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445 lines
19 KiB
C++
445 lines
19 KiB
C++
/*
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* Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
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* Copyright (C) 2016 Furrtek
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*
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* This file is part of PortaPack.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#include "adsb.hpp"
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#include "sine_table.hpp"
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#include "utility.hpp"
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#include <math.h>
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namespace adsb {
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void make_frame_adsb(ADSBFrame& frame, const uint32_t ICAO_address) {
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frame.clear();
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frame.push_byte((DF_ADSB << 3) | 5); // DF=17 and CA
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frame.push_byte(ICAO_address >> 16);
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frame.push_byte(ICAO_address >> 8);
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frame.push_byte(ICAO_address & 0xFF);
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}
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// Civil aircraft ADS-B message type starts with Dowlink Format (DF=17) and frame is 112 bits long.
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// All known DF's >=16 are long (112 bits). All known DF's <=15 are short (56 bits).(In this case 112 bits)
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// Msg structure consists of five main parts :|DF=17 (5 bits)|CA (3 bits)|ICAO (24 bits)|ME (56 bits)|CRC (24 bits)
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// Aircraft identification and category message structure, the ME (56 bits) = TC,5 bits | CA,3 bits | C1,6 bits | C2,6 bits | C3,6 | C4,6 | C5,6 | C6,6 | C7,6 | C8,6
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// TC : (1..4) : Aircraft identification Type Code . // TC : 9 to 18: Airbone postion // TC : 19 Airbone velocity .
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// In this encode_frame_identification function we are using DF = 17 (112 bits long) and TC=4)
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void encode_frame_id(ADSBFrame& frame, const uint32_t ICAO_address, const std::string& callsign) {
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std::string callsign_formatted(8, '_');
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uint64_t callsign_coded = 0;
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uint32_t c, s;
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char ch;
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make_frame_adsb(frame, ICAO_address); // Header DF=17 Downlink Format = ADS-B message (frame 112 bits)
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frame.push_byte(TC_IDENT << 3); // 5 top bits ME = TC = we use fix 4 , # Type aircraft Identification Category = TC_IDENT = 4,
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// Translate and encode callsign
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for (c = 0; c < 8; c++) {
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ch = callsign[c];
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for (s = 0; s < 64; s++)
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if (ch == icao_id_lut[s]) break;
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if (s == 64) {
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ch = ' '; // Invalid character
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s = 32;
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}
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callsign_coded <<= 6;
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callsign_coded |= s;
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//callsign[c] = ch;
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}
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// Insert callsign in frame
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for (c = 0; c < 6; c++)
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frame.push_byte((callsign_coded >> ((5 - c) * 8)) & 0xFF);
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frame.make_CRC();
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}
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std::string decode_frame_id(ADSBFrame& frame) {
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std::string callsign = "";
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uint8_t * raw_data = frame.get_raw_data();
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uint64_t callsign_coded = 0;
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uint32_t c;
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// Frame bytes to long
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for (c = 5; c < 11; c++) {
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callsign_coded <<= 8;
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callsign_coded |= raw_data[c];
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}
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// Long to 6-bit characters
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for (c = 0; c < 8; c++) {
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callsign.append(1, icao_id_lut[(callsign_coded >> 42) & 0x3F]);
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callsign_coded <<= 6;
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}
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return callsign;
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}
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/*void generate_frame_emergency(ADSBFrame& frame, const uint32_t ICAO_address, const uint8_t code) {
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make_frame_mode_s(frame, ICAO_address);
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frame.push_byte((28 << 3) + 1); // TC = 28 (Emergency), subtype = 1 (Emergency)
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frame.push_byte(code << 5);
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frame.make_CRC();
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}*/
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// Mode S services. (Mode Select Beacon System). There are two types of Mode S interrogations: The short (56 bits) . and the long (112 bits )
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// All known DF's >=16 are long frame msg (112 bits). All known DF's <=15 are short frame msgs (56 bits).(In this case 112 bits)
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// Identity squawk replies can be DF=5 (Surveillance Identity reply)(56 bits) / DF 21 (Comm-B with Identity reply) (112 bits)
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// DF 21: Comm-B with identity reply structure = |DF=21(5 bits)|FS (3 bits)|DR (5 bits)|UM (6 bits) |Identity squawk code (13 bits) |MB (56 bits) |CRC (24 bits) (total 112 bits)
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// Comm-B messages count for a large portion of the Mode S selective interrogation responses.(means, only transmitted information upon selective request)
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// Comm-B messages protocol supports many different types of msg's (up to 255).The three more popular ones are the following ones:
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// (a) Mode S ELementary Surveillance (ELS) / (b) Mode S EnHanced Surveillance (EHS) / (c) Meteorological information
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// Comm-B Data Selector (BDS) is an 8-bit code that determines which information to be included in the MB fields
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void encode_frame_squawk(ADSBFrame& frame, const uint16_t squawk) {
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uint16_t squawk_coded;
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uint8_t UM_field=0b111101, FS=0b010, DR=0b00001 ;
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// To be sent those fields, (56 bits). We should store byte by byte into the frame , and It will be transmitted byte to byte same FIFO order.
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// DF 5 bits 5 DF=21 (5 top bits) Downlink Format
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// FS 3 bits 0b000, FS (3 bottom bits) (Flight status ) = 000 : no alert, no SPI, aircraft is airborne
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// DR 5 bits 0b00001 DR (Downlink request) (5 top bits) = 00000 : no downlink request (In surveillance replies, only values 0, 1, 4, and 5 are used.)
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// UM 6 bits 0b000010 UM (Utility message)= 000000, Utility message (UM): 6 bits, contains transponder communication status information.(IIS + IDS)
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// Identity_code 13 bits squawk id_code in special interleaved format.
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// MB 56 bits
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// CRC partity 24 bits parity checksum , cyclic redundancy chek.
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frame.clear();
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frame.push_byte( ( DF_EHS_SQUAWK << 3 ) | FS ); // DF=21 (5bits) + FS (3bits, 010 : alert, NO SPI, aircraft is airborne)
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frame.push_byte(( DR <<3 ) | ( UM_field>>3) ); // DR (5bits, 00001 : downlink request + 3 top bits of UM , let's use 0b111000
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// 12 11 10 9 8 7 6 5 4 3 2 1 0 (Original notes) bit weight position----------------------
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// 32 31 30 29 28 27 26 25 24 23 22 21 20 (it was wrong , now corrected) bit order inside frame msg
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// D4 B4 D2 B2 D1 B1 __ A4 C4 A2 C2 A1 C1 standard spec order of the 13 bits, to be sent , each octal digit = 3 bits , (example A=7 binary A4 A2 A0 = 111
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// ABCD = code (octal, 0000~7777)
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// FEDCBA9876543210
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// xAAAxBBBxCCCxDDD 4 x 3 bits (each octal digit)
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// x421x421x421x421 binary weight of each binary position, example AAA = 7 = 111 -------------------------
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// Additional , expanded notes -------------------------------
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// Identity squawk code ABCD = code (octal, 0000~7777) , input concatenated squawk : 4 octal digits ,A4 A2 A1-B4 B2 B1-C4 C2 C1-D4 D2 D1.
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// 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 bit position of the frame msg, (Squawk id is bit 20-32, from C1..D4).
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// UM4 UM2 UM1 C1 A1 C2 A2 C4 A4 X B1 D1 B2 D2 B4 D4 3 lower bit UM4,UM2,UM1 of the UM (6bits), and we should re-order the 13 bits ABCD changing 12 bit poistion based on std.
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// 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Two bytes , bit position to be send.
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squawk_coded = ( (( UM_field & (0b111)) <<13) | ((squawk << 9) & 0x1000) ) | // C1 It also leaves in the top 3 lower bottom bitd part of UM field.
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((squawk << 2) & 0x0800) | // A1
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((squawk << 6) & 0x0400) | // C2
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((squawk >> 1) & 0x0200) | // A2
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((squawk << 3) & 0x0100) | // C4
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((squawk >> 4) & 0x0080) | // A4
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((squawk >> 1) & 0x0020) | // B1
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((squawk << 4) & 0x0010) | // D1
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((squawk >> 4) & 0x0008) | // B2
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((squawk << 1) & 0x0004) | // D2
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((squawk >> 7) & 0x0002) | // B4
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((squawk >> 2) & 0x0001); // D4
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frame.push_byte(squawk_coded>>8); // UM4 UM2 UM1 C1 A1 C2 A2 C4 that is the correct order, confirmed with dump1090
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frame.push_byte(squawk_coded); // A4 X(1) B1 D1 B2 D2 B4 D4 that is the correct order, confirmed with dupm1090
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// DF 21 messages , has 56 bits more after 13 bits of squawk, we should add MB (56 bits)
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// In this example, we are adding fixed MB = Track and turn report (BDS 5,0) decoding MB example = "F9363D3BBF9CE9" (56 bits)
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// # -9.7, roll angle (deg)
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// # 140.273, track angle (deg)
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// # -0.406, track angle rate (deg/s)
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// # 476, ground speed (kt)
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// # 466, TAS (kt)
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frame.push_byte(0xF9);frame.push_byte(0x36);frame.push_byte(0x3D);frame.push_byte(0x3B); // If we deltele those two lines, to send this fixed MB (56 bits),
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frame.push_byte(0xBF);frame.push_byte(0x9C);frame.push_byte(0xE9); // current fw is padding with 56 x 0's to complete 112 bits msg.
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frame.make_CRC();
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}
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float cpr_mod(float a, float b) {
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return a - (b * floor(a / b));
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}
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int cpr_NL_precise(float lat) {
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return (int) floor(2 * PI / acos(1 - ((1 - cos(PI / (2 * NZ))) / pow(cos(PI * lat / 180), 2))));
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}
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int cpr_NL_approx(float lat) {
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if (lat < 0)
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lat = -lat; // Symmetry
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for (size_t c = 0; c < 58; c++) {
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if (lat < adsb_lat_lut[c])
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return 59 - c;
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}
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return 1;
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}
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int cpr_NL(float lat) {
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// TODO prove that the approximate function is good
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// enough for the precision we need. Uncomment if
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// that is true. No performance penalty was noticed
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// from testing, but if you find it might be an issue,
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// switch to cpr_NL_approx() instead:
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//return cpr_NL_approx(lat);
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return cpr_NL_precise(lat);
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}
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int cpr_N(float lat, int is_odd) {
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int nl = cpr_NL(lat) - is_odd;
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if (nl < 1)
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nl = 1;
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return nl;
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}
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float cpr_Dlon(float lat, int is_odd) {
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return 360.0 / cpr_N(lat, is_odd);
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}
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// An ADS-B frame Civil aircraft message type starts with Dowlink Format (DF=17) and frame is 112 bits long.
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// All known DF's >=16 are long (112 bits). All known DF's <=15 are short (56 bits). (In this case 112 bits)
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// Msg structure consists of five main parts :|DF=17 (5 bits)|CA (3 bits)|ICAO (24 bits)|ME (56 bits)|CRC (24 bits)
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// Airborne position msg struct, the ME (56 bits) = |TC,5 bits| SS, 2 bits | SAF, 1 | ALT, 12 | T, 1 | F, 1 | LAT-CPR, 17 | LON-CPR, 17
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// TC : (1..4) : Aircraft identification Type Code. // TC : 9 to 18: Airbone postion and altitude // TC : 19 Airbone velocity .
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// Airborne position message is used to broadcast the position and altitude of the aircraft. It has the Type Code 9–18 and 20–22. (here , we use TC=11)
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void encode_frame_pos(ADSBFrame& frame, const uint32_t ICAO_address, const int32_t altitude,
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const float latitude, const float longitude, const uint32_t time_parity) {
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uint32_t altitude_coded;
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uint32_t lat, lon;
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float delta_lat, yz, rlat, delta_lon, xz;
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make_frame_adsb(frame, ICAO_address); // Header DF=17 (long frame 112 bits)
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frame.push_byte(TC_AIRBORNE_POS << 3); // Bits 2~1: Surveillance Status, bit 0: NICsb
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altitude_coded = (altitude + 1000) / 25; // 25ft precision, insert Q-bit (1)
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altitude_coded = ((altitude_coded & 0x7F0) << 1) | 0x10 | (altitude_coded & 0x0F);
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frame.push_byte(altitude_coded >> 4); // Top-most altitude bits
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// CPR encoding
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// Info from: http://antena.fe.uni-lj.si/literatura/Razno/Avionika/modes/CPRencoding.pdf
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delta_lat = 360.0 / ((4.0 * NZ) - time_parity); // NZ = 15
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yz = floor(CPR_MAX_VALUE * (cpr_mod(latitude, delta_lat) / delta_lat) + 0.5);
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rlat = delta_lat * ((yz / CPR_MAX_VALUE) + floor(latitude / delta_lat));
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if ((cpr_NL(rlat) - time_parity) > 0)
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delta_lon = 360.0 / cpr_N(rlat, time_parity);
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else
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delta_lon = 360.0;
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xz = floor(CPR_MAX_VALUE * (cpr_mod(longitude, delta_lon) / delta_lon) + 0.5);
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lat = cpr_mod(yz, CPR_MAX_VALUE);
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lon = cpr_mod(xz, CPR_MAX_VALUE);
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frame.push_byte((altitude_coded << 4) | ((uint32_t)time_parity << 2) | (lat >> 15)); // T = 0
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frame.push_byte(lat >> 7);
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frame.push_byte((lat << 1) | (lon >> 16));
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frame.push_byte(lon >> 8);
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frame.push_byte(lon);
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frame.make_CRC();
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}
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// Decoding method from dump1090
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adsb_pos decode_frame_pos(ADSBFrame& frame_even, ADSBFrame& frame_odd) {
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uint8_t * raw_data;
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uint32_t latcprE, latcprO, loncprE, loncprO;
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float latE, latO, m, Dlon, cpr_lon_odd, cpr_lon_even, cpr_lat_odd, cpr_lat_even;
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int ni;
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adsb_pos position { false, 0, 0, 0 };
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uint32_t time_even = frame_even.get_rx_timestamp();
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uint32_t time_odd = frame_odd.get_rx_timestamp();
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uint8_t * frame_data_even = frame_even.get_raw_data();
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uint8_t * frame_data_odd = frame_odd.get_raw_data();
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// Return most recent altitude
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if (time_even > time_odd)
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raw_data = frame_data_even;
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else
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raw_data = frame_data_odd;
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// Q-bit must be present
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if (raw_data[5] & 1)
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position.altitude = ((((raw_data[5] & 0xFE) << 3) | ((raw_data[6] & 0xF0) >> 4)) * 25) - 1000;
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// Position
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latcprE = ((frame_data_even[6] & 3) << 15) | (frame_data_even[7] << 7) | (frame_data_even[8] >> 1);
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loncprE = ((frame_data_even[8] & 1) << 16) | (frame_data_even[9] << 8) | frame_data_even[10];
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latcprO = ((frame_data_odd[6] & 3) << 15) | (frame_data_odd[7] << 7) | (frame_data_odd[8] >> 1);
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loncprO = ((frame_data_odd[8] & 1) << 16) | (frame_data_odd[9] << 8) | frame_data_odd[10];
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// Calculate the coefficients
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cpr_lon_even = loncprE / CPR_MAX_VALUE;
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cpr_lon_odd = loncprO / CPR_MAX_VALUE;
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cpr_lat_odd = latcprO / CPR_MAX_VALUE;
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cpr_lat_even = latcprE / CPR_MAX_VALUE;
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// Compute latitude index
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float j = floor(((59.0 * cpr_lat_even) - (60.0 * cpr_lat_odd)) + 0.5);
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latE = (360.0 / 60.0) * (cpr_mod(j, 60) + cpr_lat_even);
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latO = (360.0 / 59.0) * (cpr_mod(j, 59) + cpr_lat_odd);
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if (latE >= 270) latE -= 360;
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if (latO >= 270) latO -= 360;
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// Both frames must be in the same latitude zone
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if (cpr_NL(latE) != cpr_NL(latO))
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return position;
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// Compute longitude
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if (time_even > time_odd) {
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// Use even frame2
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ni = cpr_N(latE, 0);
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Dlon = 360.0 / ni;
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m = floor((cpr_lon_even * (cpr_NL(latE) - 1)) - (cpr_lon_odd * cpr_NL(latE)) + 0.5);
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position.longitude = Dlon * (cpr_mod(m, ni) + cpr_lon_even);
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position.latitude = latE;
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} else {
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// Use odd frame
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ni = cpr_N(latO, 1);
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Dlon = 360.0 / ni;
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m = floor((cpr_lon_even * (cpr_NL(latO) - 1)) - (cpr_lon_odd * cpr_NL(latO)) + 0.5);
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position.longitude = Dlon * (cpr_mod(m, ni) + cpr_lon_odd);
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position.latitude = latO;
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}
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if (position.longitude >= 180) position.longitude -= 360;
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position.valid = true;
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return position;
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}
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// An ADS-B frame is 112 bits long. Civil aircraft ADS-B message starts with the Downlink Format ,DF=17.
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// Msg structure consists of five main parts :|DF=17 (5 bits)|CA (3 bits)|ICAO (24 bits)|ME (56 bits)|CRC (24 bits)
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// Airborne velocities are all transmitted with Type Code 19 ( TC=19 ) inside ME (56 bits)
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// [units] : speed is in knots, vertical rate climb / descend is in ft/min
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void encode_frame_velo(ADSBFrame& frame, const uint32_t ICAO_address, const uint32_t speed,
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const float angle, const int32_t v_rate) {
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int32_t velo_ew, velo_ns;
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uint32_t velo_ew_abs, velo_ns_abs, v_rate_coded_abs;
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// To get NS and EW speeds from speed and bearing, a polar to cartesian conversion is enough
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velo_ew = static_cast<int32_t>(sin_f32(DEG_TO_RAD(angle) ) * speed); // East direction, is the projection from West -> East is directly sin(angle=Compas Bearing) , (90º is the max +1, EAST) max velo_EW
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velo_ns = static_cast<int32_t>(sin_f32( (pi/2 - DEG_TO_RAD(angle) ) ) * speed); // North direction,is the projection of North = cos(angle=Compas Bearing), cos(angle)= sen(90-angle) (0º is the max +1 NORTH) max velo_NS
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v_rate_coded_abs = (abs(v_rate) / 64) + 1; //encoding vertical rate source. (Decoding, VR ft/min = (Decimal v_rate_value - 1)* 64)
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velo_ew_abs = abs(velo_ew) + 1; // encoding Velo speed EW , when sign Direction is 0 (+): West->East, (-) 1: East->West
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velo_ns_abs = abs(velo_ns) + 1; // encoding Velo speed NS , when sign Direction is 0 (+): South->North , (-) 1: North->South
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make_frame_adsb(frame, ICAO_address); // Header DF=17 (long frame 112 bits)
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// Airborne velocities are all transmitted with Type Code 19 ( TC=19, using 5 bits ,TC=19 [Binary: 10011]), the following 3 bits are Subt-type Code ,SC= 1,2,3,4
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// SC Subtypes code 1 and 2 are used to report ground speeds of aircraft. (SC 3,4 to used to report true airspeed. SC 2,4 are for supersonic aircraft (not used in commercial airline).
|
||
frame.push_byte((TC_AIRBORNE_VELO << 3) | 1); // 1st byte , top 5 bits Type Code TC=19, and lower 3 bits (38-40 bits), SC=001 Subtype Code SC: 1 (subsonic) ,
|
||
|
||
// Message A, (ME bits from 14-35) , 22 bits = Sign ew(1 bit) + V_ew (10 bits) + Sign_ns (1 bit) + V_ns (10 bits)
|
||
// Vertical rate source bit VrSrc (ME bit 36) indicates source of the altitude measurements. GNSS altitude(0) / , barometric altitude(1).
|
||
// Vertical rate source direction,(ME bit 37) movement can be read from Svr bit , with 0 and 1 referring to climb and descent, respectively (ft/min)
|
||
// The encoded vertical rate value VR can be computed using message (ME bits 38 to 46). If the 9-bit block contains all zeros, the vertical rate information is not available.
|
||
// + Sign VrSrc (vert rate src) (1 bit)+ VrSrc (9 bits).
|
||
frame.push_byte(((velo_ew < 0 ? 1 : 0) << 2) | (velo_ew_abs >> 8));
|
||
frame.push_byte(velo_ew_abs);
|
||
frame.push_byte(((velo_ns < 0 ? 1 : 0) << 7) | (velo_ns_abs >> 3));
|
||
frame.push_byte((velo_ns_abs << 5) | ((v_rate < 0 ? 1 : 0) << 3) | (v_rate_coded_abs >> 6)); // VrSrc = 0
|
||
frame.push_byte(v_rate_coded_abs << 2);
|
||
frame.push_byte(0);
|
||
|
||
frame.make_CRC();
|
||
}
|
||
|
||
// Decoding method from dump1090
|
||
adsb_vel decode_frame_velo(ADSBFrame& frame){
|
||
adsb_vel velo {false, 0, 0, 0};
|
||
|
||
uint8_t * frame_data = frame.get_raw_data();
|
||
uint8_t velo_type = frame.get_msg_sub();
|
||
|
||
if(velo_type >= 1 && velo_type <= 4){ //vertical rate is always present
|
||
|
||
velo.v_rate = (((frame_data[8] & 0x07 ) << 6) | ((frame_data[9] >> 2) - 1)) * 64;
|
||
|
||
if((frame_data[8] & 0x8) >> 3) velo.v_rate *= -1; //check v_rate sign
|
||
}
|
||
|
||
if(velo_type == 1 || velo_type == 2){ //Ground Speed
|
||
int32_t raw_ew = ((frame_data[5] & 0x03) << 8) | frame_data[6];
|
||
int32_t velo_ew = raw_ew - 1; //velocities are all offset by one (this is part of the spec)
|
||
|
||
int32_t raw_ns = ((frame_data[7] & 0x7f) << 3) | (frame_data[8] >> 5);
|
||
int32_t velo_ns = raw_ns - 1;
|
||
|
||
if (velo_type == 2){ // supersonic indicator so multiply by 4
|
||
velo_ew = velo_ew << 2;
|
||
velo_ns = velo_ns << 2;
|
||
}
|
||
|
||
if(frame_data[5]&0x04) velo_ew *= -1; //check ew direction sign
|
||
if(frame_data[7]&0x80) velo_ns *= -1; //check ns direction sign
|
||
|
||
velo.speed = fast_int_magnitude(velo_ns,velo_ew);
|
||
|
||
if(velo.speed){
|
||
//calculate heading in degrees from ew/ns velocities
|
||
int16_t heading_temp = (int16_t)(int_atan2(velo_ew,velo_ns)); // Nearest degree
|
||
// We don't want negative values but a 0-360 scale.
|
||
if (heading_temp < 0) heading_temp += 360.0;
|
||
velo.heading = (uint16_t)heading_temp;
|
||
}
|
||
|
||
}else if(velo_type == 3 || velo_type == 4){ //Airspeed
|
||
velo.valid = frame_data[5] & (1<<2);
|
||
velo.heading = ((((frame_data[5] & 0x03)<<8) | frame_data[6]) * 45) << 7;
|
||
}
|
||
|
||
return velo;
|
||
|
||
}
|
||
|
||
} /* namespace adsb */
|