I have a question which I haven't seen discussed when it comes to WiMAX. Is there enough radio frequency bandwidth to support more than a few dozen high-speed users per access point?
The bottom line with any wireless system is how well engineered it is.
The following techniques help a lot:
a) broadband suppliers give a 'contention ratio' somewhere between 20 and 50. In other words they assume you are only using it 1/20 to 1/50 of the time. So a single 2M radio link can handle 20-50 customers each with 2M and a 100M radio link can handle 1000-2500 people (in principle.)
b) directional antennas help a lot. So, if they stick up a mast with antennas pointing in different directions (adjacent antennas on different frequencies) then they'll get very little contention.
c) nodes that don't 'shout'; in other words if the nodes don't transmit at any more power than they absolutely need to; this minimises the distance that any interference is likely to occur at; permitting channel reuse.
d) add base stations, (particularly in conjunction with c) ) this mean that each base station can transmit and receive at lower power- this reduces the size of the coverage area, and you gain multiple times the users (since each node only uses up the bandwidth for a smaller distance).
e) use different channels (each channel has its own customers on)
f) node routing (in other words, instead of a customer sending a signal all the way to the base station, route it through another customer that is closer).
If you use all these techniques appropriately, the amount of bandwidth per user is constant, independent of the number of users, surprisingly.
Copper is too soft and heavy so aluminum transmission lines are built but there is too much resistance so transmission distance is cut back.
Actually, that's quite wrong.
Aluminum has higher resistivity than copper, but making the aluminum wire thicker than the copper gives it the same resistance. Meanwhile the aluminum has a better cost/conductance ratio than copper, so the thicker aluminum wire is cheaper too.
Plus, the much higher strength/weight ratio means that you don't need to support it so often.
The biggest downside with aluminum is when you try to join it; the aluminum oxide surface layer makes it much hard to make a good electrical joint. That the reason the more expensive copper is used for circuit boards and in house wiring.
Actually, metallic calcium is even better (apart from its unfortunate habit of spontaneously combusting in air!)
Actually, the link with the French is nothing to do with cats directly- the reason that 85% of the French have the parasite is that they enjoy eating uncooked foods that are likely to be infected with it.
I use NiMH batteries. They're non-toxic (unlike NiCds) and they have fantastic capacity (up to 2100 mAh, twice NiCd density, about the same as alkaline capacity).
I try to use them for everything, and my electric shaver and wireless mouse runs on then. And, so they never discharge themselves through lack off use, I rotate them around, and charge them up when my razor or mouse has drained them, keeping a few spares.
If I go on a trip, my digital camera runs on them, so I just charge them before I leave and I can carry spares and swap them into my camera as needed.
Having said that, I don't dispute any of the facts you've given (except I'd just like to ask if by "sonic" you mean "transsonic" or "supersonic", as it is airspeeds BELOW that which would be "sonic").
Actually, no. Speeds above sonic are supersonic, and below sonic are subsonic. Transonic means 'around the speed of sound', usually between mach 0.85 and mach 1 or more. I have seen subsonic speeds refered to as sonic, but technically that's incorrect. Sonic, as I'm sure you're aware is when the speed is equal to the speed of sound
Sure, sure. There is indeed a shock wave at the throat, even in Carmacks 'throatless' wonders. Now explain how that relates to the comment I was replying to that says:
"If you have shock waves inside the nozzle or if you blow the shock out the end, you are losing energy, and potentially wrecking equipment.":-)
It's actually a misnomer; provided the chamber pressure is more than 2.7x the atmospheric pressure (which it always will be if you stuff enough propellant in through the injectors) then a throat spontaneously forms near where the nozzle widens out. The throat is defined to be the place in the combustion chamber where the gas goes faster than sound. Normally that would happen at the narrowest point of the nozzle, but in this case it may even move around in the combustion chamber, but it can't leave because the nozzle widening out stops it.
Cough-bullshit-cough. Hint: you can't fake rocket science on Slashdot; there's real rocket scientists here!
Ok, first, you don't get shockwaves in nozzles- not unless you've got a rough nozzle surface, which is a bad idea, because the hot gas comes to a screaming halt ("stagnates") and the local temperature goes way up, and then the nozzle melts. And yeah, Carmack knows that a nozzle and throat needs to be smooth, this isn't the first bipropellent engine he's built, and he's widely known not to be stupid.:-).
Oh yeah and actually, even these 'throatless' engines has a throat, but it's kinda hard to spot:-), the gas makes up its own mind where to put the throat, in realtime- the throat is defined to be where the gas goes sonic, and this always happens when the combustion pressure is more than 2.7 times the ambient.
You mainly get shockwaves in air inlets in jet engines, not in the nozzle. You also get shockwaves in the exhaust plume of rocket engines where the exhaust kinda bounces of the external atmosphere, but that's harmless (actually kinda pretty google on "mach diamonds"), and they form wayyy downstream of the exit. Oh yeah, and a rocket launching, once it passes about mach 0.85 gives transonic shockwave around its nosecone, and then later supersonic shockwaves there, those can cause damage, but they rarely do.
So, these non existent shockwaves can't damage any equipment, or waste any energy. Oh yeah, and did I mention there aren't any shockwaves?:-)
Still, by American presidential standards, this is pretty much par for the course.
I mean, consider Ronald 'we run some of our policy based on astrology' Reagan, or Bush 'I don't consider atheists to be citizens' senior or Bill 'oral sex with an intern isn't real sex' Clinton. They're all basket cases at the end of the day:-)
Not friction exactly- as the hot gas flows over the surface of the heat shield the fabric will cause the gas to compress in front of the fabric, and also cause turbulence downstream of the fabric; and then where the turbulent gas impinges on the tiles at a steeper angle than normal the temperatures will be higher. It doesn't take a massive amount for the tiles to start to degrade. Probably the tiles can take it, but NASA's not in the mood to cross their fingers and hope for the best.
Actually per astronaut/cosmonaut launch/reentry attempt both programs have a statistically indistinguishable death rate (0.019 deaths/launch for Soyuz versus 0.021 deaths/launch for the Shuttle).
The Soyuz probably has had more stuff go wrong, but it has better safety systems (e.g. Soyuz blew up on the pad once, but the safety system got the Cosmonauts clear; the Shuttle doesn't have a safety system to do that; it takes about 30 seconds just to swing the crane back...).
Nobody has died on a Soyuz in over 30 years, but there has been some near misses. Overall, it's too close to call.
Flight Controller to Shuttle: 'The good news is, we've accounted for all your heat shield tiles, and they're all in good shape. The one I'm holding here looks amazing in fact, considering...'
Oh well, atleast they've got another Shuttle and the ISS.
The original internet worm exploited a buffer overflow in the finger daemon. So for a Microsoft spokesman to stand up and say that this wasn't understood 10 years ago.
I mean c'mon. That was in 1988; by computing standards that was prehistoric. Everything Microsoft wrote should have been looked at for that bug ever since. They didn't. Microsoft didn't even bother to look at security issues much at all until a few years ago. Unix was ahead of that curve by 5-10 years.
What is this recurring BS about hydrogen energy? Hydrogen is only a medium for storing/transporting energy - it does not generate any more energy than used to produce it.
That's true of ethanol as well though; there's no significant natural source of ethanol. We make it from sugars which ultimately come from sunlight.
No, they're well outside it. The problem is solar radiation- they're outside the magnetosphere of the earth (where the Van Allen belts are) and that means they see solar storms.
Incidentally the Van Allen belt isn't hard to shield against- for long term habitation it just requires a lot of mass (a shield a meter or two thick). Prohibitive if you lift it from the Earth, but no problem if you launch it from the Moon.
True, although you can argue about 'significant'; but the strength of spread spectrum is *much* lower. And hairdryers aren't banned. Do they significantly increase the noise floor?
The regulatory position has improved greatly recently for spread spectrum.
The problem they had was that the regulators looked in the regulation books, and discovered that the only category that really fitted was spark gap transmitters, which were banned outright (spark gap transmitters transmit across all the wavelengths simultaneously and can cause enormous interference).
However it seemed a bit ridiculous, because the powers intended to be used for spread spectrum are really minute, and unlikely to cause interference, nevertheless 'rules are rules'.
Recently the argument was made that hairdryers often produce sparks from the brushes in the electric motors, and these don't produce significant interference, and these aren't banned; hairdryers are basically spark gap transmitters; and spreadspectrum produces much less interference than hairdryers.
The regulators hmmed and hahed, and it's looking like spreadspectrum is being permitted at very low powers in America.
Other countries like the UK have followed suit.
Incidentally, the noise floor often isn't affected measurably by this stuff, except at very close range. Noise doesn't add linearly and many of these systems are well below the noise floor. Also see Shannon Hartley theorem.
Slashdot Mirror
Never mind 100 days, personally I think that continuing to kill people in the area for decades aftewards with radiation counts as Military force :-)
The bottom line with any wireless system is how well engineered it is.
The following techniques help a lot:
a) broadband suppliers give a 'contention ratio' somewhere between 20 and 50. In other words they assume you are only using it 1/20 to 1/50 of the time. So a single 2M radio link can handle 20-50 customers each with 2M and a 100M radio link can handle 1000-2500 people (in principle.)
b) directional antennas help a lot. So, if they stick up a mast with antennas pointing in different directions (adjacent antennas on different frequencies) then they'll get very little contention.
c) nodes that don't 'shout'; in other words if the nodes don't transmit at any more power than they absolutely need to; this minimises the distance that any interference is likely to occur at; permitting channel reuse.
d) add base stations, (particularly in conjunction with c) ) this mean that each base station can transmit and receive at lower power- this reduces the size of the coverage area, and you gain multiple times the users (since each node only uses up the bandwidth for a smaller distance).
e) use different channels (each channel has its own customers on)
f) node routing (in other words, instead of a customer sending a signal all the way to the base station, route it through another customer that is closer).
If you use all these techniques appropriately, the amount of bandwidth per user is constant, independent of the number of users, surprisingly.
Yeah, but atleast it doesn't have a tiny penis, look like a frog and go broom broom. Trust me, this is better.
Actually, that's quite wrong.
Aluminum has higher resistivity than copper, but making the aluminum wire thicker than the copper gives it the same resistance. Meanwhile the aluminum has a better cost/conductance ratio than copper, so the thicker aluminum wire is cheaper too.
Plus, the much higher strength/weight ratio means that you don't need to support it so often.
The biggest downside with aluminum is when you try to join it; the aluminum oxide surface layer makes it much hard to make a good electrical joint. That the reason the more expensive copper is used for circuit boards and in house wiring.
Actually, metallic calcium is even better (apart from its unfortunate habit of spontaneously combusting in air!)
Actually, the link with the French is nothing to do with cats directly- the reason that 85% of the French have the parasite is that they enjoy eating uncooked foods that are likely to be infected with it.
The system could easily last another 5 or 10 years, at a rate of one life every 2 or 3 years it would be worth it.
I try to use them for everything, and my electric shaver and wireless mouse runs on then. And, so they never discharge themselves through lack off use, I rotate them around, and charge them up when my razor or mouse has drained them, keeping a few spares.
If I go on a trip, my digital camera runs on them, so I just charge them before I leave and I can carry spares and swap them into my camera as needed.
That's a common myth, examination of the inflation adjusted figures show that NASA's budget has been flat since Apollo was cancelled.
Every year they threaten to cut the budget, but they always work it out in the end.
The bandwidth of most peoples network connection is approaching that of 10M ethernet... so you should be able to boot over the internet pretty soon.
Actually, no. Speeds above sonic are supersonic, and below sonic are subsonic. Transonic means 'around the speed of sound', usually between mach 0.85 and mach 1 or more. I have seen subsonic speeds refered to as sonic, but technically that's incorrect. Sonic, as I'm sure you're aware is when the speed is equal to the speed of sound
"If you have shock waves inside the nozzle or if you blow the shock out the end, you are losing energy, and potentially wrecking equipment." :-)
It's actually a misnomer; provided the chamber pressure is more than 2.7x the atmospheric pressure (which it always will be if you stuff enough propellant in through the injectors) then a throat spontaneously forms near where the nozzle widens out. The throat is defined to be the place in the combustion chamber where the gas goes faster than sound. Normally that would happen at the narrowest point of the nozzle, but in this case it may even move around in the combustion chamber, but it can't leave because the nozzle widening out stops it.
Ok, first, you don't get shockwaves in nozzles- not unless you've got a rough nozzle surface, which is a bad idea, because the hot gas comes to a screaming halt ("stagnates") and the local temperature goes way up, and then the nozzle melts. And yeah, Carmack knows that a nozzle and throat needs to be smooth, this isn't the first bipropellent engine he's built, and he's widely known not to be stupid. :-).
Oh yeah and actually, even these 'throatless' engines has a throat, but it's kinda hard to spot :-), the gas makes up its own mind where to put the throat, in realtime- the throat is defined to be where the gas goes sonic, and this always happens when the combustion pressure is more than 2.7 times the ambient.
You mainly get shockwaves in air inlets in jet engines, not in the nozzle. You also get shockwaves in the exhaust plume of rocket engines where the exhaust kinda bounces of the external atmosphere, but that's harmless (actually kinda pretty google on "mach diamonds"), and they form wayyy downstream of the exit. Oh yeah, and a rocket launching, once it passes about mach 0.85 gives transonic shockwave around its nosecone, and then later supersonic shockwaves there, those can cause damage, but they rarely do.
So, these non existent shockwaves can't damage any equipment, or waste any energy. Oh yeah, and did I mention there aren't any shockwaves? :-)
I mean, consider Ronald 'we run some of our policy based on astrology' Reagan, or Bush 'I don't consider atheists to be citizens' senior or Bill 'oral sex with an intern isn't real sex' Clinton. They're all basket cases at the end of the day :-)
Not friction exactly- as the hot gas flows over the surface of the heat shield the fabric will cause the gas to compress in front of the fabric, and also cause turbulence downstream of the fabric; and then where the turbulent gas impinges on the tiles at a steeper angle than normal the temperatures will be higher. It doesn't take a massive amount for the tiles to start to degrade. Probably the tiles can take it, but NASA's not in the mood to cross their fingers and hope for the best.
You get charged for upload as well? That sucks.
LOL. You do know that Valve hired Cohen to write the download code for Steam?
The Soyuz probably has had more stuff go wrong, but it has better safety systems (e.g. Soyuz blew up on the pad once, but the safety system got the Cosmonauts clear; the Shuttle doesn't have a safety system to do that; it takes about 30 seconds just to swing the crane back...).
Nobody has died on a Soyuz in over 30 years, but there has been some near misses. Overall, it's too close to call.
Flight Controller to Shuttle: 'The good news is, we've accounted for all your heat shield tiles, and they're all in good shape. The one I'm holding here looks amazing in fact, considering...'
Oh well, atleast they've got another Shuttle and the ISS.
I mean c'mon. That was in 1988; by computing standards that was prehistoric. Everything Microsoft wrote should have been looked at for that bug ever since. They didn't. Microsoft didn't even bother to look at security issues much at all until a few years ago. Unix was ahead of that curve by 5-10 years.
It's ok, nature's on to it. Some of the elephants are being born without feet.
That's true of ethanol as well though; there's no significant natural source of ethanol. We make it from sugars which ultimately come from sunlight.
Incidentally the Van Allen belt isn't hard to shield against- for long term habitation it just requires a lot of mass (a shield a meter or two thick). Prohibitive if you lift it from the Earth, but no problem if you launch it from the Moon.
True, although you can argue about 'significant'; but the strength of spread spectrum is *much* lower. And hairdryers aren't banned. Do they significantly increase the noise floor?
The problem they had was that the regulators looked in the regulation books, and discovered that the only category that really fitted was spark gap transmitters, which were banned outright (spark gap transmitters transmit across all the wavelengths simultaneously and can cause enormous interference).
However it seemed a bit ridiculous, because the powers intended to be used for spread spectrum are really minute, and unlikely to cause interference, nevertheless 'rules are rules'.
Recently the argument was made that hairdryers often produce sparks from the brushes in the electric motors, and these don't produce significant interference, and these aren't banned; hairdryers are basically spark gap transmitters; and spreadspectrum produces much less interference than hairdryers.
The regulators hmmed and hahed, and it's looking like spreadspectrum is being permitted at very low powers in America.
Other countries like the UK have followed suit.
Incidentally, the noise floor often isn't affected measurably by this stuff, except at very close range. Noise doesn't add linearly and many of these systems are well below the noise floor. Also see Shannon Hartley theorem.