Communications Toolbox

Specifying Filters Using Input Arguments

If you have a transfer function for a raised cosine filter, then you can provide it as an input to rcosflt so that rcosflt does not design its own filter. This is useful if you want to use rcosine to design the filter once and then use the filter many times. For example, the rcosflt command below uses the 'filter' flag to indicate that the transfer function is an input argument. The input num is a vector that represents the FIR transfer function by listing its coefficients.

num = rcosine(1,8); y = rcosflt([1;0;0],1,8,'filter',num);

This syntax for rcosflt works whether num represents the transfer function for a square-root raised cosine FIR filter or an ordinary raised cosine FIR filter. For example, the code below uses a square-root raised cosine FIR filter. Only the definition of num is different.

num = rcosine(1,8,'sqrt'); y = rcosflt([1;0;0],1,8,'filter',num);

You can also use a raised cosine IIR filter. To do this, modify the fourth input argument of the rcosflt command above so that it contains the string 'iir' and provide a denominator argument. An example is below.

delay = 8;
[num,den] = rcosine(1,8,'iir',.5,delay);
y = rcosflt([1;0;0],1,8,'iir/filter',num,den,delay);

Designing Filters Automatically

Controlling the Rolloff Factor

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