# Full duplex infinity loop

**URL:** <https://www.ruby-forum.com/t/full-duplex-infinity-loop/231913>\
**Category:** GNU Radio\
**Created:** [September 5, 2014, 5:28pm UTC](https://www.ruby-forum.com/t/full-duplex-infinity-loop/231913 "2014-09-05T17:28:05Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [September 5, 2014, 5:28pm UTC](https://www.ruby-forum.com/t/full-duplex-infinity-loop/231913/1 "2014-09-05T17:28:05Z")

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Hello,  
can anyone suggest how to prevent infinity loop in case of full duplex  
RX/TX on same frequency ?  
Any ideas?

GRC example:  
UHD source -\> GMSK DEMOD -\> packet decoder -\> packet encoder -\> GMSK MOD  
-\> UHD SINK

but in this case of course its gonna be infinity loop,  
any suggestion how to avoid this?

Thx.

---

<div class="post-metadata">

**Author:** ![TSAREGORODTSEVS\_Yur](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dc4da7/32.png) [@TSAREGORODTSEVS\_Yur](https://www.ruby-forum.com/u/TSAREGORODTSEVS_Yur)\
**Post date:** [September 5, 2014, 5:33pm UTC](https://www.ruby-forum.com/t/full-duplex-infinity-loop/231913/2 "2014-09-05T17:33:02Z")

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Do you mean the fact that you’ll be receiving your own packets? There’s  
several ways to do this, e.g. You can catch your own packets in the mac  
layer.

M  
On 5 Sep 2014 17:27, “TSAREGORODTSEV, Yury”  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

---

<div class="post-metadata">

**Author:** ![TSAREGORODTSEVS\_Yur](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dc4da7/32.png) [@TSAREGORODTSEVS\_Yur](https://www.ruby-forum.com/u/TSAREGORODTSEVS_Yur)\
**Post date:** [September 5, 2014, 5:41pm UTC](https://www.ruby-forum.com/t/full-duplex-infinity-loop/231913/3 "2014-09-05T17:41:04Z")

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Dear Martin,  
yes, absolutely, idea is to do signal repeater.  
Whats the best solution can be ?

----- Original Message -----

From: “Martin B.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
To: “Yury TSAREGORODTSEV” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
Cc: removed\_email\_address@domain.invalid  
Sent: Friday, September 5, 2014 5:31:05 PM  
Subject: Re: [Discuss-gnuradio] full duplex infinity loop

Do you mean the fact that you’ll be receiving your own packets? There’s  
several ways to do this, e.g. You can catch your own packets in the mac  
layer.

M  
On 5 Sep 2014 17:27, “TSAREGORODTSEV, Yury” \<  
removed\_email\_address@domain.invalid \> wrote:

Hello,  
can anyone suggest how to prevent infinity loop in case of full duplex  
RX/TX on same frequency ?  
Any ideas?

GRC example:  
UHD source → GMSK DEMOD → packet decoder → packet encoder → GMSK MOD  
 → UHD SINK

but in this case of course its gonna be infinity loop,  
any suggestion how to avoid this?

Thx.

* * *

Discuss-gnuradio mailing list  
removed\_email\_address@domain.invalid  
[https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

---

<div class="post-metadata">

**Author:** ![TSAREGORODTSEVS\_Yur](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dc4da7/32.png) [@TSAREGORODTSEVS\_Yur](https://www.ruby-forum.com/u/TSAREGORODTSEVS_Yur)\
**Post date:** [September 5, 2014, 5:47pm UTC](https://www.ruby-forum.com/t/full-duplex-infinity-loop/231913/4 "2014-09-05T17:47:16Z")

</div>

Well, as Martin said, if you want to avoid resending your own packets  
you will need to be able to keep track of which packet you already sent;  
you can also “numb” the receiver for the duration of your TX. None of  
this hasn’t, to my knowledge, been with the GNU Radio examples, and  
since it involves logic that cannot be well represented by graphical  
flowgraphs, you’ll most likely have to get your hands dirty writing some  
MAC intelligence. Packet en/decoder is only that – Phy layer packet  
decoders; you will need some MAC on top of that to have control medium  
access.

Generally, doing it on the same frequency will effectively half your  
available time-bandwidth product, ie your transmission capacity, and it  
will lead to receivers seeing both the original and your repeated packet  
receiving things twice. In many cases, this is ok or even desirable, but  
for simpler set ups, where spectrum is not overly hard to obtain, you  
might want to go for a frequency translating repeater.

Greetings,  
Marcus