Ch. on F1,

w/o Search Set

CFSReqM, CF=F2,

Search Set = {P1,...,Pn},

Start Periodic

SendsCFSRspM

Section 3:cdma2000 Handoff

7

Inter-freq. Handoff Failure Recovery

3. Periodically searches forSearch Set on F 2 from F1

2. On F1, Search Set on F 2, no

periodic search

CFSCM, F2,

periodic on

HHO Fig. 2 IS-95-B Inter-freq. Hard Handoff Example(All hard handoffs fail)

EHDM to F2,

periodic off,HHO fails

EHDM to F2,

periodic on,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

Reports on SS +intended Active

Set on F2CFSCM, F2,

periodic off

Reports on SS +intended Active Set

on F2

EHDM to F2, periodic

off, HHO failsSendsCFSRspM

CFSReqM,CF=F2, Search

Set = {P1,...,Pn}

1. On Traffic Ch. on F1,w/o Search Set

EHDM to F2,

periodic on, HHO fails

Reports onSS + intended

Active Set on F2

Reports onSS + intended

Active Set on F2

SendsCFSRspM

CFSReqM, CF=F2, Search Set

= {P1,...,Pn}, start periodic

Section 3:cdma2000 Handoff

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

Section 3:cdma2000 Handoff

9

cdma2000 Forward Link HHO Searching

• Method can be used when excursion is less than 10 ms

tsearchN PCG

regular power controlMS sends up

commands to ramp uppower before search

PC is random

regular powercontrol resumes

MS tunes toanother

frequency

MS returnsfrom search

Fra

me

Bou

ndar

y

Fra

me

Bou

ndar

y

MS increasestarget Eb/No by

target

MS decreasestarget Eb/No by

target

Forward Link Transmitted Power

Section 3:cdma2000 Handoff

10

IF HHO Performance Example on RL

9600, 5ms, Pilot Ec/Io = 3ms

0.00001

0.0001

0.001

0.01

0.1

1

3 3.5 4 4.5 5 5.5 6 6.5

Traffic/Pilot Ratio in dB

FE

R

120kph

30kph

5kph

awgn

Section 3:cdma2000 Handoff

11

IF HHO Performance Example on RL

9600, 5ms, Pilot Ec/Io = -23.75dB

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

3 3.5 4 4.5 5 5.5 6 6.5 7

Traffic/Pilot Ratio in dB

FE

R

120kph

30kph

5kph

awgn