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Revert "[fix](trx-ais): restore adaptive AIS symbol timing"

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This reverts commit e7b38c52f7.
This commit is contained in:
Stan Grams
2026-03-02 23:56:53 +01:00
parent e7b38c52f7
commit 051d07eaab
1 changed files with 16 additions and 66 deletions
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src/decoders/trx-ais/src/lib.rs
+16 -66
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@@ -50,15 +50,10 @@ struct RawFrame {
#[derive(Debug, Clone)]
pub struct AisDecoder {
sample_rate: f32,
samples_per_symbol: f32,
sample_clock: f32,
symbol_phase: f32,
dc_state: f32,
lp_fast: f32,
lp_slow: f32,
lp_state: f32,
env_state: f32,
polarity: i8,
samples_since_transition: u32,
clock_locked: bool,
prev_raw_bit: u8,
ones: u32,
in_frame: bool,
@@ -68,18 +63,12 @@ pub struct AisDecoder {
impl AisDecoder {
pub fn new(sample_rate: u32) -> Self {
let sample_rate = sample_rate.max(1) as f32;
Self {
sample_rate,
samples_per_symbol: sample_rate / AIS_BAUD,
sample_clock: 0.0,
sample_rate: sample_rate.max(1) as f32,
symbol_phase: 0.0,
dc_state: 0.0,
lp_fast: 0.0,
lp_slow: 0.0,
lp_state: 0.0,
env_state: 1e-3,
polarity: 1,
samples_since_transition: 0,
clock_locked: false,
prev_raw_bit: 0,
ones: 0,
in_frame: false,
@@ -89,15 +78,10 @@ impl AisDecoder {
}
pub fn reset(&mut self) {
self.samples_per_symbol = self.sample_rate / AIS_BAUD;
self.sample_clock = 0.0;
self.symbol_phase = 0.0;
self.dc_state = 0.0;
self.lp_fast = 0.0;
self.lp_slow = 0.0;
self.lp_state = 0.0;
self.env_state = 1e-3;
self.polarity = 1;
self.samples_since_transition = 0;
self.clock_locked = false;
self.prev_raw_bit = 0;
self.ones = 0;
self.in_frame = false;
@@ -125,59 +109,25 @@ impl AisDecoder {
self.dc_state += 0.0025 * (sample - self.dc_state);
let dc_free = sample - self.dc_state;
// A simple band-pass-ish response makes GMSK symbol transitions stand out
// without needing a full matched filter.
self.lp_fast += 0.32 * (dc_free - self.lp_fast);
self.lp_slow += 0.045 * (dc_free - self.lp_slow);
let shaped = self.lp_fast - self.lp_slow;
// Gentle low-pass smoothing to suppress narrow impulsive noise.
self.lp_state += 0.28 * (dc_free - self.lp_state);
// Track envelope to keep the slicer stable on weak signals.
self.env_state += 0.015 * (shaped.abs() - self.env_state);
self.env_state += 0.02 * (self.lp_state.abs() - self.env_state);
let normalized = if self.env_state > 1e-4 {
shaped / self.env_state
self.lp_state / self.env_state
} else {
shaped
self.lp_state
};
let threshold = 0.12;
let next_polarity = if normalized > threshold {
1
} else if normalized < -threshold {
-1
} else {
self.polarity
};
self.samples_since_transition = self.samples_since_transition.saturating_add(1);
if next_polarity != self.polarity {
self.observe_transition();
self.polarity = next_polarity;
}
if !self.clock_locked {
return;
}
self.sample_clock += 1.0;
while self.sample_clock >= self.samples_per_symbol {
self.sample_clock -= self.samples_per_symbol;
let raw_bit = if self.polarity >= 0 { 1 } else { 0 };
self.symbol_phase += AIS_BAUD;
while self.symbol_phase >= self.sample_rate {
self.symbol_phase -= self.sample_rate;
let raw_bit = if normalized >= 0.0 { 1 } else { 0 };
self.process_symbol(raw_bit);
}
}
fn observe_transition(&mut self) {
let interval = self.samples_since_transition.max(1) as f32;
self.samples_since_transition = 0;
let nominal = (self.sample_rate / AIS_BAUD).max(1.0);
let symbols = (interval / nominal).round().clamp(1.0, 8.0);
let estimate = (interval / symbols).clamp(nominal * 0.75, nominal * 1.25);
self.samples_per_symbol += 0.18 * (estimate - self.samples_per_symbol);
self.sample_clock = self.samples_per_symbol * 0.5;
self.clock_locked = true;
}
fn process_symbol(&mut self, raw_bit: u8) {
let decoded_bit = if raw_bit == self.prev_raw_bit { 1 } else { 0 };
self.prev_raw_bit = raw_bit;