The service performance of the Global Navigation Satellite System (GNSS) has significantly decreased in complex environments such as tunnels, indoor and urban canyons. In this challenging environment, pseudolites can be used to generate and transmit signals similar to GNSS systems, providing users with uninterrupted navigation information such as location and speed in GNSS rejection environments. In addition, the pseudolite system can be modulated to be consistent with GNSS, and the user receiver can achieve synchronous reception of pseudolites/GNSS. Through integrated navigation with GNSS and inertial navigation systems, GNSS navigation and positioning enhancement in complex environments can be achieved, which is expected to play an important role in fields such as autonomous driving, indoor navigation, and automatic robots.

Beidou No.3 System is a global navigation satellite system built by China independently. The cloud platform，realizing the unified management, on-demand sharing, and real-time dynamic allocation of software and hardware resources，is essential  to the BDS-3’s ground system. This paper introduces the architecture and process of BDS-3’s cloud platform based on engineering practice and summarizes the representative technical breakthroughs in the cloud platform construction and improvement. The trend of the next generation satellite navigation system is diverse in service types, customized on service information, safe and reliable on capability. The integration between cloud-native technology and the business of navigation ground systems is put forward to improve the efficiency of development and operation; from the perspective of infrastructure structure, it is suggested that the navigation ground cloud be fully autonomous and controllable in stages. Finally, we look forward to the cloud platform architecture of the next-generation navigation ground system. The system architecture, composed of a cloud center, network and terminal, transforms from the construction of independent nodes to the unified construction of all distributed nodes. The navigation ground system will further improve operation and management efficiency and the disaster tolerance and survivability.

In recent years, satellite communication technology has developed rapidly. Relying on its advantages of rapid transmission rate and large-scale remote data transmission, as well as the low orbit constellation's characteristics of proximity to the Earth, high signal landing power, low space decay, and rapid geometric change, the low orbit Internet system is expected to make up for the defects of the satellite navigation system in broadcasting rate and signal attenuation to solve the problems of low ground rate of traditional satellite navigation system and long convergence time of real-time PPP. Regarding specific project implementation, the low-orbit constellation can play four roles. First, as a "space-based monitoring station," it can enhance the information of current GNSS. Second, it can be used as a "navigation information source" to realize signal enhancement and information enhancement; Third, the low-orbit constellation can be used as the supplement and backup of the satellite navigation system and maintain the space-time reference independently. Fourth, the integration of satellite communication and navigation services should be realized to realize "integrated communication and navigation" at the user level. By combining the overall design of constellation navigation enhancement in the low-orbit Internet with the current status of GNSS operation services, we can realize complementary advantages and provide broader coverage, higher precision, and more robust time and space services. Firstly, this paper briefly introduces the development status of low-orbit satellites at home and abroad, analyzes the critical technologies of low-orbit satellites in navigation enhancement, especially in broadcast ephemeris parameter design and low-orbit constellation configuration, and focuses on the application and benefits of low-orbit satellites in space-based monitoring information enhancement, signal enhancement and communication integration. The prospects and challenges of applying low-orbit Internet satellite navigation are summarized. 

Satellite laser ranging (SLR) is the most accurate technology in satellite orbit measurement. It is widely used in high-precision orbit determination and satellite orbit accuracy checks for satellites, laser time transfer (LTT), and so on. It is an important part of accurately measuring satellite orbits in navigation systems. This paper describes the SLR system in the Shanghai Astronomical Observatory and the International joint survey of the BeiDou navigation system. The SLR international joint surveys for satellites of BeiDou 3 observation data were obtained from global laser stations in 2023, which provided conditions for the implementation of joint research on global navigation satellite systems. The high repetition frequency of 100kHz SLR technology has been developed, and applied to BeiDou satellites. The standard point data accuracy reaches the level of 100 um, which effectively improves the quality of navigation SLR observation data. At the same time, another application of SLR technology for the BeiDou navigation system was described, including independent satellite orbit determination, Broadcast ephemeris accuracy check, LTT, and so on.

Real-time Kinematic (RTK) is widely used in surveying and mapping, monitoring, navigation and other aspects due to its advantages of a simple algorithm, fast convergence, high positioning accuracy and outstanding reliability. With the continuous advancement of Global Navigation Satellite System (GNSS) technology, the GNSS RTK positioning mode has made significant progress in theoretical algorithms, engineering applications, and data processing. This paper reviews of RTK positioning technology, focusing on the development history of long-baseline RTK positioning technology, multi-frequency and multi-system, partial ambiguity fixed algorithm, Network RTK Positioning technology and single-frequency RTK algorithm. Also, the critical factors affecting the accuracy and reliability of RTK positioning are summarized. Finally, it discussed the new development opportunities brought by RTK technology with the further construction of GNSS and continuous optimization of sensor technology.

GNSS(Global Navigation Satellite System) precision orbits and clocks product is the premise of realizing high-precision PPP(Precise Point Position) and the basis of high-precision GNSS application. Therefore, it is of great research significance and application value to develop a combination method of GNSS orbits and clocks product and realize a stable and reliable orbit and clock combined product service. This paper introduces the general situation of the GNSS constellation and IGS(International GNSS Service) service center, combs the functional model of orbit clock combination synthesis, comprehensively analyzes and discusses the progress of GNSS orbit clock combination product synthesis technology, and looks forward to the opportunities brought by existing research on GNSS real-time orbit clock combination synthesis and real-time precise single point positioning.

In order to a realize millimeter-scale terrestrial reference frame, high-precision non-linear maintenance technology must be gradually improved. Firstly, this paper introduces the progress of the establishment of the terrestrial reference frame including the establishment of the International Terrestrial Reference Frame and the epoch reference frames; Then, the research status of non-linear maintenance technology is described, and two ideas for non-linear maintenance of the terrestrial reference frame are pointed out, including the non-linear change modeling of the reference station and the establishment of the epoch reference frames. At last, the paper puts forward a prospect for the construction of the millimeter-scale terrestrial reference frame, and suggests that the ground monitoring network should be appropriately increased and improved, especially in the underdeveloped areas of the southern hemisphere, and the existing frame should be improved by using longer and broader original data accumulation; Increase the data accumulation of coordinate non-linear motion and geocentric motion, and conduct in-depth analysis, to establish an accurate correction model; Identify the noise factors in the coordinate time series as accurately as possible, and establish a grid noise model to more accurately separate the actual signal and noise.

As BeiDou Navigation Satellite System has entered a new stage of promoting its quality development via application, systematic approaches to applying BeiDou in the mobile market, which is the most sensitive, responsive, flexible, and resilient mass market, hold an essential part in prospering BeiDou industry and national economic development. Through analysis of the large-scale application of BeiDou in the mass market of smartphones from perspectives of the industry chain, value chain, and policy chain, in-depth explorations of prohibiting BeiDou's massive application in smartphones are conducted from the supply side, demand side, and environment side. With a summarization of referable measures from other global navigation satellite systems, especially GPS, policy advice is provided afterward on the large-scale application of BeiDou. Firstly, from the supply side, it is importance to make enterprises play the lead and develop industry via relevant military-to-civilian technologies, which enhances the technical capability of meeting demands. Secondly, from the demand side, it is to develop scenarios with efforts and cultivate world-class product and service providers which dig and upgrade demands. Thirdly, from the environmental side, it is to promote the BeiDou application in smartphones while building the BeiDou brand, which directs consumers' willingness and actions nationwide.