Case Analysis-Congestion by islamcode16

VIEWS: 21 PAGES: 77

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After BSC sends ASSIGN CMD, BTS transmits it transparently to MS, and abnormalities
occur:

1. MS fails to receive the assignment command (ASSIGN CMD) or the UA frame from
BTS.

2. BTS fails to receive SABM frame or assignment completed message (ASSIGN COMP)
from MS, this causes assignment failure.

The signaling analyzer can be used to analyze the cause of assignment failure of Abis
interface message.




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When hardware installation causes the unbalanced uplink and downlink level and TCH
congestion.
congestion

1. Uplink flow: antenna -->tower amplifier-->feeder-->lightning arrester-->rack-top
connector--> CDU-->TRX board.

The error with RF cable causes the uplink level difference. Maybe the connector is not
tight.

2 Downlink flow: TRX --> CDU-->rack-top connector-->lightning arrester-->feeder--
2.
>antenna

VSWR alarm occurs to the transmitting tributary of antenna feeder .

The RF cable is twisted or the connector is not tight

The error of cell antenna connection leads to the differences in the coverage, thus causing
     congestion.
TCH congestion




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Processing principles:

1. If the congestion rate are related to the blocked TRX, check whether there is
interference, check the performance of uplink and downlink.

2. If the congestion rate is not related to TRX, interference may exist in the whole cell or
the propagation environment.




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After all assignment failures are found on a specific TRX board, take the following into
consideration:

1. MS TA value in the measurement report.

2. Uplink/downlink signal level.

3. Uplink/downlink signal quality.

Analyze the causes for a certain assignment failures , and dialing test should be
performed on-site.




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1. According to the TEI values shown in the diagram, the TRX containing this SDCCH can
   identified.
be identified

2. With the ARFCN, the TRX containing this TCH can be identified.




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The way for on-site dialing test:

1. Carry out dialing test at each carrier and each channel, to check whether any timeslot or
board can not be assignable.

2. Check whether the downlink levels of all carriers are nearly the same. For TRX with
significantly abnormal level, the cause can be located step by step through changing the
board or uplink/downlink antenna & feeder system.




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The number of uplink reports of the first three TRXs in cell 5 under module 1 differs greatly
                            TRXs.
from that of the last three TRXs It can be seen that the uplink signal level of the last three
TRXs is obviously lower than that of the first three TRXs. The level values corresponding
to the receiving level grades are as follows:

Grade 0 : -110~ -100 dBm

Grade 1 : -100~-95 dBm

Grade 2 : -95~-90 dBm

Grade 3 : -90~-80 dBm

Grade 4 : -80~-70 dBm

Grade 5 : > -70 dBm




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From the TCH congestion rate (including handover) formula (refer to Page 6), we can see
     it s                            Incoming                                 Function
that it’s necessary to register the “Incoming Inter Cell Handover Measurement Function”
and to analyze which cells fail on TCH seizure during handover.




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Note: SDCCH congestion related to attempted SDCCH seizures meeting a SDCCH
        state,                           congestion.
blocked state this is different from TCH congestion

Attempted SDCCH seizures meeting a SDCCH blocked state refer to no SDCCH available.
It is different from SDCCH seizure failure which includes attempted SDCCH seizure
meeting a SDCCH blocked state, unsuccessful channel activation (NACK) and channel
activation timeout (timeout)




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Attempt SDCCH seizures measurement point: after BSC receives Channel Required.

Attempted SDCCH seizures meeting a SDCCH blocked state measurement point: BTS
finds no SDCCH channel available and cannot activate channel.




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