GPS Holdover Synchronization for Packet Backhaul Base Stations

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Solution Overview

Problem

Current CDMA base stations face challenges in maintaining oscillator stability during a loss of GPS signal, leading to communication failures due to the inherent variations and network delays in packet switched networks, which are difficult to model and correct for.

Innovation Solution

A system that creates a virtual model of the oscillator's frequency stability characteristics, allowing for time-insensitive correction factors to be sent through a packet switched network to maintain synchronization, using a primary reference clock and a secondary oscillator, with ambient temperature data to correct drift and maintain synchronization during a holdover period.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional time stamp based time synchronization is used over packet switched networks, then time reference can be provided to base stations, but the inherent variations and network delays cause synchronization accuracy to deteriorate

Engineering Contradiction:

Improvesynchronization reliabilityVSAvoidtime synchronization precision

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The system pre-calculates and stores correction factors in lookup tables before actual synchronization is needed. These correction factors account for typical network delay variations, allowing the base station to apply pre-computed corrections rather than relying on real-time timestamp measurements that are subject to network variability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent compensates for expected network delay variations by incorporating correction factors that cushion against the inherent uncertainties in packet switched network timing. This proactive compensation approach mitigates the impact of network jitter and variable delays on synchronization accuracy.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Duration of action of moving object

If crystal oscillator is used for holdover period, then base station can operate without GPS signal, but oscillator drift causes time reference to diverge from GPS reference

Engineering Contradiction:

Improveholdover period durationVSAvoidtime reference accuracy

Core Design Contradiction:

Duration of action of moving objectVSMeasurement precision

Solution Approach 1:

The system continuously monitors the crystal oscillator's frequency drift and uses this feedback to adjust the timing corrections applied during holdover. By measuring the actual oscillator behavior and comparing it against expected performance, the system can dynamically compensate for drift and maintain synchronization accuracy throughout the holdover period.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the operational parameters of the crystal oscillator by applying temperature compensation and frequency correction factors. These parameter adjustments allow the oscillator to maintain more stable frequency output during holdover, reducing drift and extending the period during which accurate synchronization can be maintained without GPS signal.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If GPS receiver antenna is placed high for best coverage, then satellite signal reception is improved, but the antenna becomes more susceptible to lightning damage and physical damage

Engineering Contradiction:

Improvesignal reception reliabilityVSAvoidlightning damage susceptibility

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The system implements protective measures beforehand by using surge protectors, lightning arrestors, and redundant antenna mounting structures. These protective elements are installed in advance to cushion against potential lightning strikes and physical damage, allowing the antenna to maintain its elevated position for optimal signal reception while being protected from harmful effects.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The patent introduces intermediary protective devices between the GPS antenna and the base station equipment. These intermediaries, such as lightning arrestors and surge suppressors, provide a safe path for lightning energy to ground while protecting the sensitive electronic equipment from damage, thus allowing the antenna to remain in its optimal high position.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS7606541B1Enhanced holdover for synchronous networks employing packet switched network backhaul

Publication Date: 2009.10.20 MALIKIE INNOVATIONS LTD

AI summary

Systems and methods are disclosed to maintain synchronous communications that uses a global positioning system satellite, a primary communication unit, and a secondary communication unit. The satellite based time reference broadcasts a reference signal to the primary communication unit and the secondary communication unit. The primary communication unit contains a high quality oscillator, and operates a virtual model of a secondary oscillator which is located in the secondary communication unit. The primary and secondary units have synchronous communications with each other by using a global positioning system satellite broadcast as a reference signal. If the secondary unit loses its signal from the global positioning system, the secondary oscillator enters a holdover state and transmits a notification of the holdover state to the primary communications unit. The primary communication unit then transmits time insensitive synchronization data based upon the virtual model through the packet switched network to the secondary communications unit to maintain synchronization.