Điện tử viễn thông slide 4 he thong CDMA khotailieu

1/8 24 48 96 192 Rate set18KQCELP & EVRC: Rate set2 13KQCELP : Full rate：9.6Kbps Full rate ：14.4Kbps Half rate：4.8Kbps Half rate ：7.2Kbps 1/4 rate：2.4Kbps 1/4 rate ：3.6Kbps 1/8 rate ：1.2

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Bài giảng Mạng TT di động Slice 1

Hệ thống CMDA

NỘI DUNG:

) Thuận lợi của CDMA ) Các Frequency channels trong CDMA ) Các tốc độ mã hoá thoại

) CDMA Call Processing ) Điều khiển công suất

) Chuyển giao mềm (Soft handoff)

Nguồn tham khảo: univ.zte.com.cn

Thuận lợi của CDMA

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Vùng phủ sóng rộng

large coverage

almost 2 times than GSM, save money for

operator

Example:cover 1000 km2： GSM need

200 BTS ，CDMA only need 50 BTS

Attention: exact result need

“Link Budget ”

Dung lượng lớn

High spectrum capacity，8 10 times than AMPS,4—6 times than GSM

Power

Fr eq

ue nc

y

Tim e

Power

Fr eq

ue nc y Tim e

Power

FDMA

TDMA

CDMA

FDMA -Different user use different

frequency

TACS、AMPS

TDMA -Different user use different

time slot of one frequency

GSM、DAMPS

CDMA -Different user use same

frequency at the same time,but with

different spreading code

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Độ bảo mật cao

¾High privacy, hard to wiretapping

Spread code

Information

signal

TX

Demodulated signal

RX

Spread code

Spread signal

Each user is below the noise deeply

z CDMA：”make before break” -soft handoff

z Other systems: “make after break” -hard handoff

Use soft handoff, decrease drop-call rate

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Chất lượng thoại cao

Good voice quality, use 8k,13K(QCELP,EVRC)voice coding—the best coding method in the world.

Voice quality

(MOS)

64k PCM 13kGSM

8k CDMA 13kCDMA 8kEVRCCDMA

Ít ảnh hưởng sức khoẻ

Perfect Power Control and voice activation make the MS Power low, healthy for body—green mobile phone.

Mean Power Max Power GSM: 125mW 2W

CDMA: 2mW 200mW

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Các công thức tính tần số sóng mang

CDMA Frequency Calculation：

450MHz

BS receiver(Uplink): 450.00+0.025(N-1)

BS sender(downlink): 460.00+0.025(N-1)

800MHz

BS receiver(Uplink): 825.00+0.03N

BS sender(downlink):870.00+0.03N

1900MHz

BS receiver(Uplink): 1850.00+0.05N

BS sender(downlink):1930.00+0.05N

Frequency channels: tần số sóng mang

991 1023 333 666 715 716 799

Channel

Numbers

1019 37 78 119 160 201 242 283 384 425 466 507 548 589 630 691 777

CDMA A-Band Carriers CDMA B-Band Carriers

8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 9 9 8

* Requires frequency coordination with non-cellular interferers

** Requires frequency coordination with A-band carrier

A Band Primary Channel 283

A Band Secondary Channel 691

B Band Primary Channel 384

B Band Secondary Channel 777

736

Up link: 825.00MHz+0.03MHz*N Down link: 870.00MHz+0.03MHz*N

frequency

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Primary Channel

Secondary channel

Total 10M

7 Frequency Carries

Total 5M

3 Frequency Carries

691

846.5MHz

845MHz 849MHz 835MHz

825MHz

Not allocation

N=

840MHz CDMA 800 MHz Cellular Spectrum Assignment

A Band Primary Channel 283 A Band Secondary Channel 691

B Band Primary Channel 384 B Band Secondary Channel 777

CDMA 1900 MHz Cellular Spectrum Assignment

1895M 1900M

1980M

925 950 975

（Downlink：1975-1980）

（Uplink：1895-1900）

1975M

N=

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Mã hoá thoại với tốc độ thay đổi

-Variable Rate Vocoding

Rate Set 2 Frame Sizes bits

Full Rate Frame 1/2 Rate Frame

1/4 Rt.

1/8 36 72 144 288

Rate Set 1 Frame Sizes bits

Full Rate Frame 1/2 Rate Frame

1/4 Rt.

1/8

24

48

96

192

Rate set1(8KQCELP & EVRC): Rate set2 (13KQCELP ):

Full rate：9.6Kbps Full rate ：14.4Kbps

Half rate：4.8Kbps Half rate ：7.2Kbps

1/4 rate：2.4Kbps 1/4 rate ：3.6Kbps

1/8 rate ：1.2Kbps 1/8 rate ：1.8Kbps

CDMA Call Processing

Power-Up

Initialization

Idle

System Access

Traffic

Mobile station

has fully acquired

system timing

Mobile station receives a Paging

Channel message requiring ACK

or response, originates a call, or

performs registration

Mobile station is directed

to a Traffic Channel

Mobile station ends use

of the Traffic Channel Mobile station receives an ACK to

an Access Channel transmission

other than an Origination Message

or a Page Response Message

Mobile station is in idle handoff with NGHBR_CONFG equal to

‘011’ or is unable to receive Paging Channel Message

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Điều khiển công suất

Power control

All CDMA users occupy the same

frequency at the same time! Frequency

and time are not used as discriminators

CDMA operates by using CODES to

discriminate between users

CDMA interference comes mainly from

nearby users

Transmit power on all users must be

tightly controlled so their signals reach

the base station

-at the same signal level

- at the absolute minimum power level

necessary to ensure acceptable service

quality

Figure of Merit: E c /I o , E b /N o

(energy per chip [bit] / interference [noise] spectral density ) CDMA: E c /I o -17 to -2 dB CDMA: E b /N o ~6 to7 dB

Phân loại điều khiển công suất

Reverse Power Control

Open-loop Power Control

Closed-loop Power Control (Forward traffic Channel)

9Outer-loop Power Control 9Inner-loop Power Control

Forward Power Control

IS-95 Power Control

IS-2000 Fast Power Control (Reverse Pilot Channel)

9Outer-loop Power Control 9Inner-loop Power Control

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Reverse Open-loop Power Control

Reverse open loop power is mobile station controlling its transmit power

Reverse open loop power control consists of :

estimating how strong the mobile station should transmit based on a coarse measurement of how much power it is receiving from the base station

some correcting parameters delivered in the access parameters message

The Reverse open loop method of power control provides a quick response to changes in signal conditions

Reverse Open Loop Power Control

Reverse Open-loop Power Control

 Problems with Reverse Open Loop Power Control

) Assumes same exact path loss in both directions; therefore, cannot account for asymmetrical path loss

) Estimates are based on total power received; therefore the power received from other cell sites by mobile station

introduces inaccuracies

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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 the mobile stations, based upon their signal strength measured at the Base Station and compared to a specified threshold (setpoint)

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

Signal Strength Measurement

Setpoint

or

Reverse Outer Loop Power Control

) Setpoint is varied/dynamic according to the FER (Frame Error Rate)

level, typically 1% on the Reverse Traffic Channel (determined at the Base Station Controller),

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

) Setpoint adjusted every 1-2 seconds

FER

Reverse Outer Loop Power Control

Setpoint

or

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Closed-loop Power Control Procedure

Received the Frame Quality Information from the Reverse Link

Eb/Nt>Eb/No?

Outer-loop Algorithm

Up Power Control Bit

Down Power Control Bit

Puncture to Power Control Subchannel

Power Control Command Measurement

Demodulate and measure Eb/Nt

Outer Loop Correction Closed-loop Control

Base Station

Mobile

Eb/No

No

Yes

Threshold

Forward Power Control in IS-95

The base station continually and slowly decreases power to each mobile station(each user’s forward traffic channel)

As the FER (determined at the mobile station) increases, the

mobile station requests a Forward Traffic Channel power increase

FER

Adjust Fwd power

Forward Link Power Control

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Forward Quick Power Control in IS-2000

In CDMA2000, there is a faster

method used for Forward

Power Control operating much

like the IS-95 Reverse Link

Power control described next

In order to implement Forward

Link Quick Power Control,we

use Reverse Pilot channel

which includes power control

subchannel

Forward Quick Power Control Procedure

Received the Frame Quality Information from the Forward Link

Eb/Nt>Eb/No?

Outer-loop Algorithm

Up Power Control Bit

Down Power Control Bit

Puncture to Power Control Subchannel

Power Control Power Control

Demodulate and measure Eb/Nt

Outer Loop Correction Closed-loop Control

Mobile Station

Base Station

Eb/No

No

Yes

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Summary of Power Control

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

capacity of the system transmit power.

Setpoint

or

Adjust Fwd power Reverse Outer

Loop Power Control

Forward Link Power Control

Reverse Open Loop Power Control

Chuyển giao mềm - Soft handoff

Handoff is the process by which a mobile station maintains communications with the Mobile Telephone Switching center (MSC), when traveling from the coverage area of one base station to that of another

Handoff keep the call established during the following

conditions:

) Subscriber crosses the boundaries of a cell ) Subscriber experiences noise or other interference above a specified threshold

) A base station component experiences an out-of-service condition during a call

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Phân loại: CDMA Handoffs

During

a Call

Idle Handoff

Soft Handoff

Softer Handoff

CDMA-to-CDMA Handoff Inter-System Soft Handoff

CDMA-to-Analog Handoff

While in the

Idle State

CDMA Idle Handoff

PN 108

A

Pa gin

g C ha

nn el

M sg s

Sy nc

C ha

nn el M sg

104 108 Ec/Io

It’s not soft and hard handoff!

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CDMA Idle Handoff

PN 104

PN 108

A

Pa gin

g C ha

nn el

M sg s

Sy nc

C ha

nn el M

sg

104 108

Ec/Io

>3dB

It’s easy to meet Access failure?

CDMA Soft Handoff

Soft Handoff:The mobile station starts communications with a target base station without interrupting communications with the current serving base station

) Make-before-break

) Directed by the mobile not the base station,Undetectable by user ) Improves call quality

Can involve up to three cells simultaneously and use all signals

) Mobile station combines the frames from each cell

Cell Site B

Cell Site A

Cell Site B

CDMA

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CDMA Soft Handoff Mechanics

CDMA soft handoff is driven by the handset

Handset continuously checks available pilots

Handset tells system pilots it currently sees

System assigns sectors (up to 6 max.), tells handset

Handset assigns its fingers accordingly

Each end of the link chooses what works best, on a frame-by-frame basis

Users are totally unaware of handoff

CDMA Softer Handoff

Softer Handoff is between sectors of the same cell, that means multiple sectors of one BTS simultaneously serve a handset

Softer handoff occurs in BTS in a single channel element

Communications are maintained across both sectors until the mobile station transition has completed

MSC is aware but does not participate

All activities are managed by the cell site

Signals received at both sectors can be

alpha

beta

gamma

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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

(ƒ 1 )

PSTN

MSC

BSC

B

PSTN

MSC

BSC

B

MSC

BSC

T1 or E1 Links TIA/EIA-41D

Handset Structure Review

Receiver

RF Section

IF, Detector

Transmitter

RF Section

Vocoder

Digital Rake Receiver

Traffic Correlator

PN xxx Walsh xx

Pilot Searcher

PN xxx Walsh 0

Viterbi Decoder

CPU

Duplexer

Transmitter Digital Section

Long Code Gen.

Transmit Gain Adjust

Messages

Audio

Bit Packets

Symbols

Symbols Chips

RF

AGC

Bit Packets

Σ

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Pilot Sets

There are 4 memorizer (pilot set) in handset, to save the related PN offset index.After power off, all memorizer will be cleared automatically

) Active Set: Pilots associated with the forward traffic channels assigned to the mobile station (max 6 pilots)

) Candidate Set: Pilots not currently in the Active Set, but received by the mobile with sufficient strength to indicate that the corresponding 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 most 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

Pilot Sets

1 Active

2 Candidate

3 Neighbor

4 Remaining

Rules of Soft Handoff

The MS assists the BS in the handoff process by measuring and reporting the strengths of received

pilots using a Pilot Strength Measurement Message

 Handset sends PSMM to the system whenever:

It notices a pilot in neighbor or remaining set

exceeds T_ADD

 An active set pilot drops below T_DROP for

T_TDROP time

A candidate pilot exceeds an active by

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IS-95 Soft Handoff Signaling

Power Control during Soft Handoff

During soft handoff, the mobile station receives

power control bits from multiple base stations

If two or more power control subchannels are

identical, their power control bits are diversity

combined into one per 1.25 ms time slot

If the mobile station receives different power

control bits from different power control

subchannels, it decreases its mean power output

level by 1 dB

Only if the power control bits from ALL power

control subchannels request a power increase,

the mobile station increases its mean power

output level by 1 dB

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