You are here:

# Satellite Communications/4 carriers

Question
Good afternoon,

I have 4 carriers consecutives frequencies

Carrier 1 BW = 400 KHz  Data rate = 682 kbps
Carrier 2 BW = 800 KHz  Data rate = 1366 kbps
Carrier 3 BW = 800 KHz  Data rate = 1366 kbps
Carrier 4 BW = 400 KHz  Data rate = 682 kbps
Total BW     =2400 KHz

WITH FEC 3/4 TPC ROLL OFF= 0.25%

so I only need 2.4 MHz to transmit the 4 carriers or do I need more BW to see the Carrier do no interfier each other
According to the formula

BW = SR( 1 + ROLL OFF)
It appears that I need more BW
Why is that?

Figure 3
Eduardo:

See attached Figure 3. The numbers were calculated using 8-PSK ¾ Rate FEC Turbo.

The numbers were calculated using the process described in previously cited article: http://www.satsig.net/symbol01.htm

•   Symbol rate = 0.444 X kbps
•   Occupied bandwidth (at -10 dB points) = 0.53 X Symbols/sec
•   Allocated bandwidth = 0.6 X Symbols/sec

Using roll off = 0.35, you need 1,091 kHz of allocated bandwidth.

I believe that you made a mistake by equating information rate (bps) with symbol rate (Sym/s).

I hope that this helps.
Thomas E. Burke, PhD, PMP

Satellite Communications

Volunteer

#### Thomas E. Burke

##### Expertise

No restrictions on questions.

##### Experience

Forty years of experience with satellite communications. Have held roles as system engineer on JPL Mariner 9 program and a program manager for a number of classified communication satellite programs. Served as head of TRW / Defense Communications Division / Engineering Development Operation, a 1,400-person organization responsible for all aspects of classified communication satellite design and development.

Education/Credentials
Ph.D. Chemistry, California Institute of Technology (1969) B.A. magna cum laude Chemistry, University of Minnesota (1962)