Glossary - Comtech EF Data DMD50 Installation And Operation Manual

DMD50 Universal Satellite Modem
3.14.17

Glossary

Allocated Bandwidth
Bandwidth or Allocated Bandwidth or Occupied Bandwidth is the frequency space required by a
carrier on a transponder.
For example, a Duplex E1 (2.048 Mbps) Circuit with 8-PSK Modulation, FEC Rate 3/4 and 1.4
Spacing requires:
2.548 MHz = 2.048 / (3 * 0.75) * 1.4 * 2
For a 36 MHz transponder, 2.548 MHz corresponds to 7.078% Bandwidth Utilization.
Power Equivalent Bandwidth
Power Equivalent Bandwidth (PEB) is the transponder power used by a carrier, represented as
bandwidth equivalent.
PEB Calculation Example:
•
•
•
•
•
•
This corresponds to 12.59% of available transponder power.
Leased bandwidth
Almost all satellite operators charge for the Leased Bandwidth (LBW). Leased Bandwidth or
Leased Resource is the greater of the Allocated Bandwidth and Power Equivalent Bandwidth.
For example, if a carrier requires 3 MHz of Allocated BW and 4.5 MHz of PEB, the Leased
Bandwidth is 4.5 MHz
Power Spectral Density (PSD)
Power Spectral Density (PSD) is the signal power per unit bandwidth: dBW / Hz or dBm / Hz
For example: Signal power = 20 dBm
PSD Ratio
PSD ratio is the ratio of power spectral density of
the interfering carrier and the desired carrier. If
looking at the 2 carriers side-by-side on a spectrum
analyzer:
MN-DMD50– Revision 3
Transponder EIRP = 37 dBW
Output Backoff (OBO) = 4 dB
Available EIRP = 37 – 4 = 33 dBW = 10
Transponder Bandwidth = 36 MHz
Power Available / MHz = 1955.26 / 36 = 54.424 W
If a carrier uses 24 dBW, its PEB = 10
Signal bandwidth = 500 kHz
PSD = 20 – 10 *log (500 * 1000)
= -36.99 dBm / Hz
3.3
= 1955.26 Watts
2.4
/ 54.424
= 4.532 MHz
Theory of Operation
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