The effect of amplifier-related signal amplitude compression in orthogonal time-frequency space (OTFS) waveform for radar and communications systems is considered. A novel approach to OTFS waveform generation is proposed, where complementary sequences are used with the Zak transform to encode delay-Doppler symbols and form an OTFS time-domain signal with a constant envelope. The high peak-to-average power ratio (PAPR) of conventional OTFS can cause amplifier saturation, leading to spectral noise and performance degradation in both communication and radar systems due to amplitude clipping. This issue can be critical in dual-function radar and communication applications, where high power may be crucial in both use cases. The proposed waveform, namely, constant modulus OTFS (CM-OTFS), offers an alternative to standard OTFS when high-power or low-cost amplification is required. The sensing and communications performances of CM-OTFS are evaluated through numerical simulations and compared with pristine and amplifier-distorted OTFS waveforms. CM-OTFS demonstrates slightly degraded sensing performance and lower communication rate than pristine OTFS but outperforms amplifier-distorted OTFS signals. The performance of CM-OTFS is evaluated through radar and communication simulations, as well as radar measurements using the waveform-agile PARSAX radar.

Automotive radar interference problem between multiple radar sensors is investigated. Phase-coded frequency modulated continuous wave (PC-FMCW) radar structure with low sampling and processing power demands is introduced to blindly mitigate mutual interference. The interference resiliency of the proposed structure is evaluated and compared with the conventional frequency modulated continuous wave (FMCW) automotive radar. It is demonstrated that the proposed approach is more robust to both coherent and non-coherent interference types, allowing resilience to both external interference of radars but also the self-interference in the simultaneous multiple input multiple output (MIMO) transmission.

This paper proposes a novel waveform, namely non-uniform OTFS (NU-OTFS), for joint radar and communication applications (Radcom) in multi-user/MIMO scenarios. Based on orthogonal time frequency space (OTFS) modulation, the proposed waveform is realized by using a non-uniform symplectic finite Fourier transform (NU-SFFT) to generate non-overlapping quasi-arbitrary time-frequency representations of OTFS messages. Non-uniform sampling and sparse reconstruction algorithms within the compressed sensing framework are employed to avoid (self-)interference and enhance radar target parameter estimation. The performance of NU-OTFS and its corresponding receivers is evaluated through numerical simulations and measurements, and compared with state-of-the-art μMIMO Radcom OTFS system concepts. NU-OTFS allows for increased flexibility in time-frequency resource allocation and larger unambiguous radar parameter estimation while showing comparable performance to state-of-the-art OTFS multi-user communication implementations in realistic high-mobility channel conditions.

A novel receiver structure for the reception of linearly frequency modulated (LFM) chirps carrying additional narrowband (phase) modulation is proposed. A linear relation between the time delay and the beat frequency shift of the target response in stretch processing is exploited to estimate the target range via correlation of the received signal with the replica in a Fractional Fourier Transform (FrFT) domain. According to numerical simulations, the proposed FrFT receiver demonstrates improved performance and computational efficiency over the state-of-the-art solutions for the moderate-to-large bandwidth of the information-carrying modulation. The receiver was integrated into the waveform-agile radar polarimetric agile radar in S band (PARSAX) and its performance has also been verified experimentally.

The calibration of a collocated MIMO radar is addressed by means of independent calibration of transmit and receive arrays. The solutions for both arrays' elements gain and phase terms only and the full coupling matrix estimation are presented. The proposed solution significantly improves over the conventional calibration of the virtual array in terms of calibration accuracy and reduced measurements requirement, as demonstrated by numerical simulation and validated by calibration of a commercial automotive radar.

A generic description for common multi-carrier radar receivers is proposed. Two multi-carrier waveforms - orthogonal frequency division multiplexing (OFDM) and orthogonal time-frequency spacing (OTFS) - which could be used for joint radar and communication (JRC) applications - are considered. Sensing performances of different waveform-receiver pairs are compared theoretically. It is shown that while qualitatively, both waveforms perform similarly under the same receiver, performance differences exist between them.

The sensing properties of the binary phase codes are investigated with their application to phase-coded (linearly) frequency modulated continuous waveform (PC-FMCW). It is shown that the ambiguity function of FMCW signal modulated with a binary phase code corresponds to sheared ambiguity function of the code itself. The range profiles of PC-FMCW with different code families are analysed and compared in terms of integrated sidelobe level (ISL).

Smoothed phase-coded frequency modulated continuous waveform (SPC-FMCW), which is aimed to improve the coexistence of multiple radars operating within the same frequency bandwidth, is studied, and the receiving strategy with a low analog-to-digital converter sampling requirement is investigated. The Gaussian filter is applied to obtain smooth waveform phase transitions, and then, quadratic phase lag compensation is performed before waveform transmission to enhance decoding. The proposed waveform is examined in different domains, and its waveform properties are analyzed theoretically and demonstrated experimentally. Both simulation and experimental results show that the introduced waveform with the investigated processing steps helps combine all advantages of the FMCW waveform, including hardware simplicity and small operational bandwidth of the receiver, with the advantages of phase coding.

The MIMO ambiguity functions of the binary phase codes as applied to phase-coded frequency modulated continuous waveform (PC-FMCW) are studied. The range-angle performance of the PC-FMCW with different code families is investigated and compared with the phase modulated continuous waveform (PMCW). An advantage of the PC-FMCW ambiguity function over the PMCW one is demonstrated in terms of the range resolution and sidelobe level for the same types of codes.

This paper presents an analysis of a new method of automotive radar self-calibration which uses targets of opportunity. While conventional offline calibration of a phased array antenna requires accurate knowledge of the positions of calibration targets relative to the radar, such information is not available in a dynamic scenario. To compensate for this, we have developed an estimation procedure based on an extended Kalman filter (EKF) to address the challenge of simultaneous localisation, mapping and calibration. The proposed technique makes it possible to compensate for moderate errors of amplitude and phase in the phased array response with just a few measured frames. A significant reduction in the sidelobe rejection of the array response, plus the ability to correct for angular steering errors, are demonstrated via numerical simulations and real data processing.