Add example application to receive decoded navigation messages

docs/CHANGELOG.md

@@ -16,11 +16,13 @@ All notable changes to GNSS-SDR will be documented in this file.
 
 ### Improvements in Usability:
 
-- Added a new monitor to extract the raw data bits in the navigation message and
-  send them elsewhere via UDP. Activated by setting
+- Added a new monitor to extract the decoded data bits of the navigation
+  messages and send them elsewhere via UDP. Activated by setting
   `NavDataMonitor.enable_monitor=true`,
   `NavDataMonitor.client_addresses=127.0.0.1` and `NavDataMonitor.port=1237` in
-  the configuration file. Format described in the `nav_message.proto` file.
+  the configuration file. Format described in the `nav_message.proto` file. A
+  simple listener application written in C++ is included in
+  `src/utils/nav-listener` as a example.
 
 ## [GNSS-SDR v0.0.15](https://github.com/gnss-sdr/gnss-sdr/releases/tag/v0.0.15) - 2021-08-23
 

src/utils/nav-listener/CMakeLists.txt

@@ -0,0 +1,38 @@
+# GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
+# This file is part of GNSS-SDR.
+#
+# SPDX-FileCopyrightText: 2021 C. Fernandez-Prades cfernandez(at)cttc.es
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required (VERSION 3.9...3.21)
+project (nav-msg-listener CXX)
+
+set(CMAKE_CXX_STANDARD 11)
+
+set(Boost_USE_STATIC_LIBS OFF)
+find_package(Boost COMPONENTS system REQUIRED)
+
+find_package(Protobuf REQUIRED)
+if(${Protobuf_VERSION} VERSION_LESS "3.0.0")
+     message(FATAL_ERROR "Fatal error: Protocol Buffers >= v3.0.0 required.")
+endif()
+
+protobuf_generate_cpp(PROTO_SRCS PROTO_HDRS ${CMAKE_SOURCE_DIR}/nav_message.proto)
+
+add_library(navmsg_lib ${CMAKE_SOURCE_DIR}/nav_msg_udp_listener.cc ${PROTO_SRCS})
+
+target_link_libraries(navmsg_lib
+    PUBLIC
+        Boost::boost
+        Boost::system
+        protobuf::libprotobuf
+)
+
+target_include_directories(navmsg_lib
+    PUBLIC
+        ${CMAKE_BINARY_DIR}
+)
+
+add_executable(nav_msg_listener ${CMAKE_SOURCE_DIR}/main.cc)
+
+target_link_libraries(nav_msg_listener PUBLIC navmsg_lib)

src/utils/nav-listener/README.md

@@ -0,0 +1,83 @@
+# nav_msg_listener
+
+Simple application that retrieves decoded navigation messages produced by
+GNSS-SDR and prints them in a terminal. This is only for demonstration purposes,
+as a example on how to retrieve data using the `nav_message.proto` file.
+
+
+# Build the software
+
+This software requires [Boost](https://www.boost.org/) and [Protocol
+Buffers](https://developers.google.com/protocol-buffers).
+
+In a terminal, type:
+
+```
+$ mkdir build && cd build
+$ cmake ..
+$ make
+```
+
+
+## Usage
+
+In order to tell GNSS-SDR to generate those messages, you need to include the
+lines:
+
+```
+NavDataMonitor.enable_monitor=true
+NavDataMonitor.client_addresses=127.0.0.1  ; destination IP
+NavDataMonitor.port=1237                   ; destination port
+```
+
+in your gnss-sdr configuration file. You can specify multiple destination
+addresses, separated by underscores:
+
+```
+NavDataMonitor.client_addresses=79.154.253.31_79.154.253.32
+```
+
+Run gnss-sdr with your configuration, and at the same time, from the computer of
+the client address (or another terminal from the same computer that is executing
+gnss-sdr if you are using `127.0.0.1`), execute the binary as:
+
+```
+$ ./nav_msg_listener 1237
+```
+
+where `1237` needs to be the same port as in `NavDataMonitor.port`. As soon as
+gnss-sdr starts to decode navigation messages, you will see them in your
+terminal:
+
+```
+$ ./nav_msg_listener 1237
+
+New Data received:
+System: E
+Signal: 1B
+PRN: 11
+TOW of last symbol [ms]: 75869044
+Nav message: 000000001001010101010101010101010101010101010101010101010101010101010101010101010101010101010101010011100101110001000000
+
+New Data received:
+System: G
+Signal: 1C
+PRN: 16
+TOW of last symbol [ms]: 75870000
+Nav message: 100010111010101010101000101111000110001011001010010100011100010001000000000000000000000011010100000000101101100001000011000000000000000000000000111111101000010000110110011011000100000101111100000111100110110101000100110100100010011011101001001010011001011111111110000110000000000000000000000010001100
+
+New Data received:
+System: E
+Signal: 5X
+PRN: 18
+TOW of last symbol [ms]: 75870260
+Nav message: 0000100001111110010000010111110100011010010000100000000000000000000000000000000000000000000000000000000010101010000001001011010010100100100100100110101110110101010000100000000000000000111001011100010010100001010100001110101001001101111000000000
+
+New Data received:
+System: G
+Signal: L5
+PRN: 6
+TOW of last symbol [ms]: 75871320
+Nav message: 100010110001100011110001100010110010100111100001110100001000000110110101100101011100110111001101100001011001110110010100101110001000000010000000100000001000000010000000100000001000000010000000100000001000000010000000100000001000000010000000100000001000000010000000100000001000001010101010111110000000
+
+```

src/utils/nav-listener/main.cc

@@ -0,0 +1,46 @@
+/*!
+ * \file main.cc
+ * \author Carles Fernandez-Prades, 2021. cfernandez(at)cttc.es
+ *
+ * -----------------------------------------------------------------------------
+ *
+ * GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
+ * This file is part of GNSS-SDR.
+ *
+ * Copyright (C) 2010-2021  (see AUTHORS file for a list of contributors)
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * -----------------------------------------------------------------------------
+ */
+
+#include "nav_msg_udp_listener.h"
+#include <boost/lexical_cast.hpp>
+#include <iostream>
+
+int main(int argc, char *argv[])
+{
+    try
+        {
+            // Check command line arguments.
+            if (argc != 2)
+                {
+                    // Print help.
+                    std::cerr << "Usage: nav_msg_listener <port>\n";
+                    return 1;
+                }
+
+            unsigned short port = boost::lexical_cast<unsigned short>(argv[1]);
+            Nav_Msg_Udp_Listener udp_listener(port);
+
+            while (true)
+                {
+                    udp_listener.print_content();
+                }
+        }
+    catch (std::exception &e)
+        {
+            std::cerr << e.what() << '\n';
+        }
+
+    return 0;
+}

src/utils/nav-listener/nav_message.proto

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: BSD-3-Clause
+// SPDX-FileCopyrightText: 2021 Carles Fernandez-Prades <carles.fernandez@cttc.es>
+syntax = "proto3";
+
+package gnss_sdr;
+
+message navMsg {
+  string system = 1;  // GNSS constellation: "G" for GPS, "R" for Glonass, "E" for Galileo, and "C" for Beidou.
+  string signal = 2;  // GNSS signal: "1C" for GPS L1 C/A, "1B" for Galileo E1b/c, "1G" for Glonass L1 C/A, "2S" for GPS L2 L2C(M), "2G" for Glonass L2 C/A, "L5" for GPS L5, and "5X" for Galileo E5a
+  int32 prn = 3;      // SV ID
+  int32 tow_at_current_symbol_ms = 4;  // Time of week of the last symbol received, in ms
+  string nav_message = 5;  // for Galileo I/NAV: decoded half page (even or odd), 120 bits, as described in OS SIS ICD 2.0, paragraph 4.3.2.3. I/NAV Page Part
+                           // for Galileo F/NAV: decoded word, 244 bits, as described in OS SIS ICD 2.0, paragraph 4.2.2. F/NAV Page Layout
+                           // For GPS LNAV: decoded subframe, 300 bits, as described in IS-GPS-200M paragraph 20.3.2 Message Structure.
+                           // For GPS CNAV: decoded subframe, 300 bits, as described in IS-GPS-200M paragraph 30.3.3 Message Content.
+}

src/utils/nav-listener/nav_msg_udp_listener.cc

@@ -0,0 +1,60 @@
+/*!
+ * \file nav_msg_udp_listener.cc
+ * \author Carles Fernandez-Prades, 2021. cfernandez(at)cttc.es
+ *
+ * -----------------------------------------------------------------------------
+ *
+ * GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
+ * This file is part of GNSS-SDR.
+ *
+ * Copyright (C) 2010-2021  (see AUTHORS file for a list of contributors)
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * -----------------------------------------------------------------------------
+ */
+
+#include "nav_msg_udp_listener.h"
+#include <sstream>
+
+Nav_Msg_Udp_Listener::Nav_Msg_Udp_Listener(unsigned short port)
+    : socket{io_service}, endpoint{boost::asio::ip::udp::v4(), port}
+{
+    socket.open(endpoint.protocol(), error);  // Open socket.
+    socket.bind(endpoint, error);             // Bind the socket to the given local endpoint.
+}
+
+
+bool Nav_Msg_Udp_Listener::read_nav_message(gnss_sdr::navMsg &message)
+{
+    char buff[1500];  // Buffer for storing the received data.
+
+    message_ = message;
+    // This call will block until one or more bytes of data has been received.
+    int bytes = socket.receive(boost::asio::buffer(buff));
+
+    std::string data(&buff[0], bytes);
+    // Deserialize a stock of Nav_Msg objects from the binary string.
+    return message_.ParseFromString(data);
+}
+
+
+bool Nav_Msg_Udp_Listener::print_content()
+{
+    if (read_nav_message(message_))
+        {
+            std::cout << "\nNew Data received:\n";
+            std::cout << "System: " << message_.system() << '\n';
+            std::cout << "Signal: " << message_.signal() << '\n';
+            std::cout << "PRN: " << message_.prn() << '\n';
+            std::cout << "TOW of last symbol [ms]: "
+                      << message_.tow_at_current_symbol_ms() << '\n';
+            std::cout << "Nav message: " << message_.nav_message() << "\n\n";
+        }
+    else
+        {
+            std::cout << "Error: the message cannot be parsed.\n";
+            return false;
+        }
+
+    return true;
+}

src/utils/nav-listener/nav_msg_udp_listener.h

@@ -0,0 +1,37 @@
+/*!
+ * \file nav_msg_udp_listener.h
+ * \author Carles Fernandez-Prades, 2021. cfernandez(at)cttc.es
+ *
+ * -----------------------------------------------------------------------------
+ *
+ * GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
+ * This file is part of GNSS-SDR.
+ *
+ * Copyright (C) 2010-2021  (see AUTHORS file for a list of contributors)
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * -----------------------------------------------------------------------------
+ */
+
+#ifndef GNSS_SDR_NAV_MSG_UDP_LISTENER_H
+#define GNSS_SDR_NAV_MSG_UDP_LISTENER_H
+
+#include "nav_message.pb.h"
+#include <boost/asio.hpp>
+
+class Nav_Msg_Udp_Listener
+{
+public:
+    Nav_Msg_Udp_Listener(unsigned short port);
+    bool print_content();
+
+private:
+    bool read_nav_message(gnss_sdr::navMsg &message);
+    boost::asio::io_service io_service;
+    boost::asio::ip::udp::socket socket;
+    boost::system::error_code error;
+    boost::asio::ip::udp::endpoint endpoint;
+    gnss_sdr::navMsg message_;
+};
+
+#endif