Radyne DMD2050, Operation Manual

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DMD2050 Universal Satellite Modem Appendix E
TM110 – Rev. 1.3
E
-3
E.2.1 Calculating the Required Satellite Bandwidth
In order to calculate the satellite bandwidth (i.e. the symbol rate), we must first calculate the
Efficient D&I Rate (i.e. the data rate plus the overhead required for Efficient Drop & Insert). From
there, the calculation of the required satellite bandwidth is identical to all other modes of operation
and simply takes into account modulation type and forward error correction.
In this section, we will cover the calculation of the basic Efficient D&I Rate, as well as, the two
cases that alter the basic rate.
E.2.2
Calculating the Basic Efficient D&I Rate
When E1 signaling is not required (all T1 and PCM31 cases) and Enhanced Async is not enabled
(the Earth Station to Earth station link is the standard ES-ES), the Efficient D&I Rate for N
timeslots is as follows:
Efficient D&I Rate = Data Rate + (N * 250 bps)
In other words, the basic Efficient Drop & Insert Rate only requires 250 bps of overhead per slot,
while at the same time providing all of the functionality found in the open network standard plus
Automatic Uplink Power Control. By comparison, the open network standard requires 4267 bps
per slot, so by utilizing Efficient Drop and Insert, Radyne customers can realize a bandwidth
savings of over 4000 bps per slot.
E.2.3
Calculating the Efficient D&I Rate with E1 Signaling
When E1 signaling is enabled (PCM-30, PCM30C), an additional 2000 bps per slot are required
to carry the E1 signaling. So the Efficient D&I Rate for N timeslots is:
Efficient D&I Rate increase = N * 2000 bps
With the open network standard requiring 4267 bps per slot, Efficient Drop and Insert provides a
bandwidth savings of over 2000 bps per slot when E1 signaling is required.
E.2.4
Calculating the Efficient D&I Rate with Enhanced Asynchronous Overhead
The amount of overhead required to carry the Enhanced Async is driven by the in-band baud
rate. The calculation is a two step process involving the in-band baud rate and the number of
slots as follows:
X = Truncation of (In-Band Baud Rate / (N * 125))
Efficient D&I Rate increase = X * N * 125 bps
Because of the truncation, this increase in bandwidth is guaranteed to be less than the baud rate
itself.