Return links from VSATs to the hub are expected to comprise a variety of
small TDMA carriers with QPSK 3/4 rate FEC such as:
210kbit/s 140 ksps burst carriers with 168 kHz noise bandwidth and 200 kHz spacing.
420kbit/s 280 ksps burst carriers with 336 kHz noise bandwidth and 400 kHz spacing.
840kbit/s 560 ksps burst carriers with 672 kHz noise bandwidth and 800 kHz spacing.
All remote sites are within the uplink contour of +6 dBK and transponder gain step is set to PFDsat=-96 dBW/m2
The transponder multi-carrier operating point is -7 dB in and -2 dB out. C/Intermod = 21 dB at this point.
Assuming whole transponder is filled with 180 carriers, each with 200 kHz allocated bandwidth. Or any other combination of carriers of various sizes.
Total power spectral density produced at the satellite of all carriers combined is -96 -7 = -103 dBW/m2
Saturated downlink EIRP towards the hub site = 54 dBW.
Operating PFD produces a total downlink EIRP = 54 - 2 = 52 dBW
This conversion (-103 in and + 52 out) has been put into the link budget. It applies to multi carrier operation.
The remote site transmit BUC is 2 watt, operated at 0.25 W in clear sky conditions with 210 kbit/s carrier or 0.5W with 420 kbit//s carrier. Note 0.25W x 180 = 45W
If a half transponder is leased the capacity is 210 x 90 carriers = 18.9 Mbit/s. This might in practice allow about 10 Mbit/s through, complementing a 40 Mbit/s outlink.
The input figures are all guesses and estimates. You need to overwrite the figures with your own assumptions.
Amend any white boxes and then click the calculate button to obtain results in the green boxes.
Any problems or comments please e-mail Eric Johnston
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