Femto Base Station Uplink Timing Synchronization
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Solution Overview
Problem
In dense deployments of small cells like femto cells, many base stations are idle most of the time and face challenges in detecting and decoding uplink signals from user equipment due to mismatched timing, and there is interference between small cell and macro cell communications, which complicates resource allocation and frequency division multiplexing.
Innovation Solution
A femto base station maintains two timings, synchronizing its downlink and uplink timings with the macro base station's timings, using the arrival times of signals from user equipment devices to align uplink transmissions, allowing for synchronized reception of both femto and macro cell signals within a cyclic prefix duration, facilitating frequency division multiplexing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If small cell base stations transmit pilot and information signals continuously, then signal coverage and detection capability are improved, but energy consumption increases and interference with macro cell transmissions worsens
Solution Approach 1:
The patent implements periodic transmission of pilot and information signals by small cell base stations instead of continuous transmission. The system uses configured grants and periodic resource allocation to enable small cells to transmit signals only when needed, reducing energy consumption while maintaining detection capability through scheduled periodic transmissions.
2Reliability
If small cell base stations use conventional uplink timing detection, then timing synchronization for served UEs is maintained, but the ability to detect signals from non-served UEs deteriorates due to timing mismatch
Solution Approach 1:
The patent introduces a macro cell base station as an intermediary to facilitate timing detection. The small cell base station uses the macro cell's downlink timing as a reference and detects uplink timing from non-served UEs by receiving their transmissions during macro cell uplink subframes, effectively using the macro cell infrastructure to overcome the timing mismatch problem.
Solution Approach 2:
The small cell base station is designed to maintain multiple uplink timings simultaneously - one for served UEs and another for detecting non-served UEs. This multi-functionality allows the same small cell to perform both functions: serving its own UEs with proper timing synchronization and detecting presence of non-served UEs using a different timing reference.
3Productivity
If small cells and macro cells operate in the same frequency band without coordination, then spectrum utilization is improved, but interference between uplink and downlink transmissions increases
Solution Approach 1:
The patent segments the frequency band usage by implementing frequency division between small cell and macro cell transmissions. Specifically, small cell uplink transmissions are coordinated to occur in frequency resources that do not conflict with macro cell downlink receptions, creating separated frequency segments for different transmission types and eliminating interference.
Solution Approach 2:
The system dynamically adjusts resource allocation and timing based on traffic conditions and interference levels. The small cell base station can switch between different uplink timing configurations and frequency resources depending on whether served or non-served UE detection is prioritized, allowing adaptive optimization of spectrum utilization while managing interference.
Data Source
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AI summary
A femto base station (BS) maintains two different timings: a femto BS downlink timing and a femto BS uplink timing. A femto base stations uplink reference timing is based on the macro uplink timing being used by one or more UE devices in the local vicinity of the femto BS. In some embodiments, the femto BS synchronizes its femto uplink timing to the macro uplink timing being used by the closest UE device transmitting uplink signals to the macro BS. In other embodiments, the femto BS determines its femto base station uplink timing based on one or more uplink signals from UE devices in its vicinity transmitting to the macro BS. In various embodiments, femto cell uplink signals and macro cell uplink signals are received at a femto cell BS in synchronization. This approach facilitates frequency division multiplexing (FDM) in the uplink between a macro cell and a femto cell.