Design Raised Cosine Filters Using MATLAB Functions
rcosdesign function designs (but does not apply) filters of
Finite impulse response (FIR) raised cosine filter
FIR square-root raised cosine filter
The function returns the FIR coefficients as output.
Example Designing a Square-Root Raised Cosine Filter
For example, the command below designs a square-root raised cosine FIR filter with a rolloff of 0.25, a filter span of 6 symbols, and an oversampling factor of 2.
sps = 2; num = rcosdesign(0.25, 6, sps)
num = Columns 1 through 7 -0.0265 0.0462 0.0375 -0.1205 -0.0454 0.4399 0.7558 Columns 8 through 13 0.4399 -0.0454 -0.1205 0.0375 0.0462 -0.0265
Here, the vector
num contains the coefficients of the filter, in
ascending order of powers of z-1.
You can use the
upfirdn function to filter data with a raised
cosine filter generated by
rcosdesign. The following code illustrates
d = 2*randi([0 1], 100, 1)-1; f = upfirdn(d, num, sps); eyediagram(f(7:200),sps)
The eye diagram shows an imperfect eye because
num characterizes a