cdma airinterfaces v imp

7/27/2019 Cdma Airinterfaces v Imp

1/389

CL8300-SG.en.UL 1

Student Guide

Understanding the CDMA Air-Interfaces

of IS-95, IS-2000, and IS-856

CL8300

CL8300-SG.en.ULIssue 1.0

June 2003

Lucent Technologies - ProprietaryUse pursuant to Company instructions


2/389

CL8300-SG.en.UL 2

This material is protected by the copyright and trade secret laws of the United States and other countries. It may not be

reproduced, distributed, or altered in any fashion by any entity (either internal or external to Lucent Technologies), except

in accordance with applicable agreements, contracts, or licensing, without the express written consent of Lucent

Technologies and the business management owner of the material.

Copyright 2003 Lucent Technologies. All Rights Reserved.

Notice

Every effort was made to ensure that this information product was complete and accurate at the time of printing.However, information is subject to change.

Mandatory customer information

This information product does not contain any mandatory customer information.

Trademarks

Flexent is a registered trademark of Lucent Technologies.

AUTOPLEX is a registered trademark of Lucent Technologies.

5ESS is a registered trademark of Lucent Technologies.

Adobe Acrobat is a trademark of Adobe Systems, Inc.

cdmaOne is a registered trademark of the CDMA Development Group

CDMA2000 is a registered trademark of the Telecommunications Industry Association (TIA-USA)

WatchMark is a registered trademark of WatchMark Corp.

Prospect is a trademark of WatchMark Corp.

Technical support

For technical support, see To obtain documentation, training, and technical support or submit feedback on the 401-010-

001 Flexent/AUTOPLEX Wireless Networks System Documentation CD-ROM or the documentation web site at

https://wireless.support.lucent.com/

Developed by Lucent Technologies


3/389

CL8300-SG.en.UL 3

Course plan prologue

Course overview

Course description

Provides an in-depth understanding of the CDMA air-interface technologies and concepts for IS-

95, IS-2000, and IS-856.

Course objectives

This course is designed to enable you to:

Demonstrate the process of spreading and despreading

Explain how processing gain is achieved

Analyze the coding steps performed on the digital signal

Compare the CDMA codes used in signal processing

Illustrate the fundamental call processing phases

Differentiate between IS-95, IS-2000, and IS-856.

Course outline

This course covers:

Understanding of wireless radio concepts

In-depth discussion of CDMA concepts, characteristics, and signal processing

Discussion of the IS-95, IS-2000, and IS-856 channels and their coding

Core call processing as specified by IS-95, IS-2000, and IS-856

Mode of delivery

This course is offered as an instructor-led or self-paced course.

Media

Instructor-led course:

Paper-based student guide

Power Point presentation

Self-paced course:

Web-browser

Duration

The class length for the instructor-led course is 4 days.

The class length for the self-paced course is 20 hours.


4/389

CL8300-SG.en.UL 4

Related courses

Other Lucent Technologies courses related to CL8300 include the following:

CL8301: CDMA IS-95 and 3G-1X Design and Growth Engineering for Cellular Systems

This course provides engineering training in RF design of coverage and capacity for LucentTechnologies cellular (850 MHz) CDMA systems. The course covers both cdmaOne (IS-95) and

CDMA2000 (IS-2000).

CL8302: CDMA IS-95 and 3G-1X RF Design and Growth Engineering for PCS Systems

Similar to CL8301 but for a PCS (1900 MHz) system.

CL8303: CDMA IS-95 and 3G-1X Base Station Call Processing

This course provides engineering training in base station call processing for Lucent Technologies

CDMA systems. The course covers both cdmaOne (IS-95) and CDMA2000 (IS-2000) as well as

cellular (850MHz) and PCS (1900MHZ) systems.

CL8304: CDMA 3G-1X RF Design Engineering and Base Station Call Processing

This course provides training in RF design of coverage and capacity, and base station call

processing for Lucent Technologies CDMA systems. The course covers IS-2000 (3G-1X). Thecourse is used as a "delta" course to give students with the prerequisites the necessary knowledge

to operate a 3G system.

CL8306: 1xEV-DO RF Design Engineering and Call Processing

This course provides experienced engineers the needed training to design a Lucent Technologies

1xEV-DO system for RF coverage and capacity. The course also provides thorough

understanding of the call processing algorithms in the access terminals and base stations.

CL3723: Wireless AMPS/PCS CDMA RF Performance Engineering

This course provides a basic overview of the RF engineering optimization processes unique to

CDMA. Lucent Technologies's suggested optimization techniques are discussed utilizing case

study data gathered from in-service systems that have recently been optimized.

CL1522: WatchMark Prospect - Lucent Technologies AMPS/CDMA/TDMA OperationsThis course is designed to instruct students in the use of the Prospect applications.

CL1523: WatchMark Prospect - Lucent Tech.-Special Engineering Studies Operations

This course is designed to instruct students in the use of the Prospect SES applications.

Course registration

Register for a course via the web or over the phone:

http://www.lucent.com/training

1-888-LUCENT8 (582-3688) (within the U.S.A.)

+1-407-767-2667 (outside the U.S.A.)


5/389

CL8300-SG.en.UL 5

Lucent Technologies - Proprietary5

Understanding t he CDMAAir-Interfaces

CL8300

CDMA RF Engineering CurriculumHistory

CDMA

Fundamentals

RF DesignEngineering

Base StationCall Processing

RF PerformanceEngineering

Topic R12 - R16 R17+

CL3721/CL3722/

CL3725

2G

CL83043G-1XDelta

CL3723

2GCL37232G/3G-1X

CL3715

2G

CL3715

2G

CL8301/

CL83022G/3G-1X

CL83032G/3G-1X

System Performance

Monitoring andAnalysis Tools

CL1517/

CL1518/CL1522

CL1522/CL1523

CL8306

1xEV-DO

(R18+)

CL8300

2G/3G-1X/1xEV-DO

CL37163G-1X

Overview

References

The following publications are major references for this course:

TIA/EIA/IS-95-A, Mobile Station-Base Station Compatibility Standard for Wideband Spread

Spectrum Cellular Systems

TIA/EIA-95-B, Mobile Station-Base Station Compatibility Standard for Wideband Spread

Spectrum Cellular Systems

TIA/EIA/IS-2000A - Family of standards for CDMA2000 Standards for Spread Spectrum

Systems

TIA/EIA/IS-856, CDMA2000 High Rate Packet Data Air Interface Specification

These publications can be ordered from TIA (http://www.tiaonline.com )

Note:

CL3715, CL3721, CL3722, CL3725,

CL1517, and CL1518 are discontinued.

Note:

CL3715, CL3721, CL3722, CL3725,

CL1517, and CL1518 are discontinued.


6/389

CL8300-SG.en.UL 6

About the student

Prerequisites

Basic understanding of telecommunication and basic engineering math concepts.

Audience

Engineers in need of an in-depth understanding of the CDMA air-interface technology and

CDMA concepts for IS-95 (2G), IS-2000 (3G-1X), IS-856 (1xEV-DO), and who will continue

taking other courses in the wireless CDMA engineering curriculum.

Class size

The class size for the instructor-led version is a minimum of 12 students, and a maximum of 20

students.


7/389

CL8300-SG.en.UL 7

End-of-course assessment

Introduction

This course uses Level 2 Assessment tools to gauge the extent to which you have met the

objectives of the course. Level 2 Assessment results should be used solely to make furthertraining and development decisions. The results may not be used for any other purpose without

the written consent of Lucent Technologies Information Products & Training.

Purpose of the assessment

As stated above, the assessment serves a developmental purpose. There are a number of benefits

to having the assessment as part of this course.

Use of the Level 2 Assessment will objectively measure effective training. The questions are

linked to the course objectives, which, in turn, are linked to the tasks performed on the job.

These links hold our course developers and instructors accountable to produce and deliver

materials that are relevant to your needs.

Additional information

See the appendix for details on how to take the Level 2 Assessment.


8/389

CL8300-SG.en.UL 8

Contents

1. Fundamental Radio Concepts and CDMA Introduction

1.1: Electromagnetic waves

1.2: RF modulation

1.3: Why digital?

1.4: Digital signal modulation

1.5: FDMA, TDMA, CDMA

1.6: Why CDMA?

1.7: CDMA Channel

1.8: FDD vs. TDD1.9: Coherent vs. non-coherent demodulation

1.10: Some CDMA terms

1.11: Standards' relationships

1.12: OSI model

2. Spreading & Despreading

2.1: Spread spectrum techniques

2.2: Direct sequence spreading

2.3: Direct sequence despreading

2.4: Integrate & dump

2.5: Detection with noise

2.6: Eb/Nt explained

2.7: Noise rise

2.8: End-to-end overview

3. Information Coding

3.1: Typical signal processing

3.2: Speech encoding

3.3: Frames and quality indicator

3.4: Forward error correction

3.5: Bit interleaving


9/389

CL8300-SG.en.UL 9

4. CDMA Codes

4.1: Typical signal processing

4.2: Code correlation

4.3: CDMA codes

4.4: Long code4.5: Short codes

4.6: Walsh codes

4.7: Scrambling & spreading

4.8: Digital modulation

4.9: Receiver

5. CDMA Concepts

5.1: RF impairments

5.2: Rake receiver

5.3: CDMA call processing overview

5.4: Random access

5.5: Soft handoff

5.6: Power control

5.7: Noise rise vs. coverage reduction

6. IS-95 Specifics

6.1: Major characteristics

6.2: Forward link channels

6.3: Forward link coding

6.4: Forward link CDMA codes

6.5: Reverse link channels

6.6: Reverse link coding

6.7: Reverse link CDMA codes

6.8: Primary and signaling traffic

7. IS-2000 Specifics




7.4: Forward link CDMA codes

7.5: Reverse link channels



7.8: Reverse access specifics

7.9: Handoff specifics

7.10: Power control specifics


10/389

CL8300-SG.en.UL 10

8. IS-856 Specifics




8.4: Forward link CDMA codes8.5: Reverse link channels



8.8: Handoff specifics

8.9: Power control specifics

8.10: Pole point specifics

Appendix

Additional coding information

Web-based end-of-course assessment job-aid

Glossary


11/389

CL8300-SG.en.UL 11

About the course contents

Study plan

The lessons to study depend on the technology of interest. Lessons 1 through 5 cover the CDMA

technology in general. Lessons 6, 7, and 8, cover IS-95, IS-2000, and IS-856, respectively.Depending on the technology of interest, study the following lessons:

IS-95 (a.k.a. 2G)

Lessons 1 through 5 are required

Lesson 6 is required

Lesson 7 is optional

Lesson 8 is optional.

IS-2000 (a.k.a. CDMA2000, 3G-1X)


Lesson 6 is recommended

Lesson 7 is required

Lesson 8 is recommended.

IS-856 (a.k.a. 1xEV-DO)




Lesson 8 is required.


12/389

CL8300-SG.en.UL 12

Notes:


13/389

CL8300-SG.en.UL 13

Notes:


14/389

CL8300-SG.en.UL 14

Notes:


15/389

CL8300-SG.en.UL 15



CL8300

Lesson 1Fundamental Radio Concepts

and CDMA Introduction


16/389

CL8300-SG.en.UL 16



CL8300

Lesson Objectives

Explain the benefits of digital transmission

Differentiate CDMA from FDMA and TDMA

Explain the benefits of CDMA

Illustrate the relationship between IS-95, IS-2000, and IS-856.


17/389

CL8300-SG.en.UL 17



CL8300

1.1 Electromagnetic Waves

Electromagnetic waves propagate better than sound

Radio frequencies (30 kHz 30 GHz) used in cellular

Signal described as

y(t) = A * sin(2 * f * t + )

Modulation allows another signal to be transported by theRF signal.

0

A

1 / f

t

Speech, or more specifically sounds that humans can hear (20 Hz - 20 kHz), propagates by

pushing air molecules around. Therefore, sound loses its energy relatively quickly and is limited

in propagation over distance. Electromagnetic waves, on the other hand, can travel a much larger

distance.

The Scottish scientist James Clark Maxwell, in 1864, predicted the possibility of propagation of

electromagnetic waves. The theory was based on work done by Michael Faraday. It was a

German scientist, Heinrich Hertz, who was able to prove Maxwells theory through a series of

experiments between 1886 and 1888.

The basic idea is to couple electromagnetic energy into a propagation medium by means of a

radiation element such as an antenna. The frequency, or wavelength (), of the electromagneticwave impacts the waves capability of propagation. Lower frequency waves, or longer

wavelength, tend to follow the earths surface and is reflected and refracted by the ionosphere

(part of the earths atmosphere about 60 km above the surface). Above about 300 MHz, the

electromagnetic waves propagate by means of line-of-sight, and somewhere above 1000 GHz,

the waves become optical in character.

Radio frequencies (RF) generally refers to frequencies from 30 kHz to 30 GHz. RF is used in

cellular communication and is assumed throughout this course.

The RF signal, y(t), is assumed to be a sinusoidal signal with amplitudeA, frequencyf, and phase

. The frequency is often expressed in radians, , where = 2*f

.y(t) = A * sin(2 * f * t + )

The main frequency, or center frequency, is called carrier frequency, or the carrier. The carrier

frequency should be much greater than the effective bandwidth of the information signal.

Since RF signals are so much better than sound to propagate (travel), we want to use the RF

signals to carry our desired information. The process of making an RF signal carry specific

information (another signal) is called modulation.


18/389

CL8300-SG.en.UL 18



CL8300

1.2 RF Modulation

Amplitude Modulation (AM)

A(t) * sin(2 * f * t + )

Simple implementation

Sensitive to noise

Frequency Modulation (FM)

A * sin(2 * f(t) * t + )

More robust against noise

Phase Modulation (PM)

A * sin(2 * f * t + (t))

Similar to FM.

Given the sinusoidal signal, y(t) = A * sin(2 * f * t + ), there are three parameters that can beadjusted, or modulated, with the original signal, m(t), that is to be transmitted. The three

parameters are amplitude (A), frequency (f), and phase ().

Amplitude Modulation (AM)

When the information signal, m(t), modulates the amplitude of the carrier, we call this

modulation technique for Amplitude Modulation (AM).

The benefit of AM is the simplicity with which it can be demodulated. One inexpensivedemodulation method is called envelope detection. One drawback with AM is that the signal can

easily be degraded by noise or interference.

Frequency Modulation (FM)

When the information signal, m(t), modulates the frequency of the carrier, we call this

modulation technique for Frequency Modulation (FM).

FM requires a more sophisticated demodulator which can detect frequency deviation. However,

a big advantage of FM over AM is that FM is less susceptible to noise.

Phase Modulation (PM)

When the information signal, m(t), modulates the phase of the carrier, we call this modulation

technique for Phase Modulation (PM).

Since both the frequency and phase parameters are impacting the sin() operation, PM issimilar to FM. See the figure. Therefore, PM and FM have similar characteristics.


19/389

CL8300-SG.en.UL 19



CL8300

1.3 Why Digital?

Analog signals are easilydistorted by noise

Analog signals can be represented in a digital form

Nyquist criterion

Digital signals can sustain morenoise than analog

Additional information canbe included in the bit stream.

In 1928, Harry Nyquist published his famous sampling theory. The sampling theory, theNyquist

criterion, states that an analog signal can be completely reconstructed from a set of uniformly

spaced discrete-time samples, if the sampling rate is equal to or greater than the bandwidth of the

signal.

Analog vs. Noise

Analog signals are more susceptible to noise than digital signals. The quality (or correctness) of

an analog signal depends on how exactly the receiver can detect the envelope, or curve, or thesignal. Shown in the figure is an analog signal with noise added; the correct signal is also shown.

When noise is added to an analog signal, the instantaneous envelope value can vary significantly

from the actual envelope, thereby degrading the quality of the signal.

Digital vs. Noise

When transmitting a digital signal, only ones and zeroes must be detected. The detection can be

done using a maximum likelihood decoder. For example, assume that a digital 1 is represented

as a -1 voltage, and a digital 0 is represented as a +1 voltage. When decoding, the maximum

likelihood detector can determine the received bit to be 1 if the received voltage is less than 0,

and a 0 is the voltage is greater than 0.

One can easily see that a digital signal can sustain more noise than an analog signal and still

yield the correct information bit in the receiver without any degradation in quality.

Other Benefits of Digital

With digital transmission schemes come all the advantages that traditional microprocessor

circuits have over their analog counterparts. Any shortfalls in the communications link can be

eradicated using software. Information can now be encrypted, and error correction can ensure

more confidence in received data. Also, additional information can be included in the data

stream.


20/389

CL8300-SG.en.UL 20



CL8300

1.4 Digital Signal Modulation

Amplitude Shift Keying (ASK)

On-Off Keying

Rarely used today

Frequency Shift Keying (FSK)

Two distinct frequencies

transmitted

Phase Shift Keying (PSK)

Phase of signal is changed

Several phase changes possible QPSK.

When transmitting digital signals, variations of AM, FM, and PM schemes are used. The digital

signal modulation schemes are often called Amplitude Shift Keying (ASK), Frequency Shift

Keying (FSK), and Phase Shift Keying (PSK). As with FM and PM, FSK and PSK offer more

immunity to noise, and are the preferred schemes today.

Amplitude Shift Keying (ASK)

Since ones and zeroes are transmitted, ASK transmits a signal with a given amplitude for one bit

value, and little or no amplitude for the other bit value. Early telegraphy used ASK to transmitMorse code, but today pure ASK is rarely used.

Frequency Shift Keying (FSK)

A simple variation from traditional analog FM can be implemented by applying a digital signal

to the modulation input. Thus, the output takes the form of a sine wave at two distinct

frequencies. To demodulate this waveform, it is a simple matter of passing the signal through

two filters and translating the resultant back into logic levels.

Phase Shift Keying (PSK)

PSK involves changing the phase of the transmitted waveform instead of the frequency. In its

simplest form, a PSK waveform can be generated by using the digital data to switch between two

signals of equal frequency but opposing phase (Binary PSK, BPSK). If the resultant waveform is

multiplied by a sinusoidal wave of equal frequency, two components are generated: one cosine

waveform of double the received frequency and one frequency-independent term whoseamplitude is proportional to the cosine of the phase shift. Thus, filtering out the higher-frequency

term yields the original modulating data prior to transmission. This is difficult to picture

conceptually, but a mathematical proof can be done.

Quadrature Phase Shift Keying (QPSK)

Taking the above concept of PSK a stage further, it can be assumed that the number of phase

shifts is not limited to only two states but multiple states. The transmitted carrier can undergo

any number of phase changes and, by multiplying the received signal by a sine wave of equal

frequency, will demodulate the phase shifts into frequency-independent voltage levels.


21/389

CL8300-SG.en.UL 21



CL8300

1.5 FDMA, TDMA, CDMA

Frequency Division Multiple Access (FDMA)

Divides bandwidth B into N channels

Supports N users

Time Division Multiple Access (TDMA)

Uses FDMA and timeslots

Divide B into N channels and TS timeslots

Supports N * TS users

Code Division Multiple Access (CDMA)

Uses entire bandwidth, BC, for all users

Supports a dynamic number of users.

Bandwidth

U1

U2

U3B

t

Bandwidth

U1

U3

U5B

t

Bandwidth

BC

t

U2

U4

U6

U1

U3

U5

U2

U4

U6

Cellular systems rely on RF as the primary means of communication between the mobile station

and the base station. In an ideal world, there is an unlimited frequency spectrum available. In our

world, though, there is not unlimited frequency spectrum because a certain amount of the

accessible frequency spectrum has been allocated for commercial and non-commercial

applications, such as AM/FM radio, TV broadcast, navigation systems, etc.

To access the limited frequency spectrum in a cellular system, several access techniques exists.

The most common techniques include Frequency Division Multiple Access (FDMA), Time

Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA).

Frequency Division Multiple Access (FDMA)

With FDMA, the available frequency bandwidth, B, is divided into N number of channels, each

with a bandwidth of BN (typically 30 kHz). Each active user is then assigned one channel. In

other words, N users can be supported.

The total number of users supported in a system can be increased by implementing a frequency

reuse plan the channels are reused in areas some distance away.

Time Division Multiple Access (TDMA)

With TDMA, the available frequency bandwidth, B, is divided into N number of channels, each

with a bandwidth of BN (typically 30 kHz for IS-136, and 200 kHz for GSM). In addition, each

channel is divided into TS number of time slots (3 useable for IS-136, 8 for GSM). Each active

user is then assigned a channel and a time slot. In other words, N*TS users can be supported.

The total capacity can be increased with a frequency reuse plan.

Code Division Multiple Access (CDMA)

With CDMA, a large bandwidth, BC, is dedicated to one CDMA Channel. BC is typically 1-5

MHz, depending on technology. An active user is assigned a unique code within the CDMA

Channel. Using the unique code, the receiver can extract the specific user information from the

CDMA Channel. The supported capacity is dynamic and a function of interference levels.

A frequency reuse plan is not needed in a CDMA system.


22/389

CL8300-SG.en.UL 22



CL8300

1.6 Why CDMA?

High and dynamic capacity

Same RF carrier frequency used in all sectors and all cells

Enhanced RF channel performance

Rake receiver

Soft handoff

No interruption of traffic channel when using soft handoff

Soft blocking

Determined by quality objective

Longer battery life for mobile station

Lower transmission power levels

Inherent privacy.

One of the main benefits of CDMA is the dynamic capacity inherent in the technology. As will

be shown later, capacity is a function of the interference levels in the system. By optimizing the

system and the hardware and software of the network components, system capacity can be

increased. In CDMA, coverage, capacity, and quality are related to each other, and one cannot

increase one without sacrificing one of the other.

Compared to other technologies such as GSM and IS-136 (TDMA), the performance of

CDMA is enhanced through Rake receivers and soft handoff. Rake receivers allow the receiver

to efficiently combat multipath. Soft handoff allows the mobile station to have a seamless

connection to the network without any interruptions as the mobile station moves around within

the system.

By transmitting digital information and using effective coding techniques, the transmission

power levels for a mobile station is lowered. This not only results in lower interference in the

system, but also a longer battery life for the mobile station.

There is a degree of privacy inherent in the CDMA technology. By the use of pseudo-noise

codes, an eavesdropper cannot intercept the information without extensive code-breaking

computations. Please note that while there is inherent privacy in CDMA, the information is not

encrypted. Encryption must be performed prior to the CDMA processing.


23/389

CL8300-SG.en.UL 23



CL8300

1.7 CDMA Channel

One CDMA Channel

Multiple CDMA Channels

fc

3dB Bandwidth

Guard bandGuard band

fc1

3dB Bandwidth

Guard bandGuard bandfc2

3dB Bandwidth

Channel spacing

The 3 dB bandwidth of a channel is the frequency range where the signal at the edges is 3 dB

lower than the peak value at the center frequency, fc. The center frequency is used to specify

where in the frequency spectrum the CDMA Channel is located.

A CDMA Channel, or carrier frequency, has a 3 dB bandwidth of 1.23 MHz for IS-95 and IS-

856. For IS-2000, the 3 dB bandwidth is 1.23 MHz or 3.69 MHz, depending on configuration

(seeIS-2000 Specifics lesson for details).

In addition to the frequency spectrum required for the CDMA Channels 3 dB bandwidth,frequency guard bands are also needed on each side of the channel if the CDMA Channel

borders to spectrum not used for CDMA. The performance standard specifications recommend

frequency guard band distance (bandwidth) for various frequency bands; e.g., IS-97 defines

performance specifications for IS-95 and IS-2000 base stations, IS-864 defines the performance

specifications for IS-856 base stations.

For adjacent CDMA Channels, no frequency guard band is needed between the CDMA

Channels. Obviously, the CDMA Channels have to be spaced at least 1.23 MHz (or 3.69 MHz)

apart. The frequency distance between two CDMA Channels is referred to as channel spacing.

The channel spacing used depends on the channel numbering scheme for the particular

frequency band. For example, in the 850 MHz spectrum (band class 0), the channel spacing is

1.23 MHz, while in the 1900 MHz spectrum (band class 1), the channel spacing is 1.25 MHz.


24/389

CL8300-SG.en.UL 24



CL8300

1.8 FDD vs. TDD

Frequency Division Duplex (FDD)

Most common

Simple implementation

May not be spectrum efficient with

asymmetrical data links

Time Division Duplex (TDD)

Efficient use of spectrum

Requires precise synchronization and

timing.

Spectrum

Reverse link

Guard band

Forward link

t

Guardtime

Forwardlink

Spectrum

Reverselink

Guardtime

Forwardlink

t

In order to support duplex operation (simultaneous or pseudo-simultaneous communication

between mobile station and base station) in a CDMA system, one of two techniques are often

used: Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

Frequency Division Duplex (FDD)

The FDD scheme is the most common scheme. For every CDMA Channel, there is a forward

link (base station to mobile station) CDMA Channel and a reverse link (mobile station to base

station) CDMA Channel. This means that if the CDMA Channel is 1.23 MHz wide, then twicethat spectrum is needed for FDD. See the figure.

Between the forward link and reverse link portions of the spectrum, there is a guard band to help

isolate the receive part from the transmit part of the mobile station (or base station).

FDD is simple to implement. However, for data transmission where the data capacity

requirements (and therefore often spectrum demand) are asymmetrical (often higher on the

forward link), FDD may not efficiently use the total spectrum.

Time Division Duplex (TDD)

Instead of dividing the frequency spectrum between the forward and reverse links, the spectrum

can be divided in time for the forward and reverse links. In other words, the available frequency

spectrum is used for forward link transmission for some time period. During another time period,

the same frequency spectrum is used for reverse link transmission. Between each transmission

period, there is a guard period to help isolate forward and reverse link transmissions from eachother.

TDD required precisely controlled synchronization and timing between forward and reverse link

transmission. Therefore, the complexity of the system increases. The benefit of TDD is a more

efficient use of the available frequency spectrum when asymmetrical capacity demands are

experienced on the RF link. A longer time period for transmission can be assigned to, for

example, the forward link. TDD also allows a CDMA Channel to be implemented in a very

limited frequency spectrum.


25/389

CL8300-SG.en.UL 25



CL8300

1.9 Coherent vs. Non-coherentDemodulation

With coherent demodulation a phase reference isprovided

Pilot Channel

Phase changes can be

anticipated

Lower signal energy for

information channel

Non-coherent demodulation operates without a phasereference

Phase has to be guessed

Higher signal energy needed.Phase

discrepancy

Real phase of signal

Phase reference at receiver

The Federal Standard 1037C defines coherent as pertaining to a fixed phase relationship

between corresponding points on an electromagnetic wave. This means that if the receiver has

a phase reference available when demodulating the received information, coherent demodulation

is performed. The phase reference in a CDMA system is provided by a Pilot Channel. The Pilot

Channel is easy to detect because it has a simple code and relatively high signal energy.

When a Pilot Channel is present, the receiver can observe the changes in the Pilot Channel (e.g.,

phase) and anticipate the changes to the information channel.

If a Pilot Channel is not present, the receiver must perform non-coherent demodulation. Non-

coherent demodulation means that the receiver must assume and guess the changes of the

information channel. This typically means that the information channel requires much more

power (theoretically 3 dB) than it would need if the Pilot Channel was present. The higher power

is needed to minimize the phase discrepancy between the signal and the phase used in the

demodulator.


26/389

CL8300-SG.en.UL 26



CL8300

1.10 Some CDMA Terms

User devices

Mobile station

Access terminal (AT)

2G

IS-95

cdmaOne

3G

IS-2000

CDMA2000

1xRTT, 3xRTT

3G-1X, 3G-3X

IS-856

1xEV-DO.

There are a number of terms in CDMA that may be confusing to the reader. The confusion may

stem from the fact that different terms often describes the same, or similar, components,

concepts, etc. A lot of terms will be described and explained throughout this course. Here, a few

of the frequently seen terms will be explained.

The network component being used when accessing the system is often called a mobile station

(MS), or simply mobile. For IS-856, the same mobile station is called an access terminal (AT).

AT is only used exclusively in theIS-856 Specifics lesson. In other lessons where mobile station

is used, the information also applies to an AT.

When discussing the technologies covered in this course, various terms may be used. The terms

can perhaps be classified as second generation (2G) terms and third generation (3G) terms.

IS-95 specifies the air-interface used for the 2G CDMA system branded as cdmaOne. For the 3G

air-interface, two specifications are discussed in this course: IS-2000 and IS-856.

IS-2000 is one of the radio transmission technologies (RTT) used for 3G systems; hence, 1xRTT

and 3xRTT for the two configurations of IS-2000. See theIS-2000 Specifics lesson for details

regarding the two configurations. Similar to IS-95 and cdmaOne, the IS-2000 based system is

called CDMA2000, and sometimes CDMA2000-1X and CDMA2000-3X.

Lucent Technologies often refers to the IS-2000 system as 3G-1X or 3G-3X.

IS-856 is an evolution of IS-2000, but is used for data applications only. The IS-856 system is

also called 1xEV-DO, CDMA2000-1X EVolutionData Only.

For other terms found throughout this course, please refer to the glossary.


27/389

CL8300-SG.en.UL 27



CL8300

What is 3G?

ITUs IMT-2000

Global roaming

High data rates

Variable

Negotiable (QoS)

Asymmetrical

Internet connectivity

E-mail push

Support for multimedia services

IS-2000 and IS-856 are approved IMT-2000

specifications.

Global

Regional

Local Area

IndoorOffice/Home

MEGA CELL

MACRO CELL

MICRO CELL

PICO CELL

> 9.6 kb/s

> 144 kb/s

> 384 kb/s

> 2.048 Mb/s

8

9

7

4 5

6

3

2

1

#

0*

The International Telecommunication Union (ITU) envisioned one unifying terrestrial air and

core network system for the next generation of wireless communication, a.k.a. 3G. ITUs

recommendations for the next generation systems are called International Mobile

Telecommunications-2000 (IMT-2000). Some of the major aspects of IMT-2000 include:

Global roaming that would allow a mobile user from anywhere in the world to expect the same

standard set of wireless services and features, regardless of where the user travels and the

country visited

High data rates optimized for different terrestrial radio environments:

Global satellite (megacell) environment, minimum 9.6 kbps

High mobility, vehicular (macrocell) environment, minimum 144 kbps

Low-mobility, pedestrian (microcell) environment, minimum 384 kbps

Indoor (picocell) environment, minimum 2 Mbps

Internet connectivity and services comparable with direct landline connection. Also supporting

asymmetric (data rate) links and e-mail push; user does not have to connect to system to receive

e-mail

Negotiable quality of service (QoS) allowing the user to negotiate the QoS with regard to data

rate, bit error rate, and latency

Variable data rates, allowing the user to get a higher data rate when the system is less busy

Support of multimedia services such as streaming video.

Two specifications classified by the ITU as 3G technologies are discussed in this course, IS-

2000 and IS-856. IS-95 is not classified as a 3G technology.


28/389

CL8300-SG.en.UL 28



CL8300

1.11 Standards Relationships

IS-95A

Original CDMA cellulartechnology

Voice and low speed data(14.4 kbps)

IS-95B

Enhanced performance Voice and medium speed

data (115.2 kbps)

IS-2000

Increased capacity,

scalability

Voice and high speed data(1,036.8 kbps)

IS-856

IP network

High speed data only(2,457.6 kbps)

Backwardcompatible

Back

ward

compa

tible

RF

compatible

IS-95 revision A, IS-95A, was the first commercial implementation of the CDMA technology as

a wireless communication system. Published in 1993, the standard specification became very

popular, especially in North America. IS-95A supports voice and low speed data applications

with a maximum data rate of 14.4 kbps.

IS-95 was revised to revision B, IS-95B, in early 1999. IS-95B improved the performance of the

CDMA systems by adding and enhancing existing algorithms and parameters. Medium speed

data, up to 115.2 kbps, is also supported in IS-95B. Few networks were deployed using IS-95B,

due to the emerge of third generation (3G) technologies.

No further revisions of IS-95 were made. The work focused instead on IS-2000 (IS-95C) with

a more timely numbering scheme. Revision A of IS-2000 was released in early 2000. Several

technology enhancements were made in IS-2000 that dramatically increased voice capacity

compared to IS-95 while still maintaining backward compatibility. True high speed data was also

implemented with data rates up to 1,036.8 kbps. More common data rates seen are data rates up

to 307.2 kbps. With the use of two different RF carrier bandwidths and additional channels, IS-

2000 proves to be more scalable than IS-95.

In early 2002, IS-856 was published. IS-856 is based on IS-2000, but removes voice-capability

and focuses on data only operation. By focusing on data only operation, the data rate for an IS-

856 system can reach 2,457.6 kbps. Another noticeable difference between IS-856 and IS-2000

is that IS-856 is an IP-based network, whereas IS-2000 relies on proprietary protocols. IS-856 is

backward-compatible with IS-2000 at the RF level. This means that RF components can beshared between the two systems.


29/389

CL8300-SG.en.UL 29



CL8300

Data Implementation

IS-95A Regular Traffic Channel can carry up to 14.4 kbps with vocoder

bypass IS-95B

Traffic Channel consists of a FCCH and optional SCCH

FCCH and aggregated SCCH can carry up to 115.2 kbps

IS-2000 Supplemental Channel carries up to 1,036.8 kbps

Efficient interference control

IS-856 Forward link Data Channel carries up to 2,457.6 kbps

Time-multiplexed between users

One user gets all the resources based on scheduling algorithm

Reverse link Data Channel carries up to 153.6 kbps.

IS-95 and IS-2000 supports voice in the system. The implementation of the voice application is

the same between the two technologies. IS-856 is a data only technology. All the technologies,

IS-95A, IS-95B, IS-2000, and IS-856, support data. The technology specific lessons further

discuss the implementation of data.

IS-95A

Data rates up to 14.4 kbps are supported in revision A of IS-95, using the Traffic Channel. This

is achieved by bypassing the vocoder (processing the speech for transmission).IS-95B

Revision B of IS-95 introduced two sub-channels of the Traffic Channel: the Fundamental Code

Channel (FCCH) and Supplemental Code Channel (SCCH). The FCCH supports voice and low

speed data rates up to 14.4 kbps. Higher data rates are achieved by aggregating up to seven

SCCHs. The maximum data rate for IS-95B is 115.2 kbps

IS-2000

In IS-2000, the Supplemental Channel is introduced. The Supplemental Channel is used for data

traffic only, and can carry up to 1,036.8 kbps, depending on the current configuration.

IS-2000 also introduced the ability to efficiently control interference generated in the system due

to the high speed data traffic.

IS-856The forward link in IS-856 can carry data rates up to 2,457.6 kbps. This is achieved by

multiplexing the forward link resources between the users. When time-multiplexing is used, all

the forward link resources can be concentrated to one user, and the data rate maximized. The

user who will received the forward link Data Channel is determined by a scheduling algorithm.

The reverse link Data Channel carries up to 153.6 kbps.


30/389

CL8300-SG.en.UL 30



CL8300

1.12 OSI Model

OSIApplication (Layer7)

Presentation (Layer6)

Session (Layer 5)

Transport (Layer 4)

Network (Layer 3)

Data Link (Layer 2)

Physical (Layer 1)

The Open System Interconnection (OSI) model was developed in 1984 by the International

Standardization Organization (ISO). It specifies a seven-layer model which is used by the

industry as the frame of reference when describing protocol architectures and functional

characteristics. The seven layers are application, presentation, session, transport, network, data

link, and physical layers. To remember the layers, the following sentence could be used: All

People Seem ToNeedData Processing.

Layer 7: The application layer supports application and end-user processes. This layer

provides application services for file transfers, e-mail, etc.

Layer 6: The presentation layer formats data to be sent across a network, providing freedom

from compatibility problems. It is sometimes called the syntax layer.

Layer 5: The session layer establishes, manages, and terminates connections between

applications. The session layer sets up, coordinates, and terminates conversations, exchanges,

and dialogues between the applications at each end.

Layer 4: The transport layer provides transparent transfer of data between end systems, or

hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data

transfer.

Layer 3: The network layer provides switching and routing technologies, creating logical paths

known as virtual circuits, for transmitting data from node to node. Routing and forwarding are

functions of this layer, as well as addressing, internetworking, error handling, congestion control,and packet sequencing.

Layer 2: The data link layer furnishes transmission protocol knowledge and management and

handles errors in the physical layer, flow control, and frame synchronization.

Layer 1: The physical layer conveys the bit stream - electrical impulse, light or radio signal -

through the network at the electrical and mechanical level. It provides the hardware means of

sending and receiving data on a carrier, including defining channels and cables (if wireline).


31/389

CL8300-SG.en.UL 31



CL8300

OSI Model vs. CDMA

OSI TCP / IP

Application (Layer7)Application

Presentation (Layer6)

Session (Layer 5)

Transport ( Layer 4) Transport (TCP)

Network (Layer 3) Internet (IP)

Data Link (Layer 2)Network Access

Physical (Layer 1)

CDMA RadioAccess Network

For voice applications, the OSI model has not been much of a concern since each voice user is

similar from a resource (RF, hardware, etc.) point of view. However, for data applications,

different users may use different applications. Each application may have significantly different

resource demands. Therefore, it is important to structure the system in order to manage the

information.

Most data applications are based on an IP network. From an RF point of view, in an IP network

the CDMA radio access network (RAN) operates in the first three layers of the OSI model,

Layers 1-3, supporting IP traffic. While the RAN may operate within the first three OSI layers to

support the IP network, the RAN may have its own internal layers resembling the OSI model

(e.g., IS-856).

Obviously, following the OSI model is not required for a communication system to function

properly.

In this course, the focus will be on Layer 1, the physical layer.


32/389

CL8300-SG.en.UL 32



CL8300

Summary

RF carrier is modulated with a digital signal

ASK

FSK

PSK

Digital is more robust against noise

CDMA is a preferred access method over FDMA/TDMA

Dynamic capacity

Enhanced RF performance

Inherent privacy

The physical layer will be covered in this course

IS-95 (cdmaOne)

IS-2000 (CDMA2000, 3G-1X, 3G-3X)

IS-856 (1xEV-DO).

RF frequencies are generally referred to as the electro magneticwaves propagating in the

frequency range of 30 kHz to 30 GHz. Using various modulation techniques, and information

signal can be carried by an RF signal (carrier frequency). Several modulation techniques for a

digital information signal exist, e.g., ASK, FSK, and PSK. Digital transmission is preferred over

analog transmission since a digital signal can sustain more noise and, at the same time,

implement error correction schemes.

With a limited frequency spectrum and multiple users, an access method must be selected to

accommodate the users. Out of the three access methods described (FDMA, TDMA, and

CDMA), CDMA is preferred due to its dynamic capacity, enhanced RF performance (Rake

receiver and soft handoff), and inherent privacy. The capacity is dynamic because the same RF

carrier frequency is used across the network. Multiple CDMA carriers can co-exist within a

network, provided that they are separated in frequency (channel spacing) and do not have

overlapping 3 dB bandwidths (1.23 MHz or 3.69 MHz).

Three CDMA air-interface technologies are discussed in this course, IS-95 (cdmaOne), IS-2000

(CDMA2000, 3G-1X, or 3G-3X), and IS-856 (1xEV-DO). Of the three technologies, IS-2000

and IS-856 are approved 3G technologies according to the ITU. IS-2000 is backward-compatible

with IS-95. IS-856 is an evolution of IS-2000, with data only capability.

This course focuses on the air-interface specifications of the technologies discussed. The air-

interface is the physical layer (Layer 1) of the OSI model.


33/389

CL8300-SG.en.UL 33



CL8300

Knowledge Check

1. Why is digital transmission more beneficial than analogtransmission?

A. More noise can be sustained without degrading quality

B. Error correction can be implemented to further improve the

signal

C. Battery life is increased for the mobile station

D. Any of the above


34/389

CL8300-SG.en.UL 34



CL8300

Knowledge Check contd

2. What uniquely identifies a TDMA user channel?

A. Channel number only

B. Time slot and unique code

C. Channel number and time slot

D. Channel number and unique code

3. What uniquely identifies a CDMA user channel?

A. Channel number only

B. Time slot and unique code

C. Channel number and time slot

D. Channel number and unique code


35/389

CL8300-SG.en.UL 35



CL8300


4. What is one of the benefits of CDMA?

A. A fixed, high capacity

B. Enhanced RF performance

C. Increased capacity using a frequency reuse plan

D. Any of the above

5. For a typical CDMA carrier, what is the minimumrequired channel spacing?

A. 1.23 MHz

B. 1.25 MHz

C. 2.5 MHz

D. 5 MHz


36/389

CL8300-SG.en.UL 36



CL8300


6. Match the following terms:

A. Mobile station 1. 1xEV-DO

B. IS-95 2. Access terminal

C. IS-2000 3. 3G-1X

D. IS-856 4. cdmaOne

7. IS-856 can share certain RF components with IS-95A.

A. True

B. False


37/389

CL8300-SG.en.UL 37



CL8300


8. An IS-95 mobile station may be able to make a call on aIS-2000 network.

A. True

B. False

9. An IS-856 access terminal may be able to make a call ona IS-2000 network.

A. True

B. False


38/389


39/389

CL8300-SG.en.UL 39


Understanding t he CDMA

Air-InterfacesCL8300

Lesson 2Spreading & Despreading


40/389

CL8300-SG.en.UL 40



CL8300

Lesson Objectives

Explain Direct Sequence spreading and despreading

Describe processing gain

Explain Eb/Nt Explain noise rise.


41/389

CL8300-SG.en.UL 41




2.1 Spread Spectrum Techniques

Spread spectrum theory created by actress Hedy Lamarr

Would be used to guide submarine torpedoes to German targets

during World War II

Military applications did not appear until 1962

Different types of spread spectrum techniques

Frequency Hopping (FH)

Time Hopping (TH)

Direct Sequence (DS)

In this course, CDMA implies DS spread spectrum.

Frequency

U1

U2

U3

t

Frequency

t

Frequency

U1 U2U3

t

U1

U1

U1

U2

U2

U3

U3

U3

U2

U1U2U3

FH TH DS

Spread Spectrum History

Spread spectrum theory dates back to a Hollywood party in 1940 and a conversation between

Austrian actress Hedy Lamarr and composer George Antheil. Prior to coming to the United

States, Hedy Lamarr had been married to an Austrian arms dealer who dealt willingly with

Hitlers Nazis and frequently brought his clients home for dinner and business discussions.

Although she was believed to be little more than window dressing, Lamarrs husband would

have been astonished to discover how much she learned from his dinner meetings.

Hedy Lamarr fled Austria before the outbreak of World War II and headed to Hollywood to

resume her acting career. Desiring to contribute to the war effort, she explained her Secret

Communication System theory to Antheil, who sketched and took notes. The theory was an

electronic means of controlling torpedoes from a submarine to its target.

The Secret Communication System used synchronized paper tapes to perform frequency

hopping to prevent guidance signals to the torpedo from being disrupted. The heart of the system

was the synchronized paper tapes. These paper tapes would automatically change the frequency

of the transmitter and receiver so that an enemy could not detect and lock onto the signal.

In 1942, Lamarr and Antheil patented their idea and offered it to the Navy for free. The Navy

could not comprehend the concept and declined the offer. Neither Lamarr nor Antheil pursued

the idea any further and the concept of spread spectrum was lost until it appeared in equipment

used during the Cuban Missile Crisis in 1962. By then, the exclusive rights to the patent had

expired and neither of its inventors received money for spread spectrum.

Spread Spectrum Techniques

The CDMA modulation technique uses three methods for spectrum spreading:

Frequency Hopping (FH); transmission frequency appears random

Time Hopping (TH); transmission time appears random

Direct Sequence (DS); the transmitted signal appears random


42/389

CL8300-SG.en.UL 42




2.2 Direct Sequence Spreading

CDMARadio

Signal

Information

coder and

processing

c(t)

InformationSignal

Modulator

DS generator

BasebandCDMA

Signaling

y(t)b(t)

b(t) 0

c(t) 0

y(t)= 0

b(t) c(t)

1

1

1

-1

-1

-1

b(f)

fb

f

Tb

fc

f

y(f)

t

t

t

c(f)

fc

f

Tc

Introduction

CDMA uses a modulation technique called spread spectrum to transport a narrowband voice

signal over a wide bandwidth channel. The wide bandwidth for IS-2000 is 1.23 MHz.

The CDMA modulation technique uses three methods for spectrum spreading:

FH (Frequency Hopping)

TH (Time Hopping)

DS (Direct Sequence).

Because Lucent systems operate only with DS spreading, it is the only spreading technique

discussed throughout the remainder of this course, so whenever CDMA is mentioned, DS

CDMA is implied.

Spreading

In a spread spectrum system, the data information signal, b(t), is multiplied by a wideband

signal, c(t), which is the output signal of the Direct Sequence (DS) generator: A pseudorandom

noise (PN) output signal. The signal which will eventually be transmitted, y(t)=b(t)c(t), will

occupy bandwidth far in excess of the minimum bandwidth to transmit the data information.

Note that Tb is the bit interval of the information stream, and Tc is the bit interval of the DS

stream. Tc is also called a chip time. It should also be noted that the ratio of T b to Tc is referred to

as the processing gain.


43/389


44/389

CL8300-SG.en.UL 44




2.3 Direct Sequence Despreading

. . .

c(t)

b(t) c(t)

c(t)

b(t)b(t) c(t)

t

output

= b(t) c(t) c(t)

= b(t)

b(t) 0

1

1

-1

-1

output = 0b(t) c(t) c(t)

= b(t)

c(t) 0

1

-1

b(t) c(t) 0

1

-1

. . . t

Waveforms

0

1 . . .

0

1

. . . t

. . .

t

t

To despread a received signal, b(t)c(t), the signal is multiplied with an exact replica of the

original spreading code, c(t). The output of the despreader will be b(t)c(t)c(t) = b(t).

Note that c(t)c(t)=+1 for all bits; this is true for any bipolar waveform encoded as +1, -1. Also, if

signal propagation delays the output b(t)c(t) by some propagation time, the second occurrence of

c(t) must be delayed by the same amount (synchronization!).


45/389

CL8300-SG.en.UL 45




Why It Works!

t

tc(t)

Receiver receives b(t)c(t), multiplies by c(t), resulting in b(t)c(t)c(t) = b(t).

Multiplying with another code would not yield the same result

1

-1

0

c(t)c(t)

1

-1

0

0 01 0 1

The reason DS CDMA despreading works is seen by understanding that multiplying c(t) with

itself produces +1 for all bits. Hence, c(t)c(t) is an identity operation producing b(t).

Note: One c(t) accompanies signal transmission and sees transmission delay. The other c(t) is

inserted at the receiver with bit boundaries aligned to the first (i.e., synchronization).


46/389


47/389

CL8300-SG.en.UL 47




Integrate & Dump Chip Errors

b(t) 0

c(t) 0

1

1

1

-1

-1

-1

Tb

t

t

t

Tc

1

-1

t

y(t) = 0

b(t) c(t)

b(t) = 0

y(t) c(t)

+1+1+1 -1+1 -16

bit1 = = +0.33

-1 -1+1 -1 -1 -1

6bit2 = = -0.83bit1 bit2

If the received chip-stream consists of chips in error, the bit may still be detected. As long as

more than 50% of the chips per bit are error-free, the integrate & dump process will make a

correct decision as to the bit-value. If a bit is received in error, higher level error-correction

algorithms may detect and correct the bad bit.


48/389

CL8300-SG.en.UL 48




Linear Summation

When transmitting multiple information signals at thesame time, linear summation is used.

Every chip magnitude, voltage (electrical field strength), is

summed up.

1

0-1

1

0-1

10

-1

3

2

1

0

-1

-2

-3

ytot = y1+ y2+ y3

y3

y2

y1

When multiple information signals, or channels, are transmitted simultaneously, their bit streams

are summarized together in a linear fashion. The graphic illustrates the concept by summarizing

the three signals electrical field strengths to yield a composite bit stream with varying

magnitude.


49/389

CL8300-SG.en.UL 49




Linear Summation Exercise 1

Use the codes below to calculate:

y1=b1*c1, y2=b2*c2, and y3=b3*c3 There are six chips per bit

Then, calculate the sum ytot=y1+y2+y3.

10

-1

b1

1

0-1

c1

10

-1b2

10

-1c2

10

-1

b3

10

-1c3


50/389

CL8300-SG.en.UL 50




Linear Summation Exercise 2

Use ytot from previous exercise (#1) and multiply with c1,and integrate & dump to extract the bit values.

Sum > 0 means +1 (0), sum < 0 means -1 (1)


51/389

CL8300-SG.en.UL 51




2.5 Detection With Noise

1/Tb 1/Tc

f

Spectrum ofN(t) c(t)

Spectrum of b(t)

Filter F

. . .

N(t)

b(t) c(t)

c(t)

b(t)b(t) c(t) N(t) + b(t) c(t)

c(t)

d(t)F e(t)

Spreading Gain = G =

Tc

Tb

d(t) = b(t) c(t) c(t) + N(t) c(t)= b(t) + N(t) c(t)

narrowband widebandEb

Nt

When the CDMA signal is transmitted it is exposed to noise, N(t), most notably from the RF

environment. The receiver receives the original CDMA signal, b(t)c(t), plus an additive noise

component, N(t).

When despreading the received signal the noise component will be, or continue to be, spread

over the wide bandwidth spreading signal. If a low-pass filter is tuned to filter out everything

except the narrowband signal, b(t), the result will be a signal with a certain bit energy, E b, for

b(t) and a narrowband noise component, filtered N(t)c(t), with an energy of NT

(or N0

). The

signal to noise ratio is then Eb/NT or Eb/N0.

The result of the despreading is that the noise energy from the despreader is decreased, and it

appears as if b(t) has experienced a gain, the so-called spreading gain, G = T b/Tc.


52/389


53/389


54/389


55/389

CL8300-SG.en.UL 55




What is the difference between Eb/NT and Ec/I0?

Eb/NT is traffic channel bit energy over noise.

Eb/N0 is often used.

Ec/I0 is pilot channel chip (bit) energy over interference.

Eb/NT and Ec/I0

One of the most common questions when discussing CDMA engineering is: What is the

difference between Eb/NT and Ec/I0?

Eb/NT and Ec/I0 both describe the ratio of energy per bit (1s and 0s) over interfering energy.

The difference is in what channels we are referring to, and whether the discussion is about bits or

chips.

Eb/NT is traffic channel bit energy over noise.

When talking about the digital signal that is spread over a wide bandwith signal, the 1s and 0sare typically called bits. The signals signal-to-noise ratio for the spread signal is often

referred to as Eb/NT; hence, traffic channel Eb/NT.

The term Eb/N0 (pronounced ebb-no) is also used. In literature, N0 is often used for thermal

noise or white noise; however, in CDMA, N0 and NT are used interchangeably.

Ec/I0 is pilot channel chip (bit) energy over interference.

The 1s and 0s of the digital signal that are being used to spread the information signal are

typically called chips. The signals signal-to-noise ratio for the spreading signal is often

referred to as Ec/I0. The pilot channel in a CDMA system is a non-spread signal (bandwidth 1.23

MHz); therefore, the term pilot channel Ec/I0 is often used.

I0 normally refers to the interference level. Theoretically, the thermal noise (and other noise

sources) impacts the Ec

/I0

ratio. In a practical CDMA system, the generated interference energy

is much greater than the thermal noise energy; therefore, the thermal noise may be ignored.

Note: It is important to understand that there is a difference between a CDMA RF carriers signal

to noise ratio (S/N or S/I) and the digital CDMA signals E c/I0.


56/389

CL8300-SG.en.UL 56




2.7 Noise Rise

Transmitted signal:

I = Desired signal

n = Other users the noise to user 1

After despreading:

Desired signal bandwidth = bw

Other signals bandwidth = BW

andBW

bw = 128 for 9.6 kbps (e.g. EVRC)

If signal power = 1, thennoise power / user = 1 X

bwBW = G

-1

For n + 1 users, total voice power =nG

S/N = G/N

2 users S/N =1

1/128= 128

3 users S/N =1

2/128= 64

5 users S/N =1

4/128= 32

9 users S/N =1

8/128= 16

17 users S/N = 116/128 = 8

Quality relatedCapacity

Every user and channel in a CDMA system will have their own unique spreading code, c(t).

Thus, if the receiver despreads and extracts the signal for user 1, all the other users (user 2, 3, ,

M) will appear as noise or interference to user 1.

In other words, the more users there are on the CDMA system, the more noise the receiver

experiences. This is called noise rise and is one of the core concepts of CDMA.


57/389

CL8300-SG.en.UL 57




Noise Rise vs. Loading

20

18

16

14

12

10

8

6

4

2

0

0 10 20 30 40 50 60 70 80 90

Percent Loading

100

NoiseRise[dB]

Reverse link loading or sector loading is a measure of the total interference from CDMA sources

allowed in the system in reference to the receiver thermal noise. As the number of users in the

system increases, the noise rise increases. The median noise rise in dB can be calculated as:

10log[ 1 / (1-loading) ]

where loading is a ratio of the number of active users to a theoretical maximum number of users,

the pole capacity.

The noise rise increases dramatically as the loading approached the pole capacity. This noise riseis also driven by the loading of neighboring cells (frequency re-use efficiency) and the

information data rate.

Since the goal is to maintain a certain communication link quality, Eb/NT, the noise rise

(increased NT) impacts the CDMA coverage.


58/389

CL8300-SG.en.UL 58




2.8 End-To-End Overview

y(t)

1.2288 Mbps RF path

with delay

Receive

c(t - )

b(t - )

coded

digital

informationdespreader

Regenerated

PN code

(1.2288 Mbps)

Mod

RF

Modulator

RF carrier

y(t - )

1.2288 Mbps

Transmit

c(t)

b(t)

coded

digitalinformation

spreader

PN code

1.2288 Mbps

Demod

RF

Demodulator

Regenerated

RF carrier

Transmit

Low bit rate speech, b(t), is spread by multiplying it with a high bit rate PN (pseudorandom

noise) code, c(t).

The spread signal, b(t)c(t), is modulated by multiplication with an RF carrier and transmitted.

Receive

The received signal is delayed seconds and is demodulated by multiplication with the RFcarrier.

The demodulated signal b(t-)c(t-), is despread by multiplication with the PN code, c(t-) toobtain b(t-)c(t-)c(t-) = b(t-).

The despread signal is detected by a bit detector (an integrate and dump lasting Tb seconds) to

obtain the original digital speech.


59/389

CL8300-SG.en.UL 59




Summary

When performing DS spreading, the information signal bitis multiplied with DS spreading code chips.

The DS spreading code should have pseudorandom noise

characteristics, orthogonal

When several information signals are transmitted the output is a

linear summation of all the chip.

By despreading the received signal with the same DSspreading code, the information signal can be extracted.

Integrate & dump

Information signals spread with other codes appear as noise,

generating noise rise

Processing gain is the number of chips per bit.

Eb/Nt indicates the quality of the information signal.

The spread spectrum theory was developed in the 1940s. Several spread spectrum techniques

exist. The technique discussed in this course is the direct sequence (DS) technique, where each

information signal is spread using a spreading code. With orthogonal spreading codes with

pseudo-random characteristics, several information signals can share the same spectrum.

Multiple information signals are linearly summed for each chip.

At the receiving end, multiplying the transmitted signal with the exact same code used to spread

an information signal will extract the original information signal. Other signals spread with other

codes will appear as noise. The more noise an information signal experiences (loading), the

higher the noise rise. The ratio (Eb/Nt) between the information signals bit energy (Eb) and the

noise energy (Nt) indicates the quality of the signal.

A term often used with spread spectrum techniques is processing gain (spreading gain).

Processing gain is an apparent gain that is introduced when a signal is despread. During

depreading, only the information signal with the exact same spreading code is extracted; all other

signals will become spread with that same code. After passing the despread signal through a low-

pass filter, the noise energy level is suppressed; hence, it appears that the original information

signal has gained energy.

Processing gain can be expressed as the number of spreading chips per information signal bit.


60/389

CL8300-SG.en.UL 60


Understanding the CDMAAir-Interfaces

CL8300

Knowledge Check

1. Discussion: What is Eb/NT?


61/389

CL8300-SG.en.UL 61



CL8300


2. Discussion: What is the difference between Eb/NT andEc/I0?


62/389

CL8300-SG.en.UL 62



CL8300

Knowledge Check

3. Why is there noise rise in a CDMA system?

A. Users are using different RF carriers and different spreading

codes

B. Users are using the same RF carriers and the same spreading

codes

C. Users are using different RF carriers but the same spreading

codes

D. Users are using the same RF carriers but different spreading

codes


63/389


64/389

CL8300-SG.en.UL 64



CL8300

Lesson Objectives

Explain the concept of frames

Describe forward error correction

Explain bit interleaving.


65/389

CL8300-SG.en.UL 65



CL8300

3.1 Typical Signal Processing

DigitalModulation

SpeechEncoding

RFModulation

QualityIndicator

FECEncoding

Interleaving

Scrambling Spreading

Information

Lesson 3

Lesson 4

Amp

CDMA Transmitter

Before the digital information signal can be transmitted in the RF environment it must undergo a

number of signal processing steps. The general steps a transmitted signal undergoes is shown in

the graphic. The steps are, but not limited to:

Speech encoding. This step is only used if speech information is transmitted. Data transmission

omits this step.

Quality indicator

Forward Error Correction (FEC) encoding

Interleaving

Scrambling

Spreading

Digital modulation

RF modulation

Amplification of RF signal.

Note: The various signal processing steps do not necessarily have to be performed in the order

shown. Additional signal processing steps may also be taking place.

CDMA Receiver

At a CDMA receiver, similar steps take place but in the reverse order, i.e., first the received

signal is demodulated, then de-spread, de-scrambled, de-interleaved, etc.

The various signal processing step shown will be discussed in more detail throughout the course.


66/389


67/389

CL8300-SG.en.UL 67



CL8300

Speech Activity

Natural speech includes active periods and quiet periods

Spurts and pauses

Variable bit rate coders tied to speech activity:

Full rate, 1/2 rate, 1/4 rate, 1/8 rate Lower coder rates means lower required transmit power.

pause

spurt

average talk cycle3.75 seconds

1.5seconds

2.25seconds

%4025.25.1

5.1=

+=factoractivityVoice

Natural speech includes active periods and quiet periods called spurts and pauses. Spurts are

generally syllables and words, while pauses include the times in a conversation when the party is

listening. In a typical conversation, the speech spurts last between one and two seconds, and the

activity factor is about 40% in a minimum talk cycle of 3.75 seconds. The average speech time

and non-speech time can be modeled as shown in the figure.

By taking advantage of the variations in speech that occur during a normal conversation, the

variable rate vocoder can dynamically change its rate. During normal speech, speakers take

pauses and breaths, events in which no speech is transmitted. During these lulls in the

conversation, the vocoder can reduce its bandwidth requirements, before the FEC encoder, from

full rate (9600 bps for EVRC) to 1/2 rate, 1/4 rate, or 1/8 rate (1200 bps for EVRC).

Since the transmitter only transmits the lowest bit rate required, the required transmit power is

minimized, and the channel interference is reduced.


68/389


69/389

CL8300-SG.en.UL 69



CL8300

3.4 Forward Error Correction

Provides channel bit error detection and correctioncapability

Generates redundancy in the bit stream

Simple example:

No encoding vs. multiply bits by 3

Two types of FEC encoders:

Convolutional encoder (IS-95, IS-2000)

Turbo encoder (IS-2000, IS-856)

Viterbi decoder.

x3111 111 000 000 111

/31100111X XX1 0X0 0XX X1111001

11001 1XXX1

RFRF

Forward error correction (FEC) encoding provides channel bit error detection and correction

capability at the receiver. FEC enables noise- and interference-free communication over a wide

range of input signal-to-impairment conditions by adding redundancy to the bit-stream.

Encoding Process Example

Lets say that the encoder receives a number of bits and multiplies them by three. If the input to

the encoder is 11001, the encoder reproduces each bit by a factor of three. The resulting output is

111 111 000 000 111.Multiplying the input data frame provides a measure of protection against loss of data caused by

interference. Assume that a given frame is damaged during transmission, it is possible that the

receiver would not be able to reconstruct the frame without having access to the additional bits.

Using the example of 11001, if we did not encode the frame and it was damaged by interference,

the received frame may be 1XXX1. The additional bits generated by the encoding process

provide the receiver with a backup source that may allow it to reconstruct the original frame.

The FEC encoders used in CDMA are more sophisticated than the one shown in the example.

Encoders, Decoders

Two types of encoders are used in the technologies discussed in this course, convolutional

encoder and turbo encoder. The decoder used is often the Viterbi decoder. The encoders and

decoder will be discussed in more detail.


70/389

CL8300-SG.en.UL 70



CL8300

r0 r1 r2 r3 r4 r5 r6 r7

+

+

Code

symbols(output)

Input

c0

c1

Convolutional Encoder

Output depends on current and previous bits.

Constraint length, K, e.g., K=9

Coding coefficient R, e.g., R=1/2

For every bit going into the encoder, two bits are coming out

Encoder tail bits set to 0 at the end of frame clear the registers.

Example: K=9, R=1/2.

95A 95B 3G 1xEV

The convolutional encoder and symbol repetition take advantage of the bandwidth in CDMA

spread spectrum systems to introduce redundancy into the original data stream. The receiver uses

the redundancy as an opportunity for error correction. Through the use of convolutional

encoding, symbol energy and transmit power can be reduced, and the system will still achieve

the same FER (frame error rate).

Convolutional Encoder Characteristics

A convolutional encoder is primarily characterized by two parameters: The coding coefficient,R, and the constraint length, K.

The coding coefficient, R, determines the amount of redundancy to be generated in the bit

stream. For example, R=1/2 means that for every bit going into the encoder, two bits are

produced by the encoder.

The constraint length, K, determines the memory of the convolutional encoder, or the number

of shift-registers (K-1). The output from the encoder depends not only on the bit currently going

into the encoder but also on the previous bit that has passed through the encoder. A long memory

creates a more robust bit stream but it also creates more delay in the transmission. Also, the

benefit of the convolutional encoder versus the complexity is diminishing as K becomes greater

than nine.

Modulo-2 Addition (XOR)

The table shows the modulo-2 addition operation.Modulo-2 addition can be realized using XOR gates.

011

101

110

000

A XOR BBA


71/389

CL8300-SG.en.UL 71



CL8300

Convolutional Encoder - Example

95A 95B 3G 1xEV

r0 r1 r2 r3 r4 r5 r6 r7

+

+

Code

symbols(output)

Input

c0

c1

11 10 10 1111000001101

10 10 11100000001101

10 11100000000111 0

11110000000011 0 1

000000001 0 1 1

Bits sent (c1 c0)c1c0r7r6r5r4r3r2r1r0InputBits left

The slide illustrates a convolutional encoder (K=9, R=1/2 ) in the process of transmitting the

information bit stream, 1 0 1 1.

The previous frame transmitted has filled the encoders shift registers (r0, r1, r2, ) with zeroes

using the encoder tail bits to clear the encoder. When each bit is fed into the encoder, the output

depends on the input an each of the shift registers values. Since the encoder has a coding

coefficient of R=1/2, two output bits (symbols) are generated for each input bit.

When the input bit stream is 1 0 1 1, the output will be 1 1 1 0 1 0 1 1.


72/389

CL8300-SG.en.UL 72



CL8300

Turbo Encoder

95A 95B 3G 1xEV Two convolutional encoders operating inparallel

Input: turbo interleaver

Output: concatenated, repeated and punctured

More robust than convolutional codes

Can increase throughput Adds additional delay to the traffic data.

TurboInterleaver

Encoder

#1

Encoder#2

Puncture &Repeat

Input

Output

The turbo encoder can be seen as two convolutional encoders operating in parallel. The

convolutional encoders are also called constituent encoders. A turbo interleaver selects the input

to each convolutional encoder. The output of the two convolutional encoders are concatenated

with the appropriate symbol repetition and puncturing to achieve the correct symbol rate.

Turbo codes are more robust than convolutional codes but add additional delay to the traffic

data. Therefore, turbo codes are not suitable for voice traffic, but function well for data traffic.

Andrew Viterbi explains: Turbo codes are mixture of simple short convolutional codes, longinterleavers and better soft decision decoding, which permit data rates to approach within 60% to

80% of the Shannon coding limit (an amazing feat), thus increasing current throughputs by more

than 60%. Putting it in simple words, turbo codes do a lot of processing to encode relatively

large chunks (frames) of information before transmission and to extract it upon reception. The

overall process is resistant to interference approaching 80% of the theoretical capacity limit.


73/389

CL8300-SG.en.UL 73



CL8300

Viterbi Decoder

Developed and analyzed in 1967 by A.J. Viterbi

Efficient in determining the most likely bit sequencebased on symbol organization

Decoding algorithm is proprietary to Qualcomm.

Reference: Viterbi, A.J., Error Bounds for Convolutional Codes and Asyptotically Optimum

Decoding Algorithm, IEEE Trans. Inf. Theory, col IT13, April 1967, pp. 260-269

Decoding an encoded signal is much more complex than encoding the signal. The Viterbi

decorder is often used as the decoder.

Viterbi Decoder

The Viterbi decoder is the final step the frame encounters as part of a CDMA-specific

transmission. The Viterbi decoder receives the frame from the deinterleaver and, based upon the

organization of the symbols in the frame, determines the most likely sequence of bits in the

frame (maximum likelihood decoding). Given the encoder bit redundancy (coding coefficient)and memory (constraint length), the decoder can detect andcorrect corrupt encoder symbols.

The algorithm used to perform Viterbi decoding is proprietary to Qualcomm, and is incorporated

in chip sets purchased or licensed from Qualcomm.


74/389

CL8300-SG.en.UL 74



CL8300

Symbol Repetition & Puncturing

Encoder symbols (output) are repeated and punctured asnecessary before interleaving.

Ensure constant symbol rate for interleaver

Depends on channel and data rate.

The output from the encoder is called encoder symbols. These symbols are repeated and

punctured as necessary before entering the bit interleaver. The purpose is to ensure a constant

symbol rate for the interleaver. Also, when a symbol is repeated N times, its transmit power can

be reduced by a factor of N and still provide the same energy for the receiver.

Repeating the symbols will generate even more redundancy, whereas puncturing of symbols will

reduce the redundancy. How often to repeat and puncture the symbols depends on the channel

used and the data rate transmitted.


75/389

CL8300-SG.en.UL 75



CL8300

3.5 Bit Interleaving

Rearranges bits to eliminate bit error bursts

Writes the bits into a matrix in a specific pattern

Transmits the bits from the matrix in a different pattern

Enables the channel decoder process to work underfading conditions

Receiver deinterleaves the bits back into correct order

Example:

Transmitter

Enter bits column-wise

Transmit bits row-wise

Receiver

Enter bits row-wise

Recover bits column-wise. Interleaver matrix

The bit interleaver works closely with the encoder to provide additional communication

reliability by interleaving the encoded bits so that the transmitted frame is, essentiall

cdma airinterfaces v imp

Documents