ACK/NACK Feedback Encoding Using CQI Bits in Carrier Aggregation
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Solution Overview
Problem
In LTE-Advanced systems, the existing ACK/NACK signalling methods for carrier aggregation are prone to errors, leading to inefficient system operation and Hybrid Automatic Repeat Request (HARQ) buffer corruption due to incorrect feedback transmissions, especially in scenarios with multiple component carriers and MIMO transmissions.
Innovation Solution
A method for encoding feedback information messages using a set of codewords, where each message can be of two kinds (ACK, NACK, or DTX) with maximally separated modulation symbols to minimize detection errors, ensuring that codewords representing different information states have maximum separation in their modulation symbols, thus reducing error probabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If channel selection with QPSK modulation is used for ACK/NACK feedback transmission, then the single-carrier property is preserved and PAPR remains low, but the system becomes vulnerable to ACK-to-NACK and NACK-to-ACK errors causing HARQ buffer corruption and inefficient retransmissions
Solution Approach 1:
The patent introduces a new dimension to the feedback signaling by using Channel Quality Indicator (CQI) bits to convey ACK/NACK information. Instead of relying solely on dedicated ACK/NACK channels, the invention maps acknowledgment states onto CQI reporting resources, thereby utilizing an additional signaling dimension (CQI bits) to transmit feedback information reliably while preserving the single-carrier property.
Solution Approach 2:
The patent changes the parameter used for feedback transmission by mapping ACK/NACK states onto CQI bit values. Different ACK/NACK states are represented by specific CQI bit patterns (e.g., ACK=00, NACK=01, DTX=10), transforming the feedback signaling from a dedicated channel approach to a parameter-encoding approach that leverages existing CQI reporting mechanisms.
2Adaptability or versatility
If multiple feedback information messages are transmitted using conventional encoding methods, then carrier aggregation support is provided, but error probabilities increase leading to system performance degradation
Solution Approach 1:
The patent segments the feedback information into multiple independent messages, each corresponding to a specific component carrier or transport block. Each feedback message is independently encoded using CQI bits, allowing the system to handle multiple component carriers in carrier aggregation while maintaining individual error protection for each feedback message through the structured mapping scheme.
Data Source
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AI summary
The invention relates to a method for encoding a number of feedback information messages in a mobile radio communications system using carrier aggregation, the method comprising: - encoding the number of feedback information messages by a set of codewords, where each feedback information message can be of at least a first kind or a second kind. The method is distinguished by that for at least one feedback information message there is at least one codeword corresponding to information of the first kind and at least one codeword corresponding to information of the second kind, wherein the modulation symbol of one of said at least one codeword corresponding to information of the first kind and the modulation symbol of one of said at least one codeword corresponding to information of the second kind have a maximum distance. The invention also relates to a terminal and radio basestation for a communications system.