www.pudn.com > PSK.zip > my_rrc.m
function f = my_rrc(fd, fs, beta, delay)
> MY_RRC Produces the impulse response of a root raised cosine filter
> F = MY_RRC(Fd, Fs, BETA, DELAY) is the impulse response of a root
> raised cosine FIR filter with rolloff factor BETA and delay DELAY.
> $Id: my_rrc.m 457 2006-11-09 08:29:13Z kleiner $
BETA = beta;
DELAY = delay;
FD = fd;
FS = fs;
> time vector
Td = 1/FD;
> Length of actual filter coefficients (rest is zero)
rrclen = FS/FD * DELAY * 2 + 1;
> Create vector of time instants (make it a column vector to behave as the
> MATLAB function rcosflt)
t = linspace(-DELAY*Td, DELAY*Td, rrclen)';
rrc_num = 4*BETA / (pi*sqrt(Td)) * ...
(cos((1+BETA)*pi*t/Td) + (1-BETA)*pi/(4*BETA) * ...
sinc((1 - BETA)*t/Td));
rrc_denom = (1 - (4*BETA * t/Td).^2);
rrc = rrc_num ./ rrc_denom;
> Determine if there is a singularity (at positions t = +/- 1/(4*BETA))
> The value at these points can be obtained by the De l'Hopital rule.
ind = find(abs(t) == Td/(4*BETA));
if ~isempty(ind)
rrc(ind) = 4*BETA / (pi * sqrt(Td)) * ...
( (-2 + pi)*cos(pi / (4*BETA)) + ...
(2+pi) * sin(pi / (4*BETA))) / (4*sqrt(2));
end
> Normalize
f = rrc / sqrt(FS);
end