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WO2012056357A1 - System and method for presence detection - Google Patents

System and method for presence detection Download PDF

Info

Publication number
WO2012056357A1
WO2012056357A1 PCT/IB2011/054559 IB2011054559W WO2012056357A1 WO 2012056357 A1 WO2012056357 A1 WO 2012056357A1 IB 2011054559 W IB2011054559 W IB 2011054559W WO 2012056357 A1 WO2012056357 A1 WO 2012056357A1
Authority
WO
WIPO (PCT)
Prior art keywords
signals
target
location
detection system
receivers
Prior art date
Application number
PCT/IB2011/054559
Other languages
French (fr)
Inventor
Ying Wang
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2012056357A1 publication Critical patent/WO2012056357A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/06—Systems determining position data of a target
    • G01S13/46—Indirect determination of position data
    • G01S13/48—Indirect determination of position data using multiple beams at emission or reception
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/04—Systems determining presence of a target
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/06—Systems determining position data of a target
    • G01S13/42—Simultaneous measurement of distance and other co-ordinates
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/02—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using radio waves
    • G01S3/14—Systems for determining direction or deviation from predetermined direction
    • G01S3/46—Systems for determining direction or deviation from predetermined direction using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
    • G01S3/48—Systems for determining direction or deviation from predetermined direction using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured

Definitions

  • the present invention relates to a sampling array arrangement for presence detection.
  • the present invention may be applied for lighting control.
  • Automatic control of the lighting is for example preferable since it does not require the operation of a person (like an employee or a client in a store), and it enables the control of several light sources at a time.
  • a configuration of e.g. radar or ultrasonic transducer arrays may be provided to obtain spatial and temporal parameters of a target, wherein the spatial parameter may refer to the direction-of-arrival (DoA) of a target and the temporal parameter may refer to the velocity and the location of a target.
  • the receiver arrays may estimate the velocity (via Doppler algorithms), the distance (via ranging algorithms) and the DoA (via beamforming algorithms) of the target.
  • tracking algorithms may be added to estimate/predict the moving trajectories of the targets.
  • an antenna or sensor element of the array may be connected to a separate front-end circuit chain.
  • Each front-end chain may take the analog signal as input and perform signal processing which may comprise analog-to-digital conversion (ADC) before yielding a digital output signal.
  • ADC analog-to-digital conversion
  • This digital output signal may then be fed to a PC or a microprocessor for further digital signal processing, i.e., estimating the spatial and temporal parameters and tracking the moving trajectories of the targets.
  • ADC analog-to-digital conversion
  • the front-end processing done by the analog circuits is much more dominant than the digital signal processing done by a microprocessor.
  • a high DoA resolution may require a front- end processing arrangement which is highly energy consuming.
  • a detection system for detecting the location of a target.
  • the detection system comprises at least one transmitter for transmitting at least one probing signal and a plurality of receivers for receiving a first plurality of signals.
  • the first plurality of signals is generated by reflection of the probing signal against the target.
  • the detection system comprises a spatial compression entity for compressing the first plurality of signals into a second plurality of signals, wherein the number of the second plurality of signals is smaller than the number of the first plurality of signals.
  • the detection system further comprises a temporal compression entity for compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals into a plurality of signal data sets.
  • the detection system comprises a processing unit configured to estimate the location of the target based on the plurality of signal data sets.
  • a method for detecting the location of a target comprises the steps of transmitting at least one probing signal and receiving a first plurality of signals.
  • the first plurality of signals is generated by reflection of the probing signal against a target.
  • the method further comprises the step of compressing the first plurality of signals into a second plurality of signals, wherein the number of the second plurality of signals is smaller than the number of the first plurality of signals.
  • the method comprises the step of compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals into a plurality of signal data sets and the step of estimating the location of the target based on the plurality of signal data sets.
  • the present invention is based on the idea of providing a detection system for detecting the location of a target, wherein a spatial compressing entity reduces the number of signals received by the receivers into a second plurality of signals. Furthermore, a temporal compression entity is provided for compressing, or sampling, the second plurality of signals at a frequency lower than the Nyquist frequency into a plurality of signal data sets. Eventually, a processing unit estimates the location of the target based on the plurality of signal data sets.
  • An advantage of the present invention is that the detection system provides a more energy efficient detection system as compared to other prior art systems.
  • the spatial compression entity can compress, i.e. reduce, the number of signals received by the receivers into a second plurality of signals (which are to be further processed in the temporal compression entity)
  • the number of operations in the temporal compression entity can be decreased, thereby decreasing the power consumption.
  • the determination of the DoA of a signal reflected against the target requires a large number of antennas or sensors, which may lead to a large and complex processing unit for sampling a received analog signal into a digital signal.
  • the spatial compression entity of the present invention alleviates this problem, as the spatial compression entity compresses, i.e. reduces, the number of signals.
  • the complexity of the temporal compression entity is decreased.
  • the temporal compression entity can sample the reduced number of signals at a sub-Nyquist frequency, the power consumption of the detection system is decreased even further.
  • the present invention provides a more energy-efficient detection system for detecting the location of a target as compared to other prior art systems. Still, the detection system of the present invention may accurately determine parameters for presence detection, as if a conventional, more power-consuming, system were used.
  • the detection system comprises a transmitter for transmitting a probing signal and a plurality of receivers for receiving a first plurality of signals, wherein the first plurality of signals is generated by reflection of the probing signal against the target.
  • the transmitter may transmit a probing signal which propagates from the transmitter into a region or zone where a target may be present. If a target is present in the region in which a probing signal emitted from the transmitter propagates, the target may reflect the probing signal. Upon reflection, the target thereby generates a first plurality of signals which is received by the plurality of receivers.
  • the present invention may be applied to improve different receiver arrangements comprising radar sensors (i.e. RF antennas) or ultrasonic sensors.
  • the plurality of receivers may comprise discrete sensor arrangements and/or integrated circuits.
  • the detection system comprises a spatial compression entity for compressing the first plurality of signals into a second plurality of signals.
  • the "spatial compression entity” may be a signal processor, a transfer function, or the like, arranged for processing and/or transferring the first plurality of signals into a second plurality of signals.
  • the spatial compression entity may compress the first plurality of signals such that the number of the second plurality of signals becomes smaller than the number of the first plurality of signals.
  • the detection system comprises N L receivers for receiving a first plurality of signals
  • the spatial compression entity may compress the N L signals into M L signals, wherein M L ⁇ N L .
  • the detection system further comprises a temporal compression entity for compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals into a plurality of signal data sets.
  • the "temporal compression entity” may be a signal processor, a transfer function, or the like, arranged for processing and/or transferring the second plurality of signals into a plurality of signal data sets.
  • the temporal compression unity may further comprise a mixer and/or a low- pass filter.
  • the second plurality of signals may then be mixed by the mixer and be filtered by the low-pass filter before being sampled.
  • mixing and low-pass filtering as such are known algorithms to the person skilled in the art, the details of these signal treatments are omitted.
  • the detection system further comprises a processing unit configured to estimate the location of the target based on the plurality of signal data sets.
  • processing unit may be a processor, a computer or the like.
  • location is herein construed to be a position in e.g. a room, an office, or a store, wherein the target, e.g. a person, is located.
  • the plurality of receivers may, for example, be realized as eight receivers in an array.
  • the eight receivers may receive eight analog signals as the first plurality of signals.
  • the eight analog signals may be compressed to e.g. four signals, being the second plurality of signals.
  • the four signals may, at the temporal compression stage, be sampled at half the Nyquist frequency into a plurality of signal data sets, which may be used for further digital signal processing such as e.g. Doppler and DoA estimation.
  • the present embodiment provides an example of a detection system, wherein the first plurality of signals are compressed in the spatial and temporal compression stages to a plurality of signal data sets.
  • the processing unit may be configured to estimate the location of the target in terms of a distance from the plurality of receivers and in terms of an angle between a boresight of the plurality of receivers and the target.
  • distance it is assumed that the target is located in a far- field region, i.e. it is assumed that the target is located at a distance from the plurality of receivers which is significantly larger than the geometrical size of the plurality of receivers.
  • boresight it is here meant a direction approximately perpendicular to the plane of the plurality of receivers.
  • the boresight of the plurality of receivers projects perpendicular to the wall or ceiling, providing an angle of estimation of a target from -90° to +90° with respect to the boresight.
  • the processing unit may be configured to estimate the location of the target based on at least one of two-dimensional beamforming and two-dimensional sparse reconstruction.
  • two-dimensional beamforming it is here meant a reconstruction of a two-dimensional signal in time and space. More specifically, in the present invention, the two-dimensional beamforming implies a reconstruction of e.g. a Doppler signal and a DoA signal, where the Doppler signal represents the temporal frequency (i.e., the velocity of the target) and the DoA represents the spatial frequency (i.e., the angle between the boresight and the target).
  • a multiple measurement vector (MMV) sparse reconstruction may be used by the processing unit.
  • An example of the two-dimensional beamforming is an iterative procedure that jointly updates a beamformer and a frequency estimator using a minimum- variance distortionless response (MVDR) estimator.
  • MVDR minimum- variance distortionless response
  • the two-dimensional beamforming and two-dimensional sparse reconstruction of the present embodiment are suggested processing algorithms when enabling spatial compression and temporal compression.
  • the processing unit may be configured to estimate the velocity of the target.
  • the processing unit may estimate the velocity of the target by means of a change in frequency based on the at least one probing signal and the first plurality of signals.
  • the velocity of the target may be estimated by means of the shift in frequency between at least one signal of the first plurality of signals and the at least one probing signal, i.e. based on the Doppler effect.
  • the processing unit may further be configured to estimate the velocity of the target based on a previously estimated location of the target.
  • the velocity may be estimated by subtracting the distances from the plurality of receivers to the target corresponding to two in-time-adjacent, estimated locations of the target, and divide this difference with the time elapsed between the two estimations to yield the estimated velocity of the target.
  • the present invention is not limited to these alternatives, and it will be appreciated that the velocity may be estimated differently.
  • the processing unit is further configured to estimate the velocity of the target towards the plurality of receivers.
  • the processing unit may estimate a target moving towards or away from the plurality of receivers, wherein the velocity of the target comprises a magnitude and a defined direction (negative if towards the plurality of receivers and positive if away from the plurality of receivers).
  • the velocity may, as an example, be estimated by the processing unit by the Doppler effect.
  • the processing unit may estimate two or more locations of the target along a radius between the plurality of receivers and the target as a function of time, for estimating the velocity.
  • the processing unit may be further configured to estimate a location and a velocity of the target such that a trajectory of the target is estimated as a function of time.
  • trajectory it is here meant e.g. a path, a route or a way.
  • An advantage with the present embodiment is that, if the processing unit estimates at least two locations at two different times, the velocity of the target may be estimated.
  • the trajectory of the target may be estimated as a function of time.
  • the target may be estimated at e.g. xi° from the boresight at a distance yi from the plurality of receivers at time t l s then at e.g. x 2 ° at distance y 2 at time t 2 , and further at e.g. x 3 ° at distance y 3 at time t 3 , etc.
  • the trajectory of the target may for instance be estimated to start e.g. close to a door of a room, continue to e.g. a desk at one end of the room, and further continue back to the door.
  • the present embodiment is particularly advantageous with respect to energy efficiency when applied to e.g. a lighting control system, wherein a light source may be controlled for lighting up an estimated trajectory of the target.
  • a light source may be controlled for lighting up an estimated trajectory of the target.
  • the target is estimated to be present at e.g. xi° at distance yi at time t l s and at e.g. x 2 ° at distance y 2 at time t 2
  • one or more light sources relatively close to the coordinate xi° at distance yi may be turned "on" at time ti, or at a time close to t l s and a light source relatively close to x 2 ° at distance y 2 , may be turned “on” at time t 2 , or at a time close to t 2 .
  • the lighting of the respective light sources may be turned "off when the predicted location of the target is relatively distant from the estimated locations.
  • the present embodiment has the further advantage that, if the target is a person, a light source may in advance "light up" the estimated trajectory of the person.
  • the person may turn his attention to areas lit up by the light source based on the estimated trajectory of the target.
  • a light source in a store may emit light to an area wherein a product is placed, such that a person, whose estimated location is predicted to be in a vicinity of the area, turns his attention to the product on which the light source emits light.
  • the spatial compression entity may comprise a plurality of sub-entities comprising a plurality of operators being arranged for transforming the first plurality of signals into the second plurality of signals.
  • the operators may be "mathematical operators" which may be weighted summers and/or multipliers for operating on the signals, which signals are inputs into the operators.
  • the spatial compression entity may comprises M L sub-entities, wherein M L and N L are integers, and wherein M L ⁇ N L .
  • Each sub-entity may comprise N L multipliers coupled in series with each receiver, such that each signal of the first plurality of signals is multiplied by a factor.
  • each sub- entity may comprise a weighted summer for summing the plurality of factorized signals into the second plurality of signals.
  • the spatial compression entity may comprise a plurality of sub- entities with a plurality of mathematical operators being arranged for spatially compressing the number of signals from N L to M L , wherein M L ⁇ N L .
  • the spatial compression entity may be represented by a spatial compression matrix ⁇ a which transforms the first plurality of signals into a smaller second plurality of signals.
  • the spatial compression matrix may comprise coefficients from a random
  • the multiplication with the coefficients from ⁇ a may be implemented by an attenuator or a phase shifter, or simply by an on-off selection switch.
  • An advantage with the present embodiment is that the arrangement of sub- entities comprising operators provides an easily realizable and structured transform of the first plurality of signals into the second plurality of signals, wherein the number of signals is decreased.
  • the temporal compression entity may comprise a plurality of sub-entities comprising at least one analog- to-information converter (AIC) arranged for analog-to-digital conversion of the second plurality of signals into the plurality of signal data sets.
  • AIC analog- to-information converter
  • the second plurality of analog signals from the spatial compression entity may be processed by the plurality of sub-entities of the temporal compression entity, thereby generating a plurality of digital signal data sets.
  • the temporal compression entity may comprise M L sub-entities arranged for processing a plurality of M L signals from the spatial compression entity.
  • the at least one analog- to-information converter may be arranged for compressing the second plurality of signals at a rate ⁇ x F N T into the signal data set, wherein ⁇ and F s is the Nyquist frequency.
  • the compression of the second plurality of signals into the plurality of signal data sets is performed at a sub-Nyquist frequency, i.e. below the Nyquist frequency.
  • ADC Nyquist-frequency analog-to-digital converter
  • AIC sub-Nyquist- frequency analog-to-information converter
  • the temporal compression entity may be represented by a temporal compression matrix O b , which may comprise coefficients from a random distribution, e.g. Gaussian and/or Bernoulli distributions.
  • the temporal compression entity may transform the second plurality of signals into a plurality of signal data sets which is smaller than the second plurality of signals, wherein the temporal compression entity represents the AIC sampling at MT/NT of the Nyquist frequency.
  • the AIC sampling may conceptually be described as a Nyquist-frequency ADC followed by the temporal compression matrix O b .
  • the AIC may operate on the second plurality of analog signals and output the plurality of digital signal data sets, wherein the
  • multiplication with the temporal compression matrix O b may be arranged by the inclusion of mixers and/or integrators.
  • sampling rate may be reduced, thereby reducing the power consumption of the AIC as compared to a sampling performed at the Nyquist frequency.
  • the reduced sampling rate may also result in a smaller size of the digital plurality of signal data sets, which consequently may lead to a reduced processing complexity in the processing unit.
  • the detection system may be configured to estimate the number of targets based on a detected direction from which the first plurality of signals are received.
  • a first target may be detected at -40° from the boresight of the plurality of receivers and at a distance of 2 m from the plurality or receivers
  • a second target may be detected at 20° from the boresight of the plurality of receivers and at a distance of 3 m from the plurality of receivers.
  • the estimation of the number of targets may be performed by "beamforming" and/or "DoA" processing.
  • the processing unit may estimate the velocity of the two targets, i.e. that the first target, located at -40°, has a velocity of 2 m/s, whereas the second target, located at 20°, has a velocity of -3 m/s.
  • Applying the present embodiment to e.g. a control of a lighting function is advantageous in that the presence of several targets in e.g. a room, instead of a single target, may be taken into account.
  • a lighting control system for controlling a lighting function of at least one light source, wherein the lighting control system comprises a detection system as defined in any one of the above described embodiments.
  • the processing unit may be further configured to control the lighting function as a function of the estimated location of the target.
  • An advantage of the present embodiment is that the lighting control system provides a more energy efficient lighting function compared to other prior art lighting systems.
  • the lighting control system can estimate a location of a target, the lighting function of a light source may be adapted such that more or less light is provided at the estimated location of the target.
  • a light source may be turned on such that light is shed on that location of the room.
  • This location may be close to e.g. a desk, a book shelf, or a chair, where the person is estimated to be located, and the control of the light source may improve the lighting for the person who e.g. will study at the desk, find a book in the shelf, or sit down in the chair to read.
  • the lighting control system may provide a control of the light source at this location.
  • the lighting control system may be configured to decrease the lighting at the location wherein the person is estimated to be present, and increase the lighting at a position to which it is desirable that the person is re-oriented.
  • Fig. 1 is a schematic illustration of a detection system for detecting the location of a target in accordance with an embodiment of the present invention
  • Fig. 2 is a schematic illustration of a transmitter and a plurality of receivers for detecting the location of a target in accordance with an embodiment of the present invention
  • Fig. 3 is a schematic block diagram of a method for detecting the location of a target in accordance with an embodiment of the present invention.
  • Fig. 4 is a schematic block diagram of a lighting control system in accordance with an embodiment of the present invention.
  • the present invention is described with reference to a detection system for detecting the location of a target.
  • the detection system comprises a transmitter, a plurality of receivers, a spatial compression entity, a temporal compression entity and a processing unit.
  • Fig. 1 is a schematic illustration of a detection system 100 for detecting the location of a target 101.
  • the target 101 may be e.g. a person present in a room.
  • At least one transmitter 102 is provided for transmitting at least one probing signal 103.
  • a plurality of receivers 104 are provided for receiving a first plurality of signals 105 being generated by reflection of the probing signal 103 against the target 101.
  • the transmitter 102 and the plurality of receivers 104 may be separated.
  • the transmitter 102 and the plurality of receivers 104 may be integrated in one single transmitter/receiver (transceiver) arrangement, as shown in Fig. 1.
  • the plurality of receivers 104 may be arranged in a linear, rectangular, triangular or circular array, or alternatively, any other irregular array geometry.
  • the plurality of receivers 104 may be spaced equally in a linear array e.g. on a wall of a room.
  • the linear array of the plurality of receivers 104 may be arranged at a height which is typically above various stationary objects present in a room, such as e.g. furniture (e.g. a table) and equipment (e.g. a computer), thereby improving the estimate of the location of the target 101.
  • the first plurality of signals 105 are transmitted from the plurality of receivers
  • the spatial compression entity 110 comprises a plurality of sub-entities 111 which comprise a plurality of mathematical operators 112.
  • the mathematical operators 112 comprise N L multipliers coupled in parallel with each other and wherein each multiplier is coupled in series with one of the plurality of receivers 104.
  • the multipliers are arranged for transforming the first plurality of signals 105 with the respective factors ⁇ ⁇ (1,1), ⁇ ⁇ (1,2), ..., ⁇ a (l,N L ).
  • the mathematical operators 112 further comprise one weighted summer in each sub-entity 111 for summing the first plurality of signals 105, yielding a second plurality of signals 113.
  • the number of signals in the second plurality of signals 113 is smaller than the number of signals in the first plurality of signals 105.
  • the detection system 100 further comprises a temporal compression entity
  • the temporal compression entity 120 comprises a plurality of sub-entities 121 arranged in parallel. Each sub-entity 121 comprises a mixer, a low-pass filter and an analog-to-information converter (AIC) arranged for analog-to-digital conversion of the second plurality of signals 113 into a plurality of signal data sets 122.
  • AIC analog-to-information converter
  • the temporal compression entity 120 compresses, at a frequency lower than the Nyquist frequency, the second plurality of signals 113 into a plurality of signal data sets 122.
  • the AIC is arranged for compressing the second plurality of signals 113 at a rate M T X Fs/ ⁇ into the plurality of signal data sets 122, wherein ⁇ and F s is the Nyquist frequency. Hence, the compression of the second plurality of signals 113 into the plurality of signal data sets 122 is performed at a sub-Nyquist frequency.
  • the second plurality of signals of N t samples may be divided into B blocks such that
  • the AIC sampling may conceptually be described as a Nyquist-frequency ADC followed by a temporal compression matrix Ob of size ⁇ .
  • the detection system 100 further comprises a processing unit 123 which may receive the plurality of signal data sets 122 as input.
  • the processing unit 123 is configured to estimate the location of the target 101, e.g. the location of a person in a room, based on the plurality of signal data sets 122.
  • Fig. 2 is a schematic view of a transmitter 201 which is positioned above a plurality of receivers 202.
  • the transmitter 201 and the plurality of receivers 202 could alternatively be closely positioned, or positioned at a longer distance from each other.
  • the transmitter 201 and the plurality of receivers 202 may be a single integrated transceiver which acts both as a transmitter and as a receiver.
  • the transmitter 201 for transmitting the probing signal may be provided on the side wall of a room, preferably on a height substantially above furniture or the like present in the room.
  • the transmitter/receiver could be provided on any wall of the room, e.g., in the ceiling.
  • the plurality of receivers 202 for receiving the fist plurality of signals is provided in a linear array of eight receivers, the array being horizontally elongated.
  • the location of a target 203 e.g. a person in a room, may be estimated by the processing unit in terms of a distance D from the plurality of receivers 202 and in terms of an angle ⁇ between a boresight B, i.e. a direction approximately perpendicular to the plane of the plurality of receivers 202, and the target 203.
  • the processing unit may be configured to estimate a velocity V of the target 203 towards, or away from, the plurality of receivers 202.
  • the processing unit may estimate the distance D of the target 203 to be 3 m from the plurality of receivers 202, the angle ⁇ between the boresight B and the target 203 to be 40°, and the velocity V to be 2 m/s towards the plurality of receivers 202.
  • Fig. 3 is a schematic block diagram of a method 300 for detecting the location of a target 101 according to an aspect of the present invention.
  • the method 300 comprises the step 301 of transmitting a probing signal 103 and the step 302 of receiving a first plurality of signals 105.
  • the method 300 further comprises the step 303 of compressing the first plurality of signals 105 into a second plurality of signals 113, wherein the number of the second plurality of signals 113 is smaller than the number of the first plurality of signals 105.
  • the method 300 comprises the step 304 of compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals 113 into a plurality of signal data sets 122. Moreover, the method 300 comprises the step 305 of estimating the location of the target 101 based on the plurality of signal data sets 122.
  • Fig. 4 is a schematic block diagram of a lighting control system 400 for controlling a lighting function 402 of at least one light source 403.
  • the lighting control system comprises a detection system 401 as defined in any one of the above described embodiments.
  • the processing unit of the detection system 401 is further configured to control a lighting function 402.
  • the lighting function 402 may be a processor, a control unit, or the like, arranged for a control of the light of the at least one light source 403.
  • the lighting function 402 may be any kind of control related to the control of the at least one light source 403, such as e.g. a gradual increase/decrease of the light source intensity, or an "on/off mode.
  • the lighting function 402 may be a separate unit, or be integrated with the processing unit of the detection system 401.
  • the coupling in the sub-entities 111 i.e. the coupling of the mathematical operators 112 in the spatial compression entity 110, for the transfer of signals from the plurality of receivers 104 to the temporal compression entity 120 may be different than that depicted in Fig. 1.
  • more weighted summers may be provided for partially summing the factorized first plurality of signals from the multipliers for the compression of the first plurality of signals 105 into the second plurality of signals 113.
  • the arrangement of the mixer, LPF and/or AIC in the sub-entities 121 may be different than that shown in Fig. 1.
  • the arrangement and/or the number of the plurality of receivers 202 may also be different from that shown.
  • the numbers and the sizes of the plurality of receivers 202, as well as the distances between them, may vary.
  • the array geometry may be any other geometrical shape, e.g. a circular or triangular shape. The same possibilities apply for the transmitter 201, which position and/or size may be different from that depicted in Fig.1.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

A detection system (100) and a method (300) for detecting the location of a target (101) are provided. The detection system (100) comprises a transmitter (102) for transmitting a probing signal (103) and a plurality of receivers (104) for receiving a first plurality of signals (105). A spatial compression entity (110) is provided for compressing the first plurality of signals into a second plurality of signals (113) being smaller than the number of the first plurality of signals. Furthermore, a temporal compression entity (120) is provided for compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals into a plurality of signal data sets (122). The processing unit (123) is configured to estimate the location of the target based on the plurality of signal data sets. The detection system of the present invention may e.g. be part of a lighting control system for controlling the lighting.

Description

System and method for presence detection
FIELD OF THE INVENTION
The present invention relates to a sampling array arrangement for presence detection. The present invention may be applied for lighting control. BACKGROUND OF THE INVENTION
Artificial lighting is used for many indoor and outdoor settings, such as e.g. offices, restaurants, museums, advertising boards, homes, shops and shop windows. During many years, the control of the lighting has been operated manually. However, manual control of the lighting may be undesired, inefficient and/or tedious.
Systems based on manual control of the lighting are therefore nowadays replaced by systems based on automatic control of the lighting. Automatic control of the lighting is for example preferable since it does not require the operation of a person (like an employee or a client in a store), and it enables the control of several light sources at a time.
Recently, more advanced automatic lighting systems have been developed, wherein presence information such as e.g. location and speed of targets (e.g. humans for indoor lighting, or vehicles for outdoor lighting) is used for an automatic setting of the light. As known in the state of the art, a configuration of e.g. radar or ultrasonic transducer arrays (receiver arrays) may be provided to obtain spatial and temporal parameters of a target, wherein the spatial parameter may refer to the direction-of-arrival (DoA) of a target and the temporal parameter may refer to the velocity and the location of a target. The receiver arrays may estimate the velocity (via Doppler algorithms), the distance (via ranging algorithms) and the DoA (via beamforming algorithms) of the target. Furthermore, tracking algorithms may be added to estimate/predict the moving trajectories of the targets.
In a conventional array, an antenna or sensor element of the array may be connected to a separate front-end circuit chain. Each front-end chain may take the analog signal as input and perform signal processing which may comprise analog-to-digital conversion (ADC) before yielding a digital output signal. This digital output signal may then be fed to a PC or a microprocessor for further digital signal processing, i.e., estimating the spatial and temporal parameters and tracking the moving trajectories of the targets. In terms of power consumption for the array-based architecture, the front-end processing done by the analog circuits is much more dominant than the digital signal processing done by a microprocessor. Generally, a high DoA resolution may require a front- end processing arrangement which is highly energy consuming.
In the light of the above observations, there is an increasing need for detection systems which may accurately determine target location and velocity information for a lighting control, yet consuming little power.
SUMMARY OF THE INVENTION
It is an object of the present invention to mitigate the above problems and to provide a system that provides a more energy efficient solution of determining target location and velocity information for lighting control.
This and other objects are achieved by providing a system having the features defined in the independent claims. Preferred embodiments are defined in the dependent claims.
Hence, according to a first aspect of the present invention, there is provided a detection system for detecting the location of a target. The detection system comprises at least one transmitter for transmitting at least one probing signal and a plurality of receivers for receiving a first plurality of signals. The first plurality of signals is generated by reflection of the probing signal against the target. Furthermore, the detection system comprises a spatial compression entity for compressing the first plurality of signals into a second plurality of signals, wherein the number of the second plurality of signals is smaller than the number of the first plurality of signals. The detection system further comprises a temporal compression entity for compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals into a plurality of signal data sets. Moreover, the detection system comprises a processing unit configured to estimate the location of the target based on the plurality of signal data sets.
According to a second aspect of the present invention, there is provided a method for detecting the location of a target. The method comprises the steps of transmitting at least one probing signal and receiving a first plurality of signals. The first plurality of signals is generated by reflection of the probing signal against a target. The method further comprises the step of compressing the first plurality of signals into a second plurality of signals, wherein the number of the second plurality of signals is smaller than the number of the first plurality of signals. Furthermore, the method comprises the step of compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals into a plurality of signal data sets and the step of estimating the location of the target based on the plurality of signal data sets.
Thus, the present invention is based on the idea of providing a detection system for detecting the location of a target, wherein a spatial compressing entity reduces the number of signals received by the receivers into a second plurality of signals. Furthermore, a temporal compression entity is provided for compressing, or sampling, the second plurality of signals at a frequency lower than the Nyquist frequency into a plurality of signal data sets. Eventually, a processing unit estimates the location of the target based on the plurality of signal data sets.
An advantage of the present invention is that the detection system provides a more energy efficient detection system as compared to other prior art systems. As the spatial compression entity can compress, i.e. reduce, the number of signals received by the receivers into a second plurality of signals (which are to be further processed in the temporal compression entity), the number of operations in the temporal compression entity can be decreased, thereby decreasing the power consumption. Moreover, in a general case, the determination of the DoA of a signal reflected against the target requires a large number of antennas or sensors, which may lead to a large and complex processing unit for sampling a received analog signal into a digital signal. The spatial compression entity of the present invention alleviates this problem, as the spatial compression entity compresses, i.e. reduces, the number of signals. As a consequence, the complexity of the temporal compression entity is decreased. Furthermore, as the temporal compression entity can sample the reduced number of signals at a sub-Nyquist frequency, the power consumption of the detection system is decreased even further.
Hence, the present invention provides a more energy-efficient detection system for detecting the location of a target as compared to other prior art systems. Still, the detection system of the present invention may accurately determine parameters for presence detection, as if a conventional, more power-consuming, system were used.
The detection system comprises a transmitter for transmitting a probing signal and a plurality of receivers for receiving a first plurality of signals, wherein the first plurality of signals is generated by reflection of the probing signal against the target. Hence, the transmitter may transmit a probing signal which propagates from the transmitter into a region or zone where a target may be present. If a target is present in the region in which a probing signal emitted from the transmitter propagates, the target may reflect the probing signal. Upon reflection, the target thereby generates a first plurality of signals which is received by the plurality of receivers.
The present invention may be applied to improve different receiver arrangements comprising radar sensors (i.e. RF antennas) or ultrasonic sensors. Furthermore, the plurality of receivers may comprise discrete sensor arrangements and/or integrated circuits.
Furthermore, the detection system comprises a spatial compression entity for compressing the first plurality of signals into a second plurality of signals. The "spatial compression entity" may be a signal processor, a transfer function, or the like, arranged for processing and/or transferring the first plurality of signals into a second plurality of signals. The spatial compression entity may compress the first plurality of signals such that the number of the second plurality of signals becomes smaller than the number of the first plurality of signals. For example, if the detection system comprises NL receivers for receiving a first plurality of signals, the spatial compression entity may compress the NL signals into ML signals, wherein ML<NL. More specifically, if the detection system comprises eight receivers, i.e. NL=8, the spatial compression entity may compress the eight signals into e.g. four signals, i.e. ML=4.
The detection system further comprises a temporal compression entity for compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals into a plurality of signal data sets. The "temporal compression entity" may be a signal processor, a transfer function, or the like, arranged for processing and/or transferring the second plurality of signals into a plurality of signal data sets. In other words, the temporal compression entity samples the second plurality of analog signals into a plurality of digital signal data sets. For example, if the temporal compression entity samples at half the Nyquist frequency, i.e. 0.5 Fs, the temporal compression entity may transform e.g. Ντ=8 samples to ΜΤ=ΝΤ .5=4 samples.
The temporal compression unity may further comprise a mixer and/or a low- pass filter. The second plurality of signals may then be mixed by the mixer and be filtered by the low-pass filter before being sampled. As both mixing and low-pass filtering as such are known algorithms to the person skilled in the art, the details of these signal treatments are omitted.
The detection system further comprises a processing unit configured to estimate the location of the target based on the plurality of signal data sets. The term
"processing unit" may be a processor, a computer or the like. Furthermore, the term "location" is herein construed to be a position in e.g. a room, an office, or a store, wherein the target, e.g. a person, is located.
According to an embodiment of the detection system, the plurality of receivers may, for example, be realized as eight receivers in an array. The eight receivers may receive eight analog signals as the first plurality of signals. At the spatial compression stage, the eight analog signals may be compressed to e.g. four signals, being the second plurality of signals. After e.g. mixing and low-pass filtering, the four signals may, at the temporal compression stage, be sampled at half the Nyquist frequency into a plurality of signal data sets, which may be used for further digital signal processing such as e.g. Doppler and DoA estimation. Hence, the present embodiment provides an example of a detection system, wherein the first plurality of signals are compressed in the spatial and temporal compression stages to a plurality of signal data sets.
According to an embodiment of the present invention, the processing unit may be configured to estimate the location of the target in terms of a distance from the plurality of receivers and in terms of an angle between a boresight of the plurality of receivers and the target. With the term "distance", it is assumed that the target is located in a far- field region, i.e. it is assumed that the target is located at a distance from the plurality of receivers which is significantly larger than the geometrical size of the plurality of receivers. By the term
"boresight", it is here meant a direction approximately perpendicular to the plane of the plurality of receivers. As an example, if the plurality of receivers is arranged in an array on a wall or in a ceiling, the boresight of the plurality of receivers projects perpendicular to the wall or ceiling, providing an angle of estimation of a target from -90° to +90° with respect to the boresight.
According to an embodiment of the present invention, the processing unit may be configured to estimate the location of the target based on at least one of two-dimensional beamforming and two-dimensional sparse reconstruction. By the term "two-dimensional beamforming", it is here meant a reconstruction of a two-dimensional signal in time and space. More specifically, in the present invention, the two-dimensional beamforming implies a reconstruction of e.g. a Doppler signal and a DoA signal, where the Doppler signal represents the temporal frequency (i.e., the velocity of the target) and the DoA represents the spatial frequency (i.e., the angle between the boresight and the target).
Details about beamforming may be found in e.g. H. L. Van Trees (2002) Optimum Array Processing, ISBN 0471093904, and such details are incorporated herein by reference. Furthermore, details about sparse reconstruction may be found in e.g. an article entitled "Sparse Solutions to Linear Inverse Problems with Multiple Measurement Vectors" by S. F. Cotter et al, IEEE Trans, on Signal Processing, vol. 53, pp. 2477-2488, July 2005.
As an example of a two-dimensional sparse reconstruction, a multiple measurement vector (MMV) sparse reconstruction may be used by the processing unit. An example of the two-dimensional beamforming is an iterative procedure that jointly updates a beamformer and a frequency estimator using a minimum- variance distortionless response (MVDR) estimator.
In contrast to an estimate of e.g. the velocity and DoA of a moving target by means of a more conventional approach (e.g. a Bartlett approach), the two-dimensional beamforming and two-dimensional sparse reconstruction of the present embodiment are suggested processing algorithms when enabling spatial compression and temporal compression.
According to an embodiment of the present invention, the processing unit may be configured to estimate the velocity of the target. The processing unit may estimate the velocity of the target by means of a change in frequency based on the at least one probing signal and the first plurality of signals. As an example, the velocity of the target may be estimated by means of the shift in frequency between at least one signal of the first plurality of signals and the at least one probing signal, i.e. based on the Doppler effect. As another alternative, the processing unit may further be configured to estimate the velocity of the target based on a previously estimated location of the target. In particular, the velocity may be estimated by subtracting the distances from the plurality of receivers to the target corresponding to two in-time-adjacent, estimated locations of the target, and divide this difference with the time elapsed between the two estimations to yield the estimated velocity of the target. However, the present invention is not limited to these alternatives, and it will be appreciated that the velocity may be estimated differently.
According to an embodiment of the present invention, the processing unit is further configured to estimate the velocity of the target towards the plurality of receivers. Hence, the processing unit may estimate a target moving towards or away from the plurality of receivers, wherein the velocity of the target comprises a magnitude and a defined direction (negative if towards the plurality of receivers and positive if away from the plurality of receivers). The velocity may, as an example, be estimated by the processing unit by the Doppler effect. Alternatively, the processing unit may estimate two or more locations of the target along a radius between the plurality of receivers and the target as a function of time, for estimating the velocity. According to an embodiment of the present invention, the processing unit may be further configured to estimate a location and a velocity of the target such that a trajectory of the target is estimated as a function of time. By the term "trajectory", it is here meant e.g. a path, a route or a way.
An advantage with the present embodiment is that, if the processing unit estimates at least two locations at two different times, the velocity of the target may be estimated. Based on target locations and velocities, the trajectory of the target may be estimated as a function of time. For example, the target may be estimated at e.g. xi° from the boresight at a distance yi from the plurality of receivers at time tl s then at e.g. x2° at distance y2 at time t2, and further at e.g. x3° at distance y3 at time t3, etc. The trajectory of the target may for instance be estimated to start e.g. close to a door of a room, continue to e.g. a desk at one end of the room, and further continue back to the door.
The present embodiment is particularly advantageous with respect to energy efficiency when applied to e.g. a lighting control system, wherein a light source may be controlled for lighting up an estimated trajectory of the target. If the target is estimated to be present at e.g. xi° at distance yi at time tl s and at e.g. x2° at distance y2 at time t2, one or more light sources relatively close to the coordinate xi° at distance yi may be turned "on" at time ti, or at a time close to tl s and a light source relatively close to x2° at distance y2, may be turned "on" at time t2, or at a time close to t2. Analogously, the lighting of the respective light sources may be turned "off when the predicted location of the target is relatively distant from the estimated locations.
The present embodiment has the further advantage that, if the target is a person, a light source may in advance "light up" the estimated trajectory of the person.
Another advantage of the embodiment is that the person may turn his attention to areas lit up by the light source based on the estimated trajectory of the target. As an example, a light source in a store may emit light to an area wherein a product is placed, such that a person, whose estimated location is predicted to be in a vicinity of the area, turns his attention to the product on which the light source emits light.
According to an embodiment of the present invention, the spatial compression entity may comprise a plurality of sub-entities comprising a plurality of operators being arranged for transforming the first plurality of signals into the second plurality of signals. The operators may be "mathematical operators" which may be weighted summers and/or multipliers for operating on the signals, which signals are inputs into the operators. In particular, for an arrangement of NL receivers, the spatial compression entity may comprises ML sub-entities, wherein ML and NL are integers, and wherein ML<NL. Each sub-entity may comprise NL multipliers coupled in series with each receiver, such that each signal of the first plurality of signals is multiplied by a factor. Furthermore, each sub- entity may comprise a weighted summer for summing the plurality of factorized signals into the second plurality of signals.
In other words, the spatial compression entity may comprise a plurality of sub- entities with a plurality of mathematical operators being arranged for spatially compressing the number of signals from NL to ML, wherein ML<NL.
The spatial compression entity may be represented by a spatial compression matrix < a which transforms the first plurality of signals into a smaller second plurality of signals. The spatial compression matrix may comprise coefficients from a random
distribution, e.g. Gaussian and/or Bernoulli distributions. Furthermore, the multiplication with the coefficients from < a may be implemented by an attenuator or a phase shifter, or simply by an on-off selection switch.
An advantage with the present embodiment is that the arrangement of sub- entities comprising operators provides an easily realizable and structured transform of the first plurality of signals into the second plurality of signals, wherein the number of signals is decreased.
According to an embodiment of the present invention, the temporal compression entity may comprise a plurality of sub-entities comprising at least one analog- to-information converter (AIC) arranged for analog-to-digital conversion of the second plurality of signals into the plurality of signal data sets. Hence, the second plurality of analog signals from the spatial compression entity may be processed by the plurality of sub-entities of the temporal compression entity, thereby generating a plurality of digital signal data sets. For example, the temporal compression entity may comprise ML sub-entities arranged for processing a plurality of ML signals from the spatial compression entity.
Details about AIC may be found in e.g. an article entitled "Random sampling for analog-to-information conversion of wideband signals" by J. Laska et al., IEEE Dallas Circuits and Systems Workshop, pp. 119-122, Oct. 2006.
According to an embodiment of the present invention, the at least one analog- to-information converter may be arranged for compressing the second plurality of signals at a rate Μτ x F NT into the signal data set, wherein Μτ<Ντ and Fs is the Nyquist frequency. Hence, the compression of the second plurality of signals into the plurality of signal data sets is performed at a sub-Nyquist frequency, i.e. below the Nyquist frequency. For example, instead of providing a Nyquist-frequency analog-to-digital converter (ADC), a sub-Nyquist- frequency analog-to-information converter (AIC) may be provided. Since the AIC may perform block-wise compression, the second plurality of signals of e.g. a total number of Nt samples (at a Nyquist frequency) for each sub-entity 121 may be divided into B blocks with NT samples per block such that Nt=B-NT .
The temporal compression entity may be represented by a temporal compression matrix Ob, which may comprise coefficients from a random distribution, e.g. Gaussian and/or Bernoulli distributions. The temporal compression entity may transform the second plurality of signals into a plurality of signal data sets which is smaller than the second plurality of signals, wherein the temporal compression entity represents the AIC sampling at MT/NT of the Nyquist frequency. As an example, the AIC may transform the NT samples to MT samples for each block, and output a total number of Mt=B MT samples. The AIC sampling may conceptually be described as a Nyquist-frequency ADC followed by the temporal compression matrix Ob. Furthermore, the AIC may operate on the second plurality of analog signals and output the plurality of digital signal data sets, wherein the
multiplication with the temporal compression matrix Ob may be arranged by the inclusion of mixers and/or integrators.
An advantage with the present embodiment is that the sampling rate may be reduced, thereby reducing the power consumption of the AIC as compared to a sampling performed at the Nyquist frequency. The reduced sampling rate may also result in a smaller size of the digital plurality of signal data sets, which consequently may lead to a reduced processing complexity in the processing unit.
As a numerical example of the Nyquist frequency, the probing signal may be a sinusoid ultrasound signal of frequency fc=40 kHz (fc =c/X, wherein c=343 m/s and λ=4.3 mm). If the target moves with an expected maximum velocity vm=4 m/s, a maximum Doppler frequency of fm=933 Hz (2vm ) requires the Nyquist frequency of Fs=1866 Hz (2fm).
According to an embodiment of the present invention, the detection system may be configured to estimate the number of targets based on a detected direction from which the first plurality of signals are received.
For example, a first target may be detected at -40° from the boresight of the plurality of receivers and at a distance of 2 m from the plurality or receivers, whereas a second target may be detected at 20° from the boresight of the plurality of receivers and at a distance of 3 m from the plurality of receivers. The estimation of the number of targets may be performed by "beamforming" and/or "DoA" processing. Furthermore, the processing unit may estimate the velocity of the two targets, i.e. that the first target, located at -40°, has a velocity of 2 m/s, whereas the second target, located at 20°, has a velocity of -3 m/s.
Applying the present embodiment to e.g. a control of a lighting function is advantageous in that the presence of several targets in e.g. a room, instead of a single target, may be taken into account.
According to an embodiment of the present invention, there is provided a lighting control system for controlling a lighting function of at least one light source, wherein the lighting control system comprises a detection system as defined in any one of the above described embodiments. The processing unit may be further configured to control the lighting function as a function of the estimated location of the target.
An advantage of the present embodiment is that the lighting control system provides a more energy efficient lighting function compared to other prior art lighting systems. As the lighting control system can estimate a location of a target, the lighting function of a light source may be adapted such that more or less light is provided at the estimated location of the target.
For example, if a target, e.g. a person, is positioned at a location in a room, a light source may be turned on such that light is shed on that location of the room. This location may be close to e.g. a desk, a book shelf, or a chair, where the person is estimated to be located, and the control of the light source may improve the lighting for the person who e.g. will study at the desk, find a book in the shelf, or sit down in the chair to read.
As a further example, if a person is estimated to be present at a location close to which products or other items are positioned, e.g. shelves in a store or paintings in a museum, the lighting control system may provide a control of the light source at this location.
Alternatively, the lighting control system may be configured to decrease the lighting at the location wherein the person is estimated to be present, and increase the lighting at a position to which it is desirable that the person is re-oriented.
It will be appreciated that the specific embodiments and any additional features described above with reference to the detection system and/or the lighting control system are likewise applicable and combinable with the method according to the second aspect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing a currently preferred embodiment of the invention, wherein:
Fig. 1 is a schematic illustration of a detection system for detecting the location of a target in accordance with an embodiment of the present invention,
Fig. 2 is a schematic illustration of a transmitter and a plurality of receivers for detecting the location of a target in accordance with an embodiment of the present invention,
Fig. 3 is a schematic block diagram of a method for detecting the location of a target in accordance with an embodiment of the present invention, and
Fig. 4 is a schematic block diagram of a lighting control system in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
In the following description, the present invention is described with reference to a detection system for detecting the location of a target.
The detection system comprises a transmitter, a plurality of receivers, a spatial compression entity, a temporal compression entity and a processing unit.
Fig. 1 is a schematic illustration of a detection system 100 for detecting the location of a target 101. For example, the target 101 may be e.g. a person present in a room. At least one transmitter 102 is provided for transmitting at least one probing signal 103. A plurality of receivers 104 are provided for receiving a first plurality of signals 105 being generated by reflection of the probing signal 103 against the target 101. The transmitter 102 and the plurality of receivers 104 may be separated. Alternatively, the transmitter 102 and the plurality of receivers 104 may be integrated in one single transmitter/receiver (transceiver) arrangement, as shown in Fig. 1.
For example, the at least one probing signal 103 may be a sinusoid ultrasound signal of frequency fc=40 kHz (fc =ο/λ, wherein c=343 m/s and λ=4.3 mm).
The plurality of receivers 104 may be arranged in a linear, rectangular, triangular or circular array, or alternatively, any other irregular array geometry. For example, the plurality of receivers 104 may be spaced equally in a linear array e.g. on a wall of a room. A separation dm between two adjacent receivers or sensors may e.g. be dm= /2, such that no grating lobes are observed. With the same numerical example as that described above, dm=2.15 mm. Furthermore, the linear array of the plurality of receivers 104 may be arranged at a height which is typically above various stationary objects present in a room, such as e.g. furniture (e.g. a table) and equipment (e.g. a computer), thereby improving the estimate of the location of the target 101.
The first plurality of signals 105 are transmitted from the plurality of receivers
104 to a spatial compression entity 110. The spatial compression entity 110 comprises a plurality of sub-entities 111 which comprise a plurality of mathematical operators 112. In each sub-entity 111, the mathematical operators 112 comprise NL multipliers coupled in parallel with each other and wherein each multiplier is coupled in series with one of the plurality of receivers 104. The multipliers are arranged for transforming the first plurality of signals 105 with the respective factors Φα(1,1), Φα(1,2), ..., < a(l,NL). The mathematical operators 112 further comprise one weighted summer in each sub-entity 111 for summing the first plurality of signals 105, yielding a second plurality of signals 113.
In mathematical terms, the operation of the spatial compression entity 110 may be expressed as follows: letting i=l,2,...,B be the block index, the first plurality of signals 105 may be written as X=[Xi, X2, .. . , XB], wherein X; has the size NLXNT, wherein X has the size NLxNt, wherein NL is the number of receivers 104, wherein Nt is the length of the time instant in total, and wherein NT is the length of the time instant per block such that
Figure imgf000013_0001
wherein < a denotes a spatial compression matrix of size MLXNL, wherein ML<NL.
Hence, after the spatial compression entity 110 has processed the first plurality of signals 105 into the second plurality of signals 113, the number of signals in the second plurality of signals 113 is smaller than the number of signals in the first plurality of signals 105.
The detection system 100 further comprises a temporal compression entity
120, receiving the second plurality of signals 113 as input. The temporal compression entity 120 comprises a plurality of sub-entities 121 arranged in parallel. Each sub-entity 121 comprises a mixer, a low-pass filter and an analog-to-information converter (AIC) arranged for analog-to-digital conversion of the second plurality of signals 113 into a plurality of signal data sets 122. The temporal compression entity 120 compresses, at a frequency lower than the Nyquist frequency, the second plurality of signals 113 into a plurality of signal data sets 122. The AIC is arranged for compressing the second plurality of signals 113 at a rate MT X Fs/Ντ into the plurality of signal data sets 122, wherein Μτ<Ντ and Fs is the Nyquist frequency. Hence, the compression of the second plurality of signals 113 into the plurality of signal data sets 122 is performed at a sub-Nyquist frequency.
Since the AIC may perform block-wise compression, the second plurality of signals of Nt samples (at a Nyquist frequency) may be divided into B blocks such that
The AIC may transform the NT samples to Μτ samples for each block, and output a total number of Mt=B MT samples.
The AIC sampling may conceptually be described as a Nyquist-frequency ADC followed by a temporal compression matrix Ob of size ΜχχΝτ. As for the previous mathematical operation performed by the spatial compression entity 110, the spatial compression entity 110 and the temporal compression entity 120 together compress the first plurality of signals into the plurality of signal data sets 122 as Y=[Yi, Y2, .. . , YB], wherein Yi=OaXi< bT, wherein the superscript T denotes the matrix transpose operator, wherein Υ; has the size MLXMT, and wherein Y has the size MLxMt.
The detection system 100 further comprises a processing unit 123 which may receive the plurality of signal data sets 122 as input. The processing unit 123 is configured to estimate the location of the target 101, e.g. the location of a person in a room, based on the plurality of signal data sets 122.
Fig. 2 is a schematic view of a transmitter 201 which is positioned above a plurality of receivers 202. However, the transmitter 201 and the plurality of receivers 202 could alternatively be closely positioned, or positioned at a longer distance from each other. Furthermore, the transmitter 201 and the plurality of receivers 202 may be a single integrated transceiver which acts both as a transmitter and as a receiver.
The transmitter 201 for transmitting the probing signal may be provided on the side wall of a room, preferably on a height substantially above furniture or the like present in the room. However, the transmitter/receiver could be provided on any wall of the room, e.g., in the ceiling.
In Fig. 2, the plurality of receivers 202 for receiving the fist plurality of signals is provided in a linear array of eight receivers, the array being horizontally elongated. The location of a target 203, e.g. a person in a room, may be estimated by the processing unit in terms of a distance D from the plurality of receivers 202 and in terms of an angle Θ between a boresight B, i.e. a direction approximately perpendicular to the plane of the plurality of receivers 202, and the target 203. Furthermore, the processing unit may be configured to estimate a velocity V of the target 203 towards, or away from, the plurality of receivers 202. For example, the processing unit may estimate the distance D of the target 203 to be 3 m from the plurality of receivers 202, the angle Θ between the boresight B and the target 203 to be 40°, and the velocity V to be 2 m/s towards the plurality of receivers 202.
Fig. 3 is a schematic block diagram of a method 300 for detecting the location of a target 101 according to an aspect of the present invention. The method 300 comprises the step 301 of transmitting a probing signal 103 and the step 302 of receiving a first plurality of signals 105. The method 300 further comprises the step 303 of compressing the first plurality of signals 105 into a second plurality of signals 113, wherein the number of the second plurality of signals 113 is smaller than the number of the first plurality of signals 105.
Furthermore, the method 300 comprises the step 304 of compressing, at a frequency lower than the Nyquist frequency, the second plurality of signals 113 into a plurality of signal data sets 122. Moreover, the method 300 comprises the step 305 of estimating the location of the target 101 based on the plurality of signal data sets 122.
Fig. 4 is a schematic block diagram of a lighting control system 400 for controlling a lighting function 402 of at least one light source 403. The lighting control system comprises a detection system 401 as defined in any one of the above described embodiments. The processing unit of the detection system 401 is further configured to control a lighting function 402. The lighting function 402 may be a processor, a control unit, or the like, arranged for a control of the light of the at least one light source 403. In other words, the lighting function 402 may be any kind of control related to the control of the at least one light source 403, such as e.g. a gradual increase/decrease of the light source intensity, or an "on/off mode. Furthermore, the lighting function 402 may be a separate unit, or be integrated with the processing unit of the detection system 401.
Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims.
For example, the coupling in the sub-entities 111, i.e. the coupling of the mathematical operators 112 in the spatial compression entity 110, for the transfer of signals from the plurality of receivers 104 to the temporal compression entity 120 may be different than that depicted in Fig. 1. As an example, more weighted summers may be provided for partially summing the factorized first plurality of signals from the multipliers for the compression of the first plurality of signals 105 into the second plurality of signals 113. Furthermore, the arrangement of the mixer, LPF and/or AIC in the sub-entities 121 may be different than that shown in Fig. 1.
In Fig. 2, the arrangement and/or the number of the plurality of receivers 202 may also be different from that shown. As an example, the numbers and the sizes of the plurality of receivers 202, as well as the distances between them, may vary. Further, the array geometry may be any other geometrical shape, e.g. a circular or triangular shape. The same possibilities apply for the transmitter 201, which position and/or size may be different from that depicted in Fig.1.

Claims

CLAIMS:
1. A detection system (100) for detecting the location of a target (101), comprising:
at least one transmitter (102) for transmitting at least one probing signal (103), a plurality of receivers (104) for receiving a first plurality of signals (105), said first plurality of signals being generated by refiection of said at least one probing signal against said target,
a spatial compression entity (110) for compressing said first plurality of signals into a second plurality of signals (113), the number of said second plurality of signals being smaller than the number of said first plurality of signals,
- a temporal compression entity (120) for compressing, at a frequency lower than the Nyquist frequency, said second plurality of signals into a plurality of signal data sets
(122) , and
a processing unit (123) configured to estimate the location of said target based on said plurality of signal data sets.
2. The detection system (100) as claimed in claim 1, wherein said processing unit
(123) is further configured to estimate the location of said target (101) in terms of a distance (D) from said plurality of receivers (104) and in terms of an angle (Θ) between a boresight (B) of said plurality of receivers and said target.
3. The detection system (100) as claimed in claim 1 or 2, wherein said processing unit (123) is further configured to estimate the location of said target (101) based on at least one of two-dimensional beamforming and two-dimensional sparse reconstruction.
4. The detection system (100) as claimed in any one of the preceding claims, wherein said processing unit (123) is further configured to estimate the velocity (V) of said target (101).
5. The detection system (100) as claimed in claim 4, wherein said processing unit
(123) is further configured to estimate the velocity (V) of said target (101) towards said plurality of receivers (104).
6. The detection system (100) as claimed in any one of the preceding claims, wherein said processing unit (123) is further configured to estimate a location and a velocity (V) of said target (101) such that a trajectory of said target is estimated as a function of time.
7. The detection system (100) as claimed in any one of the preceding claims, wherein said spatial compression entity (110) comprises a plurality of sub-entities (111) comprising a plurality of operators (112) being configured to transform said first plurality of signals (105) into said second plurality of signals (113).
8. The detection system (100) as claimed in claim 7, wherein said temporal compression entity (120) comprises a plurality of sub-entities (121) comprising at least one analog-to-information converter (AIC) arranged for analog-to-digital conversion of said second plurality of signals (113) into said plurality of signal data sets (122).
9. The detection system (100) as claimed in claim 8, wherein said at least one analog-to-information converter (AIC) is arranged for compressing said second plurality of signals (113) at a rate Μτ times Fs/Ντ into said signal data set (122), wherein Μτ is smaller than NT, and wherein Fs is the Nyquist frequency.
10. The detection system (100) as claimed in any one of the preceding claims, wherein said processing unit (123) is further configured to estimate the number of targets
(101) based on a detected direction from which said first plurality of signals (105) are received.
11. A lighting control system (400) for controlling a lighting function (402) of at least one light source (403), comprising a detection system (401) according to any one of claims 1 to 10, wherein said processing unit (123) is further configured to control said lighting function as a function of the estimated location of said target (101).
12. A method (300) for detecting the location of a target (101), comprising the steps of:
transmitting (301) at least one probing signal (103),
receiving (302) a first plurality of signals (105), said first plurality of signals being generated by reflection of said at least one probing signal that is reflected against the target,
compressing (303) said first plurality of signals into a second plurality of signals (113), the number of said second plurality of signals being smaller than the number of said first plurality of signals,
- compressing (304), at a frequency lower than the Nyquist frequency, said second plurality of signals into a plurality of signal data sets (122), and
estimating (305) the location of said target based on said plurality of signal data sets.
13. The method (300) as claimed in claim 12, wherein said step of estimating
(305) the location of said target (101) further comprises estimating the location of said target in terms of an angle (Θ) between a boresight (B) of said plurality of receivers (104) and said target (101).
14. The method (300) as claimed in claim 12 or 13, wherein said step of estimating (305) the location of said target (101) further comprises estimating the location of said target based on at least one of two-dimensional sparse reconstruction or two-dimensional beamforming.
15. The method (300) as claimed in any one of claims 12 to 14, further comprising the step of estimating a velocity (V) of said target (101).
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