Types of RLF (Radio Link Failure)

4G LTE
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1

Hello expert
Can you pls help to get information of types of RLF failures .

Admin note: this post was updated with image below.
Types of RLF image

2

I think it is generic, and depends on Vendor (specific reasons / pegging)

Generically speaking, I like @Jaeku_Ryu explanation here:

  • The measured RSRP is too low (under a certain limit)
  • It failed to decode PDCCH due to power signal quality (e.g, low RSRP, RSRQ)
  • It failed to decode PDSCH due to power signal quality (e.g, low RSRP, RSRQ)

Radio Link Failure (RLF)
When UE Report RLF ?
What UE tries to do when RLF Happens ?

@Jaeku_Ryu explains it beautifully here:
https://www.sharetechnote.com/html/Handbook_LTE_RadioLinkFailure.html

image image

3

Hello dears,

Can you explain in simple words what is RLF (Radio Link Failure) in wireless networks?

4

We will see RLF’s in our daily scenarios but we don’t know exact cause of RLF.

It can be either from UE side or Network side.

RLF is defined as Physical layer break.

→ Below reasons for RLF from UE side:

  1. The measured RSRP is too low (under a certain limit)
  2. It failed to decode PDCCH due to power signal quality (e.g, low RSRP, RSRQ)
  3. It failed to decode PDSCH due to power signal quality (e.g, low RSRP, RSRQ).

→ Below reasons for RLF from Network side:

  1. SINR from UE is much lower than what eNB configured for the UE
  2. eNodeB couldn’t detect any NACK nor ACK from UE for PDSCH.
5

Radio Link Failures (RLF) is a wide variety of issues of Radio Link Supervision mostly accounts for failures of 1. Physical Layer, 2. Radio Link Control (rlc) and 3. Random Access.
Physical Layer Issues, it comes under erroneous detection and monitoring of radio link. Issues like sudden pathloss, extreme inter symbol interference, PSS/SSS detection issues, timer reset or processing failures, etc mostly count here. N300/N310/T300 are the regulators.
RLC Issues, it is due to failure in ‘efforts’ to get the data to receiver end. In RLC-AM, when all the retransmissions exceed the maximum threshold defined at network end/specification, RLF is declared. ACK/NACK mechanism is the regulator and is independent of radio signal quality.
RA failure is like RLC failure in mechanism. It’s also controlled by a threshold of preamble transmissions. UEs in poor/Interfered coverage retransmit with ramping power (also controlled by parameters) till it gets through by receiving an RAR message or maximum number of retransmission is reached. On unsuccessful in ‘efforts’, RLF is declared.
An RLF is followed by RRC Connection RE-establisment.