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 Satellite Internet forum › LinkStar Forum: VSAT hubs and terminals › BW/ Remote Calculation
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# BW/ Remote Calculation

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 zizo9227 Member ★★ Offline Posts: 19 Jul 19th, 2011 at 1:09pm     could any body help me on how to calculate the BW/ remote in an iDirect Star network? if I give the customer 256/128kbps with 1:10/1:20 contention in the downstream and upstream respectively (QPSK with .66FEC in upstream and .793 FEC in downstream and 40% spacing) what is the consumed BW (in MHz) by the customer? please elaborate Back to top IP Logged
 Eric Johnston Senior Member ★★★ Offline Posts: 2109 Reply #1 - Jul 19th, 2011 at 9:05pm   256k is the outlink information rate.FEC = 0.793so transmission bit rate is 256/0.793 = 323 kbit/sQPSK has 2 bits per symbolso symbol rate = 323/2 =  162 kps (symbols per second)The allocated bandwidth of the carrier is approx 1.4 x symbol rate. Transponder bandwidth needed = 227 kHz.Similarly the return link (upstream)..128k is the return link information rate.FEC = 0.66so transmission bit rate is 256/0.66 = 191 kbit/sQPSK has 2 bits per symbolso symbol rate = 191/2 =  96 kps (symbols per second)The allocated bandwidth of the carrier is approx 1.4 x symbol rate. Transponder bandwidth needed = 134 kHz.Total transponder bandwidth needed = 191 + 134 = 325 kHz.Note:The satellite operator will decide the actual bandwidth needed, to protect adjacent transponder leases. They will almost certainly accept a 1.4 figure (as above), but might dispute 1.2 (i.e. a rather close spacing) if you were to suggest it.  A factor of 1.35 is often used.  I would suggest an extra 10 kHz or so for frequency errors, which is relevant for such very small carriers.The average bandwidth associated with each customer is 1/10 or 1/20 of the above if shared evenly over say one month. It depends how many are sharing and whether or not you force some fair sharing policy.  If the system is active, at any instant one customer is using the full download capacity and one customer using the full upload capacity.  If you have a free-for-all and one customer is dominant and tries to send/receive all of the time then that customer will get more than their 1/10th or 1/20th share. Best regards, Eric. Back to top « Last Edit: Jul 20th, 2011 at 10:11am by Admin1 »     IP Logged
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