Root Raised Cosine Filter

The Root Raised Cosine Filter blocks acts as a matched filter. Its primarily purpose is extracting a known digital signal out of noise; it does this more effectively than a low-pass filter, squelch, or other blocks.

This filter is a convenience wrapper for a FIR filter and a firdes taps generating function.

Parameters

(R): Run-time adjustable

FIR Type

options: [Complex->Complex (Decimating), Complex->Complex (Interpolating), Float->Float (Decimating), Float->Float (Interpolating)]

Decimation or Interpolation

decimation or interpolation factor (depending on which type is chosen above).

Gain (R)

Overall gain of filter (default 1.0)

Sample Rate (R)

Sample rate in samples per second.

Symbol Rate (R)

Symbol rate, must be a factor of sample rate. Typically ((samples/second) / (samples/symbol)).

Alpha (R)

Excess bandwidth factor, also known as alpha. (default: 0.35)

Num Taps (R)

Number of taps (default: 11*samp_rate)

Example Flowgraph

Frequency-Shift Keying

If you have demodulated Frequency-Shift Keying signal using a Quadrature Demod block, and you know the baud rate of the signal, and thus the duration of each symbol, the RRCS is useful for pulling these symbols out of the noise. Instead of square-wave symbols though, the RRCS produces a sinusoidal wave, rising from and falling to 0 and peaking at the center of each symbol. This result is also extremely advantageous for clock recovery, as blocks like Symbol Sync need to lock onto the center of each symbol in order to reliably extract bits. The RRCS accomplishes both steps at once.

Waveform Shaping

This flowgraph can be found at [1]. Two Root Raised Cosine Filters in series produce a Raised Cosine Filter which is used for keying waveform shaping, thereby reducing key clicks.

Source Files

C++ files

[2]

Header files

TODO

Public header files

Taps creation

Filter definition

Block definition

[3]