Base Station Synchronization Signal Timing in Unlicensed Bands
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Solution Overview
Problem
The LTE-A system faces challenges in efficiently communicating with multiple base stations using unlicensed or white bands due to interference from other systems, leading to prolonged detection times for synchronization signals and reduced communication efficiency.
Innovation Solution
A communication method where the base station efficiently notifies terminal apparatuses of control information using licensed bands, allowing for flexible transmission timing of synchronization signals in unlicensed bands, and utilizing carrier sense mechanisms to avoid collisions, thereby improving cell throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If base station transmits synchronization signals (PSS/SSS) in unlicensed band, then terminal can identify cell ID and measure receive power, but transmission timing becomes irregular due to carrier sense requirements
Solution Approach 1:
The patent uses licensed band as an intermediary to convey control information about unlicensed band transmission timing. The base station transmits control information in the licensed band that indicates when synchronization signals will be transmitted in the unlicensed band, allowing the terminal to prepare and measure receive power at the correct timing without needing to continuously monitor the unlicensed band for signal presence.
2Reliability
If base station performs carrier sense before transmitting in unlicensed band, then collision with other systems is avoided, but transmission cycle of synchronization signals becomes irregular
Solution Approach 1:
The base station performs carrier sense and determines transmission timing in advance, then notifies the terminal of this predetermined timing through control information in the licensed band. This allows the synchronization signal transmission in the unlicensed band to follow a predictable pattern from the terminal's perspective, even though the actual transmission timing is adapted to carrier sense results.
3Ease of operation
If terminal continuously monitors unlicensed band for synchronization signals, then cell identification is possible, but power consumption increases and detection time prolongs
Solution Approach 1:
The terminal uses control information received from the base station in the licensed band as feedback to determine when to monitor the unlicensed band for synchronization signals. This feedback mechanism allows the terminal to concentrate its monitoring efforts at specific predetermined timings rather than continuously monitoring, reducing both power consumption and overall detection time.
Data Source
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AI summary
There has been a problem that a time period between transmission of a synchronization signal and the next transmission thereof may become longer depending on a usage state of an unlicensed band and a terminal apparatus requires a long time to measure receive power of signals from a plurality of base station apparatuses that perform communication in the unlicensed band. A base station apparatus that communicates with a terminal apparatus in a second frequency band different from a first frequency band that is able to be used exclusively includes: a DL signal generation unit that generates a signal to be transmitted to the terminal apparatus; a radio transmission unit that transmits the signal; and a connected terminal management unit that receives information about a plurality of subframes in which a signal is able to be transmitted to the terminal apparatus from another base station apparatus that communicates with the terminal apparatus in the first frequency band. The DL signal generation unit generates a subframe constituted by a synchronization signal and a reference signal, and the radio transmission unit transmits the signal with at least one of subframes included in the information about the plurality of subframes.