Downlink Control Channel Separation for ACK/NACK Latency Reduction
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Solution Overview
Problem
Current wireless communication systems face latency issues due to the time required to process ACK/NACK signals, which delays retransmissions in case of data transmission failures, leading to increased latency and reduced efficiency.
Innovation Solution
The system relaxes the time constraints on processing ACK/NACK signals by separating control data related to the type of data to be sent in the next subframe from the rest of the control data, allowing the base station to continue processing the ACK/NACK signal while transmitting other control data, and then transmitting the remaining control data to inform the UE whether to receive new data or retransmit old data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the base station waits to process ACK/NACK signals before transmitting control data for the next TTI, then the processing accuracy is improved, but the latency increases and retransmission efficiency deteriorates
Solution Approach 1:
The base station transmits control data for the next TTI in advance, before the ACK/NACK signal processing is complete. This preliminary transmission of control data (without DDI) allows the system to prepare for the next transmission interval without waiting for ACK/NACK processing to finish, thereby reducing latency while maintaining processing accuracy through subsequent DDI transmission.
Solution Approach 2:
The control data transmission is segmented into two parts: first, control data without DDI is transmitted in the next TTI before ACK/NACK processing completes; second, the DDI is transmitted separately after ACK/NACK processing is complete. This segmentation allows the system to reduce latency while ensuring accurate retransmission decisions based on processed ACK/NACK signals.
2Speed
If the base station transmits control data immediately in the next TTI without waiting for ACK/NACK processing, then latency is reduced, but the ability to make accurate retransmission decisions deteriorates
Solution Approach 1:
Control data is segmented into two transmissions: first, control data without DDI is transmitted immediately in the next TTI to enable fast retransmission preparation; second, the DDI is transmitted separately after ACK/NACK processing completes to ensure accurate retransmission decisions. This segmentation maintains both speed and reliability.
Solution Approach 2:
The DDI acts as an intermediary that bridges the gap between premature control data transmission and delayed ACK/NACK processing. By transmitting DDI separately after processing completes, the system ensures that the control data received by the UE is updated with accurate retransmission information, maintaining reliability while enabling early transmission preparation.
3Reliability
If multiple TTIs are allocated for ACK/NACK decoding, then processing reliability is improved, but the overall system productivity deteriorates due to increased latency
Solution Approach 1:
The base station performs preliminary transmission of control data (without DDI) in the next TTI while ACK/NACK processing continues. This allows the system to maintain decoding reliability over multiple TTIs while improving productivity by preparing control data in advance, reducing the overall impact of processing time on throughput.
Solution Approach 2:
The system maintains continuous useful action by transmitting control data in the next TTI without waiting for ACK/NACK processing to complete. This continuous transmission preparation keeps the system productive while the DDI is added later to ensure reliable retransmission decisions, thereby maintaining both decoding reliability and system productivity.
Data Source
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AI summary
Systems and methods are disclosed for minimizing latency between receipt of a NACK at a base station from a user equipment (UE) and retransmission of data to the UE. Time constraints for processing the ACK/NACK are relaxed so the base station can decode the ACK/NACK to determine whether a NACK has been received and then prepare for transmission of the appropriate data to the UE in the immediately following transmission time interval (TTI). These constraints are relaxed by separating download data indicator (DDI) from the PDCCH control data and delaying transmission of the DDI until decoding of the ACK/NACK.