Abstract: 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.

Abstract: 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.

Abstract: A signal collection system (SCS) is used in a wireless location system that determines the geographical locations of mobile wireless transmitters. The SCS includes a first receiver module, a first digital signal processing (DSP) module, a control and communications module, a timing signal generator including an enhanced GPS receiver, and a bus coupling the DSP module to the communications and control module. The receiver module receives RF signals from the mobile transmitters via a plurality of antennas and digitizes said RF signals, and provides digitized RF data to the first DSP module.

Abstract: In a wireless location system (WLS) including a plurality of geographically separated receiver systems, a system for synchronizing the respective receiver systems includes the use of an enhanced GPS receiver including a mechanism for receiving GPS signals and removing at least a portion of the timing instability of the GPS signals. An output of the enhanced GPS receiver is provided to a low phase noise phase-locked loop circuit that is used to produce reference signals with less than 0.01 degrees RMF of phase noise.

Abstract: 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. The inventive method disclosed herein meets 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 calls.

Abstract: 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. The inventive method disclosed herein meets 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 calls.

Abstract: A centralized database system is used in a wireless location system that determines the geographical locations of mobile wireless transmitters, the wireless location system including signal collection systems, location processors for processing digitized RF data provided by the signal collection systems, and a centralized database system for managing resources in the wireless location system. The centralized database system includes a computer, a database, and a plurality of software processes for managing the wireless location system, providing interfaces to external users and applications, and storing location records and configuration information.

Abstract: An internal calibration method, used to calibrate a receiver system used in a wireless location system, comprises injecting a signal into the receiver system and utilizing the signal to obtain an estimate of the manner in which the transfer function of the receiver system varies across the bandwidth of the receiver system. This estimate is used to mitigate the effects of the variation of the transfer function on time measurements made by the receiver system. Such time measurements are used to locate mobile transmitters.

Abstract: 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.

Abstract: Methods and apparatus for calibrating a Wireless Location System to enable the system to make highly accurate TDOA and FDOA measurements are disclosed. An external calibration method in accordance with the present invention comprises the steps of transmitting a first reference signal from a reference transmitter; receiving the first reference signal at first and second receiver systems; determining a first error value by comparing a measured TDOA (or FDOA) value with a theoretical TDOA (or FDOA) value associated with the known locations of the receiver systems and the known location of the reference transmitter; and utilizing the first error value to correct subsequent TDOA measurements associated with a mobile transmitter to be located.

Abstract: A signal collection system (SCS) for use in a Wireless Location System is disclosed. The SCS performs wideband energy detection and reporting at the front end of the SCS receiver. Other aspects of the SCS include a protocol for efficiently setting levels for wideband energy detection, DSP sharing within an SCS, and recursive location processing using progressively greater bandwidth from temporarily stored wideband data. The disclosed SCS includes antennas, a wideband receiver, a DSP for wideband energy detection, a memory for temporarily storing digital samples of received signals, a digital drop receiver, demodulation and normalization processors, and a communications processor. The wideband energy detection and the demodulation and normalization processors are implemented with DSP's that detect energy in a particular band, demodulate selected signals, and extract signals of interest for forwarding.

Abstract: Methods and apparatus for calibrating a Wireless Location System to enable the system to make highly accurate TDOA and FDOA measurements are disclosed. An external calibration method in accordance with the present invention comprises the steps of transmitting a first reference signal from a reference transmitter; receiving the first reference signal at first and second receiver systems; determining a first error value by comparing a measured TDOA (or FDOA) value with a theoretical TDOA (or FDOA) value associated with the known locations of the receiver systems and the known location of the reference transmitter; and utilizing the first error value to correct subsequent TDOA measurements associated with a mobile transmitter to be located.

Abstract: A method for use in locating a mobile transmitter in an emergency situation comprises the steps of (a) upon determining that the emergency situation exists, monitoring a bandwidth of a reverse voice channel (RVC) signal transmitted by the mobile transmitter; (b) determining whether the bandwidth exceeds a predetermined threshold; (c) if the bandwidth exceeds the predetermined threshold, measuring the location of the mobile transmitter; and (d) if the bandwidth does not exceed the predetermined threshold, performing a predetermined action to increase the bandwidth and subsequently measuring the location of the mobile transmitter.

Abstract: A method for use in a dual mode wireless communication system supporting at least a first modulation method and a second modulation method, wherein the first and second modulation methods are used on different RF channels, wherein a wireless transmitter is capable of supporting both modulation methods, and wherein it is preferred that emergency 911 calls generally take place with the first modulation method, comprising the steps of: when the wireless transmitter is currently using the second modulation method and attempts to originate a call to 911, causing the wireless transmitter automatically to switch to the first modulation method; and originating the call to 911 using the first modulation method on one of the set of RF channels prescribed for use in the first modulation method.

Abstract: A method for locating a mobile transmitter comprises the steps of (a) making a first estimate of the location of the mobile transmitter on the basis of a first transmission from the mobile transmitter; (b) causing the mobile transmitter to emit a second transmission; (c) making a second estimate of the location of the mobile transmitter on the basis of the second transmission; and (d) combining at least the first and second estimates to obtain an improved, more accurate estimate of the location of the mobile transmitter. Step (b) may comprise auditing the mobile transmitter to elicit an audit response, or terminating the call (hanging up) and then initiating another call by paging the mobile transmitter to elicit a page response. Step (d) preferably comprises averaging a plurality of statistically-independent location estimates.

Abstract: A wireless location system receives signals transmitted by wireless telephones at a plurality of signal collection sites. To improve the accuracy of the location information, the system synthesizes greater bandwidth, and thus greater time resolution, than would otherwise be available. The location system commands an MTSO to make the wireless transmitter to be located change frequency channels, and a doubly-differenced carrier phase of the transmitted signal, or the time difference of arrival, is observed at each of many frequencies spanning the widest possible bandwidth. The phase-measurement data from these many frequencies are combined to resolve the inherent integer-wavelength ambiguity. To begin the process of ambiguity resolution, single-frequency channel, doubly-differenced, group delay measurements are used to resolve the ambiguity in the doubly-differenced phase difference between the most closely spaced frequency channels.

Abstract: A system for determining the location of a mobile transmitter is disclosed. The mobile transmitter receives a message signal and responds to the message signal by transmitting a responsive signal, wherein the responsive signal is indicative of the identity of the mobile transmitter. One preferred embodiment comprises at least three antenna site systems 10, a central site system 12, a database processor for use in connection with various applications, and a map system 16. The system may be employed to locate cellular telephones and/or like devices emitting bursty transmissions, e.g., over messaging or control channels.