ACK/NACK Transmission in TDD Wireless Systems
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Solution Overview
Problem
In wireless communication systems based on Time Division Duplex (TDD), the increased payload of Hybrid Automatic Repeat Request (HARQ) ACK/NACK signals complicates data rate transmission, necessitating a method to reduce the payload while maintaining transmission reliability.
Innovation Solution
A method and apparatus for transmitting ACK/NACK signals in a TDD system, where user equipment receives downlink transport blocks from multiple serving cells, processes uplink grants including piggyback information, and multiplexes ACK/NACK responses using uplink resource assignments, thereby reducing payload size and maintaining reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple downlink subframes are associated with an uplink subframe in TDD system, then HARQ transmission reliability is improved, but ACK/NACK payload size increases excessively
Solution Approach 1:
The patent segments the ACK/NACK feedback into two parts: a compact bitmap indicating the number of transport blocks received, and separate detailed feedback only when needed. This segmentation allows the system to maintain reliability through comprehensive feedback when necessary while reducing payload size when transport blocks are successfully received, directly resolving the contradiction between reliability and payload size.
Solution Approach 2:
The patent implements dynamic feedback mechanism where the feedback payload size changes based on actual reception conditions. When all transport blocks are received successfully, only compact acknowledgment is transmitted; when failures occur, detailed feedback is transmitted. This dynamic adjustment resolves the contradiction by adapting the payload size to actual transmission needs rather than always using maximum size.
2Productivity
If ACK/NACK payload size is reduced, then data rate transmission is improved, but transmission reliability may deteriorate
Solution Approach 1:
The patent performs preliminary classification of feedback types before transmission. By pre-determining whether compact or detailed feedback is needed based on reception status, the system optimizes payload size in advance. This preliminary action allows the system to maintain data rate efficiency while ensuring reliability is preserved through appropriate feedback granularity, resolving the contradiction between productivity and reliability.
3Adaptability or versatility
If multiple serving cells are used in TDD system, then service capacity is improved, but ACK/NACK payload becomes excessively large
Solution Approach 1:
The patent merges the feedback from multiple serving cells into a unified compact structure. Instead of transmitting separate detailed feedback for each cell, the system combines status information across all cells into a single bitmap and conditional feedback message. This merging approach maintains the ability to serve multiple cells (service capacity) while dramatically reducing the total feedback payload size required.
Data Source
AI summary
A method of transmitting an acknowledgement (ACK) or a negative-acknowledgement (NACK) in a wireless communication system based on Time Division Duplex (TDD) in which M downlink sub-frame(s) are associated with an uplink sub-frame, where M is equal to or greater than one (1), the method includes receiving, by a user equipment configured with a plurality of serving cells, at least one downlink block in the M downlink sub-frame(s); determining, by the user equipment, an ACK/NACK response for the at least one downlink block by using one of a plurality of mapping rules, wherein each of the plurality of mapping rules determines the ACK/NACK response based on M, wherein when an uplink grant comprising a downlink assignment index (DAI) field indicating a pre-determined index value is received by the user equipment, M is replaced by the pre-determined index value of the DAI field for determining the ACK/NACK response.