drive test problems [part 2]

8/10/2019 Drive Test Problems [Part 2]

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All about DT [DRIVE-TEST] problems

2G Cross problems [Part 2]

Prepared by:

Eng. Abdelrahman Ashraf Mostafa

EPM- Ericsson

E-mail: [email protected]

Phone: +2-0109-6739100



All about DT [Drive-Test] problems

By: Abdelrahman Ashraf Mostafa 2

NOTE: Each sector antenna in site is connected to 6 ports [sometimes reaches 12],2 ports for 2G GSM 900 MHZ

band, 2 for 2G DCS 1800 MHZ band and the last 2 for 3G UMTS 2100 MHZ band, where every 2 ports are

completely separated from any other ports in connection to the sector antenna.

So, cross [sector or feeder] can occur in 1 band while the other 2 bands are correctly connected.

You can notice that each of the 3 bands is connected to the antenna with 2 feeders as we've said before:

- 1st

feeder is TX/RX feeder which is connected to carry and deliver the transmitted power for sector ARFCNs

[BCCH & TCHs] from the sector BTS cabinet to the sector tower antenna, also it is used to deliver the signal

received by sector antenna in the up-link from the MS to the BTS cabinet, where any wrong connection for thisspecific feeder will result in a cross case for sure.

-2nd

feeder is RX feeder which is connected for the up-link RX diversity.

So, we name the case cross sector if and only if both the 2 TX/RX and RX feeders are connected to the wrong

sector antenna, where the 2 feeders of BTS 1st

cabinet are connected to sector 2 antenna and vice versa.

BUT, if only 1 of the 2 feeders whether the TX/RX feeder or the RX feeder is connected to the wrong sector

antenna, it is named a cross feeders case as we'll demonstrate.





1-2G Cross Sector;

When 2 sectors S1 and S2 in same site each is serving in the other sector main beam area with a good BCCH Rx-level

while the other non-serving sector BCCH appears as a neighbor in [GSM Serving + Neighbors] window with bad

Rx-level or not appears at all as its level is too low to be even detected by MS.

NOTE: Levels of the supposed serving sector [which is not serving due to cross case] must be very bad in its

supposed main beam serving region and vice versa to confirm this is a cross sector case not cross feeders.

Imagine a site consists of 2 sector antennas, each include only 4 ports [GSM and DCS] no 3G for now, so the normal

correct configuration for these 4 feeders from cabinets are to be connected to the sector antennas as shown in the

following snap.

As we've said before a cross case can occur in 1 band only GSM or DCS and don't have to affect the other band.

There are 3 types of Cross sector:

GSM cross sector. DCS cross sector.

Total (GSM & DCS) cross sector.





1-GSM cross sector:

When the 2 feeders from GSM BTS 1st cabinet are connected to sector 2 antenna and the 2 feeders from GSM BTS

2nd cabinet are connected to sector 1 antenna.

NOTE: The 2 feeders should both be reversed with each other's to call this a cross sector case as if only 1 of the 2

feeders is wrong connected it will be a cross feeder case not cross sector as we will demonstrate.

NOTE: When performing a cross test for any site, keep your eye on these 2 important windows [GSM Serving +

Neighbors] window as it will indicates all the serving and neighboring cells BCCH's Rx-levels and [GSM Hopping

Channels] window as it will indicates the serving cell TCH's Rx-levels received by your MS in down-link.





Example:

In front of sector 1 main beam

You find sector 2 BCCH: 8, TCH: 37 is serving with very good Rx-level in front of sector 1 main beam supposed

coverage region while sector 1 BCCH: 55 Rx-level is bad.

Clearly cross case is detected between sectors 1 and 2

But is it a cross sector or cross feeder case?!!





To confirm it as a cross sector case, moving towards sector 2 main beam.


You find sector 1 BCCH: 55, TCH: 21, 10 is serving with very good Rx-level in front of sector 2 main beam supposed

coverage region while sector 2 BCCH: 8 Rx-level is bad.

So, cross sector case is now confirmed between sectors 1 and 2 as sector 1 BCCH is serving in front of sector 2

coverage region which appears with very bad Rx-level, why?

Because the 2 GSM feeders of sector 1 BTS cabinet are connected wrong to sector 2 antenna, which means that

the 2 feeders [including TX/RX feeder] which carries sector 1 BCCH transmitted power is connected wrong to

sector 2 antenna so sector 2 antenna is actually the one generating the power for sector 1 BCCH not sector 1

antenna that's why you find BCCH of sector 1 with very good Rx-level in front of sector 2 antenna and with very

bad Rx-level in front of sector 1 antenna.

NOTE: Don't ever judge a cross case from 1 or 2 TEMS samples only also don't judge while you are under the site

as all site sectors will appear in good Rx-levels.





2-DCS cross sector:

When the 2 feeders from DCS BTS 1st cabinet are connected to sector 2 antenna and the 2 feeders from DCS BTS

2nd cabinet are connected to sector 1 antenna.

NOTE: You can notice that the 2 GSM feeders in each sector are correctly configured in the sector antenna, as

cross can occur in a band while other band is correctly connected as we've said before.

NOTE: Whenever suspecting a cross case between any 2 sectors, try locking using TEMS on each sector BCCH and

move near and far around the suspected 2 sectors to see each sector Rx-levels are they logical and serving in the

sector supposed serving area or not.





Example:

NOTE: Site in next example is concentric site where BCCH is in 900's band while TCHs are in 1800 DCS band.

As shown in the following snaps, suspecting a cross problem in site between sectors 1 and 2 as sector 2 BCCH: 47 is

serving with good Rx-level in front of sector 1 BCCH: 49 main beam which appears with bad Rx-level and vice versa.

So to confirm cross problem:

BEFORE CROSS SOLVED

Locking on sector 2 BCCH: 47


You find sector 2 BCCH:47,DCS TCH: 751,786 appear in [GSM Hopping Channels] window with non-logical very good

Rx-level in front of sector 1 main beam covering region however there Rx-levels were supposed to be bad as they

were not supposed to cover and serve there while sector 1 BCCH: 49 Rx-level is bad.






You find sector 2 BCCH: 47, DCS TCH: 751,786 appear in [GSM Hopping Channels] window with non-logical very bad

Rx-level in front of sector 2 main beam covering region however there Rx-levels were supposed to be good as you

were in front of sector 2 antenna main beam so sector 2 levels were supposed to be good while sector 1 BCCH: 49

Rx-level is good.





But what about sector 1 cabinet feeders, are they both correctly connected or what?



You find sector 1 BCCH: 49, DCS TCH: 757,784,789 appear in [GSM Hopping Channels] window with non-logical bad

Rx-level in front of sector 1 main beam covering region however there Rx-levels were supposed to be good as you

were in front of sector 1 antenna main beam so sector 1 Rx-levels were supposed to be good while sector 1 BCCH: 49

Rx-level is good.

.






You find sector 1 BCCH: 49,DCS TCH: 757,784,789 appear in [GSM Hopping Channels] window with non-logical very

good Rx-Level in front of sector 2 main beam covering region however there Rx-levels were supposed to be bad as

they were not supposed to cover and serve there while sector 2 BCCH: 47 Rx-level is bad.

.

So, cross sector case is now confirmed between sectors 1 and 2 as sector 1 BCCH is serving in front of sector 2

coverage region which appears with very bad Rx-level and vice versa.





AFTER CROSS SOLVED

Trying same procedure by locking on sector 2 BCCH: 47


You can notice that sector 2 BCCH:47,DCS TCH: 751,786 appear in [GSM Hopping Channels] window with logical bad

Rx-level in front of sector 1 main beam covering region as sector 2 originally was not supposed to serve in front of

sector 1 antenna main beam while sector 1 BCCH: 49 Rx-level is very good.






You can notice that sector 2 BCCH:47, DCS TCH: 751,786 appear in [GSM Hopping Channels] window with logical

good Rx-level in front of sector 2 main beam covering region while sector 1 BCCH: 49 Rx-level is bad.

Cross sector problem appeared to be solved as sector 2 BCCH:47 appears with good Rx-level in front of sector 2

antenna but decays and appears with bad Rx-level in front of sector 1 antenna.

But what about sector 1 feeders?







You can notice that sector 1 BCCH:49, DCS TCH: 757,784,789 appear in [GSM Hopping Channels] window with

logical good Rx-level in front of sector 1 main beam covering region while sector 2 BCCH: 47 Rx-level is bad.






You can notice that sector 1 BCCH:49, DCS TCH: 757,784,789 appear in [GSM Hopping Channels] window with

logical very bad Rx-level in front of sector 2 main beam covering region as sector 1 originally was not supposed to

serve in front of sector 2 antenna main beam while sector 2 BCCH: 47 Rx-level is good.

Clearly cross sector problem is now solved, as each sector serves properly in front of its main beam and decays in

levels in front of the other sector's main beam.





3-Total [GSM & DCS] cross sector:

When all the 4 feeders [both GSM 2 feeders and DCS 2 feeders] from sector 1 BTS cabinet are connected to sector 2

antenna and the other 4 feeders from sector 2 BTS cabinet are connected to sector 1 antenna.

Every sector cabinet is connected to the wrong other sector antenna.

NOTE: Once you notice on TEMS that a sector antenna is serving on its non-main beam, you then suspect 1 of 2

problems:

1-This sector antenna has wrong azimuth whether in reality or cell file.

2-Site suffers from a cross problem.

But, why we shall solve cross sector problem in sites?

As it may cause problems like:

Congestion which may causes blocked calls.

Missing neighbor problem.

Down-link interference [Co. or adjacent channel interference].

Dropped calls due to the last 2 before mentioned reasons.





2-2G Cross Feeders;

When 2 sectors S1 and S2 are both serving in 1 side with almost the same good Rx-levels in window [GSM Serving +

Neighbors] which may causes ping pong H.O while both have very bad Rx-levels in the other side where none of

them is serving at all as you find very bad Rx-levels from both of their BCCHs [same behavior from 2 sectors] in 2

sides.

Imagine 2 BTS cabinets S1 and S2 each is connected to its correct sector antenna through 2 feeders TX/RX 1st feeder

and RX 2nd

feeder, if by mistake 1 of these 2 feeders [Not both] is connected to the wrong sector antenna, it will be a

cross feeders case.

NOTE: Whenever suspecting a cross case between any 2 sectors, try locking using TEMS on each sector BCCH and

move near and far around the suspected 2 sectors to see each sector levels are they logical and serving in the

sector supposed serving area or not.

As we've said before a cross case can occur in 1 band only GSM or DCS and don't have to affect the other band.

There are 2 types of cross feeders:

GSM cross feeders.

DCS cross feeders.





1-GSM cross feeders:

We can say that there are 3 possibilities for this wrong connection:

Case 1 [Most famous case in cross feeders]:

When the TX/RX feeder from GSM BTS 2nd cabinet is connected wrong to sector 1 antenna or vice versa, where

sector 1 antenna will be transmitting both sector 1 and sector 2 BCCHs power.

The other sector 2 antenna will include the 2 RX diversity feeders with no transmitted power from BTS cabinets in

them.

Example:

As shown in the following snaps, suspecting a cross problem in site between sectors 2 and 3 in GSM as both sector 2

BCCH: 42 and sector 3 BCCH: 35 appears with almost same good Rx-level in front of sector 3 main beam in [GSM

Serving + Neighbors] window while both appears with very bad Rx-level in front of sector 2 main beam.





BEFORE CROSS SOLVED


You find both sector 2 BCCH: 42 and sector 3 BCCH: 35 appear in [GSM Serving + Neighbors] window with very good

Rx-level which may causes Ping-Pong H.O as both the TX/RX feeders from the 2 BTS cabinets are connected to

sector 3 antenna where all the 2 sector's BCCHs power will be transmitted by sector 3 antenna.






You find sector 2 BCCH: 42 serving with very bad Rx-level which is normal, why?

Because the 2 feeders connected to sector 2 antenna now are the up-link RX diversity feeders.

So in 1 area coverage from site 2 sectors are very good as both 2 sectors are serving there while the other area

suffers very bad coverage as none of them is serving at all, so cross feeders now is confirmed.





AFTER CROSS SOLVED


You find sector 2 BCCH: 42 appears with normal bad Rx-Level because now the TX/RX feeder carrying the power for

BCCH: 42 is not connected to sector 3 antenna but it is connected to sector 2 antenna as it should be.






You find sector 2 BCCH: 42 is serving with good normal Rx-level as now the TX/RX feeder is connected to sector 2

antenna, so coverage in the area is clearly enhanced now.

Clearly cross feeders problem is now solved, as each sector serves properly in front of its main beam and decays in

levels in front of the other sector's main beam so coverage in both sectors area is now enhanced.





Case 2 [Cross sector case]:

When the TX/RX feeder from GSM BTS 2nd cabinet is connected wrong to sector 1 antenna and the TX/RX feeder

from GSM BTS 1st cabinet is connected wrong to sector 2 antenna.

Sector 1 antenna will be transmitting sector 2 BCCH and TCHs, while sector 2 will be transmitting sector 1 BCCH and

TCHs.

In field, you find each sector serves in the other sector supposed coverage region while the other non-serving sector

appears with bad levels [S1 serves in front of S2 region and vice versa].

NOTE: To name a case a cross sector case both the 2 feeders [TX/RX and RX feeder] should be both connected to

the wrong sector antenna, but if this specific TX/RX feeder which carries the transmitted power from BTS cabinet

to antenna only is connected to wrong antenna it will appear in the field as a cross sector case not cross feeder

even if the RX feeder is connected to the correct sector antenna.





Case 3 [Cross in Rx diversity]:

When both RX feeders from BTS cabinets are cross connected to each other antennas, this case is named cross

diversity.

Both sector antennas will not be transmitting any BCCHs power.

Nothing will be detected in the field on TEMS as it shows only the down-link signal received by MS and cross

diversity problem affects only the up-link, but it will be noticed by optimizers through site KPI's.

1-DCS cross feeders:

It follows the same 3 cases of GSM cross feeders.




But, why we shall solve cross feeders problem in sites?

As it may cause problems like:

Bad coverage as in case 1 as 1 area has good coverage while the other area suffers very bad coverage from

serving site. Blocked calls.

Down-link interference [Co. or adjacent channel interference] on neighboring sites.

Dropped calls due to bad coverage or Ping-Pong H.O.

That's all about the 2G field radio problems………

But,

Stay tuned for 3G Problems [Part 3] which will be about 3G DT field problems. Thanks & good luck for you all.

For any questions, contact me on my e-mail or phone.

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drive test problems [part 2]

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