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Indoor Localization is gaining increased importance due to numerous location-based services in healthcare, logistics, and security, to name few, that are expected to be provided by next-generation wireless networks. Such services are characterized by stringent accuracy requirements, short response time, and lower cost which makes the localization problem more challenging and deserving of attention. A key element of the localization process is distance estimation (also known as ranging). In this paper, we design and analyze an efficient decimeter-level two-way ranging scheme for ubiquitous WiFi networks in the 5 GHz frequency band whose accuracy approaches ideal one-way ranging with no phase mismatches. We investigate the idea of channel frequency response (CFR) stitching across non-contiguous WiFi channels and how two-way CFR measurements help in achieving the CFR coherency necessary for accurate ranging. In addition, we quantify the decrease in ranging accuracy of two-way compared to one-way ranging due to SNR degradation, Line-of-Sight (LoS) component shrinkage, and doubling the multipath delay spread. Furthermore, We design a novel scheme to bridge the performance gap between two-way ranging and ideal one-way ranging which operates in three main steps: square-root of the two-way CFR, followed by phase unwrapping, and finally deep fade detection and phase errors correction. Our proposed scheme achieves significant performance gains over two-way ranging with only a slight performance gap from ideal one-way ranging. Moreover, our proposed scheme enjoys robustness as it preserves the ranging accuracy gains in various WiFi communication scenarios when operating at different SNR levels, different multipath channel models, and different CFR bandwidths, as well as operating under system impairments such as Sample Timing Offset (STO). The accuracy gains achieved by the proposed schemes are demonstrated using both simulations and an in-house WiFi testbed. Finally, we quantify the added complexity of our proposed scheme and show it to be insignificant compared to that of the MUSIC super-resolution ranging steps which confirms the practical viability of our proposed scheme.

In view of problem that positioning accuracy of positioning methods based on time ranging, namely arrival time, one-way ranging, two-way ranging and symmetrical double-sided two-way ranging (SDS-TWR) is disturbed by timing error factors such as clock asynchronization between nodes, timer frequency offset and equipment delay, an underground target positioning method based on differential error suppression optimization method was proposed. Combining with SDS-TWR positioning method, the method uses characteristics of target node as both transmitting node and receiving node to solve relationship between transmission time and length simultaneously. Irrelevant variables such as timer frequency offset and equipment delay are eliminated through matrix form and coordinates of unknown target node are only related to the measured time, so as to effectively eliminate influence of timing error on the positioning result of the target node, and achieve purpose of precise positioning. The simulation results show that compared with the one-way ranging and two-way ranging methods, the differential error suppression optimization method can effectively suppress influence of equipment delay and timer frequency offset on the positioning method based on time ranging, and can accurately locate the unknown node with high positioning accuracy, the range of ranging error is only ［-0.036 9 m, 0.037 7 m］, which is 0.012% of one-way ranging error and 0.061% of two-way ranging error.

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We are reporting on identification and calibration of one-way delays in satellite laser ranging systems. Satellite Laser Ranging (SLR) is a standard technique to measure the distance of satellites as a function of time with millimeter precision and a few millimeters accuracy. For one-way laser ranging, laser time transfer ground to space and for bi- and multi-static laser ranging to space objects identification and measurement of system delays related separately to transmitting and receiving parts of the system are needed. The epochs of transmission and reception of optical signals have to be referred to the coordinated time scale with the accuracy reaching one nanosecond level or better for one-way ranging and space debris multi-static ranging. For transponder ranging and laser time transfer an even higher accuracy of 50 ps or better is needed. These accuracy requirements are by several orders of magnitude higher in comparison to standard SLR applications. A new procedure of calibration of one-way delays related to the SLR systems has been developed and tested. The necessary hardware components needed for calibration measurements were designed and developed in a form of a Calibration Device. It consists of a photon counting detector, an epoch timing device and a dedicated signal cable. The signal propagation delays of these components were determined with an accuracy of better than 20 ps. The signal propagation delay stability of the Calibration Device is on a level of units of picoseconds over days of operation. The Calibration Device and calibration procedure were tested in real measurements at the SLR site in Graz, Austria. The time needed to complete a calibration of one-way delays of the SLR system is less than two days. The one-way system delays were determined with the accuracy better than 50 ps. The measurement principle, Calibration Device and the first results are presented. [ABSTRACT FROM AUTHOR]

Spaceborne laser altimeters are common instruments on-board the rendezvous spacecraft. This manuscript deals with the altimeters using a single photon approach, which belongs to the family of time-of-flight range measurements. Moreover, the single photon receiver part of the altimeter may be utilized as an Earth-to-spacecraft link enabling one-way ranging, time transfer and data transfer. The single photon altimeters evaluate actual altitude through the repetitive detections of single photons of the reflected laser pulses. We propose the single photon altimeter signal processing and data mining algorithm based on the Poisson statistic filter (histogram method) and the modified Kalman filter, providing all common altimetry products (altitude, slope, background photon flux and albedo). The Kalman filter is extended for the background noise filtering, the varying slope adaptation and the non-causal extension for an abrupt slope change. Moreover, the algorithm partially removes the major drawback of a single photon altitude reading, namely that the photon detection measurement statistics must be gathered. The developed algorithm deduces the actual altitude on the basis of a single photon detection; thus, being optimal in the sense that each detected signal photon carrying altitude information is tracked and no altitude information is lost. The algorithm was tested on the simulated datasets and partially cross-probed with the experimental data collected using the developed single photon altimeter breadboard based on the microchip laser with the pulse energy on the order of microjoule and the repetition rate of several kilohertz. We demonstrated that such an altimeter configuration may be utilized for landing or hovering a small body (asteroid, comet). [ABSTRACT FROM AUTHOR]