IP Network Frequency Synchronization for Base Station Transceivers
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Solution Overview
Problem
The transition from TDM-based networks to IP networks in basestation systems for frequency synchronization between basestation controllers and transceivers is challenging due to the lack of layer 1 reference frequency propagation, leading to unreliable synchronization methods that are costly, complex, and not optimized for GSM standards.
Innovation Solution
A method involving timestamped synchronization packets transmitted between a basestation controller and transceiver over an IP network, where timestamps are used to evaluate network delivery, estimate timing errors, and apply frequency corrections to the oscillator, utilizing a dedicated timing packet flow and confidence levels to ensure accurate synchronization without increasing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TDM-based networks are used for frequency synchronization, then layer 1 reference frequency propagation is reliable, but network infrastructure complexity and cost increase
Solution Approach 1:
The patent replaces the TDM-based mechanical/electrical synchronization system with an IP packet-based system. Instead of using dedicated TDM circuits for reference frequency propagation, the invention uses standard IP network infrastructure with timestamped packets to achieve synchronization, substituting a specialized system with a more通用 platform.
Solution Approach 2:
The invention introduces timestamped synchronization packets as intermediaries between the BSC and BTS. These packets carry timing information (timestamps) that enable the BTS to calculate and correct its frequency without direct layer 1 reference propagation, acting as a mediator that bridges the gap between IP networking and frequency synchronization requirements.
2Measurement precision
If GPS systems are deployed for synchronization at each BTS, then frequency accuracy is improved, but cost and configuration complexity increase
Solution Approach 1:
The patent makes the BSC the universal synchronization source for all BTSs in the network. Instead of each BTS needing independent GPS receivers, the BSC provides centralized frequency reference distribution through IP packets to multiple BTSs, making the BSC a multi-functional node that serves both control and synchronization purposes.
Solution Approach 2:
The invention uses timestamp information copied from the BSC's reference frequency source and embedded in IP packets. The BTS copies this timing information from received packets to establish its own frequency reference, eliminating the need for direct GPS hardware at each site while maintaining accuracy through information copying rather than physical signal replication.
3Speed
If Synchronous Ethernet is implemented in IPM transceivers, then gigabit optical transmission capability is achieved, but device cost and complexity increase
Solution Approach 1:
The patent extracts the synchronization function from the physical layer (layer 1) and implements it at higher layers (layer 2 or 3) using IP packets. Instead of requiring Synchronous Ethernet capabilities at the physical layer, the invention takes out the timing reference propagation function and implements it through software-based timestamping and packet processing, separating synchronization from high-speed transmission requirements.
4Adaptability or versatility
If standard Layer 2 techniques like 1588.2 are used, then IP network synchronization is enabled, but features are not optimized for GSM BSS requirements
Solution Approach 1:
The patent applies local quality by tailoring the synchronization packet format, timestamping mechanism, and correction algorithm specifically for GSM BSS requirements. Rather than using generic Layer 2 protocols, the invention customizes the synchronization approach at the local level to match GSM's specific frequency accuracy requirements (0.05 ppm) and network architecture, ensuring both IP compatibility and GSM optimization.
Data Source
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AI summary
The method of synchronisation of a reference frequency of a base station transceiver (BTS), to the reference frequency of a base station controller (BSC) comprises a sequence of steps, wherein synchronisation packets are transmitted and provided with a time stamp of transmission and a time stamp of reception. An evaluation network delivery is evaluated upon finalization of a period of observation. If high enough, a confidence level is established of the received synchronisation packets. Only if the confidence level is above a threshold, a correction to the reference frequency of the oscillator in the base station transceiver is applied.