Uplink Power Control for Overlapping Short TTIs
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Solution Overview
Problem
Current LTE communication systems experience latency due to the 8ms round trip delay in Hybrid Automatic Repeat Request (HARQ) processes, which is caused by the 1ms minimum Transmission Time Interval (TTI) for uplink transmissions, leading to delayed transmission and reception of communication signals.
Innovation Solution
The implementation of a method and apparatus that allows for shorter minimum Transmit Time Intervals (TTIs), such as 0.5ms or ~140us, to reduce latency by enabling User Equipment (UE) to transmit data using shortened Physical Uplink Shared Channels (PUSCH) scheduled over Physical Resource Blocks (PRBs) spanning fewer SC-FDMA symbols, and configuring UEs to operate in a shortened TTI mode to overlap transmissions in time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the minimum Transmission Time Interval (TTI) is set to 1ms for uplink transmissions, then the system maintains compatibility with current LTE standards and ensures reliable power control, but the HARQ round trip delay becomes 8ms causing transmission latency
Solution Approach 1:
The patent segments the TTI into shorter durations (e.g., 0.5ms or ~140us) to reduce the HARQ round trip delay. By dividing the transmission time into smaller intervals, the system achieves faster retransmission cycles while maintaining power control through separate parameter sets for different TTI lengths
Solution Approach 2:
The patent introduces dynamic adaptability by allowing the system to switch between different TTI lengths (1ms, 0.5ms, ~140us) based on traffic requirements. The power control parameters are dynamically adjusted according to the selected TTI length, enabling the system to optimize between latency and reliability
2Loss of time
If shorter TTIs (0.5ms or ~140us) are implemented to reduce latency, then the HARQ round trip delay decreases and transmission speed improves, but the system complexity increases due to overlapping transmissions and power control coordination
Solution Approach 1:
The patent applies different power control parameters locally to different TTI lengths and transmission types. By configuring separate power control parameter sets for each TTI length and transmission scenario, the system manages complexity through localized parameter management rather than system-wide complexity
Solution Approach 2:
The patent introduces an additional dimension of power control by adding a TTI length dimension to the power control parameter space. This allows the system to manage overlapping transmissions by controlling power across multiple dimensions (time, frequency, and TTI length)
3Productivity
If multiple uplink transmissions with different TTI lengths overlap in time, then resource utilization improves and latency is reduced, but determining appropriate transmission power becomes challenging due to conflicting power requirements
Solution Approach 1:
The patent changes the power control parameters based on the TTI length of each transmission. By associating different power control parameter sets with different TTI lengths, the system can determine appropriate transmission power for overlapping transmissions by selecting the parameters corresponding to each transmission's TTI length
Solution Approach 2:
The patent creates separate power control parameter copies for different TTI lengths and transmission types. This allows the system to maintain identical power control logic while using different parameter values for different transmission scenarios, simplifying the determination of transmission power for overlapping transmissions
Data Source
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AI summary
A method and apparatus schedule uplink transmissions with reduced latency. A first transmission power of a first uplink transmission can be determined (1030) at a device based on a first set of higher layer configured power control parameters associated with a first TTI length. The first uplink transmission can span the first TTI length. The first TTI length can include a first number of symbols. A second transmission power of a second uplink transmission can be determined (1040) based on a second set of higher layer configured power control parameters associated with a second TTI length. The second uplink transmission can span the second TTI length. The second TTI length can include a second number of symbols. The first uplink transmission can be transmitted (1050) in a subframe using the first transmission power. At least the second uplink transmission can be transmitted (1060) in the subframe using the second transmission power. The first uplink transmission and the second uplink transmission can overlap in time for at least one symbol duration.