Well, it all depends on what you're using. Some systems need at least -65 just to achieve maximum modulation.
----- Mike Hammett Intelligent Computing Solutions http://www.ics-il.com -------------------------------------------------- From: "Jayson Baker" <[email protected]> Sent: Monday, October 05, 2009 10:16 AM To: "WISPA General List" <[email protected]> Subject: Re: [WISPA] To G or not to G :-) > Agreed. We turn down power levels on a lot of things--for that reason. > > i.e. we have a handful of customers that could spit and hit our tower. > Their OP is down as low as it'll go (5dB), because if higher, not only > does > it overpower the receiver (-30dBm signal), but it will cause issues for > all > other clients on that sector. > > We've found that -70 is good, -60 is pushing it, and -50 is too hot. IN > MOST CASES -- see I said IN MOST CASES -- you don't need to flame me up > and > down, saying why I'm wrong, it'll never work, we have no idea what we're > doing. It works for us. > > On Mon, Oct 5, 2009 at 9:04 AM, Marlon K. Schafer > <[email protected]>wrote: > >> "There is no substitute for link margin, you can never really have >> enough." >> >> Sigh. THIS attitude is why there is so much noise in many areas! >> >> Use the power you need, not what's available. No one drives with thier >> foot >> well and truly glued to the floor all of the time! If you did, you'll >> crash, sooner or later. >> >> Too much power is often as big, sometimes more of one, than outside >> interference. You'll create your own interference this way. >> marlon >> >> ----- Original Message ----- >> From: "Lawrence E. Bakst" <[email protected]> >> To: "WISPA General List" <[email protected]> >> Sent: Saturday, October 03, 2009 9:15 PM >> Subject: Re: [WISPA] To G or not to G :-) >> >> >> >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! Join today! >> >>http://signup.wispa.org/ >> >> >>-------------------------------------------------------------------------------- >> >> >> >>WISPA Wireless List: [email protected] >> >> >> >>Subscribe/Unsubscribe: >> >>http://lists.wispa.org/mailman/listinfo/wireless >> >> >> >>Archives: http://lists.wispa.org/pipermail/wireless/ >> > >> > >> > -- >> > [email protected] >> > >> > >> > >> > >> -------------------------------------------------------------------------------- >> > WISPA Wants You! Join today! >> > http://signup.wispa.org/ >> > >> -------------------------------------------------------------------------------- >> > >> > WISPA Wireless List: [email protected] >> > >> > Subscribe/Unsubscribe: >> > http://lists.wispa.org/mailman/listinfo/wireless >> > >> > Archives: http://lists.wispa.org/pipermail/wireless/ >> >> >> >> >> -------------------------------------------------------------------------------- >> WISPA Wants You! Join today! >> http://signup.wispa.org/ >> >> -------------------------------------------------------------------------------- >> >> WISPA Wireless List: [email protected] >> >> Subscribe/Unsubscribe: >> http://lists.wispa.org/mailman/listinfo/wireless >> >> Archives: http://lists.wispa.org/pipermail/wireless/ >> > > > -------------------------------------------------------------------------------- > WISPA Wants You! 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