MIMO is an intriguing technology but unfortunately the acronym is used loosely to refer to many unrelated things.
The most exciting MIMO technology is also known as "space multiplexing," which lets a system with N transmit and N receive antennas transfer data at N times the rate of a system with just 1 transmit and receive antenna. The marketing departments like to use MIMO to refer to any old system with multiple antennas, because technically the definition is correct. However, most of the time those systems can't get this kind of performance gain. I believe most of the pre-n hardware out there just does fancy antenna selection; the language is usually careful to say that "802.11n supports space multiplexing," even though it is optional, and there are no performance numbers yet. Someone please correct me if I'm wrong, which I'd love to be!
The way space multiplexing works is counterintuitive: each transmit antenna sends an independent stream of data on the same frequency. The "magic" that makes it work is the fact that multiple receiving antennas observe the combined signal at different times (the article summary got it surprisingly right here); specifically, the phase offsets observed at different RX antennas should be random. This can happen when the signals bounce off a lot of objects like walls indoors, or buildings etc. outdoors.
Here is a simplified example that illustrates how this can work. Suppose we have 2 transmit antennas. Suppose at a given time we send two signals a and b. If we only had one receive antenna, we would observe (a+b), and there would be no way to extract the individual signals. However, if we have a second antenna, AND the phase offset happens to be such that the other antenna gets (a-b), we can clearly extract the original signals.
There are environments such as open outdoor fields with line-of-sight, where the received phase offsets are not random and don't happen to be "nice" like in the above example; in that case MIMO performance falls back to 1x1, or a little better if the phase offsets have some degree of randomness.
The HAL is hardly the majority of the driver. The reasons for having the HAL are mostly regulatory, and they are not going away. We should be grateful that most of the Atheros cards don't have firmware, so the extent of the reverse engineering is the host-based HAL blob instead of some totally proprietary microcontroller architecture and RTOS. The bad news is, miniPCI is dying, and the industry is moving to USB modules, which unfortunately all use firmware-driven microcontrollers. Two examples I know are USB modules from Atheros (MIPS) and Marvell (Arm).
There is a project at UCLA to test multiple-in, multiple-out (MIMO) performance of 802.11n. They use Lego robots to adjust antenna spacing. Pretty cool stuff. Link to paper: pdf.
(I'm not affiliated, just ran into that project while browsing)
I could see putting a broadcast box on your house aiming up and having a fleet of little RC helicopters flying around and doing security sweeps.
It sounds nice in concept, but the numbers just don't seem feasible at this point. An average electric-powered model plane with, say, a 6 foot wing span, uses a 1 horsepower electric motor. I have a hard time seeing how it would be efficient to beam this much power to the flyer. Heck, even making it work would be tough, since it would need to be aimed, all of the electronics would need to be shielded, and it would probably need an autopilot in case the remote control channel is drowned out by the power beam.
The most practical route to making something like this work is probably miniaturization and better batteries, or even just plain fuel. It is amazing how much energy fuel contains compared to the best batteries: check this table of energy densities.
Pshaw, that's nothing. I work with high end audio equipment, and let me tell you, a Hi-Fi 3 foot cable can easily cost several thousand dollars. The 40GHz cable would never be enough, as some people can still hear frequencies in that range.
compete for a seat with everyone else who's looking for a spot to use the Internet, most likely for pr0n surfing, AIM, WoW, reading Slashdot, and other similar non-academic activities,
In my experience the good labs tended to have anal admins who would police this sort of thing to leave room for the folks doing work. My lab example was kind of naturally formed by not having any network infrastructure in dorms in the first place, not by admin choice. As a result, there tended to be few big well-run labs because it was understood they were necessary for people to work. Nowadays the mentality is the opposite; the lab is a superficial place to check email and surf, and students are expected to have computing power of their own. I don't know which one is better, I'm just stating I did like the labs at my school.
Have you ever actually been to a campus computer lab when it's crunch time? Trust me, NO ONE wants to be there.
Countless times, and it was always a positive experience. I probably got lucky doing this before the.com thing, when CS departments became overcrowded with no-talent gold diggers.
"Bonding" is the last thing on people's mind
Perhaps, but it does happen.
when trying to get the crummy lab computer to read their floppy disc with their final project/paper on it so they can PRINT IT and GO HOME TO SLEEP.
I can't believe everybody at your lab was this apathetic. Sounds like a torture chamber, not a school.
And as someone who both worked at and used campus computer labs during my time in college, I honestly do not call that the best part of my college career. If you do, I really feel sorry for you...
It wasn't *the* best part, but it was usually enjoyable. As I said, maybe I got lucky.
What if the 4 years of this ingrains some useful habits into them? I see this with military brats who come to school, they are always really motivated and hard-working.
Without access in dorms, you would just get your lazy bum ass to a lab and do your paper writing there. The awesome social side benefit of this is bonding with other people in the same situation. Only the motivated ones would be in the lab anyway, so this is a great opportunity to create a high quality network.
Furthermore, is there any possibility of a dipole radiation distribution for the fraction of linear polarization?
I think you're on to something here. Whoever created that thing could have screwed up any number of things:
- Incorrect dipole length, creating a bad radiation pattern - Bad impedance match - Incorrect balun use-- it is not needed unless the feed is unbalanced - Forgot to factor in dielectric constants, although this is in vacuum so should be safe here
I'm puzzled by the famous computer science and networking names on the list of researchers. Maybe it's one of those umbrella efforts designed to cover each researcher's pet project, while getting lots of funding from industry.
Hey, I know, we could put all these appliances into some kind of enclosure with common power, cooling, and even super fast backplane. We would probably need to keep these "frames" in climate-controlled rooms. The main "frame" would serve the most common apps, and if some offices needed some specialized stuff they could buy small versions, kind of like miniature computers! Hah, I kill myself.
The sad thing is, his unlocked filing cabinet is probably more secure than having the information sit on some server where hackers from Bulgaria can steal it and blackmail the company.
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MIMO is an intriguing technology but unfortunately the acronym is used loosely to refer to many unrelated things.
The most exciting MIMO technology is also known as "space multiplexing," which lets a system with N transmit and N receive antennas transfer data at N times the rate of a system with just 1 transmit and receive antenna. The marketing departments like to use MIMO to refer to any old system with multiple antennas, because technically the definition is correct. However, most of the time those systems can't get this kind of performance gain. I believe most of the pre-n hardware out there just does fancy antenna selection; the language is usually careful to say that "802.11n supports space multiplexing," even though it is optional, and there are no performance numbers yet. Someone please correct me if I'm wrong, which I'd love to be!
The way space multiplexing works is counterintuitive: each transmit antenna sends an independent stream of data on the same frequency. The "magic" that makes it work is the fact that multiple receiving antennas observe the combined signal at different times (the article summary got it surprisingly right here); specifically, the phase offsets observed at different RX antennas should be random. This can happen when the signals bounce off a lot of objects like walls indoors, or buildings etc. outdoors.
Here is a simplified example that illustrates how this can work. Suppose we have 2 transmit antennas. Suppose at a given time we send two signals a and b. If we only had one receive antenna, we would observe (a+b), and there would be no way to extract the individual signals. However, if we have a second antenna, AND the phase offset happens to be such that the other antenna gets (a-b), we can clearly extract the original signals.
There are environments such as open outdoor fields with line-of-sight, where the received phase offsets are not random and don't happen to be "nice" like in the above example; in that case MIMO performance falls back to 1x1, or a little better if the phase offsets have some degree of randomness.
Step 1: Cut a hole in a box
Step 2: Put the music in a box
Step 3: Make her open the box!
and a license from the FCC
In the immortal words of Agent Smith, "What good is a phone call, when you are unable to speak?"
The HAL is hardly the majority of the driver. The reasons for having the HAL are mostly regulatory, and they are not going away. We should be grateful that most of the Atheros cards don't have firmware, so the extent of the reverse engineering is the host-based HAL blob instead of some totally proprietary microcontroller architecture and RTOS. The bad news is, miniPCI is dying, and the industry is moving to USB modules, which unfortunately all use firmware-driven microcontrollers. Two examples I know are USB modules from Atheros (MIPS) and Marvell (Arm).
There is a project at UCLA to test multiple-in, multiple-out (MIMO) performance of 802.11n. They use Lego robots to adjust antenna spacing. Pretty cool stuff. Link to paper: pdf.
(I'm not affiliated, just ran into that project while browsing)
Simple, it's the second law. Cooler on the Sun = warmer on Earth.
On second thought, what if that's true? Maybe the energy gets transferred through some kind of inductive coupling?
Well what do you think caused the sun spots to peak?
This is old news!
I could see putting a broadcast box on your house aiming up and having a fleet of little RC helicopters flying around and doing security sweeps.
It sounds nice in concept, but the numbers just don't seem feasible at this point. An average electric-powered model plane with, say, a 6 foot wing span, uses a 1 horsepower electric motor. I have a hard time seeing how it would be efficient to beam this much power to the flyer. Heck, even making it work would be tough, since it would need to be aimed, all of the electronics would need to be shielded, and it would probably need an autopilot in case the remote control channel is drowned out by the power beam.
The most practical route to making something like this work is probably miniaturization and better batteries, or even just plain fuel. It is amazing how much energy fuel contains compared to the best batteries: check this table of energy densities.
What is this about filters clogging on Dysons? I thought they were not supposed to lose suction. Evar.
Pshaw, that's nothing. I work with high end audio equipment, and let me tell you, a Hi-Fi 3 foot cable can easily cost several thousand dollars. The 40GHz cable would never be enough, as some people can still hear frequencies in that range.
The minute they get the idea to make heatsinks out of Sterling Silver.
You had dials? Spoiled brats. We had to touch the red and green wires together repeatedly to make up the number.
compete for a seat with everyone else who's looking for a spot to use the Internet, most likely for pr0n surfing, AIM, WoW, reading Slashdot, and other similar non-academic activities,
In my experience the good labs tended to have anal admins who would police this sort of thing to leave room for the folks doing work. My lab example was kind of naturally formed by not having any network infrastructure in dorms in the first place, not by admin choice. As a result, there tended to be few big well-run labs because it was understood they were necessary for people to work. Nowadays the mentality is the opposite; the lab is a superficial place to check email and surf, and students are expected to have computing power of their own. I don't know which one is better, I'm just stating I did like the labs at my school.
Have you ever actually been to a campus computer lab when it's crunch time? Trust me, NO ONE wants to be there.
.com thing, when CS departments became overcrowded with no-talent gold diggers.
Countless times, and it was always a positive experience. I probably got lucky doing this before the
"Bonding" is the last thing on people's mind
Perhaps, but it does happen.
when trying to get the crummy lab computer to read their floppy disc with their final project/paper on it so they can PRINT IT and GO HOME TO SLEEP.
I can't believe everybody at your lab was this apathetic. Sounds like a torture chamber, not a school.
And as someone who both worked at and used campus computer labs during my time in college, I honestly do not call that the best part of my college career. If you do, I really feel sorry for you...
It wasn't *the* best part, but it was usually enjoyable. As I said, maybe I got lucky.
with people like you who are there to socialize.
This reply is what happens when you let people play WoW all night: reasoning abilities and reading comprehension suffer.
What if the 4 years of this ingrains some useful habits into them? I see this with military brats who come to school, they are always really motivated and hard-working.
Without access in dorms, you would just get your lazy bum ass to a lab and do your paper writing there. The awesome social side benefit of this is bonding with other people in the same situation. Only the motivated ones would be in the lab anyway, so this is a great opportunity to create a high quality network.
Furthermore, is there any possibility of a dipole radiation distribution for the fraction of linear polarization?
I think you're on to something here. Whoever created that thing could have screwed up any number of things:
- Incorrect dipole length, creating a bad radiation pattern
- Bad impedance match
- Incorrect balun use-- it is not needed unless the feed is unbalanced
- Forgot to factor in dielectric constants, although this is in vacuum so should be safe here
I would measure the VSWR and go from there.
Just let Jack Bauer torture some legislators into voting no.
I'm puzzled by the famous computer science and networking names on the list of researchers. Maybe it's one of those umbrella efforts designed to cover each researcher's pet project, while getting lots of funding from industry.
Time to put that roomba to good use!
We are smart. We are power!
Hey, I know, we could put all these appliances into some kind of enclosure with common power, cooling, and even super fast backplane. We would probably need to keep these "frames" in climate-controlled rooms. The main "frame" would serve the most common apps, and if some offices needed some specialized stuff they could buy small versions, kind of like miniature computers! Hah, I kill myself.
The sad thing is, his unlocked filing cabinet is probably more secure than having the information sit on some server where hackers from Bulgaria can steal it and blackmail the company.