# Is there a project which implements half-duplex communications?

**URL:** <https://www.ruby-forum.com/t/is-there-a-project-which-implements-half-duplex-communications/242527>\
**Category:** GNU Radio\
**Created:** [June 30, 2015, 3:31pm UTC](https://www.ruby-forum.com/t/is-there-a-project-which-implements-half-duplex-communications/242527 "2015-06-30T15:31:43Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [June 30, 2015, 3:31pm UTC](https://www.ruby-forum.com/t/is-there-a-project-which-implements-half-duplex-communications/242527/1 "2015-06-30T15:31:43Z")

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Hello, GNU Radio users,

Very long time ago, USRP 1 was not suitable for half-duplex  
communications  
because USB 2.0 interface is too slow to achieve it.  
But now, there are USRP embedded and gigabit ethernet supporting USRP  
series.  
In my opinion, thus, half-duplex communications might be achievable  
nowadays.

I am curious that there is a project which implements half-duplex  
communications.  
If there is, how many USRPs, daughterboards and antennas are used for  
each  
node?  
Can I find such a project in pybombs?

In my guess, a half-duplex communication application can be built from  
both  
USRP sink and source being placed in one flow graph.  
But I have no idea of the rest of the flow graph. Should the flow graph  
open loop or closed loop?  
Is there a special configuration or tweak on USRP or GNU Radio required  
to  
achieve half-duplex communications?

I apologize if my question sounds quite vague.

Regards,  
Jeon.

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**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\
**Post date:** [June 30, 2015, 4:48pm UTC](https://www.ruby-forum.com/t/is-there-a-project-which-implements-half-duplex-communications/242527/2 "2015-06-30T16:48:51Z")

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Hi Jeon,

Yes, of course these things have been doable for quite some time – not  
very much because the latency of the buses went down, but more because  
the USRPs learned to use command times, which means that you could  
instruct the USRP to start to receive and transmit at sample-accurate  
times, so to hide the latencies.

By now, there’s quite some standards implemented. gr-mac, formerly  
pre-cog, is one of the frameworks you could build upon.  
Bastian B. has actually developed multiple working transceivers:  
Have a look at gr-iee802-11 (working WiFi implementation) an  
gr-iee802-15-4 (Zigbee); they do work pretty well.

Best regards,  
Marcus

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**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\
**Post date:** [June 30, 2015, 5:04pm UTC](https://www.ruby-forum.com/t/is-there-a-project-which-implements-half-duplex-communications/242527/3 "2015-06-30T17:04:02Z")

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Jeon,  
Also check out  
[http://wp.me/p55sJw-2v](http://wp.me/p55sJw-2v)  
software based half duplex burst PSK modem which can operate using a  
single USRP, file loopback, or other SDR  
-Tim

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**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\
**Post date:** [July 1, 2015, 6:10am UTC](https://www.ruby-forum.com/t/is-there-a-project-which-implements-half-duplex-communications/242527/4 "2015-07-01T06:10:22Z")

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Dear Tim and Marcus,

Thank you very much.

I’ll take a look at those projects.

Regards,  
Jeon.

2015-07-01 0:03 GMT+09:00 Tim [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):