IS-95 CDMA and cdma2000: Cellular/PCS Systems Implementation
PrefaceThe global mobile communications market is booming. There are almost 250 million users worldwide and should be nearly 1 billion by early next century. Code Division Multiple Access (CDMA) is the fastest-growing digital wireless technology, tripling its worldwide subscriber base between 1997 and 1998. There are already 30 million CDMA customers and, at the current growth rate, there will be 50 million by the millennium. The major markets for CDMA are North America, Latin America, and Asia (particularly Japan and Korea). In total, CDMA has been adopted by almost 50 countries around the world.It is not hard to see the reasons for the success of CDMA. CDMA is an advanced digital technology that can offer about 7 to10 times the capacity of analog technologies and up to 6 times the capacity of digital technologies such as Time Division Multiple Access (TDMA). The speech quality provided by CDMA systems is far superior to any other digital cellular technology, particularly in difficult radio environments such as dense urban areas and mountainous regions. In both initial deployment and long-term operation, CDMA provides the most cost-effective solution for cellular operators. After an 18-month of market rollout, Personal Communications Services (PCS) providers have adequately demonstrated the power of CDMA technology to support a marketing strategy based on low prices and superior performance in key areas such as voice quality, system reliability, and handset battery life.CDMA service providers have a strong advantage when pursuing the market to the minutes-of-use model, given the longevity of CDMA handset battery life and the higher quality of the voice signal. A recent analysis of wireless platform performance by the Telecommunications Research and Action Center (TRAC) found that CDMA outperformed other digital and analog technologies on every front, including signal quality, security, power consumption, and reliability. Although analog technology came out ahead in availability, all three digital services (GSM, IS-136 TDMA, and IS-95 CDMA) were rated equally over analog with respect to availability of enhanced service features. The TRAC study found CDMA to be superior in signal security and voice quality over the other digital air interface standards. According to TRAC, CDMA has several advantages for consumers. Lower power consumption enables CDMA handsets to support up to 4 hours of talk time or 48 hours of standby time on a single battery charge. It has also been found that the soft-handoff characteristics of CDMA lead to fewer dropped calls than with GSM and IS-136 TDMA. One possible drawback for some CDMA customers is that there are some limitations on roaming capabilities. Some PCS operators with cellular affiliates are supporting dual-mode handsets to allow roaming between CDMA and analog platforms.CDMA technology is constantly evolving to offer customers new, advanced services. The mobile data speeds offered through CDMA phones are increasing, and new voice codecs provide speech quality close to wireline. Internet access is now available through CDMA terminals. The time will soon be at hand when CDMA service providers can further exploit the enhanced service potential of their platforms. There has been much talk of so-called third-generation (3G) data capabilities, where PCS providers will be able to compete with wireline service providers at high access speeds. PCS providers are looking ahead toward providing a range of service categories such as Internet and intranet access, multimedia applications, highspeed business transactions, and telemetry. The CDMA network offers operators a smooth evolutionary path to 3G mobile systems.The IS-95B standard is quite flexible, enabling service providers to allocate data in increments of 8 kilobits per second (kbps) within the 1.25-megahertz (MHz) CDMA channel bandwidth based on how service providers configure software download to already-installed network controllers. This means operators can implement return data speeds at rates much lower than 64 kbps, ensuring much lower power consumption in handsets than would be the case at a full 64kbps return rate. While operators in GSM and IS-136 TDMA sectors are making efforts to ensure they won't be left behind as data becomes a factor, CDMA appears to have a clear edge in its ability to go to relatively high speeds over the existing infrastructure.The opportunity to use the CDMA platform to add a fixed wireless service feature represents an added advantage for operators. Because CDMA has ample spectrum to provide a fixed service on top of mobile, several operators are exploring using terminals that would be able to shift the handset between fixed and mobile service, depending on where the user is. The universal handset would serve as a cordless phone in the home and as a mobile handset outside the home. The evolution to 3G will open the wireless local loop (WLL) with Public-Switched Telephone Network (PSTN) and Public Data Network (PDN) access, while providing more convenient control of applications and network resources. It will also open the door to convenient global roaming, service portability, zone-based ID and billing, and global directory access. The 3G technology is even expected to support seamless satellite interworking.With the cornucopia of benefits surrounding CDMA, it is evident that operators using this platform will have every opportunity to grow the business once the community-based strategy begins to unfold. The question is, when will they get serious about bringing these new capabilities to market?Recently an enhanced hybrid technology combining the CDMA air interface with the GSM network has been built, tested, and evaluated. GSM operators can save over 60% in cumulative capital costs using a GSM-CDMA overlay for network expansion of the GSM network using IS-95 CDMA radio access in addition to, or as a substitute for, TDMA radio access. This combines the spectral efficiency of CDMA with all GSM features, including seamless roaming and network services. The GSM-CDMA technology provides operators with a way to serve multiple market segments economically and to offer various services on one network platform. In addition to being a cost-effective network expansion solution, GSMCDMA also paves an evolutionary path to 3G services including high-speed data, multimedia, and mobile/fixed convergence services.CDMA is the selected approach for the 3G system, as evidenced by the proposals submitted by the European Telecommunications Standards Institute (ETSI), the Association Radio Industry Business CARIB), and the Telecommunications Industry Association (TIA). The 3G cdma2000 uses a CDMA air interface based on the existing IS-95B standard to provide wireline-quality voice service and high-speed data services, ranging from 144 kbps for mobile users to 2 megabits per second (Mbps) for stationary users. It is important to note that cdma2000 is a core proposal of the TIA for International Mobile Telecommunications-2000 (IMT 2000). Moreover, support for cdma2000 is not limited to North America; Korean carriers have a great opportunity to provide 3G-like service with today's existing CDMA technology. Mobile data rates of up to 114 kbps and fixed peak rates beyond 1.5 Mbps are within reach before the end of the decade with today's CDMA technology. These capabilities will be provided without degrading the systems' voice transmission capabilities or requiring additional spectrum. This will have tremendous implications for the majority of operators that are spectrum constrained. A doubling of capacity and a 1.5-Mbps data rate capability within a 1.25-MHz channel structure look very appealing.This book is an extension of the book Applications of CDMA in Wireless Communications (Garg, Smolik, and Wilkes, Prentice Hall, 1997). In that book, the primary focus was on the CDMA systems standardized by TIA and American Telecommunications Industries Standards (ATIS) as standards IS-95 and IS-665. Since the publication of that book, CDMA technology has undergone major changes and has become a viable technology for 3G systems. In this book, I discuss those aspects of CDMA that are essential to understanding system capacity. I also provide guidelines for system parameters of a CDMA network. The book outlines a migration path for CDMA to a 3G cdma2000 system.In writing this book, I addressed the needs of practicing engineers and engineering managers by explaining CDMA concepts, system capacity, radio frequency (RF) engineering, and other important aspects of the CDMA network. Students studying courses in telecommunications will also find this book useful as they prepare for careers in the wireless industry. I included a sufficient amount of mathematics so that you can understand the operation of the CDMA network, but I tried not to overwhelm you with very complex mathematical derivations.This book can be used by practicing telecommunications engineers involved in the design and operation of CDMA-based cellular/PCS networks as well as by senior or graduate students in electrical engineering, telecommunications engineering, and computer engineering curricula. I assume that you have some basic background in mobile communications and CDMA technology. If you don't, the book mentioned above by Garg, Smolik, and Wilkes can provide that understanding. By selectively reading pertinent chapters of that book, telecommunications managers who are engaged in managing CDMA networks but who have little or no technical background can gain enough of an understanding of CDMA systems to read this book.This book can be divided into four segments: Chapters 1 through 4 provide a foundation for understanding the material in subsequent chapters. Chapters 5 through 11 deal with IS-95 CDMA standards, and chapters 12 and 13 provide design aspects of a CDMA system. Chapters 14 and 15 focus on the data applications in CDMA and the evolution of IS-95 (2G system) to cdma2000 (3G system) in order to satisfy ITU IMT-2000 specifications. The following is a synopsis of the subjects covered in each chapter.Chapter 1. Major attributes of CDMA and the access technologies used for cellular/ PCS systems. Chapter 2. The different types of Spread Spectrum (SS) systems that are used. The main focus is on the Direct Sequence Spread Spectrum (DSSS) techniques that are employed in CDMA. I provide a relationship to calculate the performance of a CDMA system. Chapter 3. Speech and channel coding applications in the IS-95 CDMA system. Chapter 4. The concepts of diversity reception used to improve signal-to-noise ratio (SNR) of the system; various combining schemes used to combine the signals; some practical antennas used in the cellular telephone industry. Chapter 5. Functional entities of the wireless network and the TIA-standardized interfaces between the entities. I examine the activities of the International Telecommunication Union (ITU) to add Intelligent Network (IN) to wireless systems. Chapter 6. A high-level description of the IS-95 CDMA air interface, including important aspects of the forward link (base station to mobile) and reverse link (mobile to base station) and modulation parameters for the channels. Chapter 7. Modulation schemes, bit repetition, block interleaving, and channel coding; these are used in processing logical channels on the IS-95 CDMA forward and reverse links. Details about information processing, message types, and message framing are presented for the pilot, sync, paging, and traffic channels on the forward link. Similar details are provided for the access and traffic channels on the reverse link. Chapter 8. IS-95 CDMA call processing states that a mobile station (MS) goes through in getting to a traffic channel; idle handoff, slotted paging operation, CDMA registration, and authentication procedures; call flows for CDMA call origination, call termination, call release, and authentication. Chapter 9. The layering concept used to develop the protocols for IS-95 CDMA; the standardized interfaces between the functional entities, mainly the A-Interface and TIA IS-634defined MSC-BS messages, message sequencing, and mandatory timers at the BS and the MSC. The chapter also provides call flow diagrams for typical supplementary services, handoff scenarios, and Over-The-Air Service Provisioning (OTASP). Chapter 10. Handoff strategy used in IS-95 CDMA; power control schemes for the reverse and forward links. Chapter 11. Various parameters used to identify an MS including International Mobile Station Identity (IMSI), Mobile Station Number (MDN), Electronic Serial Number (ESN), and station class mark. I focus on authentication procedures, including the authentication of MS registration, MS originations, MS terminations, MS data bursts, and Temporary Mobile Station Identity (TMSI) assignment. Also discussed are unique challenge response procedures. Chapter 12. Basic guidelines for engineering a CDMA system, including a discussion of propagation models, link budgets, the transition from analog operation to CDMA operation, radio link capacity, facility engineering, border cells on a boundary between two service providers, and interfrequency handoff. Chapter 13. Procedures for calculating the capacity of the reverse and forward link of a CDMA system; a procedure to develop a link safety margin parameter for each of the forward link channels. Chapter 14. Standards for data services supported by CDMA cellular/PCS systems; highlights of the TIA IS-99, TIA IS-637, and TIA IS-657 standards. I describe the architecture for each of the four data services (e.g., packet data, asynchronous data, facsimile, and short message services) and the protocol stacks supported by these services. Chapter 15. The cdma2000, 3G evolution of IS-95. The cdma2000 Radio Transmission Technology (RTT) is a wideband, SS radio interface that uses CDMA technology to satisfy the needs of 3G wireless communication systems.Appendix A presents traffic tables for a variety of blocking probabilities and channel numbers. Appendix B comprises a list of abbreviations I introduce in the text and that are common to the industry. The references cited in Appendix C are papers and texts that I have found useful and, when considered in addition to those cited in the text, provide a rich background for readers interested in looking into digital wireless technology in greater depth.I suggest chapters 1-11 for those who are interested in IS-95 standards but who do not have much background in digital communications. Those who have adequate background in digital communications may skip chapters 1-4.I recommend chapters 1, 2, 4-10, 12, and 13 for those who are involved with the design of a CDMA system. The engineering managers should use chapters 1 and 5-12 to achieve adequate knowledge of IS-95 CDMA.I suggest chapters 1-8, 10-12, 13, and 15 for a one-semester graduate course in IS-95 CDMA and its evolution to cdma2000.I would like to thank the many people who helped me prepare the material in this book. Bernard Goodwin provided his encouragement in motivating me to write the book. Professor Ted Rappaport of Virginia Tech took me under the banner of his new series. I acknowledge the many helpful suggestions I received from my many friends.Finally, I acknowledge the assistance of my wife, Pushpa Garg, and the staff of BooksCraft, Inc. during the production of this book.