diff --git a/impl/src/config.h b/impl/src/config.h
new file mode 100644
index 0000000..747bcaf
--- /dev/null
+++ b/impl/src/config.h
@@ -0,0 +1,16 @@
+#ifndef CONFIG_H
+#define CONFIG_H
+
+#include <liquid/liquid.h>
+
+#define CHANNEL_CODE   LIQUID_FEC_CONV_V27P34
+#define MODULATION     LIQUID_MODEM_QAM16
+
+#define HEADER_CHANNEL_CODE   LIQUID_FEC_NONE
+#define HEADER_MODULATION     LIQUID_MODEM_QPSK
+
+#define PREAMBLE_MSEQ_M       6
+#define PREAMBLE_MSEQ_POLY    LIQUID_MSEQUENCE_GENPOLY_M6
+#define PREAMBLE_MSEQ_INIT    0x00000001
+
+#endif // CONFIG_H
diff --git a/impl/src/main.c b/impl/src/main.c
new file mode 100644
index 0000000..e5d6609
--- /dev/null
+++ b/impl/src/main.c
@@ -0,0 +1,97 @@
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+#include <liquid/liquid.h>
+
+#include "utils.h"
+#include "packet_mod.h"
+#include "config.h"
+#include "preamble.h"
+
+int main(void)
+{
+	uint8_t msg_org[] = "Hello Liquid! This is the message to transmit. Hopefully it can be decoded correctly...";
+
+	fec q = fec_create(CHANNEL_CODE, NULL);
+
+	modem demod = modem_create(MODULATION);
+
+	channel_cccf channel = channel_cccf_create();
+
+	float snr = 20.0f;
+	channel_cccf_add_awgn(channel, -snr, snr);
+
+
+	unsigned int k = fec_get_enc_msg_length(CHANNEL_CODE, sizeof(msg_org));
+
+	packet_mod_ctx_t pmod;
+	packet_mod_init(&pmod);
+
+	packet_mod_set_data(&pmod, msg_org, sizeof(msg_org));
+	packet_mod_encode(&pmod);
+	packet_mod_modulate(&pmod);
+	packet_mod_add_header(&pmod);
+	packet_mod_add_preamble(&pmod);
+
+	size_t nsyms;
+	packet_mod_get_result_cf(&pmod, NULL, &nsyms); // determine number of symbols for allocation
+
+	float complex msg_mod[nsyms];
+	packet_mod_get_result_cf(&pmod, msg_mod, &nsyms); // get the data
+
+	// channel
+	float complex msg_received[nsyms];
+
+	nsyms = nsyms - 63 - 8;
+
+	//memcpy(msg_received, msg_mod, sizeof(msg_received)); // no noise in channel
+
+	dump_array_cf(msg_mod, nsyms, 1.0f, "/tmp/tx.cpx");
+	channel_cccf_execute_block(channel, msg_mod + 63 + 8, nsyms, msg_received);
+	dump_array_cf(msg_received, nsyms, 1.0f, "/tmp/rx.cpx");
+
+	// demodulate
+	unsigned int bps = modem_get_bps(demod);
+
+	unsigned char msg_demod_syms[nsyms];
+	unsigned char msg_demod[k+1];
+
+	for(size_t i = 0; i < nsyms; i++) {
+		unsigned int symbol;
+
+		modem_demodulate(demod, msg_received[i], &symbol);
+		msg_demod_syms[i] = symbol;
+	}
+
+	unsigned int received_bytes;
+	liquid_repack_bytes(msg_demod_syms, bps, nsyms, msg_demod, 8, k+1, &received_bytes);
+
+	//assert(received_bytes == k);
+
+	// decode
+	uint8_t msg_dec[sizeof(msg_org)];
+	//memcpy(msg_dec, msg_enc, sizeof(msg_dec));
+	fec_decode(q, sizeof(msg_dec), msg_demod, msg_dec);
+
+	// compare original to decoded message
+	for(size_t i = 0; i < sizeof(msg_org); i++)
+	{
+		printf("%02x  =>  %02x", msg_org[i], msg_dec[i]);
+		if(msg_org[i] != msg_dec[i]) {
+			printf("  <<< !!!\n");
+		} else {
+			printf("\n");
+		}
+	}
+
+	unsigned int bit_errors = count_bit_errors_array(msg_org, msg_dec, sizeof(msg_org));
+	printf("%u bit errors detected.\n", bit_errors);
+
+	fec_destroy(q);
+
+	modem_destroy(demod);
+
+	channel_cccf_destroy(channel);
+
+	printf("Done.\n");
+}
diff --git a/impl/src/packet_mod.c b/impl/src/packet_mod.c
new file mode 100644
index 0000000..2c37e6b
--- /dev/null
+++ b/impl/src/packet_mod.c
@@ -0,0 +1,251 @@
+#include <string.h>
+
+#include "preamble.h"
+#include "config.h"
+
+#include "packet_mod.h"
+
+result_t packet_mod_init(packet_mod_ctx_t *ctx)
+{
+	ctx->pkt_bytes = NULL;
+	ctx->pkt_symbols = NULL;
+
+	ctx->length = 0;
+
+	ctx->fec   = fec_create(CHANNEL_CODE, NULL);
+	ctx->modem = modem_create(MODULATION);
+
+	ctx->state = NOT_STARTED;
+
+	return OK;
+}
+
+
+result_t packet_mod_free(packet_mod_ctx_t *ctx)
+{
+	switch(ctx->state) {
+		case DATA_RAW:
+		case DATA_CODED:
+			free(ctx->pkt_bytes);
+			ctx->pkt_bytes = NULL;
+			break;
+
+		case DATA_MODULATED:
+		case HEADER_ADDED:
+		case PREAMBLE_ADDED:
+			free(ctx->pkt_symbols);
+			ctx->pkt_symbols = NULL;
+			break;
+
+		case NOT_STARTED:
+			// nothing to do
+			break;
+	}
+
+	ctx->state = NOT_STARTED;
+	ctx->length = 0;
+
+	fec_destroy(ctx->fec);
+	modem_destroy(ctx->modem);
+
+	return OK;
+}
+
+
+result_t packet_mod_set_data(packet_mod_ctx_t *ctx, const unsigned char *data, size_t length)
+{
+	if(ctx->state != NOT_STARTED) {
+		return ERR_INVALID_STATE;
+	}
+
+	ctx->pkt_bytes = malloc(length);
+	if(!ctx->pkt_bytes) {
+		return ERR_NO_MEM;
+	}
+
+	memcpy(ctx->pkt_bytes, data, length);
+	ctx->length = length;
+
+	ctx->state = DATA_RAW;
+
+	return OK;
+}
+
+
+result_t packet_mod_encode(packet_mod_ctx_t *ctx)
+{
+	if(ctx->state != DATA_RAW) {
+		return ERR_INVALID_STATE;
+	}
+
+	unsigned int enc_length = fec_get_enc_msg_length(CHANNEL_CODE, ctx->length);
+
+	unsigned char *enc_msg = malloc(enc_length);
+	if(!enc_msg) {
+		return ERR_NO_MEM;
+	}
+
+	ERR_CHECK_LIQUID(fec_encode(ctx->fec, ctx->length, ctx->pkt_bytes, enc_msg));
+
+	free(ctx->pkt_bytes);
+
+	ctx->pkt_bytes = enc_msg;
+	ctx->length = enc_length;
+
+	ctx->state = DATA_CODED;
+
+	return OK;
+}
+
+
+result_t packet_mod_modulate(packet_mod_ctx_t *ctx)
+{
+	if(!((ctx->state == DATA_RAW) || (ctx->state == DATA_CODED))) {
+		return ERR_INVALID_STATE;
+	}
+
+	unsigned int bps = modem_get_bps(ctx->modem);
+	unsigned int nsyms = (ctx->length * 8 + bps/2) / bps;
+
+	unsigned char msg_sym_idcs[nsyms];
+
+	float complex *msg_mod = malloc(sizeof(float complex) * nsyms);
+	if(!msg_mod) {
+		return ERR_NO_MEM;
+	}
+
+	ERR_CHECK_LIQUID(liquid_repack_bytes(ctx->pkt_bytes, 8, ctx->length, msg_sym_idcs, bps, nsyms, &nsyms));
+
+	for(size_t i = 0; i < nsyms; i++) {
+		ERR_CHECK_LIQUID(modem_modulate(ctx->modem, msg_sym_idcs[i], &msg_mod[i]));
+	}
+
+	free(ctx->pkt_bytes);
+	ctx->pkt_bytes = NULL;
+
+	ctx->pkt_symbols = msg_mod;
+	ctx->length = nsyms;
+
+	ctx->state = DATA_MODULATED;
+
+	return OK;
+}
+
+
+result_t packet_mod_add_header(packet_mod_ctx_t *ctx)
+{
+	if(ctx->state != DATA_MODULATED) {
+		return ERR_INVALID_STATE;
+	}
+
+	if(ctx->length >= (1 << 16)) {
+		// packet length cannot be stored in the uint16_t in the header.
+		return ERR_SIZE;
+	}
+
+	// build the header. All field are transferred in network byte order (big endian).
+	uint8_t header[4];
+
+	// set length
+	header[0] = (ctx->length >> 8) & 0xFF;
+	header[1] = (ctx->length >> 0) & 0xFF;
+	// set raw data CRC
+	header[2] = (ctx->raw_data_crc >> 8) & 0xFF;
+	header[3] = (ctx->raw_data_crc >> 0) & 0xFF;
+
+	// the header is coded and modulated differently than the data.
+	fec   hdr_fec   = fec_create(HEADER_CHANNEL_CODE, NULL);
+	modem hdr_modem = modem_create(HEADER_MODULATION);
+
+	// encode the header
+	unsigned int hdr_enc_length = fec_get_enc_msg_length(HEADER_CHANNEL_CODE, ctx->length);
+	unsigned char header_encoded[hdr_enc_length];
+
+	ERR_CHECK_LIQUID(fec_encode(hdr_fec, sizeof(header), header, header_encoded));
+
+	// modulate the header
+	unsigned int bps = modem_get_bps(hdr_modem);
+	unsigned int nsyms = (hdr_enc_length * 8 + bps/2) / bps;
+
+	unsigned char header_sym_idcs[nsyms];
+	float complex header_mod[nsyms];
+
+	ERR_CHECK_LIQUID(liquid_repack_bytes(header_encoded, 8, hdr_enc_length, header_sym_idcs, bps, nsyms, &nsyms));
+
+	for(size_t i = 0; i < nsyms; i++) {
+		ERR_CHECK_LIQUID(modem_modulate(hdr_modem, header_sym_idcs[i], &header_mod[i]));
+	}
+
+	// concatenate the modulated header and message
+	size_t packet_length_with_header = ctx->length + nsyms;
+	float complex *packet_with_header = malloc(sizeof(float complex) * packet_length_with_header);
+	if(!packet_with_header) {
+		return ERR_NO_MEM;
+	}
+
+	memcpy(packet_with_header, header_mod, sizeof(float complex) * nsyms);
+	memcpy(packet_with_header+nsyms, ctx->pkt_symbols, sizeof(float complex) * ctx->length);
+
+	// replace the data in the context struct
+	free(ctx->pkt_symbols);
+
+	ctx->pkt_symbols = packet_with_header;
+	ctx->length = packet_length_with_header;
+
+	ctx->state = HEADER_ADDED;
+
+	return OK;
+}
+
+
+result_t packet_mod_add_preamble(packet_mod_ctx_t *ctx)
+{
+	if(ctx->state != HEADER_ADDED) {
+		return ERR_INVALID_STATE;
+	}
+
+	// concatenate the preamble with the message
+	size_t pre_length = preamble_get_symbol_count();
+
+	size_t packet_length_with_preamble = ctx->length + pre_length;
+	float complex *packet_with_preamble = malloc(sizeof(float complex) * packet_length_with_preamble);
+	if(!packet_with_preamble) {
+		return ERR_NO_MEM;
+	}
+
+	memcpy(packet_with_preamble, preamble_get_symbols(), sizeof(float complex) * pre_length);
+	memcpy(packet_with_preamble+pre_length, ctx->pkt_symbols, sizeof(float complex) * ctx->length);
+
+	// replace the data in the context struct
+	free(ctx->pkt_symbols);
+
+	ctx->pkt_symbols = packet_with_preamble;
+	ctx->length = packet_length_with_preamble;
+
+	ctx->state = PREAMBLE_ADDED;
+
+	return OK;
+}
+
+
+result_t packet_mod_get_result_cf(packet_mod_ctx_t *ctx, float complex *data, size_t *length)
+{
+	if(!((ctx->state == DATA_MODULATED) || (ctx->state == HEADER_ADDED) || (ctx->state == PREAMBLE_ADDED))) {
+		return ERR_INVALID_STATE;
+	}
+
+	if(!data) {
+		// data is NULL, so we only return the required length
+		*length = ctx->length;
+		return OK;
+	}
+
+	if(*length < ctx->length) {
+		return ERR_NO_MEM;
+	}
+
+	*length = ctx->length;
+	memcpy(data, ctx->pkt_symbols, *length * sizeof(float complex));
+
+	return OK;
+}
diff --git a/impl/src/packet_mod.h b/impl/src/packet_mod.h
new file mode 100644
index 0000000..22a4637
--- /dev/null
+++ b/impl/src/packet_mod.h
@@ -0,0 +1,51 @@
+#ifndef PACKET_MOD
+#define PACKET_MOD
+
+#include <stdlib.h>
+#include <complex.h>
+
+#include <liquid/liquid.h>
+
+#include "results.h"
+
+typedef enum
+{
+	NOT_STARTED,
+	DATA_RAW,
+	DATA_CODED,
+	DATA_MODULATED,
+	HEADER_ADDED,
+	PREAMBLE_ADDED,
+} packet_mod_state_t;
+
+typedef struct
+{
+	unsigned char *pkt_bytes;
+	float complex *pkt_symbols;
+
+	packet_mod_state_t state;
+
+	modem modem;
+	fec   fec;
+
+	uint16_t raw_data_crc;
+
+	size_t length;
+} packet_mod_ctx_t;
+
+
+result_t packet_mod_init(packet_mod_ctx_t *ctx);
+result_t packet_mod_free(packet_mod_ctx_t *ctx);
+
+result_t packet_mod_set_data(packet_mod_ctx_t *ctx, const unsigned char *data, size_t length);
+result_t packet_mod_encode(packet_mod_ctx_t *ctx);
+result_t packet_mod_modulate(packet_mod_ctx_t *ctx);
+result_t packet_mod_add_header(packet_mod_ctx_t *ctx);
+result_t packet_mod_add_preamble(packet_mod_ctx_t *ctx);
+
+result_t packet_mod_dump(packet_mod_ctx_t *ctx, const char *filename);
+
+result_t packet_mod_get_result_b(packet_mod_ctx_t *ctx, unsigned char *data, size_t *length);
+result_t packet_mod_get_result_cf(packet_mod_ctx_t *ctx, float complex *data, size_t *length);
+
+#endif // PACKET_MOD
diff --git a/impl/src/preamble.c b/impl/src/preamble.c
new file mode 100644
index 0000000..07c8638
--- /dev/null
+++ b/impl/src/preamble.c
@@ -0,0 +1,37 @@
+#include <stdbool.h>
+
+#include "config.h"
+
+#include "preamble.h"
+
+#define PREAMBLE_LEN ((1 << PREAMBLE_MSEQ_M) - 1)
+
+static float complex symbol_cache[PREAMBLE_LEN];
+static bool          symbol_cache_initialized = false;
+
+const float complex* preamble_get_symbols(void)
+{
+	if(!symbol_cache_initialized) {
+		msequence mseq = msequence_create(
+				PREAMBLE_MSEQ_M,
+				PREAMBLE_MSEQ_POLY,
+				PREAMBLE_MSEQ_INIT);
+
+		for(unsigned i = 0; i < PREAMBLE_LEN; i++) {
+			unsigned int bit = msequence_advance(mseq);
+			symbol_cache[i] = bit ? 1.0f : -1.0f;
+		}
+
+		msequence_destroy(mseq);
+
+		symbol_cache_initialized = true;
+	}
+
+	return symbol_cache;
+}
+
+
+size_t preamble_get_symbol_count(void)
+{
+	return PREAMBLE_LEN;
+}
diff --git a/impl/src/preamble.h b/impl/src/preamble.h
new file mode 100644
index 0000000..aecd71d
--- /dev/null
+++ b/impl/src/preamble.h
@@ -0,0 +1,10 @@
+#ifndef PREAMBLE_H
+#define PREAMBLE_H
+
+#include <stdlib.h>
+#include <complex.h>
+
+const float complex* preamble_get_symbols(void);
+size_t               preamble_get_symbol_count(void);
+
+#endif // PREAMBLE_H
diff --git a/impl/src/results.h b/impl/src/results.h
new file mode 100644
index 0000000..fc8df70
--- /dev/null
+++ b/impl/src/results.h
@@ -0,0 +1,27 @@
+#ifndef RESULTS_H
+#define RESULTS_H
+
+typedef enum {
+	OK,
+	ERR_INVALID_STATE,
+	ERR_NO_MEM,
+	ERR_SIZE,
+	ERR_LIQUID,
+} result_t;
+
+#ifdef DEBUG_LIQUID
+#include <stdio.h>
+
+#   define ERR_CHECK_LIQUID(call) \
+	do { \
+		liquid_error_code result; \
+		if((result = (call)) != LIQUID_OK) { \
+			fprintf(stderr, "Liquid call failed in %s:%d: %s\n", __FILE__, __LINE__, liquid_error_info(result)); \
+			return ERR_LIQUID; \
+		} \
+	} while(0);
+#else
+#   define ERR_CHECK_LIQUID(call) if((call) != LIQUID_OK) { return ERR_LIQUID; }
+#endif
+
+#endif // RESULTS_H
diff --git a/impl/src/utils.c b/impl/src/utils.c
new file mode 100644
index 0000000..cdef365
--- /dev/null
+++ b/impl/src/utils.c
@@ -0,0 +1,66 @@
+#include <stdio.h>
+
+#include "utils.h"
+
+bool dump_array_cf(const float complex *data, size_t n, float T, const char *filename)
+{
+	FILE *f = fopen(filename, "w");
+	if(!f) {
+		return false;
+	}
+
+	size_t written = fwrite("CPX_", 1, 4, f);
+	if(written != 4) {
+		goto err_close;
+	}
+
+	written = fwrite(&T, sizeof(T), 1, f);
+	if(written != 1) {
+		goto err_close;
+	}
+
+	written = fwrite(data, sizeof(data[0]), n, f);
+	if(written != n) {
+		goto err_close;
+	}
+
+	fclose(f);
+
+	return true;
+
+err_close:
+	fclose(f);
+	return false;
+}
+
+
+bool dump_array_f(const float *data, size_t n, float T, const char *filename)
+{
+	FILE *f = fopen(filename, "w");
+	if(!f) {
+		return false;
+	}
+
+	size_t written = fwrite("FLT_", 1, 4, f);
+	if(written != 4) {
+		goto err_close;
+	}
+
+	written = fwrite(&T, sizeof(T), 1, f);
+	if(written != 1) {
+		goto err_close;
+	}
+
+	written = fwrite(data, sizeof(data[0]), n, f);
+	if(written != n) {
+		goto err_close;
+	}
+
+	fclose(f);
+
+	return true;
+
+err_close:
+	fclose(f);
+	return false;
+}
diff --git a/impl/src/utils.h b/impl/src/utils.h
new file mode 100644
index 0000000..5db5ad9
--- /dev/null
+++ b/impl/src/utils.h
@@ -0,0 +1,27 @@
+#ifndef UTILS_H
+#define UTILS_H
+
+#include <stdlib.h>
+#include <stdbool.h>
+#include <liquid/liquid.h>
+
+/*! Dump a array of complex numbers.
+ *
+ * \param data      Pointer to the data to dump.
+ * \param n         Number of data points to dump.
+ * \param T         The sampling interval of the data (set to 1.0 if not relevant).
+ * \param filename  The file to write to.
+ */
+bool dump_array_cf(const float complex *data, size_t n, float T, const char *filename);
+
+
+/*! Dump a array of real numbers.
+ *
+ * \param data      Pointer to the data to dump.
+ * \param n         Number of data points to dump.
+ * \param T         The sampling interval of the data (set to 1.0 if not relevant).
+ * \param filename  The file to write to.
+ */
+bool dump_array_f(const float *data, size_t n, float T, const char *filename);
+
+#endif // UTILS_H