firrcos (Signal Processing Toolbox)

Raised cosine FIR filter design.

b = firrcos(n,F0,df,Fs)
b = firrcos(n,F0,df)
b = firrcos(n,F0,r,Fs,'rolloff')
b = firrcos(...,'type')
b = firrcos(...,'type',delay)
b = firrcos(...,'type',delay,window)
[b,a] = firrcos(...)

Description

firrcos(n,F0,df,Fs)

returns an order n lowpass linear-phase FIR filter with a raised cosine transition band. The filter has cutoff frequency F0, transition bandwidth df, and sampling frequency Fs, all in Hertz. df must be small enough so that F0 ± df/2 is between 0 and Fs/2. The coefficients in b are normalized so that the nominal passband gain is always equal to one.

firrcos(n,F0,df)

uses a default sampling frequency of Fs = 2.

b = firrcos(n,F0,r,Fs,'rolloff')

interprets the third argument, r, as the rolloff factor instead of the transition bandwidth, df. r must be in the range [0,1].

b = firrcos(...,'type')

designs either a normal raised cosine filter or a square root raised cosine filter depending on the type specification, which can be

normal, for a regular raised cosine filter. This is the default, and is also in effect when the 'type' argument is left empty, [].
sqrt, for a square root raised cosine filter.

b = firrcos(...,'type',delay)

specifies an integer delay in the range [0,n+1]. The default is n/2 for even n and (n+1)/2 for odd n.

b = firrcos(...,'type',delay,window)

applies a length n+1 window to the designed filter to reduce the ripple in the frequency response. window must be a n+1 long column vector. If no window is specified, a boxcar (rectangular) window is used. Care must be exercised when using a window with a delay other than the default.

[b,a] = firrcos(...)

always returns a = 1.

Example

Design an order 20 raised cosine FIR filter with cutoff frequency 0.25 of the Nyquist frequency and a transition bandwidth of 0.25:

h = firrcos(20,0.25,0.25);
freqz(h,1,'Fs',2,'phase','no')

`fir1`	Window-based finite impulse response filter design - standard response.
`fir2`	Window-based finite impulse response filter design - arbitrary response.
`firls`	Least square linear-phase FIR filter design.
`remez`	Parks-McClellan optimal FIR filter design.