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Rework phase detector.

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Simplify calculation of gate masks.
Use entire symbol period to compute symbol value.
Correct error sign based on symbol value.
This commit is contained in:
Jared Boone 2016-06-01 15:22:21 -07:00
parent 36eefa46e7
commit 4734790518
1 changed files with 13 additions and 11 deletions
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24
firmware/baseband/phase_detector.hpp
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@ -39,30 +39,32 @@ public:
}; };
constexpr PhaseDetectorEarlyLateGate( constexpr PhaseDetectorEarlyLateGate(
const float samples_per_symbol const size_t samples_per_symbol
) : late_mask { (1U << static_cast<size_t>(std::ceil(samples_per_symbol / 2))) - 1 }, ) : sample_threshold { samples_per_symbol / 2 },
early_mask { late_mask << static_cast<size_t>(std::floor(samples_per_symbol / 2)) }, late_mask { (1UL << sample_threshold) - 1UL },
sample_bit { static_cast<size_t>(std::floor(samples_per_symbol / 2)) } early_mask { late_mask << sample_threshold }
{ {
} }
result_t operator()(const history_t symbol_history) const { result_t operator()(const history_t symbol_history) const {
static_assert(sizeof(history_t) == sizeof(unsigned long), "popcountl size mismatch");
// history = ...0111, early // history = ...0111, early
// history = ...1110, late // history = ...1110, late
const symbol_t symbol = (symbol_history >> sample_bit) & 1; const size_t late_side = __builtin_popcountl(symbol_history & late_mask);
const int late_side = __builtin_popcount(symbol_history & late_mask); const size_t early_side = __builtin_popcountl(symbol_history & early_mask);
const int early_side = __builtin_popcount(symbol_history & early_mask); const size_t total_count = late_side + early_side;
const int lateness = late_side - early_side; const auto lateness = static_cast<int>(late_side) - static_cast<int>(early_side);
const int direction = lateness; //std::min(std::max(lateness, -1), 1); const symbol_t symbol = (total_count >= sample_threshold);
const error_t error = direction; const error_t error = symbol ? -lateness : lateness;
return { symbol, error }; return { symbol, error };
} }
private: private:
const size_t sample_threshold;
const history_t late_mask; const history_t late_mask;
const history_t early_mask; const history_t early_mask;
const size_t sample_bit;
}; };
#endif/*__PHASE_DETECTOR_HPP__*/ #endif/*__PHASE_DETECTOR_HPP__*/