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Added a costas loop algorithm

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ha7ilm 2017-03-29 13:09:19 +02:00
parent b1ff051dd0
commit 7590dd78ab
1 changed files with 29 additions and 22 deletions
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51
libcsdr.c
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@ -1909,36 +1909,44 @@ char* timing_recovery_get_string_from_algorithm(timing_recovery_algorithm_t algo
typedef struct bpsk_costas_loop_state_s typedef struct bpsk_costas_loop_state_s
{ {
float pll_alpha; float rc_filter_alpha;
float pll_beta; float vco_phase_addition_multiplier;
float pll_iir_temp; float vco_phase;
float pll_phase; float last_lpfi_output;
float last_lpfq_output;
} bpsk_costas_loop_state_t; } bpsk_costas_loop_state_t;
void init_bpsk_carrier_recovery_cc(bpsk_costas_loop_state_t* state) void init_bpsk_costas_loop_cc(bpsk_costas_loop_state_t* state, float samples_per_bits)
{ {
state->pll_alpha = state->pll_beta = 0; //TODO <-- state->vco_phase = 0;
state->pll_phase = 0; float virtual_sampling_rate = 10000;
state->pll_iir_temp = 0; float virtual_data_rate = virtual_sampling_rate / samples_per_bits;
float rc_filter_cutoff = virtual_data_rate/2;
float rc_filter_rc = 1/(2*M_PI*rc_filter_cutoff); //as of Equation 24 in Feigin
float virtual_sampling_dt = 1.0/virtual_sampling_rate;
state->rc_filter_alpha = virtual_sampling_dt/(rc_filter_rc+virtual_sampling_dt); //https://en.wikipedia.org/wiki/Low-pass_filter
float rc_filter_omega_cutoff = 2*M_PI*rc_filter_cutoff;
state->vco_phase_addition_multiplier = 8*rc_filter_omega_cutoff; //as of Equation 25 in Feigin, assuming input signal amplitude of 1 (to 1V) and (state->vco_phase_addition_multiplier*<vco_input>), a value in radians, will be added to the vco_phase directly.
} }
void bpsk_costas_loop_cc(complexf* input, complexf* output, int input_size, bpsk_costas_loop_state_t* state) void bpsk_costas_loop_cc(complexf* input, complexf* output, int input_size, bpsk_costas_loop_state_t* state)
{ {
complexf ejphi; //downconvert with that
for(int i=0;i<input_size;i++) for(int i=0;i<input_size;i++)
{ {
e_powj(&ejphi, -state->pll_phase); float input_phase = atan2(input[i].q, input[i].i);
cmult(&output[i], &input[i], &ejphi); float input_and_vco_mixed_phase = input_phase - state->vco_phase;
complexf input_and_vco_mixed_sample;
float error = iof(output,i) * qof(output, i); e_powj(&input_and_vco_mixed_sample, input_and_vco_mixed_phase);
if(error>2) error=2; float loop_output_i =
if(error<-2) error=-2; input_and_vco_mixed_sample.i * state->rc_filter_alpha + state->last_lpfi_output * (1-state->rc_filter_alpha);
float loop_output_q =
state->pll_phase = error * state->pll_alpha + state->pll_iir_temp; input_and_vco_mixed_sample.q * state->rc_filter_alpha + state->last_lpfq_output * (1-state->rc_filter_alpha);
state->pll_iir_temp += error * state->pll_beta; state->last_lpfi_output = loop_output_i;
state->last_lpfq_output = loop_output_q;
while(state->pll_phase>PI) state->pll_phase-=2*PI; float vco_phase_addition = loop_output_i * loop_output_q * state->vco_phase_addition_multiplier;
while(state->pll_phase<-PI) state->pll_phase+=2*PI; state->vco_phase += vco_phase_addition;
while(state->vco_phase>PI) state->vco_phase-=2*PI;
while(state->vco_phase<-PI) state->vco_phase+=2*PI;
} }
} }
@ -2029,7 +2037,6 @@ void convert_s24_f(unsigned char* input, float* output, int input_size, int bige
} }
} }
int trivial_vectorize() int trivial_vectorize()
{ {
//this function is trivial to vectorize and should pass on both NEON and SSE //this function is trivial to vectorize and should pass on both NEON and SSE