Two-Step RACH Procedure for Lower-Latency Wireless Initial Access

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Solution Overview

Problem

Existing wireless communication systems face latency issues in the random access procedure, particularly in 4G and 5G networks, which hinder faster and more efficient communication processes.

Innovation Solution

A 2-step random access channel (RACH) procedure is introduced, where a UE transmits a first message containing both a preamble and a payload, followed by a second message from the BS in response, thereby reducing the number of steps required for synchronization and contention resolution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a 4-step random access procedure is used, then synchronization and contention resolution can be achieved, but latency increases and communication speed decreases

Engineering Contradiction:

Improvesynchronization achievementVSAvoidcommunication speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent combines Message 1 (preamble transmission) and Message 3 (payload transmission) into a single first message, and combines Message 2 (MAC RAR) and the random access response into a single second message. This merging of multiple steps into fewer steps reduces the number of transmissions required, thereby reducing latency and improving communication speed while maintaining synchronization and contention resolution functionality.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If a 4-step random access procedure is used, then contention resolution can be performed, but the number of transmissions increases causing higher latency

Engineering Contradiction:

Improvecontention resolutionVSAvoidaccess latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent merges the preamble and payload into a single first message transmission, and merges the MAC RAR and random access response into a single second message. This reduces the total number of transmissions from four to two, directly reducing access latency while the contention resolution is maintained through the integrated message structure that includes UE identity information and response identification.

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If traditional random access procedure is used, then uplink synchronization can be obtained, but the procedure is too slow for future communication needs

Engineering Contradiction:

Improveuplink synchronizationVSAvoidaccess efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent combines multiple random access steps into a two-step procedure where the first message includes both preamble and payload, and the second message includes both MAC RAR and random access response. This integration maintains uplink synchronization functionality while significantly improving access efficiency by reducing the number of sequential transmissions required.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS12418940B2Methods, apparatus and systems for performing a random access procedure in a wireless communication

Publication Date: 2025.09.16 ZTE CORP

AI summary

Methods, apparatus and systems for performing a random access procedure in a wireless communication are disclosed. In one embodiment, a method performed by a wireless communication node is disclosed. The method comprises: receiving, from a wireless communication device, a first message comprising a preamble and a payload for an access to the wireless communication node; and transmitting, to the wireless communication device, a second message in response to the first message.