Neighbor Information

In Idle mode, the MS listens only to the BCCH of its serving cell. It will decode all System Information messages sent on this channel. Some of these SI msg (SI5 and SI5bis, as far as i recall) lists all the neighbors cells declared for this serving cells (actually, it justs lists down the neighbors’ BCCHs).

The MS measures the RXLEV of the serving’s BCCH and the RXLEV of all neighbors declared in the SI msg.

In Dedicated mode, the MS does not measure the BCCH RXLEV of its serving cell. It measures the TCH RXLEV of the serving only. Plus, of course, the RXLEV neighbors. It will report back those measures to the BTS, but because there might be a lot of neighbors, it will limit the report to the serving’s RxLev and the 6 strongest neighbors’ RxLev.

I don’t know if that answers your question..
FYI, Synch. channel has nothing to do with all this.

Regards,
Pix

Hi Dangerous Mind,

Quote: “How and when does the MS scan the RxLev of the BCCH of the serving cell?”

I don’t understand.. the MS does not scan a RxLev. RxLev is a measurement: the MS measures the received power of the BCCH downlink signal.

Quote: “And also, all the System Information messages are transmitted on the SACCH, so why does the drop call rate increase for a cell if it is experiencing co channel interference? If a cell has 4 TRXs for example, most of the calls would not be established on BCCH TRX, so why does the call drop rate increase?”

No, the SI messages are transmitted on the BCCH timeslot, on the BCCH logical channel. So all MS’s can listen to them.
As soon as a MS gets a SDCCH and/or a TCH there will be a SACCH interleaved with this “dedicated” channel. The SACCH and the TCH are located on the same timeslot. And here, yes, the SI msg are sent on the downlink SACCH. But this SACCH belongs to only one user, nobody else can listen to it.

Now, what’s the relation with cacll drop ? A call drop radio is detected when the BTS or the MS cannot decode the received SACCH. We do the assumption that if the SACCH is not decoded, then the TCH is not either. And that’s correct : they both are on the same timeslot, on the same frequency. So they suffer exactly the same radio conditions.

This assumption however is not working in AMR anymore ; the TCH bursts are highly protected, while the SACCH remains sensitive to interference. Therefore the call drop is detected (no SACCH decoded), while the actual voice (the TCH) could still be decoded by the MS. In this situation the drop occurs, but the subscriber feels like there was no need for a drop.

Regards,
Pix

hi,

1) no the MS in dedicated mode does not listen to its BCCH. All necessary layer 3 msg are sent on the TCH (via the SACCH)

2 it depends on your TRX PREF MARK. Perhaps the calls are setup on the BCCH because there is a higher priority there.
Normally, if the calls are sent to TRX2,3 and 4 rather than 1, then you should at least see some call setup failures, because BCCH and SDCCH are interfered.

And finally, not all calls are sent to the TRXs 2/3/4. When all other TRXs are full (or if the 1800 TRXs cannot welcome this call due to poor radio conditions), then the BCCH TRX will welcome TCH as well.

Example… If 10% of calls are sent on BCCH trx, and if all of them are dropped, then there will be a drop rate of about 10% 🙂 Even more, because there will be a faster tch turnover on the first trx.

Hi,
It doesn’t make sense that all call drops are related only to the interference in the BCCH.
When calls are in non BCCH TRX(u can either use single TCH or Hopping for that TRX),then drops due to interference on that is because that/those TCH frequency/frequencies are getting interferences.
And calls when are in BCCH,interference due to co or adjacent BCCH.
It depends calls are where….in the BCCH TRX or in the non-BCCH TRX.
But BCCH should be more priority..as according to u..SD are on BCCH..so it should be keep clean…to reduce other drop like SD drop…in your network.

hello dangerous minds,

could you share with what was the problem and how it was solved , please?

the MS does NOT read the received power from any message. It measures it.

TEMS is a very particular mobile, which can show the RXLEV of the TCH and the RXLEV of the BCCH.

“Standard” mobiles does not report such BCCH measurements in dedicated mode.

Synchronization channel is a pure sinusoid which allows mobiles to “oscillate” at the same frequency as the BTS. So they can hear what the BTS is saying.
If MS is a little “out”-sync, then it can’t decode BTS signals.

first, MY question:
how did you solve the previous problem ?

hello dangerous minds. You have written, previously:

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Dangerous Minds – 16 Sep 2008
Problem solved 🙂

but there are a couple of related questions:
…
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I’m just asking : how did you solve the problem ?