Comtech EF Data MIDAS 4 System and Design - Manual (Page 46)

System and Design Manual, Revision 2
3–4
Theory of Operation
Modulation Factor 1 for BPSK
2 for QPSK
2 for OQPSK
3 for 8PSK
4 for 16QAM
In general, “n” modulation factor for 2 n constellation.
FEC Rate Viterbi, Sequential, or Turbo, TCM coding rate (1/2, 2/3, 3/4, 5,6, 7/8, 8/9,
5/16, or 21/44)
Reed-Solomon 1 if option is OFF
225/205 if option is On
Carrier Spacing User-selectable between 1.2 and 1.5 in steps of 0.05
The difference in center frequencies of adjacent traffic carriers is given by:
∆f = [bw
1
+ bw
2
] * 0.5
where:
∆f = spacing between the two carrier center frequencies.
bw
1
= allocated bandwidth of carrier 1.
bw
2
= allocated bandwidth of carrier 2.
Example
Assume that 1.1 MHz of bandwidth (starting at 0.0 MHz) is available to a
user. The channels are 2.5kHz, carrier spacing of 1.3, Reed-Solomon is not
used, and the additional acquisition range for the inbound control channel is
10 kHz.
Of the owned bandwidth, 25.0 kHz (24.96 kHz rounded up to the nearest
multiple of 2.5 kHz) is allocated to the outbound control channel, and 45.0
kHz (24.96 kHz plus 20 kHz for the acquisition, rounded up to the nearest
multiple of 2.5 kHz) is allocated to the inbound control channel, leaving
1030.0 kHz for user traffic.
At QPSK, FEC Rate = 1/2, a 64 kbps data channel requires 85 kHz (83.2 kHz
rounded up to the nearest multiple of 2.5 kHz). A full duplex circuit with two
channels (one for each direction) requires 170 kHz. 510.0 kHz is allocated to
three full duplex data circuits of 64 kbps each.
At QPSK, FEC Rate = 1/2, a 256 kbps simplex data circuit requires 335.0 kHz
(332.8 kHz rounded up to the nearest multiple of 2.5 kHz). 335.0 kHz is