Causes of Radio Link Fault

The causes of radio link fault can be :

Interference

Internal interference

External interference

Equipment interference

Coverage hole

Isolated island

Uplink/downlink imbalance

Improper parameter setting

Radio link timeout, SACCH multi-frames

Handover parameters

Power control parameters

Equipment problem (Antenna, feeder, combiner, TRX)

Clock problem

Transmission problem

Radio Link Fault – Interference

Category

Co-channel interference

Adjacent-channel interference

Inter-modulation interference and other external interference

Solution :

First check equipment problems.

Make an drive test, check the interference area and distribution of signal

quality. Find the interference frequency.

Further search for the interference source with the spectrum analyzer.

Activate hopping, DTX and power control functions to lower the internal

interference of the system

Radio Link Fault - Coverage

Coverage:

Overshooting

Coverage hole

Signal attenuation

Incomplete definition of adjacent cells

Imbalance of uplink/downlink

Judgment Process :

Power control measurement function

Receiving level measurement function

Cell measurement function/inter-cell handover measurement function

Call drop measurement function

Defined adjacent cell measurement function

Undefined adjacent cell measurement function

Outgoing inter-cell handover measurement function

Up-down link balance measurement function

Solution:

Adjust network parameters

Add BTS

Radio Link Fault - Parameters

Main parameters that may affect the call drop rate:

Radio link timeout and SACCH multi-frames

RACH busy threshold and RACH minimum access level.

MS minimum receiving signal level

Call re-establishment permitted.

Main parameters that may affect the call drop rate:

NCC permitted

Handover related parameters.

Power control related parameters.

Frequency planning parameters

Radio Link Fault

Judgment process:

System information data

Cell data

Radio link connection timer (T3105)

Maximum times of physical information

Call drop performance measurement function

Judge from the cause of call drop

   -->error indication

  --> connection failure.