My take is that they're using the difference in frequency between the carrier frequency and the generated sideband frequency to represent a value (ie. +10kHz = 0001; +15kHz = 0010; etc.). This seems awfully similar to the SSB modulation commonly used in shortwave radiocommunications to me.
Actually this seems awfully similar to FSK (frequency shift keying) to me. And I am not sure that I trust it:
The modulation scheme alters the frequency of individual cycles of the carrier wave, which has the effect of introducing very low power side-bands to the signal.
Information is in the side bands (obviously not in the carrier because you can just generate one at the receiver side). Low side bands == not much information being transmitted.
I am a radio engineer... well, not professionally but I know what it is about.
Digital transmission works as follows: you select a certain waveform out of a set and transmit it. At the receiver you try to figure out which one it was. Unfortunately the reception is distorted because of noise you pick up, such that the distinction is not perfect (e.g. in case you can reliably tell 8 possible waveforms apart three bits will be conveyed each time you do this). Using more power will lead to a better distinction and therefore higher bit rate. Using a larger (RF) band width allows you to send more waveforms per second hence also increasing the number of bits transferred (this is simplified somewhat).
Shannon left us a nice formula to calculate the capacity aka maximum possible throughput EVER, but first you need to calculate the signal and noise power you receive.
1) If we assume the waves travel in free space, the received signal power will be dependent on - transmit power - transmit antenna gain (dish is more focused than dipole etc.) - free space loss (FSL, i.e. field strength getting weaker far from the source because the energy is spread out in all directions) - receive antenna gain This is an optimistic assumption because their setup takes place in suburban territory!
We can assume both the antenna gains are 0dB, being small and probably not perfectly matched. The FSL is equal to: R^2*4pi^2/lambda^2 (R=distance, lambda=wavelength) At 900 MHz lambda=0.33m, R=18 miles=29e3 m. FSL= 3e11(in 'power') or 115dB. The transmit power was 50mW, i.e.17dBm, the total received power will be 17-115=-98 dBm. The thermic background noise is equal to -173dBm/Hz (best case, due to ambient temparature - this is a bit optimistic too because other wireless devices are transmitting there too).
2) The channel capacity is given by Shannon as C=B*log2(1+S/N), where C=capacity (bits/sec), B=bandwidth (physical, in Hz), S=signal power (-98dBm), N=noise power (-173dBm/Hz*B). You can now play with the bandwidth to influence the capacity. To a certain extent an increased bandwidth will increase the capacity but after a while you are just catching more noise while the signal will be spread out in frequency, so this saturates. For these numbers the (theoretical) maximum capacity would be about 4.5e7 bits/sec or 45MB/sec. But even to achieve the 3.7Mb mentioned you already need a bandwidth of 700kHz (rough estimate, I made a plot in matlab). At that point you transmit 3.7Mb/(50mW)/(0.7Mhz)=100Mb/s/W/MHz, so their figure of 7.4 MB/2/W/MHz is not impossible. However it will be difficult to achieve. We have made some assumptions (especially about the loss in the urban envorinment), and their bit rate only has a 'margin' of a factor 12 (45 to 3.7). There you have it.
IMHO it is even more deplorable that the highest ranking comments especially in this particular thread about MS have to do with either meta-observations ('why is this on front page', 'Roland Piquepaille sucks',...) or the moderation system ('karma whoring', 'MOD PARENT UP', 'mod me down if you wish',...).
What I regret about this is that the meta-stuff is often becoming more important than the actual news. Concerning the Karma: it is only a number in a data base. Why would you want a high karma modifier if the only thing you do with it is post about karma stuff?
It is a sign of boredom that we spend our time on non-info like all these meta-posts, wasting other's time too because they see a lot of posts and think they are actually going to learn something. It would be good practice to just ignore the lame threads instead of embroidering them to death (like I am doing a bit now, but hopefully for the last time).
If it's legally free to use and does the same task, why wouldn't 90% of the users in the world who only use Windows *not* care?
Because apparently it doesn't do the same task. It does a much slower task. Consumers copy MS Office anyway and companies are afraid to let THE standard package go in favour of something 'dubious'...
Why not increase the heat flux by cooling the coolant? Then you don't need such ridiculous flow rates. And the nicest coolant around right now is the liquid nitrogen.
Firstly, it is rather easy to make a permanent 'ice water reservoir' (or similar) while it is nontrivial to produce liquid nitrogen. Admittedly for a short test this is no real issue (bear in mind I never said it was BAD, just asked if it had any advantages to use liquid N).
Secondly this large temperature difference between the coolant and ambient (not all of the PCB or even CPU comes in contact with the N) can cause thermal problems of differential expansion leading to bad contacts etc.
If you can come up with a clever way of removing heat from a chip quickly without making its surroundings much cooler, I'm sure we'd all be happy to hear it.
Actually I doubt that you understand my point, but to answer your question:
anything accepting heat at a temperature which is well beyond the temperature of the uncooled system is ok. This need not be a cryogenic temperature.
If you would stick the processor in ice water it would remain at more or less zero degrees C, the only problem being that evaporating water may form a heat isolating layer and that the water would short-circuit the tracks. Ice water has an infinite capacity for accepting heat from stuff above zero degrees (as long as there is ice). While these cryo systems may be cool (obviously) they are not essential for 'normal' cooling, hence my question if they offer a real advantage.
Not quite. You are only interested in the bandwidth (expressed in Hz). If you can turn that light on and off at 100 times per second you can also do it at 10 times per second (but maybe not at 1000). In other words: you can modulate it with a bandwidth of 100Hz (*), so it makes sense to call this '100Hz' and not '100 times per second'. IMHO no engineer would ever do this because it takes some time to figure out how many GHz '100 billion times per second' represents (especially for non native speakers).
(*) I know that turning off/on _instantly_ requires a higher bandwidth because of the steep flanks but that is not the issue here.
Good point! Why must they be so cold? I always thought that the problem was removing heat (i.e. not letting it get hot) rather than making it ridiculously cold. Anyone?
Why write '100 billion times' per second instead of 100GHz? My cell phone 'generates an electromagnetic field that changes orientation almost 1 billion times per second'. Wow!
Not really. If anything unfair would have been done to him he would be able to count on everyones sympathy. However, the/. crowd is supposed to be a rather mathematicaly / logically inclined group of people. If you don't follow the rules, don't complain.
The summary mentioned microwave ovens, so some may be tempted to play around with a DIY radar. Don't!!! Of all domectic appliances a microwave is about the most dangerous to take apart. The RF radiation has a very high power and is invisible. When exposed to the electromagnetic field, currents start to flow inside the human body (mostly close to the skin) giving rise to burn-like wounds.
Especially the risk of eye injury is significant. Don't try this at home.
Actually you are right there. After my post I realised (and secretly hoped no-one else would) there is a way out of the 'exponential cycle of increase', which is that people die and new people are born. It is therefore indeed possible that people get a net raise (after subtraction of inflation) because they 'shift up' places. Thanks to the oldest employees dying (sorry) the system can be stationary:-)
Not if a small percentage is working 'really really hard' and a large percentage is being just a bit sloppy. In that case the average lies higher because many loafers are needed to balance a few Strebers.
Actually a raise equal to the cost of living sounds rather fair to me. If everybody would get a raise significantly higher than the cost of living, things (produced by those employees) would become more expensive too, making the cost of living follow the increase. It is like saying 'everybody should be above average', no?
Our goal should be to establish a viable self-sufficient colony there that would ensure, should some catastrophy strike here on Earth that wipes out all life on the planet, the survival of the human species.
What for? There will be no-one to regret it since everybody would be dead. If 'survival' of mankind is the main reason for such a project I think the money would better be invested on Earth to try and make that a better place for everyone.
One of the unpopular teachers even revisited pages students had visited minutes ago just to look at what they were looking at, effectively spying on "our" privacy
Looking into logs? Bad teacher!
And how exactly did you discover this?
Re:The show will need local humor appeal
on
Homer Becomes Omar
·
· Score: 1
Maybe they could take out all Americanisms, introduce Islamisms, remove all jokes funny to Americans, introduce jokes funny to Muslims... but keep the main concept of course.
In short: whatever they will make will have little to do with the Simpsons and they start from scratch.
By this reasoning the assembly of Frankenstein's monster was a vivisection because afterwards it was alive... same holds for zombies I guess. Better ask a bokor.
They [Microsoft] have the power to make not only Africa as a developing natuion but the entire world a better place, and they will not do it because they are too damn greedy to think of anybody else but there own profit margins.
Wouldn't it be more logical to trust the analysis of a calibration lab? I can magine that one objects arrestation etc but what use is it to want to examine that device yourself?
When buying fruit I do not examine the scale every time because I know there is an independent organisation that does this regularly. If I would be arrested because of (what I think is) a defective speedgun or breathalizer, I would rather ask for a recent calibration report than for the source code. That is what certification institutes are for in the first place.
The Untied Nations? If we turn it over to them, then it's going to become so entangled with red tape and beauracracy that it will become essentially useless within a couple years. While the US is no model of perfection when it comes to limitting beauracracy, we at least have the luxury of being in general agreement on the fact that the Internet SHOULD be free.
A have a bird that I think SHOULD be free. Therefore I keep in in a cage to avoid that others catch it and emprison it.
Another country? Why the hell would we give it up and give it to another country?? The only reason for us to give it up at all would be if it was freeing it more. Turning it over to a different country simply means that we are giving THEM the monopoly on it. Again, no progress is being made.
Slashdot Mirror
Actually this seems awfully similar to FSK (frequency shift keying) to me. And I am not sure that I trust it:
The modulation scheme alters the frequency of individual cycles of the carrier wave, which has the effect of introducing very low power side-bands to the signal.
Information is in the side bands (obviously not in the carrier because you can just generate one at the receiver side). Low side bands == not much information being transmitted.
I am a radio engineer...
well, not professionally but I know what it is about.
Digital transmission works as follows: you select a certain waveform out of a set and transmit it. At the receiver you try to figure out which one it was. Unfortunately the reception is distorted because of noise you pick up, such that the distinction is not perfect (e.g. in case you can reliably tell 8 possible waveforms apart three bits will be conveyed each time you do this). Using more power will lead to a better distinction and therefore higher bit rate. Using a larger (RF) band width allows you to send more waveforms per second hence also increasing the number of bits transferred (this is simplified somewhat).
Shannon left us a nice formula to calculate the capacity aka maximum possible throughput EVER, but first you need to calculate the signal and noise power you receive.
1) If we assume the waves travel in free space, the received signal power will be dependent on
- transmit power
- transmit antenna gain (dish is more focused than dipole etc.)
- free space loss (FSL, i.e. field strength getting weaker far from the source because the energy is spread out in all directions)
- receive antenna gain
This is an optimistic assumption because their setup takes place in suburban territory!
We can assume both the antenna gains are 0dB, being small and probably not perfectly matched.
The FSL is equal to: R^2*4pi^2/lambda^2 (R=distance, lambda=wavelength)
At 900 MHz lambda=0.33m, R=18 miles=29e3 m.
FSL= 3e11(in 'power') or 115dB.
The transmit power was 50mW, i.e.17dBm, the total received power will be 17-115=-98 dBm. The thermic background noise is equal to -173dBm/Hz (best case, due to ambient temparature - this is a bit optimistic too because other wireless devices are transmitting there too).
2) The channel capacity is given by Shannon as C=B*log2(1+S/N), where C=capacity (bits/sec), B=bandwidth (physical, in Hz), S=signal power (-98dBm), N=noise power (-173dBm/Hz*B).
You can now play with the bandwidth to influence the capacity. To a certain extent an increased bandwidth will increase the capacity but after a while you are just catching more noise while the signal will be spread out in frequency, so this saturates.
For these numbers the (theoretical) maximum capacity would be about 4.5e7 bits/sec or 45MB/sec. But even to achieve the 3.7Mb mentioned you already need a bandwidth of 700kHz (rough estimate, I made a plot in matlab).
At that point you transmit 3.7Mb/(50mW)/(0.7Mhz)=100Mb/s/W/MHz, so their figure of 7.4 MB/2/W/MHz is not impossible. However it will be difficult to achieve. We have made some assumptions (especially about the loss in the urban envorinment), and their bit rate only has a 'margin' of a factor 12 (45 to 3.7). There you have it.
Don't think the printed version will ever get beyond the word 'recursive' and the book will be _mighthy_ thick...
kill -9 -1
What I regret about this is that the meta-stuff is often becoming more important than the actual news. Concerning the Karma: it is only a number in a data base. Why would you want a high karma modifier if the only thing you do with it is post about karma stuff?
It is a sign of boredom that we spend our time on non-info like all these meta-posts, wasting other's time too because they see a lot of posts and think they are actually going to learn something. It would be good practice to just ignore the lame threads instead of embroidering them to death (like I am doing a bit now, but hopefully for the last time).
Because apparently it doesn't do the same task. It does a much slower task. Consumers copy MS Office anyway and companies are afraid to let THE standard package go in favour of something 'dubious'...
Firstly, it is rather easy to make a permanent 'ice water reservoir' (or similar) while it is nontrivial to produce liquid nitrogen. Admittedly for a short test this is no real issue (bear in mind I never said it was BAD, just asked if it had any advantages to use liquid N).
Secondly this large temperature difference between the coolant and ambient (not all of the PCB or even CPU comes in contact with the N) can cause thermal problems of differential expansion leading to bad contacts etc.
And there may be other reasons.
Actually I doubt that you understand my point, but to answer your question: anything accepting heat at a temperature which is well beyond the temperature of the uncooled system is ok. This need not be a cryogenic temperature.
If you would stick the processor in ice water it would remain at more or less zero degrees C, the only problem being that evaporating water may form a heat isolating layer and that the water would short-circuit the tracks. Ice water has an infinite capacity for accepting heat from stuff above zero degrees (as long as there is ice). While these cryo systems may be cool (obviously) they are not essential for 'normal' cooling, hence my question if they offer a real advantage.
(*) I know that turning off/on _instantly_ requires a higher bandwidth because of the steep flanks but that is not the issue here.
Good point! Why must they be so cold? I always thought that the problem was removing heat (i.e. not letting it get hot) rather than making it ridiculously cold. Anyone?
Why write '100 billion times' per second instead of 100GHz? My cell phone 'generates an electromagnetic field that changes orientation almost 1 billion times per second'. Wow!
Not really. If anything unfair would have been done to him he would be able to count on everyones sympathy. However, the /. crowd is supposed to be a rather mathematicaly / logically inclined group of people. If you don't follow the rules, don't complain.
The summary mentioned microwave ovens, so some may be tempted to play around with a DIY radar. Don't!!! Of all domectic appliances a microwave is about the most dangerous to take apart. The RF radiation has a very high power and is invisible. When exposed to the electromagnetic field, currents start to flow inside the human body (mostly close to the skin) giving rise to burn-like wounds. Especially the risk of eye injury is significant. Don't try this at home.
Actually you are right there. After my post I realised (and secretly hoped no-one else would) there is a way out of the 'exponential cycle of increase', which is that people die and new people are born. It is therefore indeed possible that people get a net raise (after subtraction of inflation) because they 'shift up' places. Thanks to the oldest employees dying (sorry) the system can be stationary :-)
Not if a small percentage is working 'really really hard' and a large percentage is being just a bit sloppy. In that case the average lies higher because many loafers are needed to balance a few Strebers.
Actually a raise equal to the cost of living sounds rather fair to me. If everybody would get a raise significantly higher than the cost of living, things (produced by those employees) would become more expensive too, making the cost of living follow the increase. It is like saying 'everybody should be above average', no?
What for? There will be no-one to regret it since everybody would be dead. If 'survival' of mankind is the main reason for such a project I think the money would better be invested on Earth to try and make that a better place for everyone.
Call me old-fashioned (at 30), but... this is a joke, right? Space mission != sex camp.
Looking into logs? Bad teacher!
And how exactly did you discover this?
In short: whatever they will make will have little to do with the Simpsons and they start from scratch.
By this reasoning the assembly of Frankenstein's monster was a vivisection because afterwards it was alive... same holds for zombies I guess. Better ask a bokor.
We do.
Unlike every other commercial company?
When buying fruit I do not examine the scale every time because I know there is an independent organisation that does this regularly. If I would be arrested because of (what I think is) a defective speedgun or breathalizer, I would rather ask for a recent calibration report than for the source code. That is what certification institutes are for in the first place.
A have a bird that I think SHOULD be free. Therefore I keep in in a cage to avoid that others catch it and emprison it.
Another country? Why the hell would we give it up and give it to another country?? The only reason for us to give it up at all would be if it was freeing it more. Turning it over to a different country simply means that we are giving THEM the monopoly on it. Again, no progress is being made.
See my previous post.