Random Access on Unlicensed Channel via Network-Side LBT

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Solution Overview

Problem

The random access procedure in 5G NR systems using unlicensed channels is delayed due to channel sensing, leading to increased latency, as devices can only transmit on unlicensed channels if they are idle at the start of a transmission occasion, resulting in inefficiencies and potential blockages by other transmissions.

Innovation Solution

Implementing a method that performs a first listen-before-talk operation to assess channel occupancy at the beginning of a random access resource and a second operation to identify idle periods within the resource, allowing for partial or fractional random access message transmission during idle parts, thereby reducing latency and enhancing signal quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the radio device performs channel sensing (LBT procedure) before PRACH transmission, then the channel availability can be determined, but the random access latency is significantly increased

Engineering Contradiction:

Improvechannel availability determinationVSAvoidrandom access latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The network performs downlink channel sensing and prepares transmission opportunities in advance. The gNB senses the channel and identifies idle periods before configuring PRACH occasions, allowing the UE to transmit without performing its own LBT procedure, thus reducing access latency while ensuring channel availability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of the conventional approach where the UE performs LBT before transmission, the invention inverts the role by having the network (gNB) perform the channel sensing and determine transmission opportunities. This reversal eliminates the UE's LBT procedure and associated delays.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If the radio device waits for the next RA occasion when channels are not available, then channel sensing can be performed again, but the access delay is increased

Engineering Contradiction:

Improvechannel sensing accuracyVSAvoidaccess delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The network performs preliminary channel sensing and identifies idle periods in advance, configuring PRACH occasions during these idle periods. This eliminates the need for the UE to wait for the next RA occasion, as transmission opportunities are pre-prepared based on network-side channel assessments.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the PRACH transmission is blocked by other transmissions, then channel occupancy is avoided, but the random access efficiency is reduced

Engineering Contradiction:

Improvechannel occupancy avoidanceVSAvoidrandom access efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The network performs preliminary channel sensing to identify idle periods and configures PRACH occasions during these periods. This ensures that PRACH transmissions are scheduled when the channel is guaranteed to be idle, avoiding collisions while maintaining high access efficiency through pre-planned transmission opportunities.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11963223B2Technique for random access on an unlicensed channel

Publication Date: 2024.04.16 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A technique for performing or providing random access, RA, to a radio access network using an unlicensed channel (400) is described. As to a method aspect of the technique, a first listen-before-talk (LBT) operation on the unlicensed channel is performed. The first LBT operation indicates that the channel is occupied at a beginning (412) of a RA resource (410) for transmitting a RA message signal (304). A second LBT operation on the unlicensed channel (400) indicates that the channel (400) is idle within a part (414) of the RA resource (410) for transmitting the RA message signal (304). The RA message signal (304) is transmitted in response to the second LBT operation.