Two-Way Ranging (TWR) is a widely used method for distance estimation in asynchronous wireless networks, but the deviation between the clocks can lead to errors in distance estimation. The ultra-wideband (UWB) technology provides the best accuracy in distance estimation, but total emission time is drastically limited by harmonized standards. Localization accuracy, latency and network scalability are key performance metrics in wireless location characterization. This article advances a new sequencing of the localization process, called Double-Beacon Two-Way Ranging (DB-TWR) algorithm, and presents the related time-of-flight (ToF) estimation formula, which is able to compensate for clock error and to reduce the localization period. The Fine Time Measurement (FTM) protocol, specified by the Wireless LAN (WLAN) standard, uses the TWR method and as a result the clock deviation leads to systematic errors in ToF estimation. The paper proposes two additional timestamps captures and a new ToF computation formula which compensates for clock deviation. The article provides a theoretical analysis and extensive simulations of errors propagation in the ranging process, both as a mean and as an uncertainty, and proves that the designed algorithms cancel the clock offsets entirely.

Due to the known issue that the ranging in the 802.15.4™-2015 standard is prone to external attacks, the enhanced impulse radio (EiR), a new amendment still under development, advances the secure ranging protocol by encryption of physical layer (PHY) timestamp sequence using the AES-128 encryption algorithm. This new amendment brings many changes and enhancements which affect the impulse-radio ultra-wideband (IR-UWB) ranging procedures. The timestamp detection is the base factor in the accuracy of range estimation and inherently in the localization precision. This paper analyses the key parts of PHY which have a great contribution in timestamp estimation precision, particularly: UWB pulse, channel sounding and timestamp estimation using ciphered sequence and frequency selective fading. Unlike EiR, where the UWB pulse is defined in the time domain, in this article, the UWB pulse is synthesized from the power spectral density mask, and it is shown that the use of the entire allocated spectrum results in a decrease in risetime, an increase in pulse amplitude, and an attenuation of lateral lobes. The paper proposes a random spreading of the scrambled timestamp sequence (STS), resulting in an improvement in timestamp estimation by the attenuation lateral lobes of the correlation. The timestamp estimation in the noisy channels with non-line-of-sight and multipath propagation is achieved by cross-correlation of the received STS with the locally generated replica of STS. The propagation in the UWB channel with frequency selective fading results in small errors in the timestamp detection.

In many circumstances, it is preferred to simultaneously use a recursive Discrete Fourier Transform (DFT) and the zero padding, the former for its computational efficiency, the latter for the interpolation in the frequency domain. In the present article, we develop a new sliding DFT algorithm, which performs recursive spectral estimation of zero-padded time series. In order to ensure the stability of the process, we selected the estimator with guaranteed stability through the damping factor. Error analysis shows that the damping factor produces systematic errors and the errors in question are dependent upon the phase of the input signal.

In the wardriving type method proposed in the paper, the localization of the base stations (BSs) is performed based on unscented Kalman filter with state constraints (UKFC). The state vector is formed by the coordinates and velocities of BSs, and the observations are localization measurements made by a mobile station. The localization measurements show that the BSs are situated on a 3D surface, and this information, fused with the constraint that the base stations form a rigid network, lead to a consistent estimator. The distances between BSs provided by cooperative localization networks, added as constraints, results in a drastic reduction of estimation uncertainty.

The 802.15.4z standard, still under development, advances the secure ranging protocol by encryption of PHY timestamp sequence using AES-128 encryption algorithm. The paper analyses the key parts of PHY which have a great contribution in range estimation precision, particularly: UWB pulse, channel sounding and timestamp estimation using ciphered sequence. The propagation analysis in UWB channel shows that the frequency selective fading gives worse effects than multipath propagation in the timestamp estimation.

The aim of this paper is to emphasize the benefits of using the information provided by the UWB network for the Adaptive Kalman Filtering (AKF). The standard 802.15.4 specifies in the section PHY UWB the field of parameters Ranging FoM, parameters that show the trust level of the receiver in determining the reception moment of leading edge of the ranging pulse. Using the specified parameters, Confidence Interval and Confidence Level, and based on statistical theory the current standard deviation is determined for every anchor of the network. The standard deviations of the anchors are combined in order to get the observation covariance for the Kalman filtering. In the steady state the innovation should be within the Confidence Region ellipsoid and if the innovation does not fall in that region the filter diverges or it is biased and it should be online tuned. The difference between the innovation and the Confidence Interval will constitute the information for adjustment of the state covariance in the Kalman Filter.