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Use matched filter for AIS GMSK demodulation demo.

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Less than optimal for plain FSK, but flexible enough to also support GFSK/GMSK. Not at all optimized for SIMD instructions, so may not perform adequately at Bluetooth/GSM rates.
This commit is contained in:
Jared Boone
2015-09-28 11:02:39 -07:00
parent a9c190b6bb
commit 0bc8f551de
2 changed files with 36 additions and 12 deletions
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firmware/baseband/proc_fsk.cpp
+12 -10
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@@ -43,7 +43,7 @@ FSKProcessor::~FSKProcessor() {
}
void FSKProcessor::configure(const FSKConfiguration new_configuration) {
demod.configure(sampling_rate, 2 * new_configuration.symbol_rate);
// TODO: Matched filter characteristics are hard-coded for the moment. YUCK!
clock_recovery.configure(sampling_rate / 4, new_configuration.symbol_rate);
access_code_correlator.configure(
new_configuration.access_code,
@@ -84,16 +84,18 @@ void FSKProcessor::execute(buffer_c8_t buffer) {
// 76.8k
const buffer_s16_t work_demod_buffer {
(int16_t*)decimator_out.p,
decimator_out.count * sizeof(*decimator_out.p) / sizeof(int16_t)
};
auto demodulated = demod.execute(channel, work_demod_buffer);
// TODO: Factor out this hidden decimation magic.
for(size_t i=0; i<demodulated.count; i+=4) {
clock_recovery(demodulated.p[i] / 32768.0f);
for(size_t i=0; i<channel.count; i+=4) {
std::complex<float> sample { channel.p[i].real(), channel.p[i].imag() };
mf_0.execute_once(sample);
if( mf_1.execute_once(sample) ) {
const auto value_0 = mf_0.get_output();
const float mag_0 = std::sqrt(value_0.real() * value_0.real() + value_0.imag() * value_0.imag());
const auto value_1 = mf_1.get_output();
const float mag_1 = std::sqrt(value_1.real() * value_1.real() + value_1.imag() * value_1.imag());
const float diff = mag_1 - mag_0;
clock_recovery(diff);
}
}
i2s::i2s0::tx_mute();