Time difference of arrival measurement system

An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter, the transmitted signal consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the audio tone having a phase that varies with time, the apparatus comprising:

• a sensor which includes:
• a receiver which receives a received signal, the received signal being a time delayed version of the transmitted signal, the receiver operable to generate a receiver output signal;
• an encoder for operating on the receiver output signal to generate an encoded signal where the audio tone of the receiver output signal is modeled as having a specific phase at a specific time;
• a decoder which decodes an encoded signal transferred from another sensor to generate a reconstructed signal representative of the transmitted signal received at the other sensor;
• and
• a correlator for correlating the reconstructed signal and the receiver output signal to determine a time difference of arrival of the receipt of the transmitted signal at the respective sensors.

An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the apparatus comprising:

• first and second sensors where each sensor includes
• a receiver for receiving a received signal, the received signal being a time delayed version of the transmitted signal, the receiver operable to generate a receiver output signal including an audio tone and a voice signal;
• an analog to digital converter for operating on the receiver output signal to generate a digitized signal including a sequence of samples representative of the receiver output signal, each sample consisting of one or more bits and the digitized signal having a bit rate proportional to a number of bits per sample and a number of samples in a given time interval;
• an encoder for operating on the digitized signal to generate an encoded signal which has a bit rate lower than the bit rate of the digitized signal;
• and
• a central processor that includes
• a decoder that operates on encoded signals received from each sensor to generate reconstructed signals representative of the received signals;
• and
• a correlator for measuring the time difference of arrival between the reconstructed signals.

An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the apparatus comprising:

• two sensors each including
• a receiver for receiving a received signal including an audio tone and a voice signal, the received signal having a first bit rate associated therewith and being a time delayed version of the transmitted signal;
• an encoder for operating on the received signal to generate an encoded signal having a second bit rate, where the first bit rate is greater than the second bit rate;
• a signal quality monitor for monitoring the signal quality of the received signal;
• means for transferring the encoded signal to another sensor;
• a decoder for decoding an encoded signal received from another sensor to generate a reconstructed signal representative of the received signal at the other sensor;
• and
• a correlator for correlating the reconstructed signal and the received signal for a given sensor to determine a time difference of arrival for receiving the received signals at the respective sensors;
• and
• a central processor including a controller for receiving signal quality results from the signal quality monitor in each sensor, for selecting a reference sensor based on the signal quality results and for prompting the reference sensor to transfer an encoded signal to another sensor.

A method for reducing network bandwidth in a cellular communication system having a plurality of remote cells each including a sensor for determining time difference of arrival measurements between two received signals, each received signal being a time delayed version of a transmitted signal as intercepted at two remote sensors in a cellular communication system, the transmitted signal being generated by a cellular telephone and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the method comprising:

• receiving a received signal from a cellular telephone at two remote sensors;
• generating an arrival signal at each remote sensor including arrival information associated with the received signals including an audio tone and a voice signal, wherein the arrival signal has a first bit rate associated therewith;
• modeling the arrival signal based on one or more signal characteristics to produce an encoded arrival signal, the encoded arrival signal having a second bit rate, where the first bit rate is greater than the second bit rate;
• transmitting the encoded arrival signal to the central processing facility;
• decoding encoded arrival signals from the two remote sensors to reconstruct the arrival signals;
• correlating the reconstructed arrival signals to determine time difference of arrival data.

A method for reducing network bandwidth while determining time difference of arrival measurements between two received signals, each received signal being a time delayed version of a transmitted signal as intercepted at two remote sensors in a cellular communication system, the transmitted signal being generated by a cellular transmitter and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the method comprising:

• receiving a received signal from a cellular telephone at two remote sensors;
• generating an arrival signal at each remote sensor including arrival information associated with the received signal;
• encoding the arrival signal;
• transmitting the encoded arrival signal to a central processing facility;
• selecting the encoded arrival signal from one of the two remote sensors as a reference signal;
• distributing the reference signal to all of the remote sensors;
• at each remote sensor
• decoding the reference signal;
• correlating an arrival signal from one of the remote sensors with the reference signal to determine time difference of arrival data;
• and
• transmitting the time difference of arrival data to the central processing facility.

A method for reducing network bandwidth while determining time difference of arrival measurements between two received signals, each received signal being a time delayed version of a transmitted signal as intercepted at two remote sensors in a cellular communication system, the transmitted signal being generated by a cellular telephone and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the method comprising:

• receiving a received signal from the cellular telephone at two remote sensors;
• selecting one of the remote sensors as a reference remote sensor based on a predetermined signal characteristic of the received signal;
• generating a reference signal at the reference remote sensor including arrival information associated with the received signal at the reference remote sensor;
• transmitting the reference signal to the other remote sensor;
• decoding the reference signal at the other remote sensor to reconstruct the received signal received at the reference remote sensor;
• correlating the received signal at the other remote sensor and the reconstructed received signal to determine time difference of arrival data.

An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the apparatus comprising:

• a first and second sensor where each sensor includes
• a receiver for receiving a received signal and generating an receiver output signal,
• a demodulator for demodulating the receiver output signal and generating a demodulator output signal including an audio tone and a voice signal,
• a filter for limiting the bandwidth of the demodulator output signal and generating a filter output signal,
• an analog to digital converter operating on the filter output signal for generating a digitized signal consisting of a sequence of samples,
• a time standard to control when the analog to digital converter generates samples, and
• network interface for communicating with a network to transmit a representation of the digitized signal to a remote processor, where the representation of the digitized signal is modeled as having a specific phase at a specific time;
• and
• the remote processor including a correlator which operates on the two digitized signals to measure the time difference of arrival between the two received signals.