Variable TTI Length for NOMA User Terminals
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Solution Overview
Problem
In the context of future radio communication systems like 5G, existing communication schemes such as LTE struggle to achieve further increases in speed and capacity while reducing delay, especially when applying Non-Orthogonal Multiple Access (NOMA) to multiple user terminals with different channel conditions.
Innovation Solution
A radio communication method and system where user terminals receive downlink signals with varying cyclic prefix (CP) lengths, symbol lengths, and transmission time interval (TTI) lengths, allowing for dynamic and semi-static adjustments to optimize communication based on user terminal conditions, such as path loss and classification, to improve spectral efficiency and reduce interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If NOMA is applied to multiplex multiple user terminals in the power domain using existing LTE communication schemes, then spectral efficiency and capacity are improved, but delay reduction and speed increases are limited
Solution Approach 1:
The patent applies dynamics by making the TTI length variable rather than fixed. Different user terminals multiplexed in the power domain are assigned different TTI lengths according to their channel conditions - terminals with poor channel conditions receive longer TTIs for more robust transmission, while terminals with good channel conditions receive shorter TTIs for faster data transmission. This dynamic TTI allocation resolves the contradiction by enabling both multiple user multiplexing and high-speed transmission simultaneously.
Solution Approach 2:
The patent changes the TTI length parameter to resolve the contradiction. By varying the TTI length parameter across different user terminals multiplexed in the power domain, the system achieves both high capacity (through power-domain multiplexing) and high speed (through shortened TTIs for appropriate users). The parameter change enables the system to overcome the limitations of existing LTE schemes while maintaining NOMA's spectral efficiency benefits.
2Device complexity
If a single TTI length is used for all user terminals in power-domain multiplexing, then system complexity is reduced, but delay reduction and adaptation to different channel conditions are limited
Solution Approach 1:
The patent applies local quality by assigning different TTI lengths to different user terminals based on their specific channel conditions. Instead of using a uniform TTI length for all users, the system tailors the TTI parameter locally to each user's needs - terminals experiencing fading or poor channel conditions receive longer TTIs, while terminals with good channel conditions receive shorter TTIs. This local differentiation reduces delay for appropriate users without significantly increasing overall system complexity.
Solution Approach 2:
The patent makes the TTI length dynamic and adaptable to different user conditions. The base station determines appropriate TTI lengths for each user terminal based on reported channel state information, enabling the system to adapt quickly to changing conditions. This dynamic approach reduces communication delay for users who can support shorter TTIs while maintaining reliability for users who need longer TTIs, without requiring complex reconfiguration of the entire system.
3Ease of manufacture
If existing LTE communication schemes are used for power-domain multiplexing, then implementation simplicity is maintained, but further increases in speed and capacity are not achieved
Solution Approach 1:
The patent introduces a parameter change to existing LTE communication schemes by making the TTI length variable rather than fixed. This modification maintains implementation simplicity to some extent (as it builds on existing LTE infrastructure) while achieving further increases in system capacity and speed. The key change is allowing different TTI lengths for different users in the power domain, which can be implemented with moderate complexity increases over existing systems.
Solution Approach 2:
The patent adds dynamic TTI length adjustment capability to existing LTE schemes. By enabling the TTI parameter to change dynamically based on user conditions and system requirements, the system achieves higher capacity and speed without completely redesigning the underlying communication framework. This dynamic enhancement to existing LTE functionality provides a practical path forward that balances implementation simplicity with performance improvement.
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
To enable communication to be performed with a communication scheme suitable for the future radio communication system where a plurality of user terminals is multiplexed in the power domain, a user terminal of the present invention is provided with a reception section that receives a downlink (DL) signal to the user terminal, and a decoding section that decodes the DL signal to the user terminal, where at least one of a cyclic prefix (CP) length, symbol length and transmission time interval (TTI) length is different between the DL signal to the user terminal and a DL signal to another user terminal multiplexed in the power domain.