General modulator for 1D or 2D signal constellations. More...
#include <itpp/comm/modulator.h>
Public Member Functions  
Modulator ()  
Default constructor.  
Modulator (const Vec< T > &symbols, const ivec &bits2symbols)  
Constructor.  
virtual  ~Modulator () 
Destructor.  
virtual void  set (const Vec< T > &symbols, const ivec &bits2symbols) 
Set the constellation to use in the modulator.  
virtual int  bits_per_symbol () const 
Returns number of bits per symbol.  
virtual int  get_k () const 
Returns number of bits per symbol.  
virtual int  get_M () const 
Returns number of modulation symbols.  
virtual Vec< T >  get_symbols () const 
Get the symbol values used in the modulator.  
virtual ivec  get_bits2symbols () const 
Get the bitmap, which maps input bits into symbols.  
virtual void  modulate (const ivec &symbolnumbers, Vec< T > &output) const 
Modulation of symbols.  
virtual Vec< T >  modulate (const ivec &symbolnumbers) const 
Modulation of symbols.  
virtual void  demodulate (const Vec< T > &signal, ivec &output) const 
Demodulation of symbols.  
virtual ivec  demodulate (const Vec< T > &signal) const 
Demodulation of symbols.  
virtual void  modulate_bits (const bvec &bits, Vec< T > &output) const 
Modulation of bits.  
virtual Vec< T >  modulate_bits (const bvec &bits) const 
Modulation of bits.  
virtual void  demodulate_bits (const Vec< T > &signal, bvec &bits) const 
Hard demodulation of bits.  
virtual bvec  demodulate_bits (const Vec< T > &signal) const 
Hard demodulation of bits.  
virtual void  demodulate_soft_bits (const Vec< T > &rx_symbols, double N0, vec &soft_bits, Soft_Method method=LOGMAP) const 
Soft demodulator for AWGN channels.  
virtual vec  demodulate_soft_bits (const Vec< T > &rx_symbols, double N0, Soft_Method method=LOGMAP) const 
Soft demodulator for AWGN channels.  
virtual void  demodulate_soft_bits (const Vec< T > &rx_symbols, const Vec< T > &channel, double N0, vec &soft_bits, Soft_Method method=LOGMAP) const 
Soft demodulator for fading channels.  
virtual vec  demodulate_soft_bits (const Vec< T > &rx_symbols, const Vec< T > &channel, double N0, Soft_Method method=LOGMAP) const 
Soft demodulator for fading channels.  
Protected Member Functions  
void  calculate_softbit_matrices () 
This function calculates the soft bit mapping matrices S0 and S1.  
Protected Attributes  
bool  setup_done 
Setup indicator.  
int  k 
Number of bits per modulation symbol.  
int  M 
Number of modulation symbols.  
bmat  bitmap 
Bit to symbol mapping table (size: M x k)  
ivec  bits2symbols 
Bit to symbol mapping in decimal form (size: M)  
Vec< T >  symbols 
Corresponding modulation symbols (size: M)  
imat  S0 
Matrix where row k contains the constellation points with '0' in bit position k.  
imat  S1 
Matrix where row k contains the constellation points with '1' in bit position k.  
Related Functions  
(Note that these are not member functions.)  
typedef Modulator< double >  Modulator_1D 
Definition of 1D Modulator (with real symbols)  
typedef Modulator < std::complex< double > >  Modulator_2D 
Definition of 2D Modulator (with complex symbols)  
General modulator for 1D or 2D signal constellations.
The Modulator class is designed for modeling any kind of 1D (real) or 2D (complex) signal constellations. Therefore it is used as a base class for such modulations like PAM, PSK, QAM, etc.
The constellation of the modulator is described with two vectors. The first one contains the real or complex values representing the constellation points, whereas the other one includes the corresponding bit to symbol mapping (in the decimal from).
Beside hard demapping, this class can also perform soft demodulation. To use it properly the received symbols should be equal to:
where is the real or complex channel gain, is the transmitted constellation symbol, and is the AWGN of the channel (with variance ).
It is also assumed that the channel estimates are perfect when calculating the soft bits.
Definition at line 75 of file modulator.h.

inlinevirtual 
Get the bitmap, which maps input bits into symbols.
The mapping is done as follows. An input bit sequence in decimal notation is used for indexing the bits2symbols
table. The indexing result denotes the symbol to be used from the symbols
table, e.g.:
Definition at line 117 of file modulator.h.

virtual 
Soft demodulator for AWGN channels.
This function calculates the loglikelihood ratio (LLR) of the received signal from AWGN channels. Depending on the soft demodulation method chosen, either full logMAP calculation is performed (default method), according to the following equation:
or approximate, but faster calculation is performed.
The approximate method finds for each bit the closest constellation points that have zero and one in the corresponding position. Let denote the distance to the closest zero point and denote the distance to the closest one point for the corresponding bit respectively. The approximate algorithm then computes
This function can be used on channels where the channel gain .
When this function is to be used together with MAPbased turbo decoding algorithms then the channel reliability factor of the turbo decoder shall be set to 1. The output from this function can also be used by a Viterbi decoder using an AWGN based metric calculation function.
rx_symbols  The received noisy constellation symbols 
N0  The spectral density of the AWGN noise 
soft_bits  The soft bits calculated using the expression above 
method  The method used for demodulation (LOGMAP or APPROX) 
Modulator_ND
) instead, which is based on the QLLR (quantized) arithmetic and therefore is faster. Please note, however, that mixed use of Modulator_1D/Modulator_2D
and
Modulator_ND
is not advised. Definition at line 417 of file modulator.h.
References itpp::exp(), it_assert_debug, itpp::LOGMAP, itpp::max(), itpp::Vec< Num_T >::size(), itpp::sqr(), and itpp::trunc_log().

virtual 
Soft demodulator for fading channels.
This function calculates the loglikelihood ratio (LLR) of the received signal from fading channels. Depending on the soft demodulation method chosen, either full logMAP calculation is performed (default method), according to the following equation:
or approximate, but faster calculation is performed.
The approximate method finds for each bit the closest constellation points that have zero and one in the corresponding position. Let denote the distance to the closest zero point and denote the distance to the closest one point for the corresponding bit respectively. The approximate algorithm then computes
When this function is to be used together with MAPbased turbo decoding algorithms then the channel reliability factor of the turbo decoder shall be set to 1. The output from this function can also be used by a Viterbi decoder using an AWGN based metric calculation function.
rx_symbols  The received noisy constellation symbols 
channel  The channel values 
N0  The spectral density of the AWGN noise 
soft_bits  The soft bits calculated using the expression above 
method  The method used for demodulation (LOGMAP or APPROX) 
Modulator_1D/Modulator_2D
and
Modulator_ND
is not advised. Definition at line 472 of file modulator.h.
References itpp::exp(), it_assert_debug, itpp::LOGMAP, itpp::max(), itpp::Vec< Num_T >::size(), itpp::sqr(), and itpp::trunc_log().
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