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New Member

Noise level increase with speed

My understanding is that the noise level in a WLAN is a result of the environment where wireless equipment is in use.

I have a site where the noise is around -98 dB when connected to an AP with the speed fixed on 11Mb. But when I connect to another AP in the same location, on a different channel with the speed not fixed (it can go up to 54Mb) the noise goes up to -72 dB.

Any suggestions why this may be occuring?

Thanks.

5 REPLIES
Super Bronze

Re: Noise level increase with speed

Hi

The noise level may vary over time, which may explain this... however a more likely explanation (especially if you can repeat this scenario reliably) is that there is simply more noise on the channel that the second AP is running on.

The art here is to make sure as far as possible (whilst still using the non-overlapping channels 1,6 and 11) that each AP is running on the channel with the lowest noise level, whilst still not using the same channel as an adjacent AP.

The noise level shouldn't be impacted too much by the speed of the transmissions from the AP.

Regards

Aaron

Please rate helpful posts....

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
New Member

Re: Noise level increase with speed

We considered this possibility while but there are 2 installed APs on the site. One on channel 1 and another channel 11. Both seem to be affected by the increase in noise when transmitting at 54 Mb.

I have attached a copy of the levels that were measured using the Cisco ADU. The installed AP is on channel 11 and we set the test AP to channel 1. I will be returning to the site and try different channels and see if fixing the speed to 11 Mb makes any difference. Thanks.

Green

Re: Noise level increase with speed

I believe what you are seeing is the effect of stuffing more data into the same timeframe.

If you have X amount of data to send, it is encoded and sent at the signaling rate. For example ...

|<------------------->| you have this much data:

|<=========>|and this much noise:

If you stuff more information into the same timeslot that the noise is occurring, you end up with:

|<-------------->| (data - same amount, shorter time)

|<==========>|.....(Noise)

Though the noise has actually remained at the same level, the effect a "chunk" of noise has on the signal with more data (per given time period) is greater, because there is more data thee to disrupt.

I'm not sure how the devices are sensing or calculating the noise figure, but it would be a possible explaination for what you are seeing.

FWIW

Scott

Bronze

Re: Noise level increase with speed

Are you using Atheros Chip cards like the Cisco ABG? There is a known bug on channel 11.

Here is what i found about the Bug

Bug number: CSCef13663

Symptom: When operating on channels 10-13 in the 2.4GHz band, the Cisco Aironet 802.11a/b/g CardBus Wireless Adapters with assembly identifier ##-####-01 or ##-####-02 exhibit a noise anomaly.

Workaround: Contact your Reseller to get replacement of the card with one in the ##-####-03

range.

Bronze

Re: Noise level increase with speed

Sorry I didn't find the bug I just copied that from this forum...my apologies

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