I have been experiencing a weird bug when transmitting packets using the USRP. I am part of the Hydra group at UT (hydra.ece.utexas.edu). We have been developing a multiple antenna system using the USRP. It seems to work quite well except for the following bug:
Since we're using two transmit chains, I set the mux value in usrp.sink_c to 0xBA98. I have noticed however, that at random the transmitter will flip the IQ channels of the transmitter. I have verified that this occurs by analyzing the trace of the received signal. I noticed that this same bug seems to occur when using a single antenna system as well (there I set the mux value to 0x0098). In the single antenna case I can just reset the mux value to 0x0098 everytime I send a packet in order to alleviate the problem. This same approach does not work in the two-antenna case. Any thoughts on why the mux value in the transmitter might be changing or why the IQ channels might get flipped? Please note that I have already verified that the EXACT same waveform is being sent to the usrp everytime I transmit a packet; hence, I am certain that the bug is not being caused in software. I am currently using a multiple antenna system, so I set the usrp.sink_c mux value to 0xBA98. This should enable the USRP to support to transmit RF chains, right? -- Ketan Mandke
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