Re: [Discuss-gnuradio] transmitter receiving its own packet

[Josh Blum]

On 04/10/2013 12:27 AM, Rahman, Muhammad Mahboob Ur wrote:
> Hi Josh,
> 
>> So it would be possible to mute the ADC samples when the device is 
>> transmitting. However, that might only be desirable in a couple of
>> use cases, and there are probably a dozen ways to solve this from
>> all the way down at the physical layer up the the MAC layer:
> 
>> * mute the RX ADC when transmitting (probably an FPGA mod)
> 
> 
> We are interested to operate our USRP N200 radios in TDM. In other
> words, we want each of our radio to transmit and receive at the same
> frequency. Since we expect very high self-interference in this case,
> we would be interested to play a little bit with the ADC mute option.
> Could you provide us some pointers on where to modify the FPGA code
> to do this? Also, how much realistic/feasible it sounds if we want to


https://github.com/EttusResearch/uhd/blob/master/fpga/usrp2/top/N2x0/u2plus_core.v

See the section at line 614? Use the run_tx signal to conditionally zero
out the values going to .adc_a and .adc_b

> control ADC (on/off) switching from within the GRC flow graph (at the
> very least, we will expect some latency associated with this
> operation).
> 

If you are running continuous receive, by knowing the transmit time of a
packet - or based on some concept of valid transmit window, you can
choose what rx samples to ignore based on the rx sample's timestamps. --
that would be the most exact way to do it.

-josh

> 
> Thanks in anticipation, Mahboob
>