rcosiir.m

经典通信系统仿真书籍《通信系统与 MATLAB (Proakis)》源代码

function [num, den, tim] = rcosiir(r, T_delay, rate, T, tol, fil_type, col)
%RCOSIIR Designs raised cosine IIR filter.
%       NOTE: The output of this function is a raised cosine FIR filter. You
%             should use function RCOSFLT to filter your digital signal
%             instead of using FILTER.
%       RCOSIIR(R, T_DELAY, RTAE, T, TOL) produces time response and
%	frequency response of the raised cosine filter at given rolloff
%	factor R. T_DELAY is an integer to specify how many times of T 
%	delay. RATE is the sample point in each T, or the sampling rate
%	of the filter is T/RATE. The default value of RTAE is 5. T is the
%	symbol interval. The order of the IIR filter is determined by TOL
%       when ORDER is an integer greater than 1. If TOL has its value less
%       than 1, it is considered as the relative tolerant in the SVD
%       computation in selecting the order. The default value of TOL is 0.01.
%       The time response of the raised cosine filter has the form of
%       h(t) = sinc(t/T) cos(pi R t/T)/(1 - 4 R^2 t^2 /T^2)
%       The frequency domain has the spectrum as 
%              /  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
%
%       RCOSIIR(R, T_DELAY, RATE, T, TOL, FILTER_TYPE) produces time response
%       and frequency response of a square root raised cosine filter if
%       FILTER_TYPE == 'sqrt'.
%
%       RCOSIIR(R, T_DELAY, RATE, T, TOL, FILTER_TYPE, COLOR) produces time
%       response and frequency response with the curve color as specified in
%       the string variable COLOR. The string in COLOR can be any type as
%       defined in PLOT.
%
%       [NUM, DEN] = RCOSIIR(...) returns the designed raised cosine IIR
%       filter. 
%   
%       [NUM, DEN, Sample_Time] = RCOSIIR(...) returns the IIR filter and the
%       sample time for the filter.
%
%       See also RCOSIIR.

%       Wes Wang 5/25/94, 10/11/95.
%       Copyright (c) 1995-96 by The MathWorks, Inc.
%       $Revision: 1.1 $  $Date: 1996/04/01 18:02:24 $

%routine check
if nargin < 1
    error('Not enough input variable for RCOSIIR')
elseif nargin < 2
    T_delay = 3; rate = 5; T = 1; tol = 0.01; fil_type='normal';
elseif nargin < 3, 
    rate = 5; T = 1; tol = 0.01; fil_type='normal';
elseif nargin < 4, 
    T = 1; tol = 0.01; fil_type='normal';    
elseif nargin < 5,
    tol = 0.01; fil_type='normal';    
elseif nargin < 6
    fil_type = 'normal';
end;

[T_delay, rate, T, tol, fil_type] = checkinp(T_delay, rate, T, tol, fil_type,...
                                             3,       5,    1, 0.01, 'normal');

if (rate < 1) | (ceil(rate) ~= rate)
    error('RATE in RCOSIIR must be a positive integer')
end

%calculation
[b, tim] = rcosfir(r, [T_delay, 3*T_delay], rate, T, fil_type);
[num, den] = imp2sys(b, tol);

% In case needs a plot
if nargout < 1
    if nargin < 7
        col = 'y-';
    end;

    cal_time = [-T_delay: tim : T_delay] / T;
    % the time response part
    hand = subplot(211);
    out = filter(num, den, [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))
        grid on;
        axis([min(cal_time), max(cal_time), min(out) * 1.1, max(out) * 1.1]);
        xlabel('time');
        title(['Impulse Response of ',num2str(length(den)),'th order Raised Cosine IIR Filter (',num2str(cal_time(1)),' sec shift)'])
    end;

    % the frequency response part
    hand = subplot(212);
    len = length(out);
    P = abs(fft(out)) * 2 * T_delay / len;
    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'
        grid on;
        xlabel('frequency');
        ylabel('Amplitude');
        title('Frequency Response of the Raised Cosine Filter (Normalized)')
    end;
end;

%---end rcosiir.m---