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hackrf_transfer: report power, not amplitude

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improve accuracy and reliability of digital signal power measurement
This commit is contained in:
Michael Ossmann
2022-09-09 05:15:15 -04:00
parent 5b4be3e078
commit 755ca960e5
1 changed files with 32 additions and 37 deletions
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69
host/hackrf-tools/src/hackrf_transfer.c
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@ -343,17 +343,8 @@ uint32_t stream_tail = 0;
uint32_t stream_drop = 0;
uint8_t* stream_buf = NULL;
/*
* To report amplitude, best would be dB(fullscale) and the variance,
* but that would require more math per sample (dB(amplitude) = log(sqrt(i^2 + q^2) and sum of squares).
* For now, just sum iabs(i)+iabs(q) and divide by the number of samples*2.
* That allows us to give a measure of dB(fullscale).
* I don't know whether overload causes wrapping or clamping the 8-bit values.
* Clamping would produce a sigmoid curve, so with a signal of variable intensity you're
* probably getting substantial overload anytime this reports more than about -6dBfs.
*/
uint64_t stream_amplitude =
0; /* sum of magnitudes of all I&Q samples, reset on the periodic report */
/* sum of power of all samples, reset on the periodic report */
volatile uint64_t stream_power = 0;
bool transmit = false;
struct timeval time_start;
@ -419,8 +410,18 @@ int rx_callback(hackrf_transfer* transfer)
return -1;
}
byte_count += transfer->valid_length;
/* Accumulate power (magnitude squared). */
bytes_to_write = transfer->valid_length;
uint64_t sum = 0;
for (i = 0; i < bytes_to_write; i++) {
int8_t value = transfer->buffer[i];
sum += value * value;
}
/* Update both running totals at approximately the same time. */
byte_count += transfer->valid_length;
stream_power += sum;
if (limit_num_samples) {
if (bytes_to_write >= bytes_to_xfer) {
bytes_to_write = bytes_to_xfer;
@ -428,11 +429,6 @@ int rx_callback(hackrf_transfer* transfer)
bytes_to_xfer -= bytes_to_write;
}
// accumulate stream_amplitude:
for (i = 0; i < bytes_to_write; i++) {
stream_amplitude += abs((signed char) transfer->buffer[i]);
}
if (receive_wav) {
/* convert .wav contents from signed to unsigned */
for (i = 0; i < bytes_to_write; i++) {
@ -487,12 +483,19 @@ int tx_callback(hackrf_transfer* transfer)
stop_main_loop();
return -1;
}
byte_count += transfer->valid_length;
/* Accumulate power (magnitude squared). */
bytes_to_read = transfer->valid_length;
uint64_t sum = 0;
for (i = 0; i < bytes_to_read; i++) {
stream_amplitude += abs((signed char) transfer->buffer[i]);
int8_t value = transfer->buffer[i];
sum += value * value;
}
/* Update both running totals at approximately the same time. */
byte_count += transfer->valid_length;
stream_power += sum;
if (file == NULL) { // transceiver_mode == TRANSCEIVER_MODE_SS
/* Transmit continuous wave with specific amplitude */
if (limit_num_samples) {
@ -1271,7 +1274,7 @@ int main(int argc, char** argv)
#endif
while ((hackrf_is_streaming(device) == HACKRF_TRUE) && (do_exit == false)) {
uint32_t byte_count_now;
uint64_t byte_count_now;
struct timeval time_now;
float time_difference, rate;
if (stream_size > 0) {
@ -1304,7 +1307,7 @@ int main(int argc, char** argv)
}
#endif
} else {
uint64_t stream_amplitude_now;
uint64_t stream_power_now;
#ifdef _WIN32
// Wait for interval timer event, or interrupt event.
HANDLE handles[] = {timer_handle, interrupt_handle};
@ -1315,13 +1318,11 @@ int main(int argc, char** argv)
#endif
gettimeofday(&time_now, NULL);
/* Read and reset both totals at approximately the same time. */
byte_count_now = byte_count;
stream_power_now = stream_power;
byte_count = 0;
stream_amplitude_now = stream_amplitude;
stream_amplitude = 0;
if (byte_count_now <
sample_rate_hz / 20) // Don't report on very short frames
stream_amplitude_now = 0;
stream_power = 0;
time_difference = TimevalDiff(&time_now, &time_start);
rate = (float) byte_count_now / time_difference;
@ -1329,21 +1330,15 @@ int main(int argc, char** argv)
hw_sync_enable != 0) {
fprintf(stderr, "Waiting for sync...\n");
} else {
// This is only an approximate measure, to assist getting receive levels right:
double full_scale_ratio =
((double) stream_amplitude_now /
(byte_count_now ? byte_count_now : 1)) /
128;
double dB_full_scale_ratio = 10 * log10(full_scale_ratio);
// Guard against ridiculous reports
if (dB_full_scale_ratio > 1)
dB_full_scale_ratio = -0.0;
double full_scale_ratio = (double) stream_power_now /
(byte_count_now * 128 * 128);
double dB_full_scale = 10 * log10(full_scale_ratio);
fprintf(stderr,
"%4.1f MiB / %5.3f sec = %4.1f MiB/second, amplitude %3.1f dBfs",
"%4.1f MiB / %5.3f sec = %4.1f MiB/second, average power %3.1f dBfs",
(byte_count_now / 1e6f),
time_difference,
(rate / 1e6f),
dB_full_scale_ratio);
dB_full_scale);
if (display_stats) {
bool tx = transmit || signalsource;
result = update_stats(device, &state, &stats);