Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-01-20
2001-07-24
Kincaid, Lester G. (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S067150, C342S357490
Reexamination Certificate
active
06266534
ABSTRACT:
BACKGROUND OF THE INVENTION
Applicants' invention relates generally to radiocommunication systems, e.g., cellular or satellite systems and, more particularly, to techniques for supporting and enhancing emergency calling procedures in such systems.
The growth of commercial radioconimunications and, in particular, the explosive growth of cellular radiotelephone systems have changed the ways in which people communicate. One survey indicates that about 80% of the people who purchase mobile communication units and service subscriptions do so to enhance their personal security. Presumably, many of these subscribers would expect to use their mobile units to aid them in urgent situations, e.g., when their vehicle has become disabled or in an emergency situation requiring rapid medical and/or police response. In these circumstances it would be desirable that the radiocommunication system be able to independently determine a location of the mobile unit, particularly in the case where the subscriber does not know his or her precise location. Moreover, it is expected that the FCC will soon require that network operators forward the position of an emergency caller to the emergency service provider.
There are many techniques available to generate mobile unit location information. In a first category, the mobile unit could estimate its own position and send a message with its coordinates when placing an emergency call. This could be accomplished by, for example, providing the mobile unit with a Global Positioning System (GPS) receiver that receives location information from the GPS satellite network. The mobile unit can then transmit this information to the system, which would then forward it to the emergency service provider. This requires, however, significant modification of existing mobile units to include GPS receivers, as well as additional signalling between the mobile units and base stations.
Alternatively, the base stations which transmit signals to, and receive signals from, the mobile units could be used to determine the mobile unit's location. Various techniques, including attenuation of a mobile unit's signal, angle-of-arrival, and difference between the time-of-arrival (TDOA) of a mobile unit's signal at different base stations, have been suggested for usage in providing mobile unit location information. See, for example, the article entitled “Time Difference of Arrival Technology for Locating Narrowband Cellular Signals” by Louis A. Stilp, SPIE Vol. 2602, pp. 134-144. These solutions also have their drawbacks including the need to modify the many existing base stations, e.g., to provide array antennas to support angle-of-arrival techniques or to synchronize base station transmissions to support TDOA techniques.
A third category of strategies for locating mobile units in radiocommunication systems involves the provision of an adjunct system, i.e., a system which may be completely independent of the radiocommunication system or which may share various components (e.g., an antenna) with the radiocommunication system but which processes signals separately therefrom. This may be advantageous, for example, as an expedient solution to providing mobile unit location without modifying the large number of existing base stations in a system. For example, consider the equipment illustrated in
FIG. 1
wherein the adjunct scanning units are not co-located with the base stations of radiocommunication system. Therein, a base station
1
supports radiocommunication within cell
2
and, in particular with mobile unit
3
. An adjunct system, partially shown by way of scanning units
4
,
5
and
6
, monitors accesses to the system by mobile unit
3
. When mobile unit
3
makes an emergency access, adjunct units
4
,
5
and
6
use the mobile unit's transmissions on either a control channel or a traffic channel to provide information to a location processing center
7
. The location processing center then uses the information provided by the various adjunct units to, for example, triangulate the position of mobile unit
3
and report this position to an emergency service center
8
. More details regarding exemplary usages of adjunct systems can be found in U.S. Pat. No. 5,327,144 to Stilp et al., entitled “Cellular Telephone Location System”, the disclosure of which is incorporated here by reference.
However, the Stilp patent relies upon TDOA techniques for estimating mobile unit location in its adjunct system. Under certain conditions, described in more detail below, TDOA techniques used alone may introduce an undesirable degree of error, for example due to a mobile's current position introducing errors into the TDOA calculations. Accordingly, it would be desirable to provide other techniques for estimating a mobile unit's position using adjunct systems.
SUMMARY OF THE INVENTION
According to one exemplary embodiment of the present invention, selective usage of either TOA or TDOA measurement techniques by the adjunct system can be employed. For example, TDOA measurements can be used unless the GDOP parameter of the received signals passes a predetermined threshold, at which point TOA measurements can be used to obtain the mobile unit's position. Alternatively, a signal-to-noise threshold can be adopted as a mechanism for the adjunct system to select either TOA or TDOA measurement techniques.
According to another exemplary embodiment of the present invention, the effective length of the synchronization word sent in a transmitted burst can be increased. For example, the adjunct system can demodulate and decode a received time slot, and then remodulate and re-encode the same information to create a new “sync” word which is longer than the fields originally known in the received burst. Moreover, since the adjunct system receives multiple copies of uplink bursts from the various adjunct scanning units, for those copies which are not properly received, timing estimates can be determined using the long “sync” words created from other, better received copies.
According to another exemplary embodiment of the present invention, signal strength measurements made by a mobile unit and reported to the radiocommunication system can be used by the adjunct system to provide an estimate of the mobile unit's position. For example, the adjunct system can receive and decode these measurement reports and, using a priori knowledge of signal attenuation and base station transmit power, determine an estimate of the mobile station's position. This technique can be used as an alternative o the above-described TDOA/TOA techniques or in combination therewith.
REFERENCES:
patent: 5055851 (1991-10-01), Sheffer
patent: 5293642 (1994-03-01), Lo
patent: 5327144 (1994-07-01), Stilp et al.
patent: 5491837 (1996-02-01), Haartsen
patent: 5519760 (1996-05-01), Borkowski et al.
patent: 5657487 (1997-08-01), Doner
patent: 5732354 (1998-03-01), MacDonald
patent: 5960341 (1999-09-01), LeBlanc et al.
Koilpillai R. David
Koorapaty Havish
Molnar Karl
Raith Alex K.
Ramesh Rajaram
Ericsson Inc.
Kincaid Lester G.
Wood Phillips VanSanten Clark & Mortimer
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