Hi Weihan - When you simulate "over the air" inside GNU Radio, there are fewer wireless issues encountered & the data is much more likely to be received. Actual OTA is somewhat more challenging, especially if you're sending just 1 frame.
Some suggestions, based on personal experience: * try sending a repeated frame & see if it -ever- gets through. * make sure the data amplification -after- OFDM but before the USRP is such that the max abs output value is < 1.0f; keeping it around sqrt(2)/2 seems like a reasonable goal. if this value is too high, then there will be clipping in the USRP which will result in an undesirable Tx spectrum & no Rx. * make sure the USRP Tx gain and USRP Rx gains are enough to get the signal at least 20 dB above the noise. this does not mean that the SNR is > 20 dB, just that when you view the spectrum using the Rx USRP the signal is obviously visible well above the noise level. * make sure the Tx packet length isn't too large ... max of 1000 Bytes. Longer packets are less likely to be properly Rx'd compared with shorter packets. * If you're using 8psk for payload, try backing off to qpsk or bpsk & see if that helps. * Make sure the various sample rates (OFDM & USRP) are aligned via a common variable. sample rate mismatches are possible, and will result in overflows or underflows that will wreck your Tx or Rx signal -- even for such simple flowgraphs as what you have. * Make sure that the USRPs are working for Rx, e.g., via receiving FM. I'm sure there are others, but the above are a good starting point. If you've covered the above then send me an off-list message with your FG attached & I'll see what I can see. Cheers! - MLD On Thu, Dec 28, 2017, at 9:32 PM, Weihan Chen via USRP-users wrote: > I'm trying to transmit one OFDM frame from one USRP to the other one using > GNURadio. The flow graph is as follows: > > TX side: vector source -> stream to tagged stream -> OFDM Transmitter -> UHD > sink > RX side: UHD source -> OFDM Receiver -> null sink > > OFDM parameters: fft_len=64, cp_len=16 > USRP parameters: sample rate=1Msps, freq=900M, gain=15. > > The problem is that at receiver side I get many incoming packets, and none of > them is correct, while in simulation (without the USRP blocks) I get exactly > one packet. Not sure what's going wrong here. Could someone help me with > this? Thanks. _______________________________________________ USRP-users mailing list [email protected] http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
