1-Blocked Calls;
While initiating a call on TEMS, your call is blocked and you hear call blocked on TEMS, this may occur due to 1 of the
following reasons:
# Congestion.
#Bad Radio conditions.
#Hardware problem in handset MS.
1-Congestion:
[Means there are no available resources in your serving cell], where in 2G there are 2 types of congestion:-SDCCH congestion problem [no SD's available for you to perform call-setup procedure] and it appears on TEMS in
Layer 3 messages as [No Immediate Assignment] message.
TEMS in Layer 3 messages as [No Traffic Channel Assignment] message.
NOTE: It's normal that Overshooting site to you may suffers congestion as it will be carrying traffic and serving
users in its region and other users in your far away serving region.
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2-Bad radio conditions:
[You then suffer from bad Rx Level or bad Rx Quality so you can't communicate with your serving cell or decode anyof its DL messages]
-Bad Rx Levels can be a result of bad 2G coverage where there is no dominant server exists in the area.
-Bad Rx Quality can be caused by bad coverage [bad levels results bad quality] or due to a high level of interference
[Up-link or Down-link interference] on either your MS or your serving cell and it appears on TEMS in Layer 3
messages as [No Service] message.
BUT how to differentiate that bad quality is due to bad coverage Rx levels or due to interference ?
-Bad Quality in case of bad levels is normal as bad levels will normally causes bad quality Whil e
-Bad Quality in case of good levels, so for sure there is interference.
3-Hardware problem in ME handset:
[Sometimes your test mobile suffers temporary sudden errors due to excessive usage, so it reports blocked calls withno apparent reason] and it may appears on TEMS in Layer 3 messages as [No Alert or Connect] message.
NOTE: TEMS is a stupid software that generates events but it doesn't receive any indicators about these events
from network, it only memorizes a specific sequence of messages, if any of these messages dropped due to any
reason and didn't received by mobile so TEMS didn't record it, it may then report blocked call with no reason.
NOTE: Not all the events that appear on TEMS during test actually occurred and stored/counted among network
KPI's, as sometimes any sudden hardware errors in your DT tools may cause events in a very good radio conditions
[Blocked calls-Dropped calls-H.O failures, etc…], that's why in analysis we sometimes neglect events which occur
in a very good radio conditions as these events occurred due to some temporary errors in your test tools.
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When noticing that quality in 2G GSM Radio Parameters window [Rx Qual] and value of C/I in GSM Hopping
Channels window are bad for a specific ARFCNs while levels of 2G coverage for the same ARFCNs are good, where
there exist 2 types of interference:
#Up-link interference.
# Downlink interference.
1-Up-link interference:
[Your serving cell will not be able to decode any of your up-link messages if your MS suffers any up-linkinterference].
Interference in up-link can be due to any external system that may be broadcasting or transmitting on a used
GSM/DCS ARFCN frequency with a high power, hitting any information that is transmitted over this ARFCN and
serving BTS will not be able to decode your up-link messages, ex. Military applications.
Up-link interference is an interference on your MS mobile handset, causes bad quality in up-link between your MS
and the network, where an external system transmits power on a specific frequency ARFCN which is the same as the
frequency you are using to communicate with your serving cell. So, any message or information you are transmitting
on this ARFCN may suffer high amount of errors due to interference causing high BER [Bit Error Rate] so quality
turned bad by time.
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2-Down-link interference:
[Your mobile will not be able to decode any of the network down-link messages if there is any down-linkinterference on the serving BTS].
There are 2 imp. Types for the down-link interference:
-Co-Channel Interference [You find a bad quality and bad C/I problems for a specific ARFCN in
good Rx levels].
- Occur when 2 same frequencies interfere with each other BCCH's or TCH's.
-Neighboring sector to your own serving sector is transmitting on [BCCH/TCH] ARFCN channel which is the same
ARFCN your serving sector is transmitting on to you in down-link.
-Adjacent-Channel Interference [You find a bad quality and bad C/I problems for a specific ARFCN in good Rx levels].
- Occur when 2 adjacent close frequencies interfere with each other BCCH's or TCH's.
-Neighboring sector to your own serving sector is transmitting on an adjacent ARFCN channel to the ARFCN channel
of your serving sector [BCCH/TCH].
Down-link interference is an interference on your serving cell, causes bad quality in down-link between your MS and
the network, meaning that a neighbor or an overshooting cell is transmitting power [Information] for its serving
users in the area on a specific ARFCN frequency in down-link which is the same as the frequency you are using to
communicate with your serving cell. So, any message or information your serving cell is transmitting on this ARFCN
may suffer high amount of errors due to interference causing high BER [Bit Error Rate] so quality turned bad by time.
Conclusion:
Interference is unwanted power, if it hits the up-link, serving cell may then not be able to decode any of the user'sup-link messages and it will be named Up-link interference and if it hits the down-link, user's MS mobile may then
not be able to decode any of the serving cell's down-link messages and it will be named Down-link interference.
NOTE: Overshooting sites may cause interference as they may be using the same ARFCN's [BCCH /TCH] of your
near-by serving cells due to the frequency reuse pattern as shown:
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Prepared by:
Eng. Abdelrahman Ashraf Mostafa
abdelrahman_ashraf@hotmail.com
1 comments:
commentsWow, thanks for putting this up for young engineers like me, I have finally found where to learn online
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