Uplink Scheduling with Shortened TTI and HARQ-ACK PUCCH Resource Selection
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Solution Overview
Problem
Current LTE communication systems experience significant latency due to the 8ms round trip delay in Hybrid Automatic Repeat Request (HARQ) processes, which affects the transmission and reception of communication signals, particularly in uplink transmissions.
Innovation Solution
Implementing a method and apparatus for scheduling uplink transmissions using a shortened Transmit Time Interval (TTI) of less than 1ms, allowing User Equipment (UE) to transmit data more quickly and reducing the latency associated with HARQ retransmissions by configuring the UE to operate in a shortened TTI mode, which can be supported through various approaches including configuration by higher layers or modified Buffer Status Reports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a 1ms minimum TTI is used for uplink scheduling, then the system maintains compatibility with current LTE standards and ensures stable operation, but the HARQ round trip delay becomes 8ms resulting in significant transmission latency
Solution Approach 1:
The patent segments the 1ms TTI into multiple shorter transmission time intervals (e.g., 2 slots of 0.5ms each, or further into mini-slots). This segmentation allows the uplink transmission to be divided into smaller units, enabling the UE to transmit data more quickly and reducing the HARQ round trip delay from 8ms to 4ms or less, while maintaining compatibility with existing LTE infrastructure through gradual deployment
Solution Approach 2:
The patent implements preliminary action by having the UE transmit scheduling requests and buffer status reports more frequently within the shortened TTI framework. This allows the network to prepare uplink grants in advance, reducing the waiting time for uplink transmission opportunities and thereby reducing overall transmission latency while maintaining standard compliance
2Loss of time
If the TTI is shortened to reduce latency, then the HARQ round trip delay is reduced from 8ms to 4ms or less, but the device complexity increases due to the need for shortened TTI mode configuration and operation
Solution Approach 1:
The patent implements dynamic TTI length adjustment where the UE can switch between normal TTI mode and shortened TTI mode based on traffic conditions and network configuration. This dynamic approach allows the system to use shortened TTIs only when low latency is required, reducing device complexity by avoiding permanent configuration changes while still achieving latency reduction when needed
Solution Approach 2:
The patent changes the TTI duration parameter from the fixed 1ms value to variable shorter values (e.g., 0.5ms, 0.25ms) through higher layer configuration. This parameter change is implemented through existing RRC signaling mechanisms, avoiding the need for new hardware structures and thereby reducing the increase in device complexity while achieving the desired latency reduction
3Adaptability or versatility
If multiple PUCCH resources are allocated for different TTI lengths, then the system supports flexible TTI operation, but the control signaling overhead increases
Solution Approach 1:
The patent makes PUCCH resources universal by designing them to handle multiple TTI lengths and multiple downlink carriers simultaneously. A single PUCCH resource can carry HARQ-ACK feedback for both shortened TTI and normal TTI transmissions, as well as for multiple carriers through carrier aggregation. This multi-functionality reduces the number of separate PUCCH resources needed, thereby reducing control signaling overhead while maintaining flexibility
Solution Approach 2:
The patent merges the feedback mechanisms for different TTI lengths into a unified PUCCH transmission framework. Instead of maintaining separate PUCCH resources for shortened TTI and normal TTI, the system combines them into a single resource pool where HARQ-ACK bits for different TTI types are multiplexed together. This merging approach reduces control signaling overhead by eliminating redundant resource allocations while preserving the ability to support variable TTI lengths
Data Source
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AI summary
A method and apparatus schedule uplink transmissions with reduced latency. A first downlink transmission can be received (1010) at a device in a first downlink TTI of a first duration in a first downlink subframe. A second downlink transmission can be received (1020) in a second downlink TTI of a second duration in a second downlink subframe. The first downlink TTI and second downlink TTI may not overlap. A first HARQ-ACK feedback and a first HARQ-ACK PUCCH resource can be determined (1030) in response to receiving the first downlink transmission in the first downlink TTI. The first HARQ-ACK PUCCH resource can be mapped to REs in a first uplink TTI of a third duration in a first uplink subframe. A second HARQ-ACK feedback and a second HARQ-ACK PUCCH resource can be determined (1040) in response to receiving the second downlink transmission in the second downlink TTI. The second HARQ-ACK PUCCH resource can be mapped to REs in a second uplink TTI of a fourth duration in the first uplink subframe. The first UL TTI can include a temporal portion that overlaps the second UL TTI. The first HARQ-ACK PUCCH resource or the second HARQ-ACK PUCCH resource can be selected (1050) based on at least the determined second HARQ- ACK feedback. A signal can be transmitted (1060) in response to the determined first HARQ-ACK feedback and second HARQ-ACK feedback on the selected HARQ-ACK PUCCH resource on the overlapped portion of first uplink TTI and second uplink TTI in the first uplink subframe.