Uplink Symbol Offset Scheduling for LBT in Unlicensed Spectrum
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Solution Overview
Problem
LTE uplink transmissions in unlicensed spectrum face performance issues due to centralized channel access and LBT regulations, leading to delays and inefficiencies compared to asynchronous Wi-Fi terminals, especially in congested networks.
Innovation Solution
Implementing multiple starting and ending positions for scheduled or autonomous uplink transmissions, combined with short transmission time intervals (sTTIs), to enhance flexibility and efficiency in channel access on unlicensed spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If centralized channel access with LBT is used in LTE uplink on unlicensed spectrum, then regulatory compliance is achieved, but transmission delay increases and system performance deteriorates
Solution Approach 1:
The patent segments the uplink transmission procedure into multiple independent LBT attempts at different starting positions within a subframe. Instead of a single centralized channel access point, the UE can attempt LBT at multiple predefined starting positions (e.g., symbol 0, symbol 3, symbol 6), allowing the transmission to start as soon as any attempt succeeds, thereby reducing transmission delay while maintaining regulatory compliance through proper LBT execution.
2Device complexity
If fixed starting position for uplink transmission is used, then scheduling simplicity is maintained, but channel access efficiency decreases in congested networks
Solution Approach 1:
The patent introduces dynamic flexibility to the uplink transmission starting position by defining multiple candidate starting positions within a subframe. The actual starting position is determined dynamically based on LBT success at different positions, rather than being fixed in advance. This dynamic approach allows the system to adapt to channel conditions and achieve faster access in congested networks while the eNB maintains scheduling control through configuration of the candidate positions.
3Loss of time
If multiple starting positions are implemented for uplink transmission, then transmission delay is reduced, but device complexity and scheduling overhead increase
Solution Approach 1:
The patent applies preliminary action by pre-configuring multiple candidate starting positions and their associated parameters (such as time offsets, resource allocations) through higher-layer signaling before actual transmission occurs. This preliminary configuration allows the UE to quickly select and execute an appropriate starting position based on LBT outcomes without requiring complex real-time scheduling decisions, thereby reducing transmission delay while limiting the increase in scheduling complexity through advance preparation.
Data Source
AI summary
A method of operating a wireless communication device comprises identifying a first start position for performing uplink (UL) transmission in unlicensed spectrum during a first transmission time interval, performing UL transmission in the first transmission time interval (TTI) according to the first start position, identifying a second start position for performing UL transmission in unlicensed spectrum during a second TTI, wherein the first and second start positions correspond to different symbol offsets within the respective first and second TTIs, and performing UL transmission in the second TTI according to the second start position.