main: restructure state management; evaluate a found preamble

impl/src/main.c

@@ -18,6 +18,17 @@ typedef enum {
 	RX_STATE_DATA,
 } rx_state_t;
 
+
+void print_complex_array(const char *varname, float complex const *array, size_t len)
+{
+	printf("%s=np.array([%f%+fj", varname, crealf(array[0]), cimagf(array[0]));
+	for(size_t k = 1; k < len; k++) {
+		printf(", %f%+fj", crealf(array[k]), cimagf(array[k]));
+	}
+	printf("])\n");
+}
+
+
 int main(void)
 {
 	uint8_t msg_org[] = "Hello Liquid! This is the message to transmit. Hopefully it can be decoded correctly...";
@@ -28,7 +39,7 @@ int main(void)
 
 	channel_cccf channel = channel_cccf_create();
 
-	float snr = 50.0f;
+	float snr = 20.0f;
 	channel_cccf_add_awgn(channel, -snr, snr);
 	channel_cccf_add_carrier_offset(channel, 0.20f, 1.00f);
 
@@ -119,9 +130,46 @@ int main(void)
 		unsigned int out_len;
 		symsync_crcf_execute(symsync, &mixed_sample, 1, symsync_out + symsync_out_len, &out_len);
 
-		switch(rx_state) {
-			case RX_STATE_ACQUISITION:
 		if(out_len != 0) {
+			float complex corr_out;
+			switch(rx_state) {
+				// Try to acquire packets by synchronizing the frequency
+				// (symbol-independent search) and correlating the preamble.
+				case RX_STATE_ACQUISITION:
+					// preamble search
+					corr_out = correlator_step(&preamble_correlator, symsync_out[symsync_out_len]);
+
+					if(cabsf(corr_out) > 0.5f * preamble_get_symbol_count()) {
+						// Preamble found!
+						printf("Preamble found at symbol %u: %.3f > %.3f\n", i/RRC_SPS, cabsf(corr_out), 0.5f * preamble_get_symbol_count());
+
+						float mean_phase_error = correlator_get_mean_phase_deviation(&preamble_correlator);
+						float mean_frequency_error = correlator_get_mean_frequency_deviation(&preamble_correlator);
+
+						printf("Preamble phase deviation:     %.6f rad\n", mean_phase_error);
+						printf("Preamble frequency deviation: %.6f rad/symbol\n", mean_frequency_error);
+
+						// adjust the frequency and phase of the NCO with the estimations from the preamble
+						nco_crcf_adjust_frequency(carrier_nco, -mean_frequency_error / RRC_SPS);
+						nco_crcf_adjust_phase(carrier_nco, mean_phase_error);
+
+						printf("New estimated carrier frequency: %.6f\n", nco_crcf_get_frequency(carrier_nco));
+
+						float complex input_history[preamble_get_symbol_count()];
+						correlator_get_input_history(&preamble_correlator, input_history);
+
+						printf("import numpy as np\n");
+						printf("import matplotlib.pyplot as pp\n");
+						print_complex_array("pre", preamble_get_symbols(), preamble_get_symbol_count());
+						print_complex_array("recv", input_history, preamble_get_symbol_count());
+						printf("pp.plot(recv * pre.conj())\n");
+						printf("pp.show()\n");
+
+						// receive and decode the header
+						rx_state = RX_STATE_HEADER;
+					} else {
+						// preamble not found.
+
 						// for all the output samples produced, run the frequency
 						// estimator. This is an implementation that works with unknown
 						// BPSK symbols and therefore can be used during ramp-up and
@@ -166,7 +214,7 @@ int main(void)
 
 							float lms_phase_change = numerator / denominator;
 
-						float freq_adjustment = (lms_phase_change / RRC_SPS / 2) * 0.3f;
+							float freq_adjustment = (lms_phase_change / RRC_SPS / 2) * 0.5f;
 							nco_crcf_adjust_frequency(carrier_nco, freq_adjustment);
 
 							printf("Frequency adjustment: %.6f - carrier frequency: %.6f\n", freq_adjustment, nco_crcf_get_frequency(carrier_nco));
@@ -187,14 +235,6 @@ int main(void)
 				case RX_STATE_DATA:
 					break;
 			}
-
-		// preamble search
-		if(out_len != 0) {
-			float complex corr_out = correlator_step(&preamble_correlator, symsync_out[symsync_out_len]);
-
-			if(cabsf(corr_out) > 0.5f * preamble_get_symbol_count()) {
-				printf("Preamble found at sample %u: %.3f > %.3f\n", i/RRC_SPS, cabsf(corr_out), 0.5f * preamble_get_symbol_count());
-			}
 		}
 
 		symsync_out_len += out_len;