Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
1999-03-29
2001-02-13
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S357490, C342S357490, C342S457000
Reexamination Certificate
active
06188354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field Of the Invention
Generally, the present invention relates to communication networks. More specifically, the invention relates to an apparatus and technique for locating a remote station in a code division multiple access system using a combination of satellite and other signal measurements.
2. Description of the Related Art
Deployment of location technologies in wireless networks is being driven by regulatory forces and carriers' desires to enhance revenues by differentiating service offering from those of competitors. In addition, in June 1996, the Federal Communications Commission (FCC) mandated support for enhanced emergency 911 (E-911) service. Phase I of the Order requires that sector and cell information be set back to a Public Safety Answering Point (PSAP) agency. Phase II of the Order requires that the location of the cellular transceiver be sent back to the PSAP. To comply with the FCC mandate, 77,000 total sites are to be equipped with automatic location technologies by the year 2005.
Many techniques are being considered to provide automatic location capability. One technique involves measuring the time difference of arrival of signals from a number of cell sites. These signals are triangulated to extract location information. Unfortunately, this technique requires a high concentration of cell sites and/or an increase in the transmission power of the sites to be effective. This is generally incompatible with a typical CDMA system, where each telephone transmits with only enough signal power to reach the closest cell site. As triangulation requires communication with at least three sites, the concentration of cell sites would have to be increased or the signal power of each wireless station would have to be increased.
In any event, each alternative has significant drawbacks. An increase in the number of cell sites would be too costly. Increases in signal power would add to the weight and cost of each wireless station and increase the likelihood of interference between wireless users. In addition, the triangulation approach does not appear to offer the accuracy required by the FCC mandate.
Another approach being considered involves the addition of complete Global Positioning System (GPS) functionality to the cellular telephone. Although, this approach would add significant cost and weight to the wireless station, would require acquisition of four satellites, and would be somewhat slow, nevertheless, it is the most accurate approach to support location services.
To speed the process, a third approach sends aiding information to the wireless station indicating where the wireless station should look in frequency for GPS carriers. Most GPS receivers use what is known as a GPS satellite almanac to minimize a search performed by the receiver in the frequency domain for a signal from a visible satellite. The almanac is a 15,000 bit block of coarse ephemeris—a table giving the coordinates of a satellite at certain times during a specified time period—and time model data for the entire constellation. The information in the almanac regarding the position of the satellite and the current time of day is approximate only. Without an almanac, the GPS receiver must conduct the widest possible frequency search to acquire a satellite signal. Additional processing is required to attain additional information that will aid in acquiring other satellites.
The signal acquisition process can take several minutes due to the large number of frequency bins that need to be searched. Each frequency bin has a center frequency and predefined width. The availability of the almanac reduces the uncertainty in satellite Doppler, or signal shift, and therefore the number of bins that must be searched. The satellite almanac can be extracted from the GPS navigation message or sent on the down (forward) link as a data or signaling message to the receiver. On receipt of this information, the receiver performs GPS signal processing to determine its location.
While this approach may be somewhat faster in determining the location of a wireless station, it still suffers from the prerequisite that the remote station first acquire at least four satellites. This is problematic in urban environments. Hence, there is a need for an invention that can speed up finding the location of a wireless station and improves service availability. Ideally, the invention would require a minimum number of satellite signals to make the determination.
The invention would be compatible with CDMA modulation systems and the techniques used in telecommunication systems servicing large numbers of system users. A more robust discussion of CDMA systems and techniques in this type of multiple access communication systems may be found in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” assigned to the assignee of the present invention and incorporated by reference herein. Further, the invention ideally would be adaptable to other modulation systems and techniques used in other communication systems, such as time division multiple access (TDMA), frequency division multiple access (FDMA), and amplitude modulation (AM) schemes.
SUMMARY OF THE INVENTION
Broadly, the present invention relates to a communication network. More specifically, the invention relates to an apparatus and technique for locating the position of a remote station in a code division multiple access network using the time of arrival of a reference pilot signal at the remote station as a time reference. The time difference of arrival (TDOA) of GPS signals and other pilot signals received by the remote are measured relative to this reference time. From these measurements, the location of the remote station is determined. The invention treats the location issue as a TDOA problem.
One embodiment of the invention provides a method to determine a location of a remote station in a synchronous communications network, such as a CDMA network. A plurality of signals is received at a remote station, where the plurality of signals includes signals from the Global Positioning System (GPS) and signals transmitted from a terrestrial base stations. One of the signals received from the terrestrial base station is used to establish a reference time. In this embodiment, the network time signal is a reference pilot signal—such as a pilot signal that includes a zero phase pilot PN sequence transmitted from a base station in the communications network—but may be any type of signal sharing similar transmission characteristics. This pilot sequence is synchronized with the GPS system. Thereafter, a time difference of arrival for the plurality of timing signals is determined based upon the reference time, and the position for the remote station is determined, as discussed in the detailed description below, using these TDOAs.
In another embodiment, the invention provides an article of manufacture containing digital information executable by a digital processing device and used to determine the location of the remote station as described above. In another embodiment, the invention yields an apparatus used to determine the location of a remote station. The apparatus may comprise a remote station and a number of satellites that include transceivers used, in part, to transmit signals to the remote station. The apparatus may also include at least one base station that has, amongst other things, a transceiver used to communicate signals to the remote station. These signals include a timing signal synchronized with the satellite systems and used to establish a reference network time. Obviously, to receive signals, the remote station also includes a transceiver communicatively coupled to the base station and satellites, adapted to receive the satellite signals. The apparatus will also include a digital processing apparatus, such as a microprocessor, that is communicatively coupled to the network or one of its component parts.
The invention provides its users with numerous advantages. One a
Soliman Samir S.
Vayanos Alkinoos Hector
Edwards Christopher O.
Greenhaus Bruce W.
Pham Dao L.
Qualcomm Incorporated
Tarcza Thomas H.
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