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更改IQ样本处理，时钟同步及解码方案 #2

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1 change: 1 addition & 0 deletions app/src/main/cpp/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@ add_library(${CMAKE_PROJECT_NAME} SHARED
native-lib.cpp
decodeMessage.cpp
${CMAKE_CURRENT_SOURCE_DIR}/dsp/firfilter.cpp
${CMAKE_CURRENT_SOURCE_DIR}/dsp/hbfiltertraits.cpp
native-lib.cpp)


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15 changes: 9 additions & 6 deletions app/src/main/cpp/decodeMessage.cpp
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Expand Up @@ -60,17 +60,20 @@ std::string decode_gb2312(const std::string &numeric_field) {
ParsedMessage p;
ParsedMessage parseMessage(const std::string &msg) {
// 简化：用前缀区分地址类型
if (msg.find("1234002") != std::string::npos) {
if (msg.find("1234002") != std::string::npos && msg.size() > 50) { // 越界检查
p.vehicleId = msg.substr(15, 8);
std::string routeRaw = msg.substr(25, 14);
std::string routeRaw = msg.substr(25, 16); // 一共四个字
std::string latRaw = msg.substr(50, 8);
std::string lonRaw = msg.substr(41, 9);

double latitude = std::stod(latRaw.substr(0, 2) + "." + latRaw.substr(2));
double longitude = std::stod(lonRaw.substr(0, 3) + "." + lonRaw.substr(3));
try { // 防止stod异常字符导致崩溃
double latitude = std::stod(latRaw.substr(0, 2) + "." + latRaw.substr(2));
double longitude = std::stod(lonRaw.substr(0, 3) + "." + lonRaw.substr(3));
p.latitude = std::to_string(latitude);
p.longitude = std::to_string(longitude);
} catch (const std::invalid_argument& e) {}
catch (const std::out_of_range& e) {}

p.latitude = std::to_string(latitude);
p.longitude = std::to_string(longitude);
p.route = decode_gb2312(routeRaw);
}
else if (msg.find("1234000") != std::string::npos) {
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168 changes: 92 additions & 76 deletions app/src/main/cpp/demod.cpp
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Expand Up @@ -9,14 +9,13 @@ MovingAverageUtil<double, double, 2048> preambleMovingAverage;
bool got_SC = false;
double dc_offset = 0.0;
bool prev_data, bit_inverted, data_bit;
int sync_cnt, bit_cnt = 0, word_cnt = 0;
int bit_cnt = 0, word_cnt = 0;
uint32_t bits;
uint32_t code_words[PAGERDEMOD_BATCH_WORDS];
bool code_words_bch_error[PAGERDEMOD_BATCH_WORDS];

std::string numeric_msg, alpha_msg;
std::unique_ptr<std::vector<pocsag_msg>> msg; // 这个其实有点激进，可能还有一些问题需要解决
int function_bits;
uint32_t address;
uint32_t alpha_bit_buffer; // Bit buffer to 7-bit chars spread across codewords
int alpha_bit_buffer_bits; // Count of bits in alpha_bit_buffer
int parity_errors; // Count of parity errors in current message
Expand All @@ -25,6 +24,9 @@ int batch_num; // Count of batches in current transmission

double magsqRaw;

float sym_phase = 0.0;
const float phaseinc = BAUD_RATE / SAMPLE_RATE;

int pop_cnt(uint32_t cw) {
int cnt = 0;
for (int i = 0; i < 32; i++) {
Expand Down Expand Up @@ -183,6 +185,7 @@ uint32_t reverse(uint32_t x)
void decodeBatch()
{
int i = 1;
msg = std::make_unique<std::vector<pocsag_msg>>();
for (int frame = 0; frame < PAGERDEMOD_FRAMES_PER_BATCH; frame++)
{
for (int word = 0; word < PAGERDEMOD_CODEWORDS_PER_FRAME; word++)
Expand All @@ -192,18 +195,19 @@ void decodeBatch()
// Check parity bit
bool parityError = !evenParity(code_words[i], 1, 31, code_words[i] & 0x1);

if (code_words[i] == PAGERDEMOD_POCSAG_IDLECODE)
if (pop_cnt(code_words[i] ^ PAGERDEMOD_POCSAG_IDLECODE) <= 3) // 0x7a89c196貌似也能过bch，不过好像只是错了一位的IDLE
{
// Idle
break;
}
else if (addressCodeWord)
{
// Address
msg->push_back({});
function_bits = (code_words[i] >> 11) & 0x3;
msg->back().func = function_bits;
int addressBits = (code_words[i] >> 13) & 0x3ffff;
address = (addressBits << 3) | frame;
numeric_msg = "";
alpha_msg = "";
msg->back().addr = (addressBits << 3) | frame;
alpha_bit_buffer_bits = 0;
alpha_bit_buffer = 0;
parity_errors = parityError ? 1 : 0;
Expand All @@ -212,6 +216,8 @@ void decodeBatch()
else
{
// Message - decode as both numeric and ASCII - not all operators use functionBits to indidcate encoding
if (msg->empty())
msg->push_back({});
int messageBits = (code_words[i] >> 11) & 0xfffff;
if (parityError) {
parity_errors++;
Expand All @@ -230,7 +236,7 @@ void decodeBatch()
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', 'U', ' ', '-', ')', '('
};
char numericChar = numericChars[numericBits];
numeric_msg.push_back(numericChar);
msg->back().numeric.push_back(numericChar);
}

// 7-bit ASCII alpnanumeric format
Expand All @@ -244,7 +250,7 @@ void decodeBatch()
c = reverse(c) >> (32-7);
// Add to received message string (excluding, null, end of text, end ot transmission)
if (c != 0 && c != 0x3 && c != 0x4) {
alpha_msg.push_back(c);
msg->back().alpha.push_back(c);
}
// Remove from bit buffer
alpha_bit_buffer_bits -= 7;
Expand All @@ -262,11 +268,9 @@ void decodeBatch()
}
}

void processOneSample(int8_t i, int8_t q) {
float fi = ((float) i) / 128.0f;
float fq = ((float) q) / 128.0f;
void processOneSample(float i, float q) {

std::complex<float> iq(fi, fq);
std::complex<float> iq(i, q);

float deviation;
double fmDemod = phaseDiscri.phaseDiscriminatorDelta(iq, magsqRaw, deviation);
Expand All @@ -283,88 +287,100 @@ void processOneSample(int8_t i, int8_t q) {
// printf("filt - dc: %.3f\n", filt - dc_offset);

if (data != prev_data) {
sync_cnt = SAMPLES_PER_SYMBOL / 2; // reset
} else {
sync_cnt--; // wait until next bit's midpoint

if (sync_cnt <= 0) {
if (bit_inverted) {
data_bit = data;
} else {
data_bit = !data;
}
/*
MultimonNG的时钟同步机制，具体可参考https://github.com/EliasOenal/multimon-ng/blob/master/demod_poc12.c
其主要为每sample给符号相位记录值sym_phase加一个增量phaseinc，之每发生位翻转时判断如果sym_phase不等于0.5就加上或减去一个
phaseinc/2的偏移量，以确保当sym_phase等于1.0读出时样本位于符号中间。采用微调偏移量而不是像原sdrangel代码那样直接重置符号
相位为0.5是因为FSK在实际接收种经常会出现符号中间抖动的情况，低通滤不干净这种抖动，如果因为这种抖动造成的位翻转而重置的话会导致后
面的符号丢失同步。
MultimonNG原代码中单次偏移量为phaseinc/8，根据其采用的11025hz采样率估算偏移一个符号周期大约需要73.5次偏移。由于这里采样率
不同故采用根据估算为偏移一个符号周期需80次偏移的phasinc/2为单次偏移量。
*/
if (sym_phase < 0.5 - phaseinc / 2)
sym_phase += phaseinc / 2;
else
sym_phase -= phaseinc / 2;
}
sym_phase += phaseinc;

// printf("%d", data_bit);
if (sym_phase >= 1.0) {
sym_phase -= 1.0;

bits = (bits << 1) | data_bit;
bit_cnt++;
if (bit_inverted) {
data_bit = data;
} else {
data_bit = !data;
}

if (bit_cnt > 32) {
bit_cnt = 32;
}
// printf("%d", data_bit);

bits = (bits << 1) | data_bit;
bit_cnt++;

if (bit_cnt == 32 && !got_SC) {
// printf("pop count: %d\n", pop_cnt(bits ^ POCSAG_SYNCCODE));
// printf("pop count inv: %d\n", pop_cnt(bits ^ POCSAG_SYNCCODE_INV));
if (bit_cnt > 32) {
bit_cnt = 32;
}

if (bits == POCSAG_SYNCCODE) {
if (bit_cnt == 32 && !got_SC) {
// printf("pop count: %d\n", pop_cnt(bits ^ POCSAG_SYNCCODE));
// printf("pop count inv: %d\n", pop_cnt(bits ^ POCSAG_SYNCCODE_INV));

if (bits == POCSAG_SYNCCODE) {
got_SC = true;
bit_inverted = false;
printf("\nSync code found\n");
} else if (bits == POCSAG_SYNCCODE_INV) {
got_SC = true;
bit_inverted = true;
printf("\nSync code found\n");
} else if (pop_cnt(bits ^ POCSAG_SYNCCODE) <= 3) {
uint32_t corrected_cw;
if (bchDecode(bits, corrected_cw) && corrected_cw == POCSAG_SYNCCODE) {
got_SC = true;
bit_inverted = false;
printf("\nSync code found\n");
} else if (bits == POCSAG_SYNCCODE_INV) {
}
// else printf("\nSync code not found\n");
} else if (pop_cnt(bits ^ POCSAG_SYNCCODE_INV) <= 3) {
uint32_t corrected_cw;
if (bchDecode(~bits, corrected_cw) && corrected_cw == POCSAG_SYNCCODE) {
got_SC = true;
bit_inverted = true;
printf("\nSync code found\n");
} else if (pop_cnt(bits ^ POCSAG_SYNCCODE) <= 3) {
uint32_t corrected_cw;
if (bchDecode(bits, corrected_cw) && corrected_cw == POCSAG_SYNCCODE) {
got_SC = true;
bit_inverted = false;
printf("\nSync code found\n");
}
// else printf("\nSync code not found\n");
} else if (pop_cnt(bits ^ POCSAG_SYNCCODE_INV) <= 3) {
uint32_t corrected_cw;
if (bchDecode(~bits, corrected_cw) && corrected_cw == POCSAG_SYNCCODE) {
got_SC = true;
bit_inverted = true;
printf("\nSync code found\n");
}
// else printf("\nSync code not found\n");
}

if (got_SC) {
bits = 0;
bit_cnt = 0;
code_words[0] = POCSAG_SYNCCODE;
word_cnt = 1;
}
} else if (bit_cnt == 32 && got_SC) {
uint32_t corrected_cw;
code_words_bch_error[word_cnt] = !bchDecode(bits, corrected_cw);
code_words[word_cnt] = corrected_cw;
word_cnt++;

if (word_cnt == 1 && corrected_cw != POCSAG_SYNCCODE) {
got_SC = false;
bit_inverted = false;
}

if (word_cnt == PAGERDEMOD_BATCH_WORDS) {
decodeBatch();
batch_num++;
word_cnt = 0;
}
// else printf("\nSync code not found\n");
}

if (got_SC) {
bits = 0;
bit_cnt = 0;

code_words[0] = POCSAG_SYNCCODE;
word_cnt = 1;
}
} else if (bit_cnt == 32 && got_SC) {
uint32_t corrected_cw;
code_words_bch_error[word_cnt] = !bchDecode(bits, corrected_cw);
code_words[word_cnt] = corrected_cw;
word_cnt++;

if (word_cnt == 1 && corrected_cw != POCSAG_SYNCCODE) {
got_SC = false;
bit_inverted = false;
is_message_ready = true;
printf("Addr: %d | Numeric: %s | Alpha: %s\n", address, numeric_msg.c_str(), alpha_msg.c_str());
// printf("Addr: %d | Numeric: %s | Alpha: %s\n", address, numeric_msg.c_str(), alpha_msg.c_str());
}

sync_cnt = SAMPLES_PER_SYMBOL;
if (word_cnt == PAGERDEMOD_BATCH_WORDS) {
decodeBatch();
batch_num++;
word_cnt = 0;
}

bits = 0;
bit_cnt = 0;

}

}

prev_data = data;
Expand Down
16 changes: 13 additions & 3 deletions app/src/main/cpp/demod.h
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Expand Up @@ -6,10 +6,13 @@
#include <stdint.h>
#include <string>
#include <iostream>
#include <memory>

#include "dsp/phasediscri.h"
#include "dsp/firfilter.h"
#include "util/movingaverage.h"
#include "util/qtypes.h"
#include "dsp/decimatorsu.h"

#define SDR_RX_SCALED 32768.0
#define SAMPLE_RATE 48000.0
Expand All @@ -24,14 +27,21 @@
#define PAGERDEMOD_CODEWORDS_PER_FRAME 2

extern bool is_message_ready;
extern std::string numeric_msg;
extern uint32_t address;

struct pocsag_msg {
uint32_t i;
uint32_t addr;
uint16_t func;
std::string numeric;
std::string alpha;
};
extern std::unique_ptr<std::vector<pocsag_msg>> msg;

extern PhaseDiscriminators phaseDiscri;
extern Lowpass<double> lowpassBaud;
extern MovingAverageUtil<double, double, 2048> preambleMovingAverage;
extern double magsqRaw;

void processOneSample(int8_t i, int8_t q);
void processOneSample(float i, float q);

#endif
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