S
Steve Sousa
- Jan 1, 1970
- 0
Hello:
The problem is what is the necessary channel separation to transmit several
gsm signals on the same medium (direct intensity modulation on an optic
fiber).
I have searched all over books, google, I've read the etsi docs but i can't
find it. I've even asked teachers and got nowhere!
I'm looking for some sort of "guard-band" spec i can use, imagine the usual
BW plot, a rectangle:
----------- -----------
| | | | | |
--------------------- how close? ---------------------
-bw/2 fc bw/2 -bw/2 fc bw/2
Say i have a gsm signal with a BW of 24 MHz and carrier at 890-914. How
close can i set another carrier? 866-890 seems too close, but i don't want
to pull a number from the air and say "MHz between them is fine", there has
to be some sort of calculation/rule/norm that applies, my understanding from
ITU-R is that from 470 MHz to 2450 MHz transmitter tolerance for mobile
stations is 500 KHz, but I'm not sure this is it. I know that the first
channel is not used, so that would give 200 KHz. Or do i have to estimate
some sort of filter crossing bw/2 at -3db and some maximum attenuation at
some harmonic beyond that, like radio-amateurs use (something around -50db?)
What if one is gsm and the other a different modulation?
Suggestions for a more appropriate group are welcome.
Thank you.
I know you'll ask, this is not homework but it is part of my studies, an
extra-curricular activity that i now see might be way above my head.
Best Regards
Steve Sousa
The problem is what is the necessary channel separation to transmit several
gsm signals on the same medium (direct intensity modulation on an optic
fiber).
I have searched all over books, google, I've read the etsi docs but i can't
find it. I've even asked teachers and got nowhere!
I'm looking for some sort of "guard-band" spec i can use, imagine the usual
BW plot, a rectangle:
----------- -----------
| | | | | |
--------------------- how close? ---------------------
-bw/2 fc bw/2 -bw/2 fc bw/2
Say i have a gsm signal with a BW of 24 MHz and carrier at 890-914. How
close can i set another carrier? 866-890 seems too close, but i don't want
to pull a number from the air and say "MHz between them is fine", there has
to be some sort of calculation/rule/norm that applies, my understanding from
ITU-R is that from 470 MHz to 2450 MHz transmitter tolerance for mobile
stations is 500 KHz, but I'm not sure this is it. I know that the first
channel is not used, so that would give 200 KHz. Or do i have to estimate
some sort of filter crossing bw/2 at -3db and some maximum attenuation at
some harmonic beyond that, like radio-amateurs use (something around -50db?)
What if one is gsm and the other a different modulation?
Suggestions for a more appropriate group are welcome.
Thank you.
I know you'll ask, this is not homework but it is part of my studies, an
extra-curricular activity that i now see might be way above my head.
Best Regards
Steve Sousa