Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828

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CDMA Technologies for Cellular Phone System , Sept. 11, 2003 1

Chapter 7. CDMA Technologiesfor Cellular Phone System

Công nghệ CDMA cho hệ thống điện thoại tổong.

Sources:1) July 7th, 2004 - Takashi INOUE –KDDI R&D Laboratories Inc.

2) IS-95 - ECE 371VV - Erik Stauffer Yu Li Yan Sun













Contents

• Introduction (giới thiệu) • Spread Spectrum Technology(công nghệ trải phổ) • DS-CDMA

• Spreading Codes(mã trải phổ) • Features of CDMA

Đặc tính của cdma – RAKE Receiver (bộ thu rake)

– Power Control (điều khiển công suất) – Frequency Allocation (cấp phép tần số) – Soft Handoff (chuyển giao mềm)




Contents

• CDMA Links – Forward Link (cdma đường xuống) – Reverse Link (cdma đường lên)

• Special Features of IS-95 CDMA

(đặc tính đặc biệt của cdma is-95)

• Brief Comparison to other second-generation standards

• Possible Improvements

• Conclusion


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7.1. Introduction (giới thiệu)



Modern Wireless Systems(hệ thống ko dây hiệnđại)

• Outdoor voice/data communication (thoại ngoài trời, giao tiếp dữliệu) – Cellular phone, PCS (điện thoại tổ ong, PCS) – Paging, Satellite (tìm gọi, vệ tinh)

• Indoor data communication (giao tiếp dữ liệu trong nhà)

– Cordless phone – WLAN

– Low cost low power: Bluetooth, Zigbee, UWB

• Outdoor data broadcast (quảng bá dữ liệu ngoài trời) – Wide area wireless data service (dịch vụ dữ liệu ko day băng

rộng) – Broadband wireless access: WLL, LMPD (truy nhập không

dây băng hẹp)



7.1. IntroductionEvolution of Cellular Systems (phát triển của hệthống điện thoại tổ ong)

1st.Generation

(1980s)(thế hệ thứ nhất) Analog

NMT CT0

TACS CT1AMPS

3rd. Generation

(2000s)

2nd. Generation

(1990s)

Digital

GSM DECT

DCS1800 CT2

PDC PHS

IS-54

IS-95

IS-136UP-PCS

IMT-2000

CDMA2000

W-CDMA



Cellular System

• Two-way voice/data communication with large

coverage (hai đường thoại/dữ liệu với vùng phủsóng rộng)

• Spectrum efficiency: frequency reuse (since powerfalls off with distance) (hiệu quả phổ, tần số tái sửdụng) (công suất tỉ lệ nghịch với khoảng cách) – Macrocells and microcells: trade-off among

capacity, interference, cost (tính thương mại giữadung lượng, nhiễu, giá cả)

– System is interference limited (hệ thống giới hạn

nhiễu) • advaced techniques for interference reduction can

enhance performance: cell sectoring, directional/smartantennas, multi-user detection, dynamic resourceallocation (công nghệ tiên tiến giảm nhiễu có thể thựchiện bằng cách sector hóa, hướng/anten thông minh,hướng đa thuê bao, cấp phép tài nguyên động)



• 1G Cellular network (mạng tổ ong thế hệ thứ nhất)

– AMPS: FDMA/FDD• 2G Cellular network (mạng tổ ong thế hệ thứ 2)

– TDMA/FDD, or CDMA/FDD

• GSM, 8 users/200KHz channel, TDMA

• IS-136, 3 users/30kHz channel, TDMA• IS-95 (CDMA One): 64 users/1.25MHz channel, CDMA



• 2.5G Cellular Network (thế hệ 2,5G)

– General objective: support packet data servicewith higher data rate (tính năng chung: hỗ trỡ dịchvụ dữ liệu gói với tốc độ cao hơn)

– GPRS: 170 kbps (max), TDMA (enhanced GSM

by channel aggregating) – EDGE: >384 kbps, TDMA (enhanced GSM by

high-level modulation)(nâng cấp GSM bởi điềuchế mức cao hơn)

– IS-95B: 115 kbps, CDMA (enhance IS-95 byaggregating spreading codes) (nâng cấp IS-95 bởimã trải phổ)



• 3G Cellular Network (thế hệ thứ 3) – Objective: support higher data rate: from 384kbps

(pedestrian) or 144 kbps (vehicular) to 2 Mbps(indoor)( hỗ trợ tốc độ dữ liệu cao)

– General: work in 2GHz band, ~2Mbps, FDD/TDD

– WCDMA (UTRA), evolved from GSM (phát triển từ

GSM)• Always on (packet radio), 2Mbps, ~8Mbps future, 5MHz

bandwidth(băng thông 5M)

– CDMA 2000, evolved from IS-95 CDMA• Use the same 1.25MHz bandwidth as IS-95(sử dụng

cùng băng thông 1.25 như IS-95)• Multi-carrier mode 3xTT (đa sóng mang) • 5 MHz bandwidth (băng thông 5M) • 2 Mbps and higher (tốc độ 2M và cao hơn)



– 3G incompatible with 2G, need much investment

for deployment, such as the cost for buyingspectrum( thế hệ thứ 3 tương thích với thế hệ thứ2 phải đầu tư phát triển giống như chi phí muaphổ tần số)

– 3G first deployed in Japan (thế hệ 3G đầu tiênđược triển khai ở Nhật)



Introduction

• Spread Spectrum Communications(giao tiếp trải phổ)

• Multiple Access Technique(công nghệ đa truy nhập)

– Direct Sequence DS-CDMA (trực tiếp tuần tự)

• CDMA standards(chẩn cdma)

– CDMAOne (2G) – IS 95A, (2.5G) IS-95B

– CDMA 2000 and WCDMA (3G) – IMT2000

• 4G in the future (tương lai thế hệ thứ 4

• Conclusions (kết luận)



Requirements for 3G mobile systems

• High Capacity (dung lượng cao) • Tolerance for interference (loại bỏ

nhiễu)

• Privacy( bảo mật)

• Tolerance for fading(giảm pha đing)

• Ability to various data ratetransmission(có khả năng truyền với tốc

độ dữ liệu thay đổi) • Flexible QoS (đảm bảo hệ số dịch vụ)



IMT-2000 systems approved by ITU-R

Popularname

Accessmethod

Body ofTechnical

Specproduction

IMT-DS IMT-MC IMT-TC IMT-SC IMT-FT

(Direct Sequence) (Multi Carrier) (Time Code) (Single Carrier) (Frequency Time)

W-CDMA CDMA2000

UTRA-TDD

UWC-136 DECT

CDMA-FDD CDMA-TDDCDMA-FDD TDMA-TDDTDMA-FDD

3GPP(FDD） 3GPP2 3GPP(TDD)

CWTS

IS-136 DECT

ESTIESTI TIA

TTA

T1

CWTS

ARIB/TTC ARIB/TTC

CWTS

TTA

ESTI

TTA

T1

CWTS

TIA

Approved in 2000 as ITU-R M.1457

TD-CDMA

TD-SCDMA

OrganizationPartners



What is CDMA ?

Sender bộ gửi Receiver bộ thu

Code A

A

Code B

B

A B

A B

C B

C

A

Code A

A B

C

Time

BC

B

A

Base-band Spectrum

băng cơ bản)

Radio Spectrum phổ

vô tuy ến

spread spectrum




Summary of Multiple Access

FDMA

TDMA

CDMA

p o w e r

p o w e r

p o w

e r




7.2. Features of CDMA Systems đặc

tính của hệ thống cdma







IS-95 CDMA - Radio Aspects

• Spread spectrum techniques adapted from military (used since 1950)

—Narrowband signal is multiplied by very large bandwidth signal(spreading signal)(tín hiệu băng hẹp được ghép bởi tín hiệu băng rộng) —All users, each with own pseudorandom codeword approximatelyorthogonal to all other codewords, can transmit simultaneously withsame carrier frequency(tất cả thuê bao, mỗi người có một mã giả ngẫunhiên và trực giao với nhau có thể truyền đồng thời trên cùng một tầnsố sóng mang) —Receiver performs a time correlation operation to detect only desiredcodeword (bộ nhận thực hiện một lần tương quan để chỉ xác định mãmong muốn)—All other codewords appear as noise due to decorrelation(tất cả cácmã khác xuất hện như là nhiễu do bộ giải mã tương quan) —Receiver needs to know only codeword used by transmitter

(bộ nhận chỉ cần biết mã hóa sử dụng ở bộ phát) —In other words, users are separated by theircodes rather than frequency and time slot (Nói một cách khác, mỗingười dùng được phân biệt bởi mã hơn là tần só và thời gian)




IS-95 CDMA Interesting Features















Drawbacks of CDMA
















Drawbacks of CDMA

So far, CDMA looks like a step backwards:Tight synchronization is required to use orthogonalcodes, which then break in a multipath channel anyway

Quasi-orthogonal codes cause self-interference, whichdominates the performance in most CDMA systems

Near-far problem is a serious hindrance, requiring fastand accurate power control (that uses up bits we couldotherwise send information with)

And for all this, the required bandwidth is now J times

larger than it was before, so there doesn‘t appear to bea capacity gain




PHYSICAL PROPERTIES

OF WIRELESSCHANNELS thuộc tính vật

lý của kênh vô tuyến

COS598u: Pervasive Information Systems




<------

----------->

<---------------

|

|

|

|

|

|

|

Recall the Model

Now we’ll focus attention on the channel.


G l C t ( á




General Comments (cácchú thích)





Noise nhiễu


Whit N i hiễ




f 0

White Noise nhiễutrắng

• The spectrum of a random process specifies how the process’ energyis distributed as a function of frequency.Phổ của ngẫu nhiên cho thấyxử lý phân bố năng lượng như một chức năng của tần số. • The integral under the spectrum over any given band of frequencies

equals the amount of energy in that band.Toàn bộ vùng dưới phổ đượctạo ra bở băng tần số bằng tổng năng lượng trong băng đó. COS598u: Pervasive Information Systems




• A key parameter of the noise is the spectral height or noise level,

often designated as No /2.

Tham số chính của nhiễu là độ cao của phổ hoặc mức nhiễu

thường định nghĩa là No/2

• A key parameter of the signal is the received energy per bit,

usually designated by Eb.

Tham số chính của tín hiệu là năng lương thu được trên bit thường

định nghĩa là Eb

• The ratio Eb /No (“ebno”) is a measure of signal-to-noise ratio

(SNR), and is a key parameter in determining the quality of acommunications link.

Tỉ lệ Eb/No là SNR đây là tham số chính để xác định chất lượng

tuyến giao tiếp.

Signal-to-Noise Ratio (SNR) tỉ số tínhiệu trên nhiễu





• The performance of a digital link can be measured in partby the bit-rate; but performance depends also on the qualityof transmission, as measured by the bit-error rate (BER).

Thực hiện tuyến số có thể đo bởi tốc độ bit nhưng phụ thuộc vào chất lượng truyền dẫ đo bở tốc độ bit lỗi BER

• The BER (also known as the “probability of bit error”) is,as its name implies, the rate at which errors are introducedinto the transmitted data stream by the channel.

BER còn được biết như là xác suất bit lỗi.• E

b

/No

determines the rate of bit errors caused by whitenoise.

Tỉ lệ này xác định tốc độ lỗi nguyên nhân do nhiễu trắng • This varies with modulation type.Điều này thay đổi tùy thuộc vào loại điều chế.

Bit Error Rate (BER)bit lỗi


BER f Bi M d l ti BER h




BERs for Binary Modulation BER chođiều chế nhị phân


BER f Hi h O d M d l ti BER ới




BERs of Higher-Order Modulation BER vớiđiều chế mức cao hơn


Error Rates of M ary Modulation tốc độ lỗi




Error Rates of M-ary Modulation tốc độ lỗicủa điều chế mảng M


Propagation Effects hiệu




Propagation Effects hiệutứng xác suất


L S l P ti Eff t hiệ




Large Scale Propagation Effects hiệuứng xác suất tỉ lệ lớn




Multipath

Multipath Fading(đa




• Multiple copies of the transmitted signal arrive at the receiver due to

reflections (off buildings, walls, etc.).nhiều tín hiệu của bộ phát đến bộ thu

bằng các đường khác nhau nhờ phản xạ

• The destructive and constructive interference of the different paths causes

fading; i.e., fluctuations in Eb: Phá hủy và khôi phục nhiễu của các đường khác

nhau là nguyên nhân fading.

– Superposition of widely separated paths causes frequency-selective

fading; modeled via a channel impulse response.

Sự chồng của các đường với kc rộng nguyên nhân bởi fading lựa chọn

tần số

– Superposition of many closely separated paths causes flat fading;

modeled as independent Gaussian random variables in I and Q

channels (so-called Rayleigh fading).

Sự chồng của nhiều đường với kc gần nhau bởi fading mỏng.

• Mobility adds dynamism to the fading:

– slow fading is steady over many symbol intervals

– fast fading changes very rapidly (bad!)

Multipath Fading(đađường)




• The use of wideband signals (e.g., spread spectrum),

allows different paths to be resolved and added

constructively. (The technique for this is called aRAKE receiver.)

Sử dụng tín hiệu băng rộng cho phép các đường khác

nhau được quyết định và thêm vào để khôi phục tín

hiệu (cộng nghệ này được gọi là bộ thu RAKE)

• With narrowband signals, frequency-selective fading is

an impairment; i.e., it negatively effects

performance.với tín hiệu băng hệ fading lựa chọn tần só

là một sự suy yếu.

Frequency-Selective Fading fadinglựa chọn tần số

Multipath: Dispersion đa




Multipath: Dispersion đađường: phân tán




Interference nhiễu




Multiple Access Capabilities

• Multiple wireless terminals

(WT) receive and send to thebase station (BS)

- WT near to the base station

receive with higher quality than

WT that a far away

- Different quality in terms of bit

error probability

- To overcome unfairness and

achieve a higher system

capacity power control is

applied

Interference Averaging dung lượng đa




Interference Averaging dung lượng đatruy nhập

Interference from neighboring cells (CCI and ICI)




Interference from neighboring cells (CCI and ICI)nhiễu từ các cell lân cận




Dynamism

Further Issues các lỗi




Further Issues các lỗikhác




Mobile Propagation EnvironmentMulti-path Fading

The peaks and bottoms of received power appear,in proportion to Doppler frequency.

Base Station (BS)Mobile Station (MS)

multi-path propagation

Path Delay

P o w e

r

path-2

path-2path-3

path-3

path-1

path-1

Time

P o w e

r










Fading in non-CDMA System

Path Delay

P o w e r path-1

path-2

path-3

With low time-resolution,

different signal paths cannot be discriminated.

••• These signals sometimes strengthen,

and sometimes cancel out each other,

depending on their phase relation.

••• This is ―fading‖. ••• In this case, signal quality is damaged

when signals cancel out each other.

In other words, signal quality is dominated

by the probability for detected power

to be weaker than minimum required level.

This probability exists with less than two paths.

Time

P o w e r

Detected Power

In non-CDMA system, ―fading‖ damages signal quality.




Fading in CDMA System ...

Because CDMA has high time-resolution,

different path delay of CDMA signalscan be discriminated.

••• Therefore, energy from all paths can be summed

by adjusting their phases and path delays.

••• This is a principle of RAKE receiver. Path Delay

P o w

e r path-1

path-2

path-3

CDMAReceiver

CDMAReceiver

• • •

S y n c h r oni z a t i on

A d d

er

Path Delay

P o w e r

CODE Awith timing of path-1

path-1

P

o w e r

path-1

path-2

path-3

Path Delay

P o w e r

CODE Awith timing of path-2

path-2

interference from path-2 and path-3

• • •




Fading in CDMA System (continued)

In CDMA system, multi-path propagation improves

the signal quality by use of RAKE receiver.

Time

P o w e r

Detected Power

RAKEreceiver

Less fluctuation of detected power,because of adding all energy .

P o w e r

path-1

path-2

path-3







Demodulation (Correlator)

.

.

.

.

.

.

.

.

.

.

Pick thelargestCross

CorrelationMetrics

receivedsignal

r(t)

c1

(t)

c2(t)

ck(t)

.

.

.

.

.

.

.

.

.

.

r1

r2

rk

outputbitsb(n)






Principles of operation-transmitter

• The narrowband message signalmi(t) is multiplied by a pseudo noisecode sequence that has a chip rate >>data rate of message.

• All users use the same carrier frequencyand may transmit simultaneously. The k-th transmitted signal is given by:

k s s k k c kS (t) (2E / T )1/ 2m (t)p (t)cos(2 f t )




CDMA Receiver

c k

cos(2 f t )

r(t) km (t)(.)dt

k

iZ ( t )

K

PN (t)




Principles of operation-receiver

At the receiver, the received signal iscorrelated with the appropriate signaturesequence to produce desired variable.

1

1

iT

1

i 1 1 c 1 1

(i 1)T

Z (t) r(t)p (t )cos[2 f (t ) ]dt




Message Signal

• m(t) is a time sequence of non-overlappingpulses of duration T, each of which has anamplitude (+/-) 1.

• The PN waveform consists of N pulses or

chips for message symbol period T.

NTC = T

where TC is the chip period.

Example:




Example:

Assume N=4

PN Wave for N =4

1

-1

-1

1




Correlator output for first user

•The multiplied signal will be p2(t) = 1 for thecorrect signal and will yield the dispersedsignal and can be demodulated to yield themessage signal m

i(t).

1

1

iT

1

i 1 1 c 1 1

(i 1)T

Z (t) r(t)p (t )cos[2 f (t ) ]dt

1/ 2

1 s s 1 1 c 1S (t) (2E / T ) m (t)p (t) cos(2 f t )

ấ ỗ




Probability of bit error xác suất của bít lỗi

• Probability of bit errorPe = Q {1/ [(K –1)/3N + (N0 /2Eb)]

1/2}

K = Number of users số người sử dụng

N = Number of chips/ symbol số chip/ký tự

• When Eb /No

Pe = Q{[3N/(K-1)]

1/2

}










Concept of CDMA Systems Diversity




Concept of CDMA Systems Diversity

• IS-95 Air Interface Standards

• Space diversity

• Frequency diversity

• Path diversity

• Time diversity

• Macro-diversity













N F P bl




Near-Far Problem

CODE B

CDMATransmitter

DATA B

CODE A

CDMAReceiverCODE A

CDMATransmitter

DATA A

P

• Desired Signal Power = P/ Lp-a

• Interfered Signal Power =

P/ Lp-b /(processing gain )

Demodulated DATA

P

Lp-a

Lp-b

When user B is close to the receiver anduser A is far from the receiver,

Lp-a could be much bigger than Lp-b.In this case, desired signal power is

smaller than the interfered power.

The Near-Far Problem




The Near Far Problem

• Users may be received with

very different powers:- Users near the base stationare received with high power

- Users far from the basestation are received with low

power- For a path loss exponent of 4and a cell size of 1 km,example:

• Nearby users will completelyswamp far away users

• Solution: Power Control




Power Control




Power Control

Power Control …




Power Control …

• Power control adjust power level while conveying data to thebase station in that way that all received signals at the basestation have the same signal strength (not trivial)

• This process needs time to adjust in case of changing in the cellin terms of power/interference

Power Control …




Power Control …

• In case of misadjusted power control entities some WTS might havebetter/worse quality conditions

• The highest cell capacity can be achieved all WTs have exactly the samepower level• For support of heterogeneous QoS support the power control is a viable

option• All signals (even the undesired ones) from the base station will receive the

WT with the same strength (some path)

Power Control …




Power Control …





Power Control




Power Control...

ＡＢ

Time

D e t e c t e d P o w e r

from A

from B

When all mobile stations transmit the signals at the same power (MS),

the received levels at the base station are different from each other,

which depend on the distances between BS and MSs.

Moreover, the received level fluctuates quickly due to fading.

In order to maintain the received level at BS, power control technique must be

employed in CDMA systems.

Power Control (continued)




Power Control (continued)

②

①

Open Loop Power Control Closed Loop Power Control

estimating pathloss

calculatingtransmission

power

transmitmeasuringreceived power

transmit receive

decidetransmission

power

transmit measuringreceived power

power controlcommand

about 1000 timesper second

①

②

Effect of Power Control





ＡＢ

Time

D

e t e c t e d P o w e r

from MS Bfrom MS A


• Power control is capable of compensating the fading fluctuation.

• Received power from all MS are controlled to be equal.

... Near-Far problem is mitigated by the power control.

Frequency Allocation (1/2)





In FDMA or TDMA,

radio resource is allocated not to interfere among neighbor cells.

f1f2

f3f4

f5f6

f7

cell :

a ―cell‖ means covered area by one base station.

• Neighbor cells cannot use thesame (identical) frequencyband (or time slot).

• The left figure shows the

simple cell allocation withseven bands of frequency.

• In actual situation, because ofcomplicated radiopropagation and irregular cellallocation, it is not easy to

allocate frequency (or timeslot) appropriately.






In CDMA,identical radio resource can be used among all cells,

because CDMA channels use same frequency simultaneously.

• Frequency allocation in CDMAis not necessary.

• In this sense, CDMA cellularsystem is easy to be designed.

Handoff in CDMA




Handoff in CDMA

• Two types of handoffs—hard handoff

—Soft handoff

•Hard handoff is needed when the call ismoved from one frequency to another and

when the mobile moves the coverage area

of another MSC

Soft handoff




• Two base stations receive signals from the mobile.

The signals are sent to the MSC that decides whichone has lowest bit error rate.

Vocoder in CDMA is in the switch.

• Mobile receives signals from two base stations and

combine them before decoding. Uses rake receiver.Each tunes to one base station.

• This requires synchronization of the base stations.All base stations are equipped with GPS and receive

information from it, including lat.., long and time.• It also requires that the mobile dedicates one

correlator for searching other pilot channels.

Soft Handoff (1/2)




Handoff :

•Cellular system tracks mobile stations in order to maintain their

communication links.•When mobile station goes to neighbor cell, communication link switches fromcurrent cell to the neighbor cell.

Hard Handoff :

• In FDMA or TDMA cellular system, new communication establishes afterbreaking current communication at the moment doing handoff.

Communication between MS and BS breaks at the moment switchingfrequency or time slot.

Hard handoff : connect (new cell B) after break (old cell A)

switching

Cell BCell A

Soft Handoff (2/2)




Σ

CellB

Cell A

Soft handoff : break (old cell A) after connect (new cell B)

transmitting same signal from both BS A and

BS B simultaneously to the MS

Soft Handoff :

•In CDMA cellular system, communication does not break even at

the moment doing handoff, because switching frequency or timeslot is not required.

Soft Handoff







CDMA and Soft Handover




CDMA and Soft Handover

• A unique advantage of CDMA issoft handover more reliable

– All cells use same carrier

– Mobile contact with 6~7nearby cells simultaneously

– No need to stop contact withcell 1 before switching to cell2

Soft-Handover





Mobility Management in CDMA




Mobility Management in CDMA

• Five type of registration—Periodic

—Power up

—Power down

—Zone change

—Distance. When the distance between the

current base station and the previously

registered base station exceeds a certain

limit.




Capacity of CDMA Systems

Voice Activity




Voice Activity

• In TDMA and FDMA systems: - If a user doesn‘t have anything to send, the time/frequency

slot allocated to them is wasted

- It is typically very difficult to dynamically allocate time and

frequency slots

• In CDMA systems:

- If a user doesn‘t have anything to send, it causes less

interference to other users of the system

- Typically, each user needs to transmit less than half the time

- Since interference-limited, this doubles the capacity



Uplink Single-cell System Model




BTS

...

.

.

.

...

.

.

.

User 1

User 2

User k

User Ku

User n

Assumptions

• Total active users Ku

• The intra-cell MAI can be

modeled as AWGN

• Perfect power control is

assumed

• Random sequences

• Coarse estimate of the reverse link (uplink) capacity

–Assumptions:




Assumptions:

1. Single Cell.

2. The interference caused by other users in the cell can be

modeled as AWGN.3. Perfect power control is used, i.e. the received power of

each user at the base station is the same.

If the received power of each user is Ps watts, and the

background noise can be ignored (ex: microcells), then the

total interference power (MAI) at the output of the desired

user’s detector is

where Ku is the total number of equal energy users in the cell.

Suppose each user can operate against Gaussian noise at abit-energy-to-noise density level of Eb /Io. Let W be the entire

spread bandwidth, then the interference spectral density can

be expressed as:

su PK I 1

)( / 0

sided one HzWattsW

I I

Interference Also, the bit energy Eb iss

b

R

P E




Interference

limited

, gy b

Thus,

b

b

R

0

01 I E

RW

R E

W I

P

I K

b

b

bbsu

Now, if we consider the factors of voice activity (Gv),

sectorized antenna gain (GA), and other-cell interface factor (f),

where

– Gv 1/v = 2.67

– GA (three sectors) 2.4

– f = (Interference form other cells)/(Interference from

given cell) 0.6

In this case, Ku can be approximated by




Ex: If Gv 2.67, GA 2.4, f 0.6

If (Eb /Io) required is 6 dB (i.e. Eb /Io = 4)

which will be larger than the TDMA or FDMA systems inthe cellular environment.

f

GG

I E

RW K Av

b

bu

10

ob

b

u I E

RW K

4

b

u R

W K

Capacity Comparison




• Comparing the capacity of TDMA/FDMA/CDMA is

very controversial• In 1991, a famous (notorious?) Qualcomm paper

claimed that due to voice activity, frequency reuse,

and sectorization, CDMA increased capacity by:

- Factor of 18 relative to AMPS

- Factor of 6 relative to US TDMA (and similar forGSM)

• This turned out to be optimistic, about 1/3 of this

gain actually happened (still depends who you ask)

• Still, twice as many users is nothing to snear at!

• All 3G systems use CDMA for multiple access










7.3. Direct Spread Spectrum Technology

Spread Spectrum Technique




p p q

• Low power spectral density• Rejection to jamming signal and interference

• Pseudorandom sequence

– Randomness and noise properties – Walsh, M-sequence, Gold, Kasami, Z4

– Provide signal privacy







Direct Sequence Spread Spectrum




q p p

• Spreading

– Source signal is multiplied by a PN signal

• Processing Gain:

• Despreading

– Spread signal is multiplied by the spreading code

DataRate

ChipRate

T

T

T

T G

b

c

c

b

p

1

1

Spreading & Despreading




p g p g

• Polar {±1} signal representation




System Block Diagram




Jammer/Noise/Interference

j(t)

BPSKModulator

BPSK

Matched

Filter

Channel

PseudorandomSequence

Generator

PseudorandomSequence

Generator

Source

DataOutput

Data

(to detector)

b(t)

c(t)

s(t) x(t) u(t)

c(t)

y(t) rn

y(t) = j(t) + x(t)

u(t) = s(t) + j(t)c(t)

rn = bn + jammer projection

s(t) = b(t)cos(wot)

x(t) = s(t)c(t)

How to spread spectrum...




Direct Sequence (DS)

Modulation(primary modulation)

user data

S p r e a d i n g

( s e c o n

d a r y m o d u l a t i o n )

Tx

Base-bandFrequency

P o w e r

D e n s i t y

RadioFrequency

P o w e r

D e n s i t y

TIME

data rate

10110100

spreading sequence (spreading code)



Demodulating DS Signals (2/2)




If you don‘t know the correct spreading sequence (code) •••

Base-bandFrequency

received signal

spreading sequence (spreading code)

you cannot findthe spreadingtimingwithout correctspreading code,and

Accumulate forone bit duration

Demodulated data

Radio

Frequency

P o w e

r

D e n s i t y

01010101 01010101 01010101

10101010 10101010 10101010

TIME

0100101110110100 10110100

No data can be detected

- --

1011010010110100 10110100

Feature of SS




Privacy, Security

Radio

Frequency

P o w e r

D e n s i t y

Power density of SS-signals could be lower than the noise density.

transmitted SS-signal

• • • • • •

Noise

P o w e r

D e n s i t y

Radio

Frequency

Noise

• • • • • •

received signal de-modulator

Base-bandFrequency

P o w e r

D e n s i t

y

With incorrect code(or carrier frequency),SS-signal itselfcannot be detected.

They cannot perceive the existence of communication,because of signal behind the noise.

With correct code(and carrier frequency),data can be detected.

Base-band

Frequency

P o w e r

D e n s i t y

Feature of SS




Direct Sequence Spread Spectrum:Transmission Technique




Cross-Correlation




Cross-Correlationbetween Code A and Code B = 6/16

Self-Correlationfor each code is 1.

one data bit duration

Spreading Code A

1 0 1 0 1 1 0 0 1 0 1 0 1 0 0 1

one data bit duration

Spreading Code A

1 0 0 1 1 1 0 0 1 0 1 0 1 0 0 1

Spreading Code A

1 0 0 1 1 1 0 0 1 0 1 0 1 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Spreading Code B

1 0 0

1 1 0 0 1 1 1 0 0 1 0 1 1

0 0 0 0 0 1 0 1 0 1 1 0 0 0 1 0

Preferable Codes




In order to minimize mutual interference in DS-CDMA ,

the spreading codes

with less cross-correlation should be chosen.

Synchronous DS-CDMA :Orthogonal Codes are appropriate. (Walsh code etc.)

Asynchronous DS-CDMA :

• Pseudo-random Noise (PN) codes / Maximum sequence

• Gold codes

Multiplexing using Walsh Code




C o d e f o r 0 0

C o d e f o r 0 1

C o d e f o r 1 0

C o d e f o r 1 1

D a t a

M o d u l a t o r

C o d e f o r 0 1

C o d e f o r 1 0

C o d e f o r 1 1

0 d t T

S e l e c t

m a x i m u m v a l u e

C o d e f o r 0 0

0 d t T

0 d t T

0 d t T

D e m o d u l a t o r

Synchronous DS-CDMA




Forward Link(Down Link)

Synchronous Chip Timing

A

A

Signal for B Station(after re-spreading)

Less Interference for A station

Synchronous CDMA Systems realized in Point to Multi-point System.e.g., Forward Link (Base Station to Mobile Station) in Mobile Phone.

Asynchronous DS-CDMA




In asynchronous CDMA system, orthogonal codes have bad cross-correlation.

Reverse Link(Up Link)

BA

Signal for B Station(after re-spreading)

Big Interferencefrom A station

Asynchronous ChipTiming

Signals from A and B areinterfering each other.

A

B

CDMA




• Code Division Multiple Access

• Start with data signal rate D ( Called bit data rate)• Break each bit into k chips by multiplying by a k bit user

code (known as a Walsh code)

• Channel has chip data rate kD chips per second

• User code (Walsh code) is orthogonal to all otherpossible user codes

– User code 1 * User code 2 = 0

– User code 1 * User code 1 = signal for user 1

• Signals for several users can be added and sent as asingle signal within the same band (multiplexed)

CDMA user code and data




Stallings 2003: Figure 9.10

CDMA Explanation




• Consider a user communicating with a base station

• Base station knows user A‘s code

• Assume communication already synchronized

• Base station receives a message from A and wants todecode it. To extract the signal from A the basestation

multiplies the signal by A‘s code • Decoder ignores other sources by using A‘s code to

decode

– For all other stations code station I * code station A =

0 so only the signal for station A remains

CDMA for DSSS




• When the basestation sends messages to nusers each message multiplied by a differentorthogonal Walsh code sequence, thosesignals are added before transmission.

• At each receiving station, the signal for thatstation is extracted by multiplying by thatstations Walsh code.

CDMA: two-senders, eight bit Walsh codes




Walsh

Code 2

WalshCode 1

DataStation 1

DataStation 2

Data multiplied by Walsh Code

Data multiplied by Walsh Code

(Sum of all stations)Transmitted data

CDMA: eight bit Walsh codes




Walsh Code 1

Received Data multiplied

by Walsh Code

Decoded Received DataStation 1

-2 -2 -2

2

-2

2 2 2

Receive Data (Sum)

Summary of Channel Partitioning

CDMA (Code Division Multiple Access)




CDMA (Code Division Multiple Access) • Used mostly in wireless broadcast channels such as cellular

phones• All users share same frequency band. Information from each useris spread throughout that frequency band

• Each user has their own orthogonal Walsh code ‗chipping‘sequence to encode data.

• encoded signal = (original data) X (Walsh code)

• Encoded signals from each channel are added, the summedsignal is transmitted

• The orthogonal property of Walsh codes guarantees that (ignoringtransmission errors) multiplying the received signal by a Walshcode will extract the data for the channel encoded using thatWalsh code from the received (summed) signal.

• Decoded signal = (received summed signal X Walsh code)

CDMA in a DSSS Environment




Stallings 2003: Figure 9.11




7.4. DS-CDMA Systems



DS-CDMA System Overview(Reverse Link)




Freq.Freq.

BPF

Despreader

Code B

Freq.Freq.

BPFDespreader

Code A

CDMA is a multiple spread spectrum.

Difference between each communication path is only the spreading code

Data B

Code B

BPF

Freq.Freq.

• • •

Data A

Code A

BPF

Freq.Freq.

• • • MS-B

MS-A

BS

Data A

Data B
















7.5. IS-95 CDMA SYSTEMS

IS-95 CDMA SYSTEMS




Interim Standard 95 – CDMA

Viterbi, Qualcomm

Outline

Forward Link

Reverse Link

Special Features of IS-95 CDMA

Brief Comparison to other second-generation standards

Possible Improvements

2G: IS-95A (1995)




• Known as CDMAOne• Chip rate at 1.25Mbps

• Convolutional codes, Viterbi Decoding

• Downlink (Base station to mobile): – Walsh code 64-bit for channel separation

– M-sequence 215 for cell separation

• Uplink (Mobile to base station):

– M-sequence 241 for channel and userseparation



2.5G: IS-95B (1998)




• Increased data rate for internet applications

– Up to 115 kbps (8 times that of 2G)

• Support web browser format language

– Wireless Application Protocol (WAP)

MC-CDMA




Network Architecture of IS-95 CDMA Systems




Mobile Station (MS)

-The Mobile Station (MS) is the subscriber‘sinterface with the CDMA network.

-Both hand-held MS units having a low-power radio transmitter and vehicle-

mounted MS units are permitted.-The manufacturer assignes a unique 32-bitElectronic Serial Number (ESN) to eachMS.

-ESN is a permanent and privateidentification code of the mobile terminal.


B St ti S b t (BSS)




Base Station Subsystem (BSS) • Each Base Station has a unique pilot PN-offset, a delay applied

to a random number sequence (PN Short Code) at the basestation.

• This sequence is applied to forward direction transmissions thatenables the terminals in a cell to decode the desired signal andreject the signals from other base stations.

• Pilot PN offsets ensure that the received signal from one cell

does not correlate with the signal from a nearby cell.• It is possible for adjacent cells to use the same CDMA radio

channel frequency (f 1).• Reusing the same frequency in every cell eliminates the need

for frequency planning in a CDMA system.

• Pilot PN-offset planning must be done in stead.

• In an area where the ranges of two cells overlap, there is anincreased interference, but this only reduces the number ofusers that can share the radio channel.





Base Transceiver Station (BTS)

• The BTS comprises several base radiotransceivers.

• Each transceiver consists of a transmitter and a

receiver which has a duplicated front end tomatch up with the two receiving antennas used inthe base antenna assembly.





Base Station Controller (BSC)

• The BSC comprises control logic, datacommunication facilities and multiplexing anddemultiplexing equipment.

• The BSC can control the radio power levelsof the various transceivers in the BTS, andalso can autonomously control the mobilestations‘ radio transmitter power levels.

• A single BSC can control several BTS radioequipment transmitters.





GPS Receiver

• CDMA ‗soft handover‘ (an MS establishescontact with a new base station before givingup its radio link to the original base station)

requires base stations to operate insynchronism with one another.

• Therefore each base station contains a GPSreceiver.





Mobile Switching Centre (MSC)

• The MSC is a switching network thatinterconnects calls between Mobile Stationsand between Mobile Stations and the Public

Switched Telephone Network (PSTN).• The MSC is also needed for ‗automatic

roaming‘ capabilities.

2G Network Architecture




Internet

BTS

BTS

BTS

BSC

BSC

M S

MSC

MSC

T-1

T-1

T-1T-1

EIR

VLR VLR

HLR/AC

PSTN

IWF



869 to 894 MHz (each channel is 1.25 MHz wide)

7.5.1. Forward Link




Subdivided into 4 sub channels

1.Pilot:

a. Timing

b. Phase Reference for Coherent Demodulation

c. Means for Signal Strength Comparison

2.Sync

a. Broadcasts future state of the long code register

3.Paginga. Call Control Information

4.Traffic

Voice Data (includes power control sub channel)







Forward Link Radio Transmission

• The forward link is by convention the transmission from




• The forward link is by convention the transmission fromBase Station to Mobile Station (MS).





Traffic Channel

• The traffic channel can accept data rates of 9600 bps,4800 bps, 2400 bps and 1200 bps comming from avariable-bit-rate speech coder (QCELP = QualcommCode Excited Linear Prediction).

• Check digits and tail bits (convolutional encoder tailsequence to drive the convolutional encoder into a knownstate at the end of each frame) are included. The signalsare processed in frames of duration of 20 ms.

• A convolutional code , with constraint length K=9 and rate½ protects each signal.





• When the rate is less than 19200 bps, the transmitter

repeats code bits (factor 1, 2, 4 or 8) to bring the rateup to 19200 bps, corresponding to 384 bits in aframe of 20 ms.

• An interleaver permutes the code bits in each frame.This will spread the influence of burst errors, typicalfor wireless communications.

• The baseband sequence is scrambled by the PNsequence derived from a Long Code Generator (aPN sequence with length 242 – 1 at a rate of 1.2288

Mbps) and Long Code Mask (a time-offsetdetermined by the ESN of the MS for trafficchannels).





•The Long Code period is :

to match the rate of the Long Code sequence to the 19200bps baseband rate, a decimator extracts 1 bit out of 64 bitsof the Long Code sequence.

IS-95 CDMA Logic Channels




IS 95 CDMA Logic channels








• The baseband symbol stream is spread by

multiplication with a Walsh sequence of length 64 ,thus creating a baseband chip rate of 1.2288 Mcps.

• There are 64 orthogonal Walsh sequences of length64, certain of which are assigned to different users of

the channel.• All user‘s transmissions occur synchronously from thebase station, so these transmissions are alsosynchronized at any individual subscriber‘s receiver (synchronous CDMA).

• The use of a set of orthogonal sequences thus allowsperfect rejection of other-user interference associatedwith any given transmission path within the cell.







• Signals received from other base stations, with

different values of ‗PN-offset‘, appear as low-level noise in the receiver of the MS, due to thecorrelation properties of the sequences.

• There are 512 possible ‗PN-offsets‘, with offseti corresponding to a time delay of 64i chips ( adelay of 64 chips @ 52 ms @ 15km).

• Since the period of the sequence is 215 chips,

there are 215 /26 = 29 = 512 possible offsets.












• The bandwidth of a CDMA signal is 1.23

MHz.

• The bandwidth of an AMPS channel (usingthe same frequency band) is 30 kHz.

• Therefore the bandwidth of a CDMA signalcorresponds to an aggregate bandwidth of41 AMPS channels.











CDMA Technologies for Cellular Phone System , Sept. 11, 2003

177

The sync channel

S




178

• The sync channel uses WALSH 32, a

sequence of 32 0s, followed by 32 1s.

• It provides the MS with critical timesynchronization data: system time (obtained

from GPS), the PN-offset of the pilotsequence and the rate of the base stationpaging channels (4.8 kbps or 9.6 kbps).




179




180






182




183

Traffic channel

Traffic channel on the forward direction has




184

• Traffic channel on the forward direction has

three components

—user data

—power control (puncturing convolutional code)

—signaling message

• Traffic channel on the reverse direction has

two components

—user data

—signaling message




185




186



W l h C d G

PN Generator

IS-95 Forward Link




Output

data

Rate:

9600 bps

4800 bps

2400 bps

1200 bps

Audio

Compressor

R=1/2

K=9

24x16

array =

384 bits

19.2kbps

Data

Scrambling

2^14-1 Permutations

(14 bit maximum

length shift register)

1.2288 Mcbs

L=64

(takesevery 64th

bit)

19.2kbps L=6(takes every 6th

bit)

4bits @

800Hz =

3200bps

Power Control

Bit

Specifies Forward

Channel Id (0-63)

One of 64 possible

19.2kbps

1.2288Mcps

I-Channel

Pilot PN

Sequence

2^15-1

Q-ChannelPilot PN

Sequence

2^15-1

1.2288Mcps

1.2288Mcps

Data to I

channel of

QPSK RF

modulator

Data to Q

channel of

QPSK RF

modulator

19.2kbps

Convolutional

Encoder

Block

Interleaver.MUX

Long Code Generator DecimatorDecimator

Walsh Code Generator

PN Generator

1.2288Mbps

Adds redundancy to data transmitionsfor error robustness.

Rate, r=1/2, where r = input bits / output bits,

Convolutional Encoder and Repetition




Maintains an output data rate of 19.2kbps regardless of input rate.

D0 D1 D2 D3 D4 D5 D6 D7 D8

9 Element Shift

Register

From Audio

Compressor

Possible

rates:

9600bps4800bps

2400bps

1200bps

752 octal =

111101011

XOR

G0

561 octal =

101110001

G1

Incoming Data

XOR

Note, while this is

easy to implement

at the transmitter,

it is nontrivial to

undue at thereceiver

Separates when consecutive data bits are sent, therefore adding to transmission

robustness.

Block Interleaver




Provides Time Diversity

2 pages, one is being filled as one is emptied

Each page contains all the data for one 20ms frame

24x16 bits = 384 bits

19.2kps * 20ms per frame = 384 bits!

Data is read in as rows and out as columns.

This sequence will be used to scramble the data and to code when to send a

power control bit.

Long PN Sequence




42 bit maximum length shift register, corresponds to 2^42-1 possiblepermutations

Contents of shift register are XOR’d with a public or a private key (depending onthe stage of the call) to generate one output bit at a rate of 1.2288Mcps

Takes a very long time to repeat.

Used for Data Encryption. Make call more secure.

Randomizes data. Prevents the transition of a long series of 1’s or 0’s

Scrambler

Dynamic, Decentralized, closed-loop power control scheme

Power Control Bit




Control Scheme: BS decides what to do based on the measured Frame ErrorRate

FER < threshold decrease mobile power by 1dB

FER > threshold increase mobile power by 1dB

One bit sent every 1.25ms = 800Hz or 16 power control bits per frame.

The power control bit is sent in one of 16 possible locations coded by the 4 bit

output of the second decimator.

(decimator #2 output = 4bits * 800Hz = 3.2kbps. This was reduced by a

factor of 6 from the 19.2kbps at the scrambler)

64 Orthogonal Channels for all users, assuming negligible multi-path delays

Provides some spreading

Orthogonal Covering Via Walsh Codes




Provides some spreading

64 X 64 Walsh Matrix. 1 Row = 1 Walsh Code

Each row of the matrix is exported at 19.2kHz (one row for each bit that is sent

from the scrambler)

64 bits per row * 19.2kHz per row = 1.2288Mbps (the output of the Walsh

generator)

Channel 0 is assigned to the pilot and is given more power then the rest of the

channels

Channel 32 is assigned to synchronization.

Mobile Paging Channels are usually on the lower Walsh ID’s

Provides more spreading, as not all Walsh codes have sufficient spreading.

Based on a 15 bits maximum length shift register (2^15 1 possible permutations)

Quadrature Modulation (Short Code)




Based on a 15 bits maximum length shift register (2^15-1 possible permutations)

-This is the pilot sequence if it’s modulated by Walsh code 0.

PN generator outputs data at 1.2288Mbps. (The same rate as the Walsh code

generator)

Different cells use different time offsets of the short code as to identify themselvesso that Walsh codes can be reused.

The PN sequence for the I channel is based on a different polynomial then the Q

channel and they therefore evolve differently.

The output I and Q channels are converted to analog and are modulated by an RF

carrier -> QPSK

• 824 to 849 MHz (each channel is 45 MHz away

7.5.2. Reverse Link




from the forward counterpart)• Access channel

– 4800 bps

– Initiate communication

– Respond to paging channel message

• Reverse voice traffic channel

– 9600, 4800, 2400, 1200 bps

• Very similar to forward link, but there are importantdifferences.




The IS-95 Reverse Link

• The reverse link is quite different




q

- Instead of Walsh Codes, ―psuedorandom noise‖ (PN)codes- PN codes are deterministic Bernoulli sequences of {-1,+1}- While not orthogonal, they have low cross-correlation,

e.g.<Ci , Ck > ≈ 1, unless i = k <Ci , Ck > = J , if i = k

- These codes have good properties even when notsynchronized

- Very strong error correcting codes make up thedifference










I-Channel

Pilot PN

Sequence

2^15-1

PN Generator

IS-95 Reverse Link




PN Generator

Output data

Rate:

9600 bps

4800 bps

2400 bps

1200 bps

Audio

Compressor

R=1/

3

K=9

32 x 18

= 576

bits

28.8kbps

Q-Channel

Pilot PN

Sequence

2^15-1

1.2288Mcps

1.2288Mcp

s

Data to I

channel of

OQPSK RF

modulator

Data to Q

channel of OQPSK RF

modulator

Convolutional

Encoder

Block

Interleaver.

Walsh Code

Generator

1.2288Mbps

1.2288Mbps

1.2288Mbps

64-ary

Orthogonal

Modulator

Codes 6 bits

Long Code PN

Generator1.2288Mcps

Data Burst

Randomizer

D

307.2kbps

½ PN chip

= 409.6ns

Total spreading gain J = 128

Orthogonal Modulation




– 64-ary orthogonal modulation using the same Walshfunction in the forward link

– Contrary to the forward link, used for orthogonal datamodulation

– One Walsh function is transmitted for six coded bits – Modulated symbol rate

• 28.8 kbps*64 chips /6 coded bits = 307.2 kcps

– Increase interference tolerance (refer to ECE459)

Data burst randomizer




– Turns off the Transmitter when the data rate fallsbelow 9.6kbps so that each redundant bit is sentonly once.

– Used to reduce interference to other users

– Each 20ms frame is divided into 16 1.25ms slotswhich are selected as a function of the long PN

code





• BS: base station

– Low-power, multi-channel, two-




way radios in a fixed location – Handling traffic between MS

and MSC

– Many BSs connected to one

central MSC• MS: mobile station

– All user equipment andsoftware needed for wireless

networks, such as cell phone

• Channel types in cellular system

– Control channel: transmit control information about




a call• Usually has only a few for each cell site

– Forward channel: used for transmission from BSto MS

– Reverse channel: used for transmission from MSto BS

– Paging channel: used to broadcast brief messageover entire service area

• Usually one channel for the entire network

• Main channels in a cell

– Four channel types

FVC for ard oice channel




• FVC: forward voice channel

• FCC: forward control channel

• RVC: reverse voice channel

• RCC: reverse control channel

– Voice channel: high rate, multiple

– Control channel: low rate, fewer

• Special working mode

– Handoff: transfer a call or data session




– Handoff: transfer a call or data sessionfrom one channel to another, or from oneBS to another, or from one MSC toanother.

• Handover: the process of transferring a call• Hard handover: the process needs to drop the

call for a short time, e.g., GSM handover

• Soft handover: MS simultaneously use multiple

BS, no need to drop the call when adding newBS, e.g., CDMA system

– Roaming:

• Extend connectivity service to locations otherthan home location




than home location

• Regional roaming, national roaming,international roaming



• MS receiving calls from PSTN




PSTN MSC

BSMS

1 (MIN)

2

3

4

5 6

7

8

9

10

3: FCC (page)4: ACK5: relay ACK6: Verify channel7: FCC (channel info)8,9,10: Voice

• MS initializing calls (to PSTN, or to another MS)




PSTN MSC

BSMS

MS

1

23

4

455

1. RCC: req. (MIN)2. Relay3. Verify (channel)4. FCC (assign channel)

5. voice

Bandwidth Recycling

Enhancing the system capacity due to the increase of reuse

7.5.3. Special Features of IS-95 CDMA System




efficiency.Achieving higher bandwidth efficiency (interference

limited) and simplifying the system planning.

Achieving flexibility due to the bandwidth on demand.

Power Control

Reducing the interference and increasing the talk time of

mobile station by using the efficient power control scheme.

Soft handoffsContributing to the achievement of the diversity and

reduce the chance of loss of link midway through the

conversation.

Diversity

Taking advantage of multiple levels of diversity: frequency

Special Features of IS-95 CDMA System




Taking advantage of multiple levels of diversity: frequency

diversity (spreading), spatial diversity (multiple antennas), pathdiversity (rake receiver) and time diversity (block interleaver), all of

which reduce the interference and improve speech quality.

Variable Rate Vocoder

Offering high speed coding and reducing background noise and

system interference based on the detection of the voice activity.

Coding Technique

Enhancing the privacy and security.

7.5.4. A Comparison between IS-95 and other 2nd

Generation Cellular Phone Systems




Generation Cellular Phone Systems

IS-54/136 GSM IS-95

TDMA/FDMA CDMA

Hard Handoff Soft Handoff

Open-loop and Slow Power

Control

Close-loop and Faster Power

Control

Fixed Rate Vocoder Variable Rate Vocoder

Increasing the channel bandwidth beyond 1.25MHz.

7.5.5. Possible Improvements on IS-95




Increasing the channel bandwidth beyond 1.25MHz.

Directional antennas on mobile stations.

Better power control algorithms.

Using MANET technology.

Adaptive filtering.

2G: IS-95A (1995)

• Known as CDMAOne




Known as CDMAOne

• Chip rate at 1.25Mbps

• Convolutional codes, Viterbi Decoding

• Downlink (Base station to mobile):

– Walsh code 64-bit for channel separation

– M-sequence 215 for cell separation

• Uplink (Mobile to base station):

– M-sequence 241 for channel and userseparation

2G: IS-95A (1995)

Standard IS-95, ANSI J-STD-008




Multiple Access CDMA

Uplink Frequency 869-894 MHz

Downlink Frequency 824-849 MHz

Channel Separation 1.25 MHz

Modulation Scheme BPSK/QPSK

Number of Channel 64

Channel Bit Rate 1.25 Mbps (chip rate)

Speech Rate 8~13 kbpsData Rate Up to 14.4 kbps

Maximum Tx Power 600 mW



MC-CDMA




Conclusions

• CDMA can increase the capacity of mobile




p y

system

• Goals of next generation cellular

– Further increase data rate

– Reduce interference among users• Future research:

– Search for good non-binary sequences

• Ideal 2-level autocorrelation• Low cross correlations

7.6. Conclusion

• CDMA is based on the spread spectrum




technique which has been used at military field.• CDMA cellular system is deemed superior to the

FDMA and TDMA cellular systems for the timebeing.

• Therefore, CDMA technique becomes moreimportant in radio communication systems.

Conclusions

• CDMA can increase the capacity of mobile




system

• Goals of next generation cellular

– Further increase data rate

– Reduce interference among users• Future research:

– Search for good non-binary sequences

• Ideal 2-level autocorrelation• Low cross correlations

Reference:

1.T. S. Rappaport, “Wireless communications principles&practice”, Prentice Hall, 1996



2.C. Y. Lin and J. Shieh, “IS-95 North American strandard-a CDMA based digital cellularsystem”, IEEE Website. 3.A. J. Viterbi, “CDMA principles of spread spectrum communication”, Addison-Wesley

Publishing Company, 1995.

4.R. Paul and K. V. Shah, “An objective comprison of second generation cellular systems -

GSM, IS-136 and IS-95”, IEEE, 1997.

5.Motorola, Inc. “CDMA Technology & Benefits: An introduction to the benefits of CDMA for wireless technology”, 1996. 6.S. G. Glisic and P. A. Leppanen, “Code division multiple access communications”,

Kluwer Academic Publishers, 1995.

7.C. Tsui, S. Cheng and C. Ling, “Using transformation to reduce power consumption of IS 95 CDMA i ” I t ti l S i L P El t i d

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