function h = root_raised_cosine(Q, b, trunc)

% h = root_raised_cosine(Q, b, trunc)
%
% Computes a truncated root raised cosine FIR filter.
%
% Input:
%   Q     = number of samples per symbol
%   b     = roll-off factor (optional, default 0.22)
%   trunc = truncation, computes impulse response in the interval
%           [-trunc*Tsymb , trunc*Tsymb ] (optional, default trunc=5)
%
% Output:
%   h     = inpulse respone

% 2000-09-03  written /Stefan

if nargin < 3
  trunc = 5;
end

if nargin < 2
  b = 0.22;
end

% The symbol time T is assumed to be unity.

T = 1*Q;
t = -trunc*Q:1:trunc*Q;

h = 4 * b * ...
    ( cos((1+b)*pi*t/T) + (1-b)*pi/(4*b) * sinc((1-b)*t/T) ) ./ ...  
    (pi*sqrt(T)*(1-16*b^2*t.^2/T^2));

% Normalize

h = h / sqrt(h*h');