On Fri, 2011-08-12 at 23:26 +0100, Nemanja Trecakov wrote: > > Hi list, > > > > > My name > is Nemanja and I am working on my master thesis trying to implement > 802.11g OFDM standard on USRP2 with XCVR2450. In order to meet the > timing requirements of the standard, I want to split the > functionality between the host and the FPGA, very similar to > Split-functionality MACs project > (https://www.cgran.org/wiki/CMUmacs). > Since 802.11g TX PHY has been developed by FTW > (https://www.cgran.org/wiki/ftw80211ofdmtx) > and further extended with MAC layer by Uwicore > (http://www.uwicore.umh.es/mhop-software.html), > both for use on the host, my approach would be to use these and > buffer the “completely baked” TX packets from the host on the > unused 1MB SRAM on the USRP2. These can then easily be sent with low > latency when the channel is sensed free. Moreover, the Carrier > Sensing with Collision Avoidance will be implemented on FGPA and > based on RSSI from the daughter card. In the RX mode FPGA should be > able to check the preamble in order to decide if the packet is for > this host or not, and accordingly proceed it to the host or discard. > However, since this standard is using OFDM, an FFT is needed. Maybe > FFT can be avoided by implementing a Look Up Table, which could be > used in closed networks where all senders are known. I will wait a > while with implementation of ACK and RTS/CTS. > > > > > > I am using the following: > > > > - Ubuntu 10.04 > - GNUradio 3.3.0 with > UHD_003.001.002-ba0e3c8 > > > > > I am a newbie to all of this and I have > a few questions: > > > > > > 1) Did anybody use this external SRAM > on USRP2 before? According to the FAQ page the usual FPGA build is > not using it. > (http://gnuradio.org/redmine/projects/gnuradio/wiki/USRP2GenFAQ) > However, my experience with these pages is that many of them are > outdated. I also found the folder called extramfifo in > uhd/fpga/usrp2 folder for which I believe has something to do with > external RAM.True?
The external SRAM is currently used for buffering TX packets. > > > > 2) How to build the new FPGA UHD image? > I have access to Xilinx 12.4 on a Windows XP machine for building the > image. At first I will try only to add more code without omitting any > of the present code. I have read the discussion at > (http://old.nabble.com/Finally-compiled-USRP2-code-works-fine-with-UDP-image-...but-not-with-compiled-Raw-Ethernet-Image-td30653029.html) > , where it is written that no project file should be made. However, > the process described is not fully clear to me. The existing makefile is really for unix installations. You will have a much easier time compiling your custom image with a Linux ISE installation. > > > > 3) Does firmware image also have to be > changed after modification with using the SRAM, or with any FPGA modification? > Generally no. Use a firmware image version that corresponds to your FPGA image though. > > > > > 4) How to read RSSI? I have read at > (http://old.nabble.com/measuring-RSSI---N210-with-RFX2400-td31773654.html#a31773654) > that this could be used: > > from the uhd api: > > usrp->get_rx_sensor("rssi") > > or in > python w/ gr-uhd > usrp.get_dboard_sensor("rssi") > > > > > But what is uhd api? UHD API refers to the host (PC side) interface. If you're reading RSSI from the FPGA it doesn't apply to you. --n > > BTW, I am aware that using RSSI from > XCVR2450 is the signal strength over wider bandwidth than used in the > software. > > > > > > > Please feel free to come with any > comment. > > > > Thank you in advance! > > > > Regards, > Nemanja Trecakov > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
