An efficient and safe approach of radar signal capturing and processing

June 04, 2015 // By Peter Aberl, Texas Instruments
On the way to autonomous driving advanced driver assistance systems (ADAS) based on vision, LIDAR and radar have to gradually supersede the driver’s visual sense. To achieve this challenging goal ADAS sensors have to further evolve to become more reliable, more accurate, safer and more efficient. This article focuses on automotive radar and specifically discusses signal processing steps of a modern fast chirp radar system. An example shows how radar signal capturing and processing can be realized in an efficient and safe way. Additional automotive radar aspects like low power, small form factor and scalability are also touched.

Automotive Radar Evolution

Radar has a substantial history in Automotive of more than two decades. In the early days radar was mainly used for applications like adaptive cruise control (ACC), which was an optional comfort feature in luxury cars. Radar systems were widely used in the military and avionics industry due to its capability to directly measure relative position and relative speed of objects in the free space. However, in the high-volume automotive market radar technology was not very attractive because of high cost.

Over the last decade advancements in micro-wave chip sets and digital signal processing devices enabled a significant cost reduction of radar systems. Meanwhile car makers start to offer car models with radar sensors as standard equipment. Besides ACC, radar sensors are used for a manifold of use cases like autonomous emergency brake, blind spot detection and rear or front collision warning. Beyond cost reduction, new radar sensors have to fulfill ever increasing technical requirements, e.g. larger detection range, higher range resolution, wider angle of view and improved object discrimination with multi-target detection capability. On top of these system requirements also other automotive-specific aspects like functional safety, lower power and reduction of form factor have to be taken into account.

In former automotive radar sensors FMCW (frequency modulated continuous wave) technique with slow ramps (aka chirps) has been used, because of restrictions in the RF front-end chip set and limited availability of baseband processing chips for the harsh automotive environment. This technique was rather slow (e.g. 30ms chirp time) and provided limited resolution and limited multi-target capability. Thanks to advancements in the development of semiconductors, modern automotive radar sensors are based on the fast chirp technique. As the name indicates the frequency ramps occur at a higher rate and have a reduced ramp time in the range of 10-100 microseconds.

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