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Wireless Location in CDMA Cellular Radio Systems / Edition 1

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Overview

The tremendous growth of the wireless communications industry demands both the extension of certain landline services to wireless services as well as entirely new services that are unique to wireless systems. Many of these applications, such as Emergency-911 (E-911), fraud detection, location-sensitive billing, and Intelligent Transportation Systems (ITS), will, in fact, require the deployment of accurate wireless position location systems, particularly in the light of the 1996 FCC report and order which requires location accuracy to within 125 m by October, 2001.
Wireless Location in CDMA Cellular Radio Systems investigates methods for wireless location in CDMA networks and analyses their performances. Techniques for measuring location parameters (AoAs, ToAs, etc.) are presented along with algorithms for calculating position from these parameters. Several impairments to accurate location are covered and analyzed including multipath propagation, non-line-of-sight propagation, and multiple-access interference. Many of the topics in this book are also applicable to FDMA- and TDMA-based communication networks.

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Chapter 1: Introduction

Over the last decade, the deployment of wireless communications has been significant with an annual increase of cellular subscribers in the world averaging about 40% [103]. Currently, it is estimated that there are between between 36-46 million cellular users in the U.S. alone [51, 168], representing over 20% of the U.S. population. In the next few years, it is expected that a total of about 200 million wireless telephones will be in use worldwide [51], and that in 10 years, the demand for mobility will make wireless technology the primary source for voice communication, with a total market penetration of 50-60% [103]. In order to provide both an increase in capacity and better quality communications, the wireless industry has begun to migrate from the analog cellular networks that were first introduced in the early 1980's, to digital networks such as time-division multiple access (TDMA) and code-division multiple access (CDMA) in the U.S., Global System for Mobile communications (GSM) in Europe and Personal Digital Cellular (PDC) in Japan [12, 51, 119]. CDMA is a very popular choice due to its claims of higher system capacity, ability to mitigate multipath fading and other-user interference, universal frequency reuse, low transmission power, soft handoff capability, message privacy and the ability to exploit voice activity cycles [51, 94, 126, 127, 149, 175, 191]. CDMA assigns each user a unique pseudonoise (PN) spreading code, unlike frequency-division multiple access (FDMA) where each user is assigned a different frequency and TDMA where each user is assigned a different time slot.

As the move is made from analog to digital technology insecond and third generation cellular and PCS systems, improved functionality and a broader spectrum of services will be made available to both system operators and consumers alike. The promise of even more enhanced services comes with the development of IMT-2000 (International Mobile Telephone 2000), the standardization process for which should be completed by the end of 1999 or early 2000. One of these new services, wireless position location, has received considerable attention over the past few years due to the Federal Communication Commission's (FCC) 1996 report and order [22]. The FCC mandate requires that all wireless service providers, including cellular, PCS, and SMR licensees, provide location information for Enhanced-911 (E-911) safety services, the provision for which requires two phases of completion. Phase 1, the deadline for which passed in 1998, required that the wireless carriers relay a caller's telephone number and the location of the cell site and/or sector receiving the call to a designated Public Safety Answering Point (PSAP). Such capabilities allow the PSAP to call back if the call is disconnected. Phase 11, to be completed by October 2001, requires that wireless carriers be able to report the location of all E-911 callers with an accuracy of 125 m (410 ft) in 67% of the cases. A further accuracy requirement of 13 m (40 ft) in 90% of the cases is possible for future mandates by the FCC [22].

1. Applications

The provision of location information for wireless E-911 calls permits rapid response in situations where callers are disoriented, disabled, unable to speak, or do not know their location. In fact, a report by the FCC indicated that over 20% of 911 calls were made by wireless users and that one-fourth of those callers could not identify their location [22]. To compound the situation, the emergency operator receives very little network-based information regarding the location of the wireless caller. This is alarming considering that an increasingly large fraction of E-911 calls are placed by cell phones which is a direct result of the growing number of cellular and PCS subscribers. In 1994, approximately 50,000 wireless E-911 calls per day were made in the U.S., a figure that increased to 60,000 in 1996. By the year 2000, it is estimated that this figure will grow to 130,000. A 1996 study by the State of New Jersey indicated that wireless E-911 calls accounted for 43% of all calls to E-911 received during wireless location trials [168]. While the E-911 requirements of the FCC are the driving factor toward accurate location technology in the United States, outside of the states, there is also an interest for emergency services and for other services which represent the potential for large revenues.

While position location using radio signals has been used by the military for years, it is a relatively new application in civilian radio systems. The military has expended great effort to build a highly accurate location system for its various branches, but civilian industry has a more difficult time justifying the tremendous cost of developing such a system. Consequently, with the E-911 mandate of the FCC, research has focused on location methods which utilize the existing and future wireless system communications components, i.e., base stations (BSs) and mobile stations (MSS).

Besides its use for emergency management, location technology promises additional services. It will be the enabling technology for location sensitive billing, improved fraud detection, improved traffic management and many other services which have a large revenue potential for system operators. It is estimated that the total annual revenue potential for all location-based services will be over $8 billion dollars per year [178].

Location sensitive billing, fraud detection, system design, fleet management and Intelligent Transportation Systems (ITS) will benefit from wireless location technologies. Location sensitive billing will allow system operators to maximize profits and encourage usage behaviors by offering different rates depending on whether the phone is used at home, in the office, on the road, etc. [171]. This also provides wireless carriers with the opportunity to offer rates which will bring new subscribers into their customer base. Moreover, a service provider who may have multiple agreements with PCS, cellular, or satellite carriers, could offer its customers the ability to choose a carrier that best suits their needs at any given time and location [54].

Additionally, location technology can play a key role in the ongoing battle against cellular phone fraud. Annual industry fraud ranges on the order of $500 million, all of which is passed on to wireless customers in the form of higher phone usage rates. Some carriers estimate that up to 1% of their customer base experiences fraud each month. With the use of wireless location systems, it will be easier to find and catch the perpetrators.

A further application of location technology will be found in wireless system design and for radio resource management [62, 122]. With the ability to locate wireless calls and match them with their serving cell sites and received power levels, system planners could dramatically improve their ability to architect cells and wireless systems. More effective resource management could be obtained through the allocation of channels based on the knowledge of the wireless caller's location. Similarly, location information could assist in handoff procedures as the MS moves from one cell to another. Thus, cells could be better positioned and tuned, spectral efficiency improved and resource management made more effective through the use of accurate location technology.

In wireless networks, the system employs various means of tracking the relative location of mobile terminals since the location of a MS must be identified before a call to the MS can be established. The "location area" of a MS in the wireless network is often maintained in databases which axe updated as the MS moves throughout the network. The use of exact location technology reduces and possibly eliminates the need for database management and reduces the system resources required since the MS can be paged in the cell in which it currently resides rather than paging several cells to identify its location.

Wireless location technology can also be used to make fleet operations more efficient and effective [84]. Having knowledge of the vehicles' locations allows a dispatcher to locate the nearest available vehicle, greatly improving response times. The improvement in field service not only applies to delivery operations, but to police and emergency vehicles as well as taxi and other service operators. Another developing technology that will rely heavily on accurate location information of mobile terminals is of Intelligent Transportation Systems. The strategic plan submitted by ITS America [79] calls for functionality in several areas, the two most important of which are listed below:

  • Advanced Traffic Management Systems (ATMS) use various technologies to manage traffic in the transportation network.
  • Advanced Traveler Information Services (ATIS) will provide information such as traffic safety alerts, routes of travel, and real-time traffic information directly to the traveler.

Route guidance, an ATIS service, will provide directions to travelers based on their known (estimated) current position. This service will inform the driver of the best route of travel based on traffic conditions, such as traffic congestion in a particular area. Furthermore, traveler information services will provide a "digital yellow pages" to give travelers the ability to locate such conveniences as nearby gas stations and hotels. References [33] and [204] provide a detailed overview of further uses of positioning technology for future transportation systems.

The author's previous research in wireless position location for CDMA networks showed that research into wireless position location leads to a diversity of research for supporting technologies. Position location not only requires efforts in the area of algorithm development but also in the technologies which provide estimates of location parameters such as times of arrival (TOAs), time differences of arrival (TDOAs) and angles of arrival (AOAs). Therefore, any research in wireless position location will necessitate the advancement of the supporting technologies required to produce accurate parameter estimates...

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Table of Contents

Foreword. Preface. 1. Introduction. 2. System and Channel Models. 3. Location Methods and Impairments. 4. Radiolocation Algorithms. 5. Performance of Location in CDMA Systems. 6. TOA Estimation in Multiple-Access Interference. 7. Analysis and Mitigation of NLoS Effects. 8. Provisions for Location in Wireless Standards. 9. Conclusions & Future Directions. Appendices: A. Derivation of RnT (xiepsilon B. Kalman Filter Equations. C. Derivation of the Cramér-Rao Bound. D. Derivation of the GWRLS Algorithm. Index.

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