Base Station Synchronization Signal Transmission in Unlicensed Bands
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Solution Overview
Problem
Conventional LTE specifications lack methods for signal transmission and synchronization between user terminals and base stations using unlicensed bands, particularly in Licensed Assisted Access (LAA) systems, which require carrier sensing to avoid interference with other communication systems.
Innovation Solution
A base station and user terminal configuration that enables synchronization using carrier aggregation between a licensed and an unlicensed band, where the base station transmits synchronization signals over the unlicensed band based on carrier sensing results and instructs the user terminal to detect these signals, allowing for efficient communication without interfering with other devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If carrier sensing is performed before signal transmission in the unlicensed band, then interference with other communication systems is avoided, but the complexity of the transmission system increases
Solution Approach 1:
The base station performs carrier sensing before transmitting synchronization signals to determine if the unlicensed band is available, avoiding interference with other communication systems while managing transmission complexity through advance channel assessment
Solution Approach 2:
The patent introduces an intermediary mechanism where the base station transmits indication information through the primary cell to instruct the user terminal about synchronization signal transmission on unlicensed carriers, mediating between carrier sensing results and actual signal transmission
2Reliability
If synchronization signals are transmitted on unlicensed carriers, then synchronization between user terminal and base station is achieved, but the reliability of signal transmission decreases due to uncertain channel availability
Solution Approach 1:
The user terminal performs detection operations on synchronization signals based on indication information from the base station and reports detection results back to the base station, creating a feedback loop that improves transmission reliability through confirmed signal reception
Solution Approach 2:
The system dynamically adjusts synchronization signal transmission based on carrier sensing results, transmitting signals only when the unlicensed band is determined to be available, making the transmission operation adaptive to channel conditions
3Loss of information
If the user terminal detects synchronization signals on all unlicensed carriers, then complete synchronization information is obtained, but the detection operation complexity increases
Solution Approach 1:
The base station transmits indication information specifying which unlicensed carriers will carry synchronization signals, allowing the user terminal to perform detection operations only on indicated carriers rather than all unlicensed carriers, reducing detection complexity while maintaining synchronization information completeness
Data Source
AI summary
A base station manages a first cell and a second cell and communicates with a user terminal by carrier aggregation which is applied to the first cell and the second cell, the first cell being allocated a licensed band requiring a license and a second cell being allocated an unlicensed band not requiring a license. The base station includes: a transmitter configured to transmit a synchronization signal used for synchronization between the second cell and the user terminal, by at least one carrier selected from the unlicensed band based on a result of carrier sensing in the second cell; and a controller configured to instruct the user terminal to perform a detection operation of the synchronization signal for all or part of the carrier through the first cell.