Fmcw Python

Fmcw PythonA chirp signal is an FM-modulated signal of a known stable frequency whose instantaneous frequency varies linearly. この記事では、 Python を使用して FMCW の動作原理のシミュレーションを実装する方法を紹介します。. The radar parameters are defined for the frequency-modulated continuous wave (FMCW) waveform, as described in the example Automotive Adaptive Cruise Control Using FMCW Technology. The fmcw package aims at generalizing the python code he open sourced on GitHub and provide the user with a lot more features. The fundamentals of millimeter wave radar sensors (Rev. A 35 GHz FMCW radar is used for the detection and tracking of small UAVs in [69]. FMCW radar ( F requency- M odulated C ontinuous W ave radar = FMCW radar ) is a special type of radar sensor which radiates continuous transmission power like a simple continuous wave radar ( CW-Radar ). I used the code (Matlab) I attached below. Those are 1 : Being a mm-wave radar: the high attenuation in mmwave frequencies. FMCW Radar Analysis and Signal Simulation Testforce Systems 3. The principle behind FMCW is that you transmit a chirped signal and receive a time delayed version of it after reflecting from a target. 037 % Maximum target speed (km/h) 30 for fall detection % Sweep time (microseconds) 50 % Sweep bandwidth (GHz) 4 % Maximum beat frequency (MHz) 73 % Sample rate (GHz) 4. The family of subspace frequency estimation techniques include RootMUSIC and ESPRIT, implemented in Python. FMCW radars have unique advantages, which cannot be presented in other radars at once. Implementation of a GNU radio and python FMCW radar toolkit. There's different motivations that lead to people adopting either: in analog systems with expensive VCOs, it's easy to do a linear chirp to. The basic features of FMCW radar are: Ability to measure very small ranges to the target (the minimal measured range is comparable to the transmitted wavelength); Ability to measure simultaneously the target range and its relative velocity; Very high accuracy of range measurement;. The FMCW package is a library designed to interact at a high level with the fmcw radar from Henrik Forstén/ @Ttl. Thus, FMCW radar is less affected by the noise in comparison to impulse. class fmcw. The basic FMCW system consists of a transmitter, receiver and mixer. Instead of using the time to measure distance (like TOF), FMCW technology emits a radar signal with a frequency that increases continuously to create a signal sweep. Target's initial position and velocity. 1 I would like to simulate a FMCW radar in the frequency domain. 通常，我们都是采用Matlab进行雷达系统设计，或者进行相关的算法仿真。. FMCW generator. matlab radar fft autonomous-driving fmcw fmcw-waveform cfar-processing. In this paper, we demonstrate a proof-of-concept FMCW radar as an advanced form of pedestrian traffic light triggering mechanism. So, there's no "general" difference; you'll need to look at actual implementations. The requirement was to design and implement an FMCW surveillance radar to detect a drone with a radar cross-section of 0. Specially I am interested in the phase spectrum of the beat signal. The FMCW package is a library designed to interact at a high level with the fmcw radar from Henrik Forstén/@Ttl. Solved: FMCW radar working principle simulation based …. Aug 30, 2022 01:45 AM FMCW radar working principle simulation based on python — Chapter 2：Velocity simulation This article will introduce how to use python to implement the simulation of FMCW working principle, the second chapter content will introduce the principle of velocity detection. Estimate FMCW beat frequencies to get range. For FMCW radar, where the frequency sweep is linear, if target A gives a 1 Hz sinusoid and target B gives a 2 Hz sinusoid, target B is twice as far away as target A. These are the top rated real world Python examples of radar_swig. Without further tests, the maximum distance is unknown. FMCW radar working principle simulation based on python — Chapter 2：Velocity simulation This article will introduce how to use python to implement the simulation of FMCW working principle, the second chapter content will introduce the principle of velocity detection. reshape() function Tutorial with examples">Python: numpy. This demonstration will show how. FMCW radars have unique advantages, which cannot be presented in other radars at once. In this paper, FMCW ground penetration radar (GPR) is implemented using SDR technology. reshape() function Tutorial with examples. Implementation of a GNU radio and python FMCW radar toolkit Abstract: The use of GNU Radio in order to explore FMCW radar is growing rapidly, where it is. After mixing and filtering, the resulting signal is a sinusoid at a frequency that is a function of the target's range. fmcw package — fmcw documentation. Currently, most basic functions and processing blocks are compatible with FMCW radars, but some of them could be used for other kinds of radars. FMCW - Creates an FMCW signal. Configuring the radar FMCW waveform based on the system requirements and simulating the radar signal propagation and moving target scenario. FMCW radar working principle simulation based on python — Chapter 2：Velocity simulation This article will introduce how to use python to implement the. An FMCW chirp consists of an electromagnetic wave that’s ramped up in frequency linearly over a period in time. 7 GHz band, and has 4 transmitting antennas and 12 receive antennas. Part 1: Principle of distance detection. FMCW Radar Analysis and Signal Simulation Testforce Systems 3. Finally, post processing the radar signal using 1st FFT, 2nd FFT, and CA-CFAR to estimate the target's range and velocity. FMCW radar: understanding of doppler fft. Python signal_generator_fmcw_c - 5 examples found. An Overview of FMCW Systems in MATLAB. An FMCW radar is built using software-defined radio USRP B210, and GNU radio in [70]. FMCW系统测量发射和反射信号频率间的瞬时差 \Delta f ，也叫做中频信号、差频信号、差拍信号，它与时间差 \Delta t 成正比，可用于估计目标的距离。. These signals are transmitted and reflected by objects and received. In an FMCW radar system, a chirp signal is launched into the free space using a transmit antenna. Python signal_generator_fmcw_c Examples">Python signal_generator_fmcw_c Examples. 89 KB) by FiltSamp This program form an image for multiple moving target through the Least Square method. Radar system Requriements The sensor fusion design for different driving scenarios requires different system configurations from a Radar. The basic features of FMCW radar are: Ability to measure very small ranges to the target (the minimal measured range is comparable to the transmitted wavelength); Ability to measure simultaneously the target range and its relative velocity; Very high accuracy of range measurement;. This chirp is then radiated with the antenna, reflected from the target and is received by the receiving antenna. If you have no idea about FMCW, the following tutorials can be a good starting point. Pedestrian Traffic Light Control with Crosswalk FMCW Radar. By lowering the threshold required to get into. 2fmcw package Here is the documentation of all the modules in the fmcw package. A chirp signal is an FM-modulated signal of a known stable frequency whose instantaneous frequency varies linearly over a fixed period of time (sweep time) by a modulating signal. Frequency-modulated continuous-wave (FMCW) radars achieve similar results using much smaller instantaneous transmit powers and physical size by continuously emitting periodic pulses whose frequency content varies with time. You can rate examples to help us improve the quality of examples. These are the top rated real world Python examples of radar_swig. In this paper, we demonstrate a proof-of-concept FMCW radar as an advanced form of pedestrian traffic light triggering mechanism. 1 Answer. Installation Pip installation Coming soon Debug Mode. Automotive Adaptive Cruise Control Using FMCW and MFSK ">Automotive Adaptive Cruise Control Using FMCW and MFSK. I want to transmit a FMCW signal. FMCW radar working principle simulation based on p. As the name implies, FMCW radars transmit a frequency-modulated signal continuously in order to measure range as well as angle and velocity. RF Tutorial Lesson 17: Simulating a Frequency. Then, I copy this recieved ADC data into fft_in array (converting it into float32_t) (fft_in array size = 512). GitHub - kopytjuk/python-fmcw: Tutorials on frequency modulated continuous wave (FMCW) and Chirp Sequence Modulation RADAR algorithms. The FMCW waveform is a common choice in automotive radar, because it provides a way to estimate the range using a continuous wave (CW) radar. I have a simulated doppler-range map of a 1Tx - 4Tx (azimuthally displaced) FMCW radar and I am doing something wrong to calculate the angle of arrival (AoA). FMCW Chirp Configuration for Short, Medium, and Long. Also, in FMCW radars the vital sign information is encoded in the received phase similar to FM signals. You may override this method in a subclass. This frequency is known as the "beat" frequency f b. Automotive Adaptive Cruise Control Using FMCW and MFSK. The signal sweeps a bandwidth of 150 MHz. These are the top rated real world Python examples of radar_swig. GitHub - kopytjuk/python-fmcw: Tutorials on frequency modulated continuous wave (FMCW) and Chirp Sequence Modulation RADAR algorithms. FMCW radar: understanding of doppler fft. この記事では、 Python を使用して FMCW の動作原理のシミュレーションを実装する方法を紹介します。最初の章の内容では、距離検出の原理を紹介します。その 1 ：距離検出の原理周波数変調連続波（ FMCW ）レーダーとも呼ばれる変調連続波レーダーは、周波数変調として知られる技術を使用してターゲットの範囲を測定できるシステムです。周波数変調では、電磁波の周波数は時間とともに直線的に増加します。つまり、送信周波数は一定の割合で変化します。周波数が時間とともに直線的に増加するこの種の信号は、チャープと呼ばれます。 FMCW システムは、反射チャープの時間差 δt に正比例する送信信号周波数と反射信号周波数の瞬間的な差 δf を測定します。. Signal processing in FMCW and SFCW. The radar operates at a center frequency of 77 GHz. TI devices implement a special class of mmWave technology called frequency-modulated continuous wave (FMCW). signal_generator_fmcw_c extracted from open source. is the signal phase at time , is the radar carrier frequency, is the sweep width, and is the pulse repetition period. DEPRECATED Legacy Writer thread used to write to the binary log file. In an FMCW radar system, a chirp signal is launched into the free space using a transmit antenna. FMCW radars have unique advantages, which cannot be presented in other radars at once. The FMCW package is a library designed to interact at a high level with the fmcw radar from Henrik Forstén/@Ttl. FMCW radar working principle simulation based on python — Chapter 1：Distance simulation This article will introduce how to use python to implement the. Based on project statistics from the GitHub. Python signal_generator_fmcw_c Examples. As such, we scored fmcw popularity level to be Limited. Implementation of a GNU radio and python FMCW radar toolkit Abstract: The use of GNU Radio in order to explore FMCW radar is growing rapidly, where it is used for radar signal processing. 本发明公开了一种FMCW雷达测距的方法和装置，方法包括步骤：对经过A/D采样后的FMCW雷达中频信号进行频谱分析；判断FMCW雷达中频信号的频谱是否满足相位差法校正条件；如果满足则应用相位差法进行频谱校正，获得校正的中频频率，并根据校正后的中频频率计算距离；如果不满足，则利用频谱分析后获得的中频频率计算距离。. 050 A target was simulated with the following. You can select the range to the target , the target radar cross section , the transmit power of the radar , and the gain of the radar transmit-receive antenna. With regard to signal processing, how is frequency modulated continuous wave (FMCW) radar similar/different from stepped frequency continuous wave (SFCW) radar? Do we actually modulate the RF carrier with a low frequency signal in order to lower the cost of analog to digital conversion?. TI devices implement a special class of mmWave technology called frequency-modulated continuous wave (FMCW). Frequency-modulated continuous-wave radar (FM-CW) – also called continuous-wave frequency-modulated (CWFM) radar – is a short-range measuring radar set capable of determining distance (. Here is some Python code that should do the trick: n_fft = 256 #size of fft AoA = np. FMCW radar multiple moving target detection Version 1. FMCW radar working principle simulation based on python — Chapter 1. The EV-TINYRAD24G uses frequency modulated continuous wave (FMCW) radio signals and an integrated antenna array in a multiple input multiple output (MIMO) radar scheme. These Python subspace estimation functions such as ESPRIT are also callable from Matlab. I am using fmcw radar to find out distance and speed of moving objects using stm32l476 microcontroller. md RADAR - FMCW & CSM Image source Contents. It uses variety of built-in parallel processing tools in Python to enhance and optimize the visualization and processing speeds suited to real-time radar system development for many applications. Frequency Modulated Continuous Wave (FMCW) radar works by transmitting a chirp which frequency changes linearly with time. FMCW radar working principle simulation based on …. In contrast to this CW radar FMCW radar can change its operating frequency during the measurement: that is, the transmission signal is. The combined antennas, similar to digital beamforming (DBF), allow the TinyRad module to detect the distance, speed, and angular position of multiple targets simultaneously. run [source] ¶ Method representing the thread’s activity. I used python program with python ADI libraries to transmit and receive this signal. The FMCW radar with the following parameters was implemented: % System parameters Value % ----- % Operating frequency (GHz) 77 % Maximum target range (m) 15 % Range resolution (m) 0. Frequency Modulated Continuous Wave (FMCW) radar works by transmitting a chirp which frequency changes linearly with time. Frequency Modulated Continuous Wave (FMCW) Radar is a special type of radar sensor which radiates continuous transmission power like a simple continuous-wave radar. The mmWave training curriculum provides foundational content and hands-on examples for you to learn the fundamentals of FMCW technology and mmWave sensors to start development quickly. In a frequency-modulated continuous-wave (FMCW) radar employing a linear upsweep in frequency, the radar signal generator produces a phase modulated signal of the form. Third version of homemade 6 GHz FMCW …. An FMCW chirp consists of an electromagnetic wave that’s ramped up in frequency linearly over a period in time. It can simultaneously imaging for many targets. FMCW Radar Analysis and Signal Simulation. FMCW radar working principle simulation based on python — Chapter 1：Distance simulation This article will introduce how to use python to implement the simulation of FMCW working principle, the first chapter content will introduce the principle of distance detection. VCO: ZX95-3800A+ Power splitter:. Python signal_generator_fmcw_c - 5 examples found. Configuring the radar FMCW waveform based on the system requirements and simulating the radar signal propagation and moving target scenario. In this paper we implement FMCW surveillance radar for drone detection on SDR using GNU Radio and the USRP B210. fft(rv_tg_va, n_fft, axis=0)/rv_tg_va. So the problem is that when simulating FMCW signals, there is some ambiguity in the convention on the mixing order. FMCW Radar Resolving the return using a FMCW radar is a different story. In an FMCW radar system, a chirp signal is launched into the free space using a transmit antenna. In order to simulate it, you must introduce the target's delay. GNU Radio FMCW radar USRP B200 and Red Pitaya">GNU Radio FMCW radar USRP B200 and Red Pitaya. FMCW radar: understanding of doppler fft. Re: FMCW radar working principle simulation based on python — Chapter 2：Velocity simulation. Third version of homemade 6 GHz FMCW radar. With regard to signal processing, how is frequency modulated continuous wave (FMCW) radar similar/different from stepped frequency continuous wave (SFCW) radar? Do we actually modulate the RF carrier with a low frequency signal in order to lower the cost of analog to digital conversion?. If you are not familiar with it, start with taking a look at Henrik's blog post on the third version of the radar: FMCW 3. This differs from traditional pulsed-radar systems, which transmit short pulses periodically. If you are not familiar with it, start with taking a look at Henrik's blog post on the third version of the radar: FMCW 3. After mixing and filtering, the resulting signal is a sinusoid at a frequency. I used the code (Matlab) I attached below. 1K Downloads Updated 27 Jun 2020 View License Follow Download Overview Functions Version History Reviews (2) Discussions (0). It is designed with ADIsimPLL under the guidance of CN-0302. master 1 branch 0 tags 13 commits Failed to load latest commit information. def test_001_t (self): # set up fg samp_cw = 300 samp_up = 200 samp_down. Matlab的确是一个十分强大的工具，但随着越来越多的雷达er 开始使用Python进行雷达设计，我们不得不对基于Python的FMCW雷达信号处理仿真做一次详细的介绍，以便于后来的雷达初学者能够. You can build receivers and transmitters for both digitally covering the whole band, or just the beat frequency. The FMCW waveform is a common choice in automotive radar, because it provides a way to estimate the range using a continuous wave (CW) radar. shape[1] #rv_tg_va is the range-doppler. VCO: ZX95-3800A+ Power splitter: ZX10-2-42+ Attenuator: VAT-3+ Our FMCW generator works in 2. FMCW radar multiple moving target detection Version 1. This chirp is then radiated with the antenna, reflected from the target and. ML on radar (classification, detection, tracking, etc). 0 documentation">FMCW Radar introduction — PyRAPID 0. Frequency Modulated Continuous Wave (FMCW) radar works by transmitting a chirp which frequency changes linearly with time. FMCW GPR is used to detect and locate underground objects and. FMCW GPR is used to detect and locate underground objects and measure the depth of an object. Pluto SDR transmitting Data samples from file using C. This Demonstration investigates the performance of a W-band (94 GHz) FMCW radar emitting an FM sweep with a 5 kHz pulse repetition frequency. 28K views 7 months ago Watch an introduction to Frequency Modulated Continuous Wave (FMCW) radar and why it’s a good solution for autonomous vehicle applications. Generating IF signal for FMCW radar. 基于Python的FMCW雷达工作原理仿真（附代码）. 1FMCW radar basics In any radar, the electromagnetic wave is sent into the environment containing various objects. Frequency Modulated Continuous Wave (FMCW) Radar is a special type of radar sensor which radiates continuous transmission power like a simple continuous-wave radar. Frequency-modulated continuous-wave (FMCW) radars achieve similar results using much smaller instantaneous transmit powers and physical size by continuously emitting periodic pulses whose frequency content varies with time. In this paper, FMCW ground penetration radar (GPR) is implemented using SDR technology. FMCW Radar introduction — PyRAPID 0. signal_generator_fmcw_c extracted from open source projects. What is mmWave Radar? : Everything You Need to Know About FMCW. (PDF) An Overview of FMCW Systems in MATLAB. signal_generator_fmcw_c extracted from open source projects. Hardware: ADF4159 evaluation board: EV-ADF4159EB3Z; Loop filter: AD8065. The basic FMCW system consists of a transmitter, receiver and mixer. FMCW radar ( F requency- M odulated C ontinuous W ave radar = FMCW radar ) is a special type of radar sensor which radiates continuous transmission power like a simple continuous wave radar ( CW-Radar ). RF Tutorial Lesson 17: Simulating a …. Automotive Adaptive Cruise Control Using FMCW and …. Welcome to PyRAPID — PyRAPID 0. FMCW Radar ">Pedestrian Traffic Light Control with Crosswalk FMCW Radar. In this paper we implement FMCW surveillance radar for drone detection on SDR using GNU Radio and the USRP B210. fmcw · GitHub Topics · GitHub. The fmcw package aims at generalizing the python code he open sourced on GitHub and provide the user with a lot more features. 下图 (左)显示了啁啾信号的频率与时间的关系，右图显示了频率随时间线性增加的啁啾信号的幅度与时间的关系. FMCW radar multiple moving target detection. These four parameters, together with the radar. The FMCW radar with the following parameters was implemented: % System parameters Value % ----- % Operating frequency (GHz) 77 % Maximum target range (m) 15 % Range resolution (m) 0. Python signal_generator_fmcw_c - 5 examples found. The proposed system uses a low-cost off-the-shelf FMCW radar as a kerbside detector which enables adaptive pedestrian crossing solutions with the support of multiple object tracking techniques. Python signal_generator_fmcw_c - 5 examples found. These functions output estimated frequencies and the singular value sigma, which can be taken as a confidence measure of the estimate. FMCW - Creates an FMCW signal. I transmit the modulation signal as sawtooth waveform and I read the recieved signal in the digital form using ADC function available. openradar · PyPI">openradar · PyPI. FMCW">What is mmWave Radar? : Everything You Need to Know About FMCW. Measuring absolute range starts with determining what zero range is in beat frequency. A very important type of FMCW radar pulse is the linear FM sweep. FMCW Frequency-modulated continuous-wave radar (FM-CW) – also called continuous-wave frequency-modulated (CWFM) radar – is a short-range measuring radar set capable of determining distance ( Continuous-wave radar wiki ). Evaluating the TinyRad 24 GHz Demonstration Platform">Evaluating the TinyRad 24 GHz Demonstration Platform. 本发明公开了一种FMCW雷达测距的方法和装置，方法包括步骤：对经过A/D采样后的FMCW雷达中频信号进行频谱分析；判断FMCW雷达中频信号的频谱是否满足相位差法校正条件；如果满足则应用相位差法进行频谱校正，获得校正的中频频率，并根据校正后的中频频率计算距离；如果不满足，则利用频谱分析后获得的中频频率计算距离。. A modulated signal is transmitted, received, and the transmitted and received signals are multiplied in the time domain and. Radar Signal Simulation and Processing for Automated …. The PyPI package fmcw receives a total of 513 downloads a week. GitHub - kopytjuk/python-fmcw: Tutorials on frequency modulated continuous wave (FMCW) and Chirp Sequence Modulation RADAR algorithms. This frequency is commonly used by automotive radars. 17: Simulating a Frequency. In a frequency-modulated continuous-wave (FMCW) radar employing a linear upsweep in frequency, the radar signal generator produces a phase modulated signal of the form. Python eazydammy / radar-target-generation-and-detection Star 9 Code Issues Pull requests Generating targets and detecting range and velocity from simulated FMCW waveform radar signals using the Range/Doppler FFT method and displaying targets using the 2D CFAR visualization. signal_generator_fmcw_c extracted from open source projects. They are also referred to as upramps and downramps. The FMCW waveform is a common choice in automotive radar, because it provides a way to estimate the range using a continuous wave (CW) radar. 1 I would like to simulate a FMCW radar in the frequency domain. With the power of less than 10 dBm, it can measure the distance of a person with a median of 5 cm. 28K views 7 months ago Watch an introduction to Frequency Modulated Continuous Wave (FMCW) radar and why it’s a good solution for autonomous vehicle applications. The mmWave training curriculum provides foundational content and hands-on examples for you to learn the fundamentals of FMCW technology and mmWave sensors to start development quickly. How to implement an RF Mixer for chirp …. Our portfolio of mmWave sensors include: Automotive mmWave radar sensors and industrial mmWave radar sensors. I am using fmcw radar to find out distance and speed of moving objects using stm32l476 microcontroller. FMCW generator. Instead of using C program to generate FMCW signal, I want to use signal generated in python, load this into a file (. Those are 1: Being a mm-wave radar: the high attenuation in mmwave frequencies provides a high isolation between the co-located operating radars even if they are separated in a few meters. The fmcw package aims at generalizing the python code he open sourced on GitHub and provide the user with a lot more features. Configuring the radar FMCW waveform based on the system requirements and simulating the radar signal propagation and moving target scenario. Within 5 meters, it has an positioning accuracy of about 20 cm. The principle behind FMCW is that you transmit a chirped signal and receive a time delayed version of it after reflecting from a target. hardware-agnostic data reading or processing. The mixing process is very similar, but with a slight tweak. FMCW Frequency-modulated continuous-wave radar (FM-CW) – also called continuous-wave frequency-modulated (CWFM) radar – is a short-range measuring radar set capable of determining distance ( Continuous-wave radar wiki ). Implementation of a GNU radio and python FMCW radar …. MATLAB's documentation makes reference to it here: "The mix operation reverses. The instantaneous frequency of the transmitted signal is. mmWave radar sensors. Writer (filename, queue, encoding='latin1', timeout=0. Future Plan Hardware Abstraction Layer, e. 3dFFT to compute angle of arrival in FCMW radars. 1 m 2 and a maximum range of 150 m for the purpose of point detection. Also, in FMCW radars the vital sign information is encoded in the received phase similar to FM signals. First, import the numpy module, Copy to clipboard import numpy as np Converting shapes of Numpy arrays using numpy. 01K subscribers Subscribe 30K views 4 years ago The move to the new 76-81 GHz band provides many improvements. By lowering the threshold required to get into building a radar, the hope is to grow a community of passionate radar makers. The distance is proportional to the frequency offset between the transmitted signal and the received echo. More tutorials to help people get started on FMCW radar. FMCW radar: understanding of doppler fft Ask Question Asked 1 year, 3 months ago Modified 1 year, 3 months ago Viewed 3k times 0 I am using fmcw radar to find out distance and speed of moving objects using stm32l476 microcontroller. FMCW radar working principle simulation based on python. Now I want to make a standalone application that runs on pluto directly. Finally, post processing the radar signal using 1st FFT, 2nd FFT, and CA-CFAR to estimate the target's range and velocity. reshape () to convert a 1D numpy array to a 2D Numpy array Let’s first create a 1D numpy array from a list, Copy to clipboard # Create a 1D Numpy array of size 9 from a list. FMCW radar working principle simulation based on python ">FMCW radar working principle simulation based on python. In a further research I would like to calculate the response of the FMCW signal when it is hitting a dielectric slab. In a further research I would like to calculate the response of the FMCW signal when it. Then the echo of the wave is captured at a. com">mmWave radar sensors. First, import the numpy module, Copy to clipboard import numpy as np Converting shapes of Numpy arrays using numpy. A Frequency Modulated Continous Wave (FMCW) is a signal in which the frequency increases/decreases with time. Aug 30, 2022 01:45 AM FMCW radar working principle simulation based on python — Chapter 2：Velocity simulation This article will introduce how to use python to implement the simulation of FMCW working principle, the second chapter content will introduce the principle of velocity detection.