4-Cdma Key Technology

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Copyright 2003, ZTE CORPORATION

CDMA KEY

TECHNOLOGY2004.10.3


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Objectives

-- Powercontrol in CDMA

why powercontrol

howtorealize

-- Handoffin CDMA

what is handoff

CDMAs softhandoffsofthandoffprocedure

Upon completion ofthis lesson, thestudent will beableto master:


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Why Power Control?

All CDMA users occupy the samefrequency at the same time! Frequencyand time are not used as discriminators.

CDMA operates by using CODES todiscriminate between users.

CDMA interference comes mainly from

nearby users

Each user is a small voice in a roaringcrowd -- but with a uniquely recoverablecode.

Transmit power on all users mustbetightlycontrolledso theirsignalsreachthebasestation atthesamesignal leveland atthe absolute minimum powerlevel necessaryto ensure acceptableservice quality

FigureofMerit: Ec/Io, Eb/No(energy perchip [bit] /

interference [noise] spectraldensity)

CDMA: Ec/Io -17to-2dB

CDMA: Eb/No ~6to7dB


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ReverseOpen Loop Power Control

The mobile station makes a coarse initial estimation of the required transmitpower, based upon the total received power.

Problems with Reverse Open Loop Power Control:

Assumes same exact path loss in both directions; therefore, cannotaccount for asymmetrical path loss

Estimates are based on total power received; therefore the power receivedfrom other cell sites by mobile station introduces inaccuracies

Mobile BTS

Reverse Open Loop

PowerControl


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EstimatedReverseOpen Loop

Output Power

meanoutput power(dBm) = - mean powerinput(dBm)

+ K+ NOM_PWR - 16 x NOM_PWR_EXT

+ INIT_PWR

Power output level for the initial probe during open loop probing

on the Access Channel (with closed loop correction inactive):

Subsequent probes in the sequence are sent at increased power levels

(each probe is incremented by a value equal to the parameter PWR_STEP)

The turnaround constant K is calculated assuming

a nominal cell Effective Radiation Power (ERP) of 5 W

and a nominal cell loading of 50%.

Its value is -73 for cellular systems and -76 for PCS systems


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EstimatedReverseOpen Loop

Output Power

Power output level for the initial transmission on the Reverse Traffic Channel:

m

eanoutput power(dBm

) = -m

ean powerinput(dBm

)+ K

+ NOM_PWR - 16 x NOM_PWR_EXT

+ INIT_PWR

+the sumofallaccess probe corrections (dB)


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Reverse Closed Loop Power

Control

Compensates for asymmetries between the forward and reverse paths

Consists of power up (0) & power down (1) commands sent to themobile stations, based upon their signal strength measured at the Base

Station and compared to a specified threshold Each command requests a 1dB increase or decrease of the mobile

station transmit power

Transmitted 800 times per second, always at full power

Allows to compensate for the effects of fast fading

Mobile BTS

Signal Strength

Measurement

Setpoint

or

Reverse Closed Loop

PowerControl


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ReverseOuter Loop Power

Control

Most gradual form of reverse link power control

Setpoint is varied according to the FER onthe Reverse Traffic Channel (determined atthe Base Station Controller)

Sampled at a rate of 50 frames per second(20 ms / frame)

Setpoint adjusted every 1-2 seconds

FER

Mobile BTS BSC

Reverse Outer

Loop Power

Control

Signal Strength

Measurement

Setpoint

or

Reverse Closed Loop

PowerControl


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ForwardTraffic Channel

Power Control

The base station slowly decreases power to each mobile station.

As the FER (determined at the mobile station) increases, the mobilestation requests a Forward Traffic Channel power increase.

FER

Mobile BTS BSC

AdjustFwd.

power

Forward LinkPowerControl


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Summary of All Power Control

Mechanisms

All types of power control work together to minimizes powerconsumption at the mobile stations, and increases the overall capacity

of the system transmit power.

FERFER

Mobile BTS BSC

Signal Strength

Measurement

Setpoint

or

AdjustFwd.

power

Reverse Outer

Loop Power

Control

Reverse Closed Loop

PowerControl

Forward LinkPowerControl

Reverse Open Loop

PowerControl


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Handoffs

Handoff is the process by which a mobile station maintainscommunications with the Mobile Telephone Switchingcenter(MSC), when traveling from the coverage area ofone base station to that of another.

Handoffs keep the call established during the followingconditions:

Subscriber crosses the boundaries of a cell

Subscriber experiences noise or other interferenceabove a specified threshold

A base station component experiences an out-of-servicecondition during a call


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CDMA Handoffs

CDMA Handoffs

Make-before-break

Directed by the mobile not the base station Undetectable by user

Improves call quality

Handoffs consist of the following phases:

Initiation (trigger), Target Selection, and Completion (execution)

Cell Site

B

Cell Site

A

Cell Site

ACell Site

B

CDMA


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CDMA Handoffs (cont.)

During

a Call

Idle Handoff

Soft Handoff

SofterHandoff

CDMA-to-CDMA Handoff

Inter-System Soft Handoff

CDMA-to-Analog Handoff

While inthe

Idle State


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SoftHandoff

Soft Handoff: the mobile station starts communications with a

target base station without interrupting communications with thecurrent serving base station.

Can involve up to three cells simultaneously and use all signals

Mobile station combines the frames from each cell

Cell Site

BCell Site

A

PSTN

MSC

B

S

C


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SofterHandoff

Handoff is between sectors ofthe same cell

Communications aremaintained across both sectorsuntil the mobile stationtransition has completed

May happen frequently

MSC is aware but does notparticipate

All activities are managed bythe cell site

Signals received at both sectorscan be combined for improvedquality

alpha

beta

gamma


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Inter-System SoftHandoffs

(ISSHO)

Mobile Station starts communications with a new cell controlled by adifferent BSC while still communicating with the cell controlled by thesource BSC

Soft Handoffs over Hard Handoffs

Fewer border cell

MSC

SVBS

HIRSE1 Links

MSC

SVBS

HIRS

A

f1

D

f1

B

f1E

f1C

f1F

f1

U

f1

X

f1

V

f1Y

f1W

f1Z

f1

CDMA Soft Handoff ISSHO CDMA Hard Handoff

E1 Links

TIA/EIA-41D


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CDMA-to-CDMA Hard

Handoff

Between cells operating on different frequencies

Between cells that could be on the same frequency, but which are

subordinated to different MSC

A

(1)

PSTN

MSC

BSC

B

(2)A

PSTN

MSC

BSC

B

MSC

BSC

T1orE1 Links

TIA/EIA-41D


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WhatsIn a Handset?

ReceiverRF SectionIF, Detector

TransmitterRF Section

Vocoder

DigitalRake Receiver

Traffic Correlator

PN xxx Walsh xx

Traffic Correlator

PN xxx Walsh xx

Traffic CorrelatorPN xxx Walsh xx

Pilot Searcher

PN xxx Walsh 0

ViterbiDecoder

CPUDuplexer

TransmitterDigital Section

Long Code Gen.

Open

Loop

Transmit Gain Adjust

Messages

Messages

Audio

Audio

Bit Packets

Symbols

SymbolsChips

RF

RF

AGC

Bit Packets

7


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SoftHandoff Key:

Ec/Io ShortPN Code Offsets

NeighborSet

Active Set

Candidate Set

Remaining Set

RakeFingers 12 3

Pilots Above Searched In This Order:

A A A C N

R

A A A C A A A C A A A C A A A C A A A C A A A CN N N N N N

A A A C N A A A C A A A C A A A C A A A C A A A C A A A CN N N N N

A A A CN A A A C A A A C A A A C A A A C A A A C A A A CN N N N N N

N A A A C A A A C A A A CN N N R A A A C N A A A C A A A C A A AN N

C A A A C A A A CN N N

R

A A A C N A A A C A A A C A A AN N C A A AN

C A A A CN N Until all are scannedthen repeat

Understandthesearcherseffectin differentstate

--- MS powerup state

--- MSidle andcallingstate


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PilotSets

Pilot sets: Active Set: Pilots associated with the forward traffic channelsassigned to the mobile station (max 6 pilots)

Candidate Set: Pilots not currently in the Active Set, but receivedby the mobile with sufficient strength to indicate that thecorresponding Traffic Channels can be successfully demodulated(max 5 pilots)

Neighbor Set: Pilots not currently on the Active or Candidate Sets,that are likely handoff candidates (at least 20 pilots) Remaining Set: All other possible pilots in the current system on

the current CDMA frequency assignment

All pilots in a set have the same frequency assignment

These sets can be updated during handoff by the base station

Pilot Sets

1. Active

2. Candidate

3. Neighbor

4. Remaining


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PilotSetInitialization(While inthe Idleorinan Active Call)

Candidate

Remaining

Active

Neighbor

Pilot whose Paging Channel

is being monitored orassociated with the assignedForward Traffic Channel

Pilots specified in the mostrecently received Extended

NeighborList Message(AGE set at NGHBR_MAX_AGE)

Empty

Any other possible pilotin the system


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PilotSet Maintenance(While inan Active Call)

Candidate

Remaining

Active

Neighbor

Pilots listed the mostrecently received Extended

HandoffDirection Msg

Pilots specified in the mostrecently received Neighbor

ListUpdate Message

(or whose AGE is still less

than NGHBR_MAX_AGE)

Pilots whose strengthexceeds T_ADD

Any other possible pilotin the system


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PilotStrength Measurement

Message (PSMM)

The Pilot Strength Measurement Message is used by the mobile station to

direct the base station in the handoff process.

Mobile station reports the strength of the pilots associated with forwardtraffic channels currently being demodulated (and whether it would like

to continue to receive traffic from them), as well as pilots from the

neighbor and remaining list which are being received with sufficient

strength so that traffic could be demodulated from them successfully.

A

B

C

Pilot Channel

Timing


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PilotSearchWindows

A search window is a range of PN offsets (in chips) where the mobilestation searches for usable multipath components of the pilots in a set

Usable means that multipath components can be used fordemodulation of an associated traffic channel

SearchWindowforpilots inthe Activeand Candidate Set:

SearchWindowforpilots inthe NeighborSet:

SearchWindowforpilots inthe Remaining Set:

Earliest arriving usable multipath component of the pilot

pilot PN offset

pilot PN offset

SRCH_WIN_N

SRCH_WIN_A

SRCH_WIN_R


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PilotStrength

Pilot Strength

exceeds T_ADD

EHOD message received,

Pilot Dropped into Neighbor Set,

EHOC message sent,

NLUmessage received

Time

Pilot strength drops below T_DROP,

Drop Timer started

T_TDROP

T_ADD

T_DROP

EHOD message received, Pilot Added to Active Set,

EHOC message sent, NLUmessage received

N C NA

(1) (2) (3) (4) (5)(6) (7)

Drop Timer expires

PSMM sent (request to add) ,Pilot added to Candidate Set

PSMM Sent (request to remove)

SoftHandoffSignaling

T_ADD: pilot detection threshold (Typically 26 = -13dB)

T_DROP: pilot drop threshold (Typically 30 = -15 dB)

T_TDROP: drop timer value (Typically 3 = 4sec)

Prevents unnecessary transmissions of PSMM when a mobile stationexperiences a fade


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Power Control duringSoft

Handoff During soft handoff, the mobile station

receives power control bits frommultiple base stations.

If two or more power controlsubchannels are identical, their power

control bits are diversity combined intoone per 1.25 ms time slot.

If the mobile station receives differentpower control bits from different powercontrol subchannels, it decreases itsmean power output level by 1 dB.

Only if the power control bits fromALL power control subchannelsrequest a power increase, the mobilestation increases its mean power outputlevel by 1 dB .


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SoftHandoff New Parameterin 1X

T_ADD

NeighborSet

ActiveSet

NeighborSet

CandidateSet

Time

(2) (4) (5) (7) (8)

PilotStrength

T_DROP

(1) (3)

P2

CandidateSet

(6)

P1

P2

P1

10log10 PSii

A

IS-2000princinple


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Handoff Parameters

T_ADD

T_DROP

T_TDROP T_COMP

SOFT_SLOPE

ADD_INTERCEPT

DROP_INTERCEPT SRCH_WIN_A

SRCH_WIN_N

SRCH_WIN_R


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Prefered ParametersSetting

name range Preferedrange

Qualcommprefered

T_ADD 0~31 24~28 28

T_DROP 0~31 28~32 32

T_TDROP 0~15 2~4 3T_COMP 0~15 4~6 5

SRCH_WIN_A 0~15 7~9 8

SRCH_WIN_N 0~15 9~11 10

SRCH_WIN_R 0~15 9~11 10SOFT_SLOPE 0~63 0~63 18

ADD_INTERCEPT 0~63 0~63 6

DROP_INTERCEP

T

0~63 0~63 2~6


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SearchWindow Setting

SRCH_WIN_val0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Width, Chips4(2)

6(3)

8(4)

10 (5)

14(7)

20 (10)

28(14)

40 (20)

60 (30)

80 (40)

100 (50)

130 (65)

160 (80)

226(113)

330 (165)

452(226)


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TheEnd!

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