On Wed, May 30, 2012 at 4:23 AM, J Mc <columbo_the_leg...@hotmail.com> wrote: > > >> Date: Tue, 29 May 2012 22:15:43 -0400 >> Subject: Re: [Discuss-gnuradio] Real-time fading simulation? >> From: bpadal...@gmail.com >> To: columbo_the_leg...@hotmail.com >> CC: discuss-gnuradio@gnu.org > >> >> On Tue, May 29, 2012 at 9:47 PM, J Mc <columbo_the_leg...@hotmail.com> >> wrote: >> > I have been considering using GnuRadio with the USRPN210 as a realtime >> > fading simulator for radio hardware testing, however any approaches I've >> > considered in doing this seem to fall down fundamentally if I limit to >> > using >> > a single USRP. I'm still relatively sure it could be done, was wondering >> > if >> > anyone had any advice/input. >> > >> > The main issue I've had is trying to understand how to do this with >> > single >> > antennas systems, if I take something like 2 cheap WiFi nodes both >> > attached >> > to a common Tx and Rx port is there any way to prevent the transmitting >> > node's signal feedback when it hits the receiving node's antenna. If >> > anyone >> > has looked at this question, opinions would be appreciated... >> >> I think you can do it with an one USRP1, or two USRPN210s using some >> circulators and a special FPGA load. >> >> Circulators move in a clockwise motion: >> >> [WiFi] <-> [ Circulator ] <-> [USRP Rx/Tx] >> ^ >> | >> v >> [ Circulator ] <-> [WiFi] >> ^ >> | >> v >> [USRP Rx/Tx] >> >> I think that diagram shows the WiFi card transmitting to the USRP >> Rx/Tx port, the Tx from the USRP goes to the other circulator, and >> into WiFi card. >> >> The second WiFi card transmits into the circulator then into the USRP >> Rx/Tx port, and the Tx from the USRP goes to the original circulator, >> and into the original WiFi card. >> >> FPGA load would essentially be programmable with your noise/fading >> profile, and with little host intervention create noise on the >> baseband then retransmit. >> >> Does that work? >> >> Brian > > I may be missing something however anyway I try construct this design on > paper (which is variations on what I've been considering) the following > issues seem to occur; > > -Many Daughterboards only have 1 Tx channel, which both the nodes must > connect to, how at transmissions "addressed" i.e. the circulator won't be > able to avoid this > -Because WiFi and other standards that use TDD share a single antenna, they > must near-simultaneously transmit and receiver. If a USRP Transmission is > heard by the original node, it will create a feedback loop
That is why you need either 2 USRPN210's or 1 USRP1. The USRP1 can have 2 daughterboards which allows you to have 2 independent RX/TX ports. The circulators handle the rest for you. You're correct that using a single TX on a single daughterboard isn't good enough. > For the fading I was thinking of just using gnuradio without any FPGA > alterations, (theres a fading model/noise sources/notch filters), my only > uncertainty is the ability to receiver and transmit to the same USRP on > different antenna ports. I believe there are latency requirements in 802.11 that may be difficult/impossible to achieve if you're shipping samples back and forth. If latency isn't a concern, I think that the above setup should be valid. Do you agree? Brian _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
