C-CF CDMA2000 1x Data Service Optimization-20071031-A-3.0

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HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

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Internal

ORG009601 CDMA2000

1x Data Service

Optimization

ISSUE 1.0



HUAWEI TECHNOLOGIES CO., LTD. All rights reserved Page 1

Introduction

CDMA 1x provides conventional voice service as well as

CDMA 2000 High Rate Packet Data. Due to the expansion and

development of network, and ever-increasing data users, the

requirements for trustworthy evaluation and perfect

optimization of data service are raised.

This training is designed for data service coexisting with voice

service (SO33). Optimization and evaluation approaches of

CDMA1X data service are put forth based on the analogy of

voice service and features of data service.




After this course, you will be able to:

Know about the basic concepts of CDMA 1x data service

Master optimization methods at air interface.

Power Control Parameter, Load Parameter, and SCH

Allocation

Master optimization concept of network side

RLP Parameters and TCP Parameters

Learn about performance evaluation of CDMA1x data

service




Chapter 1 Characteristics of Data Service

Chapter 2 Radio Performance Optimization

Chapter 3 Network Performance Optimization

Chapter 4 Optimization Case





2.1 Data Rate

2.2 User Behavior

2.3 SCH Allocation Algorithm




Physical Level Data Rate

Physical Level Data rate：

Release 0 1 SCH+1 FCH=153.6kbps+9.6kbps=163.2kbps

2 SCH+1 FCH=307.2kbps+9.6kbps=316.8kbps

Allocation of Walsh Code Resource


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2.1 Data Rate

2.2 User Behavior





User Behavior




User Behavior

1. Session Period（Session）




User Behavior

2. Data Call




User Behavior

3. Download time, upload time, server delay, and thinking time.

Download Time




User Behavior

4. Activation and dormant periods: In activation period, data is sentand air interface still exists. Activation period is converted into dormant

period because of no data sending. In dormant period, the connections

in air interface are disconnected except PPP connection.

5. Voice calls only occupy FCH with the bandwidth of 9.6 kpbs. FCH is

connected before users hook on. Each data call must occupy a FCH.The difference lies in that the system allocates a SCH to users due to

data bursts. The bandwidth is dynamically allocated according to

current loads. Release SCH after data bursts are sent in a short time.

6. The rate of SCH can be up to 19.2kbps, 38.4kbps, 76.8 kbps, or

153.6kbps.




User Behavior





2.1 Data Rate

2.2 User Behavior





SCH Allocation Strategy

1. SCH Static allocation

A user occupies SCH channel independently when a call start. The

SCH channel is allocated for the maximum rate according to load

and power. However, static SCH allocation mode results in unfair

resource use. Allocate the maximum rate to user who accesses first. And the rates allocated to the subsequent users decrease gradually.

2. SCH Dynamic allocation

Scheduling of Time Slice

Measurement and estimation of load

Resource allocation




SCH DurationScheduling of Time slice（Fixed Duration）




Load Prediction

Measurement of Estimation of Load




Resource Allocation

Resource Allocation Allocate WALSH chip, CE, bandwidth and power resource and establish air

interface connection.

Send the ESCAM to MS.

• Acknowledgement mode: Delay is long and throughput decreases.

•Re-transmission mode: MS acknowledgement is not required.

After the ESCAM is received, send data burst within a specific duration.When duration is over, release SCH and re-establish SCH for the next time

slice use.




Time Slice and Duration

4. Time slice with variable duration

Allocate a rate for a user according to current radio environment, load and

the size of data amount, and appoint flexibly the length of time slice.

5. SCH extension

SCH extension indicates that users can transmit data on SCH channel

continuously through the extension data burst within a finite duration.

Extended SCH fills up gaps of SCH released and re-applied by original

SCH to facilitate time efficiency of SCH transmission.




SCH Allocation Flow Chart

Change in Active Set?

Strongest Pilot

Different?

RLP Buffer Data <

RELEASE_THRESHLOD

?

No

Yes

Yes

Increase in Number

of Pilots?

Call Rate Request

Processing Mechanism

Rate

Acceptable?

No

Yes

Yes

Yes


Strongest Pilot

Different?

RLP Buffer Data <

RELEASE_THRESHLOD

?

No

Yes

Yes

Increase in Number

of Pilots?

Call Rate Request


Rate

Acceptable?

No

Yes

Yes

Yes

Supportable Rate

Different?


Strongest Pilot

Different?

RLP Buffer Data <

RELEASE_THRESHLOD

?

No

Yes

Yes

Increase in Number

of Pilots?

Call Rate Request


Rate

Acceptable?

No

Yes

Yes

Yes


Strongest Pilot

Different?

RLP Buffer Data <

RELEASE_THRESHLOD

?

No

No

Yes

Yes

Yes

No

Increase in Number

of Pilots?

No

Call Rate Request


Rate

Acceptable?

No

Yes

Yes

No

Yes

Supportable Rate

Different?

Do not extend the burst Extend the burst Do not extend the burst Extend the burst Do not extend the burst Extend the burst Do not extend the burst

Extend the burst




Parameters

Parameters Related to SCH extension:

Parameter Name Description Default Value

SCH Extension Switch Extension switch. After extension switch is turned on, factors

(load, pilot strength, FER changes) released by SCH do not

function, that is SCH will not be released actively.

Open

SCH Extension Duration Deliver this parameter in ESCAM message. The duration is

the same with that specified in layer-3 protocol.

10 (32 frame)

SCH Extension Overlap Duration The frame quantity of two front/back overlap SCHs 2 (2 frame)

SCH Extend Low Rate Switch Whether to allow low rate SCH extension. That is, when

current SCH rate is higher than existed SCH, whether the

extension of current SCH is allowed or not. It is caused by the

limitations of receiving same-rate extension.

Support (support low rate

extension)

SCH Extension Buffer Request Switch Whether to buffer SCH extension application message when

CRB is not in idle state (it’s in idle state during soft handoff)

Open (Perform buffer)




Parameters

SCH Extension Max Times It is identical to extension max times of the same rate. 100 (times)

SCH Extension Judge Time Offset Indicates frame amount before previous SCH ending when buffered SCH

extension application can be processed. If the time for extension

application exceeds frame amount, extension application cannot be

processed. Prevent extension C from occurring.

3 (3 frame)

SCH Extension Old Branch Gain When SCH changes branch, SCH must be applied after release.

Therefore, compensate pilot strength of original branch. The priority of original branch is higher than new branch to prevent frequent branch

handoff in soft handoff area.

6 (3DB)

SCH Extension Minimum Rate

(soft parameter)

Indicates the lowest rate of decision extension. If decision extension is

lower than the lowest rate, decision is not extended (No.224 RRM). In

MCHM table, if “SCH Extend Low Rate Switch” is disabled, this

parameter does not function. The rate of SCH extension is 16 times as

much as maximum rate.

4 (16X)

3 (8X)

2 (4X)

1 (2X)Default value: 2

SCH Extension Minimum Times

(soft parameter)

Decides whether to raise rate limitation to implement extension after low

rate is allocated. It can avoid raise rate at once after allocation.

5












2.1 Forward SCH Configuration

2.2 Reverse SCH Configuration




Target FER

Set the target FER of data service, ranging 1% through 10% or above.

Generally, you can set the same target FER such as 5% for different data

rates or set different target FERs for different data rates. Generally

speaking, the lower rate is, the smaller target FER is, as shown in the

following table.




Relationship of FER and Power

The curve in the following figure shows the relationship between FER andpower efficiency.




Time Slice Allocation Strategy

Time Slice allocated by Data Burst (Burst Duration)

Advantages of long Duration:

Fast power control algorithm ensures enough time for SCH to converge target FER

The decrease of ESCAM messages can reduce signaling burden.

Lighten the burden of scheduling process.

Advantages of short Duration:

BS has more chances to adjust data transmission rate.

Adopting short Duration, data packet with short length can facilitate high transmission efficiency.

TCP performance is superior.

It is recommended that you set Duration between 16 and 64 frames. Long Duration decreases the

times of SCH allocation and total signaling delay. Long data facilitate maximizing the throughput of

single user. However, short data burst reduces the system throughput, because the time slice does

not end after data is sent.




Power Control Parameter

FPC_MODE：Fast power control mode

0: F-FCH uses fast power control at the rate of 800 bps. F-SCH has no

power control. The power of F-SCH =Current l F-FCH power + an

offset. Offset value varies with different rates.

1: F-FCH/F – SCH use power control at the rate of 400/400 bps.

2: F-FCH/F – SCH use power control at the rate of 200/600 bps.

When SCH is allocated, FPC_MODE = 1. Otherwise, FPC_MODE = 0





Initial value of SCH power

When FPC_MODE = 1 or 2, you should set the initial power of F-SCH according

to follow.

Method 1:

Use absolute parameters. Data burst at a certain rate adopts the same

SCH power initial value.

Method 2:

Use relative parameters. Add an offset to current F-FCH power. The offset

is relative to channel rate, target FER, channel coding mode, and handoff

state and so on.

Misc Handoff Coding FER Rate P P FCH SCH

Method 3:

The initial transmit power of SCH is identical to that when the last data

burst ends. This method is easy but hard to control.





Maximum and Minimum Transmit Power of Forward SCH

In actual network, when system load is light and users who are far from

BTS apply for high rate data service, forward SCH power is high and is

within the threshold of SCH max transmit power. To use power rationally,

allocate different data rates according to the distances between MS and

BTS. Allocate high rate to the core area near to BTS. Allocate low rate to

edge area far from BTS. Some manufacturers set SCH maximum power

consumption at different rates. Therefore, MS far from BTS cannot be

allocated with high rate data service, due to power limit.




Relationship between Rate and Area

-16

-14

-12

-10

-8

-6

-4

-2

0

19.2k 38.4k 76.8k 153.6k 307.2k

Ec/Io

Data Rate

（bps）

Required Eb/Nt

（dB）

Spread Gain

（dB）

Required Ec/Io

（dB）

19200 3.9 18 -14.1

38400 3.6 15 -11.4

76800 3.4 12 -8.8

153600 3.2 9 -5.8

307200 3.2 6 -2.8




Rate Application and Work Mode

Rate Application of Forward SCH

(1) Maximum rate confirmed by service negotiation

(2) Maximum rate pre-defined in HLR

(3) Data amount in SDU and PCF buffers

Working Mode of Forward FCH in Data Service

(1) FCH only transmits data instead of signaling.

(2) When SCH is not allocated, use FCH to transmit low rate data

service. Otherwise, FCH transmits data instead of signaling.

(3) FCH can transmit data in any time.

Most manufacturers adopt mode (2) and (3). Some manufacturers

only upload re-transmission data of RLP layer on FCH.




Parameter Summary

Parameter

description Variable Meaning Recommended value

NX SCH

Eb/Nt Initial

Value

FWD_INI_SCH_SET_PT_

NX

Calculate the initial value of forward SCH outer loop

power control performing inside MS. The initial value

is equal to add current FCH outer loop power control

to this parameter.

24 (3dB)

NX SCH

Maximum

Value

FWD_MAX_SCH_SET_PT

_NX

Maximum value of SCH forward outer loop power

control Eb/Nt saved in MS.

1X. 2X. 4X: 80(10dB) 8X:

88(11dB) 16X: 96(12dB)

NX SCH

Minimum

Value

FWD_MIN_SCH_SET_PT_

NX

Minimum value of SCH forward outer loop power

control Eb/Nt saved in MS.16(2dB)

SCH

Maximum

Gain 1

FWD_SCH_MAX_GAIN_R

ATIO1

Maximum transmit power of forward SCH when calls

are not in soft handoff state.223(-8dB)

SCHMinimum

Gain 1

FWD_SCH_MIN_GAIN_R ATIO1

Minimum transmit power of forward SCH when callsare not in soft handoff state.

171(-21dB)

NX SCH

Forward Initial

Transmit Gain

FWD_SCH_INI_GAIN_NX Initial transmit power of forward fast power control.1X. 2X. 4X: 215(-10dB) 8X.

16X: 223(-8dB)




Parameter Summary

Forward NX SCH load

admission threshold in

edge area

FWD_BORDER_NX_VALVE Allow allocating maximum forward load percent of NX SCHchannel e and set admission threshold.

100%

Forward NX SCH load


transition area.

FWD_MIDDLE_NX_VALVE Allow allocating max forward load percent of NX SCH

channel in transition area and set admission threshold.100%

Forward NX SCH load


center area

FWD_CENTER_NX_VALVE Allow allocating max forward load percent of NX SCH

channel in center area and set admission threshold.100%

Pilot strength threshold in

cell center CENTER_PLT_THRESH

When pilot strength is less than (CENTER_PLT_THRESH -

64)/2(dB), users are located in pilot center area. The

highest SCH rate allowed allocating is 16X.

50(-7dB)

Pilot strength threshold at

the edge of cellBORDER_PLT_THRESH

When the pilot strength is within

[(BORDER_PLT_THRESH - 64)/2,

(CENTER_PLT_THRESH - 64)/2] dB, users are located in

pilot transition area and the highest SCH rate allowed

allocating is 8X. When pilot strength is lower than

(BORDER_PLT_THRESH - 64)/2 dB, users are located in

edge area and the highest rate allowed allocating is 4X.

44(-10dB)





2.1 Forward SCH Configuration

2.2 Reverse SCH Configuration




FER and Application

Reverse SCH Target FER

It is identical to that of forward SCH.

Rate Application of Reverse SCH

(1) Maximum rate confirmed by service negotiation

(2) Maximum rate defined in HLR

(3) MS applies for rate through SCRM message (buffer of Qualcomm

MS is about 300 bytes)

When only data service is performed (such as web page browse,

and files download), the load of reverse links is light. It is not

required to establish R-SCH, because R-FCH can send

ACKnowledgement message to TCP server.




Reverse SCH Burst Duration

Generally, reverse data service means files upload or E-mail sending. You

set long Burst Duration (an infinite duration) and short DTX Duration. DTX

Duration is the maximum time when no data is sent. If no data is sent still

beyond DTX Duration, MS sends SCRM to release R-SCH.

DTX Duration is a half of Burst Duration. Or you can also set it to a fixed

value. Generally, the value is set to 10 frames by default.




Reverse SCH Power Control

Reverse SCH transmit power=reverse pilot transmit power + an offset, as

shown in the following:

Transmit Power(dBm) = Mean Reverse Pilot channel output Power(dBm)

+ Nominal_Attribute_Gain[Rate, Frame Duration, Coding]

+ Attribute_Adjustment_Gain[Rate, Frame Duration, Coding]

+ Reverse_Channel_Adjustment_Gain[Channel]

－ Multiple_Channel_Adjustment_Gain[Channel]

+ RLGAIN_TRAFFIC_PILOT

+ RLGAIN_SCH_PILOT[Channel]s




Reverse SCH Power Control

The gain that reverse SCH is relative to reverse pilot: This group of parameters indicates offsets, which SCH channel power is relative to

reverse pilot power. Deliver the offset to MS in ESCAM message. The

higher parameters are, the higher reverse SCH transmission efficiency is.

However, reverse capacity is affected. The higher rate SCH is, the larger

required power is. Therefore, this offset should be set to a larger value.

Set rationally power offset that the SCH is relative to FCH to obtain target

FER of reverse SCH. Parameter Nominal_Attribute_Gain [Rate, Frame

Duration, Coding] shows the offset. Qualcomm proposes some

recommended values, but these values are applicable for the two followingcases:

Target FER of SCH is 5%.

Target FER of FCH is 1%.




Outer Loop Power Control of Reverse SCH

Even if you can set rationally power offset relative to reverse pilot

channel, target FER of reverse SCH is still not satisfied when FCH

active set is inconsistent with that of reverse SCH.

FCH Active Set A

FCH Active Set B

Branch A is good, while branch B is poor. Reverse SCH is established on

branch B. At this time, FCH can converge target FER, and FER of

reverse SCH is high.




Flow ChartRCAG :Reverse_ Channel _ Adjustment _ Gain

New Frame

Determine R-SCH

Eb/Nt Set point

Send PCNM During

SCH_PER?

Estimate actual

R-SCH EbNt

Difference between SCH

Eb/Nt set point and actual

Eb/Nt>0.5dB

Estimate new RCAG

Fill RCAG in PCNM

NY

Y

N




Parameter Summary

Parameter description Variable MeaningRecommended

value

1X reverse SCH relative

reverse pilot gain

RLGAIN_SCH_PILOT_

1X

Indicate offset of 1X SCH channel power relative to

reverse pilot power. Deliver it to MS in channel

allocation message (ESCAM).

40(5dB)


to reverse pilot gain

RLGAIN_SCH_PILOT_

2X




44(5.5dB)



RLGAIN_SCH_PILOT_

4X




44(5.75dB)



RLGAIN_SCH_PILOT_

8X




44(6.25dB)



RLGAIN_SCH_PILOT_

16X




44(6.5dB)




Parameter Summary

1X RC3 data serviceequivalent voice

channel amount

E_1X_DATA_EQUThe amount of equivalent voice channel of 1X RC3 data service is used for reverse

admission of data service.

25(2.5)

2X RC3 data service

equivalent voice

channel amount

E_2X_DATA_EQU

The amount of equivalent voice channel of

2X RC3 data service is used for reverse


40(4)

4X RC3 data service

equivalent voice

channel amount

E_4X_DATA_EQU




75(7.5)

8X RC3 data serviceequivalent voice

channel amount

E_8X_DATA_EQUThe amount of equivalent voice channel of 8X RC3 data service is used for reverse


130(13)

16X RC3 data

service equivalent

voice channel

amount

E_16X_DATA_EQU




220(22)












3.1 Calculation of Throughput

3.2 Abstract of TCP

3.3 PLP Layer

3.4 Performance Analysis




Throughput

Padding

Bits

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

IS-2000 1X SCH Data Tail BitsFQI

Mux Hdr RLP Frame Mux Hdr RLP Frame

RLP

header PPP DataRLP

header PPP Data

PPP

header MTU Frame

TCP/IP

header Application Data

Application Data

SDU

Layer

Mux

Layer

RLP

Layer

PPP

Layer

TCP/IP

Layer

Appli

Layer

Physical

Layer

Padding

Bits

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

Mux

PDU

IS-2000 1X SCH Data Tail BitsFQI

Mux Hdr RLP Frame Mux Hdr RLP Frame

RLP

header PPP DataRLP

header PPP Data

PPP

header MTU Frame

TCP/IP

header Application Data

Application Data

SDU

Layer

Mux

Layer

RLP

Layer

PPP

Layer

TCP/IP

Layer

Appli

Layer

Physical

Layer

Throughput (bps) = Total Sent Data (Byte) * 8 / Total Time (sec)




Overhead TCP/IP layer

TCP/IP data packet header is 40bytes.The typical length of TCP data packet is between 500 and 1500 bytes.The proportion of

transmission efficiency decrease caused by TCP header is between 2.7% and 8%.

PPP layer

To reduce influence of TCP/IP header, PPP link established between PDSN and MS uses header compression technology. We

can compress the length of data header to 4 bytes. Header compression technology affects throughput, ranging from 0.27% to

0.8%.

RLP layer

When FCH is used to transmit data, the length of RLP header and frame are 10 bits and 172 bits respectively. Throughputdecreases by 5.8%.When SCH is used to transmit data, the length of RLP header and frame are 16 bits and 352 bits respectively.

Throughput decreases by 4.55%.

Data re-transmission caused by frame error of RLP layer

Suppose twice-re-transmission is adopted. When FER is 5%, the throughput decreases by 10%. When FER is 1%, the throughput

decreases by 2%.

MUX/RF Layer

153.6 kbps: Influence of MUX/RF layer on throughput accounts for 8.3%.

9.6kpbs: Influence of MUX/RF layer on throughput accounts for 10%.

Rate(kbps) User Bits Overhead Bits RLP per 20ms frame

9.6(FCH) 172 0(MUX)+20(RF) 1 RLP（172bits）

19.2(SCH) 352 8+24 1 RLP（352bits）

38.4(SCH) 704 40+24 2 RLP（352bits）

76.8(SCH) 1408 104+24 4 RLP（352bits）

153.6(SCH) 2816 232+24 8 RLP（352bits）




Actual throughput of Application layer

The maximum data rate supported by air interface is 9.6 + 153.6 = 163.2 kpbs.FER of FCH is 1%. FER of SCH is 5%.

At the rate of 153.6kpbs, throughput decrease accounts for:

1 - (1 –nTCP)× (1 - nRLP)× (1 - nFER)× (1 - nMUX)

= 1 - 0.99 × 0.955 × 0.9 × 0.917

= 22%

At the rate of 9.6kpbs, throughput decrease accounts for:

1 - (1 - nTCP)× (1 - nRLP)× (1 - nFER)× (1 - nMUX)

= 1 - 0.99 × 0.955 × 0.98 × 0.9

= 17%

Bearer signaling on FCH is about 5kpbs.

Actual maximum throughput: (1 - 0.22)× 153.6 kpbs + (1 –0.17)× 9.6 kpbs –

5 kpbs = 122 kpbs






3.2 Abstract of TCP

3.3 PLP Layer





TCP Feature The reasons for TCP to implement reliability, flow control and sequence control are as follows:

Internet Protocol (IP) cannot perform error recovery.

IP cannot provide sequence control or communication confirmation.

IP do not provide connection function.

IP cannot guarantee correct delivering communication data.

If the amount of sites by which IP datagram passes exceeds that allowed during transmissionon Internet, this IP datagram is discarded.

TCP functions:

Connection-oriented data management

Reliable data transmission

Flow-oriented data transmission

Re-sequencing

Flow control

Inclusive acknowledgement strategy




Auto Acknowledgement and Re-send A

B

SEQ=3 sending 300bytes1

ACK=303

SEQ=303 sending 300bytes

2

X delivery failed3

ACK=3034

SEQ=603 sending 300bytes5

ACK=3036 Waiting for 303



ACK=903

7 Send the two data

in case of timeout

8 Confirm the two

data chips




Flow Control

Ack

Ack

Ack

Ack

Ack

Ack

Ack

Segment1

Segment 2, 3

Segment 4, 5

Segment 6, 7

Segment 8, 9

Segment 10, 11

Segment 12, 13

Segment 14, 15

Sender Receiver

Slow StartState

RTT 2

RTT 1

RTT 3

1 Segment

2 Segments

4 Segments

Connection Process

Ack

Ack

Ack

Ack

Ack

Ack

Ack

Segment1

Segment 2, 3

Segment 4, 5

Segment 6, 7

Segment 8, 9

Segment 10, 11

Segment 12, 13

Segment 14, 15

Sender Receiver

Slow StartState

RTT 2

RTT 1

RTT 3

1 Segment

2 Segments

4 Segments

Connection Process




Flow Control

Acks

Segments

Sender Receiver

Congestion

AvoidanceState

RTT 1

RTT 2

8 Segments

9 Segments

Acks

Segments

Sender Receiver

Congestion

AvoidanceState

RTT 1

RTT 2

8 Segments

9 Segments

If the radio

environment is

poor and a TCP

packet is lost

because of

channel fading,

TCP layer takes it

as network

congestion.

Therefore, activate

congestion

avoidance

algorithm and

decreasethroughput. At this

time, large amount

of bandwidth

resources is idle.




Flow Control

Ack for Seg1 ｢ﾙ Ack for Seg1 ｢ﾚ Ack for Seg1 ｢ﾛ

Ack for Seg11

Segment 1 - 5 Sender Receiver

Window

Size = 8 ｡ﾁ

Ack for Seg1

Seg1 Seg2

Seg3 Seg4 Seg5

Segment 2

Seg8

｣ｺ

Seg2

Seg9

Seg10Seg11

Ack for Seg1 ｢ﾙ Ack for Seg1 ｢ﾚ Ack for Seg1 ｢ﾛ

Ack for Seg11


Window

Size = 8 ｡ﾁ

Ack for Seg1

Seg1 Seg2

Seg3 Seg4 Seg5

Segment 2

Seg8

｣ｺ

Seg2

Seg9

Seg10Seg11


Window

Size = 8 ｡ﾁ

Ack for Seg1

Seg1 Seg2

Seg3 Seg4 Seg5

Segment 2

Seg8

｣ｺ

Seg2

Seg9

Seg10Seg11




Flow Control

Segment 1-5

Sender

Window

Size = 8｡ﾁ

Ack for Seg1

Ack for Seg1

Ack for Seg1

Ack for Seg1

Seg1

Seg2

Seg3

Seg4

Seg5

Segment 2

Seg8

Ack for Seg11

｣ｺ

Seg2

Seg9

Seg10

Seg11

WindowSize = 4 Seg12




RTT Loop Back Delay

RTO timeout re-transmission timer

Because of RTT variability, generally timeout timer times out so early that Internet generates a lot of data chips. On the other hand, using a

smaller value as timeout value can re-transmit lost data chips as soon as possible. Based on the above reasons, TCP does not use clocks

with fixed re-transmission time. TCP adopts a self-adaptive re-transmission clock, based on analyzing confirmed delay from far end host.

R = 0.9 × R + 0.1 × N

R: previous RTT;

N: newly tested RTT;

Re-transmission timeout: RTO = 2 × R

Later, Jacobson modified RTO:

RTO = R + 4 × d

R = (7/8) × R + (1/8) × N

d = (3/4) × D + (1/4) ×R - N (D is the variability of RTT)

In radio environment, situations of transmission delay and packet loss ratio are:

High.

Vary with radio environment.

Unstable.

Therefore, current RTO calculation methods are not applicable for TCP operating on IS-2000 physical layer. Unstable radio network

requires more unnecessary re-transmission. Therefore, network loads increase. As complexity of network increases, you should consider

variability D of RTT in calculation formula again.






3.2 Abstract of TCP

3.3 PLP Layer





Working Mechanism of RLP Layer

RLP layer is located between IS-2000 physical layer and TCP layer. Thefunction of RLP layer is to reduce high FER caused by radio side. Therefore,

packet loss ratio of TCP layer is similar to that of fixed network.




Re-transmission Mode RLP improves FER of air interface to some extent and reduces network

throughput. The mode of re-transmission also affects throughput. Currently, therecommended mode is {1,2,3}, namely three-turn re-transmission. Each turn

indicates re-transmission once, twice and three times respectively.




Mechanism for RLP Applying on SCH

(1) RLP tests forward data buffer and requires re-transmitting frame amount per 20ms.

(2) The reasons that MSG_SDU_RRM_SCH_APPLY_IND message is reported to apply for

SCH are as follows:

No forward SCH.

The data amount of forward data buffer exceeds SCH_LOCK_ THRESHOLD

Frame amount required re-transmitting by RLP exceeds EXMIT_FRAME_THRESHOLD.

(3) The reasons that MSG_SDU_RRM_SCH_STOP_IND message is reported and RRM is

informed not to perform next SCH extension are as follows:

Forward SCH exists.

Data amount of forward data buffer is less than SCH_LOCK _THRESH OLD in a period.

Frame amount required re-transmitting by RLP is less than REXMIT_FRAME _THRES

HOLD.

(4) To avoid RLP applying for SCH frequently, set time interval between last RLP application for

SCH and next application to 10 frames.




Parameters

Parameter description Meaning Recommended value

Buffer Capacity per User Indicate the size of data buffer per data service user

allocated by RLP with the unit of kbytes.

50 kbytes

SCH Stop Check Count Test current RLP decision once per frame. The

conditions for RLP submitting release are as follows:

counter reaches “SCH Stop Check Count”; data in buffer

is lower than “SCH Stop Threshold”; data in re-

transmission queue is lower than Rexmit Frame

Threshold”.

25 frames

SCH Stop Threshold (Byte) Times for RLP stopping SCH continuous testing. 500 bytes

SCH Request Threshold RLP test data in new data buffer per frame. If data

exceeds this threshold and report time is met (the time

from last RLP application is less than interval between

last RLP application for SCH and next application), report

SCH application.

1000 byte

ISCH Request Retry Interval The time interval between last application and next

application. Avoid frequent application. The unit is frame.

30 frames

Rexmit Frame Threshold RLP submits application and test data frame amount of re-transmission queue. If the frame amount is more than

threshold, submit application as well.

300 byte

Active-to-Dormant Inactive Timer Duration Duration from active state to DORMENT state when MS

does not transmit data.

20s






3.2 Abstract of TCP

3.3 PLP Layer





Main Factors Affecting TCP Performance

Three Factors Affecting TCP Performance:

High BER

Bandwidth fluctuation

Bandwidth asymmetry




Cause of High BER1

1. Impact on RLP layer from TCP layer

Error ratio is high. When re-transmission on RLP layer is timeout, re-

transmission is not performed. Frame is discarded, which lead to packet

loss.

The following table shows probability that RLP layer gives up re-transmission in case of 8X SCH and different FERs. After RLP layer gives

up re-transmission, TCP layer activates relative algorithms (fast re-

transmission and fast recovery)

FER Probability about RLP giving up Mean interval between last failure and next

1% <10-12 158 years

5% <310-9 19 days

10% <10-6 1.4 hours

15% <810-6 625 seconds




Cause of High BER22. Acknowledgement delay




Cause of High BER3

3.TCP/IP header compression

TCP/IP header compression (VJC) is the algorithm adopted between

PPP layers. When there is no packet error and the size of data packet

is 1000 bytes, throughput can increase by about 4% after the VJC is

adopted. When there is packet error, synchronization information is lost

and something is wrong with receiver ACK, because VJC algorithm only

transmits the changing bytes in TCP header instead of header itself.

Consequently, fast re-transmission algorithm is invalid. Re-transmit the

lost packet only after timer is timeout. When radio environment is not

ideal and FER is high, it is recommended to disable VJC option.




Cause of High BER4

4. MTU size

If the MTU size is large and the proportion of data header is small, the throughput is large.

Each SDU consists of eight RLP frames at most (153.6 kbps). The length of RLP frame is 44 bytes.If MTU is more than 44 bytes, two

or more SDUs transmit each TCP. The Calculation of TCP packet error ratio is shown as:

TCP packet error ratio = n × ResFER.

n indicates SDU number

ResFER indicates the FER after re-transmission of RLP.

Large MTU can lighten peer acknowledgement burden.

We should consider the above factors when setting MTU size. because these factors affect throughput. For example, when

downloading a file with a fixed size, you can set large MTU to reduce proportion of TCP/IP header and achieve the following results:

Improve throughput.

Total packet amount decreases.

TCP packet error ratio increases.

Absolute packet error number decreases.

RLP re-transmission and TCP acknowledgement can reduce data error greatly. When FER of physical layer is low, it is recommended

to use large MTU value. For CDMA2000 1x system, the recommended size of MTU is 1500 bytes. If RF environment is adverse and

FER is high, adjust MTU value. The impact of MTU on TCP throughput from field measurement result is shown as follow table

(Forward 16 ,mobility):

MTU Value 576 1000

Average throughput (kbit/s) 51.3 65.1

Improvement 27%




Cause of High BER5

5. Selective acknowledgement (SACK)

Segmen

t

1 - 8

Sender Receiver

Window Size = 8

X

Seg1 o.k .

Seg1,3 o.k. Seg2 NG

Seg1,3,4 o.k. Seg2 NG

Seg1,3,4,6 o.k. Seg2,5 NG

Seg1,3,4,6,7 o.k. Seg2,5 NG

Seg1,3,4,6,7,8 o.k. Seg2,5 NG ?

?

?

X

-

.

?

?

?




Solutions

Parameter Setting in case of High BER

RLP: You can increase re-transmission rounds. For example,

change {2,3} into {1,1,1,1,1,1}. Or increase times of each re-

transmission. For example, change {1,2,3} into {1,4,7}.

Disable VJC option.

Enable SACK option.

Reduce the MTU size in case of high TCP packet error ratio.

Activate fast re-transmission after the second duplicated ACK

is received.

Small ACK delay.




Bandwidth fluctuation

2. Impact on TCP Performance from bandwidth change




Parameter Setting

Parameter Setting about bandwidth change

Reduce size of sliding window

Reducing the size of sliding window can reduce the amount of re-transmitted

data packets as well as bandwidth efficiency. After sending data in the window,

the transmitter closes this window and an ACK of the first data packet from the

transmitter and does not send any data. The test of cable network shows that

adjustment of sliding window dimension can reduce 10 M bandwidth to 7 M – 28

kbit/s. Therefore, the size of sliding window should not be set to a too small

value.

Timestamp option

Some TCP strategies sample data packets within a window once in case of RTTcalculation. This method is applicable when bandwidth changes a little. When

bandwidth changes a lot, you can increase collection times to ensure that RTO

adjustment follows the channel change.

Adjust RTO. Add an adjustment amount A to the original RTO.




Bandwidth Asymmetry

3. Bandwidth Asymmetry

In CDMA20001X system, bandwidths provided by forward and reverse are equal. When data amount

of forward and reverse is identical, the bandwidth is asymmetric. The reasons for asymmetric

bandwidth are as follows:

The transmitter sends a large amount of data packets to receiver but the receiver returns ACK.

Allocate SCH only on a direction.

Asymmetric bandwidth results in throughput decrease.

You can adjust several parameters to reduce asymmetric bandwidth impact. Methods for reducing

asymmetric bandwidth influence are as follows:

Increase MTU dimension.

Reduce ACK amount on reverse links.

Increase ACK delay.

Increase amount of TCP packets received before sending each ACK to reduce ACK amount.

Data service test of CDMA20001X shows that large ACK delay occurs if reverse begins to transmit

data as well, forward transmits data. Therefore, test the forward and reverse throughput of data service

separately.




Summary

Parameter Suggested value

Radio factors

High BERBandwidth

fluctuation

Bandwidth

asymmetry

RLP re-transmission settings {1,2,3} X

VJ TCP/IP header compression OFF X

SACK option ON X X

RTO adjustment value X

Time stamp option ON X

Congestion window size (dimension of

congestion window)X

MTU size (max dimension of packet) X X

Fast re-transmit after 2nd duplicate

ACKX X

Minimize ACK delay X X X

Acknowledge every n-th TCP segment X X X











Case 1

Case 1: Forward frame error is high and re-transmission is serious(forward SCH) in case of soft handoff

Descriptions :Re-transmission is serious.




Analysis and SolutionsPowers of two branches are asynchronous.PN177 (reference pilot. Good

reverse capability. PN255 (Poor reverse capability, and the best forward power)

Prohibit reverse SCH allocation and test handoff of forward SCH.

Result: Forward power asynchronization affects FER a little.

Optimization suggestion: Improve SCH power control.




Case 2Case 2: Signaling setting is inappropriate, the data cannot be sent.

Descriptions:

After dial up successfully, data cannot be sent and FER is high.

BS

20msESCAM

MS

ESCAM

one way

Prop delay

SCH Duration

SCH_START_TIME

SCH allocation

request

SCH allocation Delay

SCH allocation

request




Analysis

Refer to figure at previous slide, BTS delivers ESCAM to MS at air interface, and the system must ensure that

SCH start time of MS is synchronous with that of BTS.

When the system allocates SCH, calculate SCH_START_TIME according to the required time from SCH

allocation request to successful allocation, fill SCH_START_TIME in the ESCAM and inform MS start time of

SCH Duration.

The time from SCH allocation request to successful allocation is called SCH allocation delay, namely signaling

delay (SigDelay).

Signaling delay includes:

Signaling delay between BSC and BTS.

Transmission delay when BTS delivers ESCAM to MS.

Time that MS prepares for SCH.

BSC calculates SCH _START_ TIME through current system time and SIG_DELAY. The formula is shown as:

SCH_START_Time = [(x + SignalingDelay) / (START_TIME_UNIT + 1)] mod 32,

According to protocol, START_TIME_UNIT is defaulted to 0. x indicates current system time

X is a variable, so the obtained SCH_START_TIME is a remainder, namely random quantity.

MS begin to send data at the time of {[t / (START_TIME_UNITs + 1)] - SCH_START_TIME} mod 32 =0 after

receiving the ESCAM. (t indicates the system time with the unit of 20ms)




Analysis

For Example:

System time to apply for SCH time x = 1440000(08:00:00am)

sigalingDelay=10

BSC obtains that SCH_START_TIME = 1440010 mod 32=10 based on

the calculation.

If actual signaling delay is 7 frames (less than 10 frames), MS begins to

send after the system time t is set to 1440010 and receives ESCAM

message. (1440010 – 10) mod 32 = 0.

If actual signaling delay is 20 frames (more than 10 frames). When MS

receives ESCAM message, system time t is set to 1440020 and

(1440020 –10) mod 32 ≠ 0. Therefore, MS does not send data after the

system time t is set to 1440042. BTS side sends data when t = 1440010.

consequently, asynchronization and a large amount of bit errors occur.




Case 3Case 3:

SCH has large gap when data is sent Descriptions:

The data service optimization test shows that mean download rate is low and

transmission gap is large. The forward mean download rate is only 6 kbyte and an

obvious gap occurs.

Currently, SCH signaling delay is 10 frames and SCH transmission duration is 128

frames.

View BSC maintenance console tracking signaling. During continuous downloadingprocess of MS, time interval between every two continuous Extended supplemental

channel allocation message is 6.6s. The situation viewed from MS rate window is

identical. SCH channel of 163.2 is not allocated within 2s to 3s. The radio environment

is good. EcIo is about –4 or –5. Rx is –50 dBm.




Solutions

SCH management process as follows:

1.RLP originates SCH request based on application mechanism.

2.Prepare for terrestrial link resources (3 – 5 frames)

3.Prepare for air interface resource and MS (ESCAM message adopts fast re-transmission mechanism): 3 frames

4.Integrate step (2) with (3), and the total signaling delay is 10 frames (parameter configuration).

5.Upload data on SCH (2.56s) within the Duration.

6.Release SCH.

7.RLP originates next SCH application. The above signaling analysis shows that step 1 through 6 are normal. Step 6 and 7 takes long, which is related to the following factors:

Algorithm that RLP adopts to apply for SCH.

Data amount at network side.

Data amount pouring in at network side.

The further analysis of RLP parameter shows that time interval of SCH request is 200 frames (4s). Modify it to 20. The problem is solved.



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Documents

C-CF CDMA2000 1x Data Service Optimization-20071031-A-3.0