Integrate the interleaver

impl/src/layer1/interleaver.c

@@ -1,12 +1,24 @@
+#include <math.h>
+
 #include "interleaver.h"
 
 #define INTERLEAVE_DISTANCE 16
 
-void interleaver_interleave(const float complex *in, float complex *out, size_t n)
+static size_t calculate_distance(size_t n)
+{
+	// note: benchmarking shows that this is faster than a integer-specific
+	// Newton-Raphson implementation on systems with an FPU. On amd64, sqrtf
+	// was faster by a factor of 6.
+	return ceilf(sqrtf(n));
+}
+
+void interleaver_interleave_cf(const float complex *in, float complex *out, size_t n)
 {
 	size_t interleaved_base = 0;
 	size_t interleaved_index = 0;
 
+	size_t interleave_distance = calculate_distance(n);
+
 	/* example for this algorithm with INTERLEAVE_DISTANCE = 5:
 	 * original: abcdefghijklmn
 	 * output:   adgjmbehkncfil
@@ -14,7 +26,7 @@ void interleaver_interleave(const float complex *in, float complex *out, size_t
 	for(size_t orig_index = 0; orig_index < n; orig_index++) {
 		out[interleaved_index] = in[orig_index];
 
-		interleaved_index += INTERLEAVE_DISTANCE;
+		interleaved_index += interleave_distance;
 		if(interleaved_index >= n) {
 			interleaved_base++;
 			interleaved_index = interleaved_base;
@@ -22,15 +34,58 @@ void interleaver_interleave(const float complex *in, float complex *out, size_t
 	}
 }
 
-void interleaver_deinterleave(const float complex *in, float complex *out, size_t n)
+void interleaver_deinterleave_cf(const float complex *in, float complex *out, size_t n)
 {
 	size_t interleaved_base = 0;
 	size_t interleaved_index = 0;
 
+	size_t interleave_distance = calculate_distance(n);
+
 	for(size_t orig_index = 0; orig_index < n; orig_index++) {
 		out[orig_index] = in[interleaved_index];
 
-		interleaved_index += INTERLEAVE_DISTANCE;
+		interleaved_index += interleave_distance;
+		if(interleaved_index >= n) {
+			interleaved_base++;
+			interleaved_index = interleaved_base;
+		}
+	}
+}
+
+
+void interleaver_interleave_u8(const uint8_t *in, uint8_t *out, size_t n)
+{
+	size_t interleaved_base = 0;
+	size_t interleaved_index = 0;
+
+	size_t interleave_distance = calculate_distance(n);
+
+	/* example for this algorithm with INTERLEAVE_DISTANCE = 5:
+	 * original: abcdefghijklmn
+	 * output:   adgjmbehkncfil
+	 */
+	for(size_t orig_index = 0; orig_index < n; orig_index++) {
+		out[interleaved_index] = in[orig_index];
+
+		interleaved_index += interleave_distance;
+		if(interleaved_index >= n) {
+			interleaved_base++;
+			interleaved_index = interleaved_base;
+		}
+	}
+}
+
+void interleaver_deinterleave_u8(const uint8_t *in, uint8_t *out, size_t n)
+{
+	size_t interleaved_base = 0;
+	size_t interleaved_index = 0;
+
+	size_t interleave_distance = calculate_distance(n);
+
+	for(size_t orig_index = 0; orig_index < n; orig_index++) {
+		out[orig_index] = in[interleaved_index];
+
+		interleaved_index += interleave_distance;
 		if(interleaved_index >= n) {
 			interleaved_base++;
 			interleaved_index = interleaved_base;

impl/src/layer1/interleaver.h

@@ -3,9 +3,12 @@
 
 #include <complex.h>
 #include <stddef.h>
+#include <stdint.h>
 
-void interleaver_interleave(const float complex *in, float complex *out, size_t n);
+void interleaver_interleave_cf(const float complex *in, float complex *out, size_t n);
+void interleaver_deinterleave_cf(const float complex *in, float complex *out, size_t n);
 
-void interleaver_deinterleave(const float complex *in, float complex *out, size_t n);
+void interleaver_interleave_u8(const uint8_t *in, uint8_t *out, size_t n);
+void interleaver_deinterleave_u8(const uint8_t *in, uint8_t *out, size_t n);
 
 #endif // INTERLEAVER_H

impl/src/layer1/packet_mod.c

@@ -2,6 +2,7 @@
 #include <string.h>
 
 #include "whitening.h"
+#include "interleaver.h"
 #include "preamble.h"
 #include "config.h"
 
@@ -133,6 +134,7 @@ result_t packet_mod_modulate(packet_mod_ctx_t *ctx)
 	unsigned int nsyms = (ctx->length * 8 + bps/2) / bps;
 
 	unsigned char msg_sym_idcs[nsyms];
+	unsigned char msg_sym_idcs_interleaved[nsyms];
 
 	float complex *msg_mod = malloc(sizeof(float complex) * nsyms);
 	if(!msg_mod) {
@@ -142,8 +144,11 @@ result_t packet_mod_modulate(packet_mod_ctx_t *ctx)
 
 	ERR_CHECK_LIQUID(liquid_repack_bytes(ctx->pkt_bytes, 8, ctx->length, msg_sym_idcs, bps, nsyms, &nsyms));
 
+	// interleave the message symbols
+	interleaver_interleave_u8(msg_sym_idcs, msg_sym_idcs_interleaved, nsyms);
+
 	for(size_t i = 0; i < nsyms; i++) {
-		ERR_CHECK_LIQUID(modem_modulate(payload_modem, msg_sym_idcs[i], &msg_mod[i]));
+		ERR_CHECK_LIQUID(modem_modulate(payload_modem, msg_sym_idcs_interleaved[i], &msg_mod[i]));
 	}
 
 	modem_destroy(payload_modem);

impl/src/layer1/rx.c

@@ -12,6 +12,7 @@
 #include "preamble.h"
 #include "freq_est.h"
 #include "whitening.h"
+#include "interleaver.h"
 
 #include "config.h"
 #include "options.h"
@@ -465,8 +466,12 @@ result_t layer1_rx_process(layer1_rx_t *rx, const float complex *samples, size_t
 						rx->packet_debug_info.data_rssi = agc_crcf_get_rssi(rx->agc);
 						rx->packet_debug_info.data_evm = -1e38f; // FIXME
 
+						// deinterleave the message symbols
+						uint8_t symbols_int_deinterleaved[rx->payload_len_symbols];
+						interleaver_deinterleave_u8(symbols_int, symbols_int_deinterleaved, rx->payload_len_symbols);
+
 						ERR_CHECK_LIQUID(liquid_repack_bytes(
-									symbols_int, modem_get_bps(rx->payload_demod), rx->payload_len_symbols,
+									symbols_int_deinterleaved, modem_get_bps(rx->payload_demod), rx->payload_len_symbols,
 									payload_enc, 8, sizeof(payload_enc), &nsyms));
 
 						fec payload_fec = modcod_create_fec(rx->modcod);

impl/test/CMakeLists.txt

@@ -214,4 +214,5 @@ add_executable(
 
 target_link_libraries(
 	test_interleaver
+	m
 )

impl/test/test_interleaver.c

@@ -16,8 +16,8 @@ int main(void)
 		orig[i] = (float complex)i;
 	}
 
-	interleaver_interleave(orig, interleaved, N);
+	interleaver_interleave_cf(orig, interleaved, N);
-	interleaver_deinterleave(interleaved, deinterleaved, N);
+	interleaver_deinterleave_cf(interleaved, deinterleaved, N);
 
 	for(size_t i = 0; i < N; i++) {
 		printf("%5zu %5.1f %5.1f %5.1f\n", i, crealf(orig[i]), crealf(interleaved[i]), crealf(deinterleaved[i]));