Dual TTI Structure for Low Latency in TDD Wireless Systems
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Solution Overview
Problem
Current wireless communication systems using time division duplexing (TDD) face challenges in achieving low latency due to interruptions in service caused by subframes that support transmissions in a single direction, leading to increased latency in applications like voice calls, streaming media, and gaming.
Innovation Solution
Implementing a dual transmission time interval (TTI) structure on TDD configured carriers, with symbol-level TTIs organized within subframes for both uplink and downlink transmissions, and using guard periods to enable devices to transition between receiving and transmitting modes, while maintaining backwards compatibility with LTE numerology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional TDD subframe structure is used, then system compatibility and coverage are maintained, but latency increases due to single-direction transmission interruptions
Solution Approach 1:
The patent segments the traditional subframe into multiple transmission time intervals (TTIs) at the symbol level. Each TTI can be independently configured for uplink or downlink transmission, allowing finer-grained control over transmission direction and reducing the time lost due to single-direction constraints in traditional TDD subframes.
Solution Approach 2:
The patent implements dynamic TTI configuration where the direction (uplink or downlink) and duration of each TTI can be flexibly adjusted based on traffic requirements. This dynamic structure allows the system to adapt to varying latency demands without being constrained by fixed subframe boundaries, thereby reducing latency while managing complexity through structured flexibility.
2Loss of time
If shorter TTI structure is implemented, then latency is reduced, but system complexity and transition overhead increase
Solution Approach 1:
By segmenting the subframe into multiple symbol-level TTIs, the patent enables shorter transmission intervals without requiring a complete redesign of the frame structure. This segmentation allows gradual implementation and reduces transition overhead by maintaining compatibility with existing subframe-based scheduling while introducing finer-grained TTI control.
Solution Approach 2:
The patent prepares for short TTI operation by pre-configuring guard periods and reference signals at the symbol level within the subframe structure. This preliminary arrangement of resources ensures that when short TTIs are activated, the necessary transition overhead is already in place, reducing the complexity of real-time reconfiguration.
3Reliability
If guard periods are inserted for mode switching, then transmission reliability is improved, but transmission time and latency increase
Solution Approach 1:
The patent applies guard periods selectively only where mode switching occurs between uplink and downlink TTIs, rather than inserting them throughout the entire transmission structure. This localized application maintains transmission reliability at switching points while minimizing the overall time loss and latency impact in the system.
Solution Approach 2:
The patent uses partial guard periods that are just sufficient to enable reliable mode switching, rather than using full subframe-length guard periods. This partial action approach provides the necessary reliability for transition while significantly reducing the time overhead compared to traditional guard period implementations.
Data Source
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AI summary
Methods, systems, and devices for wireless communication are described. A wireless system utilizing one or more time-division duplexing (TDD) configured carriers may utilize a dual transmission time interval (TTI) structure (e.g., at the subframe level and symbol-level). The symbol level TTIs may be referred to as low latency (LL) TTIs, and may be organized within LL subframes. A LL subframe may be a subframe that is scheduled for transmissions in one direction (e.g., uplink or downlink, according to a TDD configuration) and may include multiple LL symbols scheduled for both uplink (UL) and downlink (DL) transmissions. Guard periods may be scheduled between adjacent LL symbols that have opposite directions of transmission to enable user equipment (UEs) to transition from receiving mode to transmit mode (or vice versa). The LL subframes may be transparent to receiving devices that do not support LL operations.