Meeting with Prof A. S. Ranade
Today I had
an hour long meeting with Prof. A. S. Ranade. It was the first official meeting
where we discussed the project. I started off from point 0 – explaining what
MIMO is. Then we moved on to ‘Diversity’- i.e. in a nutshell- sending replicas
of signal to achiever better performance, which is the main idea behind mimo.
Space Diversity being the area of interest in this project, we discussed what physical
ways of achieving it are. Following that we discussed the two techniques of
Maximum Ratio Combining and Selective Ratio Combining. Then we had a lengthy detailed
discussion on the Alamouti encoding-decoding. Then we tried to discuss the
qualitative effect on the code under various impairments. In that we talked
about what kind of fading and path gain coefficients the channel can have, the ‘worst
case ideal scenario’ where the modulation is BPSK(the symbols are negation of
each other) and as a result diversity will result in complete cancellation of
the two symbols in first time slot (assuming noiseless channel and unit path
gains). But because the second time slot also involves sending manipulated same
symbols, the original data can still be recovered. Still a complete qualitative
explanation of the Alamouti code under various effects needs to be studied and
understood. Prof Ranade has recommended books written by Krauss who gives very
good qualitative analysis and explanations of the phenomena related to antennas.
This will help in knowing exactly what is happening physically as it is
difficult to visualize the phenomenon by considering mere mathematical
equations.
Another detailed
discussion we had was on that the diversity helps in providing better SNR and
Noise Performance, which ‘may’ lead to reduction of total power transmitted if
we don’t want any improvement of noise performance compared to the case where
no diversity is used. On the other side, better noise performance will mean that
we can go for more no of symbols per constellation and thus more no of bits per
symbol and ultimately higher data rate.
Next
immediate goal- to simulate Alamouti decoding and compare the results with that
of simple siso transmission without using any diversity.
Next meeting
on Friday, 8th March 2009.