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great you have reached the receiver now.
The receiver rrc filter has to be same as transmitter. Though the number of taps, sampling rate or any interpolation/decimation may be different from that of Tx filter.
The idea is both filtering of noise as well as doing correlation to maximise snr.
The correlation part requires reversal of coefficients in principle. But as long as the filter is symmetrical then you are free to reverse it and see what you get !!
since I haven't heard of anyone designing asymmetric rrc coeffs I better not swear at those unpractical dsp writers who also keep talking about infinity and minus infinity things.
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Actually, I implemented the RRC at the receiver and simulated in ModelSim. First, I thought I need to decimate by 8 in addition to filtering (I upsampled by 8 in the transmitter, if you remember) but I realized that this is gonna distort the signal since it will come out as 1 sample per symbol! I filtered without decimation. The signal looked exactly the same, like no filtering happened. Here where I thought the mathematical definition might mean something else.
I followed your advice and modeled the demodulator in MATLAB, but I got the same result... like no filtering happened. After a while, I started to put all what I read together... I need to add noise! Indeed, I added noise in MATLAB and observed the signal... this time, filtered like no noise happened! :D
PS: No need to swear at those unpractical dsp writers :D Writers whom I read for were practical I believe:
[1] Louis Litwin, "Matched filtering and timing recovery in digital receivers",
rfdesign.com, September 2001
[2] Eric Jacobsen,
http://www.dsprelated.com/showarticle/60.php These were really useful.
Thank you for assisting me during this project KAZ :) Now I'm moving to carrier and symbol recovery, wish me luck.
Cheers
Honored Contributor
