## 1 Introduction  
Although the PNT service provided by GNSS has the characteristics of all-weather, all-time and global coverage [1], GNSS also has obvious weaknesses, such as GNSS signal being easy to be obscured, interfered and deceived, resulting in the security and integrity of PNT service [2, 3]. Any single PNT information source may have risks. PNT services involving personal safety must be safe and reliable. Therefore, the utilization of \"redundant\" PNT information is very important in complex environments [4]. The fundamental significance of the research on elastic PNT navigation and positioning technology is to help the satellite navigation system, make full use of the redundant information of multisource sensors, improve the reliability, safety and robustness of indoor and outdoor dynamic navigation and positioning and form new services that are not available in the current satellite navigation system. Therefore, the significance of \"elastic PNT navigation and positioning technology\" is to solve the problem that a single satellite navigation terminal cannot realize continuous, stable and reliable submeter real-time location service indoors and outdoors in complex environments [5]. The precise and seamless space-time location service provided by multisource elastic integration positioning will become an important benchmark to measure the smart economy and smart society. The multisource elastic fusion positioning technology will promote PNT from single, individual and regional to comprehensive, group and global. In the future, the multisource elastic fusion positioning network will develop towards IOT and intelligence. Multi-source elastic fusion positioning technology has attracted extensive attention in industry because of its high positioning accuracy and high robustness. The problem of multisource elastic fusion location technology mainly focuses on the design of the fusion algorithm. The following problems must be considered in the positioning design of multisource elastic fusion [6]: a dynamic target is tracked by multiple different sensors and each sensor has different measurement results and noise characteristics. We must also consider how to dynamically adjust the weights of measurement results of multiple sensors according to environmental changes to make the final fusion estimation result better than that of a single sensor or more stable positioning [7]. Domestic and foreign experts have done a lot of research and published many papers on indoor and outdoor multisource fusion seamless positioning. For example, at the beginning, people used inertial sensors to obtain pedestrian heading and step information outdoors and fused with satellite navigation to improve the stability of navigation and positioning [8; 9]. However, when satellite navigation is not available, the integrated positioning of inertial navigation and satellite navigation cannot maintain high navigation and positioning accuracy for a long time. The combination of communication base stations and satellite navigation is used to solve the navigation and positioning problem in urban canyons [10; 11; 12], which can solve the outdoor blind supplement navigation and positioning problem of satellite navigation, but it cannot solve the indoor navigation and positioning problem. In indoor navigation and positioning, Bluetooth is used for navigation and positioning, and its coverage and positioning accuracy are related to the deployment number of Bluetooth modules. Generally, the deployment interval of Bluetooth modules with positioning accuracy of 1 m is about 1 m [13; 14; 15], and the ability of large-scale promotion is poor. Most of the existing mobile communication devices, including wireless local area networks (WLANs), smart phones and laptops, are embedded with Wi-Fi modules, which can be used to build indoor Wi-Fi positioning systems [16; 17].