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Enhancements to clock recovery

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Linearly interpolate input and delayed samples, based on phase of internal symbol clock.
This commit is contained in:
Jared Boone 2015-09-02 19:19:43 -07:00
parent 144b121b0e
commit 934936d3f6
1 changed files with 10 additions and 3 deletions
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13
firmware/baseband/clock_recovery.hpp
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@ -38,13 +38,15 @@ public:
) { ) {
const bool phase_0 = (phase_last >> 31) & (!(phase >> 31)); const bool phase_0 = (phase_last >> 31) & (!(phase >> 31));
const bool phase_180 = (!(phase_last >> 31)) & (phase >> 31); const bool phase_180 = (!(phase_last >> 31)) & (phase >> 31);
phase_last = phase;
phase += phase_increment + phase_adjustment;
if( phase_0 || phase_180 ) { if( phase_0 || phase_180 ) {
t2 = t1; t2 = t1;
t1 = t0; t1 = t0;
t0 = in;
const uint32_t phase_boundary = phase_180 ? (1U << 31) : 0;
const float alpha = (phase_boundary - phase_last) / float(phase_increment + phase_adjustment);
const float t = last_sample + alpha * (in - last_sample);
t0 = t;
} }
if( phase_0 ) { if( phase_0 ) {
@ -59,6 +61,10 @@ public:
// Correct phase (don't change frequency!) // Correct phase (don't change frequency!)
phase_adjustment = -phase_increment * error_filtered / 200.0f; phase_adjustment = -phase_increment * error_filtered / 200.0f;
} }
phase_last = phase;
phase += phase_increment + phase_adjustment;
last_sample = in;
} }
private: private:
@ -66,6 +72,7 @@ private:
uint32_t phase_last { 0 }; uint32_t phase_last { 0 };
uint32_t phase_adjustment { 0 }; uint32_t phase_adjustment { 0 };
uint32_t phase_increment { 0 }; uint32_t phase_increment { 0 };
float last_sample { 0 };
float t0 { 0 }; float t0 { 0 };
float t1 { 0 }; float t1 { 0 };
float t2 { 0 }; float t2 { 0 };