they can handle as much as you want - they just get a lot harder to implement because the feedback loop typically has to be 5x the bandwidth of the operating bandwidth to make sure it can compensate for 3rd and 5th order products.
AGC has nothing to do with linear operation of the amplifier (well it does but only to the extent that operating at really low power levels is more linear) . The problem with these modulation schemes with high Peak to average is that they require the amplifier to be "backed-off" in such a way that they are biased for linear operation but they put out only 1/10th the power that the bias condition should be able to support.
so for example a PA biased for 1/2W operation can only be operated at 50-100mW out, making your efficiency something on the order of 10-20%. A class C amplifier for GSM use, for example is pushing 60-65% efficiency.
which wouldn't be a problem except that darn near everything is moving towards OFDM type modulation.
aha - I missed that note. Now it makes more sense. Those sorts of PAs would be close to unusable even with a PD loop. still requiring a PD loop is still a big problem.
and there's still the issue that you can get these efficiencies with a pure PD loop. This scheme still has the problem that wide bandwidths are going to require a wide bandwidth feedback loop.
One way to do high efficiency is to do separate phase and amplitude modulation, the so called A-theta modulator. you get your amplitude control by adjusting the PA voltage _continuosly_ and do your phase modulation with an IQ modulator.
For wide bandwidth modulation formats this is a bit of a pain since you need a very wideband, high current, power supply. so they are doing an A/theta modulator but trying to simplify the bias control on the PA to avoid that.
What I'm not clear on is why they are doing this when they have a predistortion loop anyway. a pure predistortion loop should be able to achieve very similar results without any need for the PA bias adjust. you can also do it with 1 PA instead of two.
maybe it simplifies the PD loop substantially, I can't tell yet from the paper, but it trades this off against needing two PAs and PA bias control. And that PA bias control is a bit of a headache two, because you can't just stick a switch in there. The selectable bias levels have to come from a switching power supply which switches between different output voltages. doing this is also non-trivial.
I don't know, looks like somebody's thesis to me. Doesn't look like it's particular practical.
Also, first rule of looking at schemes like this. How much of that power they saved is being used in the more complicated digital circuitry. That's the reason you don't see PD loops in cell phones. It's a wash, you spend so much power analyzing the signal to do PD that you burn up the savings . Now if you have a 10W transmitter, PD makes lots of sense.
with enough advance warning would simply landing a rocket on the asteroid and having it provide a constant thrust be enough to have the asteroid miss ?
at a great distance it would take very little course adjustment which could be provided by a very low thrust.
the obvious complication being if it's tumbling. even then it seems that such a scheme would still work as the rocket could align itself under guidance or using the stars and provide force at the proper time.
not sure why this is never mentioned as an option.
heat causes semiconductor devices to work less well over time. The design must provide for appropriate heat dissipation. A design in which the devices are running at 110 or 120C on a consistent basis will begin to slowly fade. I'm talking about channel temperatures. your box may be "warm" but that could mean that the devices are running hotter than they should for long term reliability.
also a possibility, and my personal favorite. the clock oscillator. poor, even mediocre, clock oscillators have crummy aging characetistics. take that design which is running too hot : the crystals age faster than normal and eventually your device's frequency is too far off. as it begins to drift out, the reception will suffer.
repeat after me: modern electronics for the consumer market are designed for cost. it is expected that you will replace it in 2-3 years. when something lasts you 5 or 6, it's not by design. so if they can save $1 because they don't use the necessary heat sinking or board area to dissipate the heat, and everything is running at 90 or 100C, that's ok. ship it !
an antenna at 60GHz is about 2.5mm, and that's for a basic dipole....
you can easily put multiple antennas on a device, which means you can use beam-forming and get some very tasty antenna gain, maybe on the order of 12 to 15dB.
there are a whole lot of if's attached to that since it depends on a very solid baseband implementation, but theoretically the use of phase array antennas/beam-forming could negate the much higher path loss.
not quite right. N and AC and eventually AD use MIMO which is physically separate transmitters and receivers, i.e. multiple channels.
MIMO doesn't quite get N x (transmitters/receivers) of performance, but it comes pretty close.
AC simply provides for even wider channels than N, i.e. 80 and even 160 MHz channels, but still uses MIMO. It also has a crap load of protocol stuff in it too.
_theoretically_ having multiple receivers would give you a distinct improvement in performance through receiver diversity, but I doubt anybody implements that option.
This all assumes that your client has good radios AND good baseband peformance.
The DSP involved in MIMO is non-trivial and it's very easy to get very sucky performance with a bad implementation. and what do you think is going to happen if somebody f*cks up their baseband ? that's right they're going to try and sell out all of those chips - how the heck are you supposed to know that it's got shitty rate adaptation ? all you see is a cheap client.
the important point is that clients are cheap, and they perform that way.
so in most cases, for home use, you really don't want anything more than a/b/g. if you are doing large file transfers certainly it would be nice to have the higher data rates, but for multimedia streaming over your limited DSL connection there's no point.
what a bunch of horsshit. the greenies by no means ignore coal power. and by the way, great ignorant AC VERY LITTLE electricity is generated from oil, so that's not part of the discussion.
only right wing morons with an axe to grind things environmentalists ignore the problems associated with electricity generation via coal.
human beings have demonstrated that they are incapable of managing nuclear without major radioactive accidents.
I'm anti nuclear because people are incompetent bozos and it's just a matter of time before another disaster.
of course after the NEXT disaster we'll have to listen to the wailing and lamenting about how it couldn't possibly happen again, it only happened because of blah, blah, blad.
and the next time too, until we're all drowning in radioactive Cs, which of course, is easy to treat for, doncha know ?
137Cs and 90Sr each have a half-life of ~30yrs, making them a factor for up to 600 years. Both are beta emitters, so they're primarily a hazard only when inhaled, ingested, or with direct skin contact. However, 90Sr isn't produced in large quantities, so it's not a major factor. That leaves 137Cs. The main concern with 137Cs is with unknown/untreated exposure. It's easy and fairly cheap to treat exposure (including land) if you know about the contamination. 137Cs and 131I are the primary isotopes released at both Chernobyl and Fukushima.
it's easy and fairly cheap to treat exposure (including land) - really? so please do give me your conspiracy theory version as to why the land around chernobyl is still uninhabited. I'm sure there's some reason involving shadowy organizations as to why hundreds of square kilometers of land go unclaimed for something that's so easy to take care of.
you deride the people who claim nuclear is fairly unsafe after two major catastrophes involving nuclear, but offer no support for your lame brained presumption that it's "easy" to get rid of radioactive cesium.
I'm sure the Japanese will be moving back into the area around Fukushima once they've found your cheap and easy method of radioactive decontamination. I'm sure it's in plain sight on wikipedia somewhere, but then why didn't you provide a link to it instead of just asserting that "fact".
and you wonder why people are still skeptical about the lame brained nuclear is the answer crowd. nuclear would be the answer, if humans weren't in charge of it.
actually it is true. the rich seek to subvert the political process to continue to enrich themselves at the expense of the rest of us. and they have the resources to do it.
so, really it is true. the problem is idiots like you who claim the parties are the same.
neither of them is good, but they are most definitely not the same.
and so, I should continue to support companies that pay subsistence wages ? and ensuring that they will always be subsistence wages helps them how, exactly ?
I'm not clear what your point is.
The fact is that these countries could easily enforce policies where the employees would get paid better and we would still be able to buy cheap crap. You forget that they get shit wages because Mitt Romney doesn't have enough houses, not because that's what they have to be paid to be competitive.
Why is it that the race to the bottom is always such a popular "free market" slogan ?
this is why I can't take you 2nd amendment nutters seriously.
there more guns now in this country than there's ever been and you say the second amendment is dead.
and yet I can go down the street about 1 1/2 miles and buy myself a gun. I can even buy one when I'm insane and want to shoot 42 people on a university campus, or kill 8 people at an appearance by a congresswoman.
they believe in something that does not exist, which as far as I know means they are, in fact, somewhat of a nut-case.
are all people who believe in santa claus and the tooth fairy nut cases ? how about if they believe in Odin ? Which God and or abstract entity without any evidence to support its existence can I believe in and not be considered a nut-case ?
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they can handle as much as you want - they just get a lot harder to implement because the feedback loop typically has to be 5x the bandwidth of the operating bandwidth to make sure it can compensate for 3rd and 5th order products.
AGC has nothing to do with linear operation of the amplifier (well it does but only to the extent that operating at really low power levels is more linear) . The problem with these modulation schemes with high Peak to average is that they require the amplifier to be "backed-off" in such a way that they are biased for linear operation but they put out only 1/10th the power that the bias condition should be able to support.
so for example a PA biased for 1/2W operation can only be operated at 50-100mW out, making your efficiency something on the order of 10-20%. A class C amplifier for GSM use, for example is pushing 60-65% efficiency.
which wouldn't be a problem except that darn near everything is moving towards OFDM type modulation.
aha - I missed that note. Now it makes more sense. Those sorts of PAs would be close to unusable even with a PD loop.
still requiring a PD loop is still a big problem.
and there's still the issue that you can get these efficiencies with a pure PD loop. This scheme still has the problem that wide bandwidths are going to require a wide bandwidth feedback loop.
One way to do high efficiency is to do separate phase and amplitude modulation, the so called A-theta modulator. you get your amplitude control by adjusting the PA voltage _continuosly_ and do your phase modulation with an IQ modulator.
For wide bandwidth modulation formats this is a bit of a pain since you need a very wideband, high current, power supply. so they are doing an A/theta modulator but trying to simplify the bias control on the PA to avoid that.
What I'm not clear on is why they are doing this when they have a predistortion loop anyway. a pure predistortion loop should be able to achieve very similar results without any need for the PA bias adjust. you can also do it with 1 PA instead of two.
maybe it simplifies the PD loop substantially, I can't tell yet from the paper, but it trades this off against needing two PAs and PA bias control. And that PA bias control is a bit of a headache two, because you can't just stick a switch in there. The selectable bias levels have to come from a switching power supply which switches between different output voltages. doing this is also non-trivial.
I don't know, looks like somebody's thesis to me. Doesn't look like it's particular practical.
Also, first rule of looking at schemes like this. How much of that power they saved is being used in the more complicated digital circuitry. That's the reason you don't see PD loops in cell phones. It's a wash, you spend so much power analyzing the signal to do PD that you burn up the savings . Now if you have a 10W transmitter, PD makes lots of sense.
with enough advance warning would simply landing a rocket on the asteroid and having it provide a constant thrust be enough to have the asteroid miss ?
at a great distance it would take very little course adjustment which could be provided by a very low thrust.
the obvious complication being if it's tumbling. even then it seems that such a scheme would still work as the rocket could align itself under guidance or using the stars and provide force at the proper time.
not sure why this is never mentioned as an option.
heat causes semiconductor devices to work less well over time. The design must provide for appropriate heat dissipation. A design in which the devices are running at 110 or 120C on a consistent basis will begin to slowly fade. I'm talking about channel temperatures. your box may be "warm" but that could mean that the devices are running hotter than they should for long term reliability.
also a possibility, and my personal favorite. the clock oscillator. poor, even mediocre, clock oscillators have crummy aging characetistics. take that design which is running too hot : the crystals age faster than normal and eventually your device's frequency is too far off. as it begins to drift out, the reception will suffer.
repeat after me: modern electronics for the consumer market are designed for cost. it is expected that you will replace it in 2-3 years. when something lasts you 5 or 6, it's not by design. so if they can save $1 because they don't use the necessary heat sinking or board area to dissipate the heat, and everything is running at 90 or 100C, that's ok. ship it !
send them to the US so the US can pay to imprison them. So you've gotten rid of a "troublemaker" and you don't have to pay to deal with them.
60GHz might travel farther than you think.
an antenna at 60GHz is about 2.5mm, and that's for a basic dipole....
you can easily put multiple antennas on a device, which means you can use beam-forming and get some very tasty antenna gain, maybe on the order of 12 to 15dB.
there are a whole lot of if's attached to that since it depends on a very solid baseband implementation, but theoretically the use of phase array antennas/beam-forming could negate the much higher path loss.
not quite right. N and AC and eventually AD use MIMO which is physically separate transmitters and receivers, i.e. multiple channels.
MIMO doesn't quite get N x (transmitters/receivers) of performance, but it comes pretty close.
AC simply provides for even wider channels than N, i.e. 80 and even 160 MHz channels, but still uses MIMO. It also has a crap load of protocol stuff in it too.
_theoretically_ having multiple receivers would give you a distinct improvement in performance through receiver diversity, but I doubt anybody implements that option.
This all assumes that your client has good radios AND good baseband peformance.
The DSP involved in MIMO is non-trivial and it's very easy to get very sucky performance with a bad implementation. and what do you think is going to happen if somebody f*cks up their baseband ? that's right they're going to try and sell out all of those chips - how the heck are you supposed to know that it's got shitty rate adaptation ? all you see is a cheap client.
the important point is that clients are cheap, and they perform that way.
so in most cases, for home use, you really don't want anything more than a/b/g. if you are doing large file transfers certainly it would be nice to have the higher data rates, but for multimedia streaming over your limited DSL connection there's no point.
a bloom caused by excess nutrients, i.e. pollution, in the water ?
maybe a kind of algae ?
that would be my guess.
am I missing out ?
coporations are somehow better than an authoritarian government.
yeah, I know how the free market is going to protect me from that in some mysterious free market way, but I'm not really clear how that works.
because here how it REALLY works. corporations get really big until the market is basically monopolized and then they collude and I get screwed.
and it used to be we believe that the govt was supposed, since it's OUR government, put a stop to that.
but now the libertarians think we don't need that and the free market will somehow magically work.
and if it doesn't somehow it's always my fault.
they are raising prices because they can and they should.
why wouldn't you raise price if your customers kept paying them ?
Hard to keep tabs on government when the lazy and the idiots keep electing people like Reid, Pilossi, GWB, Obama, and Santorum.
really - who was I supposed to vote for ? McCain ? Ron Paul ?
So, yeah I elected Obama, because the alternative was so much worse.
Instead of denigrating those of us who actually voted, how about a few words of wisdom as to why my choices were so bad.
and yes, you're right, part of the reason is the number of idiots in this country.
That likes to weave propaganda into his articles:
http://shameproject.com/profile/malcolm-gladwell-2/
what a bunch of horsshit. the greenies by no means ignore coal power. and by the way, great ignorant AC VERY LITTLE electricity is generated from oil, so that's not part of the discussion.
only right wing morons with an axe to grind things environmentalists ignore the problems associated with electricity generation via coal.
wow, outrageous generalizations are modded as insightful. I'm shocked...
right on - but why are you sitting on the fence.
human beings have demonstrated that they are incapable of managing nuclear without major radioactive accidents.
I'm anti nuclear because people are incompetent bozos and it's just a matter of time before another disaster.
of course after the NEXT disaster we'll have to listen to the wailing and lamenting about how it couldn't possibly happen again, it only happened because of blah, blah, blad.
and the next time too, until we're all drowning in radioactive Cs, which of course, is easy to treat for, doncha know ?
137Cs and 90Sr each have a half-life of ~30yrs, making them a factor for up to 600 years. Both are beta emitters, so they're primarily a hazard only when inhaled, ingested, or with direct skin contact. However, 90Sr isn't produced in large quantities, so it's not a major factor. That leaves 137Cs. The main concern with 137Cs is with unknown/untreated exposure. It's easy and fairly cheap to treat exposure (including land) if you know about the contamination. 137Cs and 131I are the primary isotopes released at both Chernobyl and Fukushima.
it's easy and fairly cheap to treat exposure (including land) - really? so please do give me your conspiracy theory version as to why the land around chernobyl is still uninhabited. I'm sure there's some reason involving shadowy organizations as to why hundreds of square kilometers of land go unclaimed for something that's so easy to take care of.
you deride the people who claim nuclear is fairly unsafe after two major catastrophes involving nuclear, but offer no support for your lame brained presumption that it's "easy" to get rid of radioactive cesium.
I'm sure the Japanese will be moving back into the area around Fukushima once they've found your cheap and easy method of radioactive decontamination. I'm sure it's in plain sight on wikipedia somewhere, but then why didn't you provide a link to it instead of just asserting that "fact".
and you wonder why people are still skeptical about the lame brained nuclear is the answer crowd.
nuclear would be the answer, if humans weren't in charge of it.
that's a terrificly optimistic viewpoint. I don't suppose that you're black and live in the south, are you ?
a whole lot of people are going to die in your freedom fest you twit.
actually it is true. the rich seek to subvert the political process to continue to enrich themselves at the expense of the rest of us.
and they have the resources to do it.
so, really it is true. the problem is idiots like you who claim the parties are the same.
neither of them is good, but they are most definitely not the same.
and so, I should continue to support companies that pay subsistence wages ? and ensuring that they will always be subsistence wages helps them how, exactly ?
I'm not clear what your point is.
The fact is that these countries could easily enforce policies where the employees would get paid better and we would still be able to buy cheap crap. You forget that they get shit wages because Mitt Romney doesn't have enough houses, not because that's what they have to be paid to be competitive.
Why is it that the race to the bottom is always such a popular "free market" slogan ?
the second amendment has been dead for decades ?
this is why I can't take you 2nd amendment nutters seriously.
there more guns now in this country than there's ever been and you say the second amendment is dead.
and yet I can go down the street about 1 1/2 miles and buy myself a gun. I can even buy one when I'm insane and want to shoot 42 people on a university campus, or kill 8 people at an appearance by a congresswoman.
but the 2nd amendment is dead ?
pathetic.
they believe in something that does not exist, which as far as I know means they are, in fact, somewhat of a nut-case.
are all people who believe in santa claus and the tooth fairy nut cases ? how about if they believe in Odin ? Which God and or abstract entity without any evidence to support its existence can I believe in and not be considered a nut-case ?
as we allow more families to become homeless then will learn that they have to go that extra mile to achieve.
It's important to not provide help of any sort to anybody at anytime or they'll just turn into degenerate slackers.
America ! Fuck yeah !
and generate far less pollution, because they could have implemented pollution control technologies from the get-go.
Why they did not is a real mystery to me. Greed and corruption are almost certainly at the root of it, though.