ACK/NACK Transmission in Carrier Aggregation via DAI Piggybacking
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Solution Overview
Problem
In carrier aggregation systems, there are challenges in synchronizing the timing of acknowledgement (ACK)/non-acknowledgement (NACK) transmissions across different cells, leading to potential errors due to the mismatch in timing between downlink and uplink subframes, especially when aggregating cells with different frame structures like TDD and FDD.
Innovation Solution
A method for transmitting ACK/NACK in a carrier aggregation system involves receiving an uplink grant in a subframe n-k1 of a first serving cell, detecting a second PDSCH in a subframe n-k2 of a second serving cell, and transmitting ACK/NACK information through a physical uplink shared channel (PUSCH) based on the uplink allocation, using piggyback information that includes a downlink assignment index (DAI) to ensure accurate feedback across multiple cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carrier aggregation is used to increase bandwidth and data rate, then system capacity and throughput are improved, but timing synchronization between ACK/NACK transmission and PDSCH reception across different cells becomes difficult to maintain
Solution Approach 1:
The downlink assignment index (DAI) is included in the uplink grant message in advance, before the actual PDSCH reception and ACK/NACK generation. This preliminary information allows the terminal to pre-know the expected number of PDSCHs, enabling it to correctly generate and transmit ACK/NACK information even when timing relationships vary across aggregated cells with different frame structures (TDD/FDD)
Solution Approach 2:
The DAI acts as an intermediary parameter that bridges the timing mismatch between downlink PDSCH receptions and uplink ACK/NACK transmissions. By using the DAI to indicate the number of scheduled PDSCHs, the system mediates the timing synchronization issue across cells with different frame structures, allowing the terminal to correctly associate ACK/NACK feedback with the corresponding PDSCHs
2Adaptability or versatility
If cells with different frame structures (TDD and FDD) are aggregated, then system flexibility and bandwidth utilization are improved, but timing mismatch between downlink and uplink subframes increases
Solution Approach 1:
The system changes the parameter representation by introducing the DAI counter that tracks the number of scheduled PDSCHs across different cells and time instances. This parameter change allows the terminal to adapt to varying timing relationships between downlink and uplink subframes when aggregating cells with different frame structures, as the DAI provides a reference that is independent of the specific timing relationship
Data Source
AI summary
Provided are a method and an apparatus for transmitting acknowledgement/non-acknowledgement (ACK/NACK) of a terminal in a carrier wave aggregation system. The method comprises: receiving a UL grant by a subframe n−k1 of a first serving cell, wherein the UL grant comprises uplink allocation and piggyback information, wherein the piggyback information indicates the number of first physical downlink shared channels (PDSCHs) scheduled before the subframe n−k1; attempting a detection of a second PDSCH by a subframe n−k2 of a second serving cell; and transmitting an uplink transmission block and ACK/NACK information through a physical uplink shared channel (PUSCH) on the basis of the uplink allocation by subframe n, wherein n, k1 and k2 are constants, k1>k2, and the ACK/NACK information may comprise a first ACK/NACK according to the piggyback information, and a second ACK/NACK corresponding to the detected second PDSCH.