distributed antenna system usrp 2920

[kareem.tarek]

Hi all,

I implemented an OFDM transceiver using two usrps one as the transmitter and one as the receiver , i also did all the synchronization tasks (Frame Detection, Timing recovery, CFO correction, and channel estimation ) necessary to calculate the BER at the receiver and it worked great.

im now trying to emulate a DAS scenario where i have two USRP transmitters sending the exact same OFDM signal, they are seperated by some distance and synchronized in frequency and time using a reference clock. The receiver is a normal OFDM receiver.Thus, the signal received from the two transmitters should be perceived at the receiver side as the same signal coming from one transmitter but with higher power. Moreover, i need to induce nano-second delays between the transmitters using the start trigger time and investigate the effect on the BER is that possible?

My questions are:

1- there any phase ambiguity between the two usrp transmitters after using the reference clock or the MIMO cable ?

2- is it possible to use the Refin and PPS and different trigger time to force specific transmission delays?

Thanks

[I.B.Hating · Accepted solution]

Hi Kareem,

Yes, this should be possible. As long as you are using the same reference clock for your USRPs there should be almost no phase delay. The only delay introduced would be due to the length of wire between USRPs. 

It sounds like you have two different triggers and they are independently controlled. As long as you do not start the transmission until the USRP receives a trigger then you can specify a delay between transmission by simply delaying one of the triggers by your desired delay time.