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RTWP Problem Analysis and Solution

Summary

High RTWP will cause low performance in CSSR and CCSR. Currently the background noise is -106dBm, if the RTWP is higher than -95dBm then the load factor will more than 90%, CAC will be overload congestion status.

To troubleshooting a high RTWP issue, please refer the procedure as below.

Analysis procedure

1 Check Alarm

1.1 Check the hardware alarm.

Like RF Module Rx Branch RTWP Difference Too High Alarm etc.

1.2 Check whether VSWR alarm exists.

Command: DSP VSWR

If have alarm or high VSWR (more then 11), first escalate to BSS team, then assistant them

to check whether it is hardware problem or interference.

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2 Check NodeB configuration in NodeB LMT

2.1 Check uplink RF sensitivity

Command: DSP RFDESPARAM and DSP DESENS

Usually the value of these two parameters should be 0, if it is not 0, fallback to 0 to check

whether RTWP can restore normal.

2.2 Check Uplink Attenuation Value

Command: LST RXATTEN

This configuration will affect the RX gain. If TMA is not used, then no need to configure it;

and if TMA is used then we should configure it as per TMA gain.

The default value is 0. (Without TMA)

2.3 Check the intermodulation interference

If primary RTWP is very high but secondary RTWP is normal, it may be caused by this case.

Method: suggest to shut off the transmit power then monitor the RTWP. If RTWP become

normal after transmit power is switched off and RTWP become high when transmit power is

switched on, we can suspect that it may caused by feeder joint problem, need BSS team

check the feeder connection (primary feeder).

Command to shut off the transmit power:

SET TXSW

3 Check the interference feature

3.1 Check the RTWP trend

Check the RTWP counter VS.MeanRTWP, VS.MaxRTWP, VS.MinRTWP. Make a chart to

show the interference trend in one day.

Trace the RTWP in NodeB LMT; trace 24hours in one day and save the result to txt format

and make chart to show the primary and secondary RTWP trend in one day.

Through the chart, we can know the interference feature:

What time the interference happens, in day or night; in busy hour or always….

How about the consistency between primary and secondary RTWP trend?

Through the trend we can analyze whether heavy traffic causes the high RTWP; whether

external or internal interference?

3.2 Check the site information

Check it is indoor site or outdoor site.

For indoor site, need collect the information as below:

Whether 2nd carrier is implemented or not?

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Whether the combiner is used? Combiner frequency is match or not?

For outdoor site, need collect the information as below:

How many sectors experience high RTWP?

How about RTWP status of nearby sites?

Is repeater located near the site?

4 Find the interference source

4.1 Judge external or internal interference

Disconnect the jumper (jumper at the cabinet side) from the NodeB, and then trace the

RTWP.

If RTWP is still very high after disconnection, that means NodeB have problem. Need BSS

team check the RF module.

If RTWP become normal after disconnection, that means NodeB have no problem. We can

conclude that the problem may exist in Feeder system or external interference.

BSS team can help to do the VSWR test for the feeder and jumper to check the feeder system

ok or not. Or we can change jumper to verify.

4.2 Troubleshoot the interference

Do the frequency scanning in NodeB LMT.

From the result we can check whether there is strong interference from some special

frequency band.

If from the result we find the interference, we need visit the site to find the interference

source. We can:

If frequency scanning tool available (like frequency analyzer), we can use tool to

scan the interference.

The method to check the interference by scanning tool:

Switch off the transmit power of the interference sector. Make the test antenna of the

tool toward the direction of the antenna of the NodeB (follow the same orientation, same

down tilt, also the same attitude) and scan the interference. By this method we can check

whether external interference exists or not.

If frequency scanning tool unavailable, we can adjust the azimuth of the

interference to check from which direction the external interference comes from.

4.3 Common methods

NodeB have two sets of RTWP, primary and secondary RTWP; if only one set of

RTWP is abnormal but the other set is OK. We can swap the primary feeder with

the secondary feeder to check whether high RTWP swap or not.

If two sectors are very near but only one sector experience high RTWP and the

other sector is OK. We can swap the feeder of these two sectors at the antenna side

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to check whether high RTWP will swap from one sector to the other.

By these swap actions, we can analyze the interference feature and find the interference

source.

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