Phase-based Ranging in Narrowband Systems with Missing/Interfered Tones

The growth in the number of low-cost narrow band radios such as Bluetooth low energy (BLE) enabled applications such as asset tracking, human behavior monitoring, and keyless entry. The accurate range estimation is a must in such applications. Phase-based ranging has recently gained momentum due to its high accuracy in multipath environment compared to traditional schemes such as ranging based on received signal strength. The phase-based ranging requires tone exchange on multiple frequencies on a uniformly sampled frequency grid. Such tone exchange may not be possible due to some missing tones, e.g., reserved advertisement channels. Furthermore, the IQ values at a given tone may be distorted by interference. In this paper, we proposed two phase-based ranging schemes which deal with the missing/interfered tones. We compare the performance and complexity of the proposed schemes using simulations, complexity analysis, and two measurement setups. In particular, we show that for small number of missing/interfered tones, the proposed system based on employing a trained neural network (NN) performs very close to a reference ranging system where there is no missing/interference tones. Interestingly, this high performance is at the cost of negligible additional computational complexity and up to 60.5 Kbytes of additional required memory compared to the reference system, making it an attractive solution for ranging using hardware-limited radios such as BLE

Localization and Fingerprint of Radio Signals Employing a Multichannel Photonic Analog-to-Digital Converter

[EN] The fingerprint and localization of radio signals employing a multichannel photonic analog-to-digital converter (ADC) is proposed, analyzed, and demonstrated in a laboratory experiment. The photonic ADC detects the radio signals with high sensitivity in a large bandwidth without down-conversion stages. This is of special interest when processing emerging low-power wireless standards like ultra-wideband (UWB) radio. The optical processing in the multichannel photonic ADC is tailored for the localization and fingerprint of generic radio transmitters when orthogonal-frequency division multiplexing (OFDM) modulation is employed in the transmission. The photonic ADC includes engineered optical and electrical amplification. The experimental work demonstrates that detection of radio signals with -65 dBm power with signal-to-noise ratio better than 20 dB is feasible, which is in good accordance with the theoretical analysis. The multichannel photonic ADC comprises five optical channels which are precisely time-aligned in optical domain achieving 0.23-m spatial resolution (median) in the localization of radio transmitters. The experimental work also demonstrates that photonic-ADC processing is adequate for OFDM-based UWB radio-signal fingerprint including estimation of the average power, frequency band of operation, and time-frequency hopping pattern if applicable. UWB transmitter localization has been experimentally demonstrated with 0.4-m error.This work was supported in part by the European 7th Framework Program Project UCELLS FP7-IST-216785. The work of M. Morant was supported by Spain FPU MEC under Grant AP2007-01413.Llorente, R.; Morant, M.; Puche, JF.; Romme, J.; Amiot, N.; Uguen, B.; Duplicy, J. (2010). Localization and Fingerprint of Radio Signals Employing a Multichannel Photonic Analog-to-Digital Converter. IEEE Transactions on Microwave Theory and Techniques. 58(11):3304-3311. https://doi.org/10.1109/TMTT.2010.2076730S33043311581

Multi-Static UWB Radar-based Passive Human Tracking Using COTS Devices

Due to its high delay resolution, the ultra-wideband (UWB) technique has been widely adopted for fine-grained indoor localization. Instead of active positioning, UWB radar-based passive human tracking is explored using commercial off-the-shelf (COTS) devices. To extract the time-of-flight (ToF) reflected by the moving person, the accumulated channel impulse responses (CIR) and the corresponding variances are used to train the convolutional neural networks (CNN) model. Particle filter algorithm is adopted to track the moving person based on the extracted ToFs of all pairs of links. Experimental results show that the proposed CIR- and variance-based CNN models achieve less than 30-cm root-mean-square errors (RMSEs). Especially, the variance-based CNN model is robust to the scenario changing and promising for practical applications

Optimal Operation of RF Energy Rectifiers by Adaptive Number of Frequency Selection using Multisine Excitation

This paper is about optimal operation conditions of RF energy rectifiers that are used for wireless power transfer (WPT) with multisine (MS) excitation. We show by simulation that the optimal operation of MS signals can be achieved by properly choosing the number of frequencies Nf to transmit, which is variable with the input power, rectifier load, and topology. We found by adaptive Nf on the transmitter side, a significant power gain can be achieved only when input power is low and rectifier load is large, showing the significance of operational condition for MS to show superiority over conventional sinusoid signal. The simulation results show that by adapting Nf, the WPT is much more robust against load variation, which is a novel finding about MS's advantage. Moreover, we propose an analytical model for MS transmission with adaptive Nf based on empirical results with power and load feedback from the rectifier.</p

On the Analytical Optimal Load Resistance of RF Energy Rectifier

RF wireless power transfer (WPT) is an essential building block for simultaneous wireless information and power transfer (SWIPT) and wireless powered communication (WPC) systems. It has been shown that the efficiency of RF-DC conversion of a rectifier is dependent on both input power and the load resistance. In this paper, we present a novel analytical solution for the optimal load resistance in terms of DC power on the resistive load for two harvester topologies, namely the series-diode half-wave rectifier and Greinacher voltage doubler. Additionally, closed-form solutions are presented for low input power to obtain intuitive insights. The proposed method models the diode with the equivalent Schottky diode model, taking the parasitic and packaging effects into consideration. The validity of the method is verified by simulations with both continuous sinewave (CW) and multi-sinewave input

Analytical optimal load calculation of rf energy rectifiers based on a simplified rectifying model

Wireless power transfer (WPT) is an essential enabler for novel sensor networks such as the wireless powered communication network (WPCN). The efficiency of an energy rectifier is dependent on both input power and loading condition. In this work, to maximize the rectifier efficiency, we present a low-complexity numerical method based on an analytical rectifier model to calculate the optimal load for different rectifier topologies, including half-wave and voltage-multipliers, without needing time-consuming simulations. The method is based on a simplified analytical rectifier model based on the diode equivalent circuit including parasitic parameters. Furthermore, by using Lambert-W function and the perturbation method, closed-form solutions are given for low-input power cases. The method is validated by means of both simulations and measurements. Extensive transient simulation results using different diodes (Skyworks SMS7630 and Avago HSMS285x) and frequency bands (400 MHz, 900 MHz, and 2.4 GHz) are provided for validation of the method. A 400 MHz 1-and 2-stage voltage multiplier are designed and fabricated, and measurements are conducted. Different input signals are used when validating the proposed methods, including the single sinewave signal and the multisine signal. The proposed numerical method shows excellent accuracy with both signal types, as long as the output voltage ripple is sufficiently low

A high-accuracy phase-based ranging solution with Bluetooth Low Energy (BLE)

Nowadays, indoor positioning and asset tracking have become popular and essential for many applications and use-cases. As Bluetooth Low Energy (BLE) is widely deployed in smart tags, smart-phones, and smart-devices, adding functionality to support localization and asset tracking is crucial. In order to locate a device, either the angle or range to the device needs to be calculated. In this paper, we focus on a phase-based solution to calculate the range between devices. We introduce a multi-carrier phase-based ranging solution compatible with the BLE standard that utilizes BLE channel hopping to exchange tones in the entire 2.4 GHz frequency band to mitigate the multi-path fading problem. We recognize that in the BLE standard, slow channel-hopping, long packet size and frame spacing between two consecutive communications (named TIFS) affect ranging error/accuracy, in the case of crystal offset and phase-noise. Therefore, we introduce a new mathematical model to analyze the impact of the BLE link layer protocol on the ranging error. Finally, we evaluate the accuracy of our proposed solution through modelling, by considering the results of real experiments and by validating the correctness of our mathematical model for the ranging error