Ultrahigh axial resolution surface profiling as well as volumetric optical imaging based on time encoded optical coherence tomography in the frequency domain without any mechanical scanning element is presented. A frequency tuned broad bandwidth titanium sapphire laser is interfaced to an optical microscope (Axioskop 2 MAT, Carl Zeiss Meditec) that is enhanced with an interferometric imaging head. The system is equipped with a 640 × 480 pixel CMOS camera, optimized for the 800 nm wavelength tuning range for transmission and reflection measurements of a microscopic sample. Sample volume information over 1.3 × 1 × 0.2 mm³ with ~3 μm axial and ~4 μm transverse resolution in tissue is acquired by a single wavelength scan over more than 100 nm optical bandwidth from 860 nm with 128–2048 equidistant optical frequency steps with an acquisition time of 1 to 50 ms per step. Topography and tomography with a signal to noise ratio of 83 dB is demonstrated on test surfaces and biological specimen respectively. This novel OCT technique promises to enable high speed, three dimensional imaging by employing high frame rate cameras and state of the art tunable lasers in a mechanically stable environment, due to lack of moving components while reducing the intensity on the sample.

In the past decade, Long-Range Wire-Area Network (LoRaWAN) has emerged as one of the most widely adopted Low Power Wide Area Network (LPWAN) standards. Significant efforts have been devoted to optimizing the operation of this network. However, research in this domain heavily relies on simulations and demands high-quality real-world traffic data. To address this need, we monitored and analyzed LoRaWAN traffic in four European cities, making the obtained data and post-processing scripts publicly available. For monitoring purposes, we developed an open-source sniffer capable of capturing all LoRaWAN communication within the EU868 band. Our analysis discovered significant issues in current LoRaWAN deployments, including violations of fundamental security principles, such as the use of default and exposed encryption keys, potential breaches of spectrum regulations including duty cycle violations, SyncWord issues, and misaligned Class-B beacons. This misalignment can render Class-B unusable, as the beacons cannot be validated. Furthermore, we enhanced Wireshark’s LoRaWAN protocol dissector to accurately decode recorded traffic. Additionally, we proposed the passive reception of Class-B beacons as an alternative timebase source for devices operating within LoRaWAN coverage under the assumption that the issue of misaligned beacons can be addressed or mitigated in the future. The identified issues and the published dataset can serve as valuable resources for researchers simulating real-world traffic and for the LoRaWAN Alliance to enhance the standard to facilitate more reliable Class-B communication.

This letter introduces a ranging method which can be applied to off-the-shelf backscatter RFID tags, like standardized EPC Gen 2 tags. For this purpose a low power direct sequence spread spectrum (DSSS) sequence is superimposed onto the interrogator's signal during tag to reader communication. The chip rate and sequence length is chosen to fit an entire DSSS sequence into each backscattered bit. During the tag to reader communication, the bits sent by the tag are decoded and a time domain recording with the length of one DSSS period is made for each bit. By cyclic alignment of each recording and subtracting the averaged recording of a “0”-bit from the one of a “1”-bit, static echos and antenna coupling effects are perfectly canceled. In addition, noise variance is reduced, improving the SNR. Finally, by applying a cyclic correlation with the transmitted DSSS sequence and locating the correlation maximum, the distance to the RFID tag can be determined.

State-of-the-art quadrature-type modulators for all-digital radio-frequency (RF) transmitters operate optimally at an RF center frequency (fc) that is a fraction of the modulator switching rate. This is a major limitation if the modulators of this type are to be used in multichannel transmitter systems. In this brief, a novel quadrature modulator based on pulsewidth modulation with controllable in-band distortion is presented, which permits continuous adjustment of fc in digital domain. In addition, distortion generation related to digital upconversion of pulsed baseband signals is studied, and suitable compensation methods are given. The performance of the proposed modulator is compared with those of previously published encoding methods in terms of reconstructed RF signal quality and computational complexity. The evaluation results suggest that significant improvements in signal band distortion can be expected with a computational load suitable for real-time reconfigurable hardware realizations.

The influence of multipath propagation effects on phase-based positioning methods for UHF RFID is discussed in this paper. Thus, a propagation channel model for typical UHF RFID scenarios is derived. Several simulations have been carried out in order to understand the influence of the channel parameters on the narrowband phase-based localization methods.

The localization of internet of things (IoT) nodes in indoor scenarios with strong multipath channel components is challenging. All methods using radio signals, such as received signal strength (RSS) or angle of arrival (AoA), are inherently prone to multipath fading. Especially for time of flight (ToF) measurements, the low available transmit bandwidth of the used transceiver hardware is problematic. In our previous work on this topic we showed that wideband signal generation on narrowband low-power transceiver chips is feasible without any changes to existing hardware. Together with a fixed wideband receiving anchor infrastructure, this facilitates time difference of arrival (TDoA) and AoA measurements and allows for localization of the fully asynchronously transmitting nodes. In this paper, we present a measurement campaign using a receiver infrastructure based on software-defined radio (SDR) platforms. This proves the actual usability of the proposed method within the limitations of the bandwidth available in the ISM band at $2.4 \mathrm{GHz}$. We use the results to analyze the effects of possible anchor placement schemes and scenario geometries. We further demonstrate how this node-to-infrastructure-based localization scheme can be supported by additional node-to-node RSS measurements using a simple clustering approach. In the considered scenario, an overall positioning root-mean-square error (RMSE) of $2.19 \mathrm{m}$ is achieved.