MATLAB Source Code Example for Raised Cosine Roll-Off System

The raised cosine roll-off system is commonly used in digital communication to design baseband filters that eliminate inter-symbol interference (ISI). The core concept involves balancing bandwidth efficiency and inter-symbol interference through adjustment of the roll-off factor.

The implementation approach primarily consists of three steps: Time Domain Pulse Generation: Construct time-domain waveforms satisfying zero ISI conditions according to Nyquist criteria, with key parameters including symbol period and roll-off factor α. In MATLAB, this can be implemented using the comm.RaisedCosineTransmitFilter function or custom algorithms calculating the sinc(t/T)*cos(παt/T)/(1-(2αt/T)²) formula. Frequency Domain Characteristics Calculation: The corresponding frequency response displays a unique "flat platform + sloping transition" characteristic, where the smoothness of the transition band is determined by the α value. MATLAB's freqz function can be used to analyze the frequency response. Filter Application: Apply the generated pulse response for signal shaping or matched filtering, with typical applications including QAM modulation systems. The implementation requires proper handling of filter delay and normalization.

MATLAB's Communications Toolbox provides dedicated functions like rcosdesign, but the core algorithm can also be manually implemented. Special attention should be paid to handling edge effects caused by time-domain truncation, typically improved through window functions like Hamming or Hann windows. This technology remains widely used in modern communication systems such as 4G/5G, particularly in root raised cosine designs.