Short TTI Scheduling in FDD Wireless Systems
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Solution Overview
Problem
Current LTE systems face limitations in reducing latency and increasing system capacity due to the fixed one millisecond (ms) Transmission Time Interval (TTI) in Frequency-Division Duplexing (FDD) communication systems, which restricts faster scheduling and higher throughput.
Innovation Solution
The method involves transmitting downlink control information in multiple TTIs to schedule uplink data in corresponding uplink TTIs, allowing for flexible TTI scheduling even when there is a mismatch between downlink and uplink TTIs, and utilizing special TTIs for demodulation reference signals or sounding reference signals to optimize data transmission and feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a fixed one millisecond TTI is used in LTE FDD systems, then system stability and compatibility are maintained, but latency reduction and throughput enhancement are limited
Solution Approach 1:
The patent implements dynamic TTI configuration where the base station can flexibly adjust TTI length based on channel conditions and traffic requirements. The system transitions from fixed 1ms TTI to variable TTI lengths (including shorter TTIs), enabling adaptive time scheduling that reduces latency when needed while maintaining stability during normal operation. This dynamic adjustment resolves the contradiction by making TTI duration changeable rather than static.
Solution Approach 2:
The invention changes the TTI parameter from a fixed value (1ms) to a variable parameter that can be adjusted according to system requirements. By introducing configurable TTI lengths and flexible scheduling parameters, the system can optimize for low latency scenarios without completely abandoning the stable fixed-TTI operation mode, thus resolving the trade-off between latency reduction and system stability.
2Loss of time
If downlink control information schedules uplink data in the same uplink subframe, then scheduling latency is reduced, but resource allocation complexity increases due to TTI mismatch between downlink and uplink
Solution Approach 1:
The patent segments the scheduling process into distinct phases with separate handling for downlink and uplink TTIs. When TTI mismatch occurs between downlink and uplink, the system divides resource allocation into multiple stages, allowing flexible mapping of downlink control information to uplink data transmissions without requiring complete reconfiguration of the scheduling architecture. This segmentation reduces the overall complexity burden.
Solution Approach 2:
The invention creates a universal scheduling framework that can handle both matched and mismatched TTI scenarios through a unified resource allocation mechanism. The base station employs multi-functional scheduling capabilities that adapt to different TTI configurations, reducing the need for separate complex scheduling algorithms for each scenario and thereby managing complexity while enabling low-latency scheduling.
3Manufacturing precision
If special TTIs are allocated for demodulation reference signals or sounding reference signals, then data transmission optimization is achieved, but available resources for user data are reduced
Solution Approach 1:
The patent implements partial allocation of special TTIs for reference signals rather than dedicating entire subframes. By using only necessary portions of time-frequency resources for demodulation and sounding reference signals, the system maintains adequate transmission quality while preserving more resources for user data. This partial action approach optimizes the trade-off between signal quality and resource availability.
Solution Approach 2:
The invention employs periodic allocation of reference signal TTIs rather than continuous reservation, allowing systematic alternation between reference signal transmission and data transmission. This periodic structure ensures adequate channel estimation quality while maximizing overall data transmission opportunities, resolving the contradiction between transmission quality and resource quantity.
Data Source
AI summary
Embodiments of the present disclosure relates to the communication processes in a FDD wireless communication system based on short TTIs. According to one embodiment of the present disclosure, there provide a method for communication by a base station. The method comprise: transmitting, to a user equipment, downlink control information in a downlink TTI of a mth downlink subframe which supports two or more downlink TTIs; and receiving, from the user equipment, uplink data scheduled by the downlink control information carried in a mth or (m+1)th uplink subframe which supports two or more uplink TTIs. The downlink control information transmitted in at least one of downlink TTIs supported by downlink subframes is arranged to schedule uplink data transmission in at least two of uplink TTIs supported by uplink subframes. In the other aspects of the present disclosure, there also provides methods for communication by a user equipment and corresponding apparatuses.