Variable TTI Synchronous HARQ for Uplink Coverage and Delay

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Solution Overview

Problem

In LTE/LTE-A systems, user equipment at cell edges face uplink coverage issues due to short transmission time intervals (TTIs) and limited transmission power, leading to increased overhead and delay in VoIP services, and existing synchronous HARQ operations are inadequate for variable transmission times, causing collisions during retransmissions.

Innovation Solution

A method and apparatus for synchronous hybrid automatic repeat request (HARQ) that allocates variable transmission times per HARQ process without separate control signals, using resource allocation information with a duration field to manage HARQ errors and adjust HARQ round trip time (RTT) based on energy detection and feedback, ensuring successful data transmission and preventing collisions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If TTI bundling is applied with fixed bundling size, then uplink coverage is improved for VoIP traffic, but transmission delay increases and overhead increases

Engineering Contradiction:

Improveuplink coverageVSAvoidtransmission delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies dynamics by making the TTI bundling size variable rather than fixed. The base station determines the bundling size adaptively based on channel conditions, transmission power, and traffic requirements, allowing the system to optimize between coverage and delay dynamically. This resolves the contradiction by enabling the system to use larger bundling sizes when coverage is the priority and smaller sizes when delay is the priority.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of bundling size from a fixed value to a variable parameter that can be adjusted based on system conditions. By introducing variable bundling sizes (e.g., 2, 4, 6, 8 TTIs) instead of a fixed size, the system can adapt to different channel conditions and traffic types, thereby improving both coverage and reducing delay as needed.

Inventive Principle:

Principle #35Parameter changes

2Loss of time

If variable transmission time is allocated per HARQ process, then transmission delay is reduced, but collisions between HARQ processes occur during retransmission

Engineering Contradiction:

Improvetransmission delayVSAvoidHARQ process collision

Core Design Contradiction:

Loss of timeVSReliability

Solution Approach 1:

The patent applies feedback by having the base station monitor the status of each HARQ process and provide feedback to coordinate retransmissions. When variable transmission times are allocated, the base station tracks which processes are in retransmission phase and schedules them to avoid collisions, using feedback loops to maintain synchronization and prevent conflicts between simultaneous retransmissions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent applies preliminary action by having the base station pre-coordinate retransmission schedules before collisions can occur. When allocating variable transmission times to different HARQ processes, the base station proactively schedules retransmissions to occur at non-conflicting times, preventing collisions before they happen rather than reacting to them afterward.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If synchronous HARQ operation uses fixed HARQ RTT, then process distinction is simplified, but adaptability to variable transmission times is reduced

Engineering Contradiction:

Improveprocess distinction complexityVSAvoidadaptability to variable TTI

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent applies dynamics by making the HARQ RTT variable rather than fixed. The system dynamically adjusts the RTT based on the allocated transmission time for each HARQ process, allowing the synchronous HARQ operation to adapt to variable TTI allocations while maintaining process distinction through the dynamic RTT values.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies universality by creating a HARQ RTT mechanism that serves multiple functions: it maintains process distinction like fixed RTT does, but also adapts to variable transmission times. The variable RTT system can handle both fixed and variable TTI scenarios, making the HARQ operation universally applicable to different transmission conditions without requiring separate mechanisms.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS10142953B2Method and apparatus for performing synchronous HARQ operation according to variable TTI allocation

Publication Date: 2018.11.27 ELECTRONICS & TELECOMM RES INST

AI summary

Provided are a method and an apparatus for performing a synchronous hybrid automatic repeat reQuest (HARQ). When a variable transmission time allocation is allocated per HARQ process, resource allocation information including a duration field corresponding to a length of a transmission time interval (TTI) allocated to each of the HARQ processes is transmitted. After the resource allocation information is transmitted, it is determined whether an HARQ error occurs at a predetermined timing and if it is determined whether the HARQ error occurs, the HARQ error is handled.