Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-03-09
2003-01-28
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S450000, C455S509000, C455S517000, C370S341000, C342S357490, C342S357490
Reexamination Certificate
active
06512928
ABSTRACT:
TECHNICAL FIELD
This invention relates to location determination systems. Specifically, the present invention relates to an apparatus and method for coupling data to a position determination device.
BACKGROUND ART
Conventional GPS position determination methods and Differential Global Positioning System (DGPS) position determination methods allow for the determination of position with sufficient accuracy for many applications. However, Real-Time Kinematics (RTK) methods are commonly used for applications that require a high degree of accuracy such as, for example, surveying.
RTK systems typically include a base station and one or more rover unit(s). The base station includes a GPS receiver and a radio transmitter that is coupled to the GPS receiver. The base station is located at a known position and communicates with the rover unit via radio. The rover unit includes a radio receiver that is adapted to receive communications from the radio transmitter of the base station and a GPS receiver. The base station periodically sends specially formatted data packets to the rover unit. These specially formatted data packets include GPS data received by the base station GPS receiver.
In a typical surveying application, the surveyor or the surveyor's assistant carries the rover unit to locations for which position is to be determined. The surveyor, or the surveyor's assistant then obtains GPS derived position fix data points using the GPS receiver of the rover unit. The rover unit uses, in real time, the data received from the base station in conjunction with GPS data received by the rover unit GPS receiver to determine position relative to the location of the base station GPS receiver within a horizontal accuracy of approximately plus or minus 2 centimeters. The rover unit stores the computed position fix in real-time for later use by the surveyor. In such prior art systems, the wireless data transmission path is one way from the base station to the rover(s).
In a typical surveying application, a surveyor locates the base station at his office, taking the rover unit out into the field to perform the required survey work. If the work area is beyond 50 kilometers from his office, the surveyor must create a new reference point near the work site using well-known survey techniques and the reference point must be chosen so as to assure adequate radio coverage of the site to be surveyed. That is, the reference point must be chosen such that the base station can communicate with rover unit(s) located within the area to be surveyed. It is often very desirable to locate the base station on a high point near or in the work site, in order to get the best radio range coverage possible.
The radios used for communication between the base station and the rover unit(s) are chosen by the surveyor from a small set of radios whose parameters (operating frequency and power) depend on the surveyor's political status. For example, government agencies have a set of frequency bands available to them that is different from the frequency bands that are available to civilian users. Some frequency bands that are available for civilian use are restricted with regard to transmission power level. This leads to varying coverage ranges, depending on the frequency band used. The ideal coverage range for a surveyor has a minimum of at least five kilometers and a maximum of about 50 kilometers. The maximum is set by RTK performance. That is, at a distance of over 50 kilometers, RTK position determination methods may not provide sufficient accuracy for particular surveying applications.
There are many distinct radio bands available to the surveyor, starting at 30-50 MHz and extending into the VHF range (220 MHz to 450-470 MHz, and 900 MHz). All available frequency bands with the exception of the 900 MHz band requires a license from the Federal Communications Commission (FCC) for permission to operate, and such operation is covered by Part 90 of the FCC rules and regulations. At 900 MHz, there is a special authorization under Part
15
, that allows for spread spectrum transmissions with a restricted transmit power of less than one Watt. This low-power level severely limits the range of the radio, which was the FCC's intention in creating the service. The typical suburban range of a radio operating in the 900 MHz band is about two kilometers, with one kilometer being common.
Surveyors have gravitated towards the 450-470 MHz band because it is possible to obtain a FCC license for nationwide coverage with 35 Watt transmitters. This power level provides the five kilometer minimum coverage range that is needed for effective productivity. The 450-470 MHz band is authorized for primary use by occasional voice service, on a shared use basis with others in a particular service area. Typical users include taxi dispatch, maintenance and repair dispatch, and other business or government services that need occasional voice service and do not need access to a nationwide telecommunications service.
There is a section-of part 90 that permits use of the 450-470 MHz band for telemetry services, subject to some stringent restrictions. These restrictions include the requirement that telemetry users share the channel with other users. However, surveyors typically set up on a work site and start transmitting RTK data packets, which are typically broadcast once per second, with a duration of approximately 0.25-0.4 seconds, until the survey is complete. Thus, a particular channel is virtually occupied by the transient surveyor for a half day, up to as many as five days, depending on the magnitude of the survey job. The problem is severely exacerbated if the surveyor picks a radio channel for which there is a local area repeater system. In this event, if the data packets are picked up by the repeater system they are rebroadcast over a much larger area, thus rendering the particular channel completely useless over a large area. Even if the surveyor's signal is not repeated, the surveyor's strong signal may “capture” the repeater's receiver and thereby prevent voice users from using the repeater.
For the above reasons, a channel formerly used by local users can become unusable for the duration of the survey. When an established user, at his base of operations, cannot access the user's mobile fleet in a few seconds, his options are a few: wait until the channel clears, or reassign each radio in the fleet to a new channel. This is inconvenient and time consuming for the established user. This also can lead to complaints by the local established users to the FCC for failure to abide by the rules of operation established by the FCC that call for “sharing” the channel.
In recent years, the number of persons using licensed and unlicensed frequency bands for voice communications has increased dramatically, making these frequency bands crowded, congested and unavailable for use by GPS users. Also, persons using licensed and unlicensed frequency bands for voice communications tend to communicate during business hours and during certain times of the day. At these times, desirable frequency bands become highly congested, particularly in densely populated areas, making usage for surveying activities difficult if not impossible.
The FCC requires that voice users listen before they speak to assure that the channel is available. However, in many instances users do not listen for a sufficient amount of time. This often results in voice users talking over a surveyor's transmission. This can result in loss of data. If the voice usage is significant, the rover unit may not be able to determine position. In congested areas, this may force the surveyor to change to a less congested frequency band.
What is needed is a method and apparatus that will allow for more efficient use of available frequency bands. More particularly, a GPS system and a method for communicating is required that allows for efficient usage of available frequency bands. Also, a method and apparatus is needed that meets the above needs and that does not int
Anderson Arthur E.
Janky James M.
Nguyen Simon
Trimble Navigation Limited
Trost William
Wagner , Murabito & Hao LLP
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