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Broadcom Accuses Atheros Of WiFi Pollution
eggboard writes "We just posted a story at PC World about 802.11g chipmaker Broadcom's claims that the high-speed 108 Mbps mode available in rival Atheros's AR5004G chipset disrupts all nearby Wi-Fi networks. The Turbo mode, part of Atheros Super G, uses two Wi-Fi channels (5 and 6) to double bandwidth, but Broadcom says this can lead to 'an enormous degradation in the speed of nearby 802.11b and 802.11g networks.'. D-Link and NetGear are shipping Super G-based devices. If Broadcom is right, Atheros gear would pollute neighbors' networks. If wrong, they're putting out a pretty heavy marketing smokescreen just before Comdex - where Broadcom says they'll be demonstrating the Atheros problem."
Doesnt the FCC have to approve such item to be for sale in the US market, And part of the approval process is to check to see if the decive interfears with other electronic devices?
30% Troll, 50% Underrated, 10% Interesting
Score:5, Troll
At least we can look at the source of our Atheros drivers to find out what its up to. Anyone seen an open Broadcom driver?
Alot of gear operating in the 2.4GHz area uses the _whole spectrum_. Western Mux (Proxim?) makes Wireless T1 gear which seems to be very popular for backhauling traffic from Cellular sites. Power output is regulated, but not spectral efficiency.
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Yeah and only three of them can be used simultaneously without any interference. Basically any given channel will overlap with the four neighbouring channels(two in both directions).
All of the above!
First, there's fundamental thermodynamic/information theoretical limits on the amount of information that can be carried in a given amount of spectrum for a given number of symbol values. This is because any "modulation" of a carrier causes the carrier to have spectral products off the carrier frequency. Modulating the carrier at faster rates makes the overall signal wider. I could go deep into sampling theory here but I won't.
The wider a signal in spectrum, the more noise there is over that spectrum, and the more power must be spread over that spectrum to be detectable over the noise floor.
Maximum Theoretical Throughput in BPS = Bandwidth * Log2 (S/N+1)
Where S is the signal strength and N is the total amount of noise in the signal bandwidth. Note that N increases linearly with bandwidth in typical RF applications.
Frequency also matters because the amount of noise present on different parts of the spectrum varies. Almost all noise above 100MHz, though, is created either thermally inside the receiver.. or comes from man-made sources.
The 2.4GHz unlicensed band has 3 non-overlapping channels (1, 6 and 11). You can use up to three DSSS (Direct Sequence Spread Spectrum) devices in the same location without them interfering with one another to a great extent. This would include one or more Wi-Fi networks, 2.4GHz cordless phones (that use DSSS, not FHSS), Baby Monitor, etc.
Anytime you have more than three devices co-located some of them are going to interfere with one another. That interference is going to either degrade your connection speed or it's going to prevent you from being able to connect all together.
If this 108Mbps technology is truly setup to use channel 5 and 6, then Broadcom is right. It is going to interfere with 2/3's of the available non-overlapping channels.
On a quick side note, because wireless connections do not have collision detection, they have to rely on collision avoidance. Once a packet is sent the receiving station has to reply with a receipt acknowledgement before more data is sent, this basically works to cut the actual data transfer rate in half, not that it matters anyway, since almost all wireless networks are used for internet access from ISP's that are lucky to break 3Mbps.
Back to my point though...if you have a wireless network, then be a conscientious wireless user and keep to channels 1, 6 or 11. You can also use the site survey software that came with your wireless adapters to find out what channel other nearby users have occupied already so you can avoid those. Additionally, if you buy other wireless products, avoid the 2.4GHz band if you can. If you must get a 2.4GHz cordless phone or baby monitor then do your homework and strictly avoid those devices which use FHSS (Frequency Hopping Spread Spectrum) - they are frequency hogs which have a tendency to kill other wireless devices.
Craenor - Senior Wireless Networking Specialist for Dell, Inc.
If you look at the radiation pattern for Wi-Fi (or any spread spectrum) it has signal concentrated over a range, but there are harmonics and side lobes and out of band leakage -- it has to be within certain tolerances, but it's allowable. So if you're centered on channels 5 and 6, there will be slop into 1 and 11, but most devices are designed to have the smallest amount of slop.
Freelance tech journalist for the Economist, MIT Technology Review, Macworld, and others
THey have every right to use the entire spectrum if they so desire. If you want to start talking about ethics and sharing, maybe you should stick to licensed spectrum. There are already provisions in the law regarding ISM bands that ensure equitable sharing. They're using 2 adjacent channels - which leaves 9 for others to use. Also, the power limit is the same regardless of bandwidth, so they have half the spectral power density than a single-channel transmitter, which means their range is far less.
Broadcom has a burr up its ass because they didn't think of it first. Boo hoo.
> They're using 2 adjacent channels - which leaves 9
> for others to use
Actually, no. They're using 5 and 6, which overlap with 2, 3, 7, 8 if the device is operating perfectly (the channel bands just overlap by design). If the device actually has out-of-band leakage as the article claims, the could easily be wiping out all 11 channels.
Stock antennas are pretty unimpressive and leave a lot of room for improvement.
Antennas are cheap, especially if you build your own, and they don't burn up battery power.
Antennas work in two directions. An antenna with a better pattern improves your range for both transmit and receive. An amplifier on one side of a link doesn't help you hear the other side any better.
Antennas with radiation patterns that match where you need the network reduce interference coming in as well as interference going out.
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