IT++ 4.3.1
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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 Symbols | |
(Note that these are not member symbols.) | |
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:
\[r_k = c_k s_k + n_k,\]
where \(c_k\) is the real or complex channel gain, \(s_k\) is the transmitted constellation symbol, and \(n_k\) is the AWGN of the channel (with variance \(N_0\)).
It is also assumed that the channel estimates are perfect when calculating the soft bits.
Definition at line 75 of file modulator.h.
itpp::Modulator< T >::Modulator | ( | ) |
Default constructor.
Definition at line 280 of file modulator.h.
References bitmap, bits2symbols, k, M, S0, S1, setup_done, and symbols.
itpp::Modulator< T >::Modulator | ( | const Vec< T > & | symbols, |
const ivec & | bits2symbols ) |
Constructor.
Definition at line 285 of file modulator.h.
References bits2symbols, set(), and symbols.
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inlinevirtual |
Destructor.
Definition at line 83 of file modulator.h.
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Set the constellation to use in the modulator.
Definition at line 291 of file modulator.h.
References bitmap, bits2symbols, calculate_softbit_matrices(), itpp::dec2bin(), itpp::is_even(), it_assert, k, itpp::levels2bits(), M, itpp::max(), itpp::min(), setup_done, itpp::Vec< Num_T >::size(), and symbols.
Referenced by Modulator().
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inlinevirtual |
Returns number of bits per symbol.
Definition at line 89 of file modulator.h.
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inlinevirtual |
Returns number of bits per symbol.
Definition at line 92 of file modulator.h.
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inlinevirtual |
Returns number of modulation symbols.
Definition at line 95 of file modulator.h.
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inlinevirtual |
Get the symbol values used in the modulator.
Definition at line 98 of file modulator.h.
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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.
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Modulation of symbols.
Definition at line 313 of file modulator.h.
References it_assert_debug, itpp::Vec< Num_T >::set_size(), setup_done, and symbols.
Referenced by modulate().
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Demodulation of symbols.
Definition at line 331 of file modulator.h.
References std::abs(), it_assert_debug, M, setup_done, itpp::Vec< Num_T >::size(), and symbols.
Referenced by demodulate().
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Demodulation of symbols.
Definition at line 353 of file modulator.h.
References demodulate(), and itpp::Vec< Num_T >::length().
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Modulation of bits.
Definition at line 362 of file modulator.h.
References itpp::bin2dec(), bits2symbols, it_assert_debug, it_warning, k, itpp::Vec< Num_T >::set_size(), setup_done, and symbols.
Referenced by modulate_bits().
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Modulation of bits.
Reimplemented in itpp::BPSK, and itpp::BPSK_c.
Definition at line 378 of file modulator.h.
References modulate_bits().
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Hard demodulation of bits.
Definition at line 386 of file modulator.h.
References std::abs(), bitmap, it_assert_debug, k, M, setup_done, itpp::Vec< Num_T >::size(), and symbols.
Referenced by demodulate_bits().
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Hard demodulation of bits.
Definition at line 408 of file modulator.h.
References demodulate_bits().
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Soft demodulator for AWGN channels.
This function calculates the log-likelihood ratio (LLR) of the received signal from AWGN channels. Depending on the soft demodulation method chosen, either full log-MAP calculation is performed (default method), according to the following equation:
\[\log \left( \frac{P(b_i=0|r)}{P(b_i=1|r)} \right) = \log \left( \frac{\sum_{s_i \in S_0} \exp \left( -\frac{|r_k - s_i|^2}{N_0} \right)} {\sum_{s_i \in S_1} \exp \left( -\frac{|r_k - s_i|^2}{N_0} \right)} \right) \]
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 \(d_0 = |r_k - s_0|\) denote the distance to the closest zero point and \(d_1 = |r_k - s_1|\) denote the distance to the closest one point for the corresponding bit respectively. The approximate algorithm then computes
\[\frac{d_1^2 - d_0^2}{N_0}\]
This function can be used on channels where the channel gain \(c_k = 1\).
When this function is to be used together with MAP-based turbo decoding algorithms then the channel reliability factor \(L_c\) 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 it_assert_debug, k, itpp::LOGMAP, M, S0, S1, setup_done, itpp::Vec< Num_T >::size(), itpp::sqr(), symbols, and itpp::trunc_log().
Referenced by demodulate_soft_bits(), and demodulate_soft_bits().
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Soft demodulator for AWGN channels.
Definition at line 462 of file modulator.h.
References demodulate_soft_bits().
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Soft demodulator for fading channels.
This function calculates the log-likelihood ratio (LLR) of the received signal from fading channels. Depending on the soft demodulation method chosen, either full log-MAP calculation is performed (default method), according to the following equation:
\[\log \left( \frac{P(b_i=0|r)}{P(b_i=1|r)} \right) = \log \left( \frac{\sum_{s_i \in S_0} \exp \left( -\frac{|r_k - c_k s_i|^2}{N_0} \right)} {\sum_{s_i \in S_1} \exp \left( -\frac{|r_k - c_k s_i|^2}{N_0} \right)} \right) \]
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 \(d_0 = |r_k - c_k s_0|\) denote the distance to the closest zero point and \(d_1 = |r_k - c_k s_1|\) denote the distance to the closest one point for the corresponding bit respectively. The approximate algorithm then computes
\[\frac{d_1^2 - d_0^2}{N_0}\]
When this function is to be used together with MAP-based turbo decoding algorithms then the channel reliability factor \(L_c\) 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 \(r_k\) |
channel | The channel values \(c_k\) |
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 it_assert_debug, k, itpp::LOGMAP, M, S0, S1, setup_done, itpp::Vec< Num_T >::size(), itpp::sqr(), symbols, and itpp::trunc_log().
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Soft demodulator for fading channels.
Definition at line 519 of file modulator.h.
References demodulate_soft_bits().
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Definition of 1D Modulator (with real symbols)
Definition at line 266 of file modulator.h.
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Definition of 2D Modulator (with complex symbols)
Definition at line 272 of file modulator.h.
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Setup indicator.
Definition at line 235 of file modulator.h.
Referenced by demodulate(), demodulate_bits(), demodulate_soft_bits(), demodulate_soft_bits(), modulate(), modulate_bits(), Modulator(), and set().
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Number of bits per modulation symbol.
Definition at line 237 of file modulator.h.
Referenced by calculate_softbit_matrices(), demodulate_bits(), demodulate_soft_bits(), demodulate_soft_bits(), modulate_bits(), Modulator(), and set().
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Number of modulation symbols.
Definition at line 239 of file modulator.h.
Referenced by calculate_softbit_matrices(), demodulate(), demodulate_bits(), demodulate_soft_bits(), demodulate_soft_bits(), Modulator(), and set().
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Bit to symbol mapping table (size: M x k)
Definition at line 241 of file modulator.h.
Referenced by calculate_softbit_matrices(), demodulate_bits(), Modulator(), and set().
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Bit to symbol mapping in decimal form (size: M)
Definition at line 243 of file modulator.h.
Referenced by modulate_bits(), Modulator(), Modulator(), and set().
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Corresponding modulation symbols (size: M)
Definition at line 245 of file modulator.h.
Referenced by demodulate(), demodulate_bits(), demodulate_soft_bits(), demodulate_soft_bits(), modulate(), modulate_bits(), Modulator(), Modulator(), and set().
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Matrix where row k contains the constellation points with '0' in bit position k.
Definition at line 248 of file modulator.h.
Referenced by calculate_softbit_matrices(), demodulate_soft_bits(), demodulate_soft_bits(), and Modulator().
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Matrix where row k contains the constellation points with '1' in bit position k.
Definition at line 251 of file modulator.h.
Referenced by calculate_softbit_matrices(), demodulate_soft_bits(), demodulate_soft_bits(), and Modulator().