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 Posted - 11/26/2005 : 15:33:35
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Good Morning,
may I ask you why the function Rcosine of Matlab require that I produce SRRC filtering and at the same time an interpolation of at least 2, this is achieved only with the polyphase structure, what happens if instead I first produce SRRC filtering with a normal FIR and later interpolate for example with a CIC filter or in another way I first interpolate and later I produce SRRC filtering ???
Thanks you a lot ...
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Why not ?!? |
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Tom
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Posted - 11/26/2005 : 15:35:20
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Hello!
Upto my knowledge, RCOSINE function is related to digital
communications so we have to interpolate because we are using the
message signal to modulate a carrier wave. Since one 'symbol' requires
at least one cycle of a carrier to be modulated, so we must
interpolate the symbol to increase its data rate so that it can
modulate the wave properly. Also we are performing baseband shaping,
so we got two filters at hand : the interpolator and the shaper (the
RRCF). MATLAB embeds these two operations together in a single
function RCOSINE or RCOSFIR etc.
And about the problem why first interpolation and then RRCF, well i
think it is because you are want to shape the 'interpolated' data
symbols, not just the normal symbols, because otherwise (using RRCF
first and then interpolate) may not perform required baseband shaping.
Thats what i think! and i am not a master!
Regards
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Ian
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Posted - 11/26/2005 : 15:42:42
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Hi Antonio:
Create a simulated random data stream with 1 sample per bit (corresponding to no interpolation). Do a Fourier transform on this sequence. Note that the Nyquist frequency for this spectrum corresponds to the data rate. Now consider how you can do the required RC or RRC frequency response shaping when this is centred at the data rate.
If you interpolate by 2, there is "room" in the spectrum to do this shaping.
(You _can_ do the shaping without the interpolation, it is just easier to visualise what's needed/going on if you interpolate first.)
Ian
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Matlab function Rcosine and interpolation question
