Re: [Discuss-gnuradio] Questions on stream tags

[Hoang Ngo Khac]

Hi Martin, and all,

I meant, I want to add tx_sob and tx_eob to tell the USRP Sink to start/stop the TX chain. I intend to add tags before the modulation, where data type is byte. Since the provided block PDU to Tagged Stream takes message as input, I guess I need to make my own block(s). 

On Mon, May 5, 2014 at 7:57 PM, Martin Braun <address@hidden> wrote:

On 05.05.2014 09:56, Hoang Ngo Khac wrote:

Dear List,

I'm new to stream tags. Could someone help me to understand about stream
tags and know how to use it?

Remember that we have a lot tag debugging tools available, such as the QT GUI Time Sink and tag debug.

1. In GNU Radio Manual: "A stream tags is generated by a block's work

function and from there on flows the downstream...*until it reaches a
sink*...".

If we use tags to tell the USRP Sink to start/stop the TX chain, do we
need to modify the USRP Sink block?

Probably not... are you talking about tx_sob and tx_eob?

I found that gr_uhd_usrp_sink.cc file contains the get_tags_in_range()
function. However, this file is not, at first, in the GNU Radio 3.7.0
source folder. How to add this to project and make it work with USRP Sink?

Look in gr-uhd/, there it is.

2. I am implementing a model of ofdm-based two-way relaying network
apply network coding. Up to now, each single transmission in one time
slot are done, but the model runs without any timing synchronization.
For this, I need to use TDMA, and stream tags is the solution. I list
here the steps to make TDMA with stream tags. Could you leave some
comments if I miss some thing?
+ Add tags to stream; using provided block such as PDU to Tagged Stream,
or custom block.
+ Write a block for error checking, repeat request...

Seems right. You shouldn't need other blocks to control UHD.

M


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