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TomS_
Git-r-done
MVM
join:2002-07-19
London, UK

4 edits

1 recommendation

TomS_ to raytaylor

MVM

to raytaylor

Re: Do Satelites have routers in them?

My understanding of Sat technology is: generally no

Satellites are really actually quite "dumb." Mostly they are a bunch of transponders, each of which receives on a frequency from the earth station, and re-transmits it back down to earth on another frequency (by a simple frequency conversion) to be received by a receiver.

As an example, the Optus D3 satellite has 32 Ku transponders in total, 24 are 125 watt and there are 8 backup transponders that can operate at 44 watts. (src Wikipedia)

In the case of an Internet service which is two way, Im not exactly sure how the return path is handled. It would likely be done with a second transponder, but Im not 100% sure.

The only smarts in a typical satellite will be the command and control electronics for telemetry, monitoring, positioning/maneuvering etc. Those are usually backed up with a spare in case it fails, and there are usually a couple of spare transponders that can be used for either occasional service, or to replace one if it fails.

Even in this configuration, with minimal electronics and "things that could go wrong", satellites are sometimes rendered useless, or partially useless when components fail.

I believe that future generations of satellites will contain more smarts like routers as component reliability has increased, or at least become so small and low on power consumption that it is possible to include a spare incase of a failure. This will allow satellites to route traffic between themselves without having to return to earth and make another trip back up**.

** Im not exactly a satellite freak, so this may have already been done

edit: Iridium satellites communicate amongst themselves in space
jim_p_price7
join:2005-10-28
Henryetta, OK

jim_p_price7

Member

said by TomS_:

In the case of an Internet service which is two way, Im not exactly sure how the return path is handled. It would likely be done with a second transponder, but Im not 100% sure.

It's handled on a different plane. Customers recieve on one plane (I'll say vertical here, although it's really a 3 dimensional concept when you introduce skew) and transmit on the other. Plane isolation is critical to the two-way nature, at least it is with Hughes.

TomS_
Git-r-done
MVM
join:2002-07-19
London, UK

TomS_

MVM

As in polarisation?

Or are we beyond that at this stage?
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

Yes, broadband satellites use polarity and frequency to provide enough isolation between TX and RX.

Someone asked about 140gbps spec for viasat-1 ... imagine there was a single large antenna receiving each beam at highest modulation ... then their hub transmitter would be pushing out that much raw data. This is higher than other broadband satellites because of more beams and some frequency tricks explained here:
»www.viasat.com/broadband ··· ess-pcma
54067323 (banned)
join:2012-09-25
Tuscaloosa, AL

1 edit

54067323 (banned) to TomS_

Member

to TomS_
said by TomS_:

In the case of an Internet service which is two way, Im not exactly sure how the return path is handled. It would likely be done with a second transponder, but Im not 100% sure.

For example with HughesNet on G3c where HughesNet has only a single horizontal transponder, subscribers will receive a download stream on 12.110 Ghz horizontal and will transmit an upload stream 14.410 Ghz horizontal.

Likewise the NOC will transmit up to the bird on 14.410 H and receive 12.110 H.

The transponder which is number 21 simply receives the signal and using an IF of 2.3Ghz block converts and amplifies and then downlinks what it receives.

Satellites on the uplink/downlink RF side are really dumb devices utilizing basic block convertors to do the frequency transconverting, they don’t do any error correction or frequency correction other than the IF reference on board.

It’s KISS at its best.

54067323

1 edit

54067323 (banned) to lutful

Member

to lutful
said by lutful:

This is higher than other broadband satellites because of more beams and some frequency tricks explained here:

There are not more beams with PCMA as those are dependant upon the design of the bird, it PCMA is however for all intents and purposes predicative TDMA, that may and that is a big may, provide additional bandwidth per channel efficiency at the cost of higher transponder power demands and since on-board power is limited and metered out on a per channel/transponder basis users of PCMA may or may not realize the claimed benefit of higher bandwidth by deploying PCMA.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

said by 54067323:

said by lutful:

This is higher than other broadband satellites because of more beams and some frequency tricks explained here:

There are not more beams with PCMA ...

I wrote frequency "tricks" because I share your concerns about PCMA. Otherwise, I just implied that Viasat-1 has more beams than typical broadband satellites.
54067323 (banned)
join:2012-09-25
Tuscaloosa, AL

3 edits

54067323 (banned)

Member

said by lutful:

I just implied that Viasat-1 has more beams than typical broadband satellites.

Beams or more precisely beam shaping is an old technology that allow the designers to aim power where it is desired versus just blanketing a continent and are nothing more than precise modifications of the downlink antenna reflector.

As for Viasat1 if you look into the company it becomes clear they are the remnants of WildBlue cobbled together hoping this one will make them profitable, but I wouldn’t hold my breath waiting for that to happen.

And as for PCMA it is really nothing more than carrier within carrier versus the standard single carrier per channel and is a technology that was developed back in 2010 so it's really not breaking news either.