Technical Question about bandwidth

[Tom Snyder]

A discussion at AVS is raging about who has the necessary bandwidth to accomodate the future of HDTV... cable or satellite.  

Here's the question: How much bandwidth capacity (and thus how many potential HDTV Channels) does cable provide, and how does that compare with that of DirecTV and Dish with the satellites they have available?

[borghe]

DirecTV currently (I believe) has about 30-35Mbps on each transponder. Dish is able to pull off about the same number through normal QPSK modulation, and in theory able to pull off more like 50-60Mbps using 8PSK.  I may be wrong on these numbers but this is what I remember. DirecTV has 46 CONUS transponders and Dish has 50 CONUS transponders. In theory (and not counting spot beams taking away some transponders) this gives DirecTV a total of ~1.38Gbps and Dish ~1.5Gbps. Both of those numbers will go down by a few hundred mbps because not all transponders are available to all areas being that some are spot beam.

Cable.. yikes.. umm. despends on what they are pushing through the pipe. I mean there is enough in there to carry your digital signal as well as a 2Mbps Road Runner signal. Over shielded copper you could theoretically run speeds in excess of 1.3Gbps. But that is all really a moot point. Given the two way communication nature of cable, you really don't need a ton of bandwidth. The cable box could in effect send a request to a server to begin sending "program x" to "box y" and then the most you will ever need is the 19.2Mbps.

[Pat]

The cable box could in effect send a request to a server to begin sending "program x" to "box y" and then the most you will ever need is the 19.2Mbps

...per subscriber.  Neighbors all share the same pipe  - that is, it's not point to point.

[gparris]

It WOULD be great to know - from a TECHNOLOGICAL standpoint-WHICH is the better technology. Satellite, to my understanding, now that the merger is dead, will be  hard pressed to give up on local channel offerings in order to offer more HD channels. Cable HAS an edge over Satellite as cable does not have to offer locals for EVERY DMA in the country and eat up bandwidth and compress like DIRECTV and DISH do. Imagine if TWC had to offer the whole country's TV stations in order to provide Milwaukee's? Now,without the merger, there is duplication and wasted bandwidth-another nail on Satellite's coffin.
So when they're done with all those channels and spot-beams-very little is left for HDTV---let alone HDTV locals! Cable is slowly realizing that it has the edge it needs to conquer Satellite at its own game. Add HD DVRs and GOOD service-Satellite loses market share and cable wins. Rural areas or those without cable availablity will be Satellite's ONLY customers, probably like before with C-Band and OTA (which is still a good value if you're close enough to the stations transmitting).
Now all cable has to do is REALIZE IT!
Read that, TWC? Get busy!

[Greg Oman]

Ahhh, but wireless is cool.  Even though Gregg commented about the cost to launch and support a satellite vs installing cable infrastructure in another thread, rural areas will continue to be able to be served better via a satellite than stringing a cable in the ground.  Metro areas are another story, but a few spot beams will pretty much take care of that in the US.

Satellite will be around for some time.  Just like in 1990 when I wrote a paper about DCC vs MD.  Then DCC evaporated. :bang:

Greg O.

[gparris]

That is what I said-rural areas will be the Satellite customer...but for the rest of us (the majority) who live around cable-we will get the best HD around ONCE TWC gets its act together. The REAL competitor will be getting cable or OTA or that SAT/OTA combo some of our members enjoy (again OTA in the urban areas,where it is reachable, like cable).  You can always get more channels (HD channels) with cable but Satellite is limited when it produces locals for every local area. You can even run more cable(unlikely) but not anymore Satellites...bandwidth with them is limited-and when Sat has to add hundreds of channels for locals...you get the idea. Think about it. Is there another Sat technology so we can get HD locals, too? Think not. If DIRECTV wasn't adding 50 new markets soon, we'd have DISCOVERY HD by now.

[ReesR]

<--- thrashing through satellite transponder lists looking for what is still open.....(can ya picture it?)

If, as we now believe, the unused transponder list is empty then we have arrived at our answer.  But I have this lurking feeling that there is still bandwidth available for HD.  Remember, there are three satellites being used not one.

Because this post was inspiring enough to comment on at 445am after an (ahem, cough cough) early morning potty break, I had to start my post but will later edit this post after doing some research.  (maybe someone will beat me to it)

========

it's now 5:10am.  prelim data shows the following:

There are 3 "current" satellite positions for Directv:

101, 110 and 119 degrees west longitude.

What is interesting to note is no ku band satellites are being currently used "inbetween" 101 and 110  as well as 110 and 119 degrees.  So, it is certainly possible additional whole satellite transponder space could be implemented with the already in place satellites which have ku transponder systems.  For example, G-Star 4 has ku transponders at 105 degrees which is located right in between directv's satellite positions of 101 and 110.  

This is but only a theory on my part but I can't see why this wouldn't work.  Fancy spot beams might be in order etc but ya never know.  G-Star 4 is already in place and has little or no ku space being used for anything.

Just some food for thought.  

Now back to sleep.


zzzzzzzzzzzzzzzzzzzzz

[borghe]

Isn't there some unofficial rule saying that satellites have to be at least 9° apart from each other to avoid interfering with the other sats' signals? I know we are talking about different bads here which probably changes that, I just though I remembered that.

Although supposing that the 9° rule doesn't apply if you are talking about different bands, then you are still talking about introducing an entirely different transport for the signal which will at the bare minimum require a new dish and additional installation. At the most it will require entierly new hardware. Now us early adopters of HD through DirecTV or Dish felt this was worth it, both in effort and money, but be certain that Joe Sixpack will not at all be interested in this. They will just say screw it and switch to cable.

Whatever DirecTV does it will have to somewhat exist inside the same infrastructure. The guy who picked up his receiver in 1995 is still able to use it now with no real loss of features. I think many people with DirecTV are grateful of that. If they force everyone to upgrade, there that ace in the hole goes.

[uplinkguy]

Satellites are usually spaced every two degrees.  If satellites had to be spaced every 9 degrees, there would only be room for 40 of them around the earth.

Big ugly dishes in people's backyards are machined to look at a 2 degree slice of sky.  If the dish is bent, warped or dented, it starts to see other satellites at the same time, same frequency.  Interference from neighboring satellites is minimized by flip-flopping the polarity of the transponder between horizontal and vertical.

Uplink dishes and professional downlink dishes are of a higher quality to stay within the 2 degree requirements.  Typically the bigger the dish, the tighter the arc of sky it will see and will see less of the neighboring satellites.

I once did the math figuring out the distance of the geostationary orbit of the satellites from earth and how far apart 2 degrees is.  I think the answer is most satellites are about 800 miles apart.

G star 4 has very little traffic on it for a good reason.  It is very old.  It does not have much power left on it so most of it's transponders have been shut down.  It also needs a lot of power from an uplink source to illuminate a transponder.  The signal put out from the signal is very weak.  Only the biggest of receive dishes can see it cleanly.
  I don't have my guide at home, but its end of life must be very soon.  CNN still might use it occasionally for back-hauls of news feeds if they are in a space crunch.

There are also several other KU/C band satellites within that area of space.  AMC 1 at 103 degrees is NBC's main satellite for their network.  Canada also has 3 Anik birds in the same area.  Dish Network also has 2 satellites at 110 degrees and one at 119.

Given the sharing of frequencies, dish and directv have pretty much tied up almost all the usable spectrum at the three positions of 101, 110, and 119.  borghe's comment about a 9 degree spacing might be accurate pertaining to the DSS dishes and satellites.  Directv's 101 and 119 satellites share the same frequencies, the 110 satellite is higher in frequency, hence the need for the special 'sat c' lnb for the center position of the oval dishes.

Here is one link to a web site that tells what's up there:
http://www.lyngsat.com/

[borghe]

It may have been DBS sats to come in over a single dish. With as close as the current receptors are on the dish I couldn't see them sqeezing anymore satellite signals in between any of those spots. Maybe they can introduce more DBS dishes with less than 9° of separation, but you would most likely need a completely separate dish to receive it..

[gparris]

The reason why the other satellite companies get irritated with the 2 big providers is that they must have the 9  degrees to avoid the signal messup. I believe there is a reason technically that other companies cannot put a 105 degree satellite between DIRECTV and them  and a "FULL CONUS" thing.  
Cable does have an option for increasing bandwidth availablity and it is called "Big Band" that makes better use of the spectrum cable uses to allow for more channels without degredation. Anyone hear of it?