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function [bb, tim] = rcosfir(r, N_T, rate, T, fil_type, col) 
%RCOSFIR Design a raised cosine FIR filter. 
%   B = RCOSFIR(R, N_T, RATE, T) designs and returns a raised cosine FIR filter. 
%   A raised cosine filter is typically used to shape and oversample a symbol 
%   stream before modulation/transmission as well as after reception and 
%   demodulation.  It is used to reduce the bandwidth of the oversampled symbol 
%   stream without introducing intersymbol interference. 
% 
%   The time response of the raised cosine filter is, 
% 
%     h(t) = SINC(t/T) COS(pi R t/T)/(1 - 4 R^2 t^2 /T^2) 
% 
%   The frequency domain has the spectrum 
% 
%            /  T                                 when 0 < |f| < (1-r)/2/T 
%            |          pi T         1-R    T          1-R         1+R 
%     H(f) = < (1 + cos(----) (|f| - ----) ---    when --- < |f| < --- 
%            |            r           2T    2          2 T         2 T 
%            \  0                                 when |f| > (1+r)/2/T 
% 
% 
%   T is the input signal sampling period, in seconds.  RATE is the 
%   oversampling rate for the filter (or the number of output samples per input 
%   sample). The rolloff factor, R, determines the width of the transition 
%   band.  R has no units.  The transition band is (1-R)/(2*T) < |f| < 
%   (1+R)/(2*T). 
% 
%   N_T is a scalar or a vector of length 2.  If N_T is specified as a 
%   scalar, then the filter length is 2 * N_T + 1 input samples.  If N_T is 
%   a vector, it specifies the extent of the filter.  In this case, the filter 
%   length is N_T(2) - N_T(1) + 1 input samples (or 
%   (N_T(2) - N_T(1))* RATE + 1 output samples). 
% 
%   The default value for N_T is 3.  The default value of RATE is 5. 
%   The default value of T is 1. 
% 
%   B = RCOSFIR(R, N_T, RATE, T, FILTER_TYPE) designs and returns a 
%   square root raised cosine filter if FILTER_TYPE == 'sqrt'. The default 
%   value of FILTER_TYPE, 'normal', returns a normal raised cosine filter. 
% 
%   RCOSFIR(R, N_T, RATE, T, FILTER_TYPE, COL) produces the time response 
%   and frequency response with the curve color as specified in the string 
%   variable COL. The string in COL can be any type as defined in 
%   PLOT.  If COL is not present, the default color will be used in the plot 
% 
%   [B, Sample_Time] = RCOSFIR(...) returns the FIR filter and the output sample 
%   time for the filter. Note that the filter sample time is T / RATE. 
% 
%   See also RCOSIIR, RCOSFLT, RCOSINE, FIRRCOS, RCOSDEMO. 
 
%   Copyright 1996-2001 The MathWorks, Inc. 
%   $Revision: 1.14 $ 
 
%routine check 
if nargin < 1 
    error('Not enough input variables for RCOSFIR') 
elseif nargin < 2 
    N_T = [3 3]; rate = 5; T = 1; fil_type = 'normal'; 
elseif nargin < 3, 
    rate = 5; T = 1; fil_type = 'normal'; 
elseif nargin < 4, 
    T = 1; fil_type = 'normal'; 
elseif nargin < 5, 
    fil_type = 'normal'; 
end; 
 
if (r < 0) | (r > 1) | ~isreal(r) 
    error('The Rolloff factor in RCOSFIR must be a positive integer in the range, [0, 1].') 
end; 
 
[N_T, rate, T, fil_type] = checkinp(N_T, rate, T, fil_type,... 
    [3 3], 5,  1, 'normal'); 
if length(N_T) < 2 
    N_T = [N_T N_T]; 
end; 
 
if (rate <= 1) | (ceil(rate) ~= rate) 
    error('RATE in RCOSFIR must be an integer greater than 1') 
end 
 
% calculation 
 
N_T(1) = -abs(N_T(1)); 
time_T = [0 : 1/rate : max(N_T(2), abs(N_T(1)))]; 
cal_time = time_T * T; 
time_T_r = r * time_T; 
if ~isempty(findstr(fil_type,'root')) | ~isempty(findstr(fil_type,'sqrt')) 
    % square root raised cosine 
    b=firrcos(rate*(N_T(2)-N_T(1)),1/(2*T),r,rate/T,'r','sqrt',-N_T(1)*rate)*sqrt(rate); 
else 
    % regular raised cosine 
    b=firrcos(rate*(N_T(2)-N_T(1)),1/(2*T),r,rate/T,'r',[],-N_T(1)*rate)*rate; 
end 
 
tim = cal_time(2) - cal_time(1); 
 
% In the case needs a plot 
if nargout < 1 
    if nargin < 6 
        col = ''; 
    end; 
 
    % the time response part 
    hand = subplot(211); 
    % dont filter, plot using plot([0 : 1/rate : N_T(2) - N_T(1)],b) insteat 
    out = filter(b, 1, [1, zeros(1, length(cal_time) - 1)]); 
    plot(cal_time, out, col) 
    % if not hold, change the axes 
    hol = get(hand,'NextPlot'); 
    if (hol(1:2) ~= 'ad') | (max(get(hand,'Ylim')) < max(b)) 
        axis([min(cal_time), max(cal_time), min(out) * 1.1, max(out) * 1.1]); 
        xlabel('time'); 
        title('Impulse Response of the Raised Cosine Filter (with time shift)') 
    end; 
 
    % the frequency response part 
    hand = subplot(212); 
    len = length(b); 
    P = abs(fft(b)) * abs(N_T(2) - N_T(1)) / len * T; 
    f = (0 : len / 2) / len * rate / T; 
    ind = find(f < 1.5 / T); 
    f = f(ind); 
    P = P(ind); 
    plot(f, P, col); 
    hol = get(hand, 'NextPlot'); 
    if hol(1:2) ~= 'ad' 
        xlabel('frequency'); 
        ylabel('Amplitude'); 
        title('Frequency Response of the Raised Cosine Filter') 
    end; 
else 
    bb = b; 
end; 
%--end of rcosfir.m--