Hi,
I'm not sure if I get it, but don't you need some synchronization logic
between the branches. Consider what happens if one branch receives
frames while the other one doesn't, then data queues up in the add
block, which will sooner or later lead to overruns, independent from the
buffer size.
Best,
Bastian
On 04/27/2018 09:54 AM, Sumit Kumar wrote:
Hi,
I am working on soft bit maximal ratio combiner (SBMRC). It's basically
a MRC but instead of combining the actual signals according to their
SNR, we combine the LLRs from separate branches and send them to Soft
Decision Viterbi Decoder (SDVD). For this, I have modified gr-ieee 80211
which generates soft bits and integrated a SDVD with it. It works good
when I use either single branch or both branch separately.
In order to implement SBMRC, for every OFDM symbol decoded, a vector of
LLR (size 48 X 1) is generated from both the receiver branches. These
two vectors of LLR are further added and sent to SDVD. I configured the
ADD block to take 48 floats as input.
First I made a simulator for SBMRC, but even after increasing the output
buffer size to 500000, warnings of buffer over flow kept coming.
Then I used USRP, it simply refuses to work. I am using NI 2901 Tx/Rx A
and Tx/Rx B ports as my receive branches. The LEDs go green for a second
then stop. No error no warning.
Looks like the *ADD *block is the cause. I have never seen this, so I am
clueless where to debug. Am I missing something fundamental here ?
The attached picture *usrp_sbmrc* says details of my schematic and the
results when I use USRP.
The attached picture *sbmrc_sim* says details of my schematic and the
results when I use simulations.
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Dipl.-Inform. Bastian Bloessl
Researcher @ CONNECT Center
Trinity College Dublin
GitHub/Twitter: @bastibl
https://www.bastibl.net/
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