Re: [Discuss-gnuradio] time tags for transition time using USRPs

[Martin Braun]

USRP sinks already support tagged streams, so you're halfway there
already. Adding a 'tx_time' tag onto the first sample of the burst will
let you transmit when you like. Note that you might want to pad your
burst with zeros (at the beginning and end) to flush the signal
processing lines.

Cheers,
M

On 04/22/2016 02:29 AM, Henning Bredenberg wrote:
> Hi all,
> 
> In the attached picture a flow graph is shown where i use the "random"
> pdu generator for a fixed sized pdu (1200 bytes here). The
> pdu_to_tagged_stream block makes it accessible for a simple BPSK
> modulation to send it over a coax cable to another USRP B200. A time
> sink shows what the transmitter transmits and what the receiver should
> receive ideally.
> By inserting some different delays, e.g. a uniformly distributed (0 to
> 80 ms in the disabled block here), i want to emulate a communication
> system. My questions are:
> 
> 1. How can a realize a burst transition that transmit the fixed sized
> burst, i.d. the pdu, in a 20 ms slot whereas the last 60ms no transition
> occurs before a new pdu is generated by the message_strobe block? By now
> it is a continuous transition no matter what i change.
> 
> 2. I want to store the time from generating the pdu till my second USRP
> receives it. Tagging the time should be an option to realize that. Since
> a have no clue: How can i realize that using time tags? The simplest
> case is - without any delays - that the pdu is generated and transmitted
> in a 20ms slot plus the processing time which should be small compared
> to the 20 ms.
> 
> I am thankful for any kind of help. Thanks and have a nice weekend,
> Henning
> 
> 
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