Shortened TTI Control Channel Allocation for Reduced Latency
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Solution Overview
Problem
In next-generation mobile communication systems, particularly in LTE Rel.13 and beyond, there is a need for reduced communication latency to support high-frequency band communications such as IoT, MTC, D2D, and V2V, where existing systems lack a method to effectively control signal transmission and reception with shortened Transmission Time Intervals (TTIs) less than 1 ms.
Innovation Solution
A user terminal and radio base station configuration that allows for the implementation of shortened TTI, where the TTI length is reduced to 0.5 ms, 0.25 ms, or even shorter, while maintaining compatibility with the existing 1 ms TTI, by adjusting subcarrier spacing and configuring the number of OFDM or SC-FDMA symbols, and allocating L1/L2 control channels differently for each TTI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the TTI length is reduced to less than 1 ms to reduce communication latency, then the communication speed and responsiveness are improved, but the system complexity and difficulty of controlling signal transmission increase
Solution Approach 1:
The patent applies parameter changes by adjusting the TTI length from the standard 1 ms to shorter durations (e.g., 0.5 ms or less) to reduce communication latency. This involves modifying fundamental system parameters including TTI duration, subcarrier spacing, and the number of OFDM/SC-FDMA symbols to achieve faster communication while managing system complexity through coordinated parameter adjustment.
2Speed
If the TTI length is reduced to less than 1 ms to increase communication speed, then the data transmission rate is improved, but the control method for signal transmission becomes more difficult
Solution Approach 1:
The patent applies dynamics by making the system adaptable to different TTI lengths through dynamic configuration. The base station can flexibly adjust and notify user terminals of varying TTI durations, subcarrier spacings, and symbol counts based on communication conditions, enabling the system to optimize for speed when needed while maintaining control through adaptive rather than fixed parameters.
3Measurement precision
If different L1/L2 control channels are allocated for each TTI to manage shortened TTI communication, then the communication control accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the control channel allocation into TTI-specific assignments. Different L1/L2 control channels are allocated for each TTI duration type, allowing precise control of shortened TTIs while maintaining separate control mechanisms. This segmentation enables accurate control of individual TTIs while organizing complexity into manageable, distinct control structures rather than a monolithic system.
Data Source
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Figure 3A~3B
AI summary
To appropriately communicate even when a shortened TTI is applied. A user terminal that communicates using a first Transmission Time Interval (TTI) and a second TTI whose TTI length is shorter than a TTI length of the first TTI, includes a receiving section that receives an L1/L2 control channel transmitted from a radio base station, and a control section that controls receiving of a first L1/L2 control channel transmitted for each first TTI and a second L1/L2 control channel transmitted at the second TTI.