Electromagnetic waves called millimetre waves ( MMW ) are waves with a frequency between 30 GHz and 300 GHz ( EHF band, according to the ITU ). These waves are part of the so-called microwaves (waves in the frequency range between 300 MHz and 300 GHz, this range includes the UHF, SHF and EHF bands ). Frequencies below 50 GHz are already exploited diversely, hence the need to explore new frequency bands, in this case, higher to meet the requirements and demand (current and future).
Today one of the most important attractions of MMWs is that at such high frequencies the available bandwidths are much greater, allowing the installation of radio links with capacities of multiple Gbps. As seen in the small cells section, the backhaul of mobile wireless networks must cope with the increase in capacity necessary to satisfy the demand for services. The MMW may provide an alternative to face this type of challenges.
History of Millimeter Wave Radar
Jagdish Chandra Bose was the first to experiment with this technology, in 1895 he made the first transmission and reception of electromagnetic waves at 60 GHz, more than 23 meters away (through two intermediate walls remotely ringing a bell). Then MMW research was kept within university and government laboratories, the first applications were in the 1960s for radio astronomy, followed by military applications in the 1970s.
In the 1990s, the development of the proximity detection radar for automobiles that operated at 77 GHz was the first user-oriented application using millimetre waves above 40 GHz. In 1995 the FCC released frequencies between 59 GHz and 64 GHz for wireless communication without a license, which resulted in the development of a variety of radars with commercial application, 2003 the use of the frequency bands from 71 GHz to 76 GHz and 81 GHz to 86 GHz was authorized for licensed point-to-point links, in 2006 it was enabled in Europe.
The growing role of motion detection
Motion detection has become an increasingly important capability in a wide range of applications. In addition to its role as a practical functionality in connected buildings and home products, it provides essential safety functionality in automotive and industrial applications. Increased range and accuracy are vital for a growing number of applications, eliminating the use of traditional methods based on passive infrared sensors or time-of-flight systems.
Therefore, the frequency modulated continuous wave (FMCW) mmWave radar technology has attracted increasing interest. It uses short wavelength signals allowing object detection with submillimeter precision. It can also pass through many materials (plastic, drywall, clothing) while maintaining high performance despite harsh environmental conditions, such as rain, fog, dust and snow.
The narrow beams of mmWave energy can be focused and redirected to provide very precise object detection and locate several relatively close moving objects.
How mmWave technology works
Although this article does not cover the processing of millimetre-wave radar signals, the principles of detection are based on a familiar concept involving the reflection of energy from an object. In linear FMCW radars, this energy is made up of millimetre-wave sound, called chirp (chirp), which changes frequency linearly over time. After the generation and transmission of a chirp by the radar system, the signal of the chirp reflected from a downstream object is detected and transmitted to a mixer. The mixer mixes the RX and TX signals to produce an average frequency (IF) signal.
The delay between the transmission of the chirp and detection of the reflected signal is used to calculate the distance between the antennas of the radar system and the object. If the radar system generates multiple chirps in a single observation window, it can determine the speed of an object by measuring the phase difference between the corresponding reflected chirps. When using multiple receivers, the radar system can also determine the relative angle of arrival (AoA) between the radar system and the object. By combining these principles with more complex calculations, a high-performance radar system can locate multiple targets moving at different speeds and paths.
The design of a system with these capabilities combines RF, analogue and digital subsystems (Figure 1). As part of the subsequent analogue stages, a low pass filter and analogue-to-digital converter (ADC) produce a digital data stream for signal processing using a Fast Fourier Transform (FFT) algorithm and d ‘other algorithms.
Single-chip mmWave solution
Texas Instruments’ mmWave solution combines millimetre-wave integrated circuits and a comprehensive software environment that can dramatically simplify the implementation of millimetre wave-based motion detection applications. Industrial mmWave devices, including models IWR1443 and IWR1642 from Texas Instruments, integrate a complete set of RF subsystems, both analogue and digital, required to generate, transmit, receive and process FMCW radar signals. These devices combine an analogue / RF input circuit similar to a sophisticated digital subsystem (Figure 2). In this input circuit architecture, these devices integrate a complete 76-81 GHz band FMCW transceiver subsystem with four dedicated RX signal paths and multiple TX channels (three in IWR1443 and two in IWR1642).
Radar signal processing chain
While the choice of IWR1443 hardware accelerator or IWR1642 DSP C674x core depends on the specific requirements of each application, the operation of the selected device in an application will be largely transparent to most developers. In the Texas Instruments mmWave solution architecture, TI’s mmWave software ecosystem can use the support of both devices to run useful modules or data processing units (DPUs), which are responsible for typical individual data transformations. used in the processing of radar signals. The main functions of TI’s mmWave DPUs include:
- Range FFT Algorithm: Reads chirp data during the acquisition period into the active frame to generate the one-dimensional FFT algorithm used for range calculation and produce the radar data cube. It is a three-dimensional (3D) matrix of range, chirp, and antenna data stored in the dedicated L3 radar data memory.
- Static Spurious Echo Elimination: Subtracts the average value of the samples from the sample set.
- FFT Doppler Algorithm: Performs 2D FFT algorithm calculations to refine radar cube data between frames and generates the detection matrix used by the radar object detection algorithms.
- CFAR: Performs the constant false alarm rate (CFAR) algorithm commonly used for object detection.
- CFAR Cell Averaging: Combines the angle of arrival at the CFAR module to implement the CFAR Cell Averaging Algorithm (CFAR-CA) frequently used by radar systems to detect objects against background noise.
- Additional DPUs dedicated to clustering, clustering and classification provide better application-specific adjustments for radar signal data.
Using TI’s mmWave SDK, developers can make a call to the Data Path Manager (DPM) programming interface (API) to combine the different DPUs in the chain. detection or data processing (DPC) required. For example, implementing a DPC chain for object detection (Figure 5) requires only a few basic calls, as demonstrated in the example code included in the mmWave SDK distribution from Texas Instruments.
Millimetre-wave technology offers range and precision advantages far beyond those that could be obtained with previous methods. For developers, however, many challenges in both hardware and software have limited the deployment of this technology. The availability of mmWave devices, development tools and a comprehensive software environment from Texas Instruments significantly reduces the barrier to implementing sophisticated object detection and location applications with mmWave technology.
By Rehan Ahmed