Interference in 79 GHz Phase-Coded Automotive Radar

Abstract

Automotive radars play a crucial role in the reduction of traffic casualties and the realization of autonomous driving due to its robustness and adverse weather tolerance. However, as the penetration rate of automotive radars increases, concerns arise regarding the mutual interference. In contrast to the predominant Frequency-Modulated Continuous Wave (FMCW) radars, Phase-Modulated Continuous Wave (PMCW) radars might provide solutions for the interference problem by coding the waveforms, which brings an additional degree of freedom. In this thesis, a system level overview of the phase-coded radar is presented. Regarding the popular code families, particular attention was given to the Gold, Almost Perfect Autocorrelation Sequences (APAS), and Zero-Correlation Zone (ZCZ) sequences. This thesis has proposed three distinct designs for 16-TX-element MIMO Phase-Coded radar that drives the requirements of a Medium Range Radar (MRR). The conclusion can be drawn that APAS and ZCZ sequences have shown to provide a (sub)optimal design that is emphasized by their perfect correlation characteristics within the designated distance of interest. Furthermore, in full-transmit capacity MIMO, the proposed designs use semi-orthogonal waveforms to provide excellent performance in synchronous PMCW radars. However, performance degrades in case Doppler-shifted reflections are received, whereas sidelobes arise in range due to non-orthogonality. This thesis concludes that the APAS-coded waveforms are most tolerant to Doppler shift; besides, its Time Division Multiplexing (TDM) MIMO Transmission scheme is computationally more efficient than the Code Division Multiplexing (CDM) scheme used in Gold and ZCZ coded waveforms. Finally, the radar-to-radar interference investigation has proven that for uncorrelated PMCW- to-PMCW interference, the noise floor undergoes a consistent increase, which is according to the interference-plus-noise power level calculated from the link budget analysis. This thesis emphasizes these results, as the interference effect in FMCW-to-FMCW (provided by NXP Semiconductors) have seen similar phenomena. Therefore, results in this thesis support the conclusion that coded waveforms do not remove or suppress the energy levels of the interference. For correlated interference, ghost targets might be formed, but this depends on the starting time as well as the starting coded bit of the interferer, as the correlation peak can be formed outside the distance of interest.