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."

Comments

FCC?

[pvt_medic]

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?

Re:FCC?

[pvt_medic]

Having been bothered enough by my question I went and looked it up. I first looked at a walkie-talkie i had and Read the following "This Device complies with part 15 of the FCC rules. Operation is subject to the condition that this device does not cause harmful interference."

Then looking up Part 15 of FCC Rules available HERE. I focused in on 15.5 General conditions of operation.

Which states

TITLE 47--TELECOMMUNICATION

CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION

PART 15--RADIO FREQUENCY DEVICES--Table of Contents

Subpart A--General

Sec. 15.5 General conditions of operation.

(a) Persons operating intentional or unintentional radiators shall not be deemed to have any vested or recognizable right to continued use of any given frequency by virtue of prior registration or certification of equipment, or, for power line carrier systems, on the basis of prior notification of use pursuant to Sec. 90.63(g) of this chapter.
(b) Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by industrial, cientific and medical (ISM) equipment, or by an incidental radiator.
(c) The operator of a radio frequency device shall be required to cease operating the device upon notification by a Commission representative that the device is causing harmful interference. Operation shall not resume until the condition causing the harmful interference has been corrected.
(d) Intentional radiators that produce Class B emissions (damped wave) are prohibited.

Re:FCC?

[afidel]

Not really, the 2.4Ghz spectrum that the .11b and .11g protocols use is an ISM band which is basically the FCC's term for junk spectrum that can be used for virtually anything. This is unliscensed space and the rules are pretty lax. So long as you aren't exceeding power requirements and aren't bleeding into adjacent frequency spaces you are pretty much ok. The frequency seperations used in .11b and .11g are IEEE standards not FCC ones.

That being said we observed this with Atheros's .11b channel ganging tech. Not only were they using two channels but their side interference in that mode went from bad in their normal mode to absolutely atrocious in the "turbo" mode.

Re:FCC?

[Spazmania]

That means that you don't have to be licensed to *use* equipment that operates in that band. The systems themselves still have to go through certification testing at a licensed lab to make sure they comply with the rules for a given band.

Re:FCC?

[GigsVT]

Yeah but look at part (b). You also must accept interference. Two people with Part 15 devices that interfere with each other have to work it out between themselves. The FCC only gets involved if a Part 15 device is interfering with licensed users, like hamradio, police radar, TV, commercial radio, etc.

Spectral Efficiency

[yogensha]

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.

Re:Not much

[inburito]

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).

Improper channel useage is rampant in Wi-Fi

[craenor]

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.