rx: integrate AGC

impl/src/layer1/rx.c

@@ -1,3 +1,4 @@
+#include <liquid/liquid.h>
 #include <math.h>
 
 #include "correlator.h"
@@ -12,6 +13,9 @@
 #define HEADER_SIZE_BYTES 4
 #define FREQ_EST_L 8
 
+#define AGC_BW_ACQUISITION 2e-2
+#define AGC_BW_TRACKING    1e-4
+
 #define SHOW_DEBUG_LOG 1
 
 #if SHOW_DEBUG_LOG
@@ -22,7 +26,7 @@
 
 static void update_nco_pll(nco_crcf nco, float phase_error)
 {
-	static const float pll_alpha = 0.05f;                          // phase adjustment factor
+	static const float pll_alpha = 0.20f;                          // phase adjustment factor
 	static const float pll_beta  = (pll_alpha * pll_alpha) / 2.0f; // frequency adjustment factor
 
 	nco_crcf_adjust_phase(nco, pll_alpha * phase_error);
@@ -98,11 +102,17 @@ result_t layer1_rx_process(layer1_rx_t *rx, const float complex *samples, size_t
 	static uint8_t symbols_int[1 << 12];
 
 	for(unsigned int i = 0; i < sample_count; i++) {
+		rx_state_t last_state = rx->state;
+
+		// Apply the AGC.
+		float complex agc_out;
+		agc_crcf_execute(rx->agc, samples[i], &agc_out);
+
 		// Mix the input signal with the carrier NCO, which oscillates at the
 		// frequency coarsly estimated so far.
 		float complex mixed_sample;
 		nco_crcf_step(rx->carrier_coarse_nco);
-		nco_crcf_mix_down(rx->carrier_coarse_nco, samples[i], &mixed_sample);
+		nco_crcf_mix_down(rx->carrier_coarse_nco, agc_out, &mixed_sample);
 
 		// run the timing synchronizer (works even with shifted frequency)
 		unsigned int out_len;
@@ -118,6 +128,8 @@ result_t layer1_rx_process(layer1_rx_t *rx, const float complex *samples, size_t
 						// Preamble found and frequency corrected!
 						rx->callback(RX_EVT_PREAMBLE_FOUND, NULL, 0);
 
+						agc_crcf_set_bandwidth(rx->agc, AGC_BW_TRACKING);
+
 						// go on with decoding the header
 						rx->state = RX_STATE_HEADER;
 						symbol_counter = 0;
@@ -226,6 +238,14 @@ result_t layer1_rx_process(layer1_rx_t *rx, const float complex *samples, size_t
 					break;
 			}
 		}
+
+		if(rx->state != last_state) {
+			if(rx->state == RX_STATE_ACQUISITION) {
+				// ensure the AGC is in acquisition mode again when
+				// RX_STATE_ACQUISITION is entered.
+				agc_crcf_set_bandwidth(rx->agc, AGC_BW_ACQUISITION);
+			}
+		}
 	}
 
 	return OK;
@@ -238,6 +258,10 @@ result_t layer1_rx_init(layer1_rx_t *rx, rx_callback_t callback)
 
 	rx->state = RX_STATE_ACQUISITION;
 
+	// create the AGC
+	rx->agc = agc_crcf_create();
+	agc_crcf_set_bandwidth(rx->agc, AGC_BW_ACQUISITION);
+
 	// create NCOs for carrier frequency compensation
 	rx->carrier_coarse_nco = nco_crcf_create(LIQUID_NCO);
 	nco_crcf_set_frequency(rx->carrier_coarse_nco, 0.00f);
@@ -270,6 +294,8 @@ result_t layer1_rx_init(layer1_rx_t *rx, rx_callback_t callback)
 
 result_t layer1_rx_shutdown(layer1_rx_t *rx)
 {
+	agc_crcf_destroy(rx->agc);
+
 	nco_crcf_destroy(rx->carrier_coarse_nco);
 	nco_crcf_destroy(rx->carrier_fine_nco);
 

impl/src/layer1/rx.h

@@ -27,6 +27,9 @@ typedef void (*rx_callback_t)(rx_evt_t evt, uint8_t *packet_data, size_t packet_
 
 typedef struct
 {
+	// AGC
+	agc_crcf agc;
+
 	// NCOs for carrier frequency offset correction
 	nco_crcf carrier_coarse_nco;
 	nco_crcf carrier_fine_nco;

impl/src/main.c

@@ -32,6 +32,9 @@ void cb_rx(rx_evt_t evt, uint8_t *packet_data, size_t packet_len)
 	{
 		case RX_EVT_CHECKSUM_ERROR:
 			fprintf(stderr, "Received a message of %zu bytes, but decoding failed.\n", packet_len);
+			fprintf(stderr, "=== FAILED PAYLOAD ===\n");
+			fprintf(stderr, "%s\n", packet_data);
+			fprintf(stderr, "=======================\n");
 			break;
 
 		case RX_EVT_PACKET_RECEIVED:
@@ -68,9 +71,10 @@ int main(void)
 
 	channel_cccf channel = channel_cccf_create();
 
-	float snr = 8.0f;
+	float snr = 10.0f;
 	channel_cccf_add_awgn(channel, -snr, snr);
 	channel_cccf_add_carrier_offset(channel, 0.20f, 1.00f);
+	channel_cccf_add_shadowing(channel, 1.00f, 0.1f);
 
 	// channel
 	float complex msg_received[burst_len];
@@ -78,6 +82,12 @@ int main(void)
 	//memcpy(msg_received, whole_burst, sizeof(whole_burst)); // no noise in channel
 
 	channel_cccf_execute_block(channel, whole_burst, burst_len, msg_received);
+
+	// scale the entire signal to give the AGC something to do
+	for(size_t i = 0; i < burst_len; i++) {
+		msg_received[i] *= 0.02f;
+	}
+
 	dump_array_cf(msg_received, burst_len, 1.0f, "/tmp/rx.cpx");
 
 	// ** RX starts here **

impl/src/results.h

@@ -7,6 +7,7 @@ typedef enum {
 	ERR_NO_MEM,
 	ERR_SIZE,
 	ERR_LIQUID,
+	ERR_SYSCALL         // a syscall failed. Use errno to determine the cause.
 } result_t;
 
 #ifdef DEBUG_LIQUID