From: Dan Halperin <address@hidden>
To: George Nychis <address@hidden>
Cc: Bill Stevenson <address@hidden>; address@hidden
Sent: Thursday, November 20, 2008 9:48:52 PM
Subject: Re: [Discuss-gnuradio] inconsistency in the PER versus distance using USRP
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On Nov 20, 2008, at 6:40 PM, George Nychis wrote:
>
>
> Bill Stevenson wrote:
>
>> In door environment; the temperature are the same in these two experiments; center frequency is 2479MHz because on one hand, I want to avoid the 2400MHz to 2483MHz band which is the working band of 802.11, on the other hand the bandpass filter on the 2400MHz daugterboard (2400M to 2483M) and the bandwidth of USB port which is 8MHz together forced me to chose the center frequency to be at most 2479MHz; all other conditions in these two experiments are the same: chairs and desks are fastened, not being moved, etc.
>>
>
> Didn't you just answer your own question? You're operating within 802.11 interference range. The frequency band of channel 12 is 2456-2478MHz. You're sitting at 2479MHz and with 8MHz bandwidth, your bottom 4MHz are within
802.11 interference range. Additionally, you could use
usrp_fft.py to actually inspect the channel and determine if there is any noise on it.
To be fair, assuming 20 MHz wifi, he should be fairly interference free. Channel 11 (2.462G) is pretty well attenuated at 2.479G according to the standard. I suspect you're going to have to dig in Bill. Note that multipath can have a huge effect, as well as frequency offsets and other variables, like the output power changing on the card. There's usually not an obvious easy answer for these things without digging into the RF.
If I move my leg I can knock the PRR from 100% to 5% easily -- using commercial WiFi.
- -Dan
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Thank you for your help, you gave me a better understanding about the wireless environment!
Bill