Martin, Thanks for your response. It is disappointing to hear that the MIMO support for 4 antennas will not be available for some time.
Could you provide some more details into why this problem of aligning the transmit samples will be easier in the new m-block framework? Will these new packet oriented m-blocks utilize a different interface to the USRP which will make this alignment-task easier? On 8/29/07, Martin Dvh <[EMAIL PROTECTED]> wrote: > Ketan Mandke wrote: > > Martin, > > > > I've been searching through the mailing list for more information > > about synchronizing two USRP boards to create the transmitter for a > > 4x4 MIMO node. From what I've found, it seems that this is not > > currently implemented (see links below for relevant threads). What is > > the current status of this effort, > > Yes you do need special measures to make sure the samples are aligned. > I am the author of the usrp_multi code (and the modified usrp firmware) > I was working on the transmit site but with the current framework this got > quite complicated. > > The m-blocks framework which is currently in development will make it much > easier to synchronize multiple receive or multiple transmit streams > on seperate USRPs. > So this work has been on hold waiting for the m-blocks become available and > usuable in the main tree. > > and when (if at all) do you think > > that this functionality might be implemented? > Since the m-blocks are maturing now, in theory the work on this could be > started soon. > The problem is that I am very busy doing contract work on another part of > GnuRadio. > So at the moment I don't have time for this. > After this project it also depends on the amount of work I have, how much > time will be left for implementing 4x4MIMO. > So at the soonest in the next few months. > At the latest, in a year or two. > > It also depends on how many others will be working on this code. Until now I > have been the only one implementing the low-level MIMO stuff. > > If you have a budget for it. Matt, Eric and I could probably team up and > implement it more quickly. > If you don't have a budget you could try to help out by doing the dirty work > yourself. > We can help you on your way in this. > > > > > links: > > http://www.nabble.com/Question-about-4-x-4-MIMO-transmitting-and-receiving-tf3605863.html#a10074272 > > http://www.nabble.com/Re%3A-USRP-Tx-Question-tf1452214.html#a3924517 > > > > > One other thing is the phase relationship between the different USRPs. > At the moment we use the upconverters (DUCs) of the ADC/DAC chips. > Unfortunately the starting phase of these can not be set. > Only after power-up these are in a known state. > After you have used the usrp these are in an unknown state. > This means that every time you start a gnuradio script the phase relationship > between the multiple USRPs will have a fixed unknown phase difference. > > Depending on your application this can be a problem. > > The only solution is not to use the DUCs in the DAC but do the upconversion > in the FPGA. > This can be developed but you would probably also have to disable some other > functionality because the FPGA is already very full. > (disable the RX halfbandfilters, or reduce the number of RX channels) > > I hope this clears it up for you. > > Greetings, > Martin DvH > > > > > Olifantasia > Software Defined Radio, GnuRadio, USRP development > -- Ketan Mandke _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
