Please explain the main physical advantages of using satellites for communication as I'm sure there are many.
$\begingroup$
$\endgroup$
4
-
$\begingroup$ What is a radio wave? What is a microwave? $\endgroup$– PeltioCommented Jul 13, 2015 at 8:00
-
$\begingroup$ is it like greenhouse effect trapping radiowave instead of IR using free electrons instead of CFC gases? $\endgroup$– user6760Commented Jul 13, 2015 at 8:38
-
2$\begingroup$ With one satellite parked in geostationary orbit, you can create one stationary reference point that can simultaneously broadcast a signal to an entire continent AND it doesn't have cables, transmission lines, or relay stations that can be easily severed or destroyed, which would ordinarily isolate sections of the continent. That alone makes satellites communications worth every cent we've put into them. $\endgroup$– JimCommented Jul 13, 2015 at 13:43
-
1$\begingroup$ Here's a homework assignment for you: Try to receive a radio broadcast from as far away as you can. Try this at different times of day. You'll find that (1) the signal quality is usually pretty bad after bouncing off the ionosphere, and (2) the furthest signal you can get will often simply not be there (since the ionosphere changes with the time of day). $\endgroup$– user10851Commented Jul 13, 2015 at 21:50
Add a comment
|
2 Answers
$\begingroup$
$\endgroup$
1
This technique is only good for frequencies below about 30MHz, and tend to be omnidirectional (depending on antenna). This limits the amount of information that can be encoded and transmitted between specific Tx/Rx pairs. Satellites use tightly focused beams in the tens of GHz, providing far higher bandwidth and more discrimination between data paths.
-
2$\begingroup$ +1 Also reliability is a big issue. The ionosphere's reflectivity is highly variable, a satellite is always there with the same signalling performance. $\endgroup$ Commented Jul 13, 2015 at 10:22
$\begingroup$
$\endgroup$
5
Bandwidth, and a more specifically amount of information you can send within it is crucial. Satellites are used for video transmission (DVB-T2), audio communication (Inmarsat), data communication (Internet link) and all of this within one hardware box.
Jamming. This is the crucial issue, imagine 1000 people communicating with each other in the same channel, earth effects, sun effects. Even if coded data will propagate within your signal, you will need advanced techniques to reduce SNR.
Coverage. Time of propagation between satellites is much lower that within ionosphere. Imagine you want to send data from the UK to Australia, it will take several ,minutes to propagate and seconds within satellite constellation. Earth-Ionosphere propagation takes at least twice more distance
-
$\begingroup$ Why would reflected radio waves take hours to circle the Earth within the ionosphere? For that matter, why would a signal take minutes to travel from one satellite to another? $\endgroup$– AsherCommented Jul 13, 2015 at 15:35
-
$\begingroup$ @Asher x2 distance propagation, from earth - ionosphere-earth. Satellites - straight line from one to another in vacuum. Earth-Inosphere have bad conditions for propagation - storm, humidity zones, etc. Look at image I've add $\endgroup$– sigrlamiCommented Jul 13, 2015 at 16:23
-
$\begingroup$ Light can cover the distance between London and Brisbane in a bit more than 1/20th of a second. Even if you double the path length, that's about 1/9th of a second, not hours. Likewise, a signal can travel from one communication satellite in geostationary orbit to another on the opposite side of the Earth in less than a third of a second, not minutes. Light travels very quickly. $\endgroup$– AsherCommented Jul 13, 2015 at 20:54
-
$\begingroup$ @Asher I'm perfectly aware of the speed of light.yes, if it's 1 bit in perfect conditions. Consider transmitting something like video over ionosphere. I made example in a sense that communication complete when data is fully retrieved on the other side. You can lose a lof of data and waiting for repeat bits. Anyway, updated my answer to minutes-seconds condition. $\endgroup$– sigrlamiCommented Jul 13, 2015 at 21:16
-
$\begingroup$ Ah, I see my misunderstanding. Yes, sending a video or other large file would take hours; but since you said "send data" without specifying how much data, the natural assumption is that you're talking about the signal speed rather than the transmission speed. $\endgroup$– AsherCommented Jul 13, 2015 at 22:02