Today, the Beidou System—a global navigation satellite system independently designed and built by China—has become deeply integrated into our daily lives: when driving, navigation apps can accurately avoid traffic congestion and guide us along the optimal route; in the fields, drones follow preset trajectories to steadily complete seeding and fertilization; during logistics, every package relies on it for precise positioning and efficient delivery to the recipient. This technological marvel, which “anchors direction” for all things, acts like a tireless global guide. Yet behind its precise and reliable services lies a quietly dedicated “invisible engineer”—simulation technology.

The story begins with the early stages of the Beidou System. At that time, engineers harbored the dream of “enabling Chinese navigation to cover the globe”, but they first encountered a thorny problem: how to arrange the satellite constellation so that every corner of the Earth—whether the vast Gobi Desert or a remote island in the deep sea—could stably receive signals? One must understand that satellite launch costs are extremely high; the launch cost of a single rocket often runs into the hundreds of millions. It was simply not feasible to launch satellites one by one into space and then repeatedly test and adjust them—such an approach would not only be time-consuming and labor-intensive but also entail enormous risks of failure.

Faced with this impasse, engineers turned to simulation technology. It built a 1:1 scaled “virtual space” in the laboratory; engineers only needed to input different orbital parameters, and it could quickly and accurately calculate the satellite’s ground track and the specific percentage of ground coverage. Like a meticulous director rehearsing every “positioning plan” in advance, it clearly presented the advantages and blind spots of different configurations, helping engineers rapidly identify the optimal solution among hundreds or thousands of options. The satellite development toolkits widely used in the industry today are precisely the capable assistants of this “engineer”, enabling the Beidou constellation design to avoid countless detours and significantly shortening the research and development cycle.

With the constellation layout problem solved, the next challenge followed—the optimization of radio signals. This is akin to the “exclusive language” used for communication between the Beidou System and ground terminals. The selection of carrier wave bands, the methods of modulation and coding, and the sequence of message arrangement—each link involves countless possible combinations. Which “language” can transmit more stably when passing through the atmosphere and bypassing obstructions from high-rise buildings? Which combination can minimize the signal error rate? Engineers once again turned to simulation technology for help. In the simulation environment, they could freely combine the complete “carrier-modulation-coding-message” chain, much like building with blocks, and test each combination’s key performance indicators—such as signal attenuation and error rate—one by one. They then conducted overall optimization in conjunction with the constellation layout, ultimately refining the most suitable “communication method” for the Beidou System, ensuring that signal transmission is both efficient and reliable.

When the Beidou satellite constellation was successfully deployed, the development of its “terminal partner”—the user receiver—was put on the agenda. Receivers designed especially for high-dynamic vehicles (such as rockets and fighter jets) have extremely stringent performance requirements. It would be impractical to mount them on actual aircraft for every test, wouldn’t it? A single test flight costs tens of millions of yuan, and if the receiver malfunctions, it could lead to aircraft destruction and loss of life—making such an approach neither realistic nor safe. At this point, the “physical embodiment” of simulation technology—the Beidou System simulator—came into play. It can accurately reproduce in the laboratory the complex scenarios of high-speed flight and attitude changes of an aircraft, reconstruct the radio signals it receives, and output key indicators such as positioning accuracy, signal acquisition speed, and tracking sensitivity in real time. Engineers can conduct comprehensive performance tests of the receiver in a safe and controllable environment without leaving the lab, forming a complete technical closed loop of “design-test-optimization”.

When the Beidou System is to expand into a wider range of application fields, simulation technology continues to provide full support throughout the process. Taking the civil aviation industry as an example, the takeoff, landing, and cloud-penetrating flight of aircraft impose extremely stringent requirements on the integrity, continuity, and accuracy of navigation signals—even a one-second signal interruption could pose a serious flight safety hazard. How should a signal augmentation system be built? Which locations should be chosen for deploying ground facilities? What is the most reasonable number of stations? Engineers cannot conduct repeated tests in real airspace to answer these questions. Therefore, they constructed thousands of geometric topology and network layout models in a simulation environment, simulated signal propagation under different weather conditions and terrains, and repeatedly performed link budget and performance analyses. Ultimately, they found the optimal solution, allowing the Beidou System to steadfastly safeguard the safety of flights in the blue sky.

When facing the “special tests” of interference and anti-interference, spoofing and anti-spoofing, simulation technology has become an “acceleration engine” for developing new algorithms and new products. In a complex electromagnetic environment, ensuring that Beidou signals are neither jammed nor spoofed requires continuous iterative upgrades of protection technologies. Simulation technology can simulate various extreme interference scenarios in a virtual environment, allowing engineers to quickly verify the feasibility of new solutions without having to conduct risky tests in real-world settings, thereby shortening the research and development cycle by more than half and building a solid “technological barrier” for the safe and stable operation of the Beidou System.

From the blueprinting of the constellation layout to the repeated refinement of the signal language; from the performance calibration of receivers to the comprehensive expansion of application scenarios—every step of the Beidou System’s growth has been inseparable from the silent support of simulation technology. This “invisible engineer” has overcome one technical challenge after another in a cost-effective and highly efficient manner, enabling the Beidou System—a complex, multidisciplinary mega-system—to serve all aspects of life and production with stability and precision. Today, as we enjoy the convenience and peace of mind brought by Beidou, we may not realize that behind this precision lie millions of simulations and optimizations performed by simulation technology in the virtual world. Though invisible and intangible, it has, through the power of technology, paved a solid path for the global journey of China’s Beidou System, becoming an indispensable technological cornerstone of our era.

Yang Dongkai

Professor in Charge of Satellite Navigation, Regional Centre for Space Science and Technology Education in Asia and the Pacific (China) (Affiliated to the United Nations)