RF

[RF] A Low HSPUA Throughput Caused by
Improper RTWP
May 20, 2011 by TheBeeliever Leave a comment
RTWP : Receive Total Wideband Power, reflects the total noise level within the UMTS
frequency band of one single cell.
Phenomenon Description : In project V in country B, when a single site is tested, the
HSUPA throughput in many cells cannot reach the required value (more than 500 kbps).
Alarm Information : The alarm RRU Rx Branch RTWP Difference Too High is raised in
some cells.
Cause Analysis : We suspected the RTWP was improper. The analysis is as follows: HSUPA
scheduling is based on the RTWP. The baseline value is –105.9 dBm, and no interference
exists by default. If any interference or other cause leads to the improper RTWP, the HSUPA
throughput is affected.
Handling Process :
1. We checked the RTWP in the cell with an improper HSUPA throughput on the RNC LMT
or NodeB LMT. The main branch and diversity branch are displayed on the NodeB LMT, and
the combination of the main branch and diversity branch is displayed on the RNC LMT.
2. If the RTWP is greater than –100 dBm, we can basically determine the RWTP causes the
improper HSUPA throughput. If the RTWP is proper, we can, according to the related guide,
find other causes such as parameter configuration, cell state, and transmission configuration.
3. When the RTWP is greater than –100 dBm, the HSUPA throughput is improper. The cause
is analyzed as follows: According to the current baseline configuration, the maximum uplink
target load is 75%, that is, a rise of 6 dB is allowed for the background noise. The current
baseline of the background noise is 61, the corresponding RTWP is –105.9 dBm (–112 +
61/10).
Considering a rise of 6 dB, the RTWP is –99.9 dBm. That is, the RTWP reaches the maximum
threshold when no UE is accessed. The LST CELLCAC command can be used to view the
BackgroundNoise value.
4. After confirming the improper RTWP causes a low HUSPA throughput, we enabled the
automatic update switch for background noise with the command: MOD CELLCAC:
CellId=11111, BGNSwitch=ON; This function can automatically update the background noise
in a period every day, for example, 1:00 a.m. to 6:00 a.m. (default value). If the RTWP is
proper before, the automatic update switch for background noise can be enabled to solve the
problem.
5. If the problem is not solved after the automatic update switch for background noise is
enabled, to avoid affecting the project progress or acceptance, the following temporary
solution can be used to ensure that the acceptance of a single site is passed. The fundamental
cause for the problem is that the actual background noise differs from the configured one.
Therefore, it is necessary to manually set them to the same value.

The procedure is as follows:
1) Track the RTWP in the current cell at the RNC to obtain the current RTWP, for example,
CurrentRTWP.
Modify the background noise in the current cell with the following command:
MOD CELLCAC: CellId=11111, BackgroundNoise=(CurrentRTWP+112)*10;
Disable the automatic update switch for background noise.
2) After modification, test the HUSPA throughput at the place near to the cell. Generally, the
problem can be solved.
3) After testing, modify the background noise to the baseline value and enable the automatic
update switch for background noise.
The purpose of the temporary solution is to ensure that the acceptance of a single site can be
passed. The solution for an improper RTWP is the most fundamental, but it usually takes a
very long time.
Suggestions and Summary : After the preceding solution is applied to project V, the HSUPA
throughput is proper.
In practice, some causes may lead to an improper RTWP that affects the HSUPA throughput.
The preceding solution is applicable to such problem.