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