Timing Advance Commands for Sub-Microsecond Clock Synchronization
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Solution Overview
Problem
Current wireless communication systems face challenges in providing accurate time information to mobile devices due to the unpredictable nature of radio links, especially in indoor environments or when GNSS signals are unavailable, and existing methods like NTP offer insufficient accuracy for many applications.
Innovation Solution
A method for distributing time information in LTE cellular networks involves transmitting coarse and fine indications of propagation delay using timing advance and update commands, with the fine indication encoded as a binary number to improve clock synchronization accuracy at mobile devices, utilizing Manchester modulation to maintain carrier signal average value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NTP is used for time distribution over variable latency packet switched networks, then time information can be distributed, but accuracy is limited to tens of milliseconds which is insufficient for many applications
Solution Approach 1:
The patent uses the radio link between base station and mobile device as an intermediary to distribute time information. By measuring the propagation delay of radio signals and compensating for it, the system achieves accurate time synchronization without relying on NTP's millisecond-level accuracy. The radio link becomes a precise timing carrier rather than just a data transmission medium.
Solution Approach 2:
The patent replaces the NTP protocol-based time distribution mechanism with a radio signal propagation delay measurement mechanism. Instead of using packet-switched network timing protocols, the system uses direct radio signal transmission and measures the time of flight, achieving sub-microsecond accuracy by substituting the timing mechanism fundamentally.
2Measurement precision
If OTDOA is used for calculating time at mobile device, then time can be calculated, but it decreases the efficiency of LTE networks and is not supported by all equipment
Solution Approach 1:
The patent extracts the time synchronization function from the complex OTDOA positioning procedure. Instead of using the full OTDOA mechanism which involves multiple base stations and complex signal processing, the invention extracts only the essential propagation delay measurement component and applies it directly to time synchronization, simplifying the process and improving network efficiency.
Solution Approach 2:
Instead of using OTDOA's approach of having the mobile device calculate position based on time differences from multiple base stations, the patent inverts the approach: the base station provides timing information to the mobile device, and the mobile device uses the measured propagation delay to synchronize its clock. This reverses the traditional positioning-oriented approach to a synchronization-oriented approach.
3Adaptability or versatility
If standards are updated to include new time distribution features, then functionality can be improved, but it takes long periods for manufacturers to implement changes and incurs costs
Solution Approach 1:
The patent makes the existing timing advance mechanism serve multiple functions: it continues to provide uplink timing synchronization while simultaneously providing accurate propagation delay information for time synchronization. By making the existing infrastructure multi-functional, the patent adds advanced time distribution capability without requiring new standardized procedures or hardware updates.
Solution Approach 2:
The system uses the existing timing advance commands that are already being exchanged between base station and mobile device for uplink synchronization. These same commands are repurposed to carry propagation delay information for time synchronization, allowing the system to serve itself without requiring external standardization updates or additional signaling overhead.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables mobile devices to achieve clock synchronization with an accuracy of ±16.3 ns, addressing the limitations of existing methods by providing reliable and accurate time information without requiring changes to existing standards or hardware.
Implementation Method 1
The fine indication of propagation delay is transmitted by modulating a timing advance update command using a modulation scheme, such as Manchester modulation, which has no effect on the average value of a carrier signal
Data Source
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AI summary
Methods and systems for the distribution of timing information in cellular networks. Coarse timing information is distributed from base stations to mobile devices using conventional signalling techniques. Fine timing information is distributed form base stations to mobile devices by using the fine timing information to modulate a carrier signal. The modulation format is such that the average value of the carrier signal is not affected by the modulation. The carrier signal may be a series of values, for example timing advance update commands.