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Author Topic: Lost 40mHz band  (Read 35437 times)


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Re: Lost 40mHz band
« Reply #30 on: December 11, 2008, 07:39:56 PM »

If you can see 10 different APs from your location, you're never going to get a 40 MHz wide signal AND if you did you'd be taking a rather unfair slice.  It's the penalty for living or working in a signal-crowded environment, and you have to live with it.  If D-Link were to create an interference-causing device, the FCC rightfully would be all over them. 

This is from Atheros:
  • Q: What has Atheros done to ensure interoperability and coexistence with legacy WLAN devices with 802.11n products?

    A: Significant steps must be taken to ensure 802.11n-based products operate effectively with legacy 802.11a, b and g devices and will avoid “stepping on” such legacy devices, especially when 802.11n products shift into the highest throughput mode of 40 MHz channel operation.

    In our 802.11n solutions, we have implemented Clear Channel Assessment (CCA). This is a smart technology that allows the 802.11n device to assess the channel on a dynamic basis to determine whether legacy Wi-Fi products are transmitting on a nearby channel. When a legacy transmission is occurring, the 802.11n device “steps down”, allowing for the legacy transmission to occur without performance degradation. When no legacy traffic can be detected, the 802.11n operation resumes.

    Atheros has extensive experience in smart radio technologies to leverage the capacity of 40 MHz channel operation while avoiding interference with neighbors. In 2003, our Super A/G technology employed for the first time in WLAN history the 40 MHz channel. In order to create “legacy-friendly” operation, we developed Atheros Adaptive Radio Technology and have successfully used the technology in the three years since its development.
  • Q: Does the 2.0 draft 802.11n specification call for elements to ensure “neighbor friendly” behavior with legacy 802.11 devices?

    A: Yes.  The only significant change made to the draft 1.0 specification was the addition of the “neighbor friendly” behavior for 40MHz operation in the 2.4GHz band. However, just how “friendly” of a neighbor the 40MHz system needs to be is still in a topic of discussion at the IEEE. The current specification in draft 2.0 are these three new requirements: 1. Prior to setting up a 40 MHz access point (AP), the AP is required to scan for legacy traffic in the entire 40MHz spectrum. 2. Prior to each transmission of 40MHz packets, Clear Channel Assessment must be done to ensure that no legacy traffic exists in the entire 40MHz spectrum. 3. Stations associated to a 40MHz AP must assist in scanning for legacy traffic which may have been hidden from the AP.  In short, the IEEE’s specification requires that the 40MHz device does “no harm” to neighboring legacy systems.

As for fixing your channel situation -- Channel 7 overlaps channel 6 by 80%.   You might as well switch to channel 6 completely, the result will be the same or perhaps a bit better.  If the bulk of your neighbors are on channel 6 or higher, then you want to be on Channel 1. 

A tip -- broadcast your SSID -- "PeterF-Channel1" which will tell your neighbors that channel 1 is already in use and encourage them to choose something else when they're figuring out their own networks.  That doesn't keep them from choosing channel 2 or 3 which will also share bandwidth with your Channel 1 network, but it might help some.
« Last Edit: December 11, 2008, 07:49:53 PM by funchords »
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