Optimum SNR and Sensitivity - which one?
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Posted by papa on February 8, 2008, 4:24 pm
Please log in for more thread options This SNR/sensitivity issure arose when I installed my otherwise, decent working Netgear WG311T PCI card in my 3GHz AMD machine - and it promptly started freezing. All the usual reinstalls and upgrades did nothing to solve the issue, so I popped-in a Linksys WMP54G and all seemed OK. Well, not exactly. Although the Linksys card ultimately solved the freezing, it was clearly not as sensitive as the Netgear WG311T. Needless to say, I'm a little disappointed by this find. Linksys publishes their SNR and sensitivity specs, but Netgear does NOT. So, does anyone have or know of the specs (or which wifi card has the best SNR & sensitivity)? I'm not to concerned which has the greatest transmitting 'power',.. just the best reciever. ------------------------------------------------------------------------ View this thread: http://www.wirelessforums.org/showthread.php?t=38380 http://www.wirelessforums.org | ||||||||||||||||
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Posted by John Navas on February 8, 2008, 10:31 pm
Please log in for more thread options Such differences are small, and hard to pin down. Better to get a card with a good antenna, which makes a much bigger difference. -- Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi> Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_HowTo> Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes> | ||||||||||||||||
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Posted by Jeff Liebermann on February 8, 2008, 11:06 pm
Please log in for more thread options On Fri, 8 Feb 2008 16:24:40 -0500, papa
>This SNR/sensitivity issure arose when I installed my otherwise, decent
>working Netgear WG311T PCI card in my 3GHz AMD machine - and it promptly >started freezing. I've used the WG311T: <http://www.netgear.com/Products/Adapters/SuperGWirelessAdapters/WG311T.aspx>
in various fast machines without incident. Vista, XT, or Linux? Any
particular flavor of AMD? Latest driver? >All the usual reinstalls and upgrades did nothing to
>solve the issue, so I popped-in a Linksys WMP54G and all seemed OK. >Well, not exactly. Although the Linksys card ultimately solved the >freezing, it was clearly not as sensitive as the Netgear WG311T. >Needless to say, I'm a little disappointed by this find. > >Linksys publishes their SNR and sensitivity specs, but Netgear does >NOT. Careful here. Most vendor leak their specs somewhere, but almost all of them lie. The most common abuse is to specify the native sensitivity of the chipset used, as supplied by the chipset vendor. I got fed up and started to tabulate the rx sensitivity numbers: <http://802.11junk.com/jeffl/rx-sens/receiver%20sensitivity.htm>
I've also done some bench measurements in the distant past (when I had
access to the proper test equipment) and found a rather wide bell curve variation in sensitivity across a manufacturers production. Your WMP54G may have been a lemon. The large number of products, which amazingly have exactly the same RX sensitivity specs as competing products should give you a clue. The numbers typical vary about +/- 3dB (or worse). Note that the basic sensitivity is seriously affected by digital and RF noise coming from the board. This makes the board layout critical for good sensitivity. Sensitivity can also be ruined by too many coax cables, connectors, diversity switches, and strip lines between the antenna and the receiver chip. You can get a clue as to what's inside the WG311T and WMP45G by looking at the photos on the FCC ID web pile: <http://www.fcc.gov/oet/ea/>
which has now mutated into the Equipment Authorization web pile.
You'll find the FCC ID on the serial number tag. >So, does anyone have or know of the specs (or which wifi card has
>the best SNR & sensitivity)? I'm not to concerned which has the >greatest transmitting 'power',.. just the best reciever. I can give you a guess based on the chipset, but do not have accurate (or repeatable) numbers to justify my guesswork. I'm partial to various Atheros chipsets as being the best of the bunch for sensitivity. I've had more experience with Broadcom and they seem to be all over the map. While searching with Google, I found this Powerpoint slide show on receiver sensitivity and MIMO, which should give you a clue as to how messy it is to measure sensitivity: <https://mentor.ieee.org/802.11/public/03/11-03-0845-01-000n-11-03-0845-00-000n-receiver-sensitivity-tables-mimo-ofdm.ppt>
Got money? This is what it takes to measure sensitivity: <http://www.home.agilent.com/agilent/product.jspx?cc=US&lc=eng&ckey=736843&nid=-536900799.536908552.00&id=736843>
Only about $10,000 plus $3,000 for option 103 (Wlan testing). I think
the price tag might be a clue as to why vendors would rather lie than measure. However, there are exceptions. Looking at the numbers, I think DLink actually does measure their products. That's because the variations in results closely resemble the mess I used to obtain doing the same measurements. Incidentally, SNR (signal to noise ratio) is a reference level. Sensitivity is a signal level at which a specified SNR, BER (bit error rate), PER (packet error rate), or other reference level is achieved. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 jeffl@comix.santa-cruz.ca.us # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS | ||||||||||||||||
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>NOT. So, does anyone have or know of the specs (or which wifi card has
>the best SNR & sensitivity)? I'm not to concerned which has the
>greatest transmitting 'power',.. just the best reciever.