How Beidou + 5G and Pseudo‑Satellites Can End Indoor/Outdoor Positioning Gaps

PART1 Why Beidou + 5G? Complementary and synergistic

5G is the latest generation of mobile communication technology, offering ultra‑high data rates, ultra‑low latency, and massive connectivity. It is distinct from the 5 GHz Wi‑Fi band often confused with "5G". Beidou provides a global time‑space reference, absolute coordinates, and wide‑area coverage but suffers from blockage in indoor or dense urban environments. 5G offers dense network deployment, large bandwidth, massive antenna arrays, and deep indoor coverage, enabling high‑precision ranging, direction finding, and time synchronization, yet lacks a global time reference. Their deep fusion creates a navigation‑communication integrated system where Beidou supplies high‑precision time sync to 5G, and 5G fills Beidou’s indoor blind spots, achieving seamless outdoor‑to‑indoor positioning.

Beidou: provides a unified global time‑space baseline, absolute position coordinates, and wide‑area coverage, but is vulnerable to obstruction.

5G: offers ultra‑dense networking, large bandwidth, massive antenna arrays, deep indoor penetration, high‑precision ranging, direction finding, and time synchronization, but lacks a global time reference.

The combined system enables "outdoor Beidou, indoor 5G, tightly combined transition zones" for full‑domain seamless positioning, driving the evolution from outdoor‑dominant to indoor‑outdoor integrated services.

PART2 Core Technology 1: 5G Integrated Navigation Signal Design

The integration starts at the signal layer by embedding navigation capability directly into the 5G communication signal, achieving a single signal with dual function.

In‑band positioning signal enhancement: optimize 5G signal parameters, add dedicated positioning pilots and reference signals without consuming extra spectrum, supporting both high‑speed communication and high‑precision positioning.

Carrier‑phase and TDOA positioning: use 5G carrier‑phase observations and downlink time‑difference‑of‑arrival, leveraging the high‑resolution ranging of wide bandwidth to achieve decimeter‑level indoor positioning, with extensibility to future 6G and low‑orbit satellite signals.

Seamless indoor‑outdoor handover: unify time‑space reference for 5G and Beidou signals so terminals switch without re‑initialization or algorithm changes, greatly improving continuity and user experience.

PART3 Core Technology 2: High‑Precision Time Sync of 5G Base Stations Using Beidou

Nanosecond‑level synchronization is the prerequisite for centimeter/decimeter‑level 5G positioning. Traditional base‑station sync is only microsecond‑level.

Leverage Beidou‑III satellite signals to achieve sub‑1 ns synchronization between base stations.

Continuously estimate clock bias and hardware delay to perform local clock optimization and calibration.

Build a wide‑area unified time‑frequency network that provides reliable clock support for TOA, TDOA, AOA and other 5G positioning methods.

Beidou time‑transfer upgrades 5G from "communication sync" to "navigation‑communication dual sync", forming the core foundation for high‑precision 5G positioning.

PART4 Core Technology 3: Intelligent Error Suppression for High‑Precision 5G Positioning

Multipath effects and atmospheric delay are the main error sources in urban and indoor environments.

Multipath identification and suppression: use massive 5G antenna arrays, base‑station geometry, statistical characteristics, and post‑fit residuals to accurately identify multipath signals; construct a 3‑D signal transmission model with additional geometric constraints to greatly reduce multipath impact.

Fine‑grained atmospheric delay correction: based on 5G reference station observations, build a 3‑D atmospheric delay model to provide real‑time tropospheric and ionospheric corrections, further improving accuracy and stability.

Edge‑cloud collaborative error compensation: generate regional error fields in the cloud and deliver real‑time corrections to terminals, forming a "perceive‑model‑correct" closed loop that maintains decimeter‑level positioning even in complex environments.

PART5 Core Technology 4: Seamless Indoor‑Outdoor Fusion Positioning

Transition zones such as underpasses, tunnel entrances, and building edges are positioning blind spots for a single technology.

Unified functional model and adaptive stochastic model jointly process Beidou satellite signals and 5G network signals, adapting to differing signal characteristics, error sources, and noise levels to avoid model mismatch.

Spherical constraint and ambiguity fixing: use latitude‑based spherical constraints to quickly fix 5G carrier‑phase ambiguities, enhancing continuity and accuracy in transition areas.

Full‑domain sub‑meter positioning: achieve sub‑meter accuracy in indoor, tunnel, underground, and urban canyon scenarios while maintaining centimeter‑level accuracy outdoors, delivering truly seamless high‑precision coverage.

PART6 Application Scenarios: From Consumer Mobility to Industrial Digitalization

Smart travel: vehicle terminals provide seamless indoor‑outdoor navigation, precise parking in underground garages, and route planning.

Smart buildings: indoor navigation in malls, airports, high‑speed rail stations, reverse vehicle finding, and emergency rescue.

Industrial Internet: high‑precision positioning and safety control for AGVs, robots, and personnel in factories.

Emergency rescue: rapid location of trapped persons in underground pipelines, tunnels, or collapsed structures.

With the evolution of 5G‑A and future 6G, integrated navigation will advance toward higher accuracy, broader coverage, and lower power consumption.

PART1 Pseudo‑Satellite: Bringing Beidou Signals Indoors

A pseudo‑satellite is a ground‑deployed Beidou signal emulator that fully reproduces the characteristics of a Beidou‑III satellite, including satellite ID, time, message, Doppler, and pseudorange, allowing indoor terminals to receive signals identical to those from real satellites.

It offers the optimal solution for tunnels, underground loops, high‑speed rail tunnels, and large building interiors without requiring hardware changes or new protocols, providing a seamless user experience compatible with the existing Beidou ecosystem.

PART2 Core Technology 1: Integrated Signal System Design for Indoor/Outdoor

Signal homogeneity and system uniformity are key to seamless switching. The pseudo‑satellite must meet:

Exact frequency, format, and timing consistency with outdoor Beidou signals; synchronization accuracy better than 50 ns and frequency stability better than 0.1 Hz, allowing terminals to process signals without distinguishing source.

Error source simulation: emulate satellite clock bias, ionospheric and tropospheric delays so indoor positioning models match outdoor ones, avoiding precision jumps during switching.

High‑precision signal regeneration: based on Beidou ephemeris, compute geometric distance, carrier Doppler, clock bias, and atmospheric parameters in real time; use direct digital synthesis (DDS) to generate signals identical to real satellites.

The pseudo‑satellite transmitter provides satellite orbit simulation, time‑frequency sync, signal modulation, and health monitoring, serving as the "core source" of indoor Beidou signals.

PART3 Core Technology 2: Fiber‑Based High‑Precision Time‑Frequency Sync

Strict alignment of pseudo‑satellite time‑frequency with the outdoor Beidou system is required; technical specifications are:

PPS (pulse‑per‑second) sync accuracy better than 20 ns.

Frequency stability at the E‑11 level.

Beidou’s fiber‑based time‑frequency sync system includes:

Source side: dual‑mode Beidou‑III input, anti‑interference detection, rubidium atomic clock and temperature‑controlled crystal oscillator for a stable time base.

Transmission layer: dedicated RF link delivering 10 MHz frequency and PPS signals; NTP network distributes UTC time, providing both physical‑layer and protocol‑layer redundancy.

Core unit: multi‑source time‑difference measurement, phase‑noise suppression, and seamless handover, achieving nanosecond‑level sync and ultra‑stable frequency output.

This technology ensures unified space‑time across the pseudo‑satellite and Beidou system, a cornerstone for indoor‑outdoor integrated positioning.

PART4 Core Technology 3: Indoor High‑Fidelity Channel Modeling

Indoor signals suffer severe multipath, attenuation, and blockage, degrading accuracy. Traditional channel models cannot accurately describe indoor Beidou signal propagation.

Beidou’s indoor signal system adopts a Geometric‑Based Stochastic Model (GBSM) to construct a high‑fidelity indoor channel model:

Accurately simulate scattering, reflection, and diffraction, calculating path loss and shadow fading.

Incorporate measured data for closed‑loop correction, optimizing signal delay, transmit power, and antenna patterns.

Quantitatively assess multipath impact on positioning accuracy, guiding pseudo‑satellite deployment and parameter optimization.

With this modeling, pseudo‑satellite signals achieve uniform coverage, low multipath, and high reliability indoors, matching outdoor reception quality.

PART5 System Architecture and Deployment Advantages

Seamless switching: automatic indoor‑outdoor transition without user perception.

Full compatibility: works with all Beidou terminals, protecting existing investments.

Low cost: flexible deployment and simple maintenance, suitable for tunnels, underground spaces, and large buildings.

High precision: indoor positioning accuracy can reach centimeter level, meeting autonomous driving and industrial positioning demands.

PART6 Typical Application Scenarios

Road / rail tunnels: continuous positioning for vehicles and trains, ensuring autonomous driving safety.

Underground garages / city subsurface spaces: precise vehicle locating, smart parking, and emergency evacuation.

Large buildings / transport hubs: indoor Beidou positioning in airports, high‑speed rail stations, and malls.

Mining / underground pipelines: personnel and equipment positioning to ensure safe production.

In a real‑world example, the Chongqing Jiefangbei underground loop—first supported by Baidu Maps—uses a Beidou + pseudo‑satellite system to provide uninterrupted, high‑precision positioning throughout the complex underground structure, enabling both driver‑assisted and autonomous navigation, as well as integrated emergency evacuation guidance.

Beidou + 5G integrated navigation and pseudo‑satellite indoor‑outdoor solutions constitute two complementary paths to eliminate Beidou signal blockage. The former leverages commercial 5G networks for mass‑consumer, smart‑building, and city‑wide coverage; the latter relies on ground‑based simulated signals for extreme environments such as tunnels and mines. Together they build a "air‑space‑ground‑sea" integrated, indoor‑outdoor, navigation‑communication system delivering centimeter‑level outdoor service, sub‑meter service in urban transition zones, and decimeter‑centimeter service indoors and underground, becoming a key enabler for the digital economy, intelligent industry, and public safety.