Hi bastian,
To solve the following issue (as you predicted):
"Consider what happens if one branch receives frames while the
other one doesn't,Consider what happens if one branch receives
frames while the other one doesn't."
I combine the LLR of the SIGNAL fields from two branches and use
that to decode the SIGNAL filed. The decision is used to decode both
the branches. As of now it works, I mean doesn't crash at all!
Could you comment on this configuration.
Regards
Sumit
On 27/04/2018 10:41, Bastian Bloessl
wrote:
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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