LAA LTE Uplink Channel Access via LBT Puncturing
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Solution Overview
Problem
Current wireless cellular communication systems face challenges in improving spectral efficiency and data rate due to the scarcity of licensed spectrum in low frequency bands, prompting the need for operation in unlicensed spectrum, particularly in the 5 GHz band, while ensuring fair coexistence with incumbent WLAN systems.
Innovation Solution
The implementation of Listen-Before-Talk (LBT) mechanisms in LTE systems for uplink transmissions in unlicensed spectrum, allowing for flexible scheduling and channel access procedures to avoid collisions with existing systems, including puncturing symbols in contiguous UL subframes and employing different LBT methods based on successful LBT outcomes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If LTE systems operate in unlicensed spectrum to improve spectral efficiency and data rate, then spectral efficiency and data rate are improved, but coexistence with incumbent WLAN systems deteriorates due to potential interference and collisions
Solution Approach 1:
The system performs Listen-Before-Talk (LBT) channel access procedures before transmitting uplink signals in unlicensed spectrum. This preliminary action of sensing the channel and determining its availability prevents collisions with incumbent WLAN systems while enabling LTE operations, thereby resolving the contradiction between improving data rate and avoiding interference
Solution Approach 2:
The system implements feedback mechanisms where the eNB provides indications to the UE about LBT requirements, channel access categories, and transmission parameters based on channel conditions. This feedback loop enables dynamic adaptation of transmission behavior to maintain fair coexistence with WLAN systems while maximizing spectral efficiency and data rate
2Reliability
If LBT procedures are implemented for uplink transmissions in unlicensed spectrum, then fair coexistence with WLAN systems is achieved, but transmission delays and complexity increase
Solution Approach 1:
The LBT mechanism is segmented into different channel access categories (Category 2 and Category 4 LBT) with distinct procedures for different transmission scenarios. This segmentation allows the system to apply simplified procedures when appropriate while maintaining comprehensive conflict avoidance, thereby achieving fair coexistence without excessive complexity
Solution Approach 2:
The LBT mechanism is designed to be universal across different uplink transmission types including PUCCH, PUSCH, and SRS. The same fundamental LBT principles and procedures are applied across multiple functions and scenarios, reducing overall system complexity while ensuring reliable fair coexistence with WLAN systems
3Productivity
If multiple contiguous UL subframes are scheduled for the same UE, then spectral efficiency is improved through continuous transmission, but channel access conflicts increase with other systems
Solution Approach 1:
The system performs a single LBT procedure at the beginning of a burst of contiguous uplink subframes rather than before each individual subframe. This preliminary channel access determination enables continuous transmission across multiple subframes, improving spectral efficiency while the initial LBT action prevents channel access conflicts with other systems
Solution Approach 2:
The system maintains continuous uplink transmission across multiple contiguous subframes once channel access is successfully obtained. This continuity of useful action maximizes spectral efficiency by eliminating idle gaps between transmissions while the prior LBT procedure ensures that this continuous transmission does not create channel access conflicts with incumbent WLAN systems
Data Source
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AI summary
In the context of License Assisted Access on a wireless network, LAA LTE, to unlicensed spectrum, uplink scheduling and reception at an evolved Node B, eNB, and contention access and transmission at a User euipment, UE, are described. the eNB schedules uplink resources consisting of multiple subframes. The UE performs Listen-Before-Talk, LBT, procedures before transmitting within the scheduled subframes. transmission puncturing is applied either before a subframe or at the end of a subframe. A first, second and third circuitry are described. The first circuitry may be operable to identify a first subframe being unavailable for a first Listen-Before-Talk (LBT) procedure within the unlicensed spectrum, in which the first LBT procedure determined the unlicensed spectrum to be busy. The second circuitry may be operable to perform a second LBT procedure in a second subframe subsequent to the first subframe. The third circuitry may be operable to generate an Uplink (UL) transmission over the unlicensed spectrum in the second subframe. The UE that acquires the uplink channel sends a reservation signal, for example, a demodulation reference signal, DM-RS.