Per-SSB Back-off Timer Mitigates Ping-Pong Effects in 5G NR Random Access

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Solution Overview

Problem

In 5G New Radio (NR) wireless communication networks, the random access procedure is hindered by high frequency propagation losses and congestion issues, where user equipment (UE) may repeatedly switch between SSBs with back-off indications, rendering the back-off mechanism ineffective in managing congestion.

Innovation Solution

Implementing per-SSB back-off timers that prevent UE from selecting a beam with an active back-off timer, allowing UE to perform random access on alternative beams only after the timer expires, and enabling contention-free access if signal quality improves.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a UE ignores back-off indication when switching to a different SSB, then the UE can perform random access on alternative beams, but the back-off mechanism becomes ineffective and congestion is not managed

Engineering Contradiction:

ImproveUE ability to switch between SSBsVSAvoidback-off mechanism effectiveness

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent segments the back-off timer mechanism by SSB index, creating separate back-off timers for each SSB. This allows the UE to maintain different back-off states for different SSBs simultaneously, enabling adaptation to switch between SSBs while preserving the back-off mechanism's effectiveness for each individual SSB.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If a single back-off timer is used for all SSBs, then the back-off mechanism is simple to implement, but the UE cannot differentiate between congestion on different SSBs

Engineering Contradiction:

Improveback-off timer managementVSAvoidSSB-specific congestion response

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent divides the single back-off timer into multiple SSB-specific back-off timers, one for each SSB index. This segmentation enables the system to track and manage congestion levels for each SSB independently, allowing the UE to make informed decisions about which SSB to access based on current congestion status of each beam.

Inventive Principle:

Principle #1Segmentation

3Productivity

If the UE repeatedly switches between SSBs with back-off indications, then the UE can attempt random access on multiple beams, but ping-pong effects occur and network efficiency decreases

Engineering Contradiction:

Improverandom access success rateVSAvoidping-pong switching time

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

By implementing separate back-off timers per SSB, the patent prevents ping-pong effects because the UE must wait for the back-off timer to expire for each specific SSB before attempting access again. This segmentation creates a stabilizing effect where the UE cannot rapidly switch between SSBs, as each SSB maintains its own back-off state that must be resolved independently.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11432335B2Back-off timer per SSB in NR

Publication Date: 2022.08.30 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Methods and apparatus are provided for random access in a wireless communication network. When a UE receives a back-off indication from a base station responsive of the transmission of a preamble sequence associated with a first Synchronization Signal Block (SSB), the UE starts a back-off timer. The UE may transmit a preamble sequence associated with a different SSB before expiration of the back-off timer. In one embodiment, a per-SSB back-off timer is introduced to prevent the UE from switching back and forth between two SSBs.