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[Discuss-gnuradio] Query on simulation of MIMO on Gnuradio

From: Karan Talasila
Subject: [Discuss-gnuradio] Query on simulation of MIMO on Gnuradio
Date: Wed, 6 Aug 2014 12:17:37 +0530

     we are trying to implement alamouti encoding and decoding on an underlying ofdm communication system in Gnuradio. So we are using benchmark_tx.py. In  ofdm mapper block we have written our own block which does alamouti encoding which gives out alamouti encoded symbols across two output ports. The first output port will give x1 and -x2*. The second output port will give x2 and x1* according to the alamouti code.

Now, from each of these two output ports, we are connecting an insert preamble block followed by an IFFT block and then a cyclic prefixer block. All of these blocks are standard gnuradio blocks used  in ofdm examples directory in gnuradio( benchmark_tx.py). Now we would want to connect these two ouputs to their respective usrp sink blocks thereby implementing a mimo system with 2 transmitters.

Now we are using an alamouti decoder block which is implemented in ofdm frame acquisition block. Before we put it on usrp's which require perfect hardware time synchronisation, we  would like to test whether our end to end transmitter and receiver in software is working. So we connected the txpath1 to rxpath1 and txpath2 to rxpath2 which is like connecting two transmitters to two receivers directly. But we are not receiving the decoded symbols properly. when we are debugging, we are having doubts as to maybe the H matrix(channel matrix) values of h12 and h21 might not be received because we are connecting transmitter 1 to receiver 1 and transmitter 2 to receiver 2. can that be an issue?

In general how do you test mimo blocks in software. Is the way we are doing right i.e. connecting txpath1 to rxpath1 and txpath2 to rxpath2. Or are there other better ways of testing end to end MIMO systems without hardware?

Karan Talasila

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