Many people that write about Wi-Fi live in houses, or so I suspect. I say this, because the specific issues faced by apartment dwellers in crowded cities are rarely addressed.
A few days ago, James Kendrick wrote about his experience moving from a house to an apartment building and, although he's a techie, with his own Mobile News blog at ZDNet, he was unprepared for an urban Wi-Fi environment.
Kendrick had problem with a Samsung 4G LTE Mobile Hotspot that he has been using "... for over a year without issues". One side of the Samsung device talks to the Internet via, in his case, Verizon's 4G network. The other side of the device is a Wi-Fi router.
In the new apartment, none of his computers would connect to the Wi-Fi network created by the Samsung device. Outside his new building, everything was fine. Clearly, this was a case of radio interference.
Kendrick installed software on his Mac that provided more technical information about the neighboring networks and wrote that " ... the building I moved into is teeming with Wi-Fi networks from all the residents. This was swamping my hotspot and making it impossible to connect any device."
Most importantly, the software showed him the channel used by each network. It came as no surprise to this apartment dweller that, as Kendrick writes, all the "... common channels (1,6,11) were swamped."
Wi-Fi network channels are subsets of the available radio frequencies. It beats me why neither a Mac nor Windows 7 bothers to display this important information about the networks they detect (not that I've seen it on the few Linux distros I've tried either). Perhaps the OS developers also live in houses.
The 2.4GHz band (see Why Everything Wireless Is 2.4 GHz) is divided into 11 channels in the U.S. (this differs by country). The channels that Kendrick referred to as "common", 1, 6 and 11, are popular because they are the most spaced out within the 2.4GHz band and thus their frequencies hardly overlap. Wi-Fi channels are a very big deal to apartment dwellers who often have to dance around the channels used by their neighbors.
That said, Kendrick's problem was probably with an algorithm in his Samsung Mobile Hotspot. As soon as he reconfigured it to use a fixed channel, the problem went away.
Some routers have a default Wi-Fi channel, others try to make a smart decision in real time. Finding interference on every channel, his Samsung hotspot may have never settled on a good channel.
PICKING A Wi-Fi CHANNEL
The most useful lesson however came in Kendrick's choice of a Wi-Fi channel.
What to do when 1, 6 and 11 are swamped? Use one of them anyway, or use a channel that no one else is using? Kendrick opted for the latter, writing, "Once I changed it to a channel not being used in the building by other networks, my connectivity was assured. The LTE connection is now lightning fast in the building as expected."
He made the wrong choice and got lucky.
My favorite source for Wi-Fi related information is SmallNetBuilder.com. An excellent article there, When Wireless LANs Collide: How To Beat The Wireless Crowd, by Tim Higgins, addresses this issue head on. In it, Higgins writes, "If you're using 2.4 GHz band equipment, you probably know that your access point has eleven channels that it can be set to. You may not know, however, that only three of those channels should be used."
In other words, stick to 1, 6 and 11. Exclusively. Even if they are crowded. Higgins explains why:
If you're using Channel 1 and your neighbor is using Channel 2, you're both putting plenty of power into each other's channel. Even the best receivers have difficulty dealing with this level of "adjacent channel interference". Whatever a receiver can't understand, ends up as "noise", which can reduce performance. On the other hand, when both your WLANs use the same channel, the CSMA/CA mechanism described earlier, as well as other Wi-Fi coordination techniques, can operate as intended. Although you both will be contending for a share of the same spectrum (and bandwidth), your requests can be coordinated for most efficient sharing. In other words, you may not get the speed you want, but you'll get reliable operation.
Another article at SmallNetBuilder.com, It Takes A Neighborhood To Fix Bad Wireless, by Scott Deleeuw, makes the same point.
... when two networks are both on channel 6, traffic from each will stop and wait for the other. But when two networks are on overlapping channels (such as 3 and 6), traffic can't coordinate. Each network will see the signal from the other as interference, which degrades performance.
But, if choosing an unused channel in a crowded Wi-Fi environment just makes things worse for everyone, how come it solved James Kendrick's problem?
As noted earlier, his real problem may well have been with the algorithm in his router for dynamically choosing a channel. But, as Tim Higgins explained in an email to me,
Choosing an off-channel doesn't necessarily mean that it won't work. Depending on use patterns, receive sensitivities, etc. this can solve a "can't connect" problem. But it may create a problem for other networks by adding to the noise level. Not a very neighbor-friendly approach.
Update July 1, 2012: A discussion in the forums at SmallNetBuilder about choosing Wi-Fi channels points out that you can't tell how busy a particular channel is. That is, are the people you share channel 6 with, looking at one web page every 4 minutes or are they streaming a Netflix movie? A forum user suggested repeated Pings to your router as a way to gauge resource usage by others on your chosen Wi-Fi channel.
On a Windows machine, I recommend the free, portable, fast and simple Nirsoft WirelessNetView from Nir Sofer for learning the full technical details about detectable Wi-Fi networks. The display is flexible, columns can be resized, re-sequenced and sorted.
Below is a cropped screen shot from WirelessNetView taken on the laptop computer used to write this blog. The display is sorted by channel, normally, I sort by signal strength. Shown are 34 networks in the 2.4GHz band, there were also a few in the 5GHz band.
My network is the one in blue with 99% signal strength on channel 1. There are 6 other networks on channel 1 including one whose signal strength is 93%. Yet, I can attest, that this all works just fine.
The next strongest signal is on channel 9 (82%). No doubt this causes interference both on channels 6 and 11. So, I happily live on channel 1.
A couple articles on SmallNetBuilder.com raise another Wi-Fi issue for apartment dwellers: channel width. This comes up because one approach to speeding up Wi-Fi is to use more bandwidth, that is, to use two Wi-Fi channels. Higgins writes,
Atheros' Super-G was the first bandwidth-hogging "channel bonding" technique, and 802.11n has 40 MHz mode baked into the standard. Neither should be used in crowded 2.4 GHz band WiFi environments because there simply isn't enough available bandwidth ... you're just raising the RF noise level, causing problems for everyone. Leave your N router's defaults alone and use only 20 MHz bandwidth mode in 2.4 GHz.
Scott Deleeuw makes the same point in his article on Wi-Fi contention.
802.11n routers have what is called 40 MHz (wide mode) ... What Wide mode basically does is occupy a second channel to theoretically double your throughput. Out in the boonies this would be great. But in a crowded neighborhood, it can actually slow you down and take away available channels for your neighbors. Be sure that you have wide mode set to off, or 20 Mhz mode.
Finally, SmallNetBuilder's Wireless FAQ: The Essentials includes this interesting tidbit regarding the range of Wi-Fi G networks vs. that of N networks:
In general, 802.11n products will not increase your wireless LAN range, no matter what the companies trying to sell you their wares say. They can, however, provide higher speeds ... as long as signal strength is relatively strong ... if you're getting a weak signal in a particular spot with your current G router and card, you'll still get a weak signal with an N router and card. But you might get a bit more speed...
The ultimate solution for apartment dwellers is to move from the crowded 2.4GHz band to the less-used 5GHz band. But doing so requires that both the router and the computing device support 5GHz.
Some routers supporting both 2.4GHz and 5GHz have a single radio so they transmit in only one of these ranges at any given time. Expect to pay top dollar for a router with two radios that supports both frequency ranges concurrently. SmallNetBuilder has many router reviews.
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Update June 30, 2012.
Trying to chose the best available channel, amongst 1, 6 and 11, can be tricky in an apartment building. For example, the western neighbor may use channel 1, while the eastern neighbor is using channel 11 and the people above are using channel 6. In the worst case scenario, two routers/access points may be needed. Using the same example, a router on channel 11 would be perfect on the west side of the apartment and one on channel 1 on the eastern side.
Then too, we can change one of the rules of the game.
Consumer routers transmit their signal in all directions, but that's not the only option.
One approach, if your router has external removable antennas, is to replace them with a directional antenna so that the signal can be pointed in the direction you need it most.
This fails, of course, if you need the signal in two different directions at the same time. You may also not appreciate this approach if you have keep moving the antenna as your needs change.
Wouldn't it be great if the router was smart enough to do this on its own? That is, if the router realized where the computing devices were and only sent strong signals in the direction(s) needed at the moment?
That is exactly the claim to fame of Rukus Wireless.
I briefly used one of their routers and found it far superior to a consumer grade router in terms of providing a strong signal at a distance. A relative of mine then used this Rukus Wi-Fi G router for years to fill a house with Wi-Fi including many places in the house that were formerly dead spots.
The problem with Rukus, that I found, is that they don't deal with consumers; by and large, their customers seem to be ISPs and large enterprises. As a result, their marketing material is overly technical, I found it all but incomprehensible. And, their equipment is not widely sold to individuals. On the upside, their low end routers cost roughly the same as high end consumer models.
As noted above, Wi-Fi N does not increase the range or signal strength compared to G. Rukus increases both. And, in an apartment builidng, the dynamic and directional nature of the signal from a Rukus device should be good both for the Rukus user and their neighbors. They call this secret sauce Beamflex.