CSR Holdover Timing During GPS Flapping in Cellular Networks
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Solution Overview
Problem
Modern cellular networks, particularly 5G ORAN networks, face challenges in maintaining precise timing and synchronization during temporary GPS outages or signal degradations, leading to service disruptions and poor user experiences due to GPS signal 'flapping' events.
Innovation Solution
Implementing an enhanced holdover capability in the CSR with a configurable duration, such as 30 minutes, using an internal oscillator disciplined by historical GPS timing data to generate a stable backup frequency reference, and transitioning smoothly between primary and backup timing sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS-based timing reference is used in cell sites, then precise timing synchronization is achieved, but the system becomes vulnerable to GPS signal disruptions and flapping events
Solution Approach 1:
The system pre-disciplines the internal oscillator using GPS timing data before GPS signal loss occurs. This preliminary action stores timing information in the oscillator's memory, enabling it to continue providing accurate timing references during GPS outages without immediate degradation.
Solution Approach 2:
The system implements an extended holdover mechanism that cushions against GPS signal disruptions by maintaining timing accuracy for up to 30 minutes during outages. This beforehand cushioning prevents timing instability from propagating through the network during temporary GPS failures.
2Adaptability or versatility
If the CSR acts as a standalone PTP grandmaster at each cell site, then timing autonomy is achieved, but timing instability propagates to downstream devices during GPS outages
Solution Approach 1:
The system merges multiple cell sites into a synchronized timing domain where the CSR at each site maintains coordination with other CSRs. This merging allows timing information to be shared and validated across sites, preventing isolated timing failures from propagating while maintaining each site's operational autonomy.
Solution Approach 2:
The system implements PTP protocol for inter-CSR synchronization, where each CSR receives timing feedback from other CSRs in the network. This feedback mechanism allows CSRs to adjust their timing references and detect GPS outages collectively, maintaining network-wide timing stability even when individual sites experience GPS disruptions.
3Duration of action of stationary object
If extended holdover duration is implemented in the CSR, then service continuity is maintained during GPS outages, but device complexity increases
Solution Approach 1:
The system implements self-service by using the CSR's own internal oscillator, already present in the device, as the backup timing source during GPS outages. This eliminates the need for external backup timing equipment or complex hardware modifications, extending holdover duration while maintaining acceptable device complexity.
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 reduces the impact of GPS flapping by maintaining network stability and minimizing service interruptions, allowing operators time to address issues without requiring significant hardware changes.
Implementation Method 1
the CSR to maintain a stable and accurate timing reference for a defined period even when the primary GPS signal is lost
Data Source
AI summary
A system and method for maintaining timing synchronization in cellular networks during GPS signal loss is provided. A cloud services router (CSR) receives a primary timing reference from a GPS receiver. Upon detecting loss of the GPS signal, the CSR enters a holdover mode for a predetermined duration, utilizing a first clock class indicating a traceable backup timing source. The CSR generates a backup timing signal using its internal oscillator and provides this to downstream devices. If the GPS signal is restored within the holdover period, normal operation resumes. If the holdover period expires without GPS restoration, the CSR advertises a second clock class indicating a free-run state. The disclosed technique bridges temporary GPS outages without impacting service quality, reducing dropped calls and service interruptions. The holdover duration is configurable, with 30 minutes used in one embodiment as sufficient to outlast typical GPS signal flapping events.