L1 Channel Indication for Fast LTE-U Feedback
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Solution Overview
Problem
In LTE licensed-assisted access (LAA) communication systems, existing methods for channel measurement and feedback in unlicensed bands are slow and inefficient, particularly due to the limitations of DRS-based CQI and the inability to directly use WiFi CTS feedback, leading to interference issues like the hidden node problem.
Innovation Solution
A method and apparatus for fast channel measurement and feedback using a Layer 1 channel indication message based on energy sensing, sent via licensed channels, which includes configuring energy sensing thresholds, sensing periods, and PUCCH resource indicators to determine unlicensed channel availability, allowing for periodic or aperiodic reporting and code division multiplexing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DRS-based CQI is used for channel measurement, then the measurement can be performed periodically, but the feedback speed is too slow to reflect fast channel situation changes
Solution Approach 1:
The patent segments the channel measurement and feedback process into two distinct parts: DRS-based periodic measurements for reliability, and L1-based fast measurements for speed. The UE performs both types of measurements independently and provides separate feedback, allowing the system to use the appropriate feedback type based on channel conditions and traffic requirements.
Solution Approach 2:
The patent introduces dynamic feedback mechanisms where the UE can switch between L1 fast feedback and DRS periodic feedback based on channel conditions. The serving node can also dynamically configure the UE to use different feedback types, making the system adaptive to varying channel situations and traffic demands.
2Loss of information
If L3 layer report is used for channel indication, then the report can be generated continuously, but it cannot fast reflect the channel situation
Solution Approach 1:
The patent segments the feedback mechanism into L3 layer reports for continuous monitoring and L1 layer feedback for fast response. The L3 report provides comprehensive channel information while the L1 feedback provides rapid updates, and both operate independently to serve different purposes in the feedback hierarchy.
Solution Approach 2:
The patent introduces L1 layer feedback as an intermediary mechanism between the physical channel and the L3 layer. This L1 feedback acts as a fast messenger that can quickly convey channel availability information to the serving node without waiting for the slower L3 processing and reporting cycle.
3Reliability
If WiFi CTS feedback mechanism is directly used in LTE-U, then the hidden node problem can be addressed, but the mechanism cannot work because uplink uses licensed spectrum where neighboring nodes do not listen
Solution Approach 1:
The patent uses the UE as an intermediary that performs listening on the unlicensed downlink channel and reports the results back to the serving node via the licensed uplink. This intermediary approach allows the system to benefit from CTS-like feedback functionality while adapting to the LTE-U architecture where uplink uses licensed spectrum.
Solution Approach 2:
The patent creates a simplified version of the WiFi CTS mechanism adapted for LTE-U. Instead of using the original CTS frame structure, the patent implements a layer 1 channel indication message that copies the essential functionality of CTS (indicating channel availability) while being compatible with LTE-U's licensed uplink architecture.
Data Source
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AI summary
The present invention relates to a method and an apparatus for fast channel measurement and feedback in a LTE licensed-assisted access (LAA) based communication system. According an embodiment of the present invention, the method comprising the steps of: A. sending a RRC connection reconfiguration message to a user equipment, the RRC connection reconfiguration message including at least one energy sensing threshold corresponding to at least one unlicensed channel; and D. receiving a Layer 1 channel indication message via a licensed channel from the user equipment, the Layer 1 channel indication message indicating whether an unlicensed channel is free. With the present invention, a serving node, such as a base station, a WiFi access point, can obtain the situation of an unlicensed channel fast and reliably. Thus, the throughput of the whole system could be enhanced.