Different signal strength

[justdream]

Could you explain this phenomenon?

I have drive test made by TEMS with scanner in idle mode but during the test the driver forced to drove in some streets many times…………this is not the problem, the problem that the signal strength in the same street changed from good to bad as shown in picture,

1) Who could explain how come I get big different signal strength for the same area in the same drive test? Which one is the actual? Which one I should consider for my planning?
Note: this is the color legend range (blue -40;-65, green -65;-77, yellow -77;-82, orange -82;-92, red -92;-120d)

2) I made a drive test for UMTS by using UE in idle mode then give the result to the customer,
But the customer gave me drive test report for the same area using scanner in idle mode but with higher signal strength (better coverage)…..
So which one is more accurate?

If we assume that the scanner is more accurate, so what's the importance of scanner measurements if it gives me higher signal strength than the user will detect by his mobile !!!!!!!!

[davidbrayan]

while using scanner he might have used antenna with gain and not mentioned it in TEMS,also check if in your drive,external antenna is used with what gain.
may be a reason due antenna gain.

[justdream]

while using scanner he might have used antenna with gain and not mentioned it in TEMS,also check if in your drive,external antenna is used with what gain.
may be a reason due antenna gain.

Thanks for your concern,
I will check this point but that's may be the reason of the difference between RF Scanner and UE,

my major concern is the different signal strength ifor the same area using the same equipments as shown in attached pictures,

do you know what's the reason?

[venom]

Hello brother,

Scanner is more accurate than idle mode, now the reason behind it is, it scans more samples than the drive in an idle mode and for that reason the logs of Scan data can be used in CW Measurements. But if you are using TEMS UE as a scanner than you should use an external antenna. The reason behind is that if you don't use the external antenna then on some areas it creates saturation points. Now what are these saturation points? Lets take an example, u r driving in a region where you are having 2 BCCH , say 63 and 64 (adjacent) then sometimes scanner can not differentiate these frequencies and the discrapancy arises in the samples of either of these frequencies (i.e one of those BCCH are scanned twice, even if u r in the region of adjacent BCCH). This is why external antenna is recommended when you are Scanning !!

Idle mode is more like a realistic image, it actually tells you the information which a normal user is getting. (i.e Rx Levels). But it actually works on some relative information, like C1/C2 Cell reselection criteria, which sometimes gives u a wrong image of the RF Environment. For example you are driving in a region where 63 and 64 frequencies are present and you are hooked on 63, then the cell reselection will not place until and unless C1/C2 Criteria is passed. That is why sometimes you get the wrong image of RF Environment !

Now Drive Testing is done for several reasons, i am not sure what you wanna check, if you just want to check the spectrum usage in that area then Scanning is helpful and it should be done. This will also help you to plan the site or to create the propogation models for your tool or to see the actual coverage of that particular site. (by checking the frequency overshoots). In idle, you will not see this because as soon as C1/C2 criteria is passed, the serving cells/BCCH changes.

I hope this much explanation will help you the understanding of Idle drives and Scanning, Please also include the legends, it also justifies your question in this forum, thank you

[justdream]

Thanks lccengr,you helped me a lot,again my major concern is about geeting different signal strength for the same area (in the same drive test).that's what mt attached pictures about.

[gprastomo]

Hi Justdream,

I have also experienced like that.First of all before drivetest, pls make sure that you do drivetest using the correct methodology, check all the equipment, check the antenna, check the scanner, check the screw, all must be fix before drivetest. My problem here is solve when i change the antenna, the antenna is broken.
Pls ensure that in the same street is served by the same cell with different signal strength. If yes, the problem is on your scanner, if no, maybe the serveing cell with result in good rscp is not served again.

[venom]

You will get both different things, the purpose of idle and scanned data is different, tell me which thing you are plotting for scan data !

Plot the Strongest Scanned ARFCN (best server) against Rxlev Idle (dbm) in Actix, it should give you the closest picture!

If you are plotting the Scanned RxLev By ARFCN in Actix then it will show you the picture of the particular ARFCN.

I want to see the legends in your snaps before making any comments, if you have made any binned query then pls post in here and i'll tell you wat it is actually !

[justdream]

Guys, i'm speaking about UMTS not 2G :(

regarding my legend, I wrote it in the first post

another question to all UMTS RF Engineers,

Do you think that cell breathing and shrinking may be the reason of getting different signal strength during testing the same site????

if yes, how could I overcome it?

[venom]

i apologise, i didnt see the UMTS thing in your post, i was talkin about GSM, In UMTS you have single frequency, i have no experience of UMTS right now, so i can't make any comment on it

[justdream]

Dear Lccengr,

suppose that c1/c2 is not active, so using scanner will still be more accurate than UE_idle mode?

if yes, please tell me why?

Thanks a lot