Implement time-based carrier sensing

In the following events, the modem cannot switch to transmit mode for the
given time:

- after a preamble has been received, for 500 ms
- after a packet has been successfully decoded, for 1 ms
- after receive mode was initially enabled, for 500 ms

Note that the times are that long to work around the RX/TX switching of
the hackrf and can be hopefully reduced to <10 milliseconds in a later
version.
This commit is contained in:
Thomas Kolb 2022-05-07 21:17:53 +02:00
parent 886a78018f
commit c8e0516e80
5 changed files with 64 additions and 4 deletions

View file

@ -53,6 +53,7 @@ target_link_libraries(
${CMAKE_PROJECT_NAME}
libliquid.a
m
rt
fftw3f
fec
SoapySDR

View file

@ -3,6 +3,12 @@
#include <liquid/liquid.h>
/*** TIMING CONFIG ***/
#define TX_SWITCH_BACKOFF_PREAMBLE_MS 500 // only relevant if packet cannot be decoded
#define TX_SWITCH_BACKOFF_END_OF_PACKET_MS 1
#define TX_SWITCH_BACKOFF_AFTER_RX_ON 500 // time the transceiver must stay in RX mode
/*** LAYER 1 CONFIG ***/
#define SYMBOL_RATE 100e3f

View file

@ -36,6 +36,14 @@
static int m_tunfd = -1;
static bool m_running = true;
static double next_tx_switch_time = 0.0;
static void block_tx_for(unsigned offset_ms)
{
next_tx_switch_time = get_hires_time() + (double)offset_ms * 0.001;
}
void print_complex_array(const char *varname, float complex const *array, size_t len)
{
fprintf(stderr, "%s=np.array([%f%+fj", varname, crealf(array[0]), cimagf(array[0]));
@ -101,9 +109,12 @@ void cb_rx(rx_evt_t evt, uint8_t *packet_data, size_t packet_len)
break;
case RX_EVT_PACKET_RECEIVED:
fprintf(stderr, "=== DECODED PAYLOAD (%4zu bytes) ===\n", packet_len);
hexdump(packet_data, packet_len);
fprintf(stderr, "====================================\n");
fprintf(stderr, "A message of %zu bytes was decoded successfully.\n", packet_len);
//fprintf(stderr, "=== DECODED PAYLOAD (%4zu bytes) ===\n", packet_len);
//hexdump(packet_data, packet_len < 64 ? packet_len : 64);
//fprintf(stderr, "====================================\n");
block_tx_for(TX_SWITCH_BACKOFF_END_OF_PACKET_MS);
ret = write(m_tunfd, packet_data, packet_len);
if(ret < 0) {
@ -113,6 +124,7 @@ void cb_rx(rx_evt_t evt, uint8_t *packet_data, size_t packet_len)
case RX_EVT_PREAMBLE_FOUND:
fprintf(stderr, "Found preamble!\n");
block_tx_for(TX_SWITCH_BACKOFF_PREAMBLE_MS);
break;
}
}
@ -207,7 +219,9 @@ int main(void)
unsigned rx_retries = 0;
while(m_running) {
if(on_air || !layer1_rx_is_busy(&rx)) {
double now = get_hires_time();
if((now > next_tx_switch_time) && (on_air || !layer1_rx_is_busy(&rx))) {
int ret = poll(&pfd, 1, 0);
if(ret < 0) {
perror("poll");
@ -252,6 +266,8 @@ int main(void)
RESULT_CHECK(sdr_start_rx(&sdr));
on_air = false;
block_tx_for(TX_SWITCH_BACKOFF_AFTER_RX_ON);
}
}

View file

@ -1,5 +1,8 @@
#include <stdio.h>
#include <errno.h>
#include <time.h>
#include "utils.h"
bool dump_array_cf(const float complex *data, size_t n, float T, const char *filename)
@ -64,3 +67,33 @@ err_close:
fclose(f);
return false;
}
double get_hires_time(void)
{
struct timespec clk;
clock_gettime(CLOCK_MONOTONIC, &clk);
return clk.tv_sec + 1e-9 * clk.tv_nsec;
}
void fsleep(double d)
{
struct timespec ts;
ts.tv_sec = (time_t)d;
ts.tv_nsec = (long)(1e9 * (d - (long)d));
nanosleep(&ts, NULL);
}
void sleep_until(double hires_time)
{
struct timespec tv;
int ret;
tv.tv_sec = hires_time;
tv.tv_nsec = (uint64_t)(1e9 * hires_time) % 1000000000;
do {
ret = clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &tv, NULL);
} while(ret == EINTR);
}

View file

@ -24,4 +24,8 @@ bool dump_array_cf(const float complex *data, size_t n, float T, const char *fil
*/
bool dump_array_f(const float *data, size_t n, float T, const char *filename);
void sleep_until(double hires_time);
void fsleep(double d);
double get_hires_time(void);
#endif // UTILS_H