Sector SWAP Identification Guide

Sector SWAP Identification Guide

 

    Sector SWAP Identification Guide  By : Naveed Shaikh  RF South  26 Febuary 2008 

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Sector SWAP Identification Guide

 

1. Types of Sector SWAP  1.1. Complete Cross Feeders: (GSM or DCS) As the name suggests, this happens when the feeder cables of two different sectors are completely crossed, which in turn leads to the fact that the coverage areas of the two adjacent cells are swapped. Drive tester may observe a lot of HO failures and call drops. 1.2. Composite SWAP: (GSM or DCS) In this case feeder/ semi rigid cables of two or three sector are partly swapped. Sometimes TX cables are corrects but RX main and Diversity cables of two sector s are swapped. Some time TX cables are swapped but RX cables are in their place 1.3. GSM-DCS cable SWAP. In this case GSM feeder cables are connected to DCS DUAMCO or vice versa. Drive tester may observe frequent INTRA cell handovers, handover failures and sometimes call drops. 1.4. Wrong Antenna Installation This can be a sub case of composite swap and this usually happens on Complex expansion sites. In this case TRX and supporting DUMACO are installed in one sector but the new antenna is installed in the others sectors. Prior knowledge of the expansion and TRX configuration will be helpful in quickly identifying these types of issues. The drive tester may observe a lot of HO failures and call drops due to missing neighbors, Low RX level and Quality.

2. Reasons for Sector SWAP or Wrong Installation   Due to very huge and fast deployment sector swap and wrong antenna installation problems are common. The main reason behind this is the installation of Hardware is in steps. That is antennas and Feeders are installed at one time and the Hardware is installed and powered up at other time. Here the responsibility of acceptance team comes who need to verify these types of problems very carefully in field.

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Sector SWAP Identification Guide

 

3. CASE Study No.1: 4QLUN01  Problem: The cells QLUN01-2 and QLUN01-3 had High DCR and High IHOFR. Observed Situation & Solution: As seen from the Drive tests plots Fig: 1 & 2; there was Swap between sector 2 & 3 in 900 band and this can be categorized as “Complete Cross Feeders”. No Swap was found in complete cable tracing from BTS top to antennas. But sector swap was found inside cabinet in semi-rigid cables connecting CUs to DUAMCO resulting High number of HO failures.

  Figure 1 

 

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Sector SWAP Identification Guide

 

  Figure 2

This swap was removed by the help of BSS Engineer and Rigger. The post results are shown in Fig: 3. Here we can see that now there are no HO failures.

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Sector SWAP Identification Guide

 

  Figure 3

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Sector SWAP Identification Guide

 

4. CASE Study No.2: 3KMKR01  Problem: The KMKR01-2 had High DCR. Observed Situation & Solution: In Sector 2, GSM feeder cables and antenna was connected to DCS DUAMCO and DCS feeder cables were left unconnected on BTS top. This can be categorized as GSM/ DCS cable SWAP. In this type of there is no clear indication of swap but drive tester may observe frequent INTRA cell handovers, handover failures and sometimes call drops due to low RX levels of the affected band (in this case DCS band) even very near to BTS. Thus call was not sustaining on DCS band. Figure 4 shows a lot of HOs with week RX levels of DCS band even very near to site.

  Figure 4 

DCS feeder cables were connected to the correct DUAMCO. The post results are shown in Fig: 2.2. Here we can see that now HO count has reduced and call is sustaining on DCS band.

 

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Sector SWAP Identification Guide

 

  Figure 5

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Sector SWAP Identification Guide

  Annex-1: Siemens BTS BS-240XL

DUAMCO  DUVSWR  PORT 

DULNA  PORT 

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Sector SWAP Identification Guide

  ANNEX-2 TRX Testing 1. Stand in the main lobe of the sector whose TRXs are to be checked. Don’t be very close to the SITE keep a distance of 100 meter so that the call is not handed over to some other cell. 2. Establish a call on the test number and wait for approximately 30 seconds 3. Disconnect the call and establish a call again using the same procedure to check all the TRXs of that sector. Note: There are two ways to check every TRX in a particular cell

a) Ask NOC or BSS person to lock all other TRX except the one you are testing, so that the  faulty TRX becomes the BCCH TRX (if not so already).   .  In case of Dual band site with common BCCH on 900, if you need to check 1800 TRX, then one 900 Radio need to be kept unlocked for necessary signaling and you need to stand near to BTS around 100 -200 meters so that your call is established on 1800 TRX. b) If you have no access to NOC or BSS person then test by Hit and trial method recognizing the MAIO assigned to every TRX. Keep trying until you have tested every TRX/MAIO in that particular cell. Here 900 MHz band can be locked to quickly test the 900 TRX only.

4. Compare  the  RX  power  level  of  the  current  TRX  to  the  other  to  check  if  it  is  same  to  other TRX when they are made BCCH TRX. If the deviation is too high that is more that  15‐ 20 dBm then report O&M for low power TRX.      Note:  To  compare  the  DCS  TRXs  RX  level,  DL  power  control  should  be  disabled.    that  particular cell contains 1800 TRX.  Once the problem is identified than DL power control  must be enabled again.     5. Also check the RX Quality for any degradation  6. If call cannot be made on any one of the TRXs try for at least 20 times. If still you can’t make a call then report this to NOC or O&M. 7. Repeat the procedure until all the TRXs have been verified

Tips: The drive tester might experience a scenario in which the call establishes on the 1800 MHz band but fails to do on the 900 MHz band. This occurs due to low traffic on a particular cell site. To suppress the 1800 MHz band one has to uncheck 1800 from the band control properties of the Mobile Station. This would lead the mobile to make calls only on the 900 MHz band.

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Sector SWAP Identification Guide

  References: 1. Drive test log files, Telenor South Nework 2. Product specification Siemens BTS “BS240_BS241XL.pdf” 3. DRIVE TESTING USING TEMS by ACE Telecom

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