HARQ Timing Adjustment for Low Latency Wireless Communication
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Solution Overview
Problem
In wireless communication systems, low latency operations using reduced transmission time intervals (TTIs) can lead to insufficient processing time for user equipment (UEs) with large propagation delays, especially when frequency multiplexing different UEs within an uplink subframe, causing interference and requiring dynamic adjustment of hybrid automatic repeat request (HARQ) timing.
Innovation Solution
Implementing UE-specific uplink timing advance (TA) to align reception times at the base station, allowing for different TA commands or loops based on propagation delays and processing capabilities, and enabling explicit or implicit TA indications to adjust HARQ timing, along with fallback operations and default timing settings for synchronization loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If reduced transmission time interval (TTI) is used for low latency operation, then latency is reduced, but processing time for UE becomes insufficient
Solution Approach 1:
The patent implements dynamic HARQ timing adjustment where the timing between downlink data transmission and HARQ-ACK feedback is adapted based on UE-specific conditions. The base station configures different HARQ timing values for different UEs depending on their propagation delay and processing capability, allowing the system to maintain low latency for capable UEs while providing sufficient processing time for UEs with large propagation delays.
Solution Approach 2:
The patent changes the HARQ timing parameter dynamically based on UE conditions. Specifically, it adjusts the timing offset between downlink data reception and HARQ-ACK transmission based on the UE's timing advance value and processing capability. This parameter adaptation resolves the contradiction by allowing short HARQ timing for low latency when conditions permit, and extended timing when processing time is insufficient.
2Loss of time
If reduced HARQ timing is applied, then latency is reduced, but interference occurs when frequency multiplexing different UEs
Solution Approach 1:
The patent applies UE-specific HARQ timing configuration where each UE receives individualized timing settings based on its propagation delay and processing capability. Instead of using a uniform reduced HARQ timing for all UEs, the system tailors the timing parameter to each UE's local conditions, thereby maintaining low latency where possible while avoiding uplink interference through proper timing alignment at the base station.
Solution Approach 2:
The patent segments the HARQ timing configuration into UE-specific groups based on their timing advance values and processing capabilities. By dividing UEs into different timing categories and assigning appropriate HARQ timing values to each group, the system achieves both low latency performance and interference avoidance through frequency multiplexing.
3Reliability
If UE-specific timing advance is implemented, then synchronization is improved, but device complexity increases
Solution Approach 1:
The patent implements a mechanism where the UE autonomously determines its processing capability and reports it to the base station. The base station then uses this information along with the timing advance value to configure appropriate HARQ timing. This self-service approach improves synchronization reliability while minimizing the complexity burden on the UE by leveraging its own capability information rather than requiring complex centralized management.
Data Source
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AI summary
Methods, systems, and devices for wireless communication are described. A user equipment (UE) or a base station may identify a timing advance parameter and a processing parameter for the UE, and one or both may determine a hybrid automatic repeat request (HARQ) timing based on the identified parameters. For example, if the UE has a large timing advance or reduced processing capacity, a longer HARQ timing may be chosen. When the UE receives downlink (DL) transmissions from the base station, the UE may send an acknowledgement (ACK) or negative acknowledgement (NACK) based on the chosen HARQ timing. The base station may send a retransmission (in the case of a NACK) based on the HARQ timing. In some cases, the UE may request a specific HARQ timing, or request an updated timing advance. If HARQ synchronization is lost, the UE and the base station may default to a preconfigured HARQ timing.