I/Q Streaming (VRT)

Table of Contents

• Examples
  • Parsing Example
  • GUI Example
• Basics
  • Type and Function of Packets
    • Signal Data Packets
    • Context Packets
• Specification

The API provides the ability to stream I/Q samples contained in data packets that conform to the ANSI/VITA 49 Radio Transport (VRT) standard.

Examples

For a list of all examples, please see the examples/cpp/vita49 folder in the SDK.

 
/*
 *  Get a VRT Context packet from a Signal Hound SM Series device followed by a block of 1000 Signal Data packets
 *
 */
 
#include "sm_api.h"
#include "sm_api_vrt.h"
 
#pragma comment(lib, "sm_api")
 
void getVRTPackets() {
    // Set up device
    int device = -1;
    //SmStatus status = smOpenDevice(&device); // USB
    SmStatus status = smOpenNetworkedDevice(&device, SM_ADDR_ANY, SM_DEFAULT_ADDR, SM_DEFAULT_PORT); // Networked
    if(status != smNoError) {
        // Could not open Sm Series device
    }
 
    // Set IQ parameters
    smSetIQCenterFreq(device, 3.0e9);
    smSetIQSampleRate(device, 2);
    smSetIQBandwidth(device, smTrue, 20.0e6);
    smSetRefLevel(device, -20);
 
    // Set VRt parameters
    smSetVrtStreamID(device, 1);
    smSetVrtPacketSize(device, 16384);
 
    // Configure
    status = smConfigure(device, smModeIQStreaming); // VRT mode
    if(status != smNoError) {
        // Could not configure SM Series device
    }
 
    // Allocate memory
    uint32_t contextWordCount;
    status = smGetVrtContextPktSize(device, &contextWordCount);
    if(status != smNoError) {
        // Could not get context packet size
    }
 
    const int dataPacketCount = 1000;
 
    uint16_t samplesPerPkt;
    uint32_t dataWordCount;
    status = smGetVrtPacketSize(device, &samplesPerPkt, &dataWordCount);
    if(status != smNoError) {
        // Could not get data packet size and word count
    }
 
    uint32_t wordCount = contextWordCount + dataWordCount * dataPacketCount;
    uint32_t *words = new uint32_t[wordCount];
    uint32_t *curr = words;
 
    // Get context packet
    uint32_t actualContextWordCount;
    status = smGetVrtContextPkt(device, curr, &actualContextWordCount);
    if(status != smNoError) {
        // Could not get context packet
    }
    if(actualContextWordCount != contextWordCount) {
        // Context packet is not the expected size
    }
    curr += contextWordCount;
 
    // Get data packets
    uint32_t actualDataWordCount;
    status = smGetVrtPackets(device, curr, &actualDataWordCount, dataPacketCount, smFalse);
    if(status != smNoError) {
        // Could not get data packets
    }
    if(actualDataWordCount != dataWordCount * dataPacketCount) {
        // Block of data packets is not the expected size
    }
 
    smCloseDevice(device);
 
    if(words) delete[] words;
}
 

Parsing Example

The parsing example demonstrates how to ingest VRT packets. The code can be used directly in projects that wish to use the VRT functionality.

It is located in examples/cpp/vita49/gui.

GUI Example

The GUI application provides a user-friendly graphical interface to easily experiment with the VRT functionality.

It is located in examples/cpp/vita49/gui, and uses the Qt library.

Basics

VRT is an open radio transport protocol used to transmit and receive sample data between devices. It is defined by the VITA 49 standard. Signal Hound uses the latest version of the standard, 49.2 (2017).

At a high level, blocks of I/Q samples and information about the receiver's state are wrapped/embedded in packets with standard formats.

Type and Function of Packets

VRT uses Signal Data packets and Context packets. Both types contain headers with metadata which includes a Stream Identifier and timestamp.

Signal Data Packets

Signal Data packets encapsulate variable-sized blocks of IQ data, along with a 32-bit trailer to convey additional critical information about the state of the receiver at the time the samples were obtained. For example, if the system was being overdriven this would be reported by an indicator in the trailer.

Context Packets

Context packets contain information about the receiver’s settings. They are of variable size, depending on how many of the possible ~25 fields are used. Which fields are used is communicated by the Context Indicator field, a 32-bit value which precedes the context fields. Signal Hound uses 10 of the possible context fields.

Specification

For a full, precise specification, please see the VRT Manual in the SDK.