Q:What are the reason of TCH Drop due to bad quality Uplink

Ans:

 Probable reasons for poor Uplink Quality
1. Poor Frequency plan (TCH)
2. Interference in UL
3. Overshoot of neighboring cells.
4. Poor Level on the UL.
5. Fault in TCH TRX
6. Codec issues.
7. Transmission related issues.
8. Boosters/Repeater related issues.
9. External interferences – Restricted area/Electronics equipment Factory/Jammers.


Uplink Quality Checkpoints
1. Poor Frequency Plan
a. Always resolve DL quality issues before attempting to correct the UL.
2. Interference in UL
a. Avoid using Co & adjacent TCH frequencies in the same cell or site.
b. Avoid using co TCH on neighboring cells.
c. Wrong values of the HSN or MAIO/MAIO Offset.
i. Do not reuse HSN in nearby sites.
ii. Review MAIO & MAIO Offsets as per the TCH plan(1x1, 1x3, adhoc etc).
d. In cases where intra-cell handovers are allowed, interference will cause a lot of intra-cell handovers thus degrading the UL & DL quality
3. Overshooting of neighboring cells.
a. TCH reuse becomes tight is there’s a lot of overshooting of nearby cells. Allow only 1 or up to 3 dominant servers only.
b. Reduce the overshooting of neighboring cells.
4. Poor level on the uplink
a. Possible coverage problem.
b. Rx Level Versus Rx Quality distribution per TRX on a cell.
c. TMA’s can be used judiciously used to enhance UL level.
5. Fault in TCH TRX
a. Check the alarm printouts.
b. (BTS UL Quality history at 24 Hour/10 day resolution). Check if the BTS is within defined interference boundary limits & for how long it has been out of limits of acceptable interference.
c. BTS Analyzer. Check if the BTS is within defined interference boundary limits.
d. Path balance for TCH TRXs

6. Codec Issues
a. AMR related quality issues.
b. AMR related parameter settings. Check if the Codec (AMR/Non-AMR) settings are OK.
c. Check if the BTS s/w version is OK & supports the codec.
d. If the problem is with many sites in a BSC then that BSC’s parameter file needs to be checked/updated.
7. Transmission related issues.
a. Check the BSC ET availability & Quality profile .
b. Check the TCSM ET availability and quality,.
c. Check the QOS
8. Boosters/Repeater related issues.
a. Check for repeaters and/or booster installations. Check for spillage of the repeater signals in areas not intended to be covered.
b. If repeaters are a problem( you will know once you switch off the repeater for a short duration), adjust the gain of repeater
c. Adjust the repeater antenna & orient it to closest serving cell. DO NOT latch a repeater with a DISTANT dominant cell.
9. External Interferences
a. If you suspect external interference on single TRX, lock the TRX & see if the problem persists. If the problem is resolved then the TRX or its implementation is at fault.
b. If you suspect external interference on the entire site, Lock the site & scan the area served by the site for potential interferers. Somebody may be transmitting the same frequencies in the serving area of affected site.
c. Workaround: If you indeed found an interferer over which you have no control, try allocating a different frequency (beyond 2 MHz). There’s a high probability that the frequency which is being severely interfered now will no longer be interfered after frequency change.