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 intracell 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. Check first your Link balance UL/DL for the cells concerned by bad UL quality to make sure there is no Hrdware problem, you might be able to get it at OMCR counters. Then check Parameters for HO UL and DL (level and quality set up, if level for HO UL too low , you sometimes drag the cell too far leading to quality and drop. Check as well interference levels within bands, counters at omcr, to find out if you have external interferences, then check ur freq planning, what kind are you using as hopping, BB or SFH ? do you have 3G colocated sites ? Give me the results on those investigations, will see what tthe next step. BR YB
Many thanks for your contribution, As I told Ashish (by mistake it was a private message)this BSC serve a mountained area so there is a problem of coverage (holes), beside this co-channel interference is one of the major issues as this area is somehow dense plus a lack of frequencies(3 operators share the GSM900 band), also a sychronisation problem can also contribute as we use a synthetiser hoping frequencies, for HO success rate is acceptable (more than 98% for incoming HO, it is our reference) I don't think it is a problem as RNO is activated in this BSC, and by using NCS
neighboring is well defined. Actually we don't have 3G NodeBs in our network very glad to know you, hoping to hear from you soon. 3 months ago
Check points mentioned by ashish are ok. But one major check point is missed out. That is concept of diversity. Basic fundamental of diversity is to averging out multiple signals.So better UL signal we are having. In nokia system we can set parameter for diversity. I am not having infomation about parameter which is used by ericsson system. In nokia system it is segment level parameter. Along with this kindly check out for diversity feature of antenna which are already deployed by operator in the netowrk.It means which type of diversity(Space, Horizotal, Vertical or Cross) is used by antennas?
Djamel-Eddine Toubal • Hi Manan, As far as I know, in our network we use Kathrein Antenna which has two vertical antennas one for TX/RX second for RX, I don't think there is a parameter to set the type of diversity in Ericsson (Please Experts to correct me if I'm mistaken). and for your information there is no alarms concerning Rx diversity lost. Thanks for mentioning this issue, we can get more information from our colleagues. • Problem on Bad Quality is usually associated with Co-channel Interference on BCCH or TCH. Faulty MAIO assignment can cause frequency collisions on co-sited cells especially on 1x1 Reuse. External interference is also one possible cause of problem on quality. in UL you can have 2 kind of interference internal or external internal interfernence it's can be due to the following reason: 1.Poor MS Power regulation, The feature used to reduce the MS power when the MS is near to the BTS and hoping that it might not interfere the uplink 2.Check if the frequency hopping on or off. If more than 1 TRU, turn on the frequency hopping. Turning on the frequency will help to reduce interference by interference averaging. 3.Check if DTXU feature is on or off. If off, turn the DTX feature on. This will save the battery in the MS and reduce the interference. If changing frequency or parameter cannot solve the interference for both uplink &
downlink, it might be external interference. Check antenna installation, ensure that the antenna is correctly installed Check if another mobile network like AMPS is near to the location. Check from the statistics if there is any pattern of bad quality reason. For example, for surveillance purpose, the CCTV or wireless alarm system might be turn on during nighttime only. If external interference problem occurs, do drive test with spectrum analyser and report the usage of the frequency to authorities. if the frequency hopping is activeted be care fully to the Fraction load FL= #TRX / Number of frequencies per hopping group FL might be = 50% if FL is big than 50% it can cause the UL interference. with your band 42 to 82 BCCH take 43-63, 20 ARFCN hoping 65-82, 17 ARFCN. with 17 frequence if you use 1/3 frequency reuse each hopping group must have 6 ARFCN a good way of frequency utilisation is to have 3TRX per sector if you have more than 3 TRX you'll have an UL interfernce. so let me ask you somme question: 1. how many frequency do you have in your frequency group? 2. how many TRX do you have per sector? 3. what kind of hopping do you have BB or SYNT? 3. how do you plan you MAIO in case of Hoping SYNT ? 4.MS power control is it activated? what's the settings of MS power control? 5.DTXU is it on? 6. did you check the external interferer with a spectrum analyser? thank you
Djamel-Eddine Toubal • Hi José and many thanks for your contribution, well in our network we use Synthetiser hoping frequencies, and to be honest with you I don't know how MAIO is planned(I mean we use sequences like 0 6, 0 6 12, 2 8 14,2 8 14 20 ..., but i don't know how it is planned ), by the way is there any strategy to plan MAIO within a network, per sector it depends on the population but mostly 4 TRX per sector for Macro BTS and 2 TRX per sector for Micro BTS, and for some cases we use GSM900 and DCS1800, so 8TRX per sector, Discontinuous transmission is activated, and also Power control is also activated, MSTXPWR is 33 for macro BTS and 30 for Micro BTS, till now I didn't check extenal interference (We may do it in the future). This is globaly some information we have in this BSC. Question: The FL is calculated on sell level or Site level, and how it is calculated when we have overlaid and underlaid subcells Thanks best regards.
