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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.