Repeated Msg4 Downlink Reception for NTN Coverage Extension

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Solution Overview

Problem

In satellite communication environments, significant signal propagation loss and low received Signal-to-Noise Ratio (SNR) hinder downlink coverage, making it difficult to achieve the required coverage using existing 3GPP standard technologies, especially for downlink channels like Msg4 in Non-Terrestrial Networks (NTN), where output power restrictions further complicate the issue.

Innovation Solution

Implementing a repeated Msg4 transmission function in the downlink, allowing terminals to receive the message multiple times based on configuration information, with flexibility in repetition factors and resource allocation, to improve reception quality and extend coverage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If output power restrictions are applied to satellite transmissions, then interference with terrestrial systems is prevented, but downlink coverage and received SNR deteriorate

Engineering Contradiction:

Improveinterference with terrestrial systemsVSAvoiddownlink coverage

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The Msg4 transmission is segmented into multiple repeated transmissions instead of a single transmission. The base station transmits Msg4 multiple times with different redundancy versions, allowing the terminal to combine these segments to achieve the required reception quality while maintaining power restrictions that prevent terrestrial interference.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Msg4 is transmitted periodically multiple times rather than once. The repeated transmissions occur at regular intervals, giving the terminal multiple opportunities to receive and combine the signals, thereby improving downlink coverage without increasing the power of individual transmissions beyond regulatory limits.

Inventive Principle:

Principle #19Periodic action

2Reliability

If repeated transmissions are increased for coverage enhancement, then received SNR improves, but radio resource consumption increases

Engineering Contradiction:

Improvereceived SNRVSAvoidradio resource consumption

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The system changes the parameter of redundancy version across repeated transmissions. Each repetition uses a different redundancy version (0, 2, 3, 1 in sequence), which provides diversity gain and improves reception reliability without requiring excessive repetitions, thus balancing SNR improvement with radio resource efficiency.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If Msg4 is transmitted only once as per 3GPP NR specifications, then radio resource efficiency is maintained, but initial access success rate deteriorates in poor channel conditions

Engineering Contradiction:

Improveradio resource efficiencyVSAvoidinitial access success rate

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The base station performs preliminary repeated transmissions of Msg4 before the terminal can confirm successful reception. By proactively transmitting multiple copies with different redundancy versions in advance, the system ensures that the terminal has sufficient opportunities to decode Msg4 successfully, thereby improving initial access success rate while maintaining reasonable radio resource efficiency.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS20260095953A1Apparatus and method for downlink coverage enhancement in communication network

Publication Date: 2026.04.02 ELECTRONICS & TELECOMM RES INST

AI summary

Disclosed are an apparatus and a method for downlink coverage enhancement in a communication network. A method of a terminal according to an exemplary embodiment may comprise: receiving repeated transmission configuration information for a message 4 (Msg4) from a base station; and receiving the Msg4 from the base station in a random access (RA) procedure between the terminal and the base station, the receiving comprising performing repeated reception of the Msg4 based on the repeated transmission configuration information.