Hello everbody,
upsampling a complex data stream gives me headaches :( In my flowgraph
the upsampling is done by multiplexing 7 zeros with 1 data sample and
feeding this into a FIR filter, which is how everybody does it as I
understood. However, for further processing I have to take the delay
into account, that is introduced by the filter (length N). This delay
should be (N-1)/2, as the filter phase is linear. I do this by delaying
the data stream by one symbol length minus (N-1)/2, since causality
rules.
+----+ ------------+
|Data+---> |
+----+ | | +---------------------+ +-----+
|Stream MUX+--->Decimating FIR Filter+--->Delay|
+-----------+ | | +---------------------+ +-----+
|Null Source+---> |
+-----------+ ------------+
If I upsample as depicted above, my transmission kinda works, but I end
up having alignment problems resulting in a lower SNR. As I understood
the delay is realized by zero padding, which should work, but there
seems to be something I am missing out on. When I use the Decimating FIR
Filter block and I want the same alignment as before (symbol x starts at
sample y), so it can be further processed, what do I have to do?
Thank you for your ideas.
Regards,
Max
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