DESC:TECHNICAL FIELD
The present invention relates to a radar detection system. The invention more particularly relates to an ultrawideband, frequency hopping radar detector for detection of life signs.
BACKGROUND
One of the applications of radar technology in the present era are being used as a life detector, a combination of radar technology associated with biomedical science technology, that can penetrate non-metallic bodies such as interior walls, furniture, building, etc, and provide non-contact and long-range detection of human life signs such as breathing, heartbeat, and body movement. Radar life detector technology is an emerging technology of detection vital signs of living bodies and belongs to a very important advanced technical field.
Radar detection depends on sensing changes induced by the presence of targets of interest in the echo signal in response to the transmitted signal. For instance, the energy-based radar detectors look for instantaneous power of the received signal and compare them with background noise. In contrast target motion results in a change of frequency of the echo; the absolute value of the change in frequency depends on the radial component velocity of the target, higher the radial velocity, higher is the change in frequency. The ability of the radar to detect and discern changes in the returned signal be it in energy or frequency is tightly coupled to the waveform used for transmission and intended application. Selection of particular signal for a radar sensor, therefore, is decided by the nature of problem one intends to solve.
Non-intrusive methods for life signs detection have been much sought after for the advantages they have to offer such as remote sensing of the presence of humans in low visibility conditions or in cases when the sensor is occluded by barriers hampering detection, for example, video camera-based surveillance. Near range sensing using radar finds utility in such situations as it is not only an all-weather sensing technique but also microwave signals used in radar can penetrate through barriers.
Recent applications where radar sensing has made good use case are all-weather perimeter sensing, see-through wall sensing, detection of life signs through barriers/debris, etc. Radars meant for such applications have detection ranges of the order of few tens to hundreds of meters and are designed for high range (of the order of few centimeters to even millimeters) and radiometric resolution.
See-through barrier sensors have been built for detection of gross motion of intended targets such as walking humans. As see-through wall sensors are of inherently very wideband nature, detecting moving targets are achieved by the following techniques: 1. Wall echo, and antenna cross talk removal by the principle of stationary phase; 2. Mitigation of radar returns from non-moving scatterers such as furniture, and interior structures by the moving target indication principle which is based on the fact that the phase of the returned signal from stationary targets does not change.
Detection of walking humans by range profiling of frequency domain data sampled by the transceiver after the above two processing steps detection of humans is a challenging problem especially in the case of sensing through barriers such as walls due to the fact that the applicable cross-section of the human body is extremely small against objects generally found in see-through wall sensing case for instance. Moreover, tissues of the human body, due to high permittivity, absorb most of incident electromagnetic energy and only a fraction returns to the receiver. The electromagnetic signal transmitted by radar is severely attenuated by the barrier through which sensor illuminates resulting low signal to noise ratio (SNR) at the processor. This phenomenon makes it extremely difficult to detect the changes induced by human activity on the far side of the wall.
US 9442189 titled “Multichannel UWB-based radar life detector and positioning method thereof” describes a multichannel UWB-based radar life detector includes a transmitting antenna and three receiving antennas for forming three radar echo signal channels.
US 9610015 titled “Radar apparatus for detecting multiple life—signs of a subject, a method and a computer program product” describes an invention that relates to a radar apparatus for detecting a life-sign of a subject, comprising a transmitter system for emitting a transmission electromagnetic beam to the chest and/or the abdomen of a subject, a receiving system for receiving first reflected electromagnetic beam data from the chest and/or the abdomen, and a processor unit for processing the first received beam data retrieving breath activity information.
US 7725150 titled “System and method for extracting physiological data using ultra-wideband radar and improved signal processing techniques” discloses a ultra-wideband (UWB) radar known as micropower impulse radar (MIR) combined with advanced signal processing techniques to provide a new type of medical imaging technology including frequency spectrum analysis and modern statistical filtering techniques to search for, acquire, track, or interrogate physiological data. Range gate settings are controlled to depths of interest within a patient and those settings are dynamically adjusted to optimize the physiological signals desired.
Hence, there is a need for a method and a detector that detect the changes induced by human activity on the far side of the wall.
SUMMARY
The present invention provides a method and UWB-based radar transceiver system to detect life signs by illuminating the scene under surveillance. This summary is neither intended to identify essential features of the present invention nor is it intended for use in determining or limiting the scope of the present invention.
For, example various embodiments herein may include one or more systems to integrate the concept of realizing simultaneous detection and ranging of stationary human beings making use of Doppler induced by life signs. The UWB (ultra-wideband) based radar transceiver detector to detect life signs is employed for illuminating the scene under surveillance using digital techniques to obtain a signal having information regarding the presence of life signs while seeing through barriers. In one embodiment the UWB based radar transceiver detector includes at least two swept frequency synthesizers, one or more mixers, a transmitter, a receiver, a plurality of analog to digital converters, a data compression unit, a data acquisition unit, and a processing device.
The at least two swept frequency synthesizers is configured to generate frequency hopping (FH) UWB probing signals, wherein said synthesizers are configured on same frequency reference oscillator (REF OSC). Further, the detector includes the transmitter that transmits the FH-UWB signals towards targets. The one or more mixers are configured for frequency translation to baseband signals. The receiver of the detector receives bounced back information-bearing FH-UWB signals from the targets. The targets may be stationary or moving targets. The plurality of ADC is configured to digital down-conversion of the received FH-UWB signals. The data compression unit transports these digitized signals over Ethernet to the processing device. Further, the processing device performs signal processing method on the digitized signals.
The data acquisition unit of the detector receives phasor signals. Theses phasor signals contain phase reference signals received at phase reference channel (PRC) and bounced back echo received signals received at received echo channel (RX), the former representing phase difference between the transmitted signals and a reference synthesizer, and later representing the echo from life signs, and other unwanted obstacles signals.
The phase reference channel module (PRC) of the processing device measures phase difference between the transmitted signals and phase reference synthesizer signals, and a detection module measure a relative phase difference between the phase reference channel module signals and the received signals at receiver echo channel (RX) under low signal to noise ratio to detect micro motion due to life signs. These received signals contain life signs signals and other unwanted obstacles signals. The unwanted obstacles signals have to be removed to obtain a signal representing micro motion due to life signs. So, the phasor signals received at data acquisition unit is passed through a filter, preserves only the micromotion data due to life signs.
In another embodiment, a method to detect life signs by a UWB based transceiver radar detector is described in the present invention. The said method comprising: generating, by at least two swept frequency synthesizers, frequency hopping (FH) UWB probing signals, wherein said synthesizers are provided with same frequency reference oscillator; frequency translation, by one or mixers, to a baseband signals; transmitting, by a transmitter, the FH-UWB signals towards targets; receiving, by a receiver, bounced back information-bearing FH-UWB signals from the targets; converting, by a plurality of ADC , the received information-bearing FH-UWB signals; transporting, by a data compression unit , digitized signals over Ethernet; receiving, by a data acquisition unit, a phasor signals; performing, by a processing device, signal processing method on the digitized signals; measuring, by a phase reference channel module, phase difference between the transmitted signals and reference synthesizer signals; measuring, by a detection module, a relative phase difference between the phase reference channel module signals and the received signals under low signal to noise ratio to detect micro motion due to life signs; passing, by a filter, the phasor signals; storing, by a memory, the filtered signals; and detecting of Doppler in slow time to achieve micro motion due life signs.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and modules.
Fig. 1 illustrates a schematic diagram depicting the detection of life signs by a UWB based radar transceiver detector, according to an exemplary implementation of the present invention.
Fig. 2 illustrates a schematic diagram depicting a frequency-hopping signal, according to an exemplary implementation of the present disclosure.
Fig. 3 illustrates a schematic diagram of the movement of a heart muscle depicted as a vibrating object, according to an exemplary implementation of the present invention.
Fig. 4 illustrates a schematic diagram depicting UWB based radar transceiver detector architecture, according to an exemplary embodiment of the present invention.
Fig. 5 illustrates a schematic diagram depicting a range-Doppler matrix after colour mapping depicting heartbeat detected at 2.8 m in single target case, according to an exemplary implementation of the present invention.
Fig. 6 illustrates a schematic diagram depicting multiple stationary humans detected at 2.5m, 4.2 m, and 5.5 m, according to an exemplary implementation of the present invention.
Fig. 7 illustrates a flow chart of a method to detect life signs by a UWB based radar transceiver detector, according to an exemplary implementation of the present invention.
DETAILED DESCRIPTION
The various embodiments of the present disclosure describe a method and UWB based radar detector of realizing simultaneous detection and ranging of stationary human beings making use of Doppler induced by life signs such as heartbeat, and respiration. An ultra-wideband (UWB), frequency hopping radar detector is employed as transceiver for illuminating the scene under surveillance, the scene may include barriers such as walls, and debris in front of the sensor antenna occluding the object of interest, and stationary, inanimate objects such as interior walls, furniture, etc. In a particular realization, the method is implemented using digital techniques on processing unit with an intuitive display (not shown) for operator interface in combination with the detector to provide useful information regarding presence of life signs while seeing through barriers.
In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure may be practiced without these details. One skilled in the art will recognize that embodiments of the present disclosure, some of which are described below, may be incorporated into a number of systems.
However, the systems and method are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present invention and are meant to avoid obscuring of the present invention.
It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
In one of the embodiments of the present disclosure, a UWB based radar transceiver detector to detect micro motion due to life signs using frequency hopping ultra wide-bands signals in non-line of sight sensing scenario is disclosed. The said detector consists of a high fidelity transceiver. The radar transceiver includes at least two swept frequency synthesizers configured to generate frequency hopping (FH) UWB probing signals, said synthesizers are configured on same frequency reference oscillator, a one or more mixers for frequency translation to a baseband, a transmitter configured to transmit the FH-UWB signals towards targets, a receiver configured to receive bounced back information-bearing FH-UWB signals from the targets, a plurality of ADC configured to signal down-conversion of the received information-bearing FH-UWB signals, a data compression unit configured to transport digitized signals over Ethernet, a data acquisition unit configured to receive a phasor signals, a processing device configured to perform signal processing method on the digitized signals, a phase reference channel module configured to measure phase difference between the transmitted signals and reference synthesizer signals, and a detection module configured to measure a relative phase difference between the phase reference channel module signals and the received signals under low signal to noise ratio to detect micro motion due to life signs.
In an exemplary embodiment, detection of life signs by the UWB based radar transceiver detector is described. The UWB based radar transceiver detector is used to illuminate through the walls of the room and detect both stationary and moving subjects by analysing signals scattered by the objects inside the room. There is no direct line sight available to infer any situational awareness such as a number of subjects present inside the room using optical sensors remotely. The radar echoes or the bounced back information-bearing FH-UWB signals from inside the room represent a composite signature from subjects, and inanimate objects such as furniture, interior walls, etc. In order for identifying returns from human subjects is to separate or mitigate the radar signatures from the inanimate objects, and enhance the signatures from life signs due to the humans present inside the room.
When a radar signal interacts with the target, the information-bearing reflected signal depends on a number of factors, including the target’s RCS and time-varying range or range rate, among others. For rigid-body targets such as the aircraft in the case of a pulse-Doppler radar, virtually all points comprising the target move at the same speed relative to the radar, leading to a constant Doppler shift in the frequency of the reflected signal received by the radar.
In another exemplary embodiment of the present invention, detection of human targets through occlusions using ultra wide-band (UWB) based radar detector is provided. The said detection of human targets through occlusions using said detector is generally achieved making use of the fact that time of arrival (inferred as a range by radar) of echo changes over frames (i.e. bursts of consecutive transmissions) due to gross movement such as walking. Frame difference techniques provide information about the presence of targets of interest, by removing echoes from stationary objects like furniture, etc. The UWB nature of the waveform can measure the target range with high-resolution frame by frame. If, however, there is motion, vibration, or rotation, in addition to bulk translation, then sidebands about the target’s bulk Doppler frequency are generated. Such micro-Doppler signals may be the result of reflections from the wheels of vehicles, aircraft propellers, and helicopter blades, as well as the vibration-like movement of human heart muscles and chest wall.
In another embodiment of the present invention, detection of stationary humans through barriers is provided. Detection of stationary humans through the barriers, it is imperative to make use of echo modulation induced by breathing and heartbeat. The translational movement (i.e. projection along the line of sight of the radar) of heart muscles or chest surface is of the order that is less than the wavelength (typically 5 to 10cm) of signals used for sensing through the barrier, and gross motion will be absent which leads to failure of frame differencing technique and so forth.
It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
Fig. 1 illustrates a schematic diagram depicting the detection of life signs using frequency hopping ultra-wideband based radar transceiver detector. The detector includes at least two swept frequency synthesizers (102), a transmitter (104), a receiver (106), one or mixers (108), ADC converters (110), a data compression unit (112), a data acquisition unit (114), a processing device (116) comprises a phase detection module (118) and a detection module (120), a filter (122), a memory (124), a plurality of computing device 126n, a network (128), and a database (130).
The network (128) interconnects the devices (126n) and the database (130) with the processing device (116). The network (128) includes wired and wireless networks. Examples of the wired networks include a wide area network (WAN) or a local area network (LAN), a client-server network, a peer-to-peer network, and so forth. Examples of the wireless networks include Wi-Fi, a global system for mobile communications (GSM) network, a general packet radio service (GPRS) network, an enhanced data GSM environment (EDGE) network, 802.5 communication networks, code division multiple access (CDMA) networks, or Bluetooth networks.
In the present implementation, the database (130) may be implemented as an enterprise database, a remote database, local database, and the like. The database (130) may be located within the vicinity of the processing device (116) or may be located at different geographic locations as compared to that of the processing device (116). Further, the database (130) may themselves be located either within the vicinity of each other or may be located at different geographic locations. Furthermore, the database (130) may be implemented inside the processing device (116) or the database (130) may be implemented as a single database or a separate unit.
The memory (122) may be coupled to the processing device (116). The memory (122) can include any computer-readable medium known in the art including, for example, volatile memory, such as static random access memory (SRAM) and dynamic random access memory (DRAM), and/or non-volatile memory, such as read-only memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes. The memory (122) also includes a cache memory to work with the processing device (116) more effectively.
Furthermore, the at least two swept frequency synthesizers (102) generate FH-UWB probing signals. The at least two swept frequency synthesizers (102) are configured on same frequency REF OSC (206). The at least two swept frequency synthesizers (102) are transmitter synthesizer (102-a) and a phase reference synthesizer (102-b). The one or more mixers (108) are configured for frequency translation to the FH-UWB signals. The transmitter (104) transmits the FH-UWB signals towards targets to detect the life signs. Further, the receiver (106) receives bounced back information-bearing signals from the targets. This received back signals are passed through the ADC (110) to signal down-conversion of the received information-bearing signals. Further, a data compression unit (112) is configured to transport the digitized signals of ADC over the Ethernet to the processing device (116). The processing device (116) performs signal processing method on the digitized signals.
Further, the PRC module (118) of the processing device (116) measure the phase difference between the transmitted signals and phase reference synthesizer signals. The detection module (120) measures a relative phase difference between the PRC module (118) signals and the received signals at RX (408) under low signal to noise ratio to detect micro motion due to life signs. The data acquisition unit (114) receives the phasor signals which have the micro motion information due to life signs and other unwanted object signals.
Further, the received phasor signals are passed through a filter (124) which preserves only the micro motion data due to life signs and said micro motion is represented on Range-Doppler matrix map by representing Doppler in slow time.
Fig. 2 illustrates a schematic diagram depicting frequency-hopping signal used for the UWB based radar transceiver detector. The figure described in the present invention depicts a time vs. frequency plot of the UWB signals transmitted by the transmitter (102). Effective bandwidth (h) of transmitted signal translates to a range resolution of 15cm approximately. The initial frequency of the transmitted UWB signal is? f?_0 is chosen optimally such that composition of the wall material is transparent to electromagnetic signals belonging to the entire band of operation of the detector. In particular realization, frequency of the signal is stepped up by an amount ?f=f_(i+1)-f_i=5MHz successively after a time duration T_f=t_(i+1)-t_i=100µs which can be called dwell time per spot frequency. Step frequency ?fdecides maximum unambiguous range achievable by the UWB radar system which is 30m in the present invention.
The transmitter (102) steps through N_f=200 frequencies over a duration of? T?_s=N_f T_f=20ms. The waveform is repeated at every 40ms intervals which results in a waveform repetition frequency (WRF) of f_wrf=1/T=25Hz.The waveform silence duration td accounts for digital data transmission to the processing device (116) after signal acquisition from one burst of transmission. The WRF should be chosen such that it is twice the maximum expected Doppler to satisfy Nyquist’s sampling criterion for unambiguous detection. As the Doppler frequencies encountered in the present invention is very low, WRF of 25Hz is a good choice. For the FH signal sequence, the transmitted signal is represented by:

Here p(t) is a unit pulse of t_n=100us duration. The reflected back echo signal is a delayed and scaled replica of the transmitted signal. The delay is proportional to range from the radar based detector, and scale is proportional to the radar cross-section (RCS) of the target. So, the echo signal is:

The objective of the present invention is to find the delay t which encodes the range of the object of interest. In case of life signs the delay t is itself a function of time i.e. t(t). For example, the heart muscle can be considered as a vibrating object radiated by the radar signal with ?d being the amplitude of vibration, as shown in figure (2). As the rate of human heart beat is 72 systolic cycles per minute (on an average), the frequency of vibration works out to be f_H=1.2Hz. Delay equation which captures vibration of heart muscle will be:
t(t)=(2r(t))/c=2[r_0+?d sin(?_H t+f_H)]/c (3)
wherer_0is the range at which subject is positioned, ?_H=2pf_H is the angular frequency of the heartbeat, f_H is the initial phase of the heartbeat signal seen by the receiver, and c is the velocity of light in free space. As the frequency of heartbeat is low compared to WRF, Doppler induced is observed across successive bursts at each spot frequency, thus sampling frequency for Doppler detection will be 25Hz which satisfies Nyquist’s criterion for signal sampling (Doppler due to heartbeat in the radar echo is in the range of one to two Hz).
Fig. 3 illustrates a schematic diagram of the movement of heart muscle depicted as the vibrating object. The figure of the present invention shows that the heart muscle is considered as a vibrating object radiated by the radar signal with ?d being the amplitude of vibration. As the rate of the human heartbeat is 72 systolic cycles per minute (on an average), the frequency of vibration works out to be f_H=1.2Hz. Delay equation which captures vibration of heart muscle will be:
t(t)=(2r(t))/c=2[r_0+?d sin(?_H t+f_H)]/c (3)
wherer_0is the range at which subject is positioned, ?_H=2pf_H is the angular frequency of the heartbeat, f_H is the initial phase of the heartbeat signal seen by the receiver, and c is the velocity of light in free space.
Fig. 4 illustrates a schematic diagram depicting the UWB based radar transceiver detector architecture. The detector described in the present invention includes at least two swept frequency synthesizers (102) that generate FH-UWB signals. The at least two swept frequency synthesizers (102) two swept frequency synthesizers (102) are the transmitter synthesizer (102-a) and the phase reference synthesizer (102-b). Both the synthesizers are provided with the same reference oscillator as a frequency REF OSC (402). The output of the transmitter synthesizer (102-a) is fed to a power divider (PD) (204-a), one arm of which provides signal to the transmitter (104) through an amplifier (AMP). Power level transmitted depends on the specific application, whereas in the present invention transmitted signal power is less than one mill watts.
Further, the second arm of the PD (204-a) is fed to an RF port of mixer M1. The one or more mixers (108) are mixer M1 and mixer M2. The phase PRC module (118) measures phase difference between the transmitted signal and reference synthesizer signals. The IF port of M1 at PRC module (118) measures phase difference between transmitted FH-UWB signal and the reference synthesizer signal of the phase reference synthesizer (102-b). The phase reference synthesizer (102-b) generates the same waveform as transmitter synthesizer (102-a), but with a deviation of intermediate frequency (IF). In order to prevent intermodulation products from mixers (108), IF has to be chosen appropriately, which in the present invention is taken 10.7MHz. The microwave signal from the phase reference synthesizer (102-b) is fed to LO port of the mixers M1 and M2 after power division performed by a power divider (204-b), and suitable amplification to obtain optimum performance of the mixers (108). Thus phase reference synthesizer (102-b) provides phase-frequency reference to the mixers (108).
Further, the transmitted signal that bounces off objects from the illuminated scene is received by the receiver (106). A low noise amplifier (LNA) (210) operating in the linear region is used to scale up the received signal and fed to RF port of the mixer M2. The bounced back echo signals contain all the information including the target range, and micro motion related information which is encoded in the phase of the bounced back echo received signal. The phase of the signal at IF port of mixer M2 (Received echo channel) carries all information required for detection of life signs. The frequency hopping nature of the UWB signal implies that its phase at each spot frequency is random, i.e. each frequency step in waveform has a different phase. The frequency hopping nature of the UWB signal implies that its phase at each spot frequency is random, i.e. each frequency step in waveform has a different phase. The detection module (120) measures a relative phase difference between the PRC module (118) signals and the received signals at RX (408) low signal to noise ratio to detect the micro motion due to life signs. In order to measure the phase difference between the PRC module signals and the bounced back received echo signals, phase of the transmitted signal is required. So, the phase of the transmitted signal is measured by the PRC module (118). The phase of the transmitted IF signal at M1 of the PRC (118) is actually measurement of the phase of the transmitted signal at each frequency step.
Further, Doppler due to the life signs is detected using IF signals from PRC and RX channels. The two IF signals at 10.7MHz have required information regarding the phase of the transmitted signal, and target echo:

Here, in equation (5), N_T is the number of targets illuminated by the detector which include, in addition to the life signs, barrier in line-of-sight of the sensor, interior walls, and objects inside the room. The two IF signals are digitized using ADC (110) by employing critical sampling which results in alternate samples from each channel representing in-phase (I) and quadrature (Q) channel phasors. Normally digital receivers use numerically controlled oscillator to obtain phasor measurements from IF signals. But, here critical sampling is employed, for instance an ADC sampling frequency which is radix of two times IF frequency, the I/Q samples are naturally ordered as alternate sample points.
Data acquisition as described above results in a high data rate as there are 100us × 2^r f_if samples per spot frequency, where r is the radix factor used for critical sampling. The Phasor for PRC (118) and RX channels (408) at each spot frequency are calculated as:
I_(n,prc)+jQ_(n,prc)=1/M ?_(k=1)^M¦??if?_prc (2kT_s)?+j/M ?_(k=1)^M¦??if?_prc (2kT_s-T_s)? (6)
I_(n,rx)+jQ_(n,rx)=1/M ?_(k=1)^M¦??if?_rx (2kT_s)?+j/M ?_(k=1)^M¦??if?_rx (2kT_s-T_s)? (7)
Here 2M is the total number of samples acquired over one frequency dwell, n is the frequency step-index, T_s=1/(2^r f_if ) is the sampling interval.
One sample per spot frequency sufficiently encodes the target scene as changes in the received signal due to life signs are very gradual compared to the dwell time per frequency (100us) during the waveform burst. The averaging scheme of 2M samples in (6) and (7) helps to reduce the phasor variance due to random noise in the data acquisition process.
In an exemplary implementation of the present invention, measuring the relative phase difference to detect the life signs are provided. The signals from the phase reference channel module (118) and the received echo channel (410) as seen from equation (6) and equation (7), are the phasor quantities (complex values), the former representing phase difference between the transmitted signal and the reference synthesizer signal as in equation (4), latter representing the echo from life signs, and other the unwanted obstacles as in equation (5) (i.e. out N_T targets all are not of our interest). The Relative phase difference between the two phasors is now determined at each spot frequency as:
I_(n,diff)+jQ_(n,diff)=(I_(n,prc)+jQ_(n,prc) )^* (I_(n,rx)+jQ_(n,rx) ) (8)
Letting N_ls to be the number of objects with life signs, N_stto be number of stationary objects including barrier in the line of sight of the sensor, interior walls, and other inanimate objects in the room, the resultant phase difference signal in equation (8) is written as:

The signal sample is resolved into stationary and non-stationary components. Such decomposition is valid due to FH nature of the signal. It is seen from equation (9) that the stationary component of the signal is constant across each step of the FH waveform. An estimate of the constant part of phase difference signal (I_(n,diff)+jQ_(n,diff)) across the swept sequence is obtained as: c+jd= 1/N_f ?_(n=1)^(N_f)¦??(I?_(n,diff)+jQ_(n,diff))?.
An estimate of moving the only component of (9) is obtained as:? p?_n+jq_n=?(I?_(n,diff)+jQ_(n,diff))-(c+jd) for all n=(1,2,…,N_f). The complex sequence ? p?_n+jq_n represents target reflectivity of the life signs as all stationary contributions to the composite signal have been removed. An inverse Fourier transform (IFT) of the sequence ? p?_n+jq_n generates synthetic range profile of the objects with life signs only. The IFT can be realized in practice using fast Fourier transform (FFT) method for reduction in computational complexity. The FFT output of target reflectivity samples ? p?_n+jq_n from each waveform burst is stored as: {IFFT(? p?_n+jq_n ):n=1,2,…,N_f }_bwhere b indicates the burst index of the transmitted waveform as depicted in figure (1). An IFFT of length 512 or 1024 is sufficient for a burst of 200 frequencies as in our specific realization.
As Doppler in the returned signal due to life sign is very low on the frequency scale, echo signals have to be observed for time duration larger than the reciprocal of minimum Doppler that the sensor has to detect, i.e. T_obs=1/f_(d,min) .
As human signs cause a Doppler in the range of 1 or 2Hz, observation time of 4 seconds is sufficient for analysis.
For observation of say 6 seconds, number of waveform bursts acquired will be 25Hz ×6s=150. The IFFT sequence computed from each burst is stored as columns of an observation matrix: [O_M ] of size 1024 x 150.
The samples in the column dimension of the matrix can be considered fast time samples as successive samples are separated by 1/h sec, where h is the effective bandwidth of the FH signal. Similarly along row dimension samples can be considered as slow time samples with a time separation of 1/f_wrf sec.
Life signs can only be observed and detected in the slow time dimension, i.e. across waveform bursts, and not in one spot frequency duration (100us) due to low periodicity of the vibration of chest wall or heart muscles.
The rows of the observation matrix [O_M ] capture the phase variation in the received signal due to life signs over an interval of? T?_obs. So, a Fourier transform along the rows of [O_M ] can compute the spectrum of the slow time signal. As there are 150 samples in each row of the matrix, Fourier transform is calculated using 256 point FFT to generate the spectrum. The resultant 2-D structure can be called range-Doppler image. It is a 2-D array of complex numbers with dimension 1024 x 256. An absolute operation on the matrix abs{(? real(o?_(m,n))+j? imag(o?_(m,n) ):m=1,2,…1024,n=1,2,…,256} generates an image of the same dimension with row index representing range of objects, and column index representing Doppler value. Elements of the matrix can be mapped using a colour map that indicates strong objects brighter, and weak ones with lighter colour as shown in figure (5) and (6).
Fig. 5 illustrates a schematic diagram depicting a range- Doppler matrix after colour mapping on a map depicting heartbeat detected at 2.8 m in single target case.
Fig. 6 illustrates a schematic diagram depicting multiple stationary humans detected at 2.5m, 4.2 m, and 5.5 m, according to an exemplary implementation of the present invention. The figure shows range- Doppler matrix on the map after colour mapping depicting multiple stationary humans detected at 2.5m, 4.2 m, and 5.5 m.
Referring now to Fig.7 which illustrates a flow chart (700) of a method for detecting life signs by a UWB based radar transceiver detector, according to an exemplary implementation of the present invention. The flow chart (700) of Fig.7 is explained below.
At step 702, generating, by at least two swept frequency synthesizers, frequency hopping (FH) UWB probing signals, wherein said synthesizers are provided with same frequency reference oscillator (202);
At step 704, frequency translation, by one or mixers (108), to a baseband signal;
At step 704, transmitting, by a transmitter (104), the UWB FH signals towards targets;
At step 706, receiving, by a receiver (106), bounced back information-bearing UWB FH signals from the targets;
At step 708, converting, by a plurality of analog to digital converters (ADC) (110), the received information-bearing UWB FH signals;
At step 710, transporting, by a data compression unit (112), digitized signals over Ethernet ;
At step 712, receiving, by a data acquisition unit (114), a phasor signals;
At step 714, performing, by a processing device (116), signal processing method on the digitized signals,
At step 716, measuring, by a phase reference channel module (118), phase difference between the transmitted signals and reference synthesizer signals;
At step 718, measuring, by a detection module (120), a relative phase difference between the phase reference channel module signals and the received signals under low signal to noise ratio to detect micro motion due to life signals;
At step 720, passing, by a filter (122), the phasor signals;
At step 722, storing, by a memory (124), the filtered signals; and
At step 724, detecting of Doppler in slow time to achieve micro motion due the life signs.
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.

Reference Numerals:
Swept Frequency Synthesizers: 102
Transmitter (Tx): 104
Receiver (Rx): 106
Mixers: 108
ADC Converters: 110
Data Compression Unit: 112
Data Acquisition Unit: 114
Processing Device: 116
PRC: 118
Detection Module: 120
Memory: 122
Filter: 124
Computing Devices: 126n
Network: 128
Database: 130
Transmit Synthesizer: (102-a)
Phase Reference Synthesizer: (102-b)
REF OSC: 402
Power Divider1: (404-a)
Power Divider 2: (404-b)
Received Echo Channel: 408
LNA: 410

,CLAIMS:

1. A UWB (ultra-wideband) based radar transceiver detector to detect life signs, the detector comprising:
at least two swept frequency synthesizers (102) configured to generate frequency hopping (FH) UWB probing signals, wherein said synthesizers (102) are configured on same frequency reference oscillator (206);
a transmitter (104) configured to transmit the UWB FH signals towards targets;
a receiver (106) configured to receive bounced back information-bearing UWB FH signals from the targets;
one or more mixers (108) configured for frequency translation to the UWB FH signals;
a plurality of analog to digital converters (ADC) (110) configured to signal down-conversion of the received information-bearing UWB FH signals;
a data compression unit (112) configured to transport digitized signals over Ethernet;
a data acquisition unit (114) configured to receive a phasor signals; and
a processing device (116) configured to perform signal processing method on the digitized signals, wherein the processing device (116) comprising:
a phase reference channel module (PRC) (118) configured to measure phase difference between the transmitted signals and phase reference synthesizer signals; and
a detection module (120) configured to measure a relative phase difference between the phase reference channel module (118) signals and the received signals at receiver echo channel (RX) (408) under low signal to noise ratio to detect micro motion due to life signs.
2. The detector as claimed in claim 1, wherein the targets are stationary as well as moving targets.
3. The detector as claimed in claim 1, wherein the at least two swept frequency synthesizers (102) are transmitter synthesizer (102-a) and a phase reference synthesizer (102-b).
4. The detector as claimed in claim 3, wherein the transmitter synthesizer (102-a) output is fed to a power divider (204-a).
5. The detector as claimed in claim 4, wherein the power divider (404-a) one arm transmits signal towards the transmitter (104) through an amplifier and the second arm of the power divider (404-a) is fed to an RF port of a mixer M1.
6. The detector as claimed in claim 1, wherein the mixer M1 intermediate frequency port captures the phase difference between transmitted signal and the phase reference synthesizer signals (102-b).
7. The detector as claimed in claim 3, wherein the phase reference synthesizer (102-b) is configured to generate signals similar to transmitter synthesizer (102-a), with a deviation of intermediate frequency.
8. The detector as claimed in claim 7, wherein the generated signal is fed to the mixer M1 and a mixer M2, after power division of the signals by a power divider (404-b).
9. The detector as claimed in claim 1, wherein the received signal is transmitted to a low noise amplifier (410).
10. The detector as claimed in claim 8, wherein the low noise amplifier (410) is configured to scale up the received signal and fed to RF port of the mixer M2.
11. The detector as claimed in claim 1, wherein the micro motion-related information and other unwanted obstacles signals is within in the phase of the bounced back received echo signals.
12. The detector as claimed in claim 1, wherein the phasor signals received at data acquisition unit (114) is passed through a filter (124), preserves only the micro motion data due to life signs.
13. A method to detect life signs by a UWB based transceiver radar detector, the said method comprising:
generating, by at least two swept frequency synthesizers, frequency hopping (FH) UWB probing signals, wherein said synthesizers are provided with same frequency reference oscillator (202);
frequency translation, by one or mixers (108), to a baseband signal;
transmitting, by a transmitter (104), the UWB FH signals towards targets;
receiving, by a receiver (106), bounced back information-bearing UWB FH signals from the targets;
converting, by a plurality of analog to digital converters (ADC) (110), the received information-bearing UWB FH signals;
transporting, by a data compression unit (112), digitized signals over Ethernet;
receiving, by a data acquisition unit (114), a phasor signals;
performing, by a processing device (116), signal processing method on the digitized signals,
measuring, by a phase reference channel module (118), a phase difference between the transmitted signals and reference synthesizer signals;
measuring, by a detection module (120), a relative phase difference between the phase reference channel module signals and the received signals under low signal to noise ratio to detect micro motion due to life signs.
passing, by a filter (122), the phasor signals;
storing, by a memory (124), the filtered signals; and
detecting of Doppler in slow time to achieve micro motion due the life signs.