File ppe_core.h¶

FileList > inc > ppe > ppe_core.h

Feedforward polynomial-phase estimator (frequency + chirp rate). More...

#include "clib_common.h"
#include "jm_perf.h"
#include "fft/fft_core.h"
#include "spectral/spectral_core.h"
#include <complex.h>

Classes¶

Type	Name
struct	ppe_result_t Polynomial-phase estimate (one search).
struct	ppe_state_t PolyPhaseEstimator state (FFT plan + rate grid + scratch).

Public Functions¶

Type	Name
ppe_state_t *	ppe_create (size_t max_len, double max_rate) Create a polynomial-phase estimator.
void	ppe_destroy (ppe_state_t * state) Destroy an estimator.
ppe_result_t	ppe_estimate (ppe_state_t * state, const float complex * in, size_t n_in) Estimate (frequency, chirp rate) of `in` via the coherent surface.
void	ppe_reset (ppe_state_t * state) No-op (the estimator carries no running state).

Detailed Description¶

Estimates the normalized frequency f (cycles/sample) and chirp rate r (cycles/sample^2) of a complex sequence by a coherent 2-D matched-filter search. For each chirp-rate hypothesis r_i in [-max_rate, +max_rate] the sequence is dechirped (multiplied by exp(-j*pi*r_i*m^2)) and FFT-ed; the resulting (chirp-rate x frequency) surface peaks at the true (r, f), refined sub-bin in both axes by parabolic interpolation. Being fully coherent it is the matched-filter-optimal estimator (holds at low SNR), and it collapses to a single FFT — pure Doppler — when max_rate = 0. One knob therefore spans near-static Doppler through severe LEO chirp.

The caller strips modulation first: data-aided (multiply by conj of the known symbols) keeps full SNR; non-data-aided raises an M-PSK stream to the M-th power (BPSK: square) — which doubles f and r, so the caller halves them.

Stateless by-value analyzer (the measure-suite pattern). Composes fft_core + the spectral_core window / find_peaks free functions.

ppe_state_t *p = ppe_create(4096, 0.0);     // Doppler only (single FFT)
ppe_result_t e = ppe_estimate(p, y, n);     // e.freq_norm, e.rate_norm
ppe_destroy(p);

Public Functions Documentation¶

function ppe_create¶

Create a polynomial-phase estimator.

ppe_state_t * ppe_create (
    size_t max_len,
    double max_rate
)

Parameters:

max_len Maximum input sequence length (>= 4).
max_rate Chirp-rate search half-span (cycles/sample^2); 0 searches frequency only (a single FFT — near-static Doppler).

Returns:

Heap state, or NULL on bad args / allocation failure.

function ppe_destroy¶

Destroy an estimator.

void ppe_destroy (
    ppe_state_t * state
)

Parameters:

state May be NULL.

function ppe_estimate¶

Estimate (frequency, chirp rate) of in via the coherent surface.

ppe_result_t ppe_estimate (
    ppe_state_t * state,
    const float complex * in,
    size_t n_in
)

Parameters:

state Must be non-NULL.
in Complex sequence (modulation already stripped by the caller).
n_in Length, in [4, max_len].

Returns:

The estimate; zeroed if n_in is out of range.

function ppe_reset¶

No-op (the estimator carries no running state).

void ppe_reset (
    ppe_state_t * state
)

The documentation for this class was generated from the following file native/inc/ppe/ppe_core.h