AWR Application Notes

mmWave Automotive Radar and Antenna System Development Using AWR Software 3 www.cadence.com/go/awr Radar Architectures and Modulation For adaptive cruise control (ACC), simultaneous target range and velocity measurements require both high resolution and accuracy to manage multi-target scenarios such as highway traffic. Future developments targeting safety applications like collision avoidance (CA) or autonomous driving (AD) call for even greater reliability (extreme low false alarm rate) and signifi- cantly faster reaction times compared to current ACC systems, which utilize relatively well-known waveforms with long measurement times (50-100ms). Important requirements for automotive radar systems include the maximum range of approximately 200m for ACC, a range resolution of about 1m and a velocity resolution of 2.5km/h. To meet all these system requirements, various waveform modulation techniques and architectures have been implemented, including a continuous wave (CW) TX signal or a classical pulsed waveform with ultra-short pulse length. The main advantages of CW radar systems in comparison with pulsed waveforms are the relatively low measurement time and computation complexity for a fixed high-range resolution system requirement. The two classes of CW waveforms widely reported in literature include linear-frequency modulation (LFMCW) and frequency-shift keying (FSK), which use at least two different discrete TX frequencies. Table 1 compares the different radar architectures and their advantages and disadvantages. Table 1: Different radar architectures and their technical advantages/disadvantages in target detection, range, robustness, and resolution For ACC applications, simultaneous range and relative velocity are of the utmost importance. While LFMCW and FSK fulfill these requirements, LFMCW needs multiple measurement cycles and mathematical solution algorithms to solve ambiguities, while FSK lacks in range resolution. As a result, a technique combining LFMCW and FSK into a single waveform called multiple frequency shift keying (MFSK) is of considerable interest. MFSK was specifically developed to serve radar development for automotive applications and consists of two or more TX frequencies with an intertwined frequency shift and with a certain bandwidth and duration, as shown in Figure 2 1 . Figure 2: Multiple frequency shift keying Pulse Doppler FMCW FSK UWB Signals/Plots Description Single-carrier frequency is transmitted in a short burst Typically a sawtooth waveform with 100 - 150MHz bandwidth FSK with 1MHz steps Coherent processing interval (CPI) per fre- quency is 5ms Range info is derived from phase difference Dirac pulse Measure time-of-flight auto correlation Advantages Simple algorithm for distance Good range accuracy Easy to calculate relative speed and range Simple voltage controlled oscillator (VCO) modula- tion Short measurement cycle Simple principle Can measure at close range due to large BW Disadvantages Difficult-to-determine range rate Cannot transmit and receive simultaneously Computation to eliminate ghost targets Long measurement time for multiple chirps Coherent signal required for accuracy Poor range direction information Medium-to-low range No direct measure of range rate Sensitive to disturbance

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