dsp.hpp

#pragma once

#include <cstddef>
#include <cstdint>

#define PI 3.1415926535897932384626433

// misc
#define SAMPLE_RATE     48000
#define CARRIER_FRQ     18000

// chirp as preamble
#define PREAM_BODY      65536
#define BUBBLE_BODY     256
#define CARRIER_BODY    65536

// symbol
#define SYMBOL_BODY     512

// fir lpf: kaiser win, fs=48k, fpass=797, fstop=1385, ripple=0.5db, attenuation=30db
#define LPF_COEF {0.000124664045870304, 0.000394491129554808, 0.000684033264406025, 0.000987636274658144, 0.00129875773563981, 0.00161006837151945, 0.00191358197480440, 0.00220081000588834, 0.00246294075623155, 0.00269103818573058, 0.00287625868804753, 0.00301007856614888, 0.00308453035540879, 0.00309244147501886, 0.00302766798995435, 0.00288532115519047, 0.00266197882592678, 0.00235587405040860, 0.00196706037968397, 0.00149754434823990, 0.000951382506173104, 0.000334737851517275, -0.000344105879776180, -0.00107477628625929, -0.00184489111416042, -0.00264018424786627, -0.00344467908143997, -0.00424090726301074, -0.00501016853377223, -0.00573283154517412, -0.00638866610825062, -0.00695720640942454, -0.00741813192144036, -0.00775166787207127, -0.00793899036943913, -0.00796262640506029, -0.00780685152858496, -0.00745806470513344, -0.00690513756126165, -0.00613972963765264, -0.00515656173229218, -0.00395364407449961, -0.00253244349732995, -0.000897998164873570, 0.000941035163123161, 0.00297239725477994, 0.00518031092360616, 0.00754563184455037, 0.0100460648536682, 0.0126564437523484, 0.0153490668162704, 0.0180940944701433, 0.0208599809557199, 0.0236139558255672, 0.0263225305825472, 0.0289520286023617, 0.0314691327512264, 0.0338414162397385, 0.0360378995537758, 0.0380295440554619, 0.0397897511720657, 0.0412948206067085, 0.0425243377685547, 0.0434615388512611, 0.0440935865044594, 0.0444117970764637, 0.0444117970764637, 0.0440935865044594, 0.0434615388512611, 0.0425243377685547, 0.0412948206067085, 0.0397897511720657, 0.0380295440554619, 0.0360378995537758, 0.0338414162397385, 0.0314691327512264, 0.0289520286023617, 0.0263225305825472, 0.0236139558255672, 0.0208599809557199, 0.0180940944701433, 0.0153490668162704, 0.0126564437523484, 0.0100460648536682, 0.00754563184455037, 0.00518031092360616, 0.00297239725477994, 0.000941035163123161, -0.000897998164873570, -0.00253244349732995, -0.00395364407449961, -0.00515656173229218, -0.00613972963765264, -0.00690513756126165, -0.00745806470513344, -0.00780685152858496, -0.00796262640506029, -0.00793899036943913, -0.00775166787207127, -0.00741813192144036, -0.00695720640942454, -0.00638866610825062, -0.00573283154517412, -0.00501016853377223, -0.00424090726301074, -0.00344467908143997, -0.00264018424786627, -0.00184489111416042, -0.00107477628625929, -0.000344105879776180, 0.000334737851517275, 0.000951382506173104, 0.00149754434823990, 0.00196706037968397, 0.00235587405040860, 0.00266197882592678, 0.00288532115519047, 0.00302766798995435, 0.00309244147501886, 0.00308453035540879, 0.00301007856614888, 0.00287625868804753, 0.00269103818573058, 0.00246294075623155, 0.00220081000588834, 0.00191358197480440, 0.00161006837151945, 0.00129875773563981, 0.000987636274658144, 0.000684033264406025, 0.000394491129554808, 0.000124664045870304}
#define LPF_LEN  132

// typedefs
typedef struct {
    union {
        float L;
        float I;
    };
    union {
        float R;
        float Q;
    };
} sample_t;

typedef enum {
    MOD_BPSK = 0, // 1 bit/sym
    MOD_QPSK = 1, // 2 bit/sym
    MOD_QAM16 = 2, // 4 bit/sym
    MOD_OFDM_BPSK = 4, // 16 bit/sym
    MOD_OFDM_QPSK = 5, // 32 bit/sym
    MOD_OFDM_QAM16 = 6, // 64 bit/sym
} mod_t;

typedef int8_t int1_t;
typedef int8_t int2_t;
typedef int8_t int4_t;

typedef union {
    int1_t bpsk;
    int2_t qpsk;
    int4_t qam16;
    int16_t ofdm_bpsk;
    int32_t ofdm_qpsk;
    int64_t ofdm_qam16;
} sym_t;

// declarations
class fir_filter {
public:
    fir_filter();
    ~fir_filter();
    void init(const float* const, int); // initialize coefficients
    void clear(); // clear z
    sample_t filter(const sample_t&);
private:
    void* data;
};

class biquad_filter {
public:
    biquad_filter();
    ~biquad_filter();
    void init(const float*);
    void clear();
    sample_t filter(const sample_t&);
private:
    void* data;
};

class ofdm_modem {
public:
    ofdm_modem();
    ~ofdm_modem();
    sample_t* const fdd;    // x16, freq-domain data
    sample_t* const tdd;    // x512, time-domain data
    void modulate(void);
    void demodulate(void);
private:
    void* data;
};

float chirp(size_t);
float fast_exp(float);