Re: [Discuss-gnuradio] CSI in gr-ieee80211
I use a card from Per Vices. I do not have the option to change the cuttoff frequency of the filter without flashing the firmware. As a workaround, I tuned my device to a different frequency (+10 MHz) and using an NCO I managed to bypass the power loss at the center sub-carriers. On 03/29/2014 03:11 PM, Paul Fuxjaeger wrote: On 28.03.14 19:40, Surligas Manos wrote: Which device did you used for receiving samples? I have noticed a same phenomenon with my device, caused by a coarse implementation of a high pass filter. The filter in the Maxim2829 in the XCVR2450 that we used can be configured to 0, 100Hz and 30kHz and the default is 100Hz I believe? If you didn't change anything there this cannot explain your problem. Any filter than goes above 150kHz would be a problem for the centerish carriers in 802.11 OFDM (~300kHz carrier spacing). what happens if you TX a sinusoid and stepwise tune the RX to slightly off frequencies (take note of the *actual* RX LO frequency when doing the sweep - the difference to that one and the TX sinusoid matters). Does the RX power also start to decrease as soon as you set the TX-RX offset smaller than 150kHz? -paul PS: as Sebastian said, the outer subcarriers being lower can be explained by odd decimation factors like 5 - which causes the digital-downconversion filter chain to change to a single CIC stage I believe. -- /* Code is the Law! */ ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] CSI in gr-ieee80211
On 28.03.14 19:40, Surligas Manos wrote: Which device did you used for receiving samples? I have noticed a same phenomenon with my device, caused by a coarse implementation of a high pass filter. The filter in the Maxim2829 in the XCVR2450 that we used can be configured to 0, 100Hz and 30kHz and the default is 100Hz I believe? If you didn't change anything there this cannot explain your problem. Any filter than goes above 150kHz would be a problem for the centerish carriers in 802.11 OFDM (~300kHz carrier spacing). what happens if you TX a sinusoid and stepwise tune the RX to slightly off frequencies (take note of the *actual* RX LO frequency when doing the sweep - the difference to that one and the TX sinusoid matters). Does the RX power also start to decrease as soon as you set the TX-RX offset smaller than 150kHz? -paul PS: as Sebastian said, the outer subcarriers being lower can be explained by odd decimation factors like 5 - which causes the digital-downconversion filter chain to change to a single CIC stage I believe. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] CSI in gr-ieee80211
Which device did you used for receiving samples? I have noticed a same phenomenon with my device, caused by a coarse implementation of a high pass filter. On 03/26/2014 04:08 PM, Bastian Bloessl wrote: On 26 Mar 2014, at 15:05, alex alexleeresea...@gmail.com wrote: I am currently working on gr-ieee80211. Now I want to use the long preamble to estimate the CSI. However, after I apply fft to the long preamble, I found the power for each channel is not the same. I took an average over lots of packets. The power near the middle sub-carriers are always very lower than on the edges. I would like to ask if it is because the Power spectral density in the transmitter or some other reasons. If your sample rate is 20MHz you will see an uncompensated filter, but in that case the power of the subcarriers in the center should be higher. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio -- /* Code is the Law! */ ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] CSI in gr-ieee80211
On 26 Mar 2014, at 15:05, alex alexleeresea...@gmail.com wrote: I am currently working on gr-ieee80211. Now I want to use the long preamble to estimate the CSI. However, after I apply fft to the long preamble, I found the power for each channel is not the same. I took an average over lots of packets. The power near the middle sub-carriers are always very lower than on the edges. I would like to ask if it is because the Power spectral density in the transmitter or some other reasons. If your sample rate is 20MHz you will see an uncompensated filter, but in that case the power of the subcarriers in the center should be higher. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
