The X4 is an Impulse Radar Transceiver System on Chip (SoC) combining a 7.29/8.748 GHz transmitter for unlicensed operation in worldwide markets, a direct RF-sampling receiver, a fully programmable system controller and advanced power management functions in a single chip.

Novelda’s XeThru X4 is an ultra wide band (UWB) impulse radar chip. It provides product developers with sub-mm movement sensing accuracy at distances from 0 to 25 meters depending on target size.

The XeThru X4M300 is Novelda’s presence and occupancy sensor powered by the XeThru X4 ultra wide band radar chip. Ultra sensitive and with excellent signal to noise performance, the sensor detects even the smallest human movement in a room.What’s more, the sensor’s presence detection zone is fully programmable, and can be configured up to a distance of 9.4 metres. The sensor also accurately measures the distance to occupants.

URL: https://www.xethru.com/x4m300-presence-sensor.html

URL: https://www.xethru.com/occupancy-sensing.html

The XeThru X4M200 is Novelda’s respiration sensor powered by the XeThru X4 system on chip. The standard sleep and respiration monitoring abilities are integrated in the sensor and provide advanced respiration and movement tracking both during the day and throughout the night. The programmable detection range up to 5 meters is a key feature for the sensor.

URL: https://www.xethru.com/x4m200-respiration-sensor.html

URL: https://www.xethru.com/respiration-monitoring.html/

XeThru Module Connector is the host software(主机软件) for communicating between the X4M03 / X4M06 development kits or other XeThru radar sensors.

Module Connector runs on Windows, Max, Linux and embedded hosts, and presents a complete API of the sensor module in MATLAB, Python and C++ programming environments. This makes it easy to start streaming and analysing radar data on multiple levels (raw radar, baseband, pulse Doppler , detection list, respiration and presence data) and developing new algorithms.

XeThru Embedded Platform (XEP) is the embedded software running on the X4M03, X4M06 and X4M02 radar development kits to enable occupancy, respiration monitoring and other customs applications.

XEP is open source and comes as a ready-to-go(现成的) Atmel Studio 7 project. It implements all core functionalities for easy hardware module implementation. A compiled version of XEP is also provided and runs out-of-the-box with the following functionalities:

• Module Communication Protocol is the host communication layer including message parsing(消息解析) to make it easy to extend the API and tailor(定制) system behaviour.
• X4Driver – The API layer providing developers with direct access to all XeThru X4 SoC functionalities. It enables tailoring of radar parameters and performance to match specific project needs and is accessed from host computer via XMC.
• Well-defined access points for digital signal processing libraries to tap into X4’s radar data stream and boost system performance.
• FreeRTOS for real time system behaviour monitoring and management.

Reference: INTRODUCTION TO RADAR SIGNAL PROCESSING, Christos llioudis

• Radar is an acronym for RAdio Detection And Ranging.
• Radar is an object detection system that transmits electromagnetic(EM) waves and analyses the echoes coming from the objects.

可以从以下四个角度分类

• Operation

  • Primary: Target monitoring

  • Secondary: Transponder on the target (Fig following)

    

• Illuminator

  • Active: Uses its transmitter to illuminate the target

  • Passive: Exploit illuminators of opportunity (Fig following)

    

• Transmission rate

  • Pulsed: Emit separated pulses

  • Continuous Wave (CW): Constant transmission**(Fig following)**

    

• Geometry

  • Monostatic(单站): Transmitter and receiver in the same location (Fig. Left)

  • Bistatic(双站): Transmitter and receiver in separate locations (Fig. Right)

    

The radar equation is referring to the power of the echo returning to the radar: $$ P_{r}=\frac{P_{t} G^{2} \lambda^{2} \sigma}{(4 \pi)^{3} R^{4} L} \rightarrow R=\sqrt[4]{\frac{P_{t} G^{2} \lambda^{2} \sigma}{(4 \pi)^{3} L P_{r}}} $$ $P_{t}$ : Transmit power

$G$ : Antenna gain

$\lambda$ : Radar operating wavelength

$\sigma$ : Target radar cross section (RCS)

$R$ : Range from the radar to the target

$L$: Other losses (system, propagation)

雷达截面积(Radar Cross Section, RCS)是目标在雷达接收方向上反射雷达信号能力的度量，一个目标的RCS等于单位立体角目标在雷达接收天线方向上反射的功率(每单独立体角)与入射到目标处的功率密度(每平方米)之比。

Low frequencies are preferable for long-range radar. Low RCS targets are harder to detect.

脉冲宽度和带宽成反比关系，脉冲信号的脉冲宽度约窄，信号带宽越宽。因为信号脉宽是指脉冲信号的脉冲宽度（时间）；信号带宽是指信号频谱的宽度，也就是信号的最高频率分量与最低频率分量之差，是指一个信号所包含的所有频率成分（频率）

Pulse Repetition Interval (PRI) is defined as the time interval between consequent(后续) pulses.

The maximum unambiguous range defines the maximum distance to locate a target. $$ R_{\max }=\frac{c \mathrm{PRI}}{2}=\frac{c}{2 \mathrm{PRF}} $$ Radar is not able to discriminate between echoes from an older and the current transmission.

Radar returns from each PRI are stored in memory for further processing.

• Fast Time refers to the different time slots(时间段) composing a PRI, sampling rate dependent.
• Slow Time updates every PRI

Consider a continuous wave (CW) radar with operating frequency $f_0$. In the presence of a target moving with radial velocity $u_r$, due to the Doppler phenomenon, the echoed signal will be shifted in frequency by: $$ f_{D}=\frac{u_{r}}{c} f_{0} $$ Positive Doppler shifts ($f_D > 0$) indicate that the target is moving towards the radar, while negative ($f_D < 0$) away from it.

In most radar systems, the bandwidth of single pulse may be a few orders of magnitude(数量级) greater than the expected Doppler frequency shift: $$ \frac{1}{T} \gg f_{D} $$ Echoes from moving targets cannot be discriminated(鉴别) from stationary clatter in spectrum. Using consequent pulsed over a coherent pulse interval (CPI), the single pulse bandwidth is divided into spectral line of approximate bandwidth $1/{CPI}$

Concept of Coherence:

In a pulse radar system, coherence describes the phase relationships between the transmitted and the received pulses. Oscillations and electromagnetic waves are described as coherent if their phase relationships are constant(相位差为常数). In case of incoherence, these phase shifts are statistically distributed. Whether radar is coherent or not is determined by the type of transmitter. As transmitters different systems can work in the radar, which are either coherent, partially coherent or incoherent.

The XeThru X4 is a compact, Impulse-Radio Ultra-Wideband (IR-UWB) radar system on a chip. It is configurable and gives the developer a high degree of freedom to develop new applications from basic presence detection to advanced imaging-solutions.

XeThru X4 is a complete IR-UWB radar system on chip. To configure it correctly, it's important to have a good understanding of how an impulse radar system works and how the received data is sampled and presented. The fundamentals of an impulse radar system are shown in Fig. 1. The radar sends out an electromagnetic impulse through the Tx antenna which is reflected from any object in front of it. The reflections travel back and are received and sampled through the Rx antenna.

The pulse that X4 transmits is configurable within two different bands. The lower pulse generator setting enables transmission within the band 6-8.5 GHz, shown in Fig. 2, and the high settings within the band 7.25-10.2 GHz.

Pulse-Doppler begins with coherent pulses transmitted through an antenna or transducer. There is no modulation on the transmit pulse. Each pulse is a perfectly clean slice of a perfect coherent tone. The coherent tone is produced by the local oscillator. There can be dozens of transmit pulses between the antenna and the reflector. In a hostile environment, there can be millions of other reflections from slow moving or stationary objects. Transmit pulses are sent at the pulse repetition frequency.