Capacity for QAM
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From: Jerry Avins on 20 Mar 2010 12:03 Michael Plante wrote: > dvsarwate wrote: >> On Mar 19, 10:18=A0pm, Jerry Avins <j...(a)ieee.org> wrote: >>> dvsarwate wrote: >>>> ... it is not possible to exceed the speed limit and >>>> simultaneously achieve good gas mileage. =A0... >>> Actually, Dilip, I noticed a different effect with two of my cars. They >>> seemed to use a pretty constant amount of fuel for a given length of >>> time. The faster I went, the further a gallon took me. Go figure! >>> >> >> 75% of car accidents occur within 5 miles of home. >> So, one should be more careful while driving in the >> neighborhood? No, one should drive as fast as possible >> upon leaving home so as to get out of the danger zone >> as quickly as possible and enter the "safe" zone 5 miles >> away. > > > How is that related to gas mileage, your original argument? Anyway, there > are any number of factors why that might happen, including the pdf of your > car's position/time having its strongest amplitude near home. Plus, for > whatever reason, people like to roll through stop signs in neighborhoods, > but are more careful with other stop signs. > > To throw a wrench in things, there is also an accident factor if you're > driving at a significantly different speed than the rest of traffic. When > the envirowackos pressured Houston to drop its freeway speed limits to > 55mph about a decade ago, just about everybody ignored the change (and even > the police chief was unhappy with it), and it was fairly dangerous for the > twerps who actually did drop their speed (particularly since so many idiots > here feel entitled to drive slowly in the left lane, but that's another > story). Fortunately, it got changed back. An important reason for most accidents happening near home is that more driving is done there than on any other stretch of road. Aside from short trips for shopping and such, every longer trip starts and ends there. That the number of deaths by drowning correlates well with ice cream consumption doesn't imply cause and effect. Both are seasonal. Jerry -- Discovery consists of seeing what everybody has seen, and thinking what nobody has thought. .. Albert Szent-Gyorgi �����������������������������������������������������������������������
From: Eric Jacobsen on 20 Mar 2010 22:25 On 3/20/2010 5:38 AM, Rune Allnor wrote: > On 20 Mar, 02:24, dvsarwate<dvsarw...(a)gmail.com> wrote: >> Of course, the >> BER will be so close to 50% that nobody will want to use such a >> system, >> but hey, it *is* transmitting 10 bits per symbol rather than 4, and >> *is* >> operating above capacity as was wanted. Who cares about the BER? > > This argument plays straight into the hands of the enviro-mentalists: > If the BER is roughly 50% in the first place, why transmit at all? > One can just install random bit generator at the reciever, and > do away with the transmitter. Doing away with the RF stages in > both ends will save tremendeous amounts of power, extending > battery life with who know how many times. > > And of course, this scheme will be robust with respect to just > about any external influence, be it intereference, multipath > or anything else. > > Rune Many, many years ago, in a presentation to, believe it or not, some NSA, NRO, and CIA comm people, I proposed (as a joke, but I didn't frame it as such initially), a highly simplified communication system that operated as Dilip described. BER was guaranteed to never be worse than 50%. For the situations where the BER *was* worse than 50% a switch was provided that would be guaranteed to bring the error rate back below 50% (the switch just inverted the output). Arbitrarily high data rates could be achieved. The "receiver" system was just a single gate with a static output that was inverted by the switch signal. It was usually good for a laugh, and helped to make a couple points about comm specsmanship, capacity, etc. -- Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com
From: Michael Plante on 20 Mar 2010 23:10 Jerry wrote: >Michael Plante wrote: >> dvsarwate wrote: >>> On Mar 19, 10:18=A0pm, Jerry Avins <j...(a)ieee.org> wrote: >>>> dvsarwate wrote: >>>>> ... it is not possible to exceed the speed limit and >>>>> simultaneously achieve good gas mileage. =A0... >>>> Actually, Dilip, I noticed a different effect with two of my cars. They >>>> seemed to use a pretty constant amount of fuel for a given length of >>>> time. The faster I went, the further a gallon took me. Go figure! >>>> >>> >>> 75% of car accidents occur within 5 miles of home. >>> So, one should be more careful while driving in the >>> neighborhood? No, one should drive as fast as possible >>> upon leaving home so as to get out of the danger zone >>> as quickly as possible and enter the "safe" zone 5 miles >>> away. >> >> >> How is that related to gas mileage, your original argument? Anyway, there >> are any number of factors why that might happen, including the pdf of your >> car's position/time having its strongest amplitude near home. >> [...] > >An important reason for most accidents happening near home is that more >driving is done there than on any other stretch of road. Aside from >short trips for shopping and such, every longer trip starts and ends >there. Precisely what I said about the pdf, though you wrote it in a more down-to-earth fashion... >That the number of deaths by drowning correlates well with ice cream >consumption doesn't imply cause and effect. Both are seasonal.
From: Steve Pope on 21 Mar 2010 13:28 dvsarwate <dvsarwate(a)gmail.com> wrote: >But Eric's point about comm specsmanship brings to mind >an apocryphal story about how IBM won a contract for a >military comm. system. Both the IBM design and the >had the same data rate and same BER but the IBM design >used a rate 1/2 code while the competing design used a >rate 2/3 code. (The OP who is no doubt thoroughly bewildered >by the hijacking of this thread should work out what the >implications are for transmitter power and bandwidth in the >two designs). Anyway, IBM won because they told the >generals "In our system, we use one parity bit to protect >each data bit, whereas in the Brand X system each parity >bit has to protect *two* data bits and so their system >provides only half as much data protection as ours does." Brilliant. I'd bet someone a beer this was a system where the delivered datarate was an open figure, but the modulation order (and therefore, code rate) was classified. Steve
From: Randy Yates on 21 Mar 2010 14:13
spope33(a)speedymail.org (Steve Pope) writes: > dvsarwate <dvsarwate(a)gmail.com> wrote: > >>But Eric's point about comm specsmanship brings to mind >>an apocryphal story about how IBM won a contract for a >>military comm. system. Both the IBM design and the >>had the same data rate and same BER but the IBM design >>used a rate 1/2 code while the competing design used a >>rate 2/3 code. (The OP who is no doubt thoroughly bewildered >>by the hijacking of this thread should work out what the >>implications are for transmitter power and bandwidth in the >>two designs). Anyway, IBM won because they told the >>generals "In our system, we use one parity bit to protect >>each data bit, whereas in the Brand X system each parity >>bit has to protect *two* data bits and so their system >>provides only half as much data protection as ours does." > > Brilliant. > > I'd bet someone a beer this was a system where the delivered > datarate was an open figure, but the modulation order (and > therefore, code rate) was classified. "...the truth, the whole truth, and nothing but the truth..."? -- Randy Yates % "And all that I can do Digital Signal Labs % is say I'm sorry, mailto://yates(a)ieee.org % that's the way it goes..." http://www.digitalsignallabs.com % Getting To The Point', *Balance of Power*, ELO |