Short TTI Scheduling for Low-Latency LTE Uplink Transmission
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Solution Overview
Problem
Current LTE systems face limitations in reducing latency beyond the 14-symbol transmission time interval (TTI), which is inadequate for ultra-reliable and low-latency communications (URLLC) requiring even shorter transmission times.
Innovation Solution
Implementing short TTI (sTTI) operation by subdividing the legacy LTE subframe into shorter intervals of 2 or 7 OFDM symbols, allowing dynamic scheduling and transmission of data via short PDSCH (sPDSCH) in downlink and short PUSCH (sPUSCH) in uplink, with control information transmitted via short PUCCH (sPUCCH), and enabling devices to request resources based on logical channel maximum TTI values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the standard TTI of 14 OFDM symbols is used for transmission, then the system maintains compatibility with legacy LTE infrastructure and ensures stable scheduling, but the latency requirement for ultra-reliable and low-latency communications (URLLC) cannot be met
Solution Approach 1:
The patent divides the standard 14-symbol TTI into shorter sTTI units (2 or 7 symbols), enabling granular transmission time control. This segmentation allows the system to select appropriate TTI lengths based on service requirements, achieving low latency for URLLC while maintaining legacy compatibility for other services.
Solution Approach 2:
The patent introduces dynamic TTI length adjustment, where the TTI can be configured as either standard length or short length based on the service type. This dynamic adaptation enables the system to optimize latency for URLLC traffic while maintaining standard operation for other services, resolving the contradiction between reliability and time loss.
2Loss of time
If short TTI (2 or 7 symbols) is used for transmission, then latency is reduced for urgent data, but the system complexity increases due to multiple TTI configurations and scheduling mechanisms
Solution Approach 1:
The patent changes the TTI parameter from a fixed 14 symbols to configurable values (2 or 7 symbols for sTTI, 14 symbols for standard TTI). This parameter adjustment enables latency reduction while the network configures appropriate TTI lengths based on service requirements, managing complexity through standardized configuration options.
Solution Approach 2:
The patent creates a universal scheduling framework that handles both standard TTI and sTTI through common logical channel prioritization mechanisms. The LCP framework universally applies to different TTI types, allowing the system to manage multiple TTI configurations without proportionally increasing complexity, as the same prioritization logic serves multiple transmission modes.
3Adaptability or versatility
If logical channel prioritization with LCP values is used for scheduling, then different services with different latency requirements can be multiplexed, but transmissions are still constrained to the minimum 14-symbol TTI length
Solution Approach 1:
The patent segments the 14-symbol TTI into shorter sTTI units and associates them with specific logical channels based on latency requirements. High-priority logical channels (e.g., URLLC) are mapped to sTTI while lower-priority channels use standard TTI, enabling service multiplexing with differentiated transmission lengths that overcome the minimum 14-symbol constraint.
Solution Approach 2:
The patent applies different TTI lengths to different logical channels based on their specific latency requirements. Rather than using a uniform TTI length for all channels, the system assigns short TTI to latency-critical channels and standard TTI to other channels, creating local optimization that maintains versatility while reducing transmission time for urgent data.
Data Source
AI summary
A terminal device for a wireless communication network is configurable with a plurality of transmission time intervals. An example method comprises: receiving a grant message comprising an indication of radio resources in which the terminal device can transmit one or more wireless messages, the radio resources being configured according to a first transmission time interval of the plurality of transmission time intervals; determining the presence of data to transmit, the data being associated with a logical channel; determining a maximum transmission time interval associated with the logical channel; and, responsive to a determination that the maximum transmission time interval associated with the logical channel is less than the first transmission time interval, transmitting a scheduling request message. The scheduling request message is configured according to a second transmission time interval of the plurality of transmission time intervals, shorter than the first.