"Millimeter-Wave Phase-Coded CW MIMO Radar"
, Linz, 5-2022
Millimeter-Wave Phase-Coded CW MIMO Radar
Sprache des Titels:
Multiple concepts of realizing various kinds of radar systems are known in the literature. For example, automotive radar sensors based on integrated circuits nowadays widely use the frequency-modulated continuous wave (FMCW) principle. For reasons including cost, size, and performance, it is of interest to take advantage of the growing capabilities of digital circuits.
This work aims to investigate the promising phase-coded continuous-wave (CW) approach. As a consequence, the codes which are used become a significant design parameter. In our investigation of single-input single-output (SISO) systems, we applied three binary codes (binary m-sequence, almost perfect autocorrelation sequence, and Golay-complementary sequence), one two-valued code (Golomb?s code), and one ternary sequence (Ipatov?s ternary sequence) and used a linear FMCW signal for comparison. Codes with binary or close to binary alphabets were selected with a future realization of the radar system based on integrated circuits in mind. We provide instructions for generating each sequence and demonstrate the performance of the phase-coded signals using measurements carried out with a SiGe-based RF IQ-transceiver.
Since modern FMCW radar system make use of digital beamforming, we also investigated the concept of phase-coded CW multiple-input multiple-output (MIMO) radar systems. Due to the inherent existing modulation of the CW carrier for ranging, we choose code-division multiplexing to separate signals from multiple transmitters at the receivers. Zero-correlation-zone (ZCZ) and low-correlation-zone (LCZ) sequence sets as well as concatenated codes are selected for this purpose. In particular, the investigation using ZCZ and LCZ sequence sets includes three different sequence set types: an equidistantly shifted almost-perfect autocorrelation sequence (APAS) set, sequence sets based on mutually orthogonal Golay complementary sets (MOGCS), and a binary LCZ sequence set. The required sequence lengths are discussed according to the physical propagation behavior in a radar sensor scenario. Furthermore, we summarize the theoretical limits of LCZ/ZCZ sequence sets and provide examples taking the chosen scenario into account. The investigated concatenated codes are based on Hadamard matrices and APASs. Due to the structure of concatenated codes, the correlators can be implemented with a lower number of taps compared to the overall sequence length. However, this type of sequence set has some limitations, which we address. For all selected sequence sets, we present measurements carried out with a software-defined radar (SDR) platform, which is equipped with 16 MIMO channels operating at a frequency of 77 GHz. We investigated the behavior of the sequence sets on real hardware in the range, cross-range, and range-Doppler domain.
Since using ZCZ/LCZ sequence sets in combination with CW MIMO radar systems showed promising results, an efficient implementation of a set correlator is of particular interest for an integrated circuit realization. We present an approach for an efficient circuit realization of such a sequence set correlator for a subset of MOGCS based ZCZ sequence sets. Furthermore, we analyze and optimize its resource requirement. A logarithmic instead of linear growth of the required adders could be achieved by the proposed implementation. Furthermore, we present that the selected type of binary LCZ sequence sets is also suitable for an efficient hardware implantation on the transmitting as well as the receiving side.