SIGN APPARATUS FOR VEHICLE

Disclosed is a sign apparatus for displaying a sign for traffic or a vehicle, where the sign apparatus includes a display configured to display the sign and to permit a radar signal radiated from a source to pass, a filter configured to attenuate a signal of at least one frequency in the radar signal passing through the display and to allow a signal of a remaining frequency to pass, and a reflector configured to reflect the signal passing through the filter, wherein the reflected signal includes encoded identification information of the sign.

CROSS-REFERENCE TO RELATED APPLICATIONS

BACKGROUND

The following disclosure relates to a sign apparatus for a vehicle.

2. Description of Related Art

Advanced driver-assistance systems (ADAS) improve drivers' safety and convenience and avoid dangerous situations by using sensors mounted inside or outside a vehicle.

The sensors used for ADAS may include a camera, an infrared sensor, an ultrasonic sensor, a light detection and ranging (lidar) sensor, and a radio detection and ranging (radar) sensor. Among those sensors, the radar sensor may stably measure objects in the vicinity of a vehicle without being affected by the surrounding environment, such as weather, when compared to optical sensors.

SUMMARY

In one general aspect, there is provided an apparatus for displaying a sign including a display configured to display the sign and to permit a radar signal radiated from a source to pass, a filter configured to attenuate a signal of at least one frequency in the radar signal passing through the display and to allow a signal of a remaining frequency to pass, and a reflector configured to reflect the signal passing through the filter, wherein the reflected signal includes encoded identification information of the sign.

The identification information may have N digits, a first digit to a last digit of the N digits may correspond to different frequencies, and the filter may be configured to attenuate a signal of a frequency corresponding to a digit having a first value and to allow a signal of a frequency corresponding to a digit having a second value to pass.

The filter may be configured to attenuate a signal of a frequency corresponding to the first digit in response to the first digit having the first value, and to allow the signal of the frequency corresponding to the first digit in response to the first digit having the second value.

The filter may include unit cells, and each of the unit cells may include a resonator having a frequency corresponding to a digit having the first value as a resonance frequency.

The filter may include unit cells, and each of the unit cells may include a number of resonators corresponding to a number of first values in the identification information or equal to a multiple of the number of first values.

Each of the unit cells may include resonators of different sizes, in response to the identification information having a plurality of first values.

The resonators may be positioned on different layers.

A spacing between the unit cells corresponds to half a wavelength value of a center frequency of the radiated radar signal.

The filter may be spaced apart from the reflector by a first distance.

The first distance may be greater than a result of multiplying a wavelength value of a center frequency of the radiated radar signal with a value.

The reflector may include a trihedral corner reflector.

The source may include a radar sensor disposed in an autonomous vehicle.

In another general aspect, there is provided an apparatus for displaying a sign, the apparatus including a display configured to display the sign and to permit a radar signal radiated from a source to pass, a filter comprising resonators, the filter configured to attenuate a signal of a resonant frequency of each of the resonators in the radar signal passing through the display and to allow a signal of a remaining frequency to pass, and a reflector configured to reflect the signal passing through the filter, wherein the reflected signal includes encoded identification information of the sign.

The identification information may have N digits, a first digit to a last digit of the N digits may correspond to different frequencies, and the resonant frequency may be same as a frequency of a digit having a first value in the identification information.

The filter may include unit cells, and each of the unit cells may include one or more resonators of the resonators.

A spacing between the unit cells may correspond to half a wavelength value of a center frequency of the radiated radar signal.

The filter may be spaced apart from the reflector by a first distance value.

The first distance value may be greater than a result of multiplying a wavelength value of a center frequency of the radiated radar signal with a value.

The reflecting board may include a trihedral corner reflector.

The source may include a radar sensor disposed in an autonomous vehicle.

DETAILED DESCRIPTION

Although terms such as “first,” “second,” and “third”, or A, B, (a), (b), and the like may be used herein to describe various members, components, regions, layers, portions, or sections, these members, components, regions, layers, portions, or sections are not to be limited by these terms. Each of these terminologies is not used to define an essence, order, or sequence of corresponding members, components, regions, layers, portions, or sections, for example, but used merely to distinguish the corresponding members, components, regions, layers, portions, or sections from other members, components, regions, layers, portions, or sections. Thus, a first member, component, region, layer, portions, or section referred to in the examples described herein may also be referred to as a second member, component, region, layer, portions, or section without departing from the teachings of the examples.

Throughout the specification, when a component or element is described as being “connected to,” “coupled to,” or “joined to” another component or element, it may be directly “connected to,” “coupled to,” or “joined to” the other component or element, or there may reasonably be one or more other components or elements intervening therebetween. When a component or element is described as being “directly connected to,” “directly coupled to,” or “directly joined to” another component or element, there can be no other elements intervening therebetween. Likewise, expressions, for example, “between” and “immediately between” and “adjacent to” and “immediately adjacent to” may also be construed as described in the foregoing. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. For example, “A and/or B” may be interpreted as “A,” “B,” or “A and B.”

Hereinafter, examples will be described in detail with reference to the accompanying drawings. When describing the examples with reference to the accompanying drawings, like reference numerals refer to like elements and a repeated description related thereto will be omitted.

FIG.1illustrates an example of recognizing a surrounding environment through a radar signal processing method.

Referring toFIG.1, a radar signal processing apparatus110may be disposed in a vehicle150. In some examples, the radar signal processing apparatus110detects information on a target180ahead of the vehicle150(e.g., range, velocity, direction, and the like) by analyzing a radar signal received from a radar sensor111. In some examples, the radar sensor111may be positioned inside or outside the radar signal processing apparatus110, and the radar signal processing apparatus110may detect the information on the target180based on both the radar signal received from the radar sensor111and data collected by another sensor (e.g., an image sensor, etc.). Resolving power in radar data processing may be divided into resolving power performance in terms of hardware and resolving power performance in terms of software. Hereinafter, improvement of the resolving power performance in terms of software comprising instructions that when operated on the hardware configure the hardware to perform various operations will be mainly described.

In an example, the resolving power refers to the power of a device to discriminate a very small change, for example, smallest unit discriminative power, and it may be expressed as “resolving power=(discriminable smallest scale unit)/(total operation range)”. The smaller the resolving power value of the device, the more precise results the device may output. The resolving power value may also be referred to as the resolving power unit. For example, if the device has a small resolving power value, the device may discriminate a relatively small unit and thus, the device may output results with increased resolution and improved precision. If the device has a great resolving power value, the device may not discriminate a small unit and thus, output results with reduced resolution and reduced precision.

The radar signal processing apparatus110may be mounted on the vehicle150as shown inFIG.1. The vehicle may perform various automated driving activities, such as, for example, adaptive cruise control (ACC), automatic emergency braking (AEB), blind spot detection (BSD), lane change assistance (LCA), and other similar operations based on the range to the target180detected by the radar signal processing apparatus110. Furthermore, the radar signal processing apparatus110may generate a surrounding map130in addition to detecting the range. The surrounding map130is a map representing the positions of various targets existing around the radar signal processing apparatus110, such as the target180. The targets may include moving objects such as vehicles and people, and static objects such as guardrails, traffic signs, signs, and traffic lights present in the background.

The surrounding map130may be generated using single scan imaging. In single scan imaging, the radar signal processing apparatus110acquires a single scan image120from the sensor and generates the surrounding map130from the acquired single scan image120. The single scan image120is generated from the radar signal sensed by a single radar sensor111, and may represent the ranges indicated by radar signals received at a predetermined elevation angle with a relatively high resolving power. For example, in the single scan image120shown inFIG.1, the horizontal axis denotes the steering angle of the radar sensor111, and the vertical axis denotes the range from the radar sensor111to the target180. However, the form of a single scan image is not limited to that shown inFIG.1. The single scan image may be represented in a different format without deviating from the script and scope of the illustrative examples.

The steering angle may be an angle corresponding to a target direction from the radar signal processing apparatus110toward the target180. For example, the steering angle may be an angle between the target direction and the traveling direction of the radar signal processing apparatus110(or the vehicle150including the radar signal processing apparatus110). In an example, the steering angle is described mainly based on an angle through a horizontal plane, but is not limited thereto. For example, the steering angle may also be applied to an elevation angle.

The radar signal processing apparatus110may obtain information on the shape of the target180through a multi-radar map. The multi-radar map may be generated from a combination of radar scan images. For example, the radar signal processing apparatus110may generate the surrounding map130by spatiotemporally combining the radar scan images acquired as the radar sensor111moves. The surrounding map130may be a type of radar image map and in an example be used for pilot parking.

The radar signal processing apparatus110may use direction of arrival (DOA) information to generate the surrounding map130. The DOA information refers to information indicating the direction in which a radar signal reflected from a target is received. The radar signal processing apparatus110may identify the direction in which the target exists relative to the radar sensor111using the DOA information described above. Therefore, such DOA information may be used to generate radar scan data and surrounding maps.

Radar information, such as range, velocity, DOA, and map information, about the target180generated by the radar signal processing apparatus110may be used to control the vehicle150equipped with the radar signal processing apparatus110. For example, controlling the vehicle150may include controlling the speed and steering of the vehicle150, such as ACC, AEB, BSD, and LCA. A control system of the vehicle150may control the vehicle150directly or indirectly based on the radar information. For example, when a Doppler velocity of a target is measured, the control system may accelerate the vehicle150to follow the target or may brake the vehicle150to prevent a collision with the target.

FIG.2illustrates an example of a radar signal processing apparatus.

Referring toFIG.2, a radar signal processing apparatus200(e.g., the radar signal processing apparatus110ofFIG.1) may include a radar sensor210(e.g., the radar sensor111ofFIG.1), a processor220, an output device230, and a memory240. The radar sensor210may radiate a radar signal to the outside of the radar sensor210and receive a signal (hereinafter, referred to as the “reflected signal”) as the radiated radar signal is reflected by a target.

The radar signal may include a chirp signal with a carrier frequency modulated based on a frequency modulation model. The frequency of the radar signal may change within a band. For example, the frequency of the radar signal may linearly change within the band.

The radar sensor210may include an array antenna and be configured to transmit a radar signal and to receive a reflected signal through the array antenna. The array antenna may include a plurality of antenna elements. Multiple input multiple output (MIMO) may be implemented through the plurality of antenna elements. In this case, a plurality of MIMO channels may be formed by the plurality of antenna elements. For example, a plurality of channels corresponding to M×N virtual antennas may be formed through M transmission antenna elements and N reception antenna elements. Here, reflected signals received through the channels may have different phases according to reception directions.

Radar data may be generated based on the radar signal and the reflected signal. For example, the radar sensor210may transmit the radar signal through the array antenna based on the frequency modulation model, receive the reflected signal through the array antenna when the radar signal is reflected by the target, and generate an intermediate frequency (IF) signal based on the radar signal and the reflected signal. The IF signal may have a frequency corresponding to a difference between the frequency of the radar signal and the frequency of the reflected signal. The processor220may perform a sampling operation on the IF signal, and generate raw radar data through sampling results. However, the operation of the processor220is not limited thereto, and the processor220may perform at least one of the operations described with reference toFIGS.3to16in parallel or in a time series.

The processor220may control at least one other component of the radar signal processing apparatus200and perform processing of various pieces of data or computations. The processor220may control an overall operation of the radar signal processing apparatus200and may execute corresponding processor-readable instructions for performing operations of the radar signal processing apparatus200. The processor220may execute, for example, software stored in the memory240to control one or more hardware components, such as, sensor210of the radar signal processing apparatus200connected to the processor220and may perform various data processing or operations, and control of such components.

The processor220may be a hardware-implemented data processing device. The hardware-implemented data processing device220may include, for example, a main processor (e.g., a central processing unit (CPU), a field-programmable gate array (FPGA), or an application processor (AP)) or an auxiliary processor (e.g., a GPU, a neural processing unit (NPU), an image signal processor (ISP), a sensor hub processor, or a communication processor (CP)) that is operable independently of, or in conjunction with the main processor. Further details regarding the processor220are provided below.

The processor220may generate and use information on the target based on the raw radar data. For example, the processor220may perform range fast Fourier transform (FFT), Doppler FFT, constant false alarm rate (CFAR) detection, DOA estimation, and the like based on the raw radar data, and obtain the information on the target, such as range, velocity, and direction. Such information on the target may be provided for various applications such as AAC, AEB, BSD, and LCA.

The memory240may store radar information, such as the radar signal and the reflected signal, the surrounding map130, the single scan image120, and/or other information related to determine the sign. However, this is only an example, and the information stored in the memory240is not limited thereto. In an example, the memory240may store a program (or an application, or software). The stored program may be a set of syntaxes that are coded and executable by the processor220to operate the radar signal processing apparatus200. The memory240may include a volatile memory or a non-volatile memory.

The volatile memory device may be implemented as a dynamic random-access memory (DRAM), a static random-access memory (SRAM), a thyristor RAM (T-RAM), a zero capacitor RAM (Z-RAM), or a twin transistor RAM (TTRAM).

The non-volatile memory device may be implemented as an electrically erasable programmable read-only memory (EEPROM), a flash memory, a magnetic RAM (MRAM), a spin-transfer torque (STT)-MRAM, a conductive bridging RAM (CBRAM), a ferroelectric RAM (FeRAM), a phase change RAM (PRAM), a resistive RAM (RRAM), a nanotube RRAM, a polymer RAM (PoRAM), a nano floating gate Memory (NFGM), a holographic memory, a molecular electronic memory device), or an insulator resistance change memory. Further details regarding the memory240are provided below.

In some examples, the processor220may output the surrounding map130and/or the single scan image120through the output device230. In some examples, the output device230may provide an output to a user through auditory, visual, or tactile channel. The output device230may include, for example, a speaker, a display, a touchscreen, a vibration generator, and other devices that may provide the user with the output. The output device230is not limited to the example described above, and any other output device, such as, for example, computer speaker and eye glass display (EGD) that are operatively connected to the electronic device740may be used without departing from the spirit and scope of the illustrative examples described. In an example, the output device230is a physical structure that includes one or more hardware components that provide the ability to render a user interface, output information and speech, and/or receive user input.

In some examples, the radar signal processing apparatus200may be installed in or wirelessly connected to a vehicle. Hereinafter, a vehicle refers to any mode of transportation, delivery, or communication such as, for example, for example, an automobile, a truck, a tractor, a scooter, a motorcycle, a cycle, an amphibious vehicle, a snowmobile, a boat, a public transit vehicle, a bus, a monorail, a train, a tram, an autonomous vehicle, an unmanned aerial vehicle, a bicycle, a walking assist device (WAD), a robot, a drone, and a flying object such as an airplane. In some examples, the vehicle may be, for example, an autonomous vehicle, a smart mobility, an electric vehicle, an intelligent vehicle, an electric vehicle (EV), a plug-in hybrid EV (PHEV), a hybrid EV (HEV), or a hybrid vehicle, an intelligent vehicle equipped with an advanced driver assistance system (ADAS) and/or an autonomous driving (AD) system.

In some examples, the autonomous vehicle is a self-driving vehicle that is equipped with one or more sensors, cameras, radio detection and ranging (RADAR), light detection and ranging (LiDAR) sensor, an infrared sensor, and an ultrasonic sensor, and/or other data-capturing devices that collect information about the surrounding environment. The autonomous vehicle may be controlled by an onboard computer system that uses algorithms, machine learning, and other artificial intelligence techniques to interpret the sensor data and to make decisions based on that information. The computer system can control the vehicle's speed, direction, acceleration, and braking, as well as other systems such as lighting, heating, and air conditioning. In some examples, the autonomous vehicle may be equipped with communication technologies to interact with other vehicles, infrastructure, and/or a central control system(s). The autonomous vehicle may operate in various modes, such as, for example, fully autonomous, semi-autonomous, and remote control where it is controlled by the central control system(s).

In some examples, the radar signal processing apparatus200may be implemented as, or in, various types of computing devices, such as, a personal computer (PC), a data server, or a portable device. In an example, the portable device may be implemented as a laptop computer, a mobile phone, a smart phone, a tablet PC, a mobile internet device (MID), a personal digital assistant (PDA), an enterprise digital assistant (EDA), a digital still camera, a digital video camera, a portable multimedia player (PMP), a personal navigation device or portable navigation device (PND), or a smart device. In an example, the computing devices may be a wearable device, such as, for example, a smart watch and an apparatus for providing augmented reality (AR) (hereinafter simply referred to as an AR provision device) such as AR glasses, a head mounted display (HMD), various Internet of Things (IoT) devices that are controlled through a network, and other consumer electronics/information technology (CE/IT) devices.

FIG.3illustrates an example of a radar sensor.

Referring toFIG.3, a radar sensor310(e.g., the radar sensor111,210) may include a chirp transmitter311, antennas312and313, a frequency mixer314, an amplifier315, and a radar signal processor316.

The radar signal processor316may correspond to the processor220ofFIG.2. In some examples, the radar signal processor316may be disposed outside the radar sensor310, like the processor220. The radar sensor310may radiate a signal (e.g., a radar signal) through the transmission antenna312and may receive a signal (e.g., a reflected signal) through the reception antenna313.

AlthoughFIG.3shows a single transmission antenna312and a single reception antenna313as an example, the radar sensor310may include a plurality of transmission antennas and a plurality of reception antennas.

The radar sensor310may be, for example, a millimeter-wave (mmWave) radar and may be configured to measure the range to a target by analyzing a time of flight (ToF) and changes in the waveform of the radar signal, wherein the ToF is the time it takes for a radiated electromagnetic wave to return after being reflected by the target. In some examples, the mmWave radar may detect an object regardless of external environment changes such as fog, rain, and the like, compared to optical sensors including cameras. In some examples, the mmWave radar has better cost performance than Li DAR and may be used to compensate for the disadvantages of optical sensors described above.

In some examples, the radar sensor310may be implemented as a frequency modulated continuous wave (FMCVV) radar. The FMCW radar may be robust against external noise.

The chirp transmitter311may generate a frequency modulated (FM) signal (or FWCW signal)302with a frequency that changes with time. For example, the chirp transmitter311may generate the FM signal302by performing frequency modulation according to the frequency modulation characteristics of a frequency modulation model301. The FM signal302may also be referred to as a chirp signal. Herein, the frequency modulation model301may be a model configured to represent changes in a carrier frequency of a radar signal during a transmission time. The vertical axis of the frequency modulation model301may denote the carrier frequency, and the horizontal axis may denote time. For example, the frequency modulation model301may have a frequency modulation characteristic of linearly changing (e.g., linearly increasing or linearly decreasing) the carrier frequency. As another example, the frequency modulation model301may have a frequency modulation characteristic of non-linearly changing the carrier frequency.

FIG.3shows the frequency modulation model301having a frequency modulation characteristic where the frequency linearly increases over a time period, and after the time period the frequency linearly decreases over another time period. In the example illustrated inFIG.3, the rate of linear increase of the frequency and the rate of linear decrease of the frequency are different from each other. The chirp transmitter311may generate the FM signal302having a carrier frequency according to the frequency modulation model301. For example, as shown inFIG.3, the FM signal302may exhibit a waveform in which the carrier frequency gradually increases in some intervals, and exhibit a waveform in which the carrier frequency gradually decreases in the remaining intervals.

A portion of the FM signal302may be coupled and transmitted to the frequency mixer314, and the remaining portion of the FM signal302may be radiated as a radar signal through the transmission antenna312. In some examples, the radar sensor310may include a duplexer. In this example, radiating a radar signal and receiving a reflected signal may be performed by the same antenna (hereinafter, referred to as the “antenna A”), unlike the example shown inFIG.3. The chirp transmitter311may transmit the FM signal302to the duplexer. The duplexer may determine a transmission path and a reception path for signals through the antenna A. For example, the duplexer may form a signal path from the chirp transmitter311to the antenna A, transmit the FM signal302to the antenna A through the signal path, and then radiate the FM signal302to the outside. While the radar sensor310receives the signal reflected from the target, the duplexer may form a signal path from antenna A to the radar signal processor316.

The frequency mixer314may compare a frequency308of the reflected signal and a frequency307of the radar signal. For reference, the frequency307of the radar signal may change as the carrier frequency indicated by the frequency modulation model301changes. The frequency mixer314may detect an intermediate frequency (IF) corresponding to a frequency difference between the frequency308of the reflected signal and the frequency307of the radar signal. In a graph309shown inFIG.3, the frequency difference between the radar signal and the reflected signal is constant during an interval in which the carrier frequency linearly increases along the time axis in the frequency modulation model301, and is proportional to the range between the radar sensor310and the target. Accordingly, the range between the radar sensor310and the target may be derived from the frequency difference between the radar signal and the reflected signal. A beat frequency signal detected through the frequency mixer314may be transmitted to the radar signal processor316via the amplifier315. The beat frequency signal may be expressed by Equation 1 below.

In Equation 1, α denotes a path loss attenuation, φ0denotes a phase offset (or a direct current constant value), fcdenotes a carrier frequency, tddenotes a round-trip delay, B denotes a sweep bandwidth of a transmitted chirp, and Tcdenotes a chirp duration. Tcmay be the same value as Tchirpin the graph309.

A plurality of radar sensors may be installed in various parts of a vehicle, and the radar signal processing apparatus110,200may calculate a range to a target, a direction, and a relative velocity in all directions of the vehicle based on information sensed by the plurality of radar sensors. The radar signal processing apparatus110,200may be mounted on the vehicle, and may provide various functions, such as, for example, ACC, AEB, BSD, LCA, etc., which are useful for driving.

Each of the plurality of radar sensors may radiate a radar signal including a chirp signal with a frequency modulated based on a frequency modulation model to the outside and receive a signal reflected from the target. The radar signal processing apparatus110,200may determine a range from each of the plurality of radar sensors to a target from a frequency difference between the radiated radar signal and the received reflected signal. In addition, when the radar sensor310has a plurality of channels, the radar signal processing apparatus110,200may derive a DOA of the signal reflected from the target based on phase information in the raw radar data.

In some examples, the radar sensor310may use a wide bandwidth and MIMO to meet the demands for a wide field of view (FoV) and a high resolution (HR) for various applications. The range resolution may increase through the wide bandwidth, and the angular resolution may increase through MIMO. The range resolution may represent the smallest unit to discriminate distance information on the target, and the angle resolution may represent the smallest unit to discriminate DOA information on the target. For example, the radar sensor310may use broadband such as 4 GHz, 5 GHz, or 7 GHz instead of a narrow band such as 200 MHz, 500 MHz, or 1 GHz.

The radar sensor310may identify a transmission signal of each transmission antenna according to MIMO through time-division multiplexing (TDM). According to TDM, transmission antennas may alternately transmit transmission signals. Thus, the length of time of a rising interval of a carrier frequency of each transmission signal (that is, a chirp repetition period) may increase. This may cause a reduction in an unambiguously measurable Doppler velocity and/or in the range of the Doppler frequency. The radar signal processor316may perform signal processing that is robust against a Doppler ambiguity by compensating a coupling component between the Doppler frequency and the DOA and/or the Doppler velocity due to the movement of a target in a radar system based on TDM MIMO.

FIG.4illustrates an example of reception antennas of a radar sensor.

Equation 2 below may be derived by more specifically analyzing the round-trip delay component of the beat frequency signal of Equation 1.

In Equation 2, R denotes the range between an antenna element and a target, R ° denotes the range between the radar sensor310and the target, R ° denotes the range difference based on an interval between antenna elements of the radar sensor310, c denotes the speed of light, and d denotes the distance between the antenna elements. According to Equation 2, the round-trip delay element may be decomposed into a range component td,0and a DOA component td,θ. Equation 1 may be expressed as in Equation 3 below based on the range component td,0and the DOA component td,θof the round-trip delay component.

The range to the target may be derived by detecting a component ϕt(td,0) through a frequency analysis (e.g., a Fourier transform) of the beat frequency signal for each antenna element. The DOA may be estimated by detecting a third term 2πfctd,θof the component ϕ0from a phase change between the antenna elements.

When the radar sensor310has a plurality of reception channels, phase information in radar data (e.g., raw radar data) may indicate a phase difference between a phase of a signal received through each reception channel and a reference phase. The reference phase may be a predetermined phase, or may be set to a phase of one of the plurality of reception channels. For example, the radar signal processing apparatus200may set, for a reception antenna element, a phase of a reception antenna element adjacent to the reception antenna element as the reference phase.

In addition, the radar signal processor316may generate a radar vector of a dimension corresponding to the number of reception channels of the radar sensor310from the radar data. For example, if a radar sensor has four reception channels, the radar signal processing apparatus may generate a four-dimensional (4D) radar vector including phase values corresponding to the reception channels. The phase values corresponding to the reception channels may be numerical values representing the phase difference described above.

For example, it may be assumed that the radar sensor310has one transmission (TX) channel and four reception (RX) channels. In this case, a radar signal radiated through the TX channel may be reflected by a target and then received through the four RX channels. As shown inFIG.4, if a reception array antenna410of the radar sensor includes a first reception antenna element411, a second reception antenna element412, a third reception antenna element413, and a fourth reception antenna element414, a phase of a signal received at the first reception antenna element411may be set as a reference phase. When a reflected signal408reflected from the same target is received at the reception array antenna410, an additional distance A between the range from the target to the first reception antenna element411and the range from the target to the second reception antenna element412may be expressed as in Equation 4 below.

In Equation 4, a denotes a DOA in which the reflected signal408is received from the target, d denotes the distance between the reception antenna elements, and c denotes the speed of light.

FIG.5illustrates an example of an operation of processing chirp sequences.

A radar signal of one frame may include a plurality of chirp signals. For example, one frame may include a plurality of time slots, and the radar sensor310may transmit one chirp signal through one transmission antenna during each time slot. A time slot may be a unit time interval in which one chirp signal is transmitted. One frame may correspond to one scan. For example, one frame may include L chirp sequences, and each chirp sequence may include a plurality of time slots (e.g., M time slots). Each of the plurality of chirp sequences included in the same frame may include time slots in number equal to the number of transmission antennas included in the radar sensor310. A radar signal of one frame may include L×M chirp signals. The radar sensor310may radiate L×M chirp signals during a frame corresponding to one scan, and sense reflected signals when the L×M chirp signals are reflected. Here, L and M may each be an integer greater than or equal to “1”. The radar sensor310may include M transmission antenna elements, and each chirp sequence may include M time slots corresponding to the number of transmission antenna elements. InFIG.5, a frequency change tendency of a radar signal510shown for a frame of L=1 may include frequency change tendencies over time for the respective L×M chirp signals.

The above-described radar signal of one frame may be interpreted based on a fast-time axis and a slow-time axis. The slow-time axis may be a time axis separated by chirp signals, and the fast-time axis may be a time axis in which frequency changes of individual chirp signals are observable. For example, the radar signal processing apparatus200may transmit the radar signal510(e.g., L×M chirp signals) in one frame, and receive a reflected signal (e.g., L×M reflected signals) of the radar signal510. The radar signal processing apparatus200may obtain L×M bit signals from the transmitted chirp signals and the reflected signals. In the fast-time axis, a bit frequency signal corresponding to each chirp signal may be sampled at a plurality of sampling points. A beat frequency signal may be a signal having a frequency difference between a transmitted signal (e.g., a chirp signal) and a reflected signal of the transmitted signal. For example, an individual chirp signal may be radiated, arrive at a target, and be reflected from the target, and the reflected signal may be received by the radar sensor310. The radar signal processing apparatus200may sample the value of the beat frequency signal between the radiated chirp signal and the reflected signal. The radar signal processing apparatus200may sample a beat frequency signal corresponding to each chirp signal included in the radar signal510at every sampling interval Ts. In other words, the radar signal processing apparatus200may obtain S sample values520from a beat frequency signal corresponding to one chirp signal. Here, S may be an integer greater than or equal to “1”. Assuming that the sample values520are sample values at one virtual antenna, the sample values520may be converted into data530with a Doppler axis and a range axis.

The radar signal510may include L chirp sequences per frame, and K virtual antennas may individually receive the radar signal. Accordingly, the radar signal processing apparatus200may obtain S×L×K sample values. When the number of transmission antennas is M and the number of reception antennas is N, the number of virtual antennas may be K=M×N. Here, N may be an integer greater than or equal to “1”. Raw radar data540may be a data cube configured in S×L×K dimensions based on a Doppler axis, a range axis, and an angle axis, respectively. However, the raw radar data540is not limited to the data cube ofFIG.5, and may vary depending on a design. The raw radar data540may be converted into radar data in a form including a range profile, an angle profile, and a range-Doppler map by frequency conversion described below.

When a target is moving, a beat frequency may include a range component based on the range to the target and a Doppler frequency component due to a movement of the target.

In Equation 5, fRdenotes a range component, fDdenotes a Doppler frequency component, A denotes a wavelength, B denotes a sweep bandwidth of a transmitted chirp, Tchirpdenotes a chirp duration, and v denotes the velocity of a target.

The radar signal processing apparatus200may generate a range-Doppler map by performing frequency conversion on the raw radar data540. For example, the frequency conversion may include two-dimensional (2D) Fourier transform including first Fourier transform based on a range and second Fourier transform based on a Doppler frequency. Here, the first Fourier transform may be a range FFT, the second Fourier transform may be a Doppler FFT, and the 2D Fourier transform may be a 2D FFT. In some examples, the radar signal processing apparatus200may obtain a range profile by performing, on the raw radar data540, only the first Fourier transform based on a range. The range profile may indicate an intensity of a received signal for each range.

The radar signal processing apparatus200may detect one or more target cells from the range-Doppler map. For example, the radar signal processing apparatus may detect one or more target cells through constant false alarm rate detection (CFAR) on the range-Doppler map. CFAR detection may be a thresholding-based detection technique.

The radar signal processing apparatus200may determine an ambiguous Doppler velocity of a first target based on first frequency information of a first target cell. For example, the first target cell may be a cell corresponding to a peak intensity in a Doppler spectrum of the raw radar data540. The first frequency information may include a Doppler frequency at which the peak intensity appears. The radar signal processing apparatus200may determine a Doppler velocity corresponding to the Doppler frequency to be the first ambiguous Doppler velocity. A relationship between an unambiguous Doppler velocity and the ambiguous Doppler velocity may be expressed as in Equation 6 below.

In Equation 6, vD,unambdenotes the unambiguous Doppler velocity, vD,ambdenotes the ambiguous Doppler velocity, q denotes the ambiguity number, vD,maxdenotes the maximum range of the Doppler velocity that is unambiguously measurable through a chirp sequence signal, and q may have an integer value.

The radar signal processing apparatus200may radiate a plurality of linear chirp signals (e.g., chirp signals whose frequencies linearly increase) within one frame. For example, the radar signal processing apparatus may radiate tens to hundreds of chirp signals within one frame. The radar signal processing apparatus200may estimate a velocity based on phase differences due to a Doppler phenomenon between the radiated chirp signals and corresponding reflected signals. In some examples, the radar signal processing apparatus may estimate an angle (e.g., an angle of arrival) of a target based on a radar sensor, using a multiple-input multiple-output (MIMO) antenna structure.

The radar signal processing apparatus200may transmit the plurality of chirp signals using a plurality of transmission antennas. The radar signal processing apparatus200may identify transmission antennas having radiated transmitted signals (e.g., chirp signals) corresponding to reflected signals received at a plurality of reception antennas based on time-division multiplexing (TDM). TDM may be a technique for activating a transmission antenna with a physical time difference between operations of radiating chirp signals. Here, when a radar signal to be transmitted in one frame includes a total of L×M chirp signals, a radar signal transmitted by each transmission antenna may be modeled as in Equation 7 below.

In Equations 7 and 8 above, fcdenotes a carrier frequency, B denotes a sweep bandwidth of a transmitted chirp signal, Tcdenotes the length of an interval in which the frequency changes (e.g., linearly increases), and Tpdenotes a time interval (e.g., a chirp radiation period) from a time point at which radiation of one chirp signal is initiated to a time point at which radiation of a subsequent chirp signal is initiated, and may correspond to a time length of a time slot. T denotes a time point within a frame, and t′ denotes a time point within an individual time slot. The radar signal processing apparatus200may transmit L×M chirp signals by dividing them through M transmission antennas. The radar signal processing apparatus200may receive a reflected signal from the receiving antenna after hitting the target. The time (e.g., the round-trip time) Ti it takes for a radar signal to return from an i-th target to a reception antenna after being radiated may be expressed as in Equation 9 below according to the range to the i-th target, the velocity of the i-th target, and the angle of the i-th target.

In Equation 9 above, l·M+m denotes a chirp index, n denotes an index of a reception antenna, ridenotes the range to the i-th target, videnotes the velocity of the i-th target, θidenotes the angle of the i-th target, DTXdenotes the distance between transmission antennas, and d Rx denotes the distance between reception antennas. Assuming a uniform linear array design, dRXmay be λ/2, and dTXmay be M×dRX.

FIGS.6A and6Billustrate an example of recognizing a sign apparatus by a radar signal processing apparatus.

Referring toFIG.6A, a radar sensor610(e.g., the radar sensor310) may radiate a radar signal611(e.g., the FM signal302). A graph612shows an example of a spectrum of the radar signal611.

The radar signal611may be incident to a sign apparatus620.

The sign apparatus620may display a sign for a road or traffic. In some embodiments, the sign apparatus630may change which sign it is displaying (i.e., the sign apparatus630may have a display, an array of lamps functioning as a display, a physical means of changing the displayed sign, etc.) In the example ofFIG.6A, the sign displayed by the sign apparatus620will be referred to as the “first sign”. The first sign may include, for example, a no right turn sign, a no U-turn sign, a speed limit sign, a one way sign, and the like. The first sign is not limited to the examples listed above. In some examples, the sign apparatus620may read the name of signs identifying entities and location. In some examples, the sign apparatus620may guide an autonomous or semi-autonomous vehicle to various facilities in a hospital, such as emergency, radiology, surgery etc. In some examples, an autonomous or semi-autonomous vehicle may read the sign apparatus620to convey travelers to different gates at an airport, railway station, or bus terminus. In some examples, the sign apparatus620may guide an autonomous or semi-autonomous vehicle to various departments in a college or university. In such a scenario, the autonomous or semi-autonomous vehicle may read the sign apparatus620to determine the name of a department of the college or the university, such as History Department, Computer Sciences Department, Civil Engineering Department etc.

According to an example, the first sign may have identification information (ID). For example, as in the example shown inFIG.6A, the first sign may have 5-digit identification information “10101”, which may be big-endian or little-endian. In some examples, the most significant bit of the identification information of the first sign may represent a first digit of the identification information of the first sign, and the least significant bit of the identification information of the first sign may represent a last digit (e.g., a fifth digit) of the identification information of the first sign. Examples are not limited thereto. In some examples, the most significant bit of the identification information of the first sign may represent the last digit of the identification information of the first sign, and the least significant bit of the identification information of the first sign may represent the first digit of the identification information of the first sign.

The sign apparatus620may filter the incident radar signal611through a filter. The filter may have resonators of different frequencies (within the frequency range of the radar signal611), and each resonator/frequency may correspond to a different digit of any identification information. For example, the digits of any identification information may respectively correspond to frequencies f1to f5, and the resonators may resonate at those frequencies, respectively. Which of the resonators are active (or not) at any time may depend on which sign the sign apparatus620is current displaying and the identification information that corresponds to the current sign.

As noted, the digits of the identification information of the first sign may correspond to respective frequencies f1to f5(shown inFIGS.6A and6B), for example. The filter of the sign apparatus620may include a resonator having, as a resonant frequency, a frequency corresponding to a digit having a first value (e.g., “0”) of the identification information of the first sign. In some examples, a resonator having, as a resonant frequency, a frequency corresponding to a digit having a first value (e.g., “0”) may mean that the corresponding resonator is active, i.e., the resonators of the “0” digits of the sign info of the first sign are activated. The active resonators may negate the signal of the corresponding frequency. In some examples, a resonator having, as a resonant frequency, a frequency corresponding to a digit having a second value (e.g., “1”) may mean that the corresponding resonator is inactive, i.e., the resonators of the “1” digits of the sign info of the first sign are inactivated. The inactive resonators may permit the signal of the corresponding frequency to pass.

The second digit and the fourth digit of the first sign may have the first value. The filter of the sign apparatus620may include a resonator having, as the resonant frequency, the frequency f2corresponding to the second digit of the identification information of the first sign and a resonator having, as the resonant frequency, the frequency f4corresponding to the fourth digit of the identification information of the first sign. The filter may negate or attenuate a signal portion having the frequency f2and a signal portion having the frequency f4in the radar signal611through the resonators (for example, by the action of destructive interference). Such negating/filtering may cause the radar signal passing through the filter to be encoded with the identification information (e.g., 10101) of the first sign.

The sign apparatus620may reflect the filtered radar signal through a reflecting board or the reflector.

A reflected signal621may pass through the filter and be transmitted to the radar sensor610, and the reflected signal621may include the encoded identification information of the first sign (i.e., the identification information/number is encoded in the reflected signal621by its energy spectrum). In the example shown inFIG.6A, an energy spectrum of the reflected signal621may not include (or may have minimal/reduced or another characteristic) energy at the frequencies f2and f4, but may include energy at the frequencies f1, f3, and f5. A graph622shows an example of an energy spectrum of the reflected radar signal621encoding the identification information of the first sign.

The radar signal processing apparatus200may process (e.g., decode) the reflected signal621to recognize the first sign of the sign apparatus620based on the energy spectrum of the reflected signal621. A vehicle may then be controlled to drive according to the first sign recognized by the radar signal processing apparatus200.

Referring toFIG.6B, the radar sensor610may radiate a radar signal611.

The radar signal611may be incident to a sign apparatus630.

In the example ofFIG.6B, the sign displayed by the sign apparatus630will be referred to as the “second sign”. The second sign may be different from the first sign. The second sign may be any of, for example, a no right turn sign, a no U-turn sign, a speed limit sign, a one way sign, and the like. The second sign is not limited to the examples listed above.

According to an example, the second sign may have identification information. For example, as in the example shown inFIG.6B, the second sign may have 5-digit identification information “01001”. In some examples, the most significant bit of the identification information of the second sign may represent a first digit of the identification information of the second first sign, and the least significant bit of the identification information of the second sign may represent a last digit of the identification information of the second sign. Examples are not limited thereto. In another example, the most significant bit of the identification information of the second sign may represent the last digit of the identification information of the second sign, and the least significant bit of the identification information of the second sign may represent the first digit of the identification information of the second sign.

The sign apparatus630may filter the incident radar signal611through the filter of the sign apparatus630.

The digits of the identification information of the second sign may correspond to frequencies f1to f5ofFIG.6B, for example. The filter of the sign apparatus630may include a resonator having, as a resonant frequency, a frequency corresponding to a digit having a first value (e.g., “0”) of the identification information of the second sign. The first digit, the third digit, and the fourth digit of the second sign may have the first value. The filter of the sign apparatus630may include a resonator having, as the resonant frequency, the frequency f1corresponding to the first digit of the identification information of the second sign, a resonator having, as the resonant frequency, the frequency f3corresponding to the third digit of the identification information of the second sign, and a resonator having, as the resonant frequency, the frequency f4corresponding to the fourth digit of the identification information of the second sign. The filter may negate (or attenuate) energy of a signal portion having the frequency f1, a signal portion having the frequency f3, and a signal portion having the frequency f4in the radar signal611through the resonators. Such selective negating/attenuating (or filtering) may cause the radar signal passing through the filter to include the encoded identification information (e.g.,01001) of the second sign.

The sign apparatus630may reflect the filtered radar signal through a reflecting board.

A reflected signal631may pass through (or interact with) the filter and be transmitted to the radar sensor610, and the reflected signal631may include the encoded identification information of the second sign. In the example shown inFIG.6B, the energy spectrum of the reflected signal631may include no (or low) energy at the frequencies f1, f3, and f4, but may include full/ordinary energy at the frequencies f2and f5. A graph632shows an example of the energy spectrum of the radar signal631for the example ofFIG.2B.

The radar signal processing apparatus200may process the reflected signal631to recognize the second sign of the sign apparatus630. A vehicle may be controlled to drive according to the second sign recognized by the radar signal processing apparatus200.

FIG.7illustrates an example of a sign apparatus.

Referring toFIG.7, a sign apparatus700(e.g., the sign apparatus620ofFIG.6Aor the sign apparatus630ofFIG.6B) may include a display710, a filter720, and a reflecting board or a reflector730.

The display710may display a sign for traffic or a road. For example, signs expressed through at least one of a number, a character, or a symbol (e.g., a stop sign. a no right turn sign, a no U-turn sign, a speed limit sign, a one way sign, etc.) may be printed on a transparent film (e.g., ElectroCut (EC) film). The display710may include a transparent film on which signs are printed. The display710is not limited to the transparent film.

The display710may allow a radar signal radiated from a source (e.g., the radar sensor610) to pass.

Identification information of a sign of the sign apparatus700may have N digits. A first digit to a last digit of the N digits may correspond to different frequencies, respectively, in a frequency band of the radar signal. For example, when identification information of a sign has 5 digits, a first digit of the identification information of the sign may correspond to a frequency f1, a second digit of the identification information of the sign may correspond to a frequency f2, a third digit of the identification information of the sign may correspond to a frequency f3, a fourth digit of the identification information of the sign may correspond to a frequency f4, and a fifth digit of the identification information of the sign may correspond to a frequency f5, as described with reference toFIGS.6A and6B.

The filter720may reject or attenuate a signal of at least one frequency in the radar signal passing through the display710and allow a signal of a remaining frequency to pass. For example, the filter720may include a plurality of resonators. The filter720may include a resonator having, as a resonant frequency, a frequency corresponding to a digit having a first value (e.g., “0”) of the identification information of the sign. The filter720may reject or attenuate a signal of a resonant frequency of each of the resonators in the radar signal passing through the display710and allow a signal of a remaining frequency to pass.

In some examples, the filter720may filter a signal (e.g., a radar signal) in a mmWave band and may thus be called a mmWave filter.

The reflecting board730may reflect the signal passing through the filter720.

The filter720and the reflecting board730may be spaced apart by a first distance value h. The first distance value h may be greater than a result of multiplying a wavelength value λ of a center frequency of the radiated radar signal with a predetermined value (e.g., “10”). For example, the first distance value h may be greater than 10λ.

The signal reflected by the reflecting board730(i.e., the reflected signal) (e.g., the reflected signal621ofFIG.6Aor the reflected signal631ofFIG.6B) may pass through the filter720and the display710and be transmitted to the source. As described with reference toFIGS.6A and6B, the reflected signal may include the encoded identification information of the sign of the sign apparatus700.

FIG.8illustrates an example of a reflecting board of a sign apparatus.

Referring toFIG.8, a reflecting board800is shown. The reflecting board800may correspond to an example of the reflecting board730.

The reflecting board800ofFIG.8may have a trihedral shape. For example, the reflecting board800may be a trihedral corner reflector.

In one example, the sign apparatus700may include a reflective sheet instead of the reflecting board700.

FIG.9illustrates an example of a filter of a sign apparatus.

Referring toFIG.9, a filter900is shown. The filter900may correspond to an example of the filter720.

The filter900may include a plurality of unit cells. A spacing d between the unit cells may correspond to half a wavelength value λ of a center frequency of the radiated radar signal. For example, the spacing d may be approximately equal to λ/2.

Each of the unit cells may include one or more resonators. The resonators will be further described with reference toFIGS.10A to13.

FIGS.10A to13illustrate examples of a unit cell of a filter of a sign apparatus.

Referring toFIG.10A, a unit cell1000of the filter900may include a plurality of resonators1010-1to1010-N. According to identification information of a sign, the unit cell1000may include one resonator or may include a plurality of resonators having different resonant frequencies.

The identification information of the sign may have N digits. As in the example shown inFIG.10B, the digits of the sign may correspond to the resonant frequencies of the resonators1010-1to1010-N. A first digit1020-1of the identification information of the sign may correspond to the resonant frequency of the first resonator1010-1. A second digit1020-2of the identification information of the sign may correspond to the resonant frequency of the second resonator1010-2. A third digit1020-3of the identification information of the sign may correspond to the resonant frequency of the third resonator1010-3. A last digit (or an N-th digit)1020-N of the identification information of the sign may correspond to the resonant frequency of the N-th resonator1010-N. The first digit to the last digit of the N digits of the identification information of the sign may correspond to different frequencies (e.g., different resonant frequencies), respectively.

The unit cell1000may include a resonator having, as a resonant frequency, a frequency corresponding to a digit having a first value (e.g., “0”) of the identification information of the sign.

For example, the sign may have five-digit identification information “00000”. Each digit of the identification information of the sign may have “0”. In this case, the unit cell1000may include resonators having, as resonant frequencies, frequencies corresponding to the five digits.

An example of the unit cell1000when the identification information of the sign has five binary digits is shown inFIG.11.

In the example shown inFIG.11, a unit cell1100may include first resonators1111aand1111bhaving, as the resonant frequency, a frequency f1corresponding to the first digit, second resonators1112aand1112bhaving, as the resonant frequency, a frequency f2corresponding to the second digit, third resonators1113aand1113bhaving, as the resonant frequency, a frequency f3corresponding to the third digit, fourth resonators1114aand1114bhaving, as the resonant frequency, a frequency f4corresponding to the fourth digit, and fifth resonators1115aand1115bhaving, as the resonant frequency, a frequency f5corresponding to the fifth digit. Here. f1<f2<f3<f4<f5may be satisfied.

In the example shown inFIG.11, each resonator may have a pole shape. The first resonators1111aand1111b, the second resonators1112aand1112b, the third resonators1113aand1113b, the fourth resonators1114aand1114b, and the fifth resonators1111aand1111bmay differ in size. In some examples, the resonators may be positioned on the same layer. In other examples, the resonators may be positioned on different layers.

In the example shown inFIG.11, the number of resonators in the unit cell1100(e.g., “10”) may be twice the number of digits in the identification information.

Another example of the unit cell1000when the identification information of the sign is five binary digits is shown inFIG.12.

In the example shown inFIG.12, a unit cell1200may include a first resonator1211having, as the resonant frequency, a frequency f1corresponding to the first digit, a second resonator1212having, as the resonant frequency, a frequency f2corresponding to the second digit, a third resonator1213having, as the resonant frequency, a frequency f3corresponding to the third digit, a fourth resonator1214having, as the resonant frequency, a frequency f4corresponding to the fourth digit, and a fifth resonator1215having, as the resonant frequency, a frequency f5corresponding to the fifth digit.

In the example shown inFIG.12, each resonator may have a circular shape. The first resonator1211, the second resonator1212, the third resonator1213, the fourth resonator1214, and the fifth resonator1215may differ in size. In some examples, the resonators may be positioned on the same layer. In other examples, the resonators may be positioned on different layers.

In the example shown inFIG.12, the number of resonators in the unit cell1200(e.g., “5”) may be equal to the number of zeros in the identification information.

Still another example of the unit cell1000when the identification information of the sign is five digits is shown inFIG.13.

In the example shown inFIG.13, a unit cell1300may include a first resonator1311having, as the resonant frequency, a frequency f1corresponding to the first digit, a second resonator1312having, as the resonant frequency, a frequency f2corresponding to the second digit, a third resonator1313having, as the resonant frequency, a frequency f3corresponding to the third digit, a fourth resonator (not shown) having, as the resonant frequency, a frequency f4corresponding to the fourth digit, and a fifth resonator (not shown) having, as the resonant frequency, a frequency f5corresponding to the fifth digit.

In the example shown inFIG.13, each resonator may have a circular shape. Each resonator may be positioned on a different layer. InFIG.13, the diameter of the fourth resonator may be less than the diameter of the third resonator1313, and the diameter of the fifth resonator may be less than the diameter of the fourth resonator.

In the example shown inFIG.13, the number of resonators in the unit cell1300(e.g., “5”) may be equal to the number of zeros in the identification information.

In the examples shown inFIGS.11to13, when the radar signal passing through the display710is incident to the filter900, the first to fifth resonators may resonate. In other words, the radar signal may be an electromagnetic wave, and any combination of the first to fifth resonators may resonate. Through this resonance, the filter900may reject (or attenuate, negate, etc.) signals having the resonant frequencies of the first to fifth resonators in the radar signal passing through the display710. Such negation may be through destructive interference. The filter900may reject/reduce energy of a signal portion having a frequency (e.g., f1, f2, f3, f4, or f5) corresponding to a digit having a first value (e.g., “0”) of identification information (e.g.,01001) of a sign.

As another example, the sign may have 5-digit identification information “10101”, where the second digit and the fourth digit are “0”. In this case, the unit cell1100ofFIG.11may include (or activate) the second resonators1112aand1112band the fourth resonators1114aand1114b, and may not include (or activate) the first resonators1111aand1111b, the third resonators1113aand1113b, and the fifth resonators1115aand1115b. The unit cell1200ofFIG.12may include (or activate) the second resonator1212and the fourth resonator1214, and may not include (or activate) the first resonator1211, the third resonator1213, and the fifth resonator1215. The unit cell1300ofFIG.13may include (or activate) the second resonator1312and the fourth resonator, and may not include (or activate) the first resonator1311, the third resonator1313, and the fifth resonator.

Each unit cell of the filter of the sign apparatus620described with reference toFIG.6Amay include (or activate) the second resonators1112aand1112band the fourth resonators1114aand1114bofFIG.11, or may include (or activate) the second resonator1212and the fourth resonator1214ofFIG.12, or may include (or activate) the second resonator1312and the fourth resonator ofFIG.13.

The filter900may reject a signal portion having the resonant frequency of the second resonator and a signal having the resonant frequency of the fourth resonator in the radar signal passing through the display710. The filter900may reject a signal of a frequency (e.g., f2or f4) corresponding to a digit having a first value (e.g., “0”) of the identification information (e.g.,10101) of the sign, and allow a signal of a frequency (e.g., f1, f3, or f5) corresponding to a digit having a second value (e.g., “1”) to pass.

As still another example, the sign may have 5-digit identification information “01001”. The first digit, the third digit, and the fourth digit of the identification information of the sign may have “0”. In this case, the unit cell1100ofFIG.11may include (or activate) the first resonators1111aand1111b, the third resonators1113aand1113b, and the fourth resonators1114aand1114b, and may not include (or activate) the second resonators1112aand1112band the fifth resonators1115aand1115b. The unit cell1200ofFIG.12may include (or activate) the first resonator1211, the third resonator1213, and the fourth resonator1214, and may not include (or activate) the second resonator1212and the fifth resonator1215. The unit cell1300ofFIG.13may include (or activate) the first resonator1311, the third resonator1313, and the fourth resonator, and may not include (or activate) the second resonator1312and the fifth resonator.

Each unit cell of the filter of the sign apparatus630described with reference toFIG.6Bmay include (or activate) the first resonators1111aand1111b, the third resonators1113aand1113b, and the fourth resonators1114aand1114bofFIG.11, or may include (or activate) the first resonator1211, the third resonator1213, and the fourth resonator1214ofFIG.12, or may include (or activate) the first resonator1311, the third resonator1313, and the fourth resonator ofFIG.13.

The filter900may reject a signal having the resonant frequency of the first resonator, a signal having the resonant frequency of the third resonator, and a signal having the resonant frequency of the fourth resonator in the radar signal passing through the display710. The filter900may reject a signal of a frequency (e.g., f1, f3, or f4) corresponding to a digit having a first value (e.g., “0”) of the identification information (e.g.,01001) of the sign, and allow a signal of a frequency (e.g., f2or f5) corresponding to a digit having a second value (e.g., “1”) to pass.

FIGS.14to16illustrate an example of an operation of a radar signal processing apparatus. The operations ofFIG.14may be performed in the sequence and manner as shown. However, the order of some operations may be changed, or some of the operations may be omitted, without departing from the spirit and scope of the shown example. Additionally, operations illustrated inFIG.14may be performed in parallel or simultaneously. One or more blocks ofFIG.14, and combinations of the blocks, can be implemented by special purpose hardware-based computer that perform the specified functions, or combinations of special purpose hardware and instructions, e.g., computer or processor instructions. For example, operations1410through1417may be performed by a computing apparatus (e.g., processor220or the system200ofFIG.2). In addition to the description ofFIG.4below, the descriptions ofFIGS.1-13are also applicable toFIG.14.

Referring toFIG.14, in operation1410, the radar signal processing apparatus200may generate raw radar data (e.g., the raw radar data540) based on a radar signal of the radar sensor310and a reflected signal. For example, the radar signal processing apparatus200may generate an IF signal based on the radar signal and the reflected signal, and generate the raw radar data through a sampling operation and frequency conversion (e.g., FFT) on the IF signal. An example of the raw radar data is shown inFIG.15. In the example shown inFIG.15, the radar signal processing apparatus200may generate raw radar data1510with a range axis, an angle axis, and a Doppler axis.

Referring toFIG.14, in operation1411, the radar signal processing apparatus200may process the raw radar data1510. For example, the radar signal processing apparatus200may process the raw radar data1510according to the operation described above with reference toFIG.5. Through this processing, the radar signal processing apparatus200may detect the velocity and the direction of a target.

In operation1412, the radar signal processing apparatus200may estimate an ego velocity. The ego velocity may be the velocity of an ego vehicle (e.g., a vehicle equipped with the radar signal processing apparatus200). For example, the radar signal processing apparatus200may estimate the ego velocity based on results of processing the raw radar data1510. The radar signal processing apparatus200may determine a stationary target (e.g., the sign apparatus700, etc.) and a moving target (e.g., a moving vehicle, etc.) using the estimated ego velocity.

In operation1413, the radar signal processing apparatus200may perform Doppler integration on the raw radar data1510. Doppler integration may refer to integrating data on a Doppler axis, for example. Since the vehicle equipped with the radar signal processing apparatus200is moving, the radar signal processing apparatus200may correct the data on the Doppler axis through the estimated ego velocity and integrate the corrected data. An example of radar data on which Doppler integration is performed is shown inFIG.15. In the example shown inFIG.15, the radar signal processing apparatus200may generate radar data1520by performing Doppler integration on the raw radar data1510. The radar signal processing apparatus200may integrate data in the same position on the range axis, in the same position on the angle axis, and in different positions on the Doppler axis. For example, data1521may be derived by integrating data1511to1517on the Doppler axis of the raw radar data1510. In this case, the radar signal processing apparatus200may correct the data1511to1517through the estimated ego velocity, and derive the data1521by integrating the corrected data. In the manner described above, the radar signal processing apparatus200may derive each piece of data on the radar data1520with respect to the range and the angle.

As the radar signal processing apparatus200performs Doppler integration, the radar data1520with an improved signal-to-noise ratio (SNR) may be obtained.

Referring toFIG.14, in operation1414, the radar signal processing apparatus200may perform frequency conversion (e.g., FFT) on the angle axis of the radar data on which Doppler integration is performed (e.g., the radar data1520ofFIG.15). In operation1415, the radar signal processing apparatus200may determine an angle at which a target is present, from frequency conversion results. In operation1416, the radar signal processing apparatus200may decode range data at the determined angle. In operation1417, the radar signal processing apparatus200may recognize a sign of a sign apparatus based on decoding results. An example of operations1414to1417will be described with reference toFIG.16.

In the example shown inFIG.16, the radar signal processing apparatus200may perform FFT on the angle axis of the radar data1520on which Doppler integration is performed. In other words, the radar signal processing apparatus200may perform angle FFT on the radar data1520.

The radar signal processing apparatus200may detect a first angle and a second angle at which the target (or a reflected signal) is present, through peak detection in FFT results1610. The radar signal processing apparatus200may extract range data1630at the first angle and range data1620at the second angle.

The radar signal processing apparatus200may detect “10101”, for example, by decoding the range data1620at the second angle. The radar signal processing apparatus200may recognize or identify the sign of the sign apparatus700based on the detected “10101”. A vehicle may be controlled to drive according to the recognized sign. The range data1630at the first angle may exhibit a continuous waveform (i.e., does not have frequency “holes” due to sign filtering). Even if the radar signal processing apparatus200decodes the range data1630at the first angle, valid information (e.g., identification information of the sign) may not be obtained. The target present on the first angle may not encode its own identification information in a reflected signal, and thus, the range data1630at the first angle may exhibit a continuous waveform. A target that does not perform encoding may be referred to as a general target inFIG.16.

In one example, the radar signal processing apparatus200detecting the angle at which the target (or the reflected signal) is present through angle axis FFT may reduce the time it takes to find an encoded signal and enhance the SNR of a signal of the angle. The SNR enhancement operation (e.g., Doppler integration and angle axis FFT) of the radar signal processing apparatus200may increase the range for recognizing (or identifying) a sign of a sign apparatus and improve the recognition accuracy.

According to the examples described above, it is possible to recognize (or identify) a road sign with radar. According to the examples described above, sign information may be encoded without adding an electrical device to an existing sign. According to the examples described above, a sign may be recognized through a decoding algorithm without changing the hardware of a radar sensor (or the configuration of a radar system in a vehicle). According to the examples described above, it is possible to improve sign recognition performance (e.g., recognition range and accuracy) may be improved.