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psk.hh
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psk.hh
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/*
Phase-shift keying
Copyright 2018 Ahmet Inan <[email protected]>
*/
#ifndef PSK_HH
#define PSK_HH
template <int NUM, typename TYPE, typename CODE>
struct PhaseShiftKeying;
template <typename TYPE, typename CODE>
struct PhaseShiftKeying<2, TYPE, CODE>
{
static const int NUM = 2;
static const int BITS = 1;
typedef TYPE complex_type;
typedef typename TYPE::value_type value_type;
typedef CODE code_type;
static constexpr value_type DIST = 2;
static code_type quantize(value_type precision, value_type value)
{
value *= DIST * precision;
if (std::is_integral<code_type>::value)
value = std::nearbyint(value);
if (std::is_same<code_type, int8_t>::value)
value = std::min<value_type>(std::max<value_type>(value, -128), 127);
return value;
}
static void hard(code_type *b, complex_type c)
{
b[0] = c.real() < value_type(0) ? code_type(-1) : code_type(1);
}
static void soft(code_type *b, complex_type c, value_type precision)
{
b[0] = quantize(precision, c.real());
}
static complex_type map(code_type *b)
{
return complex_type(b[0], 0);
}
};
template <typename TYPE, typename CODE>
struct PhaseShiftKeying<4, TYPE, CODE>
{
static const int NUM = 4;
static const int BITS = 2;
typedef TYPE complex_type;
typedef typename TYPE::value_type value_type;
typedef CODE code_type;
// 1/sqrt(2)
static constexpr value_type rcp_sqrt_2 = 0.70710678118654752440;
static constexpr value_type DIST = 2 * rcp_sqrt_2;
static code_type quantize(value_type precision, value_type value)
{
value *= DIST * precision;
if (std::is_integral<code_type>::value)
value = std::nearbyint(value);
if (std::is_same<code_type, int8_t>::value)
value = std::min<value_type>(std::max<value_type>(value, -128), 127);
return value;
}
static void hard(code_type *b, complex_type c)
{
b[0] = c.real() < value_type(0) ? code_type(-1) : code_type(1);
b[1] = c.imag() < value_type(0) ? code_type(-1) : code_type(1);
}
static void soft(code_type *b, complex_type c, value_type precision)
{
b[0] = quantize(precision, c.real());
b[1] = quantize(precision, c.imag());
}
static complex_type map(code_type *b)
{
return rcp_sqrt_2 * complex_type(b[0], b[1]);
}
};
template <typename TYPE, typename CODE>
struct PhaseShiftKeying<8, TYPE, CODE>
{
static const int NUM = 8;
static const int BITS = 3;
typedef TYPE complex_type;
typedef typename TYPE::value_type value_type;
typedef CODE code_type;
// c(a(1)/2)
static constexpr value_type cos_pi_8 = 0.92387953251128675613;
// s(a(1)/2)
static constexpr value_type sin_pi_8 = 0.38268343236508977173;
// 1/sqrt(2)
static constexpr value_type rcp_sqrt_2 = 0.70710678118654752440;
static constexpr value_type DIST = 2 * sin_pi_8;
static constexpr complex_type rot_cw = complex_type(cos_pi_8, -sin_pi_8);
static constexpr complex_type rot_acw = complex_type(cos_pi_8, sin_pi_8);
static code_type quantize(value_type precision, value_type value)
{
value *= DIST * precision;
if (std::is_integral<code_type>::value)
value = std::nearbyint(value);
if (std::is_same<code_type, int8_t>::value)
value = std::min<value_type>(std::max<value_type>(value, -128), 127);
return value;
}
static void hard(code_type *b, complex_type c)
{
c *= rot_cw;
b[1] = c.real() < value_type(0) ? code_type(-1) : code_type(1);
b[2] = c.imag() < value_type(0) ? code_type(-1) : code_type(1);
b[0] = std::abs(c.real()) < std::abs(c.imag()) ? code_type(-1) : code_type(1);
}
static void soft(code_type *b, complex_type c, value_type precision)
{
c *= rot_cw;
b[1] = quantize(precision, c.real());
b[2] = quantize(precision, c.imag());
b[0] = quantize(precision, rcp_sqrt_2 * (std::abs(c.real()) - std::abs(c.imag())));
}
static complex_type map(code_type *b)
{
value_type real = cos_pi_8;
value_type imag = sin_pi_8;
if (b[0] < code_type(0))
std::swap(real, imag);
return complex_type(real * b[1], imag * b[2]) * rot_acw;
}
};
#endif