HARQ Timing Adjustment for Flexible TTI Lengths
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Solution Overview
Problem
The existing HARQ timing relationship in LTE/LTE-A systems is not adaptable to further reduction in TTI length, which is necessary for supporting low-delay services in 5G systems, particularly in scenarios where TTIs of different lengths are required for downlink and uplink data transmission.
Innovation Solution
A method and device for adjusting HARQ timing by transmitting ACK or NACK responses within a kth TTI after a second target TTI, where the number of symbols in TTIs for downlink or uplink data transmission can be configured to meet specific conditions, allowing for flexible TTI lengths and supporting low-delay services.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If TTI length is reduced to support low-delay services, then transmission delay is reduced, but existing HARQ timing relationship becomes inapplicable
Solution Approach 1:
The patent applies dynamics by making the HARQ timing relationship flexible and adaptable to different TTI lengths. Instead of a fixed timing relationship, the system dynamically adjusts the timing based on the actual TTI configuration, allowing the same HARQ mechanism to work with both long and short TTIs. This is achieved by defining timing relationships in terms of TTI indices rather than fixed time intervals, enabling the system to adapt to varying transmission time requirements.
Solution Approach 2:
The patent changes the parameter representation of HARQ timing from fixed time intervals to TTI-based indexing. By expressing timing relationships as offsets in TTI indices (e.g., uplink TTI index = downlink TTI index + k), the system can maintain consistent timing logic across different TTI lengths. This parameter transformation allows the HARQ mechanism to remain applicable regardless of whether TTIs are long or short, resolving the contradiction between delay reduction and timing relationship validity.
2Adaptability or versatility
If different TTI lengths are used for downlink and uplink transmission, then flexibility for low-delay services is improved, but timing relationship configuration becomes complex
Solution Approach 1:
The patent achieves universality by creating a unified timing relationship framework that works for both equal and different downlink/uplink TTI lengths. The same basic formula (uplink TTI index = downlink TTI index + k) applies regardless of whether the TTI lengths are equal or different. This universal approach simplifies configuration compared to having separate timing rules for different scenarios, as the system automatically adapts to the specific TTI length configuration through the indexing mechanism.
3Speed
If TTI length is shortened from 1 ms to fewer OFDM symbols, then transmission speed increases, but processing time constraints become tighter
Solution Approach 1:
The patent applies segmentation by dividing the transmission timeline into discrete TTI units with specific indexing. This segmentation allows the system to manage processing time constraints by clearly defining when each processing stage must complete relative to TTI boundaries. The indexed timing relationship ensures that even with shorter TTIs, there is sufficient processing time allocated within each TTI cycle, as the timing offsets are configured to account for the reduced duration while maintaining adequate margins for decoding and feedback preparation.
Data Source
AI summary
Provided are a hybrid automatic repeat request timing method and apparatus. The method comprises: in the case where a device detects physical shared channel transmission within a first target transmission time interval (TTI), the device transmitting an acknowledgement instruction (ACK) response or a negative acknowledgement instruction (NACK) response of a hybrid automatic repeat request (HARQ) of a corresponding physical shared channel within the (pre-set number)th TTI after a second target TTI, wherein the number of symbols L1 contained in a TTI for downlink data transmission and the number of symbols L2 contained in a TTI for uplink data transmission satisfy the following condition: LI∈{1, 2, 3, 4, 5, 6, 7}, I=1 or 2. According to the embodiments of the present invention, the problem in the relevant art that an HARQ timing relationship cannot satisfy the further shortening of a TTI length is solved.