Re: [Discuss-gnuradio] Implementing feedback loops

[Marcus Müller]

Hi Vipin,

sorry, I don't fully understand. So you only have one block, A, but it implements multiply functions x() and y()? What are y0 and y1? Are they just two values, or are they two streams?

I think I would very greatly benefit from having a drawing. Really, just anything on a piece of paper, photographed with a potato.

Thanks!
Marcus

On 10/05/2017 06:46 PM, Vipin Sharma wrote:

I am aware that GNURadio doesn't support feedback loops in the flow graph. However, I have an application scenario where every execution of a GRC block, I need some of the previous outputs of that block.

For example, if I have a block called A which produces y0,y1 and consumes i0, i1. Assume all input/output buffers are of size d. Also assume the block implements some signal processing function, y0[n] = x(i0[n], i1[n]) and y1[n] = y(i0[n]) where 'x' and 'y' are some arbitrary functions that the GRC block implements. i0 is some BPSK independent source. i1 is the delayed output y1. In other words, i1 = y[n - d].

In the flow graph, y1 will go through a delay block and become i1 to the GRC block. However this creates a feedback loop in the flow graph.

How do I go about implementing such a scenario?

A few solutions I have read online say that all feedbacks can be done internal to the custom block. The problem i have is that my application will no longer be real time. 

Ideally I would like to have the block process a sample size of 'd' at a time where a USRP board dumps the BPSK stream in real time. 

Any pointers?

Vipin

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