itpp::Root_Raised_Cosine< T1 > Class Template Reference

(Square) Root Raised Cosine (RRC) Pulse Shaper More...

#include <itpp/comm/pulse_shape.h>

Inheritance diagram for itpp::Root_Raised_Cosine< T1 >:

Public Member Functions
	Root_Raised_Cosine ()
	Constructor.
	Root_Raised_Cosine (double roll_off_factor, int filter_length=6, int upsampling_factor=8)
	Constructor.
virtual	~Root_Raised_Cosine ()
	Destructor.
void	set_pulse_shape (double roll_off_factor, int filter_length=6, int upsampling_factor=8)
	Set pulse_shape, roll_off_factor between 0 and 1, filter_length even.
double	get_roll_off (void) const
	Get the Roll-off factor.
void	set_pulse_shape (const Vec< double > &impulse_response, int upsampling_factor)
	Set the general impulse response of the FIR filter.
Vec< double >	get_pulse_shape (void) const
	Get the pulse shape.
int	get_upsampling_factor () const
	Get the over sampling factor.
int	get_pulse_length () const
	Get the length of the pulse in number of symbols.
int	get_filter_length () const
	Get the length of the internal FIR filter.
void	shape_symbols (const Vec< T1 > &input, Vec< T1 > &output)
	Shape the input symbols performing upsampling.
Vec< T1 >	shape_symbols (const Vec< T1 > &input)
	Shape the input symbols performing upsampling.
void	shape_samples (const Vec< T1 > &input, Vec< T1 > &output)
	Shape the input samples already upsampled.
Vec< T1 >	shape_samples (const Vec< T1 > &input)
	Shape the input symbols already upsampled.
void	clear (void)
	Clear internal states.

Protected Attributes
double	roll_off_factor
	The roll off factor (i.e. alpha)
Vec< double >	impulse_response
	The impulse resounse of the pulse shaping filter.
MA_Filter< T1, double, T1 >	shaping_filter
	The pulse shaping filter.
int	pulse_length
	Length in symbols.
int	upsampling_factor
	Samples per input symbol.
bool	setup_done
	Ensures that setup is called before any other member function.

Detailed Description

template<class T1>
class itpp::Root_Raised_Cosine< T1 >

(Square) Root Raised Cosine (RRC) Pulse Shaper

Upsamples and shapes symbols as square root raised cosine pulses with a given roll-off factor (zero is not allowed

• use raised cosine instead). The Root Raised Cosine pulse shape is defined as:

  

It is called square root raised cosine since it is defined as the square root of the raised cosine pulse in the frequency domain. Thus with a transmitter pulse shape of root raised cosine and a receiver filter that is root raised cosine, the overall response will be a raised cosine.

For more details see e.g. Lee & Messerschmitt, p. 228. Observe that the shaping is done with a FIR filter where the size is given by filter_length * over_sample_factor + 1. The first samples in the output will therefore be zero or small before the memory of the filter is filled.

What is important, when using RRC shaping in a transmission system with the AWGN channel, the mean power of the output samples is not normalised, so the channel noise variance (or shaped signal) should be scaled appropriately.

The class is templated as follows: T1 is the type of the input and the output samples. An example of usage is:

#include "itpp/itcomm.h"

Root_Raised_Cosine<double> rrc(0.5,6,8);
BPSK bpsk;
vec symbols, samples;

symbols = bpsk.modulate_bits(randb(20));
samples = rrc.shape_symbols(symbols);

Definition at line 226 of file pulse_shape.h.

Member Function Documentation

void itpp::Pulse_Shape< T1, double , T1 >::set_pulse_shape ( const Vec< double > &  impulse_response, int  upsampling_factor  )

inherited

Set the general impulse response of the FIR filter.

Observe that the pulse shape must have a duration of an integer number of symbols. Thus the length of the impulse response-1 modulo over sampling is an integer.

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The documentation for this class was generated from the following file:

• itpp/comm/pulse_shape.h