Method and apparatus for detecting a signal from a noisy environment and fetal heartbeat obtaining method

The method of generating a noise-cancelled output signal in a system comprising a primary sensor for detecting a primary signal from a primary signal source and a plurality of reference sensors for detecting noise source signals, comprising the steps of:

• detecting a primary output signal from said primary sensor;
• detecting a reference output signal from each of said reference sensors;
• comparing said primary output signal with each of said reference output signals and generating primary comparison data;
• comparing each of said reference output signals with other reference output signals and generating reference output signal comparison data;
• processing said comparison data for identifying data representing mutually independent noise source signals in said reference sensor output signals;
• generating filter constants based on information derived from said data representing mutually independent noise source signals, and said primary comparison data;
• applying said filter constants to said reference sensor output signals to generate filtered reference sensor output signals;
• and
• subtracting said filtered reference sensor output signals from said primary sensor output signal to generate a noise-cancelled primary signal.

A method for generating a noise-cancelled primary signal in a noisy environment, comprising the steps of:

• placing at least one primary sensor in a position to primarily detect said primary signal;
• placing a plurality of reference sensors, at least equal in number to the number of known noise sources, in a position to detect primarily noise source signals;
• detecting over a predetermined period of time a primary output signal from said at least one primary sensor and an output signal from each of said reference sensors;
• defining a plurality of time delays;
• comparing said primary output signal and each of said reference output signals at a specified time with all of said reference output signals at a time delayed from said specified time by said defined delay times, and generating correlation data;
• constructing a matrix having as the matrix component data values representing correlation among said reference output signals;
• mathematically reducing said matrix to a diagonal matrix having diagonal matrix components;
• comparing said diagonal matrix components to a predetermined threshold value;
• inverting certain of said diagonal matrix components having values greater than said threshold value;
• computing filter constants using said inverted components and data defining correlation among said primary output and said reference output signals;
• generating filtered output signals by applying said filter constants to each of said reference output signals;
• subtracting said filtered output signals from said primary output signal, thereby generating data representing said noise-cancelled primary signal;
• and
• synthesizing said noise-cancelled primary signal.

A method of generating a modified output signal in a system comprising at least one primary sensor for detecting signals generated by a primary signal source and a plurality of reference sensors for detecting signals from sources other than said primary source, comprising the steps of:

• detecting a primary sensor output signal from said at least one primary sensor and reference sensor output signals from each of said plurality of reference sensors;
• comparing said reference sensor output signals and identifying mutually independent noise source components of said reference sensor output signals;
• generating filter constants using said identified components;
• modifying each of said reference sensor output signals by said filter constants to generate modified reference output signals;
• and
• generating a modified output signal by subtracting components corresponding to said modified reference output signals from said primary sensor output.

Apparatus for generating an output signal representative of a signal source, comprising:

• a primary sensor for detecting signals from a primary signal source and generating a primary sensor output signal;
• a plurality of reference sensors, each for detecting signals from other signal sources and for generating a reference sensor output signal;
• means responsive to receipt of the reference sensor output signals to identify mutually independent noise source components of the received reference sensor output signals;
• means for generating filtered reference signals from received reference sensor output signals using identified mutually independent noise source components;
• and
• means responsive to a received primary sensor output signal for generating a system output signal by subtracting from the primary sensor output signal components corresponding to the filtered reference signals.

The method of generating a noise-cancelled output signal in a system comprising a primary sensor for detecting a signal from a primary signal source and a plurality of reference sensors for detecting noise source signals, comprising the steps of:

• detecting primary output signals from the primary sensor;
• detecting reference output signals from each of the reference sensors;
• storing a data record of signal values representative of values of the detected primary output signals and reference output signals;
• performing a transformation into the frequency domain of the stored signal values;
• comparing frequency domain values representative of output signals of each of said reference sensors with frequency domain values representative of output signals of the primary sensor and other reference sensors and generating reference output comparison values;
• processing said reference output comparison values for identifying values representing mutually independent noise source signals in the reference sensor output signals;
• generating filter constants based on information derived from the values representing mutually independent noise source signals and storing the filter constants;
• retrieving the stored data record and performing a transformation into the frequency domain of signal values representative of the primary sensor output signals and the reference sensor output signals;
• applying the stored filter constant values to the data record values to generate values representative of filtered reference sensor output signals;
• generating difference values by subtracting the values representative of filtered reference sensor output signals from values representative of primary sensor output signals;
• and
• performing an inverse transformation from the frequency domain into the time domain of the difference values to generate a time-domain representation of a noise-cancelled primary signal.

An arrangement for generating an output signal representative of a primary signal source in the presence of other signal sources, comprising:

• a primary sensor for detecting signals from the primary signal source and generating an analog primary sensor output signal comprising a plurality of signal components;
• a plurality of reference sensors for detecting signals from the other signal sources and generating a corresponding plurality of analog reference sensor output signals comprising signal components attributable to mutually independent signal sources;
• analog to digital converter circuitry connected to the primary and reference sensors for converting the analog primary sensor output signal and the reference sensor output signals to a digital primary output signal and a plurality of digital reference output signals;
• signal generating apparatus connected to the converter circuitry and responsive to the plurality of reference output signals to generate a corresponding plurality of modified reference output signals, the modified reference output signals comprising only signal components corresponding to signal components other than signal components attributable to mutually independent signal sources;
• and
• signal generating apparatus responsive to the primary output signal to modify the primary output signal and to generate a modified primary output signal having only signal components other than signal components corresponding to components of the modified reference output signals.