I am reading your response and can not decipher all your algorithms? Point that out and I will have a much more understanding of what you are scientifically trying to say. Most WISPS have absolutely no scientific background!
John ---------- Original Message ---------------------------------- From: "Lawrence E. Bakst" <m...@iridescent.org> Reply-To: WISPA General List <wireless@wispa.org> Date: Sun, 4 Oct 2009 00:15:45 -0400 >I think you guys know most of this already, but here is my take FWIW. > >I'm not a WISP, but I spent 5 years leading the design and development of an >802.11[agb] security system. We did our own polling solution based on 802.11e >HCCA to solve the RTS/hidden node problem. > >All things being equal (which they often aren't) 802.11b will give you a >higher S/N and C/I than 802.11g, because in almost all cases and especially at >higher speeds. 802.11g has to lower the PA power because of the PAPR of OFDM >and meeting the 802.11g EVM spec. > >It is true that 2.4 GHz can be very polluted. We found the noise floor to be >really awful. You would be surprised by the number of "entities" that know >they are way over the FCC max power in 2.4 GHz, but I digress. We once >measured over 300 PHY errors a second on an "unused" 2.4 GHz channel. The >number went down to 150 PHY errors a second inside an FCC chamber, if you can >believe that. > >Having said all that we didn't use 802.11b at all because it's data rates are >too low for video. > >Also while we supported 2.4 GHz, we mostly deployed at 5.8 GHz ISM because of >the increased power available there and the pollution was much less, but that >maybe different now. > >For 802.11[ag] mutlipoint, the sweet spot speed wise is 18-36 Mbps. It's very >hard to keep a multipoint system at 48 or 54 Mbps because you need a great >deal of link margin and with all cards you loose power as the speed increases >to maintain PAPR/EVM. For point to point with direction antenna relief you can >often maintain 48 or 54. > >Antennae make a big difference, as others have noted horizontal polarization >is usually best and make the beam as narrow as you can afford because it >raises the effective gain. However, if you are in an area where everyone else >is horizontal it can make sense to try vertical. With some of the antennae we >used that was as simple as rotating the antenna 90 deg at both ends. > >Watch out for crappy antennae, cheap cable, bad connectors, and so on. That >can often cost you a few dB. In the product I designed I spent more time then >I care to admit trying to make a very tough loss budget that I set out as a >goal. > >There is no substitute for link margin, you can never really have enough. > >I can confirm that our sweeps with a spectrum analyzer show lots of >opportunity to use 5 and 10 MHz channels, as others have also noted. For WISPs >it would be "nice" if chip vendors designed the radios so that you could set >the channel bandwidth from 5-40 MHz in 1 MHz increments. It can be done but >probably won't be, although maybe the Microsoft WhiteFI stuff force the chip >vendors to do it. In WiMax and LTE they are already doing some things close to >this. Still 5, 10, and 20 isn't bad and probably hits the sweet spot or 80/20 >rule. > >One of the down sides of fitting a 5 or 10 MHz channel in a sweet spot is that >it can change at any time. > >Best, > >leb > >At 9:58 AM -0500 10/1/09, Jason Hensley wrote: >>In 2.4 land, if you have a lot of noise, which protocol is better - B or G? >>Is it better to run an AP as locked into one mode or is it OK to do a mix? >> >>Max I want off of 2.4 customers is 3meg so not that worried about the extra >>speed that G will provide, but, I would like to know which is more stable? >>I've always thought that B was more stable overall but just provided less >>bandwidth. I've gotten some info that may counter that. What's the >>real-world experience with folks in a high-noise environment, combined with >>a higher useage AP? >> >>I've got an AP that we've run in B mode only for a while. We've started >>having problems with it - speeds go from 3meg at the customer to 200k and >>fluctuate constantly. We've worked with RTS, ACK timeouts, etc etc and >>nothing seems to have improved the stability. For testing purposes we put >>up another AP right next to the one we're having trouble with. Switched two >>of our gaming clients to that one (setup as G mode only) and they seem to be >>doing better, but not quite as good as we feel they could be. This is on >>Deliberant AP's (Duos). The backhaul part of it is not the issue - we can >>pull close to 15meg back to our office when cabled into the AP. We have >>other Deliberant APs that are running MANY more clients than this one so we >>know it's not limitations of the equipment. AP is on top of a water tower. >>Have taken all clients off and brought them back on one by one and it did >>not reveal anything significant. With just one customer on the AP started >>acting up again. Swapped radios in the AP thinking we could have one going >>bad and still no luck. >> >>2.4 antennas are H-pol. We have a ton of noise in the area, but we've been >>through basically every channel and it did not help either. Other AP's in >>the vicinity are performing fine. Thought of the multipath issue so we >>raised our test AP up a little higher than the other one. As I said, the >>test AP seems to be better, but next to it on top of the tower we can get >>around 8 or 9 meg down (locked into G mode), but at the CPE's we're still >>barely getting 2.5-2.8meg. >> >>Any thoughts? We changed everything we can. The new "test" AP has a 9db >>antenna compared to the 13db on the "production" AP. Other than that, they >>are identical as far as equipment goes. >> >>So, back to the subject question though, what's real-world experience with >>G-only mode in the field? >> >> >> >> >>-------------------------------------------------------------------------------- >>WISPA Wants You! 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