7 replies to this topic

[coe]

If a total of 40 MHz of bandwidth is allocated to a cellular system which uses two 30 KHz simplex channels to provide full duplex voice and control channels. The system uses guard of 50 KHz at the beginning and at the end of the available spectrum. Compute the number of channels available per cell if the system uses 7 cell reuse pattern.

I don't know what to do with the additional 50Khz added to spectrum?

can someone help,


lisa,

[sirkozz]

I know it might seem excessive however in cell systems (TDMA/GSM) a set channel is allocated to each mobile, one for uplink, one for downlink. A frequency guard is the spacing between the transmit and receive channels. This ensures that co-channel interference will not impede clear data transmission.
50KHz(guard) 30KHz(data) 50KHz(guard) 30KHz(data) 50KHz(guard)= 210KHz per call, typically 200MHz per call is engineered for.

40MHZ/200KHz= 20 calls per given bandwidth *7(cell reuse)= 140, although in both TDMA/GSM the number is far greater because each mobile is reserved a time slot to transmit that will not interfere with either the MS or BS.

7 cell reuse requires the use of sectorization of the BS antennas allowing for the cell reuse; with omnis this would be impossible.

Hope this helps.

btw if you don't mind my asking what are you trying to do? These questions are really telco/mobile engineering questions?

[coe]

Hello Sirkozz,

I am trying to prepare for comprehensive exam , thanks for help.

question here:

since it uses 50 KHz at each side, shouldn't be like this:

50KHz(guard) 30KHz(data) 50KHz(guard) 30KHz(data) = 160KHz per call, why the additional 50 KHz?

also shouldn't be 40MHZ/200KHz= 200 calls instead of 20 calls as you said?

and to calculate no. of channels / cell i will divide 200/7= 28 channles / cell


don't you think my answer is correct....??

sorry to take so much of your time.

Regards,
lisa

I know it might seem excessive however in cell systems (TDMA/GSM) a set channel is allocated to each mobile, one for uplink, one for downlink. A frequency guard is the spacing between the transmit and receive channels. This ensures that co-channel interference will not impede clear data transmission.
50KHz(guard) 30KHz(data) 50KHz(guard) 30KHz(data) 50KHz(guard)= 210KHz per call, typically 200MHz per call is engineered for.

40MHZ/200KHz= 20 calls per given bandwidth *7(cell reuse)= 140, although in both TDMA/GSM the number is far greater because each mobile is reserved a time slot to transmit that will not interfere with either the MS or BS.

7 cell reuse requires the use of sectorization of the BS antennas allowing for the cell reuse; with omnis this would be impossible.

Hope this helps.

btw if you don't mind my asking what are you trying to do? These questions are really telco/mobile engineering questions?

[sirkozz]

50-30-50-30-50-30-50-30-->ect.

That’s why its 210KHz per call, although because every other channel requires only 1 50KHz guard, RF engineers use 200KHz per call, it’s just the figure that’s used.

40MHz/200KHz=200 you are correct sorry about that haven’t had a math class in years
200/7=28 correct sorry * when I should have /.

Sitting in my van in Danbury CT, been on conference calls all day and have to go to work @9pm.

Good luck on your test!!!

sirkozz

[coe]

Hello Sirkozz,
Do you know where I can find some notes about this problem? I want to see more examples.

thanks a lot for your help. wish you a good day. when do you finish work?

50-30-50-30-50-30-50-30-->ect.

That’s why its 210KHz per call, although because every other channel requires only 1 50KHz guard, RF engineers use 200KHz per call, it’s just the figure that’s used.

40MHz/200KHz=200 you are correct sorry about that haven’t had a math class in years
200/7=28 correct sorry * when I should have /.

Sitting in my van in Danbury CT, been on conference calls all day and have to go to work @9pm.

Good luck on your test!!!

sirkozz

[sirkozz]

See if you can get a hold of a copy of WIRELESS NETWORKING by: Anurag Kumar, D. Manjunath, Joy Kuri
It’s a pretty intense RF engineering tome, full equations ect. Published in 08 so it’s recent. Try google, MIT, and IEEE, all have great engineering docs.

Tonight about midnight, the problem is that the phone and email never stop!!! 24/7/365 phone and email support!!! My current project is 30+ sites in 30 days!!! 4500 miles!!! 2-3hours onsite each, life of the field tech sometimes is the “life of riley”!!!

[coe]

Hello Sirkozz,
just hope things are well with you and thanks. I know you might be at work now, just wanted to wish you good luck, you are my hero. Thanks for all help and talk to you later.


lisa

See if you can get a hold of a copy of WIRELESS NETWORKING by: Anurag Kumar, D. Manjunath, Joy Kuri
It’s a pretty intense RF engineering tome, full equations ect. Published in 08 so it’s recent. Try google, MIT, and IEEE, all have great engineering docs.

Tonight about midnight, the problem is that the phone and email never stop!!! 24/7/365 phone and email support!!! My current project is 30+ sites in 30 days!!! 4500 miles!!! 2-3hours onsite each, life of the field tech sometimes is the “life of riley”!!!

[sirkozz]

Lisa sorry for some of the ambiguity its been 10+ years since I’ve done any cell work, used to work for Nortel in both cellular and CO telephony.