Frequency-division multiple-access (FDMA) in frequency-modulated continuous-wave (FMCW) radar comprises range-division multiple-access (RDMA) and Doppler-division multiple-access (DDMA). In this article, we present a method using RDMA and DDMA to realize multiple-input multiple-output (MIMO) functionality for FMCW radars. We use single-sideband modulation and quadrature phase shift keying (QPSK) modulation to implement RDMA and DDMA, respectively. These two approaches enable the simultaneous transmission of fast chirp waveforms from multiple transmitting (TX) antennas. Compared to existing works, our proposed system shows the following advantages. First, in RDMA FMCW radar, we apply overlapping binary masking to improve the unambiguous range. Second, in DDMA FMCW radar, we introduce a phase compensation method to reduce the image signals from the nonideality of QPSK symbols. Finally, we leverage these advantages of combining both RDMA and DDMA to balance the performance for FMCW MIMO radar in angular resolution, unambiguous range, and unambiguous velocity. In particular, the FMCW radar system combining RDMA and DDMA allows us to increase the numbers of TX antennas in MIMO applications. We verify our proposed radar system with measurement data on a prototype using three TX and four receiving antennas.

In this article, a precise phase-based radar distance measurement system using a Viterbi decoder to resolve phase ambiguity is presented. Relying on the frequency-modulated continuous-wave radar principle, the introduced method evaluates both the frequency and the phase of the intermediate frequency signal, thus achieving absolute distance measurement with high accuracy. To avoid ambiguity in the distance estimates by half the wavelength of the radio frequency signal, which commonly arises due to 2 π ambiguity in the measurement of the phase, the proposed Viterbi-based method estimates the most likely sequence of distances between the radar front end and the target. To verify the system concept, measurements using a commercial 77 GHz radar module were carried out, whereby the contour of a predefined surface containing steps in the height profile had to be determined. The experimental results confirm that the Viterbi-based approach is suitable to resolve phase ambiguity since accurate and repeatable distance estimates were obtained.

Phase-of-arrival-based localization systems for passive ultrahigh frequency (UHF) radio-frequency identification (RFID) transponders must typically be calibrated to account for unknown phase offset values. Usually, reference measurements are performed using known tag positions. However, if the measurement scenario changes or other types of transponders are used, the system must be recalibrated. This paper introduces an automatic blind calibration method based on a Viterbi algorithm that requires no reference measurements. With this approach, the phase offset values are determined autonomously based on the measurement data set without any prior knowledge of the transponder positions, which are also estimated. To prove the calibration approach, a multichannel system demonstrator was used comprising a commercial off-the-shelf RFID reader, conventional passive UHF RFID tags, eight transceiver front ends, baseband hardware, and signal processing. Measurements were carried out in a 2-D indoor office environment, which was defined to be 3.5 m x 2.5 m. Compared with the common exhaustive calibration method using reference measurements at known tag positions, the automatic blind Viterbi-based approach offers similar results with a root-mean-square deviation of the phase offset values of 0.33 rad, which corresponds to an electrical length of 18 mm. Regarding the localization, the experiments showed accurate results with a root-mean-square error of 56 mm and a median absolute error of 21 mm.

Being able to measure and track positions of mobile systems is an important capability in many applications, autonomous driving being one major example. With the Robust Radon Radar Odometry algorithm, this paper presents an approach for estimating the odometry of vehicles based on radar data only. The algorithm embodies a robust method for estimating the change in orientation as a key feature. The odometry algorithm is under the realm of direct methods, and it exploits properties of the Fourier transform for decoupling the changes in orientation from the changes in translation. In the first step, the Radon transform along with phase-correlation, outlier removal, robust measure of central tendency, keyframe selection and graph optimization are used in order to achieve a robust method for estimating the change in orientation, next the translation is estimated with the support of phase-correlation. The algorithm's performance was evaluated with real world data. Significant improvements in position and orientation error in terms of relative pose error and the KITTI odometry error metric are shown as compared to other direct methods for radar based odometry.

The need for accurate positioning and tracking of mobile sensor nodes arises in many applications. To compute position estimates from raw measurements in positioning systems, Bayesian filtering techniques such as Kalman, histogram, or particle filters are frequently employed. A major disadvantage of these techniques is the fact that they compute only a single position estimate in every timestep, and therefore do not utilize the available information to full extent. The work presented in this paper improves over this current state of the art by instead estimating full node trajectories, and therefore, the most plausible sequence of positions in every timestep. We present two distinct algorithms—for a discrete and for a continuous state-space—and highlight the particular advantages of each variant. Achievable results are shown by simulation and measurement to be more accurate than the traditional Bayesian filtering approach. The most prominent advantage of much more accurate total track length estimation is particularly emphasized.

This article introduces a precise radar-based direction-of-arrival measurement system using a Viterbi decoder. Based on the frequency-modulated continuous-wave principle, the presented method employs both the frequency difference and the round-trip phase difference of the radio wave signal impinging at two widely spaced receiving antennas, thereby accomplishing highly accurate and absolute measurements of the direction-of-arrival. In order to resolve angular ambiguity, which is inherently caused by the 2π ambiguity in phase measurement, the proposed Viterbi decoder determines the most likely sequence of direction-of-arrivals of the impinging radio wave signals. For proof of concept, experiments based on a 77 GHz radar unit equipped with one transmitting and two widely spaced receiving antennas were carried out. The measurement results show that angular ambiguity can be resolved by the presented Viterbi decoder since absolute, accurate, and repeatable direction-of-arrival estimates were obtained, even for receiver antenna spacings significantly larger than the signal wavelength.