Re: [Discuss-gnuradio] Explanation on how the preamble is inserted and how the packet is detected

[李博远]

Hi Adhitha,

The tx_stage6.grc outputs BPSK packets. If you want to use OFDM, the OFDM examples are good references. To detect OFDM packets, use schmidl & cox OFDM sync module. Anyway, I'm glad that you've got your system going.

Regards,

Edwin  

Adhitha Dias <address@hidden>于2017年8月10日周四 上午10:18写道：

Hi Edwin,

I used OFDM examples and now I can transmit and receive packets. I am sorry about mentioning the name as Derek, Derek helped me earlier to set up the USRPs from UHD USRP mailing list.

Your information was very helpful. Thank a lot for your help.

Best regards,

Adhitha Dias

On Thu, Aug 10, 2017 at 12:36 PM, Adhitha Dias <address@hidden> wrote:

Hi Edwin,

tx_stage6.grc outputs a packet that is not modulated, right? The communication should be based on WiFi 802.11. When I insert an OFDM Mod OOT at the end of tx_stage.grc with the USRP sink, the USRP does not give an output. I used /src/gnuradio/gr-digital/examples/packet/ofdm/tx_ofdm.grc with the USRP, then it transmits the OFDM modulated packets but I am uncertain how to detect the packet at the receiving end once it is modulated with OFDM. The example rx_ofdm does not correlate the incoming packet so as to detect the preamble and it does not yield any output when used with another USRP at the receiving end.

Furthermore, there is an OOT OFDM Insert Preamble but there is no example on how to use it. Please help me if can figure out a way to detect the preamble for OFDM WiFi based communication 802.11

Thank you!

Regards,

Adhitha

On Thu, Aug 10, 2017 at 12:27 PM, Adhitha Dias <address@hidden> wrote:

Hi Derek,

tx_stage6.grc outputs a packet that is not modulated, right? The communication should be based on WiFi 802.11. When I insert an OFDM Mod OOT at the end of tx_stage.grc with the USRP sink, the USRP does not give an output. I used /src/gnuradio/gr-digital/examples/packet/ofdm/tx_ofdm.grc with the USRP, then it transmits the OFDM modulated packets but I am uncertain how to detect the packet at the receiving end once it is modulated with OFDM. The example rx_ofdm does not correlate the incoming packet so as to detect the preamble and it does not yield any output when used with another USRP at the receiving end.

Furthermore, there is an OOT OFDM Insert Preamble but there is no example on how to use it. Please help me if can figure out a way to detect the preamble for OFDM WiFi based communication 802.11

Thank you!

Regards,

Adhitha Dias

On Thu, Aug 10, 2017 at 12:28 AM, 李博远 <address@hidden> wrote:

Hi Adhitha,

If you check out the tx_stage6.grc example in the folder /src/gnuradio/gr-digital/example/packet/, you can see a Protocol Formatter. It generates a header which contains a preamble and some additional information, and pumps it out through the header output port.  The other output port, called payload, outputs the original information from the signal source. And there is another module called Tagged Stream Mux. It combines the header and the payload, producing a packet.

As for the receiver, check out the packet_rx.grc. The Correlation Estimation correlates the received signal with the modulated preamble and finds out the beginning of each packet. The Header/Payload Demux splits the header from the payload.

Hope this answers your question.

Regards,

Edwin

Adhitha Dias <address@hidden>于2017年8月9日周三 上午5:34写道：

Hi Edwin,

I tried the examples but there is no information on how to detect the preamble. What I need to do is, once the Short Training Field is identified record the packet so that I can use the Long Training Field can be used for processing.

I've been looking in to the examples for a couple of days but I still don't have an idea on how the preamble is inserted and how to detect the Short Training Field in order to record the un-modulated, raw, time domain received signal.

I really appreciate if you can kindly provide some information on this.

Thanks a lot!

Regards,

Adhitha Dias

On 9 Aug 2017 00:12, "李博远" <address@hidden> wrote:

Hi Adhitha,

Just check out the examples in the folder /src/gnuradio/gr-digital/examples/packet/

Regards,

Edwin