Uplink Control Signaling Mapping on Shortened TTI PUSCH
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Solution Overview
Problem
Current LTE systems face challenges in reducing packet latency due to fixed transmission time intervals (TTIs) in SC-FDMA, which limits the efficiency of uplink control information (UCI) transmission, especially with shorter TTIs where some SC-FDMA symbols become unavailable, affecting HARQ ACK/NACK decoding accuracy.
Innovation Solution
The proposed solution involves dynamic mapping of HARQ ACK/NACK data to either earlier or later SC-FDMA symbols relative to user data, based on whether the DMRS is transmitted before or after the data, ensuring accurate decoding by positioning HARQ ACK/NACK close to the most recent DMRS, even in varying channel conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If shorter TTIs are used to reduce packet latency, then latency is improved, but the number of available SC-FDMA symbols for control information transmission is reduced
Solution Approach 1:
The patent implements dynamic TTI length adjustment, allowing the system to switch between short and long TTI configurations based on channel conditions and traffic requirements. This enables the system to use shorter TTIs when low latency is critical while falling back to longer TTIs when more symbols are needed for reliable control information transmission.
Solution Approach 2:
The patent changes the parameter of TTI duration from a fixed value to a variable parameter that can be dynamically adjusted. By modifying the TTI length parameter, the system can optimize the balance between latency reduction and control information transmission reliability according to current network conditions.
2Productivity
If HARQ ACK/NACK is mapped to SC-FDMA symbols farther from DMRS in short TTI configurations, then more symbols are available for data transmission, but decoding accuracy deteriorates
Solution Approach 1:
The patent applies different mapping strategies for different control information types and different TTI configurations. For short TTIs, HARQ ACK/NACK is mapped to symbols closest to DMRS to ensure high decoding accuracy, while other control information may be mapped to different symbol positions. This localized optimization ensures critical control information maintains high reliability even in compressed time intervals.
Solution Approach 2:
The patent implements dynamic mapping position selection that adapts to the specific TTI configuration and channel conditions. The mapping algorithm dynamically determines the optimal symbol position for HARQ ACK/NACK based on the distance to DMRS and the available symbol resources, rather than using a fixed mapping rule.
3Device complexity
If a fixed TTI structure is used, then system simplicity is maintained, but adaptability to different latency requirements is reduced
Solution Approach 1:
The patent transforms the fixed TTI structure into a dynamic one that can adapt to different latency requirements. The system maintains a set of predefined TTI configurations with different lengths and symbol allocations, and dynamically selects the appropriate configuration based on current traffic conditions and QoS requirements, thereby achieving adaptability without excessive complexity.
Solution Approach 2:
The patent designs a universal TTI framework that can support multiple TTI lengths and configurations within a single system. This multi-functional TTI structure allows the same physical layer framework to handle both low-latency applications and traditional traffic patterns, eliminating the need for separate systems for different service types.
Data Source
AI summary
According to an aspect, a transmitting device determines, for each of a plurality of transmissions, whether user data to be transmitted within a time transmission interval, TTT, will be closest in time to a DMRS transmitted before the user data or after the user data. If before the user data, all HARQ ACK/NACK data for the transmission is mapped to the earliest in time SC-FDMA symbol carrying user data in the transmission, and to pre-DFT symbols closest in time to the DMRS transmitted before the user data. If after the user data, all HARQ ACK/NACK data for the transmission is mapped to the last in time SC-FDMA symbol carrying user data in the transmission, and to pre-DFT symbols closest in time to the DMRS transmitted after the user data. SC-FDMA signals are formed from user data and control information for the transmission, based on the mapping.