Patent Publication Number: US-2022234534-A1

Title: Centralized occupancy detection system

Description:
BACKGROUND 
     Vehicle manufacturers employ occupancy sensors to detect which seats are occupied during operation. Such sensors enable manufacturers to offer features for enhancing passenger safety or comfort, e.g., seatbelt reminders, seatbelt pretensioning, airbag enablement, child presence reminders, accessory power timeout adjustment. In cars or other vehicles having a relatively small number of seats, each seat may be equipped with an occupancy sensor, traditionally in the form of a weight sensor. However, weight sensors often suffer from “false positive” detections when objects such as backpacks or purses are placed on the seat. Moreover, as the number of seats in a vehicle increases, manufacturers typically choose to omit the occupancy sensors, foregoing the associated benefits due to the added costs. 
     SUMMARY 
     The problems identified above may be addressed at least in part by a centralized occupancy detection system that enables monitoring of multiple seats, or more generally, multiple stations, with a single sensor. As one example, an illustrative vehicle includes: one or more stations each configured to accommodate an occupant of the vehicle, a radar-reflective surface, and a radar transceiver configured to use the radar-reflective surface to detect an occupant of at least one of the stations. 
     As another example, an illustrative vehicle includes: multiple stations to each accommodate an occupant of the vehicle, and a radar transceiver configured to examine each of the multiple stations to determine whether that station has an occupant. 
     As yet another example, an illustrative multi-station occupancy detector includes: an antenna array; a radar transceiver coupled to the antenna array to provide transmit signals and to accept receive signals; a memory having a set of azimuth-elevation-range parameter values for each of multiple stations configured to accommodate vehicle occupants; and a controller configured to adjust relative phases of the transmit signals and analyze receive signals in accordance with each set of azimuth-elevation-range parameter values to derive radar measurements indicating occupancy of each station. 
     Each of the foregoing examples can be employed individually or in conjunction, and may include one or more of the following features in any suitable combination: 1. the radar transceiver uses an antenna array to obtain separable occupancy measurements of the multiple stations. 2. the radar transceiver is configured to detect an occupant of a second station of the multiple stations via line of sight. 3. the radar-reflective surface is formed by a roof of the vehicle. 4. the radar-reflective surface is attached to a roof of the vehicle. 5. the radar transceiver is attached to or incorporated in a dashboard of the vehicle. 6. at least one station is in a second row of seating. 7. at least one station is in a third row of seating. 8. at least one of the azimuth-elevation-range parameter value sets corresponds to a signal transmission and reception path that reflects from a radar-reflective surface. 9. at least one of the azimuth-elevation-range parameter value sets corresponds to a direct line-of-sight signal transmission and reception path. 10. at least one of the azimuth-elevation-range parameter value sets corresponds to a station in a second row of seating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cutaway perspective view of an illustrative vehicle cabin with a centralized occupancy detection system. 
         FIG. 1B  is a cross section of an illustrative vehicle cabin with a centralized occupancy detection system. 
         FIG. 2  is a cutaway top view of an illustrative vehicle cabin with a centralized occupancy detection system. 
         FIG. 3  is a block diagram of an illustrative centralized occupancy detector. 
         FIG. 4  is a flow diagram of an illustrative calibration method. 
         FIG. 5  is a flow diagram of an illustrative centralized occupancy detection method. 
         FIG. 6  is a graph of illustrative radiation patterns from a four-element phased antenna array. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood that the following description and accompanying drawings are provided for explanatory purposes, not to limit the disclosure. To the contrary, they provide the foundation for one of ordinary skill in the art to understand all modifications, equivalents, and alternatives falling within the scope of the claims. 
       FIG. 1A  shows an illustrative vehicle  102  having five stations designed to accommodate occupants, each of the stations having an associated volume (labeled A through E) that would be at least partially filled by the occupant of that station. The vehicle  102  further includes a centralized occupancy detector  104  configured to monitor the volumes associated with each of the five stations to detect whether the stations are occupied. Occupants are expected to be living beings, which generally have a large water percentage and are accordingly reflective to radar signals (at least to a higher degree than the air that would occupy the volume in the absence of an occupant). 
     The centralized occupancy detector  104  includes a radar transceiver and an antenna array that can direct radar signal energy to each of the multiple stations and sense reflected radar energy from each of the multiple stations. The occupancy detector  104  may drive the antenna elements in a phased fashion that steers the transmitted signal energy along a desired direction (expressible in terms of azimuth and elevation angles from the antenna array), and may further combine signals received via the antenna elements in a phased fashion that provides directional sensitivity to reflected signal energy along the desired direction. Alternatively, the occupancy detector  104  may drive the antenna elements in an independent fashion (e.g., using time division multiplexing, frequency division multiplexing, code division multiplexing), determine each element&#39;s response when a given transmission element is used, and process the measurements mathematically to provide virtual steering of the transmitted energy and directional sensitivity. In either case, the occupancy detector  104  uses the antenna array to obtain directionally separable measurements of the volumes associated with the multiple stations. 
       FIG. 1A  shows illustrative paths along which transmitted radar signal energy may propagate from the detector  104  (shown here on or in the dashboard near the front door post on the passenger side) to each of the volumes A through E. The paths to front seat volumes A and B are direct, line-of-sight paths  106 . Because the front seats obstruct a direct view of the back seat volumes C-E, the remaining paths reflect from a radar-reflective surface such as the cabin roof  108 . The transmitted signal energy for the back seat volumes C-E is directed from the detector  104  to corresponding reflection points  110  on the cabin roof. In each case, the radar signal energy reflected from the occupant (if any) returns along the transmission path. 
       FIG. 18  shows a side cross section of illustrative vehicle  102 , with a front seat volume A and a back seat volume C. Centralized occupancy detector  104  can direct radar signal energy along direct, line-of-sight path  106  to volume A, and along a reflected path  112  from reflection point  110 . Observe that added reflectors, such as reflector  114 , can provide alternative reflected paths  116  if the geometry of the cabin roof  108  is unsatisfactory (e.g., due to the presence of a sunroof). The added reflector can take the form of an angled plane, but a convex surface (e.g., a semi-dome) may be preferred if an increased range of view is desired, or a concave surface (e.g., parabolic reflector) may be preferred for increased measurement separability and gain. The added reflectors can be attached to the cabin roof, or alternatively, the cabin roof may be shaped to provide the desired shapes to the reflection points. Where it is desired to minimize the profile of the surfaces for the reflection points, those surfaces may alternatively be formed or “shaped” using segmented surfaces such as Fresnel reflectors, or using reflection-type holographic optical elements. 
       FIG. 2  shows a cutaway top view of a twelve passenger van  202 , which like most vehicles designed to accommodate more than six passengers provides seating that is more upright than most cars and has a correspondingly higher cabin roof that may permit a dashboard-mounted occupancy detector  204  to monitor additional rows of seating. Reflection points  206  on the cabin roof may correspond to volumes C-E for the second row of seats. Roof reflection points  208  may correspond to volumes F-H for the third row of seats. Roof reflection points  210  may correspond to volumes I-L for the fourth row of seats. (Front row volumes A-B may be monitored via direct line of sight from the occupancy detector  204 .) If the existing roof profile provides suboptimal positioning of the reflection points, added reflectors or surface shaping may be used to improve the reflection point positions. 
       FIG. 3  shows an illustrative centralized occupancy detector, which includes a transceiver chip  300  coupled to an antenna array having four transmit elements  301  and eight receive elements  302 . Power amplifiers  303 A- 303 D drive the transmit antenna elements  301  with amplified signals from transmitter circuitry  304 . Circuitry  304  generates a transmit signal within a programmable frequency band, using a programmable chirp rate and range. The transmit signal generator may employ a phase-locked loop (PLL) with suitable frequency multipliers. Splitters and phase shifters derive the transmit signals for the multiple power amplifiers  303 A- 303 D to transmit concurrently with adjustable phase differences to enable beam steering, and further provide a reference “local oscillator” signal to the receivers for use in the down-conversion process. In the illustrated example, the transceiver chip  300  includes 4 transmitters, each of which is fixedly coupled to a corresponding transmit antenna element  301 . 
     Chip  300  further includes 4 receivers (RX-1 through RX-4) each of which is selectably coupled to two of the receive antenna elements  302 , providing a reconfigurable MIMO arrangement with  8  receive antenna elements, four of which can be employed concurrently to collect measurements. Four analog to digital converters (ADCs)  306 A- 306 D sample and digitize the down-converted receive signals from the receivers RX-1 through RX-4, supplying the digitized signals to a microcontroller unit (MCU)  308  for filtering and processing, or directly to a high-bandwidth interface  310  to enable off-chip processing of the digitized baseband signals. If used, the MCU  308  generates image data that can be conveyed to an electronic control unit (ECU) or other host processor via the high-bandwidth interface  310 . 
     A control interface  312  enables the ECU or other host processor to configure the operation of the transceiver chip  300 , including the test and calibration peripheral circuits  314  and the transmit signal generation circuitry  304 . As discussed further below, the MCU  308  may configure the transmitter circuitry  304  to drive the transmit antenna elements with relative phase differences that provide beam-steering of the transmitted signal energy, and may analyze the receive signals with various relative phase differences to provide enhanced directional sensitivity to the received signal energy. 
     An internal memory may hold a lookup table of azimuthal angles, elevation angles, and ranges, which are also expressible in terms of the desired relative phase differences and frequency offsets (or FFT bins, as described further below). The lookup table stores the parameter values associated with each of the stations to be monitored by the occupancy detector. The MCU  308  may iterate through the table, applying the relative phase differences and determining reflected energy amplitude at the specified range and direction for comparison with a predetermined threshold. The MCU  308  or external processor may determine that each station where the reflected energy amplitude exceeds the threshold is occupied. 
       FIG. 4  is a flow diagram of an illustrative occupancy detector calibration method, which may be a one-time factory calibration to determine the appropriate parameter values to be stored in the internal (nonvolatile) memory. The illustrative method includes a series of blocks  402 - 416  that are performed for a first selected station in the vehicle and repeated for each subsequently selected station. In block  402 , a reflector is placed in the detection volume for the first selected station and any reflectors in the detection volumes of other selected stations preferably removed. The reflector may be a passive reflector such as a corner reflector. If active reflectors are used, a reflector may be positioned in each detection volume, with only the reflector at the first selected station enabled and the rest being disabled. 
     In block  404 , the occupancy detector steps through its full range of azimuth and elevation steering angles, transmitting radar signal energy and measuring the responses of each receive antenna element. The transmitted radar signals are preferably chirps, so that after downconversion the reflected signal energy is at a frequency offset corresponding to its travel time (and thus corresponding to the path distance or “range” of the reflector). In block  406 , the occupancy detector performs a two dimensional frequency transform, such as a fast Fourier transform (FFT), for the response signals at each given azimuth and elevation steering angle. The 2D FFT converts the response signals into frequency coefficients representing reflected signal energy as a function of range and incidence angle. The frequency coefficients should exhibit a peak at a range and incidence angle corresponding to the selected station, and with the strength and location of the peak varying as a function of the transmit signal azimuth and elevation angles. 
     In some implementations, the transmit signal azimuth and elevation angles that maximize the peak strength are chosen as the parameter values for the selected station in block  414 , along with the FFT bin location (range, incidence angle) of the peak. While this approach may work well when using antenna arrays with narrow beamwidths (e.g., with larger numbers of antenna elements), it may be suboptimal for antenna arrays designed for lower-cost occupancy detectors. Antenna arrays with smaller numbers of antenna elements may have larger beam widths and more significant grating lobes. See, for example,  FIG. 6  which shows radiation patterns for a four-element phased antenna array steered to zero degrees and to 15 degrees from the normal vector. Even when the main beam is steered to a selected station, other stations may receive (and their occupants may reflect) significant radar signal energy. To account for such potential interference, alternative calibration method implementations may include optional blocks  408 - 412  for measuring interference to enable determination of the signal-to-interference ratio. 
     In optional block  408 , the reflector for the selected station is removed or disabled, and reflectors are provided or enabled for all other stations. In optional block  410 , the occupancy detector again steps through the full range of azimuth and elevation steering angles, transmitting radar signal energy and measuring the responses of each receive antenna element. In optional block  412 , the 2D FFT is performed for the response signals at each given transmit azimuth and elevation direction to obtain interference energy as a function of range and incidence angle. The magnitudes of the frequency coefficients from block  406  are each divided by the corresponding frequency coefficient magnitudes from block  412 , producing a signal-to-interference ratio as a function of the parameter values. As before, the coefficient magnitudes should exhibit a peak at a range and incidence angle corresponding to the selected station, with the maximum value and location varying as a function of the transmit signal azimuth and elevation angles. The parameter values yielding the maximum signal-to-interference ratio can be chosen for the selected station in block  414 . 
     In block  416 , the method determines whether parameter values have been chosen for each of the stations, and if not, blocks  402 - 416  are repeated for the next selected station. Once parameter values have been determined for each station, the calibration method concludes with the storage of the parameter values in internal memory. In some implementations, the occupancy detection threshold is determined by positioning a standardized replica of occupants at one or more stations, measuring the reflected signal energy, and setting the threshold at a value that reliably distinguishes between the presence and absence of an occupant at each station. 
       FIG. 5  is a flow diagram of an illustrative occupancy detection method that may be implemented by a centralized occupancy detector. The method includes a series of blocks that are performed for each of the multiple stations, and the method itself may be repeated in a periodic or in an event-triggered fashion to monitor station occupancy as it changes over time. 
     In block  502 , the occupancy detector selects a first or next station. In block  504 , the occupancy detector retrieves the parameter values for the selected station from memory. The parameter values may be those values chosen during the calibration process as the best transmit azimuth angle, transmit elevation angle, FFT range bin, and FFT incidence angle bin. In block  506 , the occupancy detector uses the parameter values for transmitting a radar signal, obtaining the associated response signals, and processing the response signals to derive a reflected radar signal energy measurement. In block  508 , the occupancy detector compares the reflected radar signal energy measurement to a predetermined threshold to determine whether the selected station is occupied. 
     In block  510 , the occupancy detector checks to determine if a measurement has been obtained for each station, and if not, blocks  502 - 510  are repeated for the next selected station. Otherwise, in block  512  the occupancy detector updates a register indicating the occupancy status for each of the stations. In at least some implementations, the update process combines multiple measurements for each station to provide enhanced reliability. 
     Numerous other modifications, equivalents, and alternatives, will become apparent to those of ordinary skill in the art once the above disclosure is fully appreciated. For example, the illustrative methods are shown and described as if they occur in a sequential fashion, but those skilled in the art will recognize that many of the operations can be pipelined or otherwise performed in parallel, potentially with out-of-order operations and speculative execution where it is deemed desirable to trade off hardware complexity for faster execution. 
     As another example, the foregoing discussion describes occupant stations as seats in a vehicle, but the principles and techniques of this disclosure are also applicable to any enclosed or partially enclosed space having stations to accommodate occupants, including not only seats, but also designated areas for standing, kneeling, reclining, and for securing wheelchairs, gurneys, child seats, or other transport mechanisms. Though the drawings show a car and a passenger van, other suitable vehicles include shuttles, buses, trains, boats, private airplanes, commercial jets, space transports, submersibles, and elevators. For large vehicles having multiple seating sections, multiple centralized occupancy detectors may be employed, e.g., one for each section. 
     As yet another example, the drawings show the centralized occupancy detector as part of the vehicle dashboard, but it should be recognized that any position enabling separable measurements of the various stations can be used. As one contemplated variation, the centralized occupancy detector is positioned in a console between or just behind the front seats, acquiring each of its measurements via reflections from the cabin roof. It is intended that the following claims be interpreted to embrace all such modifications, equivalents, and alternatives where applicable.