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From: | Sumit Kumar |
Subject: | [Discuss-gnuradio] Issue while adding streaming data : Integrating MRC in gr-ieee 80211 |
Date: | Fri, 27 Apr 2018 09:54:10 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 |
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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