Listen-Before-Talk Preamble Structure for LAA-LTE Channel Access
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Solution Overview
Problem
LAA-LTE systems face challenges in co-existing with other technologies in unlicensed bands due to the random nature of interference, requiring modifications to comply with Listen-Before-Talk regulations while maintaining LTE system advantages, particularly in aligning channel access with OFDM symbol or subframe boundaries.
Innovation Solution
A new frame structure is introduced for LBE access in LAA-LTE, where a short preamble is transmitted in an available subframe to occupy the channel, align symbol boundaries, and implicitly indicate data transmission start, allowing data transmission to begin in the middle of a subframe, with a fractional part of a symbol for alignment and an optional integral part for synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LAA-LTE transmitter performs CCA or Extended CCA to determine channel availability in unlicensed spectrum, then channel access flexibility is improved, but channel access may occur in the middle of a subframe which misaligns with OFDM symbol or subframe boundaries
Solution Approach 1:
The subframe structure is segmented into two parts: a first part before the OFDM symbol boundary and a second part starting from the OFDM symbol boundary. This segmentation allows the transmitter to perform CCA at any time while ensuring that data transmission begins precisely at the OFDM symbol boundary, resolving the misalignment issue.
Solution Approach 2:
The transmitter performs CCA or Extended CCA in advance to determine channel availability before the OFDM symbol boundary. By completing the channel assessment preliminarily in the first part of the subframe, the system ensures that data transmission can start exactly at the symbol boundary without misalignment, while still maintaining the flexibility of random channel access.
2Device complexity
If LAA-LTE system maintains strict frame structure with scheduling, then system coordination and resource management are improved, but compliance with LBT regulations requiring flexible channel sensing and occupancy is compromised
Solution Approach 1:
The subframe is divided into a first part and a second part, where the first part accommodates flexible CCA/eCCA operations and the second part maintains strict OFDM symbol structure for data transmission. This segmentation enables the system to comply with LBT regulations while preserving LTE's scheduled frame structure advantages.
Solution Approach 2:
The system dynamically adapts the frame structure by allowing flexible channel sensing in the first part of the subframe while maintaining the rigid OFDM symbol boundaries in the second part. This dynamic approach enables compliance with LBT regulations without sacrificing the coordination benefits of LTE's scheduled frame structure.
3Productivity
If data transmission starts in the middle of a subframe to comply with LBT, then channel access efficiency is improved, but resource waste increases due to incomplete subframe utilization
Solution Approach 1:
By segmenting the subframe into a first part for CCA and a second part for data transmission starting at the OFDM symbol boundary, the system maximizes the utilization of the second part for productive data transmission. This reduces resource waste compared to starting transmission in the middle of a subframe, while still improving channel access efficiency by allowing flexible CCA timing.
Data Source
AI summary
The present invention relates to a method and an apparatus for implementing Listen-Before-Talk. According to an embodiment of the present invention, if the channel assessment does not stop at a boundary of the first symbol, the preamble comprises at least a first part, and if the channel assessment stops at the boundary of the first symbol, the preamble comprises a second part. And the first part is transmitted on a remaining portion of the first symbol until the end of the first symbol, and the second part is transmitted on at least one symbol following the first symbol. Besides, the data is transmitted to the receiving device in at least one symbol in the subframe in which the preamble transmission ends.