Femtocell Frequency Synchronization With Holdover Packet Updates

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Solution Overview

Problem

Femtocell basestations in mobile communications networks face challenges in maintaining frequency synchronization due to the high cost of highly accurate crystal oscillators, and existing synchronization protocols like IEEE1588 require significant data transmission, compromising between precision and communication load.

Innovation Solution

A basestation system that includes a frequency synthesizer, packet data interface, and a method for determining elapsed synchronization time, requesting synchronization packets only when necessary, and calculating frequency offsets to maintain synchronization with a master device, reducing network traffic and using temperature compensation to adjust the crystal oscillator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If highly accurate crystal oscillators are used in femtocell basestations, then frequency synchronization accuracy is improved, but cost increases prohibitively

Engineering Contradiction:

Improvefrequency synchronization accuracyVSAvoidcost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent uses inexpensive crystal oscillators in femtocell basestations instead of expensive highly accurate oscillators. The system accepts that these cheaper oscillators will drift over time and compensates through periodic synchronization with master basestations, treating the oscillators as short-living components that are replaced or recalibrated periodically rather than requiring permanent high accuracy

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent introduces synchronization packets as an intermediary mechanism between femtocell basestations and master basestations. These packets carry timing information that mediates the frequency synchronization process, allowing cheap oscillators to maintain acceptable synchronization accuracy by periodically referencing the master clock

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If synchronization packets are sent with short time intervals, then receiver clock precision is improved, but network data traffic increases

Engineering Contradiction:

Improvereceiver clock precisionVSAvoidnetwork data traffic

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent implements periodic synchronization where femtocell basestations send synchronization requests at predetermined intervals rather than continuously. The system determines elapsed time since last synchronization and only requests packets when the interval exceeds a threshold, creating a periodic rather than continuous synchronization pattern that reduces network traffic while maintaining acceptable precision

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent makes the synchronization interval dynamic by adjusting it based on elapsed time and predetermined hold-over periods. The system adapts the synchronization frequency to actual needs, sending packets more frequently when drift is detected and less frequently when synchronization is stable, optimizing the balance between precision and traffic

Inventive Principle:

Principle #15Dynamics

3Quantity of substance

If synchronization packets are sent with long time intervals, then network data traffic is reduced, but receiver clock precision deteriorates

Engineering Contradiction:

Improvenetwork data trafficVSAvoidreceiver clock precision

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent implements feedback mechanisms where the femtocell basestation monitors its own clock drift and elapsed time since last synchronization. Based on this feedback, the system dynamically determines when to request synchronization packets, sending them only when the predetermined hold-over period is exceeded, thus maintaining precision while minimizing unnecessary traffic

Inventive Principle:

Principle #23Feedback

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 allows femtocell basestations to achieve high-frequency accuracy with reduced network traffic and cost, by minimizing the need for continuous synchronization packet transmission and using temperature-dependent frequency corrections, thus maintaining synchronization with minimal bandwidth overhead.

Implementation Method 1

a frequency synthesizer, for generating signals at desired frequencies

Methodology Applied

Scientific EffectFrequency synthesis:

Implementation Method 2

each of the basestations is provided with a highly accurate crystal oscillator

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 3

each of the basestations is provided with a highly accurate crystal oscillator, which is able to maintain the required degree of frequency synchronization

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 4

using temperature-dependent frequency corrections

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS8638774B2Controlling timing of synchronization updates

Publication Date: 2014.01.28 CISCO TECHNOLOGY INC

AI summary

A base station for use in a mobile communications network includes a frequency synthesizer for generating signals at desired frequencies and a packet data interface for transmitting and receiving packet data signals over a wide area network. The basestation is configured to determine an elapsed time since it last synchronized the frequency synthesizer to a master device. The basestation is also configured to request synchronization packet data signals from the master device when the elapsed time exceeds a predetermined holdover period.