PRACH Preamble Transmission Timing for Collision Reduction

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Solution Overview

Problem

In LTE radio communications networks, the limited number of preamble sequences leads to preamble collisions and overhearing, which negatively impacts system performance and user experience, especially in scenarios requiring enhanced coverage and repeated PRACH transmissions.

Innovation Solution

A method and system where user equipment and network nodes determine a starting subframe for repeated preamble transmissions based on the system frame number, preamble repetition level, and random access channel configuration, ensuring a defined starting point for each transmission to avoid collisions and reduce overhearing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If preamble transmission is repeated to enhance coverage, then reliability is improved, but preamble collisions and overhearing increase

Engineering Contradiction:

Improvecoverage reliabilityVSAvoidpreamble collisions and overhearing

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The random access procedure is segmented into multiple independent preamble transmission attempts, each with its own starting subframe determined by a formula. This segmentation allows the system to maintain multiple transmission opportunities while reducing collisions through distributed timing

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The starting subframe is determined in advance using a deterministic formula based on system frame number, subframe number, and cell ID. This preliminary determination of transmission timing prevents collisions before they occur by ensuring unique starting points for different cells

Inventive Principle:

Principle #10Preliminary action

2Device complexity

If the number of preamble sequences is limited, then device complexity is reduced, but preamble collisions increase

Engineering Contradiction:

Improvepreamble sequence management complexityVSAvoidrandom access reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The solution adds a time dimension to the preamble transmission by introducing specifically determined starting subframes. This transforms the problem from a frequency-domain collision issue to a time-domain separation issue, allowing limited sequences to serve more users through temporal distribution

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If repeated PRACH transmissions are performed, then coverage is enhanced, but false alarms increase

Engineering Contradiction:

ImprovecoverageVSAvoidfalse alarm rate

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The starting subframe determination formula acts as an intermediary mechanism that coordinates between different cells and UEs. It mediates the repeated transmission process by ensuring each transmission has a unique, predetermined starting point, thereby reducing false alarms while maintaining coverage enhancement

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11711845B2User equipment, network node and methods therein for handling preamble transmissions on a random access channel in a radio communications network

Publication Date: 2023.07.25 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

The embodiments herein relate to a user equipment (121) and a method performed by the UE (121) for performing preamble transmissions, on a random access channel, to a network node (110). The method comprising: determining (801) a starting subframe for the preamble transmissions based on at least a system frame number (SFN), a number of times (R) the preamble transmissions is to be repeated and a random access channel configuration, and transmitting (802), to the network node (121) the preamble repeatedly starting in the determined starting subframe. The embodiments herein also relate to a network node (110) and a method performed by the network node (110).