Design and signal processing for CMOS automotive radar

© 2014 Dr. John Zhong-Chen LiThere is an increasing use of radar for sensing the environment in automotive applications to provide data for applications such as collision avoidance and adaptive cruise control systems. In this thesis, the waveform design, signal processing and architecture of automotive radars are explored. A particular emphasis is placed on reducing the implementation cost to enable widespread adoption of safety systems. While an automotive radar is unlikely to experience intentional jamming, the anticipated increase in density of radars with falling cost and improved availability is expected to lead to more interference as more users begin to share the available band. It is thus important that the performance of the system is understood in the presence of interference. This thesis provides some insight into the severity of the problem and some strategies for mitigating the impact. The requirements of automotive radar typically mandate the use of full-amplitude continuous-wave radar transmitters which occupy as much bandwidth as possible to meet the constraints on transmitted power for detecting targets at long range. Thus, some of the usual interference mitigation techniques in mobile communications such as power control or frequency or time division are not readily applicable. Instead, the available spectrum must be shared with a code-division multiple access scheme. It is important to have an understanding of the availability of safety applications under interference. Thus, a simple but typical automotive interference environment is modelled under the assumption that a multiple access scheme is employed. The model is used to determine empirical guides on the number of effective channels required under various scenarios, as well as to understand the average and worst case times that users will be blocked. Two classes of frequency modulated waveforms are investigated in this thesis. First, Linear Frequency Modulated Continuous Wave (LFM-CW), which has emerged as a popular choice in automotive radar because it readily admits a simple transceiver architecture. The return signals are usually processed using FFTs. However, mitigating interference with such waveforms requires the sacrifice of some estimation performance. A second scheme of using Random Stepped Frequency (RSF) waveforms scheduled in conjunction with single tone continuous wave (CW) waveforms is also presented. A common transceiver architecture can be used but the estimation performance of the RSF waveform can be improved with more sophisticated signal processing beyond the typical limits imposed by the FFT processing typically used with LFM-CW waveforms, while still maintaining low sampling and data rates. The performance of the algorithm when the system is in a non-optimal state due to interference or hardware limitations is demonstrated to degrade gracefully. The waveform also lends itself to interference mitigation as in each time slot each user is only concerned with a small part of the full band. The increased flexibility of RSF waveforms will thus allow radars to operate cognitively by rearranging their transmitted sequence when spurious returns from other users are detected