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.
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@ -53,6 +53,7 @@ target_link_libraries(
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${CMAKE_PROJECT_NAME}
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libliquid.a
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m
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rt
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fftw3f
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fec
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SoapySDR
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@ -3,6 +3,12 @@
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#include <liquid/liquid.h>
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/*** TIMING CONFIG ***/
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#define TX_SWITCH_BACKOFF_PREAMBLE_MS 500 // only relevant if packet cannot be decoded
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#define TX_SWITCH_BACKOFF_END_OF_PACKET_MS 1
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#define TX_SWITCH_BACKOFF_AFTER_RX_ON 500 // time the transceiver must stay in RX mode
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/*** LAYER 1 CONFIG ***/
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#define SYMBOL_RATE 100e3f
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@ -36,6 +36,14 @@
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static int m_tunfd = -1;
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static bool m_running = true;
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static double next_tx_switch_time = 0.0;
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static void block_tx_for(unsigned offset_ms)
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{
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next_tx_switch_time = get_hires_time() + (double)offset_ms * 0.001;
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}
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void print_complex_array(const char *varname, float complex const *array, size_t len)
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{
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fprintf(stderr, "%s=np.array([%f%+fj", varname, crealf(array[0]), cimagf(array[0]));
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@ -101,9 +109,12 @@ void cb_rx(rx_evt_t evt, uint8_t *packet_data, size_t packet_len)
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break;
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case RX_EVT_PACKET_RECEIVED:
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fprintf(stderr, "=== DECODED PAYLOAD (%4zu bytes) ===\n", packet_len);
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hexdump(packet_data, packet_len);
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fprintf(stderr, "====================================\n");
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fprintf(stderr, "A message of %zu bytes was decoded successfully.\n", packet_len);
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//fprintf(stderr, "=== DECODED PAYLOAD (%4zu bytes) ===\n", packet_len);
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//hexdump(packet_data, packet_len < 64 ? packet_len : 64);
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//fprintf(stderr, "====================================\n");
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block_tx_for(TX_SWITCH_BACKOFF_END_OF_PACKET_MS);
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ret = write(m_tunfd, packet_data, packet_len);
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if(ret < 0) {
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@ -113,6 +124,7 @@ void cb_rx(rx_evt_t evt, uint8_t *packet_data, size_t packet_len)
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case RX_EVT_PREAMBLE_FOUND:
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fprintf(stderr, "Found preamble!\n");
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block_tx_for(TX_SWITCH_BACKOFF_PREAMBLE_MS);
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break;
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}
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}
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@ -207,7 +219,9 @@ int main(void)
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unsigned rx_retries = 0;
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while(m_running) {
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if(on_air || !layer1_rx_is_busy(&rx)) {
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double now = get_hires_time();
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if((now > next_tx_switch_time) && (on_air || !layer1_rx_is_busy(&rx))) {
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int ret = poll(&pfd, 1, 0);
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if(ret < 0) {
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perror("poll");
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@ -252,6 +266,8 @@ int main(void)
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RESULT_CHECK(sdr_start_rx(&sdr));
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on_air = false;
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block_tx_for(TX_SWITCH_BACKOFF_AFTER_RX_ON);
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}
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}
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@ -1,5 +1,8 @@
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#include <stdio.h>
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#include <errno.h>
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#include <time.h>
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#include "utils.h"
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bool dump_array_cf(const float complex *data, size_t n, float T, const char *filename)
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@ -64,3 +67,33 @@ err_close:
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fclose(f);
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return false;
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}
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double get_hires_time(void)
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{
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struct timespec clk;
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clock_gettime(CLOCK_MONOTONIC, &clk);
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return clk.tv_sec + 1e-9 * clk.tv_nsec;
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}
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void fsleep(double d)
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{
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struct timespec ts;
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ts.tv_sec = (time_t)d;
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ts.tv_nsec = (long)(1e9 * (d - (long)d));
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nanosleep(&ts, NULL);
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}
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void sleep_until(double hires_time)
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{
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struct timespec tv;
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int ret;
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tv.tv_sec = hires_time;
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tv.tv_nsec = (uint64_t)(1e9 * hires_time) % 1000000000;
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do {
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ret = clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &tv, NULL);
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} while(ret == EINTR);
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}
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@ -24,4 +24,8 @@ bool dump_array_cf(const float complex *data, size_t n, float T, const char *fil
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*/
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bool dump_array_f(const float *data, size_t n, float T, const char *filename);
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void sleep_until(double hires_time);
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void fsleep(double d);
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double get_hires_time(void);
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#endif // UTILS_H
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