Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
1999-10-29
2003-05-27
Urban, Edward F. (Department: 2685)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S456500, C455S067700, C455S067700, C342S451000, C342S452000
Reexamination Certificate
active
06571082
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to field simulation and field testing of wireless systems, and more particularly to methods and systems for field testing network-based location determination technologies for wireless communication systems.
BACKGROUND OF THE INVENTION
Location determination technologies are increasingly being incorporated into, or being deployed in conjunction with, wireless communication service systems. An important application of wireless communications caller location determination technologies involves 911 emergency calls. Often, persons making 911 calls using wireless devices, e.g., cellular phones do not know their location or, due to injury, are unable to adequately convey this information. When a 911 caller's location can be quickly and accurately ascertained by location determination technologies, emergency assistance can be provided in a more timely manner. Caller location determination technologies may be directly integrated into a wireless communication service provider's existing communication system, or may be independent of the provider's existing wireless communication network.
In order to determine a wireless caller's location, a Location Determination Technology (LDT) estimates the parameters of a received signal(s) corresponding to a transmitted signal(s) originating from one or more transmitters. An LDT can be classified as network-based, handset-based or hybrid variations thereof.
For a network-based LDT, a signal is transmitted from a single handset transmitter and the received signal(s) are measured by one or more LDT receivers, which may be co-located with the wireless communication system's base station(s).
For a handset-based LDT, signals are transmitted from multiple sources. In the case of Global Positioning Satellite (GPS) Navigation System type handset-based systems, for example, signals are transmitted from multiple satellites. Measurement of received signals is performed by a single LDT receiver integrated into the handset. An LDT that is handset-based may be one of two types. One type uses signals from the GPS Navigation System as discussed above. The other type, a network-type handset-based system, uses signals sent from the wireless network base stations to the handset.
For hybrid variations of an LDT, both network-based and handset-based technologies are utilized to estimate a caller's location. For a network-based LDT and hybrid variations, the location of a caller is usually estimated or determined at a position determining equipment (PDE), i.e., a central, location determination estimator processor. For a handset-based LDT, the caller location estimation functionality may be integrated into the handset or it may reside in a PDE. For hybrid variations, the location of a caller is usually estimated at a PDE since the PDE determines which estimate is more reliable, the estimate determined by the network-based technology or the one from the handset-based technology.
A network-based LDT can use either Time Difference of Arrival (TDOA), Angle of Arrival (AOA), Location Fingerprinting (LF) or a combination of these techniques to determine the caller's location. TDOA determines the caller's location by measuring the time required for a transmitted signal to travel to several different receivers. Note that this use of “receivers” may include equipment such as one or more antennas in addition to electronic equipment necessary to detect and measure signals. With this technology, a minimum of three receivers with known locations are needed. The caller's relative distance from a receiver antenna is determined by multiplying the time it takes the signal to travel to the receiver by the signal's estimated speed, i.e. the speed of light. The difference of the caller's distances from any two receivers may be represented by a hyperbola, since the difference in distances of any point on the hyperbola from the two focii is constant and can be set equal to the measured difference. In this case the two focii are the two receiver locations, and the points on the hyperbola represent all possible caller locations. A minimum of two hyperbolae is determined using the difference in distances between the caller and two pairs of receivers. The caller's location is found by determining the location of the point at which the two hyperbolae intersect.
AOA technology requires a minimum of two receivers with known locations. At each receiver, the relative angle of the incoming signal is determined. The relative angle of the incoming signal can be represented as a straight line emanating from the receiver. The caller's location is found by determining the intersection of the two straight lines emanating from the receivers, i.e., by triangulation.
LF technology requires at a minimum a single receiver with a known location. In this approach, a receiver's area of coverage is “mapped” by transmitting signals from known locations and measuring and recording the received signals characteristics. For each location in a receiver's area of coverage, a corresponding signal characteristic is determined. This information may be compiled into a database for the receiver's area of coverage. When a signal is later received at the receiver, the caller's location is determined by comparing the characteristics of the incoming signal with the information in the database.
A caller's location, as determined by using the foregoing location determination technologies, is generally an approximation of a caller's true location. Network-based location determination technologies estimate the location of the signal source by analyzing the parameters of the received signal(s). The signal parameters, i.e., signal amplitude, frequency, and relative time delays, are affected by the propagation impairment conditions that are present in the signal transmission/reception area. The propagation impairment conditions are generally a function of both the distance between the signal transmitter and receiver, and the operating conditions found between those locations. “Geographic locations” (i.e., where something is actually physically located) of the signal transmitter and receiver determine the actual path distance that a signal travels to get from the transmitter to the receiver. The “operating conditions” are the physical conditions found between (and at) the locations of the signal transmitter and receiver that affect the signal parameters. The operating conditions affect upon a signal depends on many factors, such as whether the area is rural or suburban, the height and composition of any surrounding buildings, and whether the signal transmitter is located indoors or is in motion, to name just a few. Wireless communication LDTs utilize complex signal processing techniques to mitigate for possible propagation impairments. Wireless communication LDTs must be able to estimate a caller's location accurately, i.e., within some acceptable range of error, over the wide range of propagation conditions that may exist within the service provider's operating area. To comprehensively verify the accuracy of a LDT, these technologies should be tested under the wide range of conditions in which they are expected to operate.
Wireless communication LDTs are often tested in the laboratory, in the field (operating the system at known geographic locations and under actual propagation impairment conditions), or with a combination of both. Comprehensive field testing of a wireless communication LDT often involves traveling to many different test areas so that the location determination capabilities of the technology can be evaluated under different propagation impairment conditions. The disadvantages of conducting comprehensive field testing include: the amount of time required to conduct all the testing; the expenses incurred in setting-up the tests and traveling to the different test areas; and requiring the testing organization to obtain permission from many different service provide
Hinnawi Nabil
Rahman Iftekhar
Davis Temica M
Suchyta Leonard Charles
Urban Edward F.
Verizon Laboratories Inc.
Weixel James K.
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