_Article_  
Bias Analysis of Parameter Estimator Based on Gauss-Newton Method Applied to  
Ultra-Wideband Positioning  
[PERSON] 1,2(r), [PERSON] 1,2, [PERSON] 3,* and [PERSON] 4  
NASG Key Laboratory for Land Environment and Disaster Monitoring, China University of Mining and Technology (CUMT), Xuzhou 22116, China; [EMAIL_ADDRESS] (C.W. ); [EMAIL_ADDRESS] (H.Y.) School of Environment Science and Spatial Informatics, China University of Mining and Technology (CUMT), Xuzhou 22116, China School of Geomatics and Urban Information, Beijing University of Civil Engineering and Architecture (BUCEA), Beijing 100044, China GNSS Research Center, Wuhan University (WHU), Wuhan 430079, China; [EMAIL_ADDRESS] Correspondence: [EMAIL_ADDRESS]; Tel. : +86-150-5084-1419 20 November 2019; Accepted: 27 December 2019; Published: 30 December 2019 20  
(GNSS), people pay more and more attention to the location based on service [1]. Urban dwellers spend more than 80% of their time indoors. However, the intensity of GNSS signal is not strong enough to penetrate through different materials used in construction, and the phenomena of reflection and multipath fading limit the utility of GNSS in dense urban or in the indoor environment, which increases the demand for indoor positioning [2,3]. In general, indoor positioning technologies include: Bluetooth, Wi-Fi, radio-frequency identification (RFID), ultra-wideband (UWB) and so on [4]. Compared with other localization technologies, the UWB is capable of providing robust signaling, through-wall propagation [5]. Due to a large bandwidth, it can obtain high-resolution distance estimation and enables reliable distance estimation. Therefore, UWB technology is well-suited for indoor positioning applications. In order to employ this technology, different positioning methods have been developed. The positioning system can employ various information obtained from radio signals, such as time-of-arrival (TOA), time difference of arrival (TDOA), angle of arrival (AOA), and received signal strength (RSS) [6]. The accuracy of positioning system in term of positioning, ranging and navigation could reach easily a decimeter level. However, in order to provide the position, it depends on the network installation and this could represent a limitation in term of cost, time and infrastructure requirements [7]. The performance of a dynamic ad-hoc UWB-based positioning system was introduced, which can accommodate any arbitrary number of nodes operating in the same region, additionally. it can provide much more flexibility to supports the dynamic inclusion or removal of nodes from the network [8]. To solve the limitation in terms of tag density, a UWB indoor localization system that allows an unlimited number of tags was presented, it allows tags to obtain responses from multiple anchors simultaneously. This system enables decimeter-level accuracy at fast update rates for countless tags and is highly suited for supporting mobile applications [9]. Meanwhile, to ensure people and objects can be localized in real-time, the integration of UWB and other technologies such as RFID and Wi-Fi are developed. The passive UWB RFID based on the backscatter modulation signal increases significantly the performance for tags detection and localization at low and complexity by employing energy sprinklers [10, 11, 12]. The integration of UWB and Wi-Fi are implemented for localization, the Wi-Fi networks guarantee broad coverage while the UWB would increase the overall system accuracy and robustness [13]. In practical applications, an unbiased estimation of the positioning result will be expected. However, the positioning estimation is subject to different error sources, including signal blockage, multipath, clock drift, algorithm model, thermal noise and so on. Meanwhile, the positioning system is prone to become ill-posed. The performance and the reliability of the positioning algorithms are inevitably influenced.