FDMA and TDMA
FDMA and TDMA
(OP)
Hi,
THe GSM network uses a combination of FDMA , TDMA and frequency hopping to share the radio spectrum.
The allocated 25 MHz bandwidth is divided into 124 carrier frequencies. And within each carrier frequency, it's divided in time into 8 burst, hence giving a total of 992 channels.
Can anyone tell me if this 992 channels are enough to support the number of subscribers worldwide? (or am i getting the facts right??)if not, how else does it cope with the large number of subscribers all over the world? ALso, how does frequency hopping fit into the picture?
beadCraze
THe GSM network uses a combination of FDMA , TDMA and frequency hopping to share the radio spectrum.
The allocated 25 MHz bandwidth is divided into 124 carrier frequencies. And within each carrier frequency, it's divided in time into 8 burst, hence giving a total of 992 channels.
Can anyone tell me if this 992 channels are enough to support the number of subscribers worldwide? (or am i getting the facts right??)if not, how else does it cope with the large number of subscribers all over the world? ALso, how does frequency hopping fit into the picture?
beadCraze





RE: FDMA and TDMA
RE: FDMA and TDMA
I would have thought 992 is to be distributed among the cluster of 7 cells, and have that 7 cells pattern repeated. So approximately 193 in a cell? I m not sure myself.. just trying to figure it out.
beadCraze
RE: FDMA and TDMA
RE: FDMA and TDMA
To assign each user a varying time slot would be extremely complex, so presumably there is a guard time between transmissions. Will this not cut into bandwidth significantly, or are my assumptions wrong? (won't be the first time!)
Also, mobile companies are advertising internet connection over mobile links. Any ideas about the actual bandwidth (B/s) offered here?
John
RE: FDMA and TDMA
Check it out on the web for details--here is a newsgroup that may help
http://www.erlang.com/forum/
Don't ever rely on only one place (like eng-tips) for all your interactive news-grouping.
RE: FDMA and TDMA
To overcome the propagation delays (when transmitting from the mobile to the base station), timing advance is used to help with the timing synchronisation. Mobiles at different location in a cell will have different propagation delay since their distance from the base station varies. The base station caters for this problem by telling the mobile to advance its timing. This timing advance is then superimposed onto the 3 time-slots.
This is how the burst are transmitted and received accurately within the 'real-time' time slots.