In the preceding thread the following link was mentioned
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which as the author writes that one can expect an indoor range of 150m using 802.11b and outdoors a range of greater than 500 meters !
I have read plenty of Faqs on this and some are often quoted such as the Navas Faq
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in which there are interesting comments on this type of concern and links such as that of the Intel Hotspot. ftp://download.intel.com/business/bss/infrastructure/wireless/deployment/hot spot.pdf
In fact John Navas justly coments :
The rather optimistic ranges listed are probably with a better than
>standard omnidirectional antenna and with unobstructed line of sight.
Does anybody know of an updated Field Performance Test Comparison Table ?
eg : Card Name/AP Name/Mode/Distance/Signal/Throughput etc and then testing through the various distances until the signal is lost. Then change mode, then change X, change Y etc.
One could the compare the Named product couple with others [entered as records] dealing with, for example, the same AP but a different card.
The throughput should be tested using an impartial Net Tool not the Product Control Module if it has one. Ixia QCheck is a good Win possibility and in Linux there are plenty of choices.
Personally I have never witnessed a fully working efficient Wlan link at 150m indoors going through numerous walls and other obstructions. I have read of several firms who pretend such performance and yet when I went out and tested the stuff the result was disappointing, disastrous would be more appropriate.
eg: Table for AP's/Card's expected field performance Conditions : Perfect LOS, Standard Antennae and Original FW. Standard environmental conditions and a non tweaked setup [==> Little interference for optimal initial conditions]
On 100+m (not >400m) I have found that the signal was low and the througput was only usable for an Internet connection. Little chance of considering a real Office Client/Server connection. It was down to a variable 1-peaks of 2 Mbs. At 150m the signal/connection dropped too often]
Some other experts consider that there is far too much Hype around and that a good connection is only available at around
60m max In fact this is far closer to my findings than that written on the Product Spec Sheets.
To have a Signal Connection or Throughput Peak is of little interest here.
Take for example the often quoted' standard WAP54 series with a standard setup, no encryption etc. Take a standard Card (eg. WPC54 series) What have you found ? At 10 meters save a 10 MB file to you server,? What was the duration/signal stability/throughput ? Note other ranges up to unusable. Has anybody managed to upload a 10 MB file over a 500 meter link with a fully efficient B connection using standard out of box 2dB antennae?
Any comments, suggestions or links would be most appreciated.
A table with the conclusions could be published here for benefit of all, including any comments on the efficiency of the Firms Support team to resolve any issues evolving during your experience.
I just hate it when someone posts an interesting question and I don't have enough time for a proper answer. This may come in two or more parts.
Ummm... I wrote that part. The numbers used by Intel are rather optimistic and assume an ideal location, no interference, no reflections, no obstructions, and radios that actually meet their published specifications. The tests were also performed at fairly low and useless speeds (1 or 2 Mbit/sec association).
No, but you can make your own quite easily. I'll do it when I have time. Start with your favorite access point and 802.11g laptop. Start in close to the access point and start moving some streaming data. Streaming video or large file copies are good. Watch the connection speed. When it drops from 54Mbits/sec to 48Mbit/sec, stop and measure the distance. Move VERY slowly as it takes a while for the system to react. It's usually about 15ft when I try it. Do it again at different speeds until you run out of walking room. Make the speed transition points on a graph. The points will be all over the graph but a pattern will emerge.
Another (better but more tedious) way to do the test is to lock the speed at the access point to some speed (i.e. 54Mbits/sec) and move away until the error rate goes up sufficiently to be useless. Notice I didn't say until it disconnects because that can take quite some time. Using the Windoze performance meter to monitor thruput for a file copy is a good indication of error rate. Repeat at different fixed speeds.
You can also extrapolate from a few points by using the receiver sensitivity change versus connection speed. See the first table at:
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square law says that -6dB change in power results from a time two change in range. If you get 15ft at 54Mbits/sec, and the receive sensitivity is -68dBm, then at 6dB less, you'll have twice the range. Looking at the chart -74dBm sensitivity is 36Mbits/sec. Therefore, at
30ft, you should slow down to 36Mbits/sec.
I have some results but they belong to the client. However, I can easily run the tests again. Be prepared for huge variations from theoretical.
That's fine. Just remember that there needs to be a reference level for BER (bit error rate) or thruput drop at the various distances. You could do something sloppy like "when the file copy thruput drops in half" or something similar. It doesn't matter what reference you use as long as it is consistently applied.
How many indoor buildings are there that are the size of a football field or larger? Obviously, 150meters is not an indoor test.
What's a wall worth in dB? I collected a few charts of material attenuation and posted them at:
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's pretend that a "typical" wall is good for -6dB attenuation. That means for every wall the signal has to go through, the maximum range is cut in half. Actually, the combination of reflections and material attenuation result in far worse range loss.
Yep. They probably tested this with a production access point, an insipid antenna, a highly reflective office environment, interfernce coming in through large windows, and a laptop with its worthless antenna. These are far from ideal, but represent the most common wireless arrangement.
Let's play with the numbers and see what worst case produces instead of best case. Going to the link calcs at:
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plugging in some numbers. A WRT54G dribbles about +15dBm tx power. The antenna is about 2dBi gain, but the coax and connectors eat about -1dB in loss. The laptop uses an marginal receiver with about -88dBm sensitivity at 6Mbits/sec connection speed, the slowest OFDM speed. The ceramic backed antennas in the laptop lid are good for about -2dBi gain and another -2dB in coax and connector losses. I'll aim for 20dB fade margin (just to be consistent).
TX power = +15dBm TX coax loss = 1dB TX ant gain = 2dBi Distance = unknown RX ant gain = -2dBi RX coax loss = -2dB RX sens = -88dBm (at 6Mbits/sec) Fade margin = 20dB
Plugging into:
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trying various distances until I get about 20dB fade margin, I get a range of 0.06 miles or 316ft. That's quite good at 6Mbits/sec. Maybe I'm being too optimisitic somewhere.
Now, running the same numbers with a receive sensitivity of -68dBm at
54Mbits/sec, I get 0.006 miles or 32ft. So, your range is going to be between those numbers (for OFDM).
Gaaak. Where am I going to find an interference and reflection free environment the size of a football field? Over water?
Well, what are you standards for an acceptable connection? The 20dB fade margin is 100 times the signal necessary to produce the BER of
1*10^5 reference ( 1 error for every 10^5 bits). That's more than adequate for office communications.
As an asside, I have a customer that has some goofy cash register program that absolutly will not tolerate any packet loss. Their database client server program literally hangs or dies if even one packet is lost. It's not a security feature, just old crappy design. If you're having problems maintaining database intergrity over a wireless link, check on how well you application tolerates packet loss before you assume it's a wireless issue. May I suggest DummyNet at:
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simulating packet loss.
What were you using for testing? How many walls?
"Good" is how how many dB of fade margin over the receiver sensitivity (at a BER of 1*10^5). Per my first calculation, one should be able to do 300ft at 6Mbit/sec OFDM association. If not, either one of my assumptions is off, my calculations suck, or some part of the puzzle is not meeting published specifications. I really don't know which is the case here.
I suspected that was too good to be true. The range is about twice what I would expect from worst case calcs. Let's try again with better numbers.
The RX coax loss and RX sensitivity on the laptop end are the problem. I just ripped apart a Toshiblah A75-S213:
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noticed that the tiny coax cables to the antennas are about 2ft long. I only allowed for -2dB coax and connector loss. The connectors are Hirose u-FL or iPex MHF connectors. The coax appears to be Sumitomo 0.4DS-PBA-H with an attentuation of about 7dB/meter (extrapolated from unreadable graph), or about -5dB loss for the coax and about 0.5dB for the connector.
I dug out some tests I made with an Intel 2200BG card at various speeds. The numbers from my chart came from a DLink DI-624 and tend to be somewhat better than those found in the typical MiniPCI client radio. I found that the RX sensitivity at 6Mbits/sec (slowest ODFM speed) was about -84dB at the connector (including compensation for test leads). Therefore, the numbers should look like:
TX power = +15dBm TX coax loss = 1dB TX ant gain = 2dBi Distance = unknown RX ant gain = -2dBi RX coax loss = -5.5dB (including connectors) RX sens = -84dBm (at 6Mbits/sec) Fade margin = 20dB
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now get 0.025 miles or 132ft. That's about right.
For 54Mbits/sec, the sensitivity is about -63dBm from my 2200BG tinkering, which yields a range of 0.0022 miles or 11.6ft. Yeah, that's a bit shorter than I expect but in the ballpark.
Hello Jeff, How nice of you to participate. Its a little late. Hope this is readable ...
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Glad that at least you find this argument of some interest.
I do beg your pardon, I was under the impression that it was from a text snip from John Navas, but I was working very late and perhaps I mistook the author.
The idea was basically that of a common pool of data. On my own I cannot test all the combinations or even all the models The participation of any interested Wlan technician would be appropriate here
In fact this was more or less the method I had adopted last weekend going from
0 - 150m ca and using a Net Performance tool to measure the corresponding throughput. Due to lack of time I examined only distance as the pivot factor and noted the measured throughput and corresponding SNR. 5 distances tested over the range each run several times. The result was really rather upsetting. Considering the quotes promised in the Tech Specs of the components employed and the assurances, or should I say 'lack of ', of the so called qualified techicians on a well known Firms Support Desk, I am concerned that something is amiss.
I am a little surprised that this type of chart has not been developed by members of this and other similar Forums. It would not be difficult to create a simple Web Form with the necessary fields and relate it to a Database which can be interrogated or which can be downloaded. As a simple base meter it would be simple to read as a reference and I believe very useful for elementary tests. [Of course this supposes a professionally scrupulous and honest behaviour of the colleagues who wish to insert the records.]
This is an interesting point. Sometimes AP's (and cards) when set to a modest fixed mode and speed transfer data with a more stable signal and, in the long run, better throughput than when set to Auto which may start at G/54 Mbs and then drop to a wavering B/11,14,8,12,
17,6 etc. I have read confirmations of this from others also. Comments?
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Concerning this theme, I would be very interested to hear from you.
This of course was a rather caustic comment of mine :-) It was based precisely on a couple of Spec Sheets from Linksys in which they state that the cards cover such 'indoor ranges' (B mode.) However it is equally true to say that I have not witnessed a fully fledged Wlan running G Mode over an 80m Warehouse with a constant 24 Mbs. I would be interested to know who has and how many walls etc the signal passed through. [Remember I proposed this query considering standard Antennae and non boosted cards or AP's.]
Thanks for the link, tonight however it seemed dead. Please post an update, I am interested to add your data to another table that I have been assembling recently.
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100 m at 6 Mbs ? Perhaps the 88dBm sensitivity at 6Mbits/sec is better than the common cards on the market.. I guess much much better than the card I had during one of the tests (WPC54G WAP54G). I have noted that few cards (Orinoco, Cisco, Senao, Denmarc etc) approach or surpass the 90dBm and generally they are already down to a couple of Mbs. Do you agree ? Coincidently I had downloaded the Terabeam SW some weeks ago.
Exactly.
:-) As you stated before, one needs a base reference. I was merely considering typical differences in well known conditions. eg: in the city center /in the country (obviously not under a high tension cabling, in a nuclear power station, near industrial motors etc. and of course during the primary tests if possibile without GSM, faulty electrical equipment nearby, nieghbours disturbing stuff on etc Or the difference from in the work office surrounded by offices and all the general 'background noise' to a slightly less EMF polluted area temporarily without the usual interferences (residential or otherwise) Just to enable a slightly simpler interpretation of the primary results from the tests. This does not of course pretend the unattainable silence.
I was considering her basically two types of simple 'acceptable connections'.... (for simple client setups that is.) We are yet considering medium or large installations. The aim here is to to be able to obtain a reasonable idea of the working real life potential of the components in recognisable conditions and then extrapolate from there to have an idea on how best to work in less favourable conditions
The first is a connection stable and fast enough to support general modest size office work (text files, spread sheets, printing, modest DB client server apps, and of course Internet apps. I believe from experience that people start complaining when they go under 10 Mbs for the first part and nowadays, with DSL around, also if they go under a constant 0,75 Mbs x Internet Apps. This is for point to point, we are not yet considering concurrent users and shared bandwidth. As said, its to test what can be done as a max in basic P2P test. It's pretty clear that for any installation that forsees a large number of users and/or several floors and/or certain apps a survey and a study needs to be planned. However notwithstanding this a simlar impartial table of field results might be very useful to many persons. (Suppliers included !)
Interesting link, thanks.
As stated before Outdoors pure LOS = no walls (WPC54G WAP54G). In fact I am concerned that the AP might be faulty in some way.
Interesting. As stated above the Receive Sensitivity you mentioned for that throughput IMHO may be better than some common AP's/Cards offer. Apart from this Linksys does not include this value in their Spec Sheets and after a hopeless series of encounters with their Support desk it seems that they still refuse to give out this technical type of info. [Other firms are far more efficient and mention plenty of values at different frequencies and ranges.]
Really interesting. Thanks. Confirms some of my ideas on this. We could build a Spread sheet on this with calculations included. Great Expectations vs. Unforgiving Reality :-() I'll be back later in the day. Thanks __________________________________________________________ "Jeff Liebermann" ha scritto nel messaggio news: snipped-for-privacy@4ax.com...
What I really would like is the PHP source for the various calculations on the page:
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are others available but I like this one because it's simple. (Warning: I'm a truely horrible programmist and can't even make my own web pile look good and work well). I could probably scribble my own but it's so much easier to just steal one that works.
Incidentally, see my assortment of RF path calculators and spreadsheets at:
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Please note that one can accurately predict the range, at any connection speed with only:
The transition point where the speed changes from one speed to another.
The RX sensitivity at various speeds and modulation modes at some fixed reference level (BER = 1*10^5).
The desired fade margin. 20dB minimum is good enough for most calcs.
I'll post the material attenuation specs when
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comes back online.
Some work has already been done on comparing hardware.
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problem is that the Receive sensitivity page link seems to have been "reorganized":
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there has been some number juggling designed to make someones products look good. No clue how any of the measurements were actually done, or whether they were just plagerized from the manufacturers or chipset data sheets. Got one of these handy?
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as I like Wiki's, the common vandalism makes me wonder if it's really such a good idea.
Back to meetings, work, interruptions, more meetings, etc... Sigh.
it has the same problem. No clue where the numbers came from, whether they are test results or from data sheets, and if measured, what proceedure was used.
How to measure receiver sensitivity (one of several ways):
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doubt if any of those posting numbers to the Wiki bothered to do any of this.
Hello Jeff, [Just before leaving for out of office business] Many thanks for this post
"Jeff Liebermann" ha scritto nel messaggio news: snipped-for-privacy@4ax.com...
Which is why I commented on a Open Web Database. I have seen a couple in thepast but they were relevant to HW performance. The Terabeam work is in fact an excellent example.
Great, I also had seen a couple of these (Cisco etc), but the others are very appropriate.
In fact it's interesting to note that 'expected range' calcs based on specsheet data are hard to come by. It might be nice to devise one. Based on your approach above it should not be difficult.
OK
I had exemined these 2 well known sites several times but it seems that the data is not as updated as one might hope and the list of suppliers are rather limited.
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Much as I like Wiki's, the common vandalism makes me wonder if it's
Do you know how much does the Anritsu costs? A site that might interest you is the following which offers a reasonably sophisicated Survey Tool for an acceptable price.
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I should be back in the evening, Thank you and best wishes for a nice day.
The Sputnik spreadsheet claims to calculate range for their products.
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don't know how accurate it is becauase I haven't played with their equipment.
I have some issues with the Proxim spreadsheet, which uses 12dB as the target fade margin, and the Cisco spreadsheet, which uses 10dB.
10-12dB is barely functional and not very reliable. I deal with one
5.6GHz link with a 13dB caculated fade margin. (The aesthetics committee would not allow larger dish antennas.) It's down about 10% of the time, which is acceptable because all it does is unload non-time sensitive collected data.
Yet another project. However, it's something I find interesting. However, I will NOT concoct a fixed table or chart showing "typical" speeds and ranges. There are far too many variations and I don't wanna spend my life defending the numbers.
The site is back up. No clue what happened (or why it only happens when I post a link to it). Probabaly a conspiracy.
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that the material attenuation numbers are all over the place and vary with the source. I once read a report where an instructor had students measure wall, door, and window attenuation. The result was huge variations in attenuations. I was also amused at reading the table of attenuations "accurate" to 3 decimal places. Sigh.
I've also had some entertainment dealing with people that claim they have perfectly good coverage going through 4 or 5 walls. It's possible, but more often, the signal arrives via a reflection through open windows that simply bypass the walls. I got involved in such a mystery when a company was doing a site survey and noticed that the signal was useable no matter how many walls they went through. When I showed up, I blocked a few windows with aluminum foil and wall attentuation returned to normal. In another, it was leaking through the HVAC ducts. Still another leaked trough the plenum above a suspended acoustic ceiling. Translation: It's REALLY difficult to get accurate material attenuation numbers as much depends on the layout.
It was just released in Dec 2005 so it hasn't hit the used market yet. List price is about 3 million Yen, which is about $26,000 or 15,000 UK pounds at current exchange rates.
Just for fun, look at the prices for Anritsu accessories and tools:
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$25 for a wrench that costs $2 at any hardware store?
Agilent 802.11 test equipment and software: |
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N4010A Wireless test set. |
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$13,000 for the basic box. About $6,000 more for the software.
My apologies for the delay in responding with followup. As mentioned in the last posting I was looking into various aspects of this question and also on some of the information which came from your links.
I looked at this, there is little help on the interpretation of the optional sheet's cells. The PDF is compensates a little.
Looked at it briefly but I had already read these notes of yours with pleasure. Sputnik Firmware for Linksys WRT54GL ? AFAYK they write FW's for other Linksys products? (Not mentioned there.)
Interesting story :-)
Hey Jeff, you might be mistaken here. I have found several quotes going from
3,500 ca. down. It all depends on which packet you buy. The developpers kit is over 5,000 but the basic Survey is much less. In professional circuits it is quoted as being a good product. In case your interested in an excellent comparison review of Wlan tools :
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I have seen it priced at less under $. 2,000 in some places. Hope to get back with some other info on estimation/calculation/comparison. If you have anything else let me know. Thanks for the help.
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