Reduce the number of samples being moved around for sync burst detection

[m17rt] / m17core / src / modem.rs

diff --git a/m17core/src/modem.rs b/m17core/src/modem.rs
index b2ab77312f62806a83150038469bbbd9c06f1d4f..b45982668aa1a492d190a4f8cc926c68fbba2e37 100644 (file)
--- a/m17core/src/modem.rs
+++ b/m17core/src/modem.rs
@@ -65,9 +65,9 @@ impl Demodulator for SoftDemodulator {
             return None;
         }
 
             return None;
         }
 

-        let mut burst_window = [0f32; 71];
-        for i in 0..71 {
-            let c = (self.rx_cursor + i) % 1920;
+        let mut burst_window = [0f32; 8];
+        for i in 0..8 {
+            let c = (self.rx_cursor + (i * 10)) % 1920;

             burst_window[i] = self.rx_win[c];
         }
 
             burst_window[i] = self.rx_win[c];
         }
 


@@ -311,12 +311,11 @@ impl SoftModulator {
         for i in 0..10 {
             // Right now we are encoding everything as 1.0-scaled dibit floats
             // This is a bit silly but it will do for a minute
         for i in 0..10 {
             // Right now we are encoding everything as 1.0-scaled dibit floats
             // This is a bit silly but it will do for a minute

-            // Max theoretical gain from the RRC filter is 4.328
-            // Let's bump everything to a baseline of 16383 / 4.328 = 3785.35
-            // This is not particularly high but at least we won't ever hit the top
+            // Max possible gain from the RRC filter with upsampling is about 0.462
+            // Let's bump everything to a baseline of 16383 / 0.462 = 35461
+            // For normal signals this yields roughly 0.5 magnitude which is plenty

             if i == 0 {
             if i == 0 {

-                // 10x the impulse with zeroes between for upsampling
-                self.filter_win[self.filter_cursor] = dibit * 3785.0 * 10.0;
+                self.filter_win[self.filter_cursor] = dibit * 35461.0;

             } else {
                 self.filter_win[self.filter_cursor] = 0.0;
             }
             } else {
                 self.filter_win[self.filter_cursor] = 0.0;
             }


@@ -420,7 +419,7 @@ impl Modulator for SoftModulator {
 
         // if we have pre-TX padding to accommodate TxDelay then expend that first
         if self.tx_delay_padding > 0 {
 
         // if we have pre-TX padding to accommodate TxDelay then expend that first
         if self.tx_delay_padding > 0 {

-            let len = out.len().max(self.tx_delay_padding);
+            let len = out.len().min(self.tx_delay_padding);

             self.tx_delay_padding -= len;
             for x in 0..len {
                 out[x] = 0;
             self.tx_delay_padding -= len;
             for x in 0..len {
                 out[x] = 0;