I recently installed a couple of D-Link DWL-3200AP in a couple of buildings. Then I did a range survey with a laptop. It seems that the range was quite good - going a couple of city blocks outdoors and behind some of the adjacent buildings.
At the same time, it seems that commodity wireless routers provide less range coverage.
How many cubits is a city block? Try not to obscure the numbers.
Did you try a comparison with a commodity router or access point?
The DWL-3200AP beleches +20dBm in xmit. The commodity access point usually does only about +15dBm. Rule of thumb is 6dB difference is equal to double your range.
If you tested your DWL-3200AP using Netstumbler or Kismet you will effectively see the range of the higher power xmitter. For entertainment, try actually using the access point to download files at extreme range and see if you have a reliable connection. I doubt it because the higher power xmitter will have about twice the range on one direction, as comapared to your +15dBm laptop xmitter.
The DWL-3200AP receiver seems to be about typical: |
12Mbits/sec, the DWL-3200AP claims -82dBm sensitivity while the commodity DI-624 claims -84dBm. The commodity receiver is 2dB better. This is not terribly important as everyone lies (or gets sloppy) on their specificiations.
In my limited experience, antenna pattern and gain are the most important factor in determining coverage and range. Line of sight is second. Lack of interference is a close third.
Thanks for the reply. Good thoughts / insights. I'd not thought of the file transfer test. It all makes sense. Somehow I had thought that the signal strength reported by the softwarewas a "system" measure (i.e. 2-way) but I guess that was only a hopeful notion per your comment. I'll try it.
No, I didn't try it side-by-side. Thus my question.
A city block "standard" is 1/20th of a mile in my world. 200 feet plus one
60-foot wide street each is typical. It varies. At least I didn't state the estimated distance in "ells".
So, "a couple of blocks" is around 500 feet. I wasn't out there with a tape measure - just walking around the streets in an area where there is medium building density of 1-story wooden buildings (as in perhaps 70% occupied ground without counting the streets).
I should add: A couple of years ago there was a survey of coverage published with coverage test results from a number of mainstream commodity wireless routers (B or G) and D-Link stood out. Are there any similar, more recent, reports? Where might I find them?
I've not tried Netstumbler so I'm off to do that! In surveying a very high wireless site density in a small city area I found that the site survey software would not drop sites off the list as I moved away from them. That made it really hard to figure out where the sites were likely located and what sites were likely sources of interference.
Regarding interference: I did find that setting the DWL-3200AP in an automatic mode for deciding the best channel at any time seemed to be *not a good idea* in a high-density location. That's of course, the opposite of what I'd expected. It was creating lots of client dropouts. Performance is much better, and remains so today, to just manually select what appears to be a mostly unused channel and leaving it there. This is in that same high-wireless-density location.
Do you find that most interference is from other 802.11x sites, other related wireless devices or totally unrelated device EMI? Or is it a mix?
The Signal Strength and S/N ratio are reported by both the access point and the client radios. Unfortunately, the DWL-3200AP firmware scribblers elected to only supply the signal strength. |
S/N ratio is more important because it is used to set the speed of transmission. The lower the S/N ratio, the slower the data rate. Of course, Dlink also didn't include the speed. Sigh.
Anyway, some of the management packets include both the signal strength and S/N ratio, which can be sniffed and extracted. Methinks Kismet (Linux) is the appropriate tool. See: |
It's difficult to guesstimate how far you can RELIABLY communicate. The data sheet has a table of ranges: 802.11g (Full Power with 5dBi Gain Diversity Dualband Dipole Antenna) Indoors: 98ft (30m) @ 54Mbps 112ft (34m) @ 48Mbps 128ft (39m) @ 36Mbps 154ft (47m) @ 24Mbps 184ft (56m) @ 18Mbps 217ft (66m) @ 12Mbps 259ft (79m) @ 9Mbps 325ft (99m) @ 6Mbps Outdoors: 367ft (112m) @ 54Mbps 820ft (250m) @ 18Mbps 1640ft (500m) @ 6Mbps Methinks they're being a bit optimistic, but it does show what obstacles (indoors) can do, and approximately the effects of speed changes. At the range extremes, you're probably at 1 or 2 Mbits/sec if you have that enabled.
In other words, you had obstructions between you and the access point. You probably also had reflections and definitely had some trees or building with the Fresnel Zone. Sounds like a challenge.
The best reports I've seen are at:
various reviews are VERY illuminating. Tim Higgins goes out of his way to produce accurate reports using realistic conditions and reproducible procedures. However, the various web pages are designed to deliver advertising, so each report is chopped into 10-20 pages. It's worth the effort slogging through them. Nothing on the DWL-3200AP.
Methinks Kismet would be better, but Netstumbler will suffice. Note that there are several Signal Strength, S/N ratio, and noise level numbers shown (scroll horizontally). These do NOT come from the access point. They come from the NDIS5 driver on whatever laptop you're using for testing. Therefore, an overly strong access point xmitter will show up as a very strong signal with NetStumbler, while the ability to communicate reliably is limited by the laptop xmitter, which is not shown by Netstumbler.
Yep, you've noticed. The big problem with the channel hopping scheme is "what happens when there are 20 connected clients, the access point changes channel, and some of them don't notice the change"? Well, the one's that missed the channel change have to re-associate. Some wireless clients do this very well (i.e. Intel Proset). Others suck.
Yep. You might also try fixing the wireless speed to 12Mbits/sec. This locks out the 802.11b only clients, but is a good compromise speed. I've found that disconnects and weird stalls are reduced (but not eliminated) by fixing the speed.
Almost all the interference I see come from other access points or municipal networks. These are fairly easy to see and find with Kismet. The worst are glass wall office buildings with literally hundreds of access points and clients spraying RF all over the view. During lunch time, the same building also has plenty of leaky microwave ovens running. I've also run into a few 2.4GHz wireless security cameras. Non-802.11 interference is where I get involved. I drag out the dish and spectrum analyzer, and do the transmitter hunting thing.
I have seen some EMI, but usually it's very local. Switching power supply wall warts sometimes generate lots of RFI. One particular monitor had a huge field that affected any nearby electronics. See the FAQ for a list of probable interference sources at: |