Other

Massachusetts Institute of Technology

Trueposition, Inc.

Alan E E Rogers

Robert J Anderson

Louis A Stilp

Joseph W Sheehan

Andrew F Harbison

Vineet Sachdev

A method, used in locating a mobile transmitter, includes providing a set of cross-correlation values, wherein each cross-correlation value is associated with a corresponding TDOA and/or FDOA estimate and is produced by cross-correlating a reference signal with a cooperating signal. The reference signal comprises a copy of a signal transmitted by the mobile transmitter as received at a first antenna and the cooperating signal comprises a copy of the same signal as received at a second antenna. The method further includes determining a most likely range of TDOA and/or FDOA estimates, and then identifying an optimal cross-correlation value within a subset of cross-correlation values corresponding to the most likely range of TDOA and/or FDOA estimates. The TDOA and/or FDOA value corresponding to the optimal cross-correlation value is then employed in calculating the location of the mobile transmitter.

Method for estimating TDOA and FDOA in a wireless location system

An antenna selection method is used in a wireless location system that determines the geographic location of a mobile wireless transmitter. The wireless location system includes signal collection systems connected to multiple antennas at a plurality of cell sites and a location processor for processing digital data provided by the signal collection systems. The antenna selection method comprises evaluating segments of data collected from a plurality of antennas at a signal collection system, selecting a subset of the segments of data, and using only the selected segments of data in location processing.

Antenna selection method for a wireless location system

A collision recovery method for use in a Wireless Location System includes receiving a transmission from a wireless transmitter at multiple signal collection systems and multiple antenna ports of each of the multiple signal collection systems. At each of the multiple signal collection systems, the transmission received at each antenna port is converted into a digital format, and digital data representative of the received transmission is stored. The transmission is then demodulated, and TDOA analysis is performed on the digital data from pairs of signal collection systems. The location of the wireless transmitter is determined using the TDOA data. The method further involves verifying that the RF data from each antenna port is from the wireless transmitter to be located, e.g., by demodulating a segment of the transmission received at each antenna port and verifying that at least a combination of the following fields is correct: MIN, MSID, TMSI, IMSI, and ESN.

Collision recovery in a wireless location system

A Wireless Location System includes signal collection systems and location processors for processing digital data provided by the signal collection systems. To determine the geographic location of a mobile wireless transmitter, time difference of arrival, or TDOA, data is determined with respect to a plurality of first signal collection system/antenna second signal collection system/antenna baselines. A method for selecting baselines for use in location processing comprises calculating a number of parameters for each of the plurality of baselines, and including in a final location solution only those baselines meeting or exceeding predefined threshold criteria for each of the parameters.

Baseline selection method for use in a wireless location system

The accuracy of the location estimate of a Wireless Location System is dependent, in part, upon both the transmitted power of the wireless transmitter and the length in time of the transmission from the wireless transmitter. In general, higher power transmissions and transmissions of greater transmission length can be located with better accuracy by the Wireless Location System than lower power and shorter transmissions. Wireless communications systems generally limit the transmit power and transmission length of wireless transmitters in order to minimize interference within the communications system and to maximize the potential capacity of the system. Several methods meet the conflicting needs of both systems by enabling the wireless communications system to minimize transmit power and length while enabling improved location accuracy for certain types of calls, such as wireless 9-1-1 (emergency) calls. Such methods include mobile-assisted techniques in which the mobile unit includes functionality to assist in improving location accuracy. The WLS locates the transmitter (mobile unit) while the latter is using a modified transmission sequence comprising a message sent from the wireless transmitter using transmission parameters different from the normal transmission parameters broadcast on the forward control channel by the base stations in the associated wireless communications system. A trigger event, such as the user dialing 9-1-1, causes the mobile unit to operate in the mode in which the modified transmission sequence is used.

Mobile-assisted network based techniques for improving accuracy of wireless location system

A station-based method for use in a wireless location system determines the geographic location of a mobile wireless transmitter. The wireless location system includes signal collection systems and location processors for processing digital data provided by the signal collection systems. The station-based method comprises receiving a transmission from a wireless transmitter at multiple antennas and at multiple signal collection systems. The transmission is converted into a digital format in a receiver connected to each antenna at the multiple signal collection systems. At each signal collection system, digital data representative of the received transmissions are stored in a memory. The transmission is then demodulated at a first signal collection system, and appropriate phase correction intervals are determined. At the first signal collection system, for each such phase correction interval, appropriate phase correction parameters are calculated, and the phase correction parameters are encoded along with the demodulated data. The demodulated data and phase correction parameters are sent from the first signal collection system to a location processor. At the location processor, the signal collection systems and receiving antennas to use in location processing are determined. The demodulated data and any needed phase correction parameters are then sent from the location processor to a plurality of signal collection systems that will be used in location processing. At each signal collection system to be used in location processing, a first re-modulated signal based upon the demodulated data and any needed phase correction parameters is created; and a time difference of arrival (TDOA) determination is performed using the digital data stored in memory and the first re-modulated signal. The TDOA and multipath mitigation data are sent from the signal collection systems to the location processor. Finally, the location of the wireless transmitter is determined at the location processor using the TDOA data.

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Ayer, MA, United States of America

Alan E E Rogers