Hi, all. (I recently shared this issue in USRP forum but it seems not properly shared so I sent it again)
I am testing frequency offset estimation by using the preamble of Wi-Fi packet (IEEE 802.11). My setting is as follows: two USRPs are connected to one laptop (i7 quad-core, SSD, 8GB ram). One is used for Tx. and the other for Rx. I chose 1MHz bandwidth and set proper packet length and inter-packet time (50ms) so packets are almost continuously transmitted. During the test (very stationary environment), 1.5 m distance between Tx. and Rx. and good SNR is guaranteed (by checking constellation). At the receiver side, I estimated frequency offset value of every packet using the preamble of each packet. I compared these values. Of course, I know that the frequency offset between two USRP varies due to several reasons (e.g., temperature). Anyway, we can see similar frequency offset values during a given period (e.g., 5 sec) and this is what I exactly expected. For example, 2001 Hz (packet 1), 2003 Hz (packet 2), 1997 Hz (packet 3) and so on. The problem is that, sometimes, I see unusually a high frequency offset value for some packets. Then, frequency offset values return back to the reasonable value again. For example, 2001 Hz (packet 1), 2003 Hz (packet 2), 2307 Hz (packet 3), 2310 Hz (packet 4), 1997 Hz (packet 5) and so on. Can anyone help me to understand this phenomenon? Thank you in advance. - Inkyu
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