Hello everyone, I am using a USRP B210 with the Python (3.7.6) API with UHD 3.15 (from conda-forge).
RF setup is as follow: one USRP, one TX/RX connected with a SMA cable, 60 dB attenuator, central freq is 1GHz, sampling rate is 1,6 MHz (oversampling value is 4) and RX gain is fixed to 50 dB. I send burst of data composed of a zadoff-chu 256 followed by a payload modulated with M-QAM and Gray mapping. This is a wideband transmission, there is no additional filtering, nor OFDM modulation. I use a 1031-long ZC sequence to locate the frame. In reception, I use the 256-long ZC sequence to fine synch (select the right sample version to go back to symbol rate), to estimate the channel (1-tap) and more especially the phase shift, and to estimate the SNR. I could confirm the performance for 4-QAM and 16-QAM. BER vs SNR performance curves obtained in experimentation follow perfectly the theoretical curves for AWGN. However not in the case of the 64-QAM. Actually, I can't obtain a SNR above 22 / 23 dB, independently of the QAM order used. To increase the SNR and draw the performance curves, I simply increase the TX gain. I start getting some problem from 45/50 dB. I observe a noise floor which looks like classic AWGN, but which is increasing with the TX gain, since the estimated SNR is constant at 22.5 dB. I have also confirm the performances of the 4-QAM, 16-QAM and 64-QAM in simulation on AWGN channel. At the moment I have no clue of what is happening. I have manually activated dc offset and iq imbalance correction based on UHD API to be sure. What do I miss? I can provide more information if needed. Best regards, Louis-Adrien _________________________________________________________________________________________________________________________ Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration, Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci. This message and its attachments may contain confidential or privileged information that may be protected by law; they should not be distributed, used or copied without authorisation. If you have received this email in error, please notify the sender and delete this message and its attachments. As emails may be altered, Orange is not liable for messages that have been modified, changed or falsified. Thank you.
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