3G CDMA2000 Wireless System Engineering

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3G CDMA2000

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3G CDMA2000

Wireless System Engineering

Samuel C. Yang

Artech House, Inc.

Boston • London

www.artechhouse.com

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A catalog record for this book is available from the U.S. Library of Congress.

British Library Cataloguing in Publication Data Yang, Samuel C.

3G CDMA2000 wireless system engineering.—(Artech House mobile communications library)

1. Wireless communication systems. 2. Code division multiple access I. Title

621.3'845

ISBN 1-58053-757-x

Norwood, MA 02062

All rights reserved. Printed and bound in the United States of America. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, includ-ing photocopyinclud-ing, recordinclud-ing, or by any information storage and retrieval system, without permission in writing from the publisher.

All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Artech House cannot attest to the accuracy of this informa-tion. Use of a term in this book should not be regarded as affecting the validity of any trade-mark or service trade-mark.

International Standard Book Number: 1-58053-757-x 10 9 8 7 6 5 4 3 2 1

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References 185 CHAPTER 12 Network Architecture 187 12.1 Introduction 187 12.2 2G Network 187 12.2.1 Network Elements 187 12.2.2 Protocols 189 12.3 3G Network 189 12.3.1 Network Elements 190 12.3.2 Protocols 191 12.4 Simple IP 192 12.5 Mobile IP 193 12.6 Concluding Remarks 196 References 197 CHAPTER 13 1xEV-DO Network 199 13.1 Introduction 199 13.2 1xEV-DO Network 201 13.3 Protocol Architecture 202 13.3.1 Application Layer 204 13.3.2 Stream Layer 205 13.3.3 Session Layer 205 13.3.4 Connection Layer 206 Contents xi

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13.3.5 Security Layer 210

References 211

CHAPTER 14

1xEV-DO Radio Interface: Forward Link 213

14.2 MAC Layer 213

14.2.1 Forward Traffic Channel MAC Protocol 214

14.2.2 Control Channel MAC Protocol 215

14.3 Physical Layer 215

14.3.1 Pilot Channel 215

14.3.2 Forward Traffic Channel/Control Channel 216

14.3.3 MAC Channel 219

14.3.4 Time Division Multiplexing 221

14.3.5 Modulation 225

14.4 Concluding Remarks 226

References 226

CHAPTER 15

1xEV-DO Radio Interface: Reverse Link 227

15.2 MAC Layer 227

15.2.1 Reverse Traffic Channel MAC Protocol 227

15.2.2 Access Channel MAC Protocol 228

15.3 Physical Layer 229

15.3.1 Reverse Traffic Channel 231

15.3.2 Access Channel 236

15.3.3 Modulation 238

15.4 Reverse Power Control 239

15.4.1 Open-Loop Power Control 239

15.4.2 Closed-Loop Power Control 240

References 240

About the Author 241

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Preface

Over the past few years, many fundamental changes have taken place in wireless communications that will influence the future of this dynamic field. One phenome-non driving these changes has been the integration of wireless communication devices in people’s lives. While the 1990s were the years when wireless voice teleph-ony became popular, the 2000s should be the time when wireless data applications are truly un-tethered from homes and offices. As more people adopt wireless com-munication devices and applications effected by these devices, the demand on wire-less networks will continue to grow.

Although code division multiple access (CDMA) has become an integral part of the ensemble of third generation (3G) standards, many wireless network operators have found the implementation of IS-2000 affords a good balance between cost and performance of providing 3G services, especially if an operator evolves its network from IS-95 to IS-2000. As such, IS-2000 has become a popular choice of 3G for operators around the world, notably in Asia and the Americas.

This book has been written to address the technical concepts of IS-2000. The focus is on basic issues, and every effort has been made to present the material in an expository and interesting fashion. One strategy is to utilize examples not to offer proofs (as they cannot) but to help the reader grasp the fundamental issues at hand. In this regard, mathematical details and models have an important role but serve as means to an end. While CDMA is by nature theory-intensive, every attempt is made to strike a balance between theory and practice. In addition, to minimize the dupli-cation of foundational material of spread spectrum communidupli-cations and IS-95, this book does not describe those introductory concepts (e.g., synchronization of PN codes) in detail and assumes that the reader is familiar with basic material such as those found in CDMA RF System Engineering (Samuel Yang, Artech House, 1998). Furthermore, this book assumes that the reader is familiar with the layered frame-works of the Internet Model and OSI Model.

In 3G, the system requires the full participation of not only the physical layer but also medium access control, link access control, and upper layers to provide not only circuit voice call but also packet data call functions. Hence in 3G, one needs to focus on the entire system rather than just on a particular layer. To that end, the book starts with a layer-by-layer treatment of IS-2000. In Chapters 1 to 6, it follows the protocol layer framework and describes IS-2000 from Layers 1 to 3. Chapter 1 introduces basic concepts and requirements of 3G and highlights key differences between IS-2000 and IS-95. Chapters 2 and 3 describe physical layers of forward and reverse links, respectively. The channel structure and functions of different channels are described in these two chapters. Chapter 4 covers medium access

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control and focuses on radio link protocol, signaling radio burst protocol, and sys-tem access. Then, Chapter 5 goes into link access control; this chapter first reviews the functions of the sublayers of link access control, then it illustrates sublayer proc-essing on both forward and reverse links. Chapter 6 goes over Layer 3 or upper layer signaling of IS-2000; the emphasis here is on call processing, state transition, and mode transitions.

After building the foundation of the structure of an IS-2000 system, the book proceeds to the systems aspects of IS-2000 in Chapters 7 to 12. Since IS-2000 con-tains power control and handoff functions that are superior to those in IS-95-A, Chapters 7 and 8 describe in detail power control and handoff functionalities, respectively. Chapter 9 then proceeds to cover system performance and describes those features adopted by IS-2000 to increase performance such as code manage-ment, turbo codes, and transmit diversity.

Since a CDMA system essentially trades off coverage versus capacity, these design aspects are presented in Chapters 10 and 11. In particular, Chapter 10 covers coverage, and Chapter 11 covers capacity. These two chapters contain systematic developments of key concepts, and necessary mathematical developments are included where necessary to clarify the material.

Chapter 12 is on network architecture and serves as a capstone on all the chap-ters presented thus far. It describes the IS-2000 architecture from a network perspec-tive and shows how a 3G network differs and evolves from a 2G network. This chapter introduces how IS-2000 works and interacts with other elements in the net-work. Advanced concepts such mobile IP are also introduced here.

The last three chapters concern a special topic that is of particular inter-est—1xEV-DO (1x Evolution for Data Optimized), which has gained popularity in recent years and is designed to work with an IS-2000 system. The topics related 1xEV-DO are included to make the book a more complete reference. Specifically, Chapter 13 focuses on the top five layers of 1xEV-DO (i.e., application, stream, ses-sion, connection, and security), and Chapters 14 and 15 cover medium access con-trol and physical layers of forward and reverse links, respectively.

Without a loss generality, this book emphasizes Spreading Rate 1 at 1.25 MHz. The discussions on Spreading Rate 1 can be readily extended to direct-spread or multiple-carrier options of wider bandwidths. In addition, throughout the book we cite specific examples of radio configurations instead of exhaustively describe the details of every radio configuration. These selective descriptions serve to illustrate more fully the reason for a particular implementation. Overall, the emphasis of the book is on the conceptual understanding of the salient points, focusing on the “how” and “why” instead of the “what.” It is hoped that the mastery of the material presented will serve as a strong foundation from which readers can further explore the technology.

This book is intended as a reference for radio frequency (RF) and system engi-neers, technical managers, and short-course students who desire to quickly get up to speed on the essential technical issues of IS-2000. The material covered in the book is broad enough to serve students of various backgrounds and interests and to allow teachers much flexibility in designing their course material. As such, this book should be a good complement to advanced undergraduate or first-year graduate level courses in wireless communications as well.

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Finally, the material presented in this book is given for informational purpose and instructional value and is not guaranteed for any particular purpose. The pub-lisher or the author does not offer any warranties or representations and does not accept any liabilities with respect to the material presented in this book. Further-more, as technical information changes quickly, the purchaser of the book or user of the information contained in this book should seek updated information from other sources. The publisher or the author assumes no obligation to update or modify the information, nor does the publisher or the author undertake any obligation to notify the purchaser of the book or user of the information contained in the book of any update. The purchase of the book or the use of the information contained in the book signifies the purchaser’s or user’s agreement to the above.

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Acknowledgments

As always, the completion of a book would not be possible without the support of many people. I would like to thank Barry Pasternack who has given me encourage-ment during this project as well as guidance in other areas, Mabel Kung who has spent many hours giving me support and words of wisdom, Paul Minh who has given me advice during the writing of this book, and Joseph Sherif who is always willing to make himself available for conversations. I appreciate Samir Chatterjee who often meets with me to discuss various technical topics, and Lorne Olfman who has continued to give me guidance out of his busy schedule. I also thank the reviewer whose suggestions have made this a better book.

I am also grateful to the editors at Artech: Mark Walsh who has given me much valuable feedback in the initial formulation of this project, and Barbara Lovenvirth who has done a great job managing the project and keeping me on track. I also thank Jill Stoodley and the staff at Artech for their help in the production of the book.

No acknowledgment will be complete without mentioning my wife, Jenny, who has supported all my endeavors with a gentle spirit and has always encouraged me. I can always count on her for being there, and I am very much thankful for her. Last and not the least, I would like to mention my son, Daniel, who has been a source of my joy; his laughter and cheerful spirit have always given me strength during chal-lenging parts of this project, and this book is also dedicated to him.

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C H A P T E R 1

Introduction to 3G CDMA

1.1 Third Generation Systems

While there are several wireless standards and systems that qualify as third genera-tion (3G) systems, this book specifically deals with the IS-2000 implementagenera-tion of 3G. In the mid-1990s, the International Telecommunication Union (ITU) initiated an effort to develop a framework of standards and systems that will provide wireless and ubiquitous telecommunications services to users anywhere at anytime. Subse-quently, International Mobile Telecommunications-2000 (IMT-2000), a subgroup of the ITU, published a set of performance requirements of 3G. It is useful to review the performance requirements of a 3G wireless system, which are as follows (for both packet-switched and circuit-switched data):

• _{A minimum data rate of 144 Kbps in the vehicular environment;} • _{A minimum data rate of 384 Kbps in the pedestrian environment;}

• _{A minimum data rate of 2 Mbps in the fixed indoor and picocell environment.}

In addition, in all environments the system must support same data rates for both forward and reverse links (symmetric data rates), as well as support different data rates for both forward and reverse links (asymmetric data rates) [1].

Some standards and systems such as Universal Mobile Telephone System (UMTS) are implemented in the new 3G spectrum (e.g., in Europe). While other standards and systems such as IS-2000 can introduce 3G services in spectrums already used by second generation (2G) systems (e.g., in North America). The latter case takes into account those investments already deployed in the field where useful and necessary [2]. The correction in the valuation of high-technology assets in early 2000 underscores the importance of making calculated infrastructure investment while taking into account the market demand for these services. This consideration is one reason why IS-2000 has gained popularity in the initial deployment of 3G [3].

In addition, as will be seen in later chapters of this book, IS-2000 is backward compatible with existing 2G IS-95 systems. This backward compatibility gives IS-2000 two important advantages. First, IS-2000 is able to support the reuse of existing IS-95 infrastructure equipment and hence requires only incremental invest-ment to provide 3G services. Second, because IS-2000 represents a natural technical evolution from its predecessor, there is a lower implementation risk when transi-tioning to 3G.

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1.2 Protocol Architecture

One architectural difference between the IS-2000 standard and the IS-95 standard is that IS-2000 calls out explicitly the functions of four different protocol layers. These layers are the physical layer, medium access control, signaling link access control, and upper layer.

Physical layer (Layer 1) [4]: The physical layer is responsible for transmitting and receiving bits over the physical medium. Since the physical medium in this case is over the air, the layer would have to convert bits into waveforms (i.e., modulation) to enable their transmission through air. In addition to modulation, the physical layer also carries out coding functions to perform error control functions at the bit and frame levels.

Medium access control (MAC) sublayer (Layer 2) [5]: The MAC sublayer con-trols higher layers’ access to the physical medium that is shared among different users. In this regard, MAC carries out analogous functions as a MAC entity that controls a local area network (LAN). Whereas a LAN MAC controls different com-puters’ access to the shared bus, the IS-2000 MAC sublayer manages the access of different (low-speed voice and high-speed data) users to the shared air interface.

Signaling link access control (LAC) sublayer (Layer 2) [6]: The LAC sublayer is responsible for the reliability of signaling (or overhead) messages that are exchanged. Recall that the over-the-air medium is extremely error-prone, and infor-mation messages are at times received (and accepted) with errors. On the other hand, since signaling messages provide important control functions, these messages have to be reliably transmitted and received. The LAC sublayer performs a set of functions that ensure the reliable delivery of signaling messages.

Upper layer (Layer 3) [7]: The upper layer carries out the overall control of the IS-2000 system. It exercises this control by serving as the point that processes all and originates new signaling messages. The information (both data and voice) messages are also passed through Layer 3.

Recall that the IS-95 standard does not explicitly and separately describe the functions of each layer. However in IS-95 those functions that are carried out by the layers do exist. For example, in IS-95 mobile access is logically a function of the MAC sublayer, but its descriptions are lumped together with the other functions within a single standard.

At this point the reader may ask why the layered architecture was not employed in IS-95 but now used in IS-2000. The layered architecture is now used in IS-2000 because it brings the system into conformance with the 3G architecture delineated in IMT-2000. The IMT-2000 framework calls for different networks to cooperate to provide services to end users, and the level and extent of these cooperation are more clearly organized if viewed from the perspective of the layered architecture. Well-defined layer functions provide modularity to the system. As long as a layer still per-forms its functions and provides the expected services, the specific implementation

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of its functions can be modified or replaced without requiring changes to the layers above and below it [8].

Figure 1.1 shows the structure of the protocol architecture used by IS-2000. Without a loss of generality, this figure is shown from the perspective of the mobile station; a similar figure can also be drawn from the perspective of the base station by reversing the direction of some arrows and changing the placement of some entities. Figure 1.1 is a rather important figure and we will refer to it from time to time throughout the book. For now, note the three different layers (Layers 1, 2, and 3), the two sublayers in Layer 2 (MAC and LAC), the entities in the layers [e.g., Signal-ing Radio Burst Protocol (SRBP)], and the communication paths among the layers and entities. Also note that the layer structure shown in Figure 1.1 resembles that of the Open Systems Interconnection (OSI) Reference Model [9].

1.3 Other Elements of Protocol Architecture

In addition to the individual layers themselves, other important elements of the pro-tocol architecture are described as follows:

Physical channels: The physical channels are the communication paths between the physical layer and the common/dedicated channel multiplex sublayers. The physical channels are designated by uppercase letters. In the designation, the first

1.3 Other Elements of Protocol Architecture 3

Reverse link: coding and modulation Forward link: demodulation and decoding Common channel multiplex sublayer Dedicated channel multiplex sublayer SRBP f-csch f-csch r-csch LAC PDU RLP f-dtch f-dsch r-dtch r-dsch Signaling LAC f-dtch voice r-dtch voice Signaling RLP SDU RLP SDU L3PDU L3PDU Upper layers LAC sublayer MAC sublayer Physical layer Layer 3 Layer 2 Layer 1 Data services Voice services Data burst Data burst RL FL R-CCCH R-EACH

R-ACH F-SYNCH F-CPCCH F-CACH F-PCH F-CCCH F-BCCH R-FCH R-SCH R-DCCH F-FCH F-SCH F-DCCH

Figure 1.1 Structure of the protocol architecture used by IS-2000. (Note that this structure is shown from the perspective of the mobile station. After: [5].)

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letter and the dash stand for either forward link (F-) or reverse link (R-), and the last two letters “CH” always stand for “channel.” For example, R-ACH stands for reverse access channel, and F-FCH stands for forward fundamental channel. A list of physical channel names and their designations is shown in Table 1.1; note that legacy IS-95 physical channels are denoted with asterisks.

Logical channels: The logical channels are the communication paths between the common/dedicated channel multiplex sublayers and higher layer entities. One can think of logical channels as carrying the logical units of signaling or user informa-tion. Contrast those with physical channels which can be thought of as the actual physical vehicles that transport the signaling or user information over the air.

The logical channels are designated by lower-case letters. The first letter and the dash stand for either forward link (f-) or reverse link (r-), and the last two letters “ch” always stand for “channel.” For example, r-csch stands for reverse common signaling channel, and f-dtch stands for forward dedicated traffic channel. A list of logical channel names and their designations are shown in Table 1.2.

Data unit: The data units are logical units of signaling and user information that are exchanged between SRBP entity/Radio Link Protocol (RLP) entity and higher layer entities. There are two types of data units: payload data units (PDU) and serv-ice data units (SDU). PDU is used to designate those data units that are accepted by a

Table 1.1 Physical Channel Designations in IS-2000

Forward Link Channel

Designation Channel Name

Reverse Link Channel

F-SCH Forward supplemental channel R-SCH Reverse supplemental channel

F-SCCH Forward supplemental code channel R-SCCH Reverse supplemental code_channel

F-FCH* Forward fundamental channel R-FCH* Reverse fundamental channel F-DCCH Forward dedicated control channel R-DCCH Reverse dedicated control

chan-nel F-PCH* Paging channel

F-QPCH Quick paging channel

R-ACH* Access channel

R-EACH Enhanced access channel

F-CCCH Forward common control channel R-CCCH Reverse common control channel

F-BCCH Broadcast control channel F-CPCCH Common power control channel F-CACH Common assignment channel F-SYNCH* Sync channel

F-PICH* Forward pilot channel R-PICH Reverse pilot channel F-TDPICH Transmit diversity pilot channel

F-APICH Auxiliary pilot channel

F-ATDPICH Auxiliary transmit diversity pilot channel

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provider of service from a requester of service, and SDU those data units that are given to a provider of service by a requester of service1

. The use of PDUs and SDUs is discussed in more detail later in Chapter 4 (medium access control), Chapter 5 (link access control), and Chapter 6 (upper layer signaling).

In the MAC sublayer, there are four different entities: SRBP, RLP, common channel multiplex sublayer, and dedicated channel multiplex sublayer. Common channel multiplex sublayer performs the mapping between the logical com-mon channels (channels that are shared acom-mong multiple users) and the physical common channels. Dedicated channel multiplex sublayer performs the mapping between the logical dedicated channels (channels that are dedicated to specific users) and the physical dedicated channels. Note that while dedicated channels can be used for both signaling and user data, common channels are only used for signaling.

SRBP and RLP are protocol entities in the MAC sublayer. They are described in more detail in Chapter 4. It suffices to say now that SRBP handles common-channel signaling (as opposed to dedicated-channel signaling) and RLP handles user infor-mation that is packetized in nature.

1.4 Spreading Rate 1 and Spreading Rate 3

Without a loss of generality, this book will focus on Spreading Rate 1 (also known as “1x”) of IS-2000. Spreading Rate 1 by definition uses one times the chip rate of IS-95 (i.e., 1.2288 Mcps). See Figure 1.2. In addition, the IS-2000 standard also sup-ports Spreading Rate 3 (also known as “3x”). Spreading Rate 3 is used when higher data rates are desired. Spreading Rate 3 has two implementation options: direct spread (DS) or multicarrier (MC).

On the forward link, Spreading Rate 3 uses the MC option by utilizing three separate RF carriers, each spread using a chip rate of 1.2288 Mcps. In this case, the user data is multiplexed onto three separate RF carriers that are received by the mobile. On the reverse link, Spreading Rate 3 uses the DS option. The DS option allows the mobile to directly spread its data over a wider bandwidth using a chip rate of 3.6864 Mcps. See Figure 1.3. To harmonize with other 3G systems such as

1.4 Spreading Rate 1 and Spreading Rate 3 5

Table 1.2 Logical Channel Designations in IS-2000

Forward Link Channel

Reverse Link Channel

f-csch Forward common signaling channel r-csch Reverse common signaling channel

f-dsch Forward dedicated signaling channel r-dsch Reverse dedicated signaling_channel

f-dtch Forward dedicated traffic channel r-dtch Reverse dedicated traffic channel

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UMTS, a Spreading Rate 3 signal can have 625 kHz of guard band on each side resulting in a total RF bandwidth of 5 MHz.

These options for the forward and reverse links are included in the standard in order to reduce the complexity of the mobile’s receiver. As readers may have already noticed, the above-stated configurations mean that the mobile’s receiver only has to receive and demodulate 1x carriers and does not have to receive and demodulate any 3x carrier.

Incidentally, a mobile can also receive at Spreading Rate 3 and transmit at Spreading Rate 1. See Figure 1.4. This particular arrangement takes advantage of the fact that data rates required for downstreaming are typically higher than those required for upstreaming.

Wider bandwidth options such as 6x, 9x, and 12x are under consideration for even higher data rate applications. As far as 3G systems are concerned, Spreading Rate 3 satisfies all the performance requirements as set forth by IMT-2000.

Base station Mobile station 1.25 MHz Forward link Reverse link 1.25 MHz

Figure 1.2 Spreading Rate 1. A chip rate of 1.2288 Mcps occupies an RF bandwidth of 1.25 MHz. Base station Mobile station 3.75 MHz Forward link Reverse link 3.75 MHz

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As a final note: The original intention of the IS-2000 family of standards is to evolve progressively to higher data rates using wider bandwidths (i.e., 3x…12x). However, the current trend seems to be one of deploying high data rate solutions that use 1.25 MHz of bandwidth (e.g., 1xEV-DO). There are several advantages of using solutions like 1xEV-DO, one of which is that wireless operators can carve out selected 1.25 MHz carriers dedicated to and optimized for high rate data. 1xEV-DO is covered later in Chapters 13–15.

1.5 Differences Between IS-2000 and IS-95

IS-2000 represents a natural technical extension from its IS-95 predecessor, and this extension can be seen in the fact that IS-2000 users and IS-95 users can coexist in the same carrier. Although IS-2000 is backward compatible with IS-95, there are many differences between IS-2000 and IS-95. We will point out now, by way of introduc-tion, those differences that represent a substantial departure from IS-95. Since the requirement of 3G and IS-2000 is transmitting and receiving at a higher data rate, two types of improvements are needed to enable data rates at or above 144 Kbps: improvements in signaling and improvements in transmission.

1.5.1 Signaling

In order to implement high-rate packet-switched data, IS-2000 needs to dynami-cally acquire and release air link resources, and efficient signaling is required to per-form quick acquisitions and releases of these resources. These new signaling mechanisms include:

• _{On the forward link, there are new overhead/signaling physical channels.}

They are quick paging channel (F-QPCH), forward common control channel (F-CCCH), broadcast control channel (F-BCCH), common power control channel (F-CPCCH), and common assignment channel (F-CACH).

1.5 Differences Between IS-2000 and IS-95 7

Base station Mobile station 3.75 MHz Forward link Reverse link 1.25 MHz

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• _{On the reverse link, there are new overhead/signaling physical channels. They}

are reverse dedicated control channel (R-DCCH), enhanced access channel (R-EACH), and reverse common control channel (R-CCCH).

• _{On the reverse link, there are shorter signaling messages. IS-2000 can transmit}

shorter 5-ms frames on the enhanced access channel (R-EACH). This is done to reduce the probability of access collision.

• _{On the forward link, IS-2000 can also transmit shorter signaling messages. It}

can use shorter 5-ms frames (i.e., 1/8 rate) on the forward fundamental chan-nel for this purpose.

In addition, an IS-2000 mobile can now be in one of several modes (e.g., dor-mant mode) to accommodate bursty packet data transmissions and to conserve air link resources. These modes are described in more detail in Chapter 6 on upper layer signaling.

The new overhead/signaling physical channels on the forward link are discussed in Chapter 2, and the new overhead/signaling physical channels on the reverse link are discussed in Chapter 3.

1.5.2 Transmission

A higher air link capacity is obviously needed to implement high-rate data, and vari-ous changes are made to improve air link capacity to beyond that of IS-95. These changes are also made to effect a more efficient use of air link resources. Some major changes are listed below:

• _{Forward supplemental channel (F-SCH) and reverse supplemental channel}

(R-SCH) are added to transport high-rate user data.

• _{Reverse link now has a reverse pilot channel (R-PICH) to support coherent}

modulation on the reverse link.

• _{Forward link now has fast closed-loop power control (compared with the}

slower power control in IS-95). Power control groups are transmitted on the reverse pilot channel to enable fast closed-loop power control of the forward link.

• _{In addition to power controlling the traffic channels, IS-2000 can also power}

control the signaling channel (i.e., forward dedicated control channel [F-DCCH]).

Supplemental channels are discussed in more detail in Chapter 2 and Chapter 3. IS-2000 power controls are discussed in more detail in Chapter 7. Other transmis-sion improvements include the implementation of a more efficient quadrature phase-shift keying (QPSK) in the modulation stage and the use of more efficient turbo codes for high date rate transmissions.

1.5.3 Concluding Remarks

The differences between IS-2000 and IS-95 are not limited to those introduced above. Throughout the book, we will regularly point out, where appropriate, more

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differences to which system engineers and planners should pay attention. Noting these differences is important because being aware of them not only facilitates the understanding of 3G IS-2000, but also leverages the experience already gained in operating 2G IS-95 systems.

References

[1] ITU-R Recommendation M.1225, Guidelines for Evaluation of Radio Transmission Tech-nologies for IMT-2000, International Telecommunication Union, 1997.

[2] Prasad, R., W. Mohr, and W. Konhauser (eds.), Third Generation Mobile Communication Systems, Norwood, MA: Artech House, 2000, p. 2.

[3] The Economist, “Mobile Telecoms: Time for plan B,” Economist, September 28–October 4, 2002, pp. 57–58.

[4] TIA/EIA/IS-2000.2-A, Physical Layer Standard for cdma2000 Spread Spectrum Systems, Telecommunications Industry Association, March 2000.

[5] TIA/EIA/IS-2000.3-A, Medium Access Control (MAC) Standard for cdma2000 Spread Spectrum Systems, Telecommunications Industry Association, March 2000.

[6] TIA/EIA/IS-2000.4-A, Signaling Link Access Control (LAC) Standard for cdma2000 Spread Spectrum Systems, Telecommunications Industry Association, March 2000. [7] TIA/EIA/IS-2000.5-A, Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread

Spectrum Systems, Telecommunications Industry Association, March 2000.

[8] Forouzan, B. A., Data Communications and Networking, New York: McGraw-Hill, 2004. [9] ITU-T Recommendation X.210, Information Technology–Open Systems

Interconnec-tion–Basic Reference Model: Conventions for the Definition of OSI Services, International Telecommunication Union, 1993.

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C H A P T E R 2

Physical Layer: Forward Link

2.1 Introduction

The physical layer is responsible for transmitting and receiving bits (organized in frames) over the physical medium. The physical layer carries out coding functions to enable error correction and detection at the bit and frame levels. Besides coding, the layer would have to convert bits into waveforms (i.e., modulation) and vice versa to enable their transmission over the air.

In addition to coding and modulation, the physical layer also carries out the channelization function by which different users of the system can be distinguished from one another. In a shared direct sequence spread spectrum system (such as IS-2000 and IS-95), channelization is done via the use of orthogonal and near-orthogonal codes.

This chapter deals with the physical channels that exist on the forward link in the IS-2000 system, and their descriptions are organized into two broad categories: signaling channels and user channels.

Signaling channels, described in Section 2.3, are those channels that carry sig-naling and control information. Sigsig-naling channels can be further classified into two types: dedicated and common channels. The F-DCCH is a dedicated signaling chan-nel because this chanchan-nel, once assigned, is only used by one user. The remaining sig-naling channels, such as the F-CCCH and F-QPCH are examples of common signaling channels because they are shared among multiple users.

User channels, described in Section 2.4, are those channels that carry user infor-mation. The user information may be voice, low-rate data (e.g., short message serv-ice or SMS), or high-rate data (e.g., video streaming). There are three physical channels primarily used to carry user information: (1) F-FCH which is equivalent to forward traffic channel in IS-95, (2) F-SCCH which is equivalent to forward supple-mental code channel in IS-95 (more specifically, IS-95-B [1]), and (3) F-SCH which is a new channel in IS-2000. Figure 2.1 shows the categorization of these forward link channels, both signaling and user.

Table 2.1 is a list of physical channels used by the physical layer. Both forward link and reverse link channels and their descriptions are shown for completeness. Also, for each forward link physical channel, its counterparts on the reverse link are shown in the same row for correspondence. Asterisked channel designations show those channels that also exist in IS-95 systems. Note that (forward and reverse) fun-damental channels are equivalent to the IS-95 traffic channels. In addition, bold-faced channel names show those channels that are collectively known as the

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Signaling channels User channels Common channels

Forward dedicated control channel (F-DCCH) Paging channel (F-PCH*)

Quick paging channel (F-QPCH)

Forward common control channel (F-CCCH) Broadcast control channel (F-BCCH) Common assignment channel (F-CACH) Common power control channel (F-CPCCH) Sync channel (F-SYNCH*)

Forward pilot channel (F-PICH*)

Transmit diversity pilot channel (F-TDPICH) Auxiliary pilot channel (F-APICH)

Auxiliary transmit diversity pilot channel (F-ATDPICH)

Forward fundamental channel (F-FCH*) Forward supplemental channel (F-SCH) Forward supplemental code channel (F-SCCH*) Dedicated

channels

Figure 2.1 Categories of forward link physical channels. Legacy IS-95 physical channels are denoted with asterisks.

Table 2.1 Forward Link Physical Channels and Their Reverse Link Counterparts

Channel Channel Name Description Channel Channel Name Description

F-SCH

Forward supplemental channel

For transmitting user data while a call is active; uses convolu-tional or turbo coding

R-SCH

Reverse supplemental channel

For transmitting user data while a call is active; uses convolu-tional or turbo coding F-SCCH* Forward supplemental code channel

For transmitting user data while a call is active; uses convolu-tional coding R-SCCH* Reverse supplemental code channel For transmitting user data while a call is active; uses convolu-tional coding F-FCH* Forward fundamental channel

For transmitting user and signaling data while a call is active; uses convolutional coding R-FCH* Reverse fundamental channel For transmitting user and signal-ing data while a call is active; uses convolu-tional coding F-DCCH Forward dedicated control channel

For transmitting sig-naling and user data while a call is active

R-DCCH Reverse dedicated control channel For transmitting signaling and user data while a call is active

F-PCH* Paging channel

For transmitting MS-specific and system overhead data

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2.1 Introduction 13

Table 2.1 (continued)

F-QPCH Quick paging_channel

For telling MS (oper-ating in slotted mode while in the idle state) whether or not it should receive F-CCCH or F-PCH starting in the next F-CCCH or F-PCH slot

R-ACH* Access channel

For initial communications with BS, i.e., initiating access and responding to pages

R-EACH Enhanced access channel For initial communications with BS, i.e., initiating access or responding to MS-specific messages F-CCCH Forward common control channel

For transmitting sig-naling data when F-FCH, F-SCCH, F-SCH, or F-DCCH is not active R-CCCH Reverse common control channel For transmitting signaling and user data when R-FCH, R-SCCH, R-SCH, or R-DCCH is not active F-BCCH Broadcast control channel For transmitting signaling data when F-FCH, F-SCCH, F-SCH, or F-DCCH is not active

F-CPCCH Common power_{control channel}

For transmitting common power con-trol subchannels (one bit per subchannel) to power-control multi-ple R-CCCHs and R-EACHs

F-CACH Common assign-_{ment channel}

For transmitting sig-naling data to allocate R-CCCH resources

F-SYNCH* Sync channel

For providing MS time and frame synchronization

F-PICH* Forward pilot_channel

For assisting MS to acquire initial time synchronization

R-PICH Reverse pilot_channel

For assisting BS to detect MS transmission

F-TDPICH Transmit diversity_{pilot channel}

For implementing transmit diversity on the forward link

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“IS-2000 traffic channels” (not to be confused with IS-95 traffic channels) since these channels can all carry user traffic data in IS-2000 systems.

2.2 Radio Configurations

In IS-2000, each traffic channel (i.e., forward fundamental channel, forward supple-mental code channel, forward supplesupple-mental channel, and forward dedicated control channel) can assume different configurations to implement different data rates. For any one configuration, the associated coding rate, modulation characteristics, and spreading rate would have to be matched to achieve a specified final transmitted data rate. Table 2.2 shows these different radio configurations [2]. For these radio configurations, the data rates shown in the table are maximum data rates. For a given radio configuration, data rates lower than the maximum are possible.

Note that Radio Configuration 1 and Radio Configuration 2 are backward compatible with IS-95 in that they are equivalent to Rate Set 1 and Rate Set 2 of IS-95. For each radio configuration, the table shows the maximum achievable data rate (instead of all possible data rates). For example, for Radio Configuration 1 the system is capable of transmitting at 1.2 Kbps, 2.4 Kbps, 4.8 Kbps, and 9.6 Kbps; only the maximum data rate of 9.6 Kbps is shown. In addition, for each radio

Table 2.1 (continued)

F-APICH Auxiliary pilot channel

For supporting the use of spot beam

F-ATDPICH Auxiliary transmit diversity pilot channel For implementing transmit diversity in the spot beam

Table 2.2 Radio Configurations on the Forward Link

Radio

Configuration Coding Rate R Modulation Spreading Rate

Maximum Data Rate 1 1/2 BPSK 1 9.6 Kbps 2 1/2 BPSK 1 14.4 Kbps 3 1/4 QPSK 1 153.6 Kbps 4 1/2 QPSK 1 307.2 Kbps 5 1/4 QPSK 1 230.4 Kbps 6 1/6 QPSK 3 307.2 Kbps 7 1/3 QPSK 3 614.4 Kbps 8 1/4 (20 ms) QPSK 3 460.8 Kbps 1/3 (5 ms) 9 1/2 (20 ms) QPSK 3 1.0368 Mbps 1/3 (5 ms)

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configuration the coding rate R is normally the same regardless of the size of the frame (20 ms or 5 ms). But for Radio Configurations 8 and 9 (i.e., Spreading Rate 3), the coding rate is dependent on the size of the frame transmitted.

2.3 Signaling Channels

One of the key requirements of 3G is high-data rate. In order to meet this require-ment one needs to make the physical layer more efficient. Recall that in 2G IS-95, while a call is active signaling information is typically carried by the traffic channel (i.e., fundamental channel). In doing so, signaling bits rob traffic channel’s ability to carry user data bits.

3G IS-2000 deals with this issue by implementing separate signaling channels that carry signaling information. Although signaling data can still be carried by the fundamental channel, IS-2000 has the option of sending signaling data on separate signaling channels. This frees up fundamental channel’s and supplemental channel’s capability to transport more user data.

2.3.1 Forward Dedicated Control Channel (F-DCCH) The F-DCCH is a unique signaling channel in two respects:

• _{Unlike other signaling channels, the F-DCCH is a dedicated signaling channel.}

Once assigned, the F-DCCH is only allocated to one designated user. All other signaling channels (to be described later) are common to and shared with other users.

• _{Just as the forward fundamental channels can carry signaling data (through}

dim-and-burst and blank-and-burst), the F-DCCH can carry user data. The kind of user data that the F-DCCH carries is typically low-rate (such as SMS). Such data service requests are sporadic in nature and short in duration. For such transmission requests, instead of expending resources to set up a full-fledge fundamental channel or supplemental channel, the system can choose to temporarily suspend transmitting signal data and start sending user data over the F-DCCH.

In addition, both 20-ms and 5-ms frame formats are supported by the F-DCCH. For example, one 20-ms frame format for the F-DCCH is 192 bits in length consist-ing of 172 information bits, 12 cyclic redundancy check (CRC) bits, and 8 encoder tail bits. This gives an F-DCCH data rate of (192 bits/20 ms) 9.6 Kbps. See Figure 2.2. Note that in this case, this F-DCCH frame has the same capacity as an IS-95 Rate Set 1 paging channel frame. On the other hand, a 5-ms frame structure for the F-DCCH is 48 bits in length consisting of 24 information bits, 16 CRC bits, and 8 encoder tail bits. This gives an F-DCCH data rate of (48 bits/5 ms) also 9.6 Kbps. Also see Figure 2.2. Note that a 5-ms frame obviously does not have as much data-carrying capacity as a 20-ms frame.

The reason why 5-ms frames are necessary is that at times a signaling message is short and cannot fill up the entire (traditional) 20-ms frame, and it would be

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inefficient to transmit a short minimessage using a 20-ms frame. Using a 5-ms frame to transport a short signaling message is a more efficient use of the air link resources.

An important type of signaling data that the F-DCCH carries is power control bits used to power-control the reverse link. Recall that in IS-95 the power control bits are multiplexed onto the forward traffic channel at 800 bps in power control groups. In a similar fashion, the power control bits can be multiplexed onto the F-DCCH as well. The structure and organization of the power control groups on the F-DCCH is referred to as forward power control subchannel. In effect, a forward power control subchannel exists on the F-DCCH to transport the power control bits.

The mobile uses these power control bits to perform closed-loop power control of the reverse dedicated control channel, reverse fundamental channel, and reverse supplemental channel.

2.3.2 Quick Paging Channel (F-QPCH)

The F-QPCH is a new physical channel used in IS-2000 to improve the efficiency of sending page messages. The IS-95 F-PCH, while effective, does have some drawbacks:

• _{In the nonslotted mode the mobile has to monitor continuously the entire}

pag-ing channel slot, which in IS-95 lasts 80 ms. As a result, the mobile expends a lot of battery power to perform this continuous monitoring.

• _{In the slotted mode the mobile monitors only those time slots that are assigned}

to it. While this does save some battery power, it is still inefficient. From the base station’s perspective, it is inefficient because when the base station has a

20-ms frame (9.6 Kbps) 5-ms frame (9.6 Kbps) 172 information bits 24 information bits 8 encoder tail bits 12 CRC bits 8 encoder tail bits 16 CRC bits

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mobile-specific page to send, it cannot immediately send it. The base station has to wait for the correct slot to come along to send the page. As a result, the mobile often does not receive its designated pages immediately. From the mobile’s perspective, while the mobile saves some battery power by only monitoring its assigned slot, the assigned slot still lasts 80 ms. At the begin-ning of its assigned slot, the mobile still has to wake up to monitor the entire 80-ms slot, and most of the time there is no page directed at the mobile.

In IS-2000, the F-QPCH is added to alleviate the drawbacks cited above. If there is a page directed to a mobile, the base station first uses the F-QPCH to send shorter paging indicator bits to the mobile. The mobile monitors its designated paging indi-cators. If the paging indicators show that there is no mobile-specific page, then the mobile does nothing. If the paging indicators show that there is a mobile-specific page coming in, then the mobile wakes up and monitors its assigned paging channel slot. Note that in this regard, the F-QPCH works with a paging channel operating in slotted mode. In addition, the F-QPCH can also work with a forward common con-trol channel operating in slotted mode.

2.3.2.1 Paging Indicators

Figure 2.3 shows in more detail how the F-QPCH works in conjunction with the F-PCH. As one can see in the figure, a paging channel slot and a quick paging chan-nel slot both last 80 ms, and quick paging chanchan-nel slots are offset from (ahead of) paging channel slots by 20 ms. Each quick paging channel is divided into four 20-ms portions. In this case, let’s assume that a mobile’s assigned paging channel slot is slot Y. Instead of always monitoring paging channel slot Y, the mobile would monitor

Paging channel slot (Y)

Quick paging channel slot (y)

Z 20-ms portion y2 y4 z2 z4 y1 y3 z1 z3 Y X p p p: Paging indicator 80-ms 80-ms

Figure 2.3 Channel format: F-QPCH. As an example, the figure shows two paging indicators located in the second and fourth 20-ms portions of the quick paging channel slot (y).

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its paging indicators in the quick paging channel slot (y) that comes before the assigned paging channel slot (Y).

In a quick paging channel slot, the mobile always monitors two paging indica-tors. The two paging indicators either fall in the first 20-ms portion and in the third 20-ms portion (e.g., y1 and y3), or fall in the second 20-ms portion and in the fourth 20-ms portion (e.g., y2 and y4). So in our example, if two mobiles are both assigned paging channel slot Y, the first mobile may monitor a paging indicator in y1 and a paging indicator in y3; the second mobile may monitor a paging indicator in y2 and a paging indicator in y4. In actuality, the exact position of a paging indicator in the 20-ms portion is determined by a hash algorithm, the same type of algorithm that determines the assigned paging channel slot for a mobile operating in the slotted mode.

2.3.2.2 Other Indicators

In addition to carrying paging indicators, the F-QPCH also carries two other types of indicators: broadcast indicators and configuration change indicators. The mobile monitors its broadcast indicators to check if it needs to monitor its assigned slot (for broadcast messages) on the forward common control channel or paging channel. Furthermore, all mobiles monitor configuration change indicators; these indicators are used to inform mobiles of a change in configuration parameters (e.g., neighbor list) [2].

The relative positions of broadcast and configuration change indicators are shown in Figure 2.4. As shown in the figure, the number of broadcast and configura-tion change indicators depends on the data rate of the F-QPCH.

2.3.2.3 Characteristics of Quick Paging Channel

One distinguishing feature of the F-QPCH is that this physical channel has no error protection. This means that the bits sent on the F-QPCH do not have CRC bits

Quick paging channel slot (y)

20-ms portion y2 y4 z2 z4 y1 y3 z1 z3 bc bc bc bc b: Broadcast indicator

c: Configuration change indicator

b=4 and c=4 if F-QPCH data rate = 4.8 bpsK b=2 and c=2 if F-QPCH data rate = 2.4 bpsK 80-ms

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added, are not convolutionally coded, and are not block-interleaved. The reason for this design choice is that paging indicator bits need to be quickly demodulated at the receiver so a decision can be made quickly regarding whether or not to monitor the paging channel slot that follows. Not needing to check the CRC bits, convolution-ally decode all the bits, and deinterleave save a lot of processing time. Note that this is the same reason for not error-protecting the power control bits in IS-95 (and in IS-2000). Power control bits need to be demodulated quickly so that power control decisions can be made quickly to adapt to changing channel conditions.

An IS-2000 carrier can have up to three quick paging channels. However, con-figuration change indicators and broadcast indicators are only used on the first quick paging channel [2].

2.3.3 Forward Common Control Channel (F-CCCH)

To further improve the signaling efficiency of the link, IS-2000 added two addi-tional physical signaling channels: F-CCCH and F-BCCH. Recall that the functions of the paging channel in IS-95 are to deliver (1) specific messages that are intended for specific mobiles (e.g., channel assignment message), and (2) broadcast messages that are intended for all mobiles (e.g., system parameters message and neighbor list message).

Using a single paging channel for these two functions is not very efficient because of the queuing characteristics of these two types of messages. The broadcast messages are sent at more regular intervals, while the specific messages are sent more irregularly on-demand. As a result, mixing two statistically different types of messages on the same channel results in less-than-optimal scheduling of the paging channel. Furthermore, recall that IS-95 allows up to seven paging channels per car-rier; since each mobile only monitors one paging channel, if there are more than one paging channels in the carrier then broadcast system messages would have to be duplicated on all paging channels.

To alleviate the responsibilities of the paging channel, IS-2000 added two addi-tional channels: F-CCCH and F-BCCH. The F-CCCH is used to transmit specific messages intended for specific mobiles, while the F-BCCH is used to transmit broadcast system messages intended for all mobiles. Note that although the F-CCCH is “common” in the sense that it is shared by many mobiles, its purpose is to carry mobile-specific messages. The broadcast control channel is described in Section 2.3.4.

Since the function of the F-CCCH is to carry messages (e.g., channel assignment message) that are previously carried by the paging channel, it is no surprise that the structure of the F-CCCH is similar to that of the paging channel. For example, the F-CCCH consists of F-CCCH slots each lasting 80 ms. What is new in IS-2000 is that it supports three different frame duration: 20 ms, 10 ms, and 5 ms. For exam-ple, a 20-ms frame for the F-CCCH may be 192 bits in length consisting of 172 information bits, 12 CRC bits, and 8 encoder tail bits. This gives an F-CCCH data rate of (192 bits/20 ms) 9.6 Kbps. See Figure 2.5. Note that in this case, this F-CCCH frame has the same capacity as an IS-95 Rate Set 1 paging channel frame. Other data rates of 19.2 Kbps and 38.4 Kbps are also supported. Figure 2.5 gives some examples of F-CCCH frame structures.

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The F-CCCH can also be used in conjunction with the F-QPCH. Recall that the quick paging channel is a new physical channel used in IS-2000 to improve the effi-ciency of sending page messages. For example, a mobile does not have to monitor the F-CCCH all the time for page messages intended for it. Rather, by monitoring its paging indicators on the quick paging channel, the mobile knows whether or not it should start receiving the F-CCCH in the next F-CCCH slot [2].

2.3.4 Broadcast Control Channel (F-BCCH)

As mentioned previously, the purpose of the F-BCCH is transmitting broadcast sys-tem messages (e.g., syssys-tem parameters message and access parameters message) to those mobiles in a base station’s coverage area. Although the F-BCCH performs a function that is previously carried out by the IS-95 paging channel, the structure of the F-BCCH is somewhat different. See Figure 2.6.

20-ms frame (9.6 Kbps) 5-ms frame (38.4 bps)K 172 information bits 172 information bits 8 encoder tail bits 12 CRC bits 8 encoder tail bits 12 CRC bits 20-ms frame (38.4 bps)K 744 information bits 8 encoder tail bits 16 CRC bits 10-ms frame (38.4 bps)K 8 encoder tail bits 16 CRC bits 360 Information bits

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As shown in Figure 2.6 instead of using a single slot duration of 80 ms (like the paging channel and the forward common control channel), the F-BCCH can have slots that last 40 ms, 80 ms, or 160 ms. In addition, unlike the paging channel and the forward common control channel the F-BCCH has only one frame format that lasts 40 ms. Therefore, it is obvious that a 160-ms slot always contains four frames, an 80-ms slot always contains two frames, and a 40-ms slot always contains one frame.

An F-BCCH frame always lasts 40 ms and always contains 744 information bits, 16 CRC bits, and 8 encoder tail bits, resulting in a total of 768-bits-per-frame. This gives a (peak) F-BCCH data rate of (768 bits/40 ms) 19.2 Kbps. With sequence repetition (similar to symbol repetition in IS-95), this peak data rate of 19.2 Kbps can be throttled down. For example, 2x sequence repetition drops the data rate by half to 9.6 Kbps, and 4x sequence repetition drops the data rate by a quarter to 4.8 Kbps [2].

2.3.5 Common Assignment Channel (F-CACH)

The function of the F-CACH is for the base station to quickly allocate reverse com-mon control channel (R-CCCH) resources to the different mobiles. As will be dis-cussed in Section 3.3.2, the R-CCCH is used by mobiles to transmit signaling information when the R-DCCH or the R-FCH is not active. The scheduling infor-mation for the use of the reverse common control channel is transmitted by the F-CACH.

Because the F-CACH is used to control another signaling channel R-CCCH, the F-CACH is really a signaling channel for a signaling channel. In other words, the F-CACH has to quickly transmit signaling information (to the mobile) so that an

2.3 Signaling Channels 21 40-ms frame (19.2 Kbps peak) 744 information bits 8 encoder tail bits 16 CRC bits 40-ms F-BCCH slot 80-ms F-BCCH slot 160-ms F-BCCH slot

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R-CCCH resource can be quickly allocated to transmit some other signaling infor-mation (back to the base station). As such, the F-CACH uses 5-ms frames exclu-sively. Figure 2.7 shows the frame format of the F-CACH. As shown in Figure 2.7, the F-CACH frame consists of 48 bits which yield 9.6 Kbps (= 48 bits/5 ms) [2].

2.3.6 Common Power Control Channel (F-CPCCH)

In addition to power controlling the reverse fundamental channel (R-FCH) and the reverse supplemental channel (R-SCH), IS-2000 has the ability to power control sig-naling channels to further improve air link capacity. The function of the F-CPCCH is to carry signaling information to power control the following reverse link signal-ing channels:

• _{Reverse common control channel (R-CCCH);} • _{Enhanced access channel (R-EACH).}

The F-CPCCH consists of a stream of (power control) bits that is not error-protected. This is because power control bits need to be demodulated rapidly so that power control decisions can be made quickly to adapt to changing channel condi-tions. Not needing to check the CRC bits, convolutionally decode all the bits, and de-interleave save a lot of processing time. Note that this is the same reason for not error-protecting the power control bits in IS-95 (and in IS-2000).

Figure 2.8 shows an example format of the F-CPCCH. Here each F-CPCCH frame (which lasts 20 ms) consists of 16 power control groups. Each power control group lasts 1.25 ms, hence the transmission rate of the power control groups is 800-times-per-second (= 1 / 1.25 ms). Each power control group contains 12 power control bit positions. This gives a total of 192 power control bit positions per 20-ms frame.

In IS-2000, the forward link uses QPSK modulation which consists of two paths: the in-phase (I) path and the quadrature (Q) path. The F-CPCCH is struc-tured in such a way that each path contains separate and distinct power control bits. As Figure 2.8 shows, in the I path the first bit position of each power control group is used to transmit power control subchannel 0; the second bit position is used to

5-ms frame (9.6 bps)K 32 information bits 8 encoder tail bits 8 CRC bits

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transmit power control subchannel 1, and so on. In the Q path the first bit position of each power control group is used to transmit power control subchannel 12, and the last bit position in the same power control group is used to transmit power con-trol subchannel 23. Therefore, in this example each power concon-trol group is capable of carrying 24 power control subchannels (0–23). Since the same 24 power control subchannels are replicated in subsequent common power control groups1_{, the}

trans-mission rate of the power control bits for each subchannel is 800-times-per-second.

2.3 Signaling Channels 23 1.25-ms I (path) 0 11 Power control subchannels 12 23 20-ms frame (9.6 Kbps) PCG 0 PCB 11 PCB 11 PCB 2 PCB 2 PCB 1 PCB 1 PCB 0 PCB 0 PCG 1 PCG 15 Q (path) PCG 0 PCG 1 PCG 15

Figure 2.8 F-CPCCH: 16 power control groups per 20-ms frame.

1. IS-2000 refers to a power control group in the I path and its corresponding power control group in the Q path as a common power control group.

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In actuality, the power control bit positions (and their corresponding power control subchannels) are not arranged sequentially in a power control group. Rather, they are arranged pseudorandomly in a power control group. The long code mask and the long code generator are used to pseudorandomize the bit positions in a power control group. Since the mobile also possesses the same long code mask and the same long code generator, the exact position of a given power control subchan-nel is known perfectly to the mobile.

In addition to supporting 16 power control groups per 20-ms frame, IS-2000 can also support 8 power control groups per 20-ms frame and 4 power control groups per 20-ms frame. It is an easy exercise then to calculate the number of power control subchannels supported by these formats:

• _{For 8 power control groups per 20-ms frame, the F-CPCCH can support a}

total of 48 power control subchannels.

• _{For 4 power control groups per 20-ms frame, the F-CPCCH can support a}

total of 96 power control subchannels.

For a F-CCCH, a CDMA carrier can have a maximum of 32 R-CCCHs and a maximum of 32 R-EACHs. Plus if an F-CACH is also active, the same carrier can have another (maximum) set of 32 R-CCCHs. For each carrier, this gives a maxi-mum total of 96 reverse common control channels and enhanced access channels. These 96 channels can all be power controlled using the 96 power control subchan-nels provided by the 4 power control groups per 20-ms frame on the F-CPCCH [2]. Note that each common power control subchannel is used to control the power of a single mobile.

2.3.7 Pilot Channels

In IS-2000, there are actually four types of pilot channels on the forward link. They are:

• _{Forward pilot channel (F-PICH);}

• _{Transmit diversity pilot channel (F-TDPICH);} • _{Auxiliary pilot channel (F-APICH);}

• _{Auxiliary transmit diversity pilot channel (F-ATDPICH).}

2.3.7.1 Forward Pilot Channel (F-PICH)

The F-PICH is equivalent to the IS-95 pilot channel. This channel is identified by Walsh code w0

128

. It contains no baseband information in that the baseband sequence is a stream of 1s that are spread by Walsh code w0

128

, which is also a sequence of 1s2_{. The resulting sequence (still all 1s) is then multiplied by a pair of}

quadrature PN codes. Thus the forward pilot channel is effectively the PN code itself. As in IS-95, the forward pilot channel provides the mobile with timing and phase reference. Each base station sector has only one forward pilot channel.

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2.3.7.2 Transmit Diversity Pilot Channel (F-TDPICH)

The F-TDPICH is a new signaling channel in IS-2000. This channel is identified by Walsh code w₁₆128_{. It also carries no baseband information in that the baseband}

sequence is a stream of 1s that are spread by Walsh code w16 128

. The transmit sity pilot channel works with the forward pilot channel to support transmit diver-sity on the forward link (see Chapter 9).

Each base station sector can have at most one transmit diversity pilot channel. If there is one, then the transmit diversity pilot channel is transmitted continuously at a power level that is the same as or lower than that of the forward pilot channel.

2.3.7.3 Auxiliary Pilot Channel (F-APICH)

The F-APICH is a new signaling channel in IS-2000. This channel can be identified by a Walsh code or by a quasi-orthogonal function . It carries no baseband informa-tion in that the baseband sequence is a stream of 1s that are spread by its assigned Walsh code or quasi-orthogonal function. The auxiliary pilot channel supports the use of spot beam on the forward link. If a base station sector has a spot beam (formed by a single antenna or an array antenna) within the coverage area defined by its forward pilot channel, then that spot beam must have an auxiliary pilot channel.

The auxiliary pilot channel is optional in that IS-2000 does not specify how many auxiliary pilot channels (or spot beams) a base station sector can have. If there is one, then the auxiliary pilot channel is transmitted continuously. In addition, if there are more than one spot beams then each spot beam is assigned a different aux-iliary pilot channel (which is in turn spread by a different Walsh code or quasi-orthogonal function).

From the mobile’s perspective, the mobile reports the number of auxiliary pilots that it sees using the NUM_AUX_PILOTS field in the origination message and page response message. For each reported auxiliary pilot, the mobile also reports parameters such as the phase (PILOT_PN_PHASE), strength (PILOT_STRENGTH), and Walsh code (PILOT_WALSH) if a Walsh code is used to spread the auxiliary pilot. If a quasi-orthogonal function is used to spread the auxiliary pilot, then the mobile reports that quasi-orthogonal function (QOF)3_{. In}

addition, the mobile can report information regarding its received auxiliary pilots in the supplemental channel request message and extended pilot strength measure-ment message.

From the base station’s perspective, the base station specifies information regarding the auxiliary pilots in messages such as the extended channel assignment message, general neighbor list message, extended neighbor list update message, and candidate frequency search request message.

2.3.7.4 Auxiliary Transmit Diversity Pilot Channel (F-ATDPICH)

A spot beam itself can also support its own transmit diversity to increase forward link gain. If it does, then the spot beam uses the F-ATDPICH in addition to its