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1. June, 2009
C2 – Company Confidential
SOURCE: David Rossetti and Jialin Zou
CONTACT: jialinzou@alcatel-lucent.com
ABSTRACT: This is a stage 2 proposal on CSFB performance enhancement. It is for C.S0087-0 v2.0.
TITLE: Performance Enhancement for CSFB
TSG-C
RECOMMENDATION: Review and adopt.
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This document has been prepared by The source companies of this contribution to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be
construed as a binding proposal on The source companies of this contribution . The source companies of this contribution specifically reserves the right to amend or modify the material contained herein and to any
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2. C2 – Company Confidential2 | CSFB | June, 2009
1xRTT CSFB Performance
3GPP TS23.272 v8.3.0 defines Circuit Switched FallBack procedures to 1xRTT. In
these procedures, upon indication of the need to switch to 1x to make a
circuit (voice) call, the dual mode first suspends its LTE session, then switches
to 1xRTT mode and uses normal 1x paging/access procedures to setup the
voice call.
There is concern about CSFB call setup latency. Alcatel-Lucent would like to
propose enhancements that have no impact to 3GPP Release 8 standards, but
will reduce CSFB call setup latency, especially for single receiver dual mode
devices.
If further latency reductions are desired for 3GPP Release 9, adding optional
CSFB callflows using SRVCC-type tunneled handover procedures may be
considered.

3. C2 – Company Confidential3 | CSFB | June, 2009
1 x C S
C S F B
U E
E-
U T R A N
M M E 1 x C S
IW S
1 x R T T
M S C
. -
3 . 1 x R T T C S P a g ing
5 b . U L /D L In form a tio n
T ra n s fe r
5 a. U L/D L S1 c d m a 2 0 0 0
T u n ne llin g
S 10 2 D ire c t T ra n s fe r
5 . 1 x R T T C S P a g ing
1 . U E is E-U T R A N a tta c he d a nd re g is te re d w ith 1 x R T T C S
4 . If U E is id le, M M E p erfo rm s N e tw o rk - in itia te d
s e rv ic e re q u e s t
2 . P a g in g R e q u e s t
1 5 . 1 x M T c a ll e s ta b lis hm e n t pe r 3 G P P 2 s p e c ific a tio n s
. -
1 4 . 1 x R T T C S P a g e R e s p o n s e M e s s a g e
7. S 1 U E C o n te x t
M o d ific a tion
6 . E x ten d e d S e rv ic e
R e q ue s t
S -G W
8 . O p tio n a l m e a s u re m e n t rep o rt
s o lic ita tio n
1 0 . S 1 U E C on te x t R e le a s e
R eq u e s t
1 1 . S u s p e n d R eq u e s t
1 2 . S u s p e n d R eq u e s t A c k
1 3 . S 1 U E C on te x t R e le a s e
9 . E - U T R A N trig g e rs R R C c o nn e c tio n
re lea s e w ith red ire c tio n o r C C O to 1 x C S
CS Fallback from LTE to 3G1X:
Call Termination from 3G1X over LTE [From TS23.272 v8.3.0]
Optimizations will be
done here, inside of 1x
procedures.

4. C2 – Company Confidential4 | CSFB | June, 2009
CS Fallback from LTE to 3G1X:
Call Origination from 3G1X over LTE [From TS23.272 v8.3.0]
Optimizations will be
done here, inside of 1x
procedures.

5. C2 – Company Confidential5 | CSFB | June, 2009
CSFB Latency Requirements
•1x CSFB Latency needs to be on par with traditional 1x call delivery latency (and
fallback to GERAN/UTRAN from LTE).
•Minimize user perception of change
•No impact to abandon call rate or redirection to secondary treatment
•Competition between CDMA operators and GPRS/UMTS operators migrating to LTE.
•UE already needs to perform CSFB suspend procedures on LTE, so any impact on 1x call
setup latency will be problematic.
•For normal 1x call establishment, the MS is already in the idle state, ready to transmit
an origination or page response in short order.
•Locked onto strongest pilot
•Synchronized with CDMA timing
•Hashed to correct CDMA carrier and paging channel
•These may not be the case for CSFB (especially for single receiver device)

6. C2 – Company Confidential6 | CSFB | June, 2009
Current Steps to acquire traffic channel upon CSFB redirection
time
Sync
Channel
Timing
Change
Overhead/
Hash
Access
Procedures
Network
Setup
Channel
Assignment
Traffic
Acquisition
Steps with proposed
optimizations
RRC
Redirection
1x Pilot
Search

7. C2 – Company Confidential7 | CSFB | June, 2009
Existing Mobile State Diagram for CSFB Page Response (based on IS-2000.5)
Update Overhead
Information
substate (2.6.3.2)
Page Response
substate (2.6.3.3)
RRCConnection
Release (Redirect
to 1x)

8. C2 – Company Confidential8 | CSFB | June, 2009
Pilot Channel Acquisition
A dual-receiver UE would presumably already have acquired 1x pilots prior to
the redirection.
If the optional 1x measurements were used (step 8 of 23.272 MT callflow), then
the single receiver UE should have already acquired 1x pilots using
measurement gaps.
If pilots had not yet been acquired at the time of the CSFB redirection, the
acquisition time will be UE dependent, but this is expected to be a small
component in the total delay, and thus I don’t think it needs to be addressed.
Note that the acquisition latency can benefit from SIB 8 info such as CDMA
timing and 1x Neighbor List.

9. C2 – Company Confidential9 | CSFB | June, 2009
Sync Channel Acquisition
1x Sync Channel Message is (generally) three 80ms superframes. It is sent every
240ms and requires 240ms to receive. UE doesn’t need to know CDMA timing
to receive.
 Typical latency to receive is therefore 240-480 ms.
Contains CDMA timing info, Long Code State, plus the configuration of the
forward common signaling channel.
Paging Channel Rate (4800 or 9600 bps).
BCCH Rate and Code Channel
Even if the UE has CDMA timing from LTE SIB8, under current procedures it
still needs to wait for the sync channel message in order to determine the
overhead channel configuration.
We shouldn’t preclude future deployment of Basic Access mode, so the UE
shouldn’t assume that the 9600bps paging channel is being used.

10. C2 – Company Confidential10 | CSFB | June, 2009
Timing Change Substate
Fixed 320ms delay until the long code state in the sync channel message
becomes valid.
 Based on hardware implementation delays from the early days of CDMA.
 If the UE has received the CDMA long code state from LTE SIB8, then it
should be allowed to skip this substate before it attempt to receive the
paging channel/broadcast control channel.

11. C2 – Company Confidential11 | CSFB | June, 2009
Update Overhead Information
Mobile must tune to paging channel and receive all the overhead messages (e.g. System Parameters,
Access Parameters, Neighbor List, etc).
Per standard, these messages must be sent at least every T1b = 1.28 seconds, but could be sent
faster. It is common in 1x networks using Alcatel-Lucent infrastructure to repeat every 7 slots
(560ms).
When MS receives CDMA Channel List or Extended CCLM, it will perform the hashing algorithm to
select a CDMA channel.
 A large fraction of UEs will suffer hashing latency [ (n-1)/n] where n=# of 1x carriers in CCLM.
When the MS receives the System Parameters message, it will perform the hashing algorithm to select
a paging channel on the serving CDMA carrier.
 Most operators use 2 paging channels, so only 50% of the UE would suffer hashing latency.
Broadcast of messages on paging channels on different carriers may be unsynchronized. The messages
may be independently transmitted. When the UE hashes, it needs to re-receive any previously
received overhead messages on the new channel.

12. C2 – Company Confidential12 | CSFB | June, 2009
Impact of hashing on overhead acquisition
Carrier 1
PCH 1 SPM APM ECCLM ESPM GNLM
PCH 2 SPM APM ECCLM ESPM GNLM
Carrier 2
PCH 1 SPM APM ECCLM ESPM GNLM
PCH 2 SPM APM ECCLM ESPM GNLM
Carrier 3
PCH 1 SPM APM ECCLM ESPM GNLM
PCH 2 SPM APM ECCLM ESPM GNLM
Mobile
{1,1} SPM APM ECCLM ESPM GNLM
Mobile
{1,2} SPM APM ECCLM ESPM GNLM SPM
Mobile
{2,1} SPM APM ECCLMECCLM ESPM GNLM SPM APM
Mobile
{2,2} SPM APM ECCLMECCLM ESPM GNLM SPM APM ECCLM ESPM GNLM SPM
Mobile
{3,1} SPM APM ECCLM APM ECCLM ESPM GNLM SPM
Mobile
{3,2} SPM APM ECCLM APM ECCLM ESPM GNLM SPM APM ECCLM ESPM GNLM SPM
Example of overhead sequence
In this example, carrier 2
is 1 slot behind carrier 1,
and carrier 3 is 2 slots
behind.
1 80ms
Paging Slot
Hash Events
{x,y} means Carrier x,
channel y
Mobile {1,1} acquired overhead in
just 400ms, but Mobile {3,2}
required 1360ms.

13. C2 – Company Confidential13 | CSFB | June, 2009
Hashing in CDMA
The intent of Carrier and paging channel hashing are to balance the paging channel load
across multiple carriers and paging channels. It is am imperfect method in that the
mobiles in a given area may not be evenly distributed.
There is already a capability in IS2000 to turn off hashing for a limited time to reduce
latency. Immediately following an Access Handoff, the MS does not perform carrier
hashing. A similar method could be used to not perform hashing for the duration of the
CSFB attempt.
 The eNB balances loading as necessary by redirecting UEs to different carriers as
required.
Alternatively, a pre-hashing technique could be used where the source eNB provides
information about the 1x network and the MS first attempts to acquire the hashed
carrier & channel.
 For pre-hashing to be effective, the source eNB needs to be tightly coordinated with
the underlying 1x system; otherwise it will add delay relative to the no-hash option
above.
 Due to the complexity of handling this option, the no-hash option is preferred.

14. C2 – Company Confidential14 | CSFB | June, 2009
Near-Term CSFB Performance Enhancement concept
Proposed solution is targeted toward 3GPP Release 8 CSFB.
 No impact to existing 1x network beyond support of paging over S102
tunnel.
 No change to 3GPP standards.
 Changes in 3GPP2 C.S0087
 Changes in 1x device
 Change in eNB
Solution combines elements of existing 1x features to minimize latency.
Use RELEASE_TO_IDLE procedures to find overhead configuration without
receiving sync channel message.
Use access handoff procedures to avoid hashing delays during CSFB call
attempts.

15. C2 – Company Confidential15 | CSFB | June, 2009
Near-Term CSFB Performance Enhancement details
Add optional fcsch configuration information into the
MobilityParametersCDMA2000 IE in the CSFBParameters ResponseCDMA2000
RRC message.
 PRAT – Paging Channel Rate
 PAGE_CHAN – Paging Channel which the MS should acquire (NOT hash over)
 or
 SR1_BRAT_NON_TD – BCCH Rate
 SR1_CRAT_NON_TD – BCCH Code Rate
 BCCH_CODE_CHAN_NON_TD – BCCH Code Channel
 CDMA_FREQ & BAND_CLASS – CDMA Carrier Frequency and band class on
which the UE should operate for this CSFB attempt unless otherwise
specified (e.g. in RRC Connection Release).

16. C2 – Company Confidential16 | CSFB | June, 2009
MS Procedures with new Information
MS adds new Tunneled Acquisition State
 If the UE has CDMA timing (e.g. from SIB8), then MS enters this state after
redirection instead of normal initialization substates.
 Mobile goes to the specified carrier, and attempts to acquire the f-csch
(including the specified paging channel).
 If no valid paging channel messages are received within a timer, then the
MS falls back to normal sync procedures.
 If CCLM is received in this state, it does not perform channel hashing (i.e.
the MS assumes that the AN distributed the load). If the SPM is received in
this state, the MS does not perform paging channel hashing.
 This is similar to existing behavior after an access handoff.
 In the normal case, on average over 1 second of latency is removed with
this approach.

17. C2 – Company Confidential17 | CSFB | June, 2009
New State Diagram
Update Overhead
Information
substate (2.6.3.2)
Page Response
substate (2.6.3.3)
RRCConnection
Release (Redirect
to 1x)
Timing Change
Substate (2.6.1.4)
Sync Channel
Acquisition
Substate (2.6.1.3)
Pilot Channel
Acquisition
Substate (2.6.1.2)
Tunneled
Acquisition
Substate
If failure

18. C2 – Company Confidential18 | CSFB | June, 2009
Proposed Modified Steps to acquire traffic channel upon redirection
time
Tunneled
Acquisition
Access
Procedures
Network
Setup
Channel
Assignment
Traffic
Acquisition
RRC
Redirection
1x Pilot
Search