UE-Assisted Synchronization for Small Cell Clock Drift
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Solution Overview
Problem
Femtocells in LTE networks face challenges in achieving time and frequency synchronization due to low-cost oscillators, unreliable backhaul connectivity, and varying GPS and macrocell signal reception, which affects their operation and coverage, especially in indoor environments with limited operator control.
Innovation Solution
A UE-assisted synchronization method where small cells, such as femtocells, request and obtain time and frequency offset information from associated user equipment (UEs), allowing the small cells to discipline their clock drift. This involves the UE measuring and reporting time and frequency offsets between the small cell and neighboring macrocells, with the small cell optionally calculating frequency offsets from multiple time offset measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If femtocells use low-cost oscillators to reduce deployment cost, then device cost decreases, but synchronization accuracy deteriorates due to frequent clock drift
Solution Approach 1:
The patent introduces user equipment (UE) as an intermediary to measure and report time and frequency offsets between the femtocell and macrocells. The UE acts as a mediator that collects synchronization measurement data and provides it to the femtocell, enabling the low-cost femtocell to achieve accurate synchronization without requiring expensive precision oscillators
Solution Approach 2:
The patent implements a feedback mechanism where UEs continuously measure time and frequency offsets and report these measurements back to the femtocell. The femtocell uses this feedback information to adjust its transmission timing and frequency, compensating for clock drift from the low-cost oscillator and maintaining synchronization accuracy
2Device complexity
If femtocells rely on backhaul-based synchronization to reduce complexity, then device complexity decreases, but synchronization reliability deteriorates due to unreliable backhaul connectivity
Solution Approach 1:
The patent uses UEs as intermediaries to obtain synchronization information from macrocells directly over the air interface, bypassing the unreliable backhaul connection. The UE measures the time difference of arrival from macrocells and reports this information to the femtocell, providing a reliable synchronization path that does not depend on backhaul connectivity
Solution Approach 2:
The patent enables UEs to perform multiple functions: normal communication with the femtocell and simultaneous measurement/reporting of synchronization information. This multi-functionality allows the system to maintain simple device architecture while achieving reliable synchronization through the UE's dual role
3Measurement precision
If femtocells use GPS-based synchronization to improve accuracy, then synchronization accuracy improves, but device complexity increases due to additional hardware requirements
Solution Approach 1:
The patent transfers the GPS reception function to the UE, which acts as an intermediary. The UE receives and processes GPS signals to obtain precise timing information, then reports this information to the femtocell. This approach allows the femtocell to achieve GPS-level synchronization accuracy without requiring expensive GPS receivers in each femtocell unit
Solution Approach 2:
The patent enables UEs to self-configure for synchronization measurements by automatically detecting neighboring macrocells and reporting time difference measurements. The UE performs synchronization acquisition autonomously using available macrocell signals, eliminating the need for complex centralized synchronization management
Data Source
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AI summary
Aspects of the present disclosure provide a user equipment (UE) assisted synchronization method in which a small cell can request and obtain time and frequency offset information from one or more UEs currently associated with the small cell, and the small cell can discipline its clock drift accordingly.