Regarding Frequency Channels in GSM(Urgent)

[karthik537]

Hi friends,
Please help me in replying to the below 3 queries.. I am undergoing GSM Traning... Please help me to know the concepts...

When a mobile is switched on, it synchronizes itself to the Frequency using FCCH Channel. That means it scanns each and every GSM frequency channel for a beacon frequency.

My first query is What is this beacon frequency?

If we say, the answer is that the beacon freq. is the freq to which the mobile synchronizes for further communications!!! then my second query is

I read in some book that a bast station(BTS) uses one freq. channel to broadcast beacon freq. and some for user data and Signalling. If one frequency channel is used to broadcast and lets say 20 mobiles in the cell has chosen that frequency, How all the 20 mobiles can communicate on the same frequency as we know that a frequency channel is divided only among 8 users (we can say 7 users as timeslot 0 is used for signalling)?

Third quer is:

The frequency channel that is used to find the beacon signal by MS and the freq channel that is used for signalling and the frequency channel that is used for user data are different?

[mountain]

Hi friends,
Please help me in replying to the below 3 queries.. I am undergoing GSM Traning... Please help me to know the concepts...

When a mobile is switched on, it synchronizes itself to the Frequency using FCCH Channel. That means it scanns each and every GSM frequency channel for a beacon frequency.

My first query is What is this beacon frequency?

If we say, the answer is that the beacon freq. is the freq to which the mobile synchronizes for further communications!!! then my second query is

I read in some book that a bast station(BTS) uses one freq. channel to broadcast beacon freq. and some for user data and Signalling. If one frequency channel is used to broadcast and lets say 20 mobiles in the cell has chosen that frequency, How all the 20 mobiles can communicate on the same frequency as we know that a frequency channel is divided only among 8 users (we can say 7 users as timeslot 0 is used for signalling)?

Third quer is:

The frequency channel that is used to find the beacon signal by MS and the freq channel that is used for signalling and the frequency channel that is used for user data are different?
I'm not expert for gsm, but I found some basic info from my school time.
In gsm "channel" mean "timeslot".

GSM frequency channel 200 kHz is time multiplexed into 8 timeslots.
Each of those slots is called PCH - physical “channel”.
This timeslot could be: traffic channel (TCH) or signaling channel (SCH).
So FCCH channel and others “channels” are just timeslots and does not occupy whole 200 kHz frequency.

Traffic channel could be full rate (TCH/F) or half rate (TCH/H).
So if you are using half rate traffic channel, you can have more than 7 conversation per 1 frequency channel. (up to “16” minus signaling timeslots)

In practice you have more than one frequency channel per cell, so users are not only TDMA but also FDMA separated. Additional frequency hopping is useful against frequency fading and of course more frequencies increase cell capacity.

Don’t rely on my data/info!
Read some book or go to wikipedia!
Um interface - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Um_interface)

Google Books (http://books.google.com/)
2G Mobile Networks By Narang, page 84

[karthik537]

Thanks for your reply...
Can u answer my third query?

[mountain]

Thanks for your reply...
Can u answer my third query?
As I sad, I'm not gsm expert. By my understanding:
1. What is this beacon frequency? – its one frequency per cell containing broadcast FCCH, SCH and BCCH channels (that definition from book 2G Mobile Networks By Narang, page 84)
2. ... number of users – you can increase number of users with half rate traffic coding and additional frequencies.
3. are beacon frequency, signaling channel and user data channel different – No, it can be the same frequency - time multiplexed on the same frequency.

[karthik537]

Hi...

I think you are confusing b/n the terms "radio frequency channel" and normal channel...

Radio freq. channel is the combination of one uplink and one downlok freq with a duplex spacing of 45 MHz.

The channel that you stated is the logical channel that will be mapped on to the physical channel.

[cocoloco]

Thanks for your reply...
Can u answer my third query?

It can be the same or it can be different, it depends on how Traffic and signalling channels are distributed among frequencies or physical channels in the cell.

[leo3000]

Hi friends,
Please help me in replying to the below 3 queries.. I am undergoing GSM Traning... Please help me to know the concepts...

When a mobile is switched on, it synchronizes itself to the Frequency using FCCH Channel. That means it scanns each and every GSM frequency channel for a beacon frequency.

My first query is What is this beacon frequency?

If we say, the answer is that the beacon freq. is the freq to which the mobile synchronizes for further communications!!! then my second query is

I read in some book that a bast station(BTS) uses one freq. channel to broadcast beacon freq. and some for user data and Signalling. If one frequency channel is used to broadcast and lets say 20 mobiles in the cell has chosen that frequency, How all the 20 mobiles can communicate on the same frequency as we know that a frequency channel is divided only among 8 users (we can say 7 users as timeslot 0 is used for signalling)?

Third quer is:

The frequency channel that is used to find the beacon signal by MS and the freq channel that is used for signalling and the frequency channel that is used for user data are different?

Dear karthik537

In GSM, the beacon frequency is the frequency that carries at certain time slots the Signalling and control channels including the BCCH (Broad casting channel), and each cell got one BCCH not each BTS (BTS could have several GSM cells), and BCCH shall be on TS 0

When you switch your mobile on, the MS looks for these BCCH's from all operates, starting from the last GSM band the MS was on before it was turned off.

lets say that the operator is using one time slot in it for control and signalling and BCCH (TS0), firstly, the MS reads this TS and it will contain the FCCH, then next time it reads it (frame terminology) gets the SCCH, then BCCH, now the MS knows this operator and knows by the SIM card info if its an allowed operator or not (Home operator), and camps on the cell with higher power.

Now for the second third questions:
how 20 MS can communicate using the same cell, now lets say The MS was camped on a Cell with only frequency only, the MS sends a Request for accessing the Network using RACH (Random Access Channel), using the Uplink TS of the pair frequency of the beacon frequency, the cell replies with access granted channel (AGCH) and both channels are considered from the common control channels family that may be transmitted on the same TS that is used for BCCH (Remember that we send a frame on each TS not the same info each time), after getting the AGCH, the cell also send an SDCCH to the MS (stand alone Dedicated Control channel) to the MS, telling the MS the New Frequency that the MS will use and at what TS to do what is Needed (e.g Voice Call) this could be another frequency in the cell only used for traffic or a TS in the beacon frequency but not TS0, if a 20 user needs to be served in a cell with one carrier, for sure you'll get blocking rate in it unless you use capacity enhancing techniques such as adding new carriers, half rate or congestion relief or any other techniques.

i attached what I consider personally the Best Manual for GSM to my reply, hope its useful for you also, it contain all the answer with exact description

contact me for any help you need :)

[karthik537]

Hai leo...

Thank you very much for info...

I am unable to download the GSM Manual because of some privilege issue..

Kindly help me in sendign any other link to this manual to download.

[leo3000]

here is the file link
enjoy


GSM.rar - 4shared.com - online file sharing and storage - download (http://www.4shared.com/file/woQgjoaC/GSM.html)

:)