rcosine.m

数字通信第四版原书的例程

function [num, den] = rcosine(Fd, Fs, type_flag, R, Delay, tol)
%RCOSINE Designs a raised cosine filter.
%       NUM = RCOSINE(Fd, Fs) designs a FIR raised cosine filter to filter a
%       digital signal with the digital transfer sampling frequency Fd. The
%       filter sample frequency is Fs. Fs must be larger than Fd. Fs/Fd must
%       be an integer. The rolloff factor is a default of .5. The time delay
%       is a default of 3, which means the filter has delay 3 / Fd second.
%
%       [NUM, DEN] = RCOSINE(Fd, Fs, TYPE_FLAG) gives specific filter design
%       instruction. TYPE_FLAG could be 'iir', 'sqrt', or a combination
%       such as 'iir/sqrt'. The order of the string is not important.
%         'fir'    Design FIR raised cosine filter (default).
%         'iir'    Design using IIR raised cosine filter.
%         'normal' Design the regular raised cosine filter (default).
%         'sqrt'   Design square root raised cosine filter.
%         'default' Use all of the default (FIR, Normal raised cosine filter).
%
%       [NUM, DEN] = RCOSINE(Fd, Fs, TYPE_FLAG,  R) specifies the 
%       rolloff factor. In general, it is a real number in range [0, 1].
%
%       [NUM, DEN] = RCOSINE(Fd, Fs, TYPE_FLAG, R, DELAY) specifies the delay
%       step. DELAY should be a positive integer. Delay/Fd will be the time
%       delay in the raised cosine filter design.
%
%       [NUM, DEN] = RCOSFLT(Fd, Fs, TYPE_FLAG, R, Delay, Tol) provides the
%       tolerance in IIR filter design. The default value is .01.
%
%       When the designed filter is a FIR filter, the output in DEN is 1.
%
%       See also RCOSFLT, RCOSIIR, RCOSFIR.

%       Wes Wang 10/11/95.
%       Copyright (c) 1995-96 by The MathWorks, Inc.
%       $Revision: 1.1 $  $Date: 1996/04/01 18:02:29 $

%assigned default value
if nargin < 6
    tol = .01;
end;

%default delay
if nargin < 5
    Delay = 3;
elseif Delay <= 0
    error('DELAY must be a positive integer in RCOSINE.')
elseif ceil(Delay) ~= Delay
    error('DELAY in RCOSINE must be an integer.')
end;

%default rolloff factor
if nargin < 4
    R = .5;
elseif R < 0
    error('The Rolloff factor in RCOSINE cannot be a negative number.')    
end;

%default type_flag
if nargin < 3
    type_flag = 'default';
elseif ~isstr(type_flag) & ~isempty(type_flag)
    error('TYPE_FLAG in RCOSINE must be a string.');
end;

%not enough input varible.
if nargin < 2
    error('Not enough input variable for RCOSINE.')
end;

type_flag = lower(type_flag);

%filter type.
if findstr(type_flag, 'sqrt')
    filt_type = 'sqrt';
else
    filt_type = 'normal';
end;

FsDFd = Fs/Fd;
if ceil(FsDFd) ~= FsDFd
    error('Fs/Fd must be an integer.')
end;

%design the filter.
if findstr(type_flag, 'iir')
    [num, den] = rcosiir(R, Delay, FsDFd, 1/Fd, tol, filt_type);
else
    num = rcosfir(R, Delay, FsDFd, 1/Fd, filt_type);
    den = 1;
end;
%end of RCOSINE.