Dynamic ACK/NACK Repetition for LTE HARQ Collision Avoidance
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Solution Overview
Problem
In LTE architecture, multiple acknowledgements (ACK/NACK) for important MAC PDUs can lead to collisions due to simultaneous transmission in adjacent time slots, causing latency and decoding errors, as the enhanced Node B struggles to distinguish between feedback signals from different User Equipments (UEs).
Innovation Solution
The use of differentiating factors such as multiple physical downlink control channels (PDCCHs), cyclic shifts, and frequency blocks allows the enhanced Node B to distinguish between HARQ feedbacks from different UEs by assigning specific channels, shifts, or blocks based on time slots or network conditions, thereby avoiding collisions and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple acknowledgements are sent in adjacent time slots to increase reliability, then the probability of correct HARQ feedback signal detection is improved, but collisions between acknowledgements occur causing latency and decoding errors
Solution Approach 1:
The patent applies dimensionality change by introducing cyclic shifts as an additional dimension to differentiate acknowledgements. Instead of only using time slots, the system now uses cyclic shifts of reference signals to create distinct dimensions for multiple UEs, allowing simultaneous transmissions without collision while maintaining reliability.
Solution Approach 2:
The patent applies local quality by assigning specific cyclic shift values to different UEs or different time slots. Each UE receives a unique cyclic shift configuration, creating localized differentiation that allows the eNB to distinguish between multiple acknowledgements in the same time slot, thereby avoiding collisions while maintaining high detection accuracy.
2Reliability
If multiple acknowledgements are sent in adjacent time slots to increase reliability, then the probability of correct HARQ feedback signal detection is improved, but collisions between acknowledgements occur causing decoding errors
Solution Approach 1:
The patent applies parameter changes by modifying the cyclic shift parameter of reference signals used in acknowledgement transmissions. By dynamically adjusting cyclic shift values based on UE identity or time slot, the system transforms identical transmissions into distinguishable signals, eliminating collisions while maintaining reliability.
Solution Approach 2:
The patent introduces cyclic shifts as an additional differentiation dimension beyond time slots. This creates a multi-dimensional resource allocation space where acknowledgements from different UEs can coexist without collision, effectively eliminating the harmful collision effect while preserving high detection reliability.
3Reliability
If messages requiring multiple feedbacks are sent in adjacent time slots, then robust HARQ feedback is achieved, but collisions occur and the enhanced Node B cannot decode the acknowledgements properly
Solution Approach 1:
The patent applies preliminary action by pre-configuring cyclic shift values for different UEs before actual data transmission. The eNB assigns specific cyclic shift patterns to UEs in advance, so that when multiple acknowledgements need to be transmitted, the differentiation is already established, simplifying the decoding process and reducing real-time complexity.
Data Source
AI summary
A method and apparatus for dynamic acknowledgement repetition for a downlink medium access control packet data unit transmission ‘MAC PDU’ requiring multiple acknowledgements, the method having the steps of: receiving the downlink MAC PDU requiring multiple acknowledgements; and utilizing a differentiating factor and acknowledgement scheme, sending the multiple acknowledgements.