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Aggressive mode implemented.

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This commit is contained in:
antirez 2013-01-15 01:41:10 +01:00
parent 0bf65d8646
commit dc91712741
2 changed files with 128 additions and 33 deletions
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19
README.md
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@ -173,6 +173,25 @@ resources:
* http://www.lll.lu/~edward/edward/adsb/antenna/ADSBantenna.html
* http://modesbeast.com/pix/adsb-ant-drawing.gif
Aggressive mode
---
With --aggressive it is possible to activate the *aggressive mode* that is a
modified version of the Mode S packet detection and decoding.
THe aggresive mode uses more CPU usually (especially if there are many planes
sending DF17 packets), but can detect a few more messages.
The algorithm in aggressive mode is modified in the following ways:
* Preamble detection is weakened to be more liberal in what is consdered valid.
* Up to two demodulation errors are tolerated (adjacent entires in the magnitude
vector with the same eight). Normally only messages without errors are
checked.
* It tries to fix DF17 messages trying every two bits combination.
The use of aggressive mdoe is only advised in places where there is low traffic
in order to have a chance to capture some more messages.
Debug mode
---

142
dump1090.c
View file

@ -163,6 +163,7 @@ struct {
int stats; /* Print stats at exit in --ifile mode. */
int onlyaddr; /* Print only ICAO addresses. */
int metric; /* Use metric units. */
int aggressive; /* Aggressive detection algorithm. */
/* Interactive mode */
struct aircraft *aircrafts;
@ -174,6 +175,8 @@ struct {
long long stat_goodcrc;
long long stat_badcrc;
long long stat_fixed;
long long stat_single_bit_fix;
long long stat_two_bits_fix;
long long stat_http_requests;
} Modes;
@ -225,6 +228,8 @@ void interactiveShowData(void);
void interactiveReceiveData(struct modesMessage *mm);
void modesSendRawOutput(struct modesMessage *mm);
void useModesMessage(struct modesMessage *mm);
int fixSingleBitErrors(unsigned char *msg, int bits);
int fixTwoBitsErrors(unsigned char *msg, int bits);
/* ============================= Utility functions ========================== */
@ -259,6 +264,7 @@ void modesInitConfig(void) {
Modes.interactive = 0;
Modes.interactive_rows = MODES_INTERACTIVE_ROWS;
Modes.interactive_ttl = MODES_INTERACTIVE_TTL;
Modes.aggressive = 0;
}
void modesInit(void) {
@ -300,6 +306,8 @@ void modesInit(void) {
Modes.stat_goodcrc = 0;
Modes.stat_badcrc = 0;
Modes.stat_fixed = 0;
Modes.stat_single_bit_fix = 0;
Modes.stat_two_bits_fix = 0;
Modes.stat_http_requests = 0;
Modes.exit = 0;
}
@ -496,13 +504,22 @@ void dumpRawMessage(char *descr, unsigned char *msg,
uint16_t *m, uint32_t offset)
{
int j;
int msgtype = msg[0]>>3;
int fixable = 0;
if (msgtype == 11 || msgtype == 17) {
int msgbits = (msgtype == 11) ? MODES_SHORT_MSG_BITS :
MODES_LONG_MSG_BITS;
if (fixSingleBitErrors(msg,msgbits) != -1) fixable = 1;
else if (fixTwoBitsErrors(msg,msgbits) != -1) fixable = 2;
}
printf("\n--- %s\n ", descr);
for (j = 0; j < MODES_LONG_MSG_BYTES; j++) {
printf("%02x",msg[j]);
if (j == MODES_SHORT_MSG_BYTES-1) printf(" ... ");
}
printf("\n");
printf(" (DF %d, Fixable: %d)\n", msgtype, fixable);
dumpMagnitudeVector(m,offset);
printf("---\n\n");
}
@ -603,6 +620,44 @@ int fixSingleBitErrors(unsigned char *msg, int bits) {
return -1;
}
/* Similar to fixSingleBitErrors() but try every possible two bit combination.
* This is very slow and should be tried only against DF17 messages that
* don't pass the checksum, and only in Aggressive Mode. */
int fixTwoBitsErrors(unsigned char *msg, int bits) {
int j, i;
unsigned char aux[MODES_LONG_MSG_BITS/8];
for (j = 0; j < bits; j++) {
int byte1 = j/8;
int bitmask1 = 1 << (7-(j%8));
for (i = j+1; i < bits; i++) {
int byte2 = i/8;
int bitmask2 = 1 << (7-(i%8));
uint32_t crc1, crc2;
memcpy(aux,msg,bits/8);
aux[byte1] ^= bitmask1; /* Flip j-th bit. */
aux[byte2] ^= bitmask2; /* Flip i-th bit. */
crc1 = ((uint32_t)aux[(bits/8)-3] << 16) |
((uint32_t)aux[(bits/8)-2] << 8) |
(uint32_t)aux[(bits/8)-1];
crc2 = modesChecksum(aux,bits);
if (crc1 == crc2) {
/* The error is fixed. Overwrite the original buffer with
* the corrected sequence, and returns the error bit
* position. */
memcpy(msg,aux,bits/8);
return j | (i<<8);
}
}
}
return -1;
}
/* Hash the ICAO address to index our cache of MODES_ICAO_CACHE_LEN
* elements, that is assumed to be a power of two. */
uint32_t ICAOCacheHashAddress(uint32_t a) {
@ -823,6 +878,11 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
if ((mm->errorbit = fixSingleBitErrors(msg,mm->msgbits)) != -1) {
mm->crc = modesChecksum(msg,mm->msgbits);
mm->crcok = 1;
} else if (Modes.aggressive && mm->msgtype == 17 &&
(mm->errorbit = fixTwoBitsErrors(msg,mm->msgbits)) != -1)
{
mm->crc = modesChecksum(msg,mm->msgbits);
mm->crcok = 1;
}
}
@ -1133,35 +1193,39 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
continue;
}
/* The samples between the two spikes must be < than the average
* of the high spikes level. */
high = (m[j]+m[j+2]+m[j+7]+m[j+9])/4;
if (m[j+3] >= high ||
m[j+4] >= high ||
m[j+5] >= high ||
m[j+6] >= high)
{
if (Modes.debug == MODES_DEBUG_NOPREAMBLE &&
m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Too high level in samples between 3 and 6",
msg, m, j);
continue;
}
if (Modes.aggressive) {
/* The samples between the two spikes must be < than the average
* of the high spikes level. */
high = (m[j]+m[j+2]+m[j+7]+m[j+9])/4;
if (m[j+3] >= high ||
m[j+4] >= high ||
m[j+5] >= high ||
m[j+6] >= high)
{
if (Modes.debug == MODES_DEBUG_NOPREAMBLE &&
m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage(
"Too high level in samples between 3 and 6",
msg, m, j);
continue;
}
/* Similarly samples in the range 10-15 must be low, as it is the
* space between the preamble and real data. */
if (m[j+10] >= high ||
m[j+11] >= high ||
m[j+12] >= high ||
m[j+13] >= high ||
m[j+14] >= high ||
m[j+15] >= high)
{
if (Modes.debug == MODES_DEBUG_NOPREAMBLE &&
m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Too high level in samples between 10 and 15",
msg, m, j);
continue;
/* Similarly samples in the range 10-15 must be low, as it is the
* space between the preamble and real data. */
if (m[j+10] >= high ||
m[j+11] >= high ||
m[j+12] >= high ||
m[j+13] >= high ||
m[j+14] >= high ||
m[j+15] >= high)
{
if (Modes.debug == MODES_DEBUG_NOPREAMBLE &&
m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage(
"Too high level in samples between 10 and 15",
msg, m, j);
continue;
}
}
Modes.stat_valid_preamble++;
@ -1218,12 +1282,12 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
/* If we reached this point, and error is zero, we are very likely
* with a Mode S message in our hands, but it may still be broken
* and CRC may not be correct. This is handled by the next layer. */
if (errors == 0) {
if (errors == 0 || (Modes.aggressive && errors < 3)) {
struct modesMessage mm;
/* Decode the received message and update statistics */
decodeModesMessage(&mm,msg);
Modes.stat_demodulated++;
if (errors == 0) Modes.stat_demodulated++;
if (mm.errorbit == -1) {
if (mm.crcok)
Modes.stat_goodcrc++;
@ -1232,12 +1296,17 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
} else {
Modes.stat_badcrc++;
Modes.stat_fixed++;
if (mm.errorbit < MODES_LONG_MSG_BITS)
Modes.stat_single_bit_fix++;
else
Modes.stat_two_bits_fix++;
}
/* Output debug mode info if needed. */
if (Modes.debug == MODES_DEBUG_DEMOD)
dumpRawMessage("Demodulated with 0 errors", msg, m, j);
else if (Modes.debug == MODES_DEBUG_BADCRC && !mm.crcok)
else if (Modes.debug == MODES_DEBUG_BADCRC &&
(!mm.crcok || mm.errorbit != -1))
dumpRawMessage("Decoded with bad CRC", msg, m, j);
else if (Modes.debug == MODES_DEBUG_GOODCRC && mm.crcok &&
mm.errorbit == -1)
@ -2002,6 +2071,7 @@ void showHelp(void) {
"--net-http-port <port> HTTP server port (default: 8080).\n"
"--no-fix Disable single-bits error correction using CRC.\n"
"--no-crc-check Disable messages with broken CRC (discouraged).\n"
"--aggressive More CPU for more messages (two bits fixes, ...).\n"
"--stats With --ifile print stats at exit. No other output.\n"
"--onlyaddr Show only ICAO addresses (testing purposes).\n"
"--metric Use metric units (meters, km/h, ...).\n"
@ -2072,6 +2142,8 @@ int main(int argc, char **argv) {
Modes.onlyaddr = 1;
} else if (!strcmp(argv[j],"--metric")) {
Modes.metric = 1;
} else if (!strcmp(argv[j],"--aggressive")) {
Modes.aggressive++;
} else if (!strcmp(argv[j],"--interactive")) {
Modes.interactive = 1;
} else if (!strcmp(argv[j],"--interactive-rows")) {
@ -2153,7 +2225,11 @@ int main(int argc, char **argv) {
printf("%lld demodulated with zero errors\n", Modes.stat_demodulated);
printf("%lld with good crc\n", Modes.stat_goodcrc);
printf("%lld with bad crc\n", Modes.stat_badcrc);
printf("%lld single bit errors corrected\n", Modes.stat_fixed);
printf("%lld errors corrected\n", Modes.stat_fixed);
printf("%lld single bit errors\n", Modes.stat_single_bit_fix);
printf("%lld two bits errors\n", Modes.stat_two_bits_fix);
printf("%lld total usable messages\n",
Modes.stat_goodcrc + Modes.stat_fixed);
}
rtlsdr_close(Modes.dev);