Belal Al-Qudsi

Design of a multi-band FMCW radar module

This paper presents a multi-band frequency-modulated continuous wave (FMCW) radar module. The module can perform ranging in a wide frequency range, including the 2.4GHz and 5.8GHz ISM bands. It incorporates an application specific integrated circuit (ASIC) for processing the analogue signals and a field programmable gate array (FPGA) as digital signal processing backend, providing a reconfigurable test platform. Using multiple stations, positioning measurements are performed which demonstrate the benefits of the multi-band system in different scenarios.

Crystal oscillator frequency offset compensation for accurate FMCW radar ranging

Accurate ranging and positioning systems encounter several practical limitations. Crystal oscillator (XO) tolerance is a major challenge that impairs the accuracy of these systems. Two-way ranging with frequency modulated continues wave (FMCW) radars in particular are more influenced by XO tolerance as compared to primary FMCW radars. So this work focuses on the measurement and compensation of the relative frequency offsets between the different XOs in FMCW radar systems in order to improve their ranging accuracy. With a two-way ranging synchronization protocol, a ±1 part per million (ppm) relative XO frequency offset may translate to ranging errors in the range of ±1.2 m. In this work, a three-way ranging synchronization protocol is proposed to compensate for the relative XO offset. The approach was tested in a practical ranging setup. Compared to the conventional two-way ranging synchronization protocol, the precision was enhanced by a factor of around 2.

Fundamental limitations of crystal oscillator tolerances on FMCW radar accuracy

Crystal oscillators (XOs) are widely used in fractional-N phase locked loops (Frac-N PLLs) as reference frequency sources due to their good phase noise performance. However, these XOs have manufacturing tolerances in the range of few tens of parts per million (ppm). When a Frac-N PLL is used in frequency modulated continuous wave (FMCW) radar applications, the XO accuracy affects the frequency and timing accuracies of the radar chirps and so it directly affects the distance measurement accuracy. In this work, the fundamental limits of XO tolerance on distance measurement accuracy of FMCW radars are discussed and modelled. Moreover, an FMCW radar system hardware prototype is developed. Measurement results are in good agreement with the expectations of the simulation model.

A hybrid TDoA/RSSI model for mitigating NLOS errors in FMCW based indoor positioning systems

In this paper, the received signal strength indicator (RSSI) is combined with the time-difference-of-arrival (TDoA) technique as a hybrid approach to mitigate positioning errors due to non-line-of-sight (NLOS) propagation in indoor positioning systems. In order to study the effect of NLOS propagation on frequency modulated continuous wave (FMCW) radars, a simple model based on ray tracing was developed to calculate the positioning error profiles inside an area of interest. The model also calculates the RSSI values inside the area. The model showed a correlation between positioning errors and low RSSI values for some base stations (BSs). Therefore, an algorithm is proposed that uses the RSSI values of each BS as a weighting factor to rule out the NLOS BSs and rely only on the line-of-sight (LOS) BSs. Applying this algorithm on a test scenario with NLOS conditions, an improvement of more than a factor of 3 in the maximum positioning error was achieved. Also the average positioning error was improved by more than a factor of 5.

A coverage efficient FMCW positioning system

Accurate positioning with a limited number of reference stations is challenging. Several commercial systems achieve good accuracy by increasing the system complexity. Simplifying the system and reducing the number of reference stations is highly desirable. This paper presents a coverage efficient highly integrated local positioning system. The system is optimized for minimum positioning error with maximum effective coverage area. It is highly integrated and relies on the traditional frequency modulated continuous wave (FMCW) radar to provide the position information. Starting from the hardware to the final positioning algorithm, the research provides an intensive insight into the system details. The proposed system was practically tested for reliability and accuracy. To mitigate the multipath propagation issue, the system switches between the 2.4 and 5.8 GHz industrial, scientific and medical (ISM) bands. An overall positioning precision of around 10 cm and accuracy of less than or equal to 0.39 m was achieved with a coverage area of around 48 and 24 m2 per reference station, in both outdoor and indoor conditions, respectively.

Fundamental limitations of phase noise on FMCW radar precision

This work presents an approach for estimating the effect of the fractional-N phase locked loop (Frac-N PLL) phase noise profile on frequency modulated continuous wave (FMCW) radar precision. Unlike previous approaches, the proposed modelling method takes the actual shape of the phase noise profile into account leading to insights on the main regions dominating the precision. Estimates from the proposed model are in very good agreement with statistical simulations and measurement results from an FMCW radar test chip fabricated on an IBM7WL BiCMOS 0.18 μm technology. At 5.8 GHz center frequency, a close-in phase noise of −75 dBc/Hz at 1 kHz offset is measured. A root mean squared (RMS) chirp nonlinearity error of 14.6 kHz and a ranging precision of 0.52 cm are achieved which competes with state-of-the-art FMCW secondary radars.

NFC/INS integrated navigation system: The promising combination for pedestrians' indoor navigation

It is well known that there are many limitations of the current positioning systems either indoors or outdoors. Moreover, most of the current positioning systems require preinstalled infrastructure in the surrounding environment, which is costly in most cases and requires special devices from the user side. The near field communications (NFC), inertial sensors, pressure sensor for height, magnetometers for heading are built in sensors in most modern smart devices. Therefore, they can be used as a low-cost platform for gathering and processing location information. The main target of this work is to reduce the needed infrastructure as much as possible and maximize the use of the components that are built-in or can be connected to the smart devices. The accurate solution which we propose combines the NFC with an inertial navigation system (INS). The advantage of the inertial sensors based approach is that it does not need a preinstalled infrastructure and it starts on basis of a reference location given by the other positioning methods. The NFC approach can work based on simple sensors located in smart shoes that interacts with non-expensive NFC tags preinstalled at the desired floor of the building. Experimental results show that the combination can keep accurate positioning of a pedestrian and limit the error growth of inertial sensors using properly distributed NFC tags. The maximum error in NFC/INS pedestrian dead reckoning (PDR) position is below 1.7 m in the whole track using direct position resetting approach.

A dual band FMCW radar receiver with integrated active balun and baseband AGC loop

This work presents the design of a dual band frequency modulated continuous wave (FMCW) radar receiver (RX) at the 2.4 and 5.8 GHz industrial, scientific and medical (ISM) bands. The designed low noise amplifier (LNA) has a single ended 50 Ω input stage followed by an active balanced-to-unbalanced (balun) stage. The radio frequency (RF) signal is then down-converted to a low intermediate frequency (IF) by a multi-tanh Gilbert cell mixer whose local oscillator (LO) port is driven by an integrated fractional-N phase locked loop (Frac-N PLL). After down-conversion, the resulting IF signal is low pass filtered and amplified by a baseband variable gain amplifier (VGA). Fabricated on an IBM 0.18 μm BiCMOS process, the measured RX performance is in good agreement with simulations achieving a measured maximum conversion gain (CG) of 82.0 and 77.2 dB and a noise figure (NF) of 7.3 and 8.0 dB at the 2.4 and 5.8 GHz bands respectively. The receiver consumes 22.3 mA from a 3 V supply and occupies a chip area of 0.32 mm2. When used as a primary FMCW radar transceiver (TRX), the designed chip achieves a ranging precision of 0.30 and 0.31 mm at the 2.4 and 5.8 GHz bands respectively. To the best of the authors knowledge, this dual band FMCW radar TRX has the highest level of integration reported in the literature.

Enhanced zero crossing frequency estimation for FMCW radar systems

This paper presents a spectral peak estimation technique for tight resources systems. Based on a basic zero-crossing (ZC) frequency estimator, an enhanced ZC frequency estimation technique is proposed. The technique conducts a tunable band-pass filter (BPF) that relies on a primary estimation from another ZC block. In principle, the filter reduces the noise content of the signal, hence increasing the quality of the ZC algorithm. The technique is computationally very efficient and can be easily implemented on low cost systems. It was evaluated in a practical frequency modulated continuous wave (FMCW) ranging system. A ranging precision of around 2.24 cm was practically achieved.

Zoom FFT for precise spectrum calculation in FMCW radar using FPGA

The zoom FFT (ZFFT) has been utilized in various digital signal processing systems, it is used when a fine spectral resolution is needed within a small portion of a signals overall frequency range. It has been implemented in different fields and for different applications. This paper presents an implementation method of the ZFFT approach to estimate the spectral peak in the FMCW radar using a field programmable gate arrays (FPGA). It has been utilized to decrease the calculations complexity, hence, reduction the power consumption. The approach has been realized and a complexity reduction factor of up to 8 has been gained and tested on an FMCW radar processing system.