Communications Toolbox

Raised Cosine Filters in Communication Systems

Raised cosine filters reduce the spectral side lobes of a transmitted signal while introducing controlled intersymbol interference. The interference is controlled in the sense that it exists only at sample times other than the original signal's sample times.

The filtered signal

• Has the same bandwidth as the original signal
• Has a higher sampling rate than the original signal
• Has a spectral rolloff that conforms to the raised cosine spectrum
• Is identical to the original signal at sample times matching those of the original signal

Typically, the receiver decimates the received signal by sampling it precisely at the sample times of the original signal. Because these are times at which the filtered signal is identical to the original signal, the receiver can recover the values of the original signal without intersymbol interference.

Designing Hilbert Transform Filters

Filtering with Raised Cosine Filters