TTI Bundling Collision Avoidance in LTE VoIP HARQ
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Solution Overview
Problem
In wireless access systems, bundling Transmission Time Intervals (TTIs) according to the 4-TTI technique in the 3GPP LTE/LTE-Advanced system can lead to collisions with new Voice over Internet Protocol (VoIP) packets during the Hybrid Automatic Repeat and reQuest (HARQ) process, limiting VoIP service coverage.
Innovation Solution
The method involves improving TTI bundling to prevent collisions by allowing automatic retransmissions in non-reserved subframes and adjusting the PHICH period, enabling flexible TTI bundle sizes, and using different cyclic shift values for new VoIP packets to distinguish them from HARQ retransmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If 4-TTI bundling is used to reduce transmission error probability, then VoIP performance is improved, but collision with new VoIP packets occurs in HARQ process
Solution Approach 1:
The patent segments the TTI bundling process into distinct phases: initial transmission phase using 4-TTI bundling for reliability, and subsequent retransmission phase using dynamic TTI selection. This segmentation allows the system to achieve both high reliability through bundled transmission and high efficiency by avoiding collisions in later retransmissions through adaptive resource allocation.
Solution Approach 2:
The patent introduces dynamic TTI bundling where the number of TTIs used for retransmission is adjusted based on channel conditions and collision detection. The system dynamically selects between using reserved subframes or non-reserved subframes for retransmission, allowing adaptive optimization of both reliability and productivity based on real-time system state.
2Area of stationary object
If more TTIs are bundled to increase transmitted energy per information bit, then coverage is improved, but collision with new VoIP packets increases
Solution Approach 1:
The patent reserves specific subframes in advance for HARQ retransmissions, creating a predetermined structure that prevents collisions with new VoIP packets. By pre-allocating resources for retransmission purposes, the system ensures that extended TTI bundling for coverage enhancement does not lead to resource conflicts, thereby maintaining both coverage and throughput.
Solution Approach 2:
The patent changes the TTI bundling parameter dynamically based on system conditions. For initial transmissions, a larger number of TTIs is used to maximize coverage, while for retransmissions, the system adjusts the TTI count and selects appropriate subframes to avoid collisions. This parameter adaptation allows the system to achieve coverage enhancement without sacrificing productivity.
3Productivity
If TTI bundling is extended to prevent collisions, then resource allocation flexibility is reduced, but system complexity increases
Solution Approach 1:
The patent implements periodic TTI bundling patterns where reserved subframes occur at regular intervals for HARQ retransmissions. This periodic structure provides predictable resource allocation that maintains flexibility while reducing the complexity of collision avoidance, as the system follows a established rhythm rather than requiring complex real-time decisions for each transmission.
Data Source
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AI summary
The present invention relates to a transmission time interval (TTI) bundling method in wireless access systems and to an apparatus for same. In particular, the TTI bundling method includes the following steps: a terminal receives information indicating the bundling size value from a base station; the terminal automatically re-transmits packets through a predetermined number of TTIs following four TTIs without the reception of Acknowledgement/Negative-ACK (ACK/NACK) information for the packets from the base station; the terminal receives the ACK/NACK information for the packets from the base station; and the terminal retransmits packets in a Hybrid Automatic Repeat and Request (HARQ) scheme when receiving the NACK, wherein the predetermined number of TTIs is determined according to the bundling size value.