Clemens Pfeffer

A 77-GHz Cooperative Radar System Based on Multi-Channel FMCW Stations for Local Positioning Applications

In this paper, a radar system for local positioning applications is presented. The system consists of frequency modulated continuous-wave (FMCW) stations operating in W-band that are loosely coupled using time-delayed ramp start signals. A centralized signal processing approach allows to relax the required synchronization accuracy between the stations and further leads to a cancellation of phase noise and phase distortions caused by imperfect FMCW ramps. All stations are equipped with an antenna array and multiple receivers. Thus, a signal processing approach is developed in this work that combines the positive effects from the centralized processing with the information from the antenna array in a digital-beamforming based approach to improve the multipath robustness of the overall system. The developed theory is confirmed in measurements carried out with a prototype system consisting of two stations. Various measurements in multipath environments confirm the improved robustness leading to a worst-case root-mean-square position error of 15 mm under strong multipath conditions which were simulated inside an anechoic chamber.

FMCW MIMO Radar System for Frequency-Division Multiple TX-Beamforming

In this paper, a prototype automotive radar sensor is presented that is capable of generating simultaneously multiple transmit (TX) beams. The system is based on a four-channel 77-GHz frequency-modulated continuous-wave (FMCW) radar system. The number of beams, their radiated power, steering angle, and beam pattern can be changed adaptively. This is achieved by the utilization of orthogonal waveforms applied to different beams in combination with digital beamforming on the receive side. Key components are vector modulators in the TX path controlled by digital-to-analog converters. The performance of the system is shown in measurements focused on beam pattern, signal-to-noise ratio, and susceptibility in case of interfering targets at cross-range. Measurement results are discussed and compared to theory and simulations. Furthermore, crest factor minimization of the vector modulators control signals is introduced and used to increase the achievable TX power, which will be also shown in measurements.

An IQ-modulator based heterodyne 77-GHz FMCW colocated MIMO radar system

In this work the realization of a 77-GHz frequency-division multiple-access-based frequency-modulated continuous-wave multiple-input multiple-output radar with four transceiver channels in conjunction with a non-uniform linear antenna array is presented. The radar system, consisting of an RF-frontend utilizes transceiver chips with integrated inphase/quadrature-modulators to generate the frequency shifted transmit signals and a field programmable gate array-based baseband board, is used for test measurements to verify the system performance and to demonstrate the beamforming capability as well as the accuracy of the digital-beamforming method.

A Frequency-Division MIMO FMCW Radar System Based on Delta–Sigma Modulated Transmitters

In this paper, we present a hardware-efficient method, which allows to implement multiple-input multiple-output (MIMO) radars with a separation of the transmit (TX) signals in the frequency domain. The proposed architecture uses binary phase-shift keying (BPSK) modulators within the TX paths of a multi-channel frequency-modulated continuous-wave (FMCW) radar. These BPSK modulators are driven by 1-bit sequences, which are generated using ΔΣ-modulators to shift the quantization noise towards high frequencies. Thus, neither multi-bit digital-to-analog converters, nor vector modulators or phase shifters are required for the proposed approach. Since the FMCW principle relies on the evaluation of beat frequencies within a narrow frequency band, the shaped quantization noise is outside the frequencies of interest and can thus be filtered out. The chosen hardware setup is optimized for integration into monolithic microwave integrated circuits (MMICs), which is demonstrated by a prototype system based on 77-GHz chips. Several MMICs are combined to realize a radar frontend with six TX and eight receive channels resulting in 48 MIMO channels. A signal-processing approach is derived and a method to reduce ambiguities is presented. Measurements demonstrate a range resolution of 15 cm and a 3-dB beamwidth of 3 ° with position standard deviations better than 1 mm. Furthermore, a measurement example with a target placed outside the unambiguous range of the radar shows an 8-dB power reduction of the unwanted signal from the target at the ambiguous distance. This improvement is achieved by choosing nonidentical frequency spacings for the TX signals.

Millimeter-wave phase-coded CW MIMO radar using zero-correlation-zone sequence sets

We present a phase-coded continuous-wave (CW) multiple-input multiple-output (MIMO) radar approach based on code-division multiplexing. We use zero-correlation-zone (ZCZ) sequence sets to separate at the receivers signals from multiple transmitters. In particular, our approach uses equidistantly shifted almost-perfect autocorrelation sequences for efficient implementation. We carried out measurements using a software-defined radar platform with 16 MIMO channels to demonstrate the capability of the proposed approach.

A 77-GHz software defined OFDM radar

In this paper we present a 77-GHz software defined orthogonal frequency-division multiplexing (OFDM) radar. A single channel RF frontend equipped with a 77-GHz SiGe chip which includes an integrated IQ modulator in the transmit path and an IQ receive mixer is used for range and range/Doppler measurements. Digital-to-analog converters (DACs) with a sampling rate of 500MSPS and 14 bit resolution are used to generate OFDM symbols with 201 sub-carriers and a bandwidth of 200 MHz. Sampling of the received signal is realized by analog-to-digital converters which, like the DACs used to generate the TX signal, run at 500MSPS and deliver a resolution of 14 bit. The performance of the overall system was optimized by a peak-toaverage power-ratio reduction technique. A standard deviation of 12.4mm was achieved for range measurements which were carried out in an anechoic chamber. Furthermore, first test measurements demonstrate that the system can be applied to moving target scenarios.

A frequency-division MIMO FMCW radar system using delta-sigma-based transmitters

In this paper, we present a system that allows to realize frequency-division multiplexing multiple-input multiple-output (MIMO) radars which are based on the frequency-modulated continuous-wave (FMCW) principle. Multiple frequency-shifted FMCW signals, which can be separated in the receiver, are used as transmit (TX) signals. The frequency shifting is implemented using digitally generated sinusoids in conjunction with delta-sigma-based transmitters. The proposed principle requires only little adaptions compared to conventional FMCW-setups. Furthermore a fast Fourier-transform stage, being present in many conventional FMCW radars, can be used to separate the TX signals leading to an efficient usage of existing building blocks. Measurements carried out using a prototype system with 48 MIMO channels demonstrate the feasibility of the proposed approach.

A multimode-beamforming 77-GHz FMCW radar system

In this work a multimode-beamforming 77-GHz frequency-modulated continuous-wave radar system is presented. Four transceiver chips with integrated inphase/quadrature modulators in the transmit path are used in order to simultaneously realize a short-range frequency-division multiple-access (FDMA) multiple-input multiple-output (MIMO) and a long-range transmit phased-array (PA) radar system with the same antennas. It combines the high angular resolution of FDMA MIMO radars and the high-gain and steerable beam of PA transmit antennas. Several measurements were carried out to show the potential benefits of using this concept for a linear antenna array with four antennas and methods of digital beamforming in the receive path.

A sige-based 140-GHz four-channel radar sensor with digital beamforming capability

This paper presents a multi-channel radar sensor operating at 140 GHz. The sensor employs fundamental-wave SiGe-based chips that feature HBTs with 340-GHz ƒmax. A separate voltage-controlled oscillator chip provides the LO signal with frequencies from 136 to 150GHz for four cascaded transceiver chips. The saturated transceiver output power is approximately 4 dBm, the maximum receiver gain is 19.5 dB, and the minimum double-sideband noise figure is 13.5 dB. The equivalent isotropically radiated power of a single channel is 5 dBm. The sensor was field-tested with frequency-modulated continuous-wave chirps from 140 to 145 GHz. Targets were resolved in range and angle by means of digital beamforming.

A 77-GHz cooperative secondary radar system for local positioning applications

In this paper a cooperative radar system for local positioning applications operating at 77 GHz is presented. The proposed system is based on multiple frequency-modulated continuous-wave based stations which transmit their measured signals to a common processing unit. The required station synchronization accuracy is relaxed due to the centralized processing. Furthermore phase noise and sweep non-linearity effects can be mitigated in the signal processing. Measurements carried out using a realized prototype with two stations show a performance improvement of approx. 6 dB compared to conventional methods that are based on the exchange of preprocessed data.