<div dir="ltr">One of the features of DVB-S2 is that Gold sequence are used in the final physical layer scrambler. These are derived from an 18 bit number n. The use of Gold sequences has the effect of reducing the correlation between two signals which reduces the effects of co-channel interference. It can also be used to identify particular DVB-S2 sources. <div><br></div><div>By default, broadcast applications use a default n = 0 so that receivers can descramble all signals without knowing the value for n. But for applications such as ours, n can be set to a different value for each DVB-S2 source to minimize co-channel interference. The ASIC chips we are looking at have this capability. </div><div><br></div><div>When DVB-S2 receivers are validated, the validation involves both the wanted signal and one or more adjacent and/or co-channel unwanted signals at various power levels (as well the usual AWGN and clock phase noise impairments). This is an important component in the process of "validating" a receiver for an application, either in simulation or on real hardware. When we talk about the performance of a receiver it is not just the performance over a clean AWGN channel that is relevant but rather the performance in the RF environment of the final system. So this is always the caveat as well as one of the reasons that additional margin is almost always required beyond theoretical link budgets, a fact that many find easy to ignore. </div><div><br></div><div>I agree that it doesn't appear likely that we would have much interference between LOP-G and GEO for reasons pointed out by Kent. However, it's not too early to think about some band-planning. We have frequency re-use for geo slots but LOP-G will follow the moon. We have 50MHz allocation up and down (if we can hold on to it). This is not all one would ever need any more than 640K is all the memory one would ever need. (I'm writing this on a machine that is +50dB over that and servers processing it are another +10dB over that). </div><div><br></div><div>As an aside, we might also want to consider Gold codes for the uplink. It's relatively easy at both ends and it's likely they could improve adjacent channel interference at little cost. </div><div><br></div><div>WU1Y</div><div><br></div><div><br></div><div><br><div><br></div><div><br></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Feb 14, 2020 at 4:22 PM Michelle Thompson via Ground-Station <ground-station@lists.openresearch.institute> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">OK I see what you mean. <br><br>In doing a BOE for GEO, the occlusion is longer lasting, because the moon moves more slowly across the sky than a lower satellite, but the outcome appears to be the same. It's rare.<br><br>If we can put this on a single slide, for that one time someone with authority requires an answer, then the work to come up with numbers is worth it. I think Kent is correct in the order of magnitude for LEO and pretty close numerically. <br><br>I am interested in generating a solid number. Does anyone have good software for this, or want to write up a python script that encapsulates the problem? <br><br clear="all"><div><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr">-Michelle W5NYV<br><div><br></div></div></div></div></div></div></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Feb 14, 2020 at 1:07 PM KENT BRITAIN <<a href="mailto:wa5vjb@flash.net" target="_blank">wa5vjb@flash.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div style="font-family:"Helvetica Neue",Helvetica,Arial,sans-serif;font-size:16px"><div></div>
<div dir="ltr">Interference would be rare, and momentary.</div><div dir="ltr"><br></div><div dir="ltr">OK, the bird goes though a 360 deg arc in about 80 minutes.</div><div dir="ltr"><br></div><div dir="ltr">So in a typical overhead pass that's about 4 deg a min..</div><div dir="ltr">( Yes, a lot of variables in that equation! )<br></div><div dir="ltr"><br></div><div dir="ltr">The antenna beam is 6 deg if we allow for the -10 dB points.</div><div dir="ltr">So 90 seconds would put the 2nd bird well out of the pattern from the</div><div dir="ltr">ground station.</div><div dir="ltr"><br></div><div dir="ltr">Lots of orbits, a parallel orbit is not impossible, but in most cases they</div><div dir="ltr">would only be in common view of the ground dish for a minute or so.</div><div dir="ltr">I'll let someone else do this calculation. Take two LEO Birds, and when</div><div dir="ltr">looking from a common point on the ground, how often do they pass within</div><div dir="ltr">6 deg of each other? Not often I suspect. Kent WA5VJB<br></div><div dir="ltr"><br></div><div dir="ltr"><br></div><div><br></div>
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On Friday, February 14, 2020, 1:17:53 PM CST, Michelle Thompson <<a href="mailto:mountain.michelle@gmail.com" target="_blank">mountain.michelle@gmail.com</a>> wrote:
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<div><div id="gmail-m_6818384205080656734gmail-m_2564777488799449917gmail-m_6900171524736840917gmail-m_-1707047246837786919ydpd08fb6b4yiv6188454366"><div><div dir="ltr">Good point on frequency management.<br clear="none"><br clear="none">We plan to use (up to) the entire 10MHz amateur allocation. <br clear="none"><br clear="none">Gateway appears to be using less.<br clear="none"><br clear="none">Given that one can model this as a narrowband interferer to a broader band signal, in your opinion, can we accept or ignore the potential interference?<br clear="none"><br clear="all"><div><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr">-Michelle W5NYV<br clear="none"><br clear="none"><div dir="ltr"><br clear="none"></div></div></div></div></div></div></div></div></div><br clear="none"></div><br clear="none"><div id="gmail-m_6818384205080656734gmail-m_2564777488799449917gmail-m_6900171524736840917gmail-m_-1707047246837786919ydpd08fb6b4yiv6188454366yqt66897"><div><div dir="ltr">On Fri, Feb 14, 2020 at 10:20 AM KENT BRITAIN <<a shape="rect" href="mailto:wa5vjb@flash.net" rel="nofollow" target="_blank">wa5vjb@flash.net</a>> wrote:<br clear="none"></div><blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div><div></div>
<div dir="ltr">The typical Direct TV style dish looks at 1/4000 th of the sky.</div><div dir="ltr">Well, we only see 1/2 of the sky at any given time, so even if both birds are visible</div><div dir="ltr">at the same time, only 1/2000 of the time would they both be in the same beam</div><div dir="ltr">even if on the same frequency.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Yea, can crunch these numbers several ways but with a little frequency management</div><div dir="ltr">interference is going to be pretty rare. Kent WA5VJB<br clear="none"></div><div><br clear="none"></div><div><br clear="none"></div><div><br clear="none"></div><div><br clear="none"></div>
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On Friday, February 14, 2020, 12:03:12 PM CST, Michelle Thompson via Ground-Station <ground-station@lists.openresearch.institute> wrote:
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<div><div id="gmail-m_6818384205080656734gmail-m_2564777488799449917gmail-m_6900171524736840917gmail-m_-1707047246837786919ydpd08fb6b4yiv6188454366gmail-m_-5241446838015378738ydp20b95d1cyiv7388914926"><div dir="ltr">With AREx and Lunar Orbiting Platform Gateway (usually just called "Gateway") developing and progressing, Paul KB5MU brought up something we need to check on.<br clear="none"><br clear="none">If Gateway uses the 10GHz amateur downlink (and they plan to) how much impact do other 10GHz payloads present? QO-100, Phase 4X, CatSat, etc.?<br clear="none"><br clear="none">I think any interference or outages are going to be very small, but I'd like to have an answer before someone like ARISS asks. <br clear="none"><br clear="none">If we all use DVB-S2/X, then it would seem that there would be a potential for brief interference. <br clear="none"><br clear="none">Assuming 10GHz downlinks from Gateway<br clear="none">1) how often would potential interference occur for GEO, HEO, LEO? <br clear="none">2) is there anything that we (or Gateway) should do about it? <br clear="none">3) is there anything that we (or Gateway) could do about it?<br clear="none"><br clear="none">Goal: Quantify and document. <br clear="none"><br clear="all"><div><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr">-Michelle W5NYV<br clear="none"><br clear="none"><div dir="ltr"><br clear="none"></div></div></div></div></div></div></div></div></div></div></div></div>
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