# Re: Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission **URL:** \ **Category:** GNU Radio\ **Created:** [June 4, 2014, 11:53am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193 "2014-06-04T11:53:05Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![jason\_sam](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7993a0/32.png) [@jason\_sam](https://www.ruby-forum.com/u/jason_sam)\ **Post date:** [June 4, 2014, 11:53am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/1 "2014-06-04T11:53:05Z")
On Wed, Jun 4, 2014 at 4:59 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Hi! > > This shouldn’t be the case. But is there any easy way to allow different > rates on the two streams, so I could produce more zeros on stream 1 than > items on stream 0? Or vice versa? > > David Please stay on the list. To have different rates on different inputs, [1] [http://lists.gnu.org/archive/html/discuss-gnuradio/2014-05/msg00166.html](http://lists.gnu.org/archive/html/discuss-gnuradio/2014-05/msg00166.html) [2] [http://gnuradio.4.n7.nabble.com/set-relative-rate-td46167.html](http://gnuradio.4.n7.nabble.com/set-relative-rate-td46167.html) ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 4, 2014, 11:56am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/2 "2014-06-04T11:56:38Z")
Sorry – I meant to hit reply all! From: Activecat [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)] Sent: 04 June 2014 10:51 To: removed\_email\_address@domain.invalid Cc: David Halls Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission On Wed, Jun 4, 2014 at 4:59 PM, David Halls \ wrote: Hi! This shouldn’t be the case. But is there any easy way to allow different rates on the two streams, so I could produce more zeros on stream 1 than items on stream 0? Or vice versa? David Please stay on the list. To have different rates on different inputs, [1] [http://lists.gnu.org/archive/html/discuss-gnuradio/2014-05/msg00166.html](http://lists.gnu.org/archive/html/discuss-gnuradio/2014-05/msg00166.html) [2] [http://gnuradio.4.n7.nabble.com/set-relative-rate-td46167.html](http://gnuradio.4.n7.nabble.com/set-relative-rate-td46167.html) * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 4, 2014, 12:42pm UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/3 "2014-06-04T12:42:35Z")
Hi, Thank you for those links. Unfortunately the rates for the two ports are not an exact ratio, so I am not sure how this will work. Also I have ninput\_items\_required[0] = noutput\_items; ninput\_items\_required[1] = 0; I am not quite sure how to change this… Maybe it will help to show more clearly what I am doing. Attached is a flow graph that shows how I have managed to achieve what I want - but clearly it is a real fudge. I am doing a 2x1 transmission, so in time-domain (TD), I have [ Header 1 (240 samples), Header 2 (240 samples), superimposed Payload Tx1 + Tx2 (1280 samples) ] then this repeats. Header TD Tx1, Header TD Tx2 and Payload TD Tx1 always have items available, _but_ Payload TD Tx2 has no items at time=0. I would like the header data (both Tx1 and Tx2 to always be transmitted, so that even when Payload TD Tx2 is not available, the protocol/frame structure does not break down. Regards, David * * * From: Activecat [removed\_email\_address@domain.invalid] Sent: 04 June 2014 10:51 To: removed\_email\_address@domain.invalid Cc: David Halls Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission On Wed, Jun 4, 2014 at 4:59 PM, David Halls \ wrote: Hi! This shouldn’t be the case. But is there any easy way to allow different rates on the two streams, so I could produce more zeros on stream 1 than items on stream 0? Or vice versa? David Please stay on the list. To have different rates on different inputs, [1] [http://lists.gnu.org/archive/html/discuss-gnuradio/2014-05/msg00166.html](http://lists.gnu.org/archive/html/discuss-gnuradio/2014-05/msg00166.html) [2] [http://gnuradio.4.n7.nabble.com/set-relative-rate-td46167.html](http://gnuradio.4.n7.nabble.com/set-relative-rate-td46167.html) * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 4, 2014, 1:12pm UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/4 "2014-06-04T13:12:05Z")
Activecat, In fact my horrible hack doesn’t work properly. Once items start arriving at Payload TD Tx 2, they still don’t arrive as ‘consistently’ (for want of a better word), as those from the Noise Source block, and thus zeros are inserted when they are not required! David ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 4, 2014, 5:03pm UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/5 "2014-06-04T17:03:14Z")
Please do not top post. Refer [http://gnuradio.org/redmine/projects/gnuradio/wiki/MailingLists#Guidelines-for-posting](http://gnuradio.org/redmine/projects/gnuradio/wiki/MailingLists#Guidelines-for-posting) ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 4, 2014, 7:10pm UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/6 "2014-06-04T19:10:38Z")
On Wed, Jun 4, 2014 at 7:10 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Activecat, > > In fact my horrible hack doesn’t work properly. Once items start arriving > at Payload TD Tx 2, they still don’t arrive as ‘consistently’ (for want of > a better word), as those from the Noise Source block, and thus zeros are > inserted when they are not required! > > David David, Could you please explain in details, what is this Payload TD Tx 2? How does it generate data, is it getting data from a hardware or console, why it sometime idle but sometime transmitting? This is a virtual source. Where is it associated virtual sink? ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 4, 2014, 9:09pm UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/7 "2014-06-04T21:09:07Z")
Hi Activecat, I have disconnected the rest of the flow graph because it is extremely complex. In the system I have a Source, a Relay (1 rx USRP, 1 tx USRP), a Destination. S —\> R\_rx/R\_tx → D The two transmitters that you see on that flow graph snippet I sent you are the the Source Tx and the Relay Tx. Payload TD Tx 1 is derived from input codewords that are generated in MATLAB and stored in a file, then loaded into the flow graph. The payload is created in a similar fashion to Martin’s original OFDM\_tx. This is then transmitted from Source Tx. Until this point, no packets are received by Relay Rx but once the source transmits, these packets are then received by Relay Rx, and then there is a decode-and-forward chain of blocks, and this then creates Payload TD Tx 2. The full flow graph is attached, but may be missing many blocks for you… David * * * From: Activecat [removed\_email\_address@domain.invalid] Sent: 04 June 2014 13:45 To: removed\_email\_address@domain.invalid Cc: David Halls Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission On Wed, Jun 4, 2014 at 7:10 PM, David Halls \ wrote: Activecat, In fact my horrible hack doesn’t work properly. Once items start arriving at Payload TD Tx 2, they still don’t arrive as ‘consistently’ (for want of a better word), as those from the Noise Source block, and thus zeros are inserted when they are not required! David David, Could you please explain in details, what is this Payload TD Tx 2? How does it generate data, is it getting data from a hardware or console, why it sometime idle but sometime transmitting? This is a virtual source. Where is it associated virtual sink? * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 12:53am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/8 "2014-06-05T00:53:42Z")
On Wed, Jun 4, 2014 at 8:53 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > How many USRP are controlled by this flowgraph? It seems at least three, what is the exact number? ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 12:57am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/9 "2014-06-05T00:57:49Z")
* * * From: Activecat [removed\_email\_address@domain.invalid] Sent: 04 June 2014 15:21 To: David Halls Cc: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission On Wed, Jun 4, 2014 at 8:53 PM, David Halls \<[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)\> wrote: Hi Activecat, I have disconnected the rest of the flow graph because it is extremely complex. In the system I have a Source, a Relay (1 rx USRP, 1 tx USRP), a Destination. S —\> R\_rx/R\_tx → D The two transmitters that you see on that flow graph snippet I sent you are the the Source Tx and the Relay Tx. Payload TD Tx 1 is derived from input codewords that are generated in MATLAB and stored in a file, then loaded into the flow graph. The payload is created in a similar fashion to Martin’s original OFDM\_tx. This is then transmitted from Source Tx. Until this point, no packets are received by Relay Rx but once the source transmits, these packets are then received by Relay Rx, and then there is a decode-and-forward chain of blocks, and this then creates Payload TD Tx 2. The full flow graph is attached, but may be missing many blocks for you… ## How many USRP are controlled by this flowgraph? It seems at least three, what is the exact number? Yes, there are 3. The Source Tx, the Relay Tx, and the Relay Rx. * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 1:11am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/10 "2014-06-05T01:11:22Z")
On Wed, Jun 4, 2014 at 10:25 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Yes, there are 3. The Source Tx, the Relay Tx, and the Relay Rx. To clarify, i). the “Source Tx” USRP may or may not receive data at any time interval. ii). the “Relay Tx” USRP transmit data only when the “Source Tx” USRP receive data, and there is a delay due to signal processing iii). the “Relay Rx” USRP will receive data only when the “Relay Tx” USRP transmit it, is this correct? ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 4, 2014, 9:53pm UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/11 "2014-06-04T21:53:58Z")
On Wed, Jun 4, 2014 at 8:53 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Could you send the source code of the missing blocks to me? I am trying hard to help you out. ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 1:24am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/12 "2014-06-05T01:24:20Z")
* * * From: Activecat [removed\_email\_address@domain.invalid] Sent: 04 June 2014 15:39 To: David Halls Cc: removed\_email\_address@domain.invalid Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission On Wed, Jun 4, 2014 at 10:25 PM, David Halls \ wrote: Yes, there are 3. The Source Tx, the Relay Tx, and the Relay Rx. To clarify, i). the “Source Tx” USRP may or may not receive data at any time interval. ii). the “Relay Tx” USRP transmit data only when the “Source Tx” USRP receive data, and there is a delay due to signal processing iii). the “Relay Rx” USRP will receive data only when the “Relay Tx” USRP transmit it, is this correct? Not quite… i). the “Source Tx” USRP has a constant stream of data, and is constantly transmitting. If the codewords in the file are exhausted it repeats. ii). the “Relay Tx” USRP transmits data only when data has been received by the “Relay Rx” (I will use tx\_time to control when the received burst is re-transmitted) iii). the “Relay Rx” USRP will receive data only when the “Source Tx” USRP transmits (section where Relay Tx’s too will be ignored), I have changed the block you suggested, to avoid inserting 0’s mid burst. ``` void avoid_block_impl::forecast (int noutput_items, gr_vector_int ``` &ninput\_items\_required) { ninput\_items\_required[0] = noutput\_items; ninput\_items\_required[1] = 0; } ``` int avoid_block_impl::general_work (int noutput_items, gr_vector_int &ninput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items) { const gr_complex *in0 = (const gr_complex*) ``` input\_items[0]; const gr\_complex _in1 = (const gr\_complex_) input\_items[1]; gr\_complex _out0 = (gr\_complex_) output\_items[0]; gr\_complex _out1 = (gr\_complex_) output\_items[1]; ``` //if(DEBUG) fprintf(stderr, " noutput_items = %d, ``` ninput\_items[0] = %d, ninput\_items[1] = %d.\n", noutput\_items, ninput\_items[0], ninput\_items[1]); ``` // For first input, just copy for (int i=0; i < noutput_items; i++) out0[i] = in0[i]; // Count number of output items int num_out1 = 0; // If items available for second input, copy for (int i=0; i < ninput_items[1]; i++) { out1[i] = in1[i]; if(!d_burst) { if(DEBUG) fprintf(stderr, " Entering ``` burst…\n"); d\_burst = true; } // Number of (actual) items tx’d this call num\_out1++; // Total number of items in burst transmitted so far d\_items\_sent++; } ``` // For the rest of second output, fill with zeros if(!d_burst) { for (int i=ninput_items[1]; i < noutput_items ; ``` i++) { // Fill zeros out1[i] = 0.0; // Number of (zero) items tx’d this call num\_out1++; } } ``` // Mark end of burst if(d_items_sent >= 1280*6) //TODO change to external ``` burst length parameter { if(DEBUG) fprintf(stderr, " Finishing burst…\n"); d\_burst = false; d\_items\_sent = 0; } ``` consume( 0, noutput_items); consume( 1, ninput_items[1]); // Consume all available ``` items ``` produce( 0, noutput_items); produce( 1, num_out1); // Only produce the required ``` number of items ``` return WORK_CALLED_PRODUCE; } ``` * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 1:34am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/13 "2014-06-05T01:34:56Z")
On Wed, Jun 4, 2014 at 10:52 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Not quite… > > i). the “Source Tx” USRP has a constant stream of data, and is constantly > transmitting. If the codewords in the file are exhausted it repeats. > ii). the “Relay Tx” USRP transmits data only when data has been received > by the “Relay Rx” (I will use tx\_time to control when the received burst is > re-transmitted) > iii). the “Relay Rx” USRP will receive data only when the “Source Tx” USRP > transmits (section where Relay Tx’s too will be ignored), What do you mean by “section where Relay Tx’s too will be ignored” ? > I have changed the block you suggested, to avoid inserting 0’s mid burst. So does this give better results? ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 1:45am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/14 "2014-06-05T01:45:32Z")
On Wed, Jun 4, 2014 at 10:52 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Not quite… > > i). the “Source Tx” USRP has a constant stream of data, and is constantly > transmitting. If the codewords in the file are exhausted it repeats. > ii). the “Relay Tx” USRP transmits data only when data has been received > by the “Relay Rx” (I will use tx\_time to control when the received burst is > re-transmitted) > iii). the “Relay Rx” USRP will receive data only when the “Source Tx” USRP > transmits (section where Relay Tx’s too will be ignored), To clarify, is it true that both the “Source TX” USRP and “Relay Tx” USRP are controlled by the same UHD Sink in the flowgraph? ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 1:57am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/15 "2014-06-05T01:57:19Z")
* * * From: Activecat [removed\_email\_address@domain.invalid] Sent: 04 June 2014 16:02 To: David Halls Cc: removed\_email\_address@domain.invalid Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission On Wed, Jun 4, 2014 at 10:52 PM, David Halls \ wrote: Not quite… i). the “Source Tx” USRP has a constant stream of data, and is constantly transmitting. If the codewords in the file are exhausted it repeats. ii). the “Relay Tx” USRP transmits data only when data has been received by the “Relay Rx” (I will use tx\_time to control when the received burst is re-transmitted) iii). the “Relay Rx” USRP will receive data only when the “Source Tx” USRP transmits (section where Relay Tx’s too will be ignored), What do you mean by “section where Relay Tx’s too will be ignored” ? I have changed the block you suggested, to avoid inserting 0’s mid burst. So does this give better results? 1. this is to avoid loop interference, the Relay Rx will ignore the received signal during the time that the Relay Tx is transmitting. 2. Yes avoiding adding 0’s gives me pretty much the performance I require, I need to work on some other parts of the implementation to be sure. (it is definitely not the neatest way yet!!) * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 8:58am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/16 "2014-06-05T08:58:44Z")
On Wed, Jun 4, 2014 at 7:10 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Activecat, > In fact my horrible hack doesn’t work properly. Once items start arriving > at Payload TD Tx 2, they still don’t arrive as ‘consistently’ (for want of > a better word), as those from the Noise Source block, and thus zeros are > inserted when they are not required! > > David David, Basically my idea to solve the problem may involve an overhaul of your existing flowgraph, as below: 1). You must understand that the output of UHD source is at constant rate. In particular I am referring to the “Relay Rx” USRP. Even when the USRP does not receive any RF signal, it keeps sending out zeros (plus noise) as its output, at constant rate. ``` Try to make all your blocks behave in this way. I am referring to ``` the blocks between the “Relay Rx” and “Relay Tx”. The idea is: keep transmitting, don’t produce no output at any time. If nothing need to be produced, then output zeros at constant rate. In this case all your custom blocks are either sync block, decimation or interpolation blocks. You don’t need any general block. 2). With above condition fulfilled, we could ensure that the data fed into the “Relay Tx” USRP is at constant rate, and we could then determine this rate by simple calculations. The data stream into the “Relay Tx” USRP will not stop at any instance. It is ‘consistent’. 3). You want the “Relay Rx” USRP ignores the received signal during the time that the “Relay Tx” USRP is transmitting, that is fine. But just try to make the downstream block of “Relay Rx” USRP keep transmitting zeros rather than stop transmitting during this period. 4). With these, you will have both “Relay Tx” USRP and “Source” USRP transmitting at constant data rate and nonstop. They could be transmitting at different rates, that is ok, and this is not difficult to handle. With this, you avoid the initial problem (problem of occasionally there is no items at one of the inputs) mentioned in this thread, which is the root cause of your problem. Then your problem is solved ! ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [June 5, 2014, 1:58am UTC](https://www.ruby-forum.com/t/re-scheduling-a-block-even-with-no-input-items-re-flow-graph-blocking-when-doing-2x1-transmission/230193/17 "2014-06-05T01:58:30Z")
* * * From: Activecat [removed\_email\_address@domain.invalid] Sent: 04 June 2014 16:13 To: David Halls Cc: removed\_email\_address@domain.invalid Subject: Re: [Discuss-gnuradio] Scheduling a block even with no input items RE: Flow graph blocking when doing 2x1 transmission On Wed, Jun 4, 2014 at 10:52 PM, David Halls \ wrote: Not quite… i). the “Source Tx” USRP has a constant stream of data, and is constantly transmitting. If the codewords in the file are exhausted it repeats. ii). the “Relay Tx” USRP transmits data only when data has been received by the “Relay Rx” (I will use tx\_time to control when the received burst is re-transmitted) iii). the “Relay Rx” USRP will receive data only when the “Source Tx” USRP transmits (section where Relay Tx’s too will be ignored), To clarify, is it true that both the “Source TX” USRP and “Relay Tx” USRP are controlled by the same UHD Sink in the flowgraph? Yes, they are both controlled by the same UHD sink. This ensures, in a simple fashion, that the Source Tx and Relay Tx transmissions have sample-level synchronicity - a must for my Quantize Map and Forward scheme. * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl