23-07-2012, 02:47 PM
3G CD MA Wireless System Engineering
[attachment=28518]
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 phenomenon
driving these changes has been the integration of wireless communication
devices in people’s lives. While the 1990s were the years when wireless voice telephony
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 communication
devices and applications effected by these devices, the demand on wireless
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 duplication
of foundational material of spread spectrum communications 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 frameworks
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
xiii
control and focuses on radio link protocol, signaling radio burst protocol, and system
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 processing
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 contains
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 management,
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 chapters
presented thus far. It describes the IS-2000 architecture from a network perspective
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 network.
Advanced concepts such mobile IP are also introduced here.
The last three chapters concern a special topic that is of particular interest—
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, session,
connection, and security), and Chapters 14 and 15 cover medium access control
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 engineers,
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.
xiv Preface
Finally, the material presented in this book is given for informational purpose
and instructional value and is not guaranteed for any particular purpose. The publisher
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. Furthermore,
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.
Preface xv
.
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 encouragement
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 challenging
parts of this project, and this book is also dedicated to him.
xvii
.
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 generation
(3G) systems, this book specifically deals with the IS-2000 implementation 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. Subsequently,
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 investment
to provide 3G services. Second, because IS-2000 represents a natural technical
evolution from its predecessor, there is a lower implementation risk when transitioning
to 3G.
1
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 controls
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 computers’
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 information
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. Welldefined
layer functions provide modularity to the system. As long as a layer still performs
its functions and provides the expected services, the specific implementation
2 Introduction to 3G CDMA
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., Signaling
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 protocol
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
shown from the perspective of the mobile station. After: [5].)
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 information.
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 service
data units (SDU). PDU is used to designate those data units that are accepted by a
4 Introduction to 3G CDMA
Table 1.1 Physical Channel Designations in IS-2000
Forward Link
Channel
Designation Channel Name
Reverse Link
Channel
Designation Channel Name
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 channel
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
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 common
channels (channels that are shared among 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 information
that is packetized in nature.
[attachment=28518]
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 phenomenon
driving these changes has been the integration of wireless communication
devices in people’s lives. While the 1990s were the years when wireless voice telephony
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 communication
devices and applications effected by these devices, the demand on wireless
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 duplication
of foundational material of spread spectrum communications 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 frameworks
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
xiii
control and focuses on radio link protocol, signaling radio burst protocol, and system
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 processing
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 contains
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 management,
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 chapters
presented thus far. It describes the IS-2000 architecture from a network perspective
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 network.
Advanced concepts such mobile IP are also introduced here.
The last three chapters concern a special topic that is of particular interest—
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, session,
connection, and security), and Chapters 14 and 15 cover medium access control
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 engineers,
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.
xiv Preface
Finally, the material presented in this book is given for informational purpose
and instructional value and is not guaranteed for any particular purpose. The publisher
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. Furthermore,
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.
Preface xv
.
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 encouragement
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 challenging
parts of this project, and this book is also dedicated to him.
xvii
.
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 generation
(3G) systems, this book specifically deals with the IS-2000 implementation 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. Subsequently,
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 investment
to provide 3G services. Second, because IS-2000 represents a natural technical
evolution from its predecessor, there is a lower implementation risk when transitioning
to 3G.
1
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 controls
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 computers’
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 information
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. Welldefined
layer functions provide modularity to the system. As long as a layer still performs
its functions and provides the expected services, the specific implementation
2 Introduction to 3G CDMA
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., Signaling
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 protocol
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
shown from the perspective of the mobile station. After: [5].)
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 information.
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 service
data units (SDU). PDU is used to designate those data units that are accepted by a
4 Introduction to 3G CDMA
Table 1.1 Physical Channel Designations in IS-2000
Forward Link
Channel
Designation Channel Name
Reverse Link
Channel
Designation Channel Name
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 channel
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
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 common
channels (channels that are shared among 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 information
that is packetized in nature.