Hello Hamzeh, Sorry, but I think we need more details about your configurations (maybe flowgraphs, pictures of the hardware, captured data, etc) in order to answer your questions properly.
But here are a few generic answers to the question: 1. It depends. There is no single answer. 2. You can either implement a software-level automatic gain control (harder), or do this experimentally. Try to choose the gain level that maximises the SNR of the received signal. Plotting out the periodogram of the signals is helpful (USRP Source -> QT Frequency Sink). Some USRP boards and daughterboards have hardware AGCs on them. This includes USRP B series units, if I recall correctly. You can try enabling that. This not not necessarily optimal, however. 3. Yes, different SDR transceivers have different RF frontends and therefore different gain stages. It is less application-dependent, but some applications work well on non-linear conditions while others dont, so applications matter, too. You should figure this out experimentally (easier) or by actually going thorugh hardware schematics and software source codes (harder). 4. I don't know, there are insufficient information to tackle your problem. Maybe your flowgraph has issues. Maybe the spectrum is too crowded. Maybe you used wrong antennas (RP-SMA) or antenna ports. There are too many possibilities. One thing that you should try is plotting the received data, before actually putting them into the processing chain. You can try hooking up a QT Frequency Sink to the USRP source on GNU Radio and see if the periodogram makes sense (looks OFDM-ish). Regards, Kyeong Su Shin ________________________________ 보낸 사람: hamzeh elsayed <hamzehelsaye...@gmail.com> 대신 Discuss-gnuradio <discuss-gnuradio-bounces+ksshin=postech.ac...@gnu.org> 보낸 날짜: 2019년 12월 10일 화요일 오후 6:33 받는 사람: discuss-gnuradio@gnu.org <discuss-gnuradio@gnu.org> 제목: gr-ieee802-11 with USRP N210 and B200mini problems Dear all, I installed the gr-ieee802-11 project and run the wifi_loopback.grc file and the output is correct. Then I edited the file to transmit and receive from socket using “socket PDU” block, also the output is correct. After that, I tried to transmit and receive from USRP SDRs, the following are the tested I done: 1- I transmit and receive from the same SDR “B200mini” with the same configuration found in the wifi_transceiver.grc file. a. If the rx_gain and tx_gain are approximately 0.27 (normalized) and encoding BPSK 1/2 , then the sent data are received for (95%) and the constellation sink is approximately good. b. If the rx_gain and tx_gain are less than or greater than 0.27 and encoding BPSK 1/2 , then any data id not received and the constellation sink is very bad. c. If the encoding is anyone except BPSK ½ for example 16 QAM ½ etc.. any data is not received for any value of gain. 2- I transmit and receive from the same SDR “N210” with the same configuration found in the wifi_transceiver.grc file. Any data is not received for any gain and encoding configurations. 3- I transmit from USRP N210 and received from B200mini also any data is not received for any gain and encoding configurations. 4- I transmit from USRP B200mini and received N210 from B200mini also any data is not received for any gain and encoding configurations. Tests were done by using the following: OS: Ubuntu 16.04 LTS Gnuradio: 3.7.11 First SDR: USRP N210 with CBX daughter board Second SDR: B200mini Frequency: 2.415Ghz Bandwidth: default (0) Therefore, 1- what are the best settings I have to select in order to transmit and receive data correctly for all cases? 2- how to select the best gain for any SDR? 3- Is there any relation between the SDR type and gain and the application? 4- In general, where is the problem or the mistake I am doing? in advance, thanks for your time and help. Best Regards, Hamzeh Elsayed
