EDN Senior Technical Editor Brian Dipert exposes, analyzes and
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Monday, November 23, 2009
802.11n: Another Tangible Demonstration Of A Wireless Range Limitation
Nov 23 2009 10:53AM | Permalink |Comments (6) |
In past writeups, I've discussed the range-versus-frequency tradeoffs of 802.11's two ISM bands (2.4 GHz and 5 GHz), along with the more fundamental limitations of wireless versus other networking technologies. Here's some more quantification of the disquieting situation, in a testing environment different than the one I normally use (i.e. different from my Truckee, CA home office).
As I type these words, my friend's simultaneous-dual-band Apple Time Capsule is 22 feet (and one stucco wall) away from me. WiFind reports that the 5 GHz beacon (specifically channel 149, i.e. 5.745 GHz) coming from the HDD-augmented router has a 19%-of-max signal strength at my MacBook Air, while the 2.4 GHz (channel 6, i.e. 2.437 GHz) signal strength is 35% of peak.
If I sit outside on the deck, less than 10 incremental feet (and only one more stucco wall) away from where I am now, the 5 GHz signal's strength drops to low single digits in percentage and a sustained connection is not possible. The 2.4 GHz signal also plummets to below 20% of peak but doesn't completely drop. Nearby neighbors' Wi-Fi signals are 2.4 GHz-only, have single-digit strength percentages, and are on non-overlapping channels (1 and 11).
I suspect that the attenuation is caused by Faraday cage-reminiscent chicken wire construction materials in the wall. And I also suspect I might also be able to improve things if I overrode the router's default channel selections. But as I pointed out the other day, most consumers don't have either the time, understanding or interest in doing such tech-twiddling. As such, I think the operating range results I'm seeing are pretty sad. What do you think?
Reader Comments
at 11/23/2009 12:51:31 PM, Andy T said:
Properly done stucco does have wire lath in it, which would explain your predicament as surmised, Brian. Maybe you should try to get that site Tempest Certified :-)
Time to break out the sawzall and give her that serving portal she's always wanted in that wall.....
at 11/25/2009 11:35:18 AM, Eric Kinast said:
For an outstanding quantitative discussion of the propagation losses vs frequency through a great variety of common building materials, see the paper
"Propagation Losses Through Common Building Materials 2.4 GHz vs 5 GHz"
by Robert Wilson, who performed these detailed measurements under highly controlled conditions as a student at USC. Refer to the graphs in the text and appendix labeled "T" for the transmission propagation loss through the materials (the other graphs are the reflection and absorption).
It is interesting to note that there are measurements on two kinds of stucco lath. The diamond lath ("chicken wire") has about 20 dB of loss at 2.5 GHz and 15dB at 5 GHz. However, a different type of wire lath has only about 1 dB of loss. Unfortunately, the only plots for complete stucco (lath+concrete) are for the high loss diamond lath. So, building codes permitting, it appears builders could make new construction more technology-friendly by changing small details of the construcion materials.
at 11/25/2009 2:56:32 PM, John said:
I have a 900 Mhz phone that works over 500' down the road and the base unit is in the house that has foil lined wall board with metal siding. The newer 2.5 Ghz has trouble just on the other side of the house.
at 12/3/2009 1:11:08 AM, thinklet said:
Im also had trouble with 2 dual and routers, I switched to WNDR 3700 and it works great, my neibor 150' away also gets great speed.
at 12/4/2009 8:28:14 AM, DaveC said:
Unfortunately we have yet another example where the product is too complex for the user to understand the real performance beyond a simple abstract number (GHz in this case) and marketing is only driven to check the box. "Yes, we have more GHz".
I learned this the hard way a few years ago when I got a PDA that advertised 2 modes of voice recorder as one of it's features. The long play mode was totally unintelligible unless I was hearing my own voice from a close distance. The standard play mode was slightly more usable. The spec simple said voice recorder: yes, two modes.
I have experienced the same with cordless phones, wireless phones, wireless networks, wired networks and DVD recording quality. It's newer -- it must be better. It has the latest feature -- it must be better. It has a higher spec number -- it must be better.
Unfortunately these numbers rarely relate to specific and variable real world experiences. In the best case they "may" be duplicable only under carefully controlled and documented (hopefully standard) lab conditions.
Caveat Emptor!!
at 1/25/2010 10:40:09 PM, forex robot said:
Keep posting stuff like this i really like it
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