Aggressive mode implemented.
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antirez
parent
0bf65d8646
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dc91712741
19
README.md
19
README.md
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@ -173,6 +173,25 @@ resources:
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* http://www.lll.lu/~edward/edward/adsb/antenna/ADSBantenna.html
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* http://modesbeast.com/pix/adsb-ant-drawing.gif
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Aggressive mode
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---
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With --aggressive it is possible to activate the *aggressive mode* that is a
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modified version of the Mode S packet detection and decoding.
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THe aggresive mode uses more CPU usually (especially if there are many planes
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sending DF17 packets), but can detect a few more messages.
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The algorithm in aggressive mode is modified in the following ways:
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* Preamble detection is weakened to be more liberal in what is consdered valid.
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* Up to two demodulation errors are tolerated (adjacent entires in the magnitude
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vector with the same eight). Normally only messages without errors are
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checked.
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* It tries to fix DF17 messages trying every two bits combination.
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The use of aggressive mdoe is only advised in places where there is low traffic
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in order to have a chance to capture some more messages.
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Debug mode
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---
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90
dump1090.c
90
dump1090.c
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@ -163,6 +163,7 @@ struct {
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int stats; /* Print stats at exit in --ifile mode. */
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int onlyaddr; /* Print only ICAO addresses. */
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int metric; /* Use metric units. */
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int aggressive; /* Aggressive detection algorithm. */
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/* Interactive mode */
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struct aircraft *aircrafts;
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@ -174,6 +175,8 @@ struct {
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long long stat_goodcrc;
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long long stat_badcrc;
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long long stat_fixed;
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long long stat_single_bit_fix;
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long long stat_two_bits_fix;
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long long stat_http_requests;
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} Modes;
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@ -225,6 +228,8 @@ void interactiveShowData(void);
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void interactiveReceiveData(struct modesMessage *mm);
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void modesSendRawOutput(struct modesMessage *mm);
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void useModesMessage(struct modesMessage *mm);
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int fixSingleBitErrors(unsigned char *msg, int bits);
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int fixTwoBitsErrors(unsigned char *msg, int bits);
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/* ============================= Utility functions ========================== */
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@ -259,6 +264,7 @@ void modesInitConfig(void) {
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Modes.interactive = 0;
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Modes.interactive_rows = MODES_INTERACTIVE_ROWS;
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Modes.interactive_ttl = MODES_INTERACTIVE_TTL;
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Modes.aggressive = 0;
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}
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void modesInit(void) {
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@ -300,6 +306,8 @@ void modesInit(void) {
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Modes.stat_goodcrc = 0;
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Modes.stat_badcrc = 0;
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Modes.stat_fixed = 0;
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Modes.stat_single_bit_fix = 0;
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Modes.stat_two_bits_fix = 0;
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Modes.stat_http_requests = 0;
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Modes.exit = 0;
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}
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@ -496,13 +504,22 @@ void dumpRawMessage(char *descr, unsigned char *msg,
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uint16_t *m, uint32_t offset)
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{
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int j;
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int msgtype = msg[0]>>3;
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int fixable = 0;
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if (msgtype == 11 || msgtype == 17) {
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int msgbits = (msgtype == 11) ? MODES_SHORT_MSG_BITS :
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MODES_LONG_MSG_BITS;
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if (fixSingleBitErrors(msg,msgbits) != -1) fixable = 1;
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else if (fixTwoBitsErrors(msg,msgbits) != -1) fixable = 2;
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}
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printf("\n--- %s\n ", descr);
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for (j = 0; j < MODES_LONG_MSG_BYTES; j++) {
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printf("%02x",msg[j]);
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if (j == MODES_SHORT_MSG_BYTES-1) printf(" ... ");
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}
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printf("\n");
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printf(" (DF %d, Fixable: %d)\n", msgtype, fixable);
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dumpMagnitudeVector(m,offset);
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printf("---\n\n");
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}
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@ -603,6 +620,44 @@ int fixSingleBitErrors(unsigned char *msg, int bits) {
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return -1;
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}
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/* Similar to fixSingleBitErrors() but try every possible two bit combination.
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* This is very slow and should be tried only against DF17 messages that
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* don't pass the checksum, and only in Aggressive Mode. */
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int fixTwoBitsErrors(unsigned char *msg, int bits) {
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int j, i;
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unsigned char aux[MODES_LONG_MSG_BITS/8];
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for (j = 0; j < bits; j++) {
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int byte1 = j/8;
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int bitmask1 = 1 << (7-(j%8));
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for (i = j+1; i < bits; i++) {
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int byte2 = i/8;
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int bitmask2 = 1 << (7-(i%8));
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uint32_t crc1, crc2;
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memcpy(aux,msg,bits/8);
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aux[byte1] ^= bitmask1; /* Flip j-th bit. */
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aux[byte2] ^= bitmask2; /* Flip i-th bit. */
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crc1 = ((uint32_t)aux[(bits/8)-3] << 16) |
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((uint32_t)aux[(bits/8)-2] << 8) |
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(uint32_t)aux[(bits/8)-1];
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crc2 = modesChecksum(aux,bits);
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if (crc1 == crc2) {
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/* The error is fixed. Overwrite the original buffer with
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* the corrected sequence, and returns the error bit
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* position. */
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memcpy(msg,aux,bits/8);
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return j | (i<<8);
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}
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}
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}
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return -1;
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}
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/* Hash the ICAO address to index our cache of MODES_ICAO_CACHE_LEN
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* elements, that is assumed to be a power of two. */
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uint32_t ICAOCacheHashAddress(uint32_t a) {
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@ -823,6 +878,11 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
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if ((mm->errorbit = fixSingleBitErrors(msg,mm->msgbits)) != -1) {
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mm->crc = modesChecksum(msg,mm->msgbits);
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mm->crcok = 1;
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} else if (Modes.aggressive && mm->msgtype == 17 &&
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(mm->errorbit = fixTwoBitsErrors(msg,mm->msgbits)) != -1)
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{
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mm->crc = modesChecksum(msg,mm->msgbits);
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mm->crcok = 1;
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}
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}
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@ -1133,6 +1193,7 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
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continue;
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}
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if (Modes.aggressive) {
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/* The samples between the two spikes must be < than the average
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* of the high spikes level. */
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high = (m[j]+m[j+2]+m[j+7]+m[j+9])/4;
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@ -1143,7 +1204,8 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
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{
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if (Modes.debug == MODES_DEBUG_NOPREAMBLE &&
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m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
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dumpRawMessage("Too high level in samples between 3 and 6",
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dumpRawMessage(
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"Too high level in samples between 3 and 6",
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msg, m, j);
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continue;
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}
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@ -1159,10 +1221,12 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
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{
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if (Modes.debug == MODES_DEBUG_NOPREAMBLE &&
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m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
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dumpRawMessage("Too high level in samples between 10 and 15",
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dumpRawMessage(
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"Too high level in samples between 10 and 15",
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msg, m, j);
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continue;
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}
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}
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Modes.stat_valid_preamble++;
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/* Decode all the next 112 bits, regardless of the actual message
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@ -1218,12 +1282,12 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
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/* If we reached this point, and error is zero, we are very likely
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* with a Mode S message in our hands, but it may still be broken
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* and CRC may not be correct. This is handled by the next layer. */
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if (errors == 0) {
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if (errors == 0 || (Modes.aggressive && errors < 3)) {
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struct modesMessage mm;
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/* Decode the received message and update statistics */
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decodeModesMessage(&mm,msg);
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Modes.stat_demodulated++;
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if (errors == 0) Modes.stat_demodulated++;
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if (mm.errorbit == -1) {
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if (mm.crcok)
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Modes.stat_goodcrc++;
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@ -1232,12 +1296,17 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
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} else {
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Modes.stat_badcrc++;
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Modes.stat_fixed++;
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if (mm.errorbit < MODES_LONG_MSG_BITS)
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Modes.stat_single_bit_fix++;
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else
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Modes.stat_two_bits_fix++;
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}
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/* Output debug mode info if needed. */
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if (Modes.debug == MODES_DEBUG_DEMOD)
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dumpRawMessage("Demodulated with 0 errors", msg, m, j);
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else if (Modes.debug == MODES_DEBUG_BADCRC && !mm.crcok)
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else if (Modes.debug == MODES_DEBUG_BADCRC &&
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(!mm.crcok || mm.errorbit != -1))
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dumpRawMessage("Decoded with bad CRC", msg, m, j);
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else if (Modes.debug == MODES_DEBUG_GOODCRC && mm.crcok &&
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mm.errorbit == -1)
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@ -2002,6 +2071,7 @@ void showHelp(void) {
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"--net-http-port <port> HTTP server port (default: 8080).\n"
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"--no-fix Disable single-bits error correction using CRC.\n"
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"--no-crc-check Disable messages with broken CRC (discouraged).\n"
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"--aggressive More CPU for more messages (two bits fixes, ...).\n"
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"--stats With --ifile print stats at exit. No other output.\n"
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"--onlyaddr Show only ICAO addresses (testing purposes).\n"
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"--metric Use metric units (meters, km/h, ...).\n"
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@ -2072,6 +2142,8 @@ int main(int argc, char **argv) {
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Modes.onlyaddr = 1;
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} else if (!strcmp(argv[j],"--metric")) {
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Modes.metric = 1;
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} else if (!strcmp(argv[j],"--aggressive")) {
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Modes.aggressive++;
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} else if (!strcmp(argv[j],"--interactive")) {
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Modes.interactive = 1;
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} else if (!strcmp(argv[j],"--interactive-rows")) {
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@ -2153,7 +2225,11 @@ int main(int argc, char **argv) {
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printf("%lld demodulated with zero errors\n", Modes.stat_demodulated);
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printf("%lld with good crc\n", Modes.stat_goodcrc);
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printf("%lld with bad crc\n", Modes.stat_badcrc);
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printf("%lld single bit errors corrected\n", Modes.stat_fixed);
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printf("%lld errors corrected\n", Modes.stat_fixed);
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printf("%lld single bit errors\n", Modes.stat_single_bit_fix);
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printf("%lld two bits errors\n", Modes.stat_two_bits_fix);
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printf("%lld total usable messages\n",
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Modes.stat_goodcrc + Modes.stat_fixed);
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}
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rtlsdr_close(Modes.dev);
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