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`clock. Although accuracy is improved, the number of users is limited because the terminals must
`
`transmit. This method was proposed in Geostar’s RDSS system. In any case, users must know their
`
`height (the geocentric height and not simply height above sea-level).
`
`Three satellites can give two ranges and hold a clock synchronized However, users still need
`
`to input their height to get a two dimensional fix. With four satellites, three distance measurements and
`
`one time measurement are obtained. Thus, a three-dimensional position fix is obtained without any
`
`external references.
`
`In summary, a system based on two or three satellites can only provide low accuracies, in the
`
`order of few miles, depending on the kind of height information provided by the user. However, these
`
`low accuracies may be acceptable for some land-based applications (e.g., when locating a truck in a
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`remote area, as opposed to locating a rail car at a classification yard).
`
`A civil navigation system using dedicated satellites has yet to be launched although specific
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`frequencies have been allocated to RDSS systems. This is understandable if one considers the staggering
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`costs of designing, manufacturing, insuring, launching and operating the necessary satellites. To achieve
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`90% world coverage from geosynchronous orbits (one of several orbits used by satellites) at least 10
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`satellites would be required [5]. With an average satellite life of 7 to 10 years, capital costs would be
`
`great and to cover costs, large number of users would have to be served. Geostar proposed such a
`
`system and was in the process of implementing it. However, its financial difficulties and eventual
`
`bankruptcy confirm the hardships facing anyone wanting to undertake the development of a satellite
`
`positioning system.
`
`Two alternatives exist for a civilian system with dedicated satellites:
`
`l.
`
`2.
`
`The use of navigation systems designed for and operated by the military;
`
`The sharing of payloads with communications satellites.
`
`These alternatives are not without problems. Military and civilian needs are not similar. Military
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`designers have to take costly precautions against jamming. Satellites must continue operating even if
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`ground contact is lost, and a broadcast system is necessary so that users need not disclose their positions.
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`These considerations add to the complexity of a system such as the GPS. From an international
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`perspective, an open question remains as to whether the user community is prepared to accept a system
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`which is under the control of the military of a single country.
`
`In the second alternative, the use of transponders on board existing communications satellites and
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`the different engineering requirements for location and communications need to be reconciled.
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`Communications satellite systems do not need to keep track of the precise location of the space platforms.
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`When using satellites to derive locations using satellites, however, the exact position of the satellites must
`
`be known. The geometries of a geosynchronous orbit (popular with communications satellites) are such
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`that the calculated location has a considerable uncertainty in latitude. Also, equatorial regions (about 5
`
`from the equator) are at a disadvantage.
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`In addition, satellite operators adjust the orbit so the satellite
`
`can better “see” an earth station [5]. These station-keeping manoeuvres must be known, otherwise
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`accurate positions cannot be calculated.
`
`Three satellite radiodeterrnination systems will be outlined in the following sections: the Global
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`Positioning System (GPS), Qualcomm’s QASPR, and Geostar’s RDSS proposal.
`
`4.2.2.1 The Global Positioning Svstem (GPS:
`
`The Global Positioning System (GPS), also known as Navstar, is the most prominent of the
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`satellite positioning systems.
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`It is a military system that will eventually replace other federally operated
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`radionavigation systems (e.g., OMEGA, TRANSIT, LORAN-C). GPS has many advantages compared
`
`to other satellite systems [6]:
`
`1.
`
`2.
`
`3.
`
`4.
`
`GPS allocates frequencies more efficiently and uses only 2 MHz of bandwidth;
`
`As a broadcast system, GPS can serve an infinite number of users. Other RDSS proposals (e.g.,
`
`Geostar’s) were frequency-limited because they both received and transmitted data via satellites
`
`and, therefore, could only serve a certain number of users;
`
`With GPS, the user would pay once to purchase the receiver and would not pay for the use of
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`positioning information;
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`If it becomes the predominant technology, the cost of GPS receivers should drop substantially.
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`The system will ultimately comprise a constellation of 21 satellites (plus three operating spares)
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`on circular orbits at about 20,000 km of altitude. The satellites are arranged so that four will always be
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`visible from all points on the earth. The U.S. Department of Defense is expected to declare the system
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`fully operational in 1993. By then it will be possible to get a three-dimensional position 24 hours a day.
`
`Position fixes are obtained now at the user’s risk. Currently 15 satellites are operational, 10 of which
`
`are Block 11 satellites (eventually all 24 satellites will be Block 11 or later). These provide a minimum
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`of 2 1 .5 cumulative hours of two-dimensional positioning per 24-hour period, and 15.5 cumulative hours
`
`of three-dimensional positioning per 24-hour period [18]. The next satellite will be launched before the
`
`end of the summer of 1991.
`
`GPS receivers are passive. Built-in microprocessors in the receivers not only determine the
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`optimal set of satellites for use, but also perform calculations. The equipment is easily built, and is
`
`getting smaller and less expensive. A GPS receiver in the form of a board complete with its antenna,
`
`mounting bracket, cable driver software, and user manual has been priced at about $3,000 in recent
`
`years. Currently, some receivers are available for about $1,000, and industry experts expect that the
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`price will eventually come down to about $500. The most significant recent development has been the
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`announcement of small, low-cost, multichannel receivers that can be integrated into other electronics
`
`equipment.
`
`For national security reasons, civilian accuracy has been restricted to about 100 meters, making
`
`use of the Standard Positioning Service (SPS). Military users on the other hand, have access to the
`
`Precise Positioning Service (PPS). Some ways to boost accuracy include the use of processed satellite
`
`orbiting data (post-processed satellite ephemerides) and differential techniques (where positions are
`
`derived relative to precisely surveyed points). The limited availability of the PPS to selected civilian
`
`users is much discussed. However, accuracy is not the only controversy surrounding GPS. The question
`
`of user fees (none, for the time being) is an issue that may affect the operational success of the system.
`
`Lastly, as with all military systems, responsiveness to civilian users and the question of control are major
`concerns.
`
`There has been recent interest in integrating the GPS with the GLONASS system, to improve the
`
`accuracy of both [19]. GLONASS is a Navstar-like Soviet radionavigation system, consisting of 12
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`satellites.
`
`Experts on both systems are conducting joint tests to determine how the U.S.- and
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`Soviet-manufactured products perform in real-life environments. Preliminary data from tests on board
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`an airliner showed that the differences between the two systems were mainly due to the different earth
`
`models used by each [20]. Additional investigations of GPS/GLONASS interoperability will undoubtedly
`
`follow.
`
`4.2.2.2 QUALQOMM’§ OASPR
`
`In February of 1990, Qualcomm, a vendor of satellite communications services, announced the
`
`introduction of the Qualcomm Automatic Satellite Position Reporting (QASPR) system to the U.S.
`
`market. This system is claimed to have an accuracy of better than 1000 feet under any circumstances,
`
`significantly improving the accuracy of position reporting when compared to LORAN-C systems. Using
`
`existing civilian communications satellites, it processes the signal from one satellite and monitors a beacon
`
`signal from a second. A vehicle can be tracked 24 hours a day anywhere within the continental United
`
`States. QASPR is part of Qualcomm’s OmniTRACS mobile communications system.
`
`4.2.2.3 Geostar’s RDSS Proposal
`
`The FCC granted a license to Geostar for a private RDSS system in 1984. Geostar’s technical
`
`design was also adopted as a baseline for RDSS systems. At the time the FCC held the view that
`
`providing spectrum for an alternative system to GPS was beneficial in that services could be tailored to
`
`the needs of the market. Presently, however, the company has ceased operations, and the filture of
`
`Geostar is uncertain.
`
`The Geostar system in its full implementation would consist of three geostationary satellites
`
`carrying the necessary transponders. User terminals would both receive and transmit but would not
`
`perform calculations or accurate timing functions. Precise timing signals would be transmitted from an
`
`operations center in Washington D.C., and then retransmitted by one of the three satellites. User
`
`terminals would receive the signals, synchronize themselves, and transmit their own signals. These
`
`signals would be picked up by all satellites and relayed back to the operations center along with other
`
`information such as user identity. When the signals reached the operations center their travel time and
`
`19
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`other pertinent data would be extracted. That information would be routed to fleet headquarters after
`
`being processed at the central facility. Users, however, would have to input their geocentric height,
`
`information that may not be readily available. Geostar, then patented a satellite compass system which
`
`according to company officials will indicate position within 2 to 7 meters, using a portable 20-ounce radio
`
`costing several hundred dollars (assuming mass production). Accuracy would be achieved using a
`
`nationwide digital terrain map stored in a ground-based computer. Heights would be calculated from the
`
`terrain map starting with an initial position estimate and iterating a number of times. Position information
`
`would be given in plain English, e.g., “You are 70 feet north of the intersection of East Road and West
`
`Street.” The time for a fix would depend on the accuracy of the initial estimate. The system’s accuracy
`
`may never be demonstrated, and the quoted 2 to 7 meters may be optimistic.
`
`20
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`5
`
`MOBILE COMMUNICATIONS SYSTEMS
`
`Mobile communications services use either a terrestrial or satellite network to relay information
`
`from vehicles to dispatchers and vice versa. All systems allow a certain degree of message transmission
`
`(data or voice) that may or may not include position information. A satellite network can provide service
`
`to rural or other areas not covered by a terrestrial system. Therefore, the two networks are seen as
`
`complementary to each other and may result in an integrated telecommunications network.
`
`In the following sections a variety of land and satellite systems will be described.
`
`Services
`
`offered by so called “system integrators” are not specifically mentioned.
`
`System integrators are
`
`companies which specialize in creating custom systems with off-the-shelf hardware and software products.
`
`Their services are currently geared towards large fleets with sophisticated dispatching needs. The
`
`discussion will close with a look at the European developments and some emerging technologies.
`
`5.1
`
`LAND-BASED SYSTEMS
`
`Satellite systems tend to be expensive and geared toward nationwide coverage, a capability many
`
`trucking firms do not require. The need to maintain a line of sight with a satellite may also prove an
`
`impediment to pickup and delivery fleets that operate in urban areas. Other technologies are available
`
`for these fleets and these will be discussed.
`
`5.1.1 Meteor Burst
`
`The use of meteor bursts is a newcomer to the field of mobile communications, although the
`
`technology itself has been in existence for more than 20 years. The in-truck terminals are similar to those
`
`used by other systems, and positioning is provided by LORAN-C. Meteor-burst technology offers an
`
`alternative at almost half the price of satellite systems. Transtrack Inc. is holder of the first FCC license
`
`to market the service to the transportation industry and already operates several tracking stations.
`
`Pegasus, although now bankrupt, followed suit and emphasized its ability to provide software which was
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`compatible with carriers’ management information systems. A third contender is Broadcom, a R&D
`
`house in New Jersey. The company claims to have found a way to bring the time between two
`
`transmissions down to 30 seconds and states the possibility exists to reduce the time to four seconds.
`
`Besides the lower cost, another advantage that meteor—burst has over satellite communications is
`
`the theoretically increased reliability. Because there is no space segment, all of the support equipment
`
`is on the ground. However, messages have to be short, only 32 characters long, and are constrained by
`
`the size of the burst, although longer messages can be linked over several bursts. Furthermore, satellite
`
`messages can be transmitted in as little as 15 seconds, while meteor bursts typically require several
`
`minutes (depending on the availability of a meteor burst). Time requirements do not facilitate interactive
`
`dialogue.
`
`5.1.2 Telephone and Cellular Systems
`
`The telephone is the simplest of the communications technologies. Despite the surging popularity
`
`of new systems, the vast majority of the trucking business is conducted with a telephone and/or a voice
`
`radio. The telephone is mainly used by long haul drivers who have to make check calls at regular
`
`intervals.
`
`It is not uncommon for a driver to spend an hour a day of unproductive time trying to reach
`
`the dispatcher.
`
`Voice mail systems and pagers enhance the usability of the phone. Simple voice mail systems
`
`are offered by all telephone companies. A more sophisticated voice mail system allows the driver calling
`
`from either a regular or cellular phone to not only access the firrn’s database, but modify information
`
`stored in it as well.
`
`In its current configuration this system is not linked to any positioning systems and
`
`is geared toward small scale regional operators.
`
`Pagers have been available for some time. Currently, there are about 9 million subscribers in
`
`the U.S., 67% of whom use numeric and 4% alphanumeric pagers [21]. Pagers provide an inexpensive
`
`alternative for sending simple messages to drivers. Vendors are attempting to establish alphanumeric
`
`pagers as low cost data receivers. CUE Paging offers numerical paging which covers almost all the
`
`heavily populated areas.
`
`It offers a one-way link between dispatch centers and truck drivers who still
`
`require the facilities of a truckstop to get the messages through voice mail or fax.
`
`In combination with
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