Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2000-06-23
2001-09-11
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C701S207000
Reexamination Certificate
active
06288676
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for determining the location of a mobile radio transmitter, especially a mobile radio transmitter positioned in the service area of a cellular communications telephone system.
Cellular telephone systems now provide ready access to wireless telephone communications. Cellular telephones operate in an analog system of frequency division multiple access (EDMA). Digital technologies, including time division multiple access (TDMA) or code division multiple access (CDMA), offer greater capacity and should give more individuals simultaneous access to cellular telephone services. In addition, cellular-like communications systems, such as personal communication systems (PCSs), will further increase the number of individuals with access to a wireless communication network.
A cellular-telephone or cell-like communication system involves a network of fixed base stations that provide an integrated communication service to a plurality of mobile transmitter/receiver (“transceiver”) units, e.g., cellular telephones. The communications network attempts to communicate with each transceiver from the base station which provides the optimal communication. The optimal base station is usually, but not necessarily, the one nearest the mobile transceiver. To provide the optimal communications support, the network need not locate the geographic position of the mobile transceiver more accurately than needed to determine which base station to use.
The inability of existing communication networks for cellular-telephone or cell-like communication systems to accurately determine the location of a mobile transmitter is a major disadvantage in an emergency. For example, public safety officials in Los Angeles estimate that, today, a quarter of all who call the emergency number (“9-1-1”) from a cellular telephone do not know where they are when they call. The time spent in finding their location delays emergency assistance units, for example, police or ambulance services, in providing assistance. Other studies indicate that in excess of sixty percent of traffic fatalities in the United States occur on rural roadways. Delays caused by uncertainty in location also exacerbate the inherently longer response times for providing emergency services in rural areas.
Monitoring mobile transceivers that are located on vehicles has advantages other than providing support for responses to requests for assistance. One such advantage is enabling the cost effective monitoring of traffic flow. Unplanned traffic incidents (“traffic jams”) clog the highways with resulting deleterious effects on safety, environment, and economy. The volume of message traffic in a major metropolitan area is a type of collateral information, and it can be combined with observed location- and speed-related information and topographic information (e.g., road maps), to indicate which roads are passable and which are congested. However, traffic flow information, emergency services, and roadside assistance are not primaly reasons for establishing a communication system and thus are not currently provided by the system. The cost of adding equipment to the communications infrastructure to provide such information and services seems justifiable to communications companies only if it can be done using the most modest of infrastructure enhancements.
The problem of locating the position of a mobile radio transceiver has been solved in many ways for many years but in systems other than that of a cellular-telephone or cell-like communication system. No simple, low-cost solution has been found that is practical when applied to the wide-scale monitoring of mobile telephones. One practical difficulty in implementing any type of localization for mobile radio transceivers is the cost of the modifications either to the transceiver or to the communications network (infrastructure) that are needed to determine the location of the mobile transceiver. Any given transceiver would rarely, if ever, be used in placing a request for emergency or roadside assistance. Thus, the suppliers of transceivers and the operators of communications networks have little economic incentive to increase the complexity (and cost) of the transceivers or to install an extensive and expensive infrastructure to support such rarely used services absent government mandate. However unprofitable in the short term, emergency assistance and roadside assistance services have unquestionable value for providing and enhancing personal and public safety. Ameliorating the increasing incidence of violence and the related, growing concern for personal security with a mobile communications system is a worthy policy goal with the potential for realizing enormous benefit to subscribers, network operators, and the general public alike however, realizing the objective, even one so important and valuable, requires a practical, inexpensive infrastructure for uniquely identifying people requesting or reporting the need for assistance, communicating with them, and providing their locations to a responding assistant.
Today, techniques exist that provide partial and complex solutions to the problem of providing geographical locations with sufficient accuracy to aid emergency and roadside assistance personnel. For example, a radio transmitter may typically be attached to a vehicle which would enable the vehicle to be localized for purposes of protecting endangered cargo or persons, controlling the deployment of delivery trucks in an urban area or any other of a number of applications.
Several localization systems are presently commercially available. Some of the systems use navigational instruments such as ring laser devices. Others use magnetic field sensors that are sensitive to the earth's magnetic field. Yet another type uses radio beacons such as the LORAN-C system. While the systems perform satisfactorily, they are not suited for consumer use due to their inherent complexity and cost as well as the need for frequent reinitialization or calibration.
Techiniques exist for accurately determining one's position in applications other than that of providing emergency or roadside assistance. For example, the satellite-based Global Positioning System (GPS) allows determination of the location of the point of GPS signal reception with a special-purpose receiver for the wireless GPS signals that are broadcast from the satellites. However, obtaining the position of a communications transceiver by using GPS requires the mobile transceiver to include a GPS receiver. GPS receivers are expensive. Even if their cost were to be reduced through mass production, GPS receivers would still have to be integrated with all existing and future mobile transceivers. The cost associated with this solution seems to be prohibitive in view of the infrequency of use of the service and especially in terms of the large number of mobile transceivers for which the localization capability is desired.
Several attempts have been made over time to use terrestrial-based radio direction finding and positioning systems. One type of radio positioning system measures the time required for a radio signal to travel between a mobile transmitter station and fixed antenna locations. Time difference measurements are obtained by comparing the wide band signal wave forms transmitted from the mobile station with some form of pulsed amplitude modulation or specific coding modulation so that the timing resolution and related position resolution is proportional to the inverse of the signal bandwidth. Yet another radio positioning system uses time difference measurements obtained by comparing narrow band signal wave forms to obtain a difference in the phase of the received signal. The radio frequency signals have a wavelength comparable to the separation of the antenna sites and the ability to resolve the location of the mobile transmitter station is proportional to the wavelength of the signal. Either radio positioning system, however, requires synchronizing separated antenna site
KSI Inc.
Phan Dao
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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