Instead of having towers everywhere for cell phones, why do they not have Satellites run all cell phone signals? Is it too expensive? Too technical?
Because I remember reading about 8 years ago that there was a cell phone coming out that uses satellites instead of a tower to get it’s signal and they said you would get a signal no matter where you are in the country. Then, I never heard anymore about it.
So, why is there not a Verizon satellite network?
There are such a networks - Globalstar and Iridium. Iridium had to be saved from bankruptcy and shutdown by the US government.
There are many reasons why cell phones are a better idea, but the big one is battery life and phone size. It takes a lot more power to transmit a signal a few hundred miles to a satellite than it does to a cell tower down the block. Also, satellites are really expensive to launch - you can put up a lot of cell towers for the price of a single satellite.
Not a cell phone expert, but I am a Ham radio operator and can think of several reasons.
More power required to reach a satellite that’s maybe 200 miles up than a cell tower that’s five miles away. Hand held phones are limited to .6 watts of power.
Cell tower spacing allows many calls to be handled as each tower only needs to handle the call in it’s immediate area. Even then cell companies bring in portable towers to handle the increased load for special events.
Satellite phones don’t work with out a clear view of the open sky. Won’t work in buildings or other obstructed places.
I’m certain that there are many other reasons I’ve not thought of.
In short, because of the incredible expense.
There exist more than one satellite phone service with global or near-global coverage already. But the density of calls they can handle is limited by the bandwidth and power available, and you can only cram so much onto a single satellite.
Take, for example, the Iridium system. Its parent company went bankrupt trying to launch and commission the constellation. 66 satellites are necessary to provide continuous global coverage, plus ground stations and other infrastructure. Launching dozens of satellites is expensive. And the total system can handle, in theory, no more than 172,000 users at once, globally. You might have that many phone conversations going on in just one or two fair-sized cities.
Comparatively, cellphone towers are cheap and easy to erect, and much, much easier to repair or replace. The network can grow piecewise, wherever there’s market for it; a satellite constellation is pretty much a one-shot deal that isn’t very useful until the whole thing is in place.
Oh, I know they exist and have existed for many years. I just mean, why don’t companies offer that option. But it looks as if it’s been answered a little… tx
Having worked for the satphone industry, I can tell you they’re not really ready for primetime, and probably won’t be for some time. While Iridium, GlobalStar, and Thuraya all make satphones comparable in size to a smartphone, they’re extremely limited in what they can do.
At one point in time, the sats were unable to successfully pass calls to one another, so you’d have about a 4 minute window in which you could talk. After that, the call would be dropped. Data transmission rates for the handheld units were a blistering 14.4K, and in the case of Thuraya, the parts of the world you can use the phone are limited.
Larger units like Thrane & Thrane make are more capable, but not exactly easy to use, plus you can’t use them in certain latitudes. (They use birds in geosynch orbit.)
Iridium units also have the issue that they have a bizarre country code designation for the phone system, and some companies won’t allow you to dial the phones as they have no idea what the 8816 prefix means. If you do manage to reach an Iridium phone (and some other makes) via a landline, expect to pay $10/min for the call (the person receiving the call has to pay about $1/min). Until the cost of putting things in orbit comes down, don’t expect to see satphones have much of a footprint in the consumer market.
There are two main reasons to have cells vs satellites.
The main one is capacity. A satellite can only handle so many calls at once. If the satellite is over a big city with tons of people who want to make calls not every body will be able to make a call. With a cell system you can add more cells to crowded areas reducing the number of people served by a cell to something that allows people to make the calls they want.
The second is power. The phone has to transmit much more power if it wants to talk to a satellite 500 miles above the earth than it does to talk to a tower 3 miles away.
Another factor is signal delay. You’ve probably seen newscasts on CNN where the anchor is talking with someone in Iraq or somewhere via satellite transmission. There is a noticeable delay between the time the anchor asks the question and the other person responds.
Even at the speed of light, it takes a measurable amount of time for the signal to reach the satellite in orbit and be beamed back down to earth.
So, if you’re trying to have a conversation with someone, even next door, via satellite phone, there will always be a couple of seconds lag time between responses.
One other factor is the time delay due to the length the signal has to travel.
Like GaryM, I’m a ham radio operator, and have used some of the amateur radio satellites that are up there, one thing that you notice is the delay of your voice. (You transmit on one frequency, and listen on another, in different frequency bands, meaning that after you speak, a fraction of a second later, you hear your own voice coming back to you. It’s a bit wierd when you hear both sides, and you tend to slow down your speech, expecting the heard version to start matching the spoken version, which of course never happens). The further away the satellite handling your call is, the longer the delay.
Tower based systems are never more than a few dozen miles from your handset, so the delays are minimal, and more accurately replicate the landline system.
You can see a demonstration of satellite delay next time you watch the news, and they are interviewing someone in another location via satellite link. A question is asked, then you’ll notice a 1/2 - 1 second delay as the person on the other end “finishes listening to the question” and begins answering. This is not “thought time delay,” it’s communication time delay.
(of course, FatBaldGuy had to beat me to the submit button… dang work getting in the way of post submission!!! :D)
True, although the delay to and from a LEO satellite (485 miles) is much less than the delay to and from a geostationary satellite (22,236 miles). The network reporters are communicating via two C or Ku satellites, which are always geostationary (the Russians do have some LEO TV sats). When it is not possible to set up an earth station, they might use multiple LEO sat phone channels.
I don’t think this is related to signal travel time though, is it? The speed of light is fast enough to go around the planet 7 times in a second.
If I’m wrong someone correct me, but I’d guess that the delay is more likely taken up by making the analog video image/audio and turning it digital, compressing it, possibly encrypt it and transmit it, then decrypt/process it once it reaches the target.
Nevermind, I didn’t realize satellites were so damn far away.
Keep in mind that for a geosynchronous satellite, the round trip path for a signal (up to the satellite, and down to the receiver) is aproximately 46,000 miles. Light travels at 186,000 miles/second, which means that the delay, one way, is about .25 seconds. As a communication is 2 way, this results in a 1/2 second delay total.
It’s not the only factor, but it is a significant one. Even for satellites in LEO (<1000 miles), the delay is noticeable, as I mentioned with the amateur radio satellites. I used to use RS10/11 (a Russian weather satellite, with an amateur radio payload added on), and I could easily recognize the delay when listening to my own transmission in my headset. (you listen on one frequency, and transmit on another, and need to adjust your receive frequency to compensate for doppler shifts as the satellite moves overhead).
The biggest factor though, is still cost of the satellites, and the power required for a signal to reach them. Your tower based phone uses (handheld versions) less than 1 Watt of power to transmit. I used 25 to 100 Watts to reach the LEO RS10/11 amateur radio satellite. Your phone’s battery would either have to be much bigger, or would have unacceptable battery life.
Capacity is also a big factor. Your 1Watt signal doesn’t reach very far, and an individual tower doesn’t need to handle as much traffic.
It was not that long ago that transatlantic calls were routed via satelite and the time delay was a PITA.
While the physics of transmission is an important factor, the primary reason for land-based base stations is this:
Each base station (whether in a cell tower or on a satellite) can only handle a certain number of calls at any given time. Sat stations are made to handle more, but they are still limited. Quite simply, it’s orders of magnitude cheaper to build many stations that can handle a few calls then a few stations that can handle many.