A psk31 modulator in the works

rcbpsk.c

/* This produces raised cosine bpsk*/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

typedef struct {
	long sample_rate;
	long samples_per_symbol;
	long max_amp;
	short int* buffer;
	long buffer_size;
}	audioparams;

typedef struct {
	float baud_rate;
	float frequency;
}	comparams;

float phase = 0;

short int* bit_to_audio(audioparams aud, comparams com, char bit)
{
	/* make sure theres only one bit */
	bit &= 0x01;
	short int* buffer = (short int*)malloc(aud.samples_per_symbol*sizeof(short int));

	/* produce bpsk tones */
	float w_f = (2.0*(float)M_PI*(float)com.frequency)/((float)(aud.sample_rate));
	long i;
	if (bit == 1) {
    printf("phase: %f\nmod phase: %f\n", (phase + w_f * (float)aud.samples_per_symbol), phase );
		for (i = 0;i < aud.samples_per_symbol; i++) {
			buffer[i] = (signed short int)(aud.max_amp * sin(w_f * i + phase));
		}
		phase = fmod( (phase + w_f * (float)aud.samples_per_symbol), (2*M_PI) );

	} else if (bit == 0) {

		for (i = 0; i < aud.samples_per_symbol; i++) {
			buffer[i] = (signed short int)(aud.max_amp * -1 * sin(w_f * i + phase));
		}
		phase = fmod( (phase + w_f * (float)aud.samples_per_symbol), (2*M_PI) );
		printf("phase: %f\nmod phase: %f\n", (phase + w_f * (float)aud.samples_per_symbol), phase );

	} else {

		printf("\nSomething went horribly wrong. You shouldn't get here.\nExiting...\n");
		return 0;

	}

	/* apply raised cosine filter */
	for (i = 0; i <aud.samples_per_symbol; i++) {
		buffer[i] = buffer[i] * sin((M_PI*i)/(aud.samples_per_symbol));
	}

	return buffer;
}

short int bits_to_aud(audioparams aud, comparams com, char bits, char num_of_bits, FILE* fout)
{

	if(num_of_bits > 8){
		printf("\nError in bits_to_aud, num_of_bits must be <= 8\n");
		return 0;
	}

	short int* buffer;

	int i;
	for (i = 0; i < num_of_bits; i++) {
		char bit = 0x01 & (bits>>i);
		buffer = bit_to_audio(aud, com, bit);
		fwrite(buffer, aud.samples_per_symbol*sizeof(short int), 1, fout);
	}

	return 0;
}

int main(int argc, char* argv[])
{

	FILE* fout;
	if( (fout = fopen(argv[1], "wb")) == NULL ){
		printf("\nError opening output file.\nExiting...\n");
		return 0;
	}

	audioparams audio;
	comparams coms;

	coms.baud_rate = 31.25;
	coms.frequency = 650;

	audio.sample_rate = 8000;
	audio.samples_per_symbol = (long)floor(audio.sample_rate/coms.baud_rate);
	audio.max_amp = pow(2, (8*sizeof(short))-1);

	char bitpattern = 0xaa;
	int i;
	for(i = 0; i < 100; i++){
		bits_to_aud(audio, coms, bitpattern, (char)(sizeof(bitpattern)*8), fout);
	}

	printf("\nSample Rate: %ld\nBaudrate: %f\nFrequency: %f\nMax amplitude: %ld\nSamples Per Symbol: %ld\n", audio.sample_rate, coms.baud_rate, coms.frequency, audio.max_amp, audio.samples_per_symbol);

	return 0;
}