AirStack Software

The AIR-T comes pre-loaded with a full software stack, AirStack. AirStack includes all the components necessary to utilize the AIR-T, such as an Ubuntu based operating system, AIR-T specific device drivers, and the FPGA firmware. The operating system is based off of the NVIDIA Jetpack and is upgraded periodically. Please check for the latest software at www.deepwavedigital.com.

Application Programming Interfaces

Applications for the AIR-T may be developed using almost any software language, but C/C++ and Python are the primary supported languages. Various Application Programming Interfaces (APIs) are supported by AirStack and a few of the most common APIs are described below.

Hardware Control

SoapyAIRT

SoapySDR is the primary API for interfacing with the AIR-T via the SoapyAIRT driver. SoapySDR is an open-source API and run-time library for interfacing with various SDR devices. The AirStack environment includes the SoapySDR and the SoapyAIRT driver to enable communication with the radio interfaces using Python or C++. The Python code below provides an operational example of how to leverage the SoapyAIRT for SDR applications.

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#!/usr/bin/env python3
from SoapySDR import Device, SOAPY_SDR_RX, SOAPY_SDR_CS16
import numpy as np
sdr = Device(dict(driver="SoapyAIRT"))          # Create AIR-T instance
sdr.setSampleRate(SOAPY_SDR_RX, 0, 125e6)       # Set sample rate on chan 0
sdr.setGainMode(SOAPY_SDR_RX, 0, True)          # Use AGC on channel 0
sdr.setFrequency(SOAPY_SDR_RX, 0, 2.4e9)        # Set frequency on chan 0
buff = np.empty(2 * 16384, np.int16)            # Create memory buffer
stream = sdr.setupStream(SOAPY_SDR_RX,
                         SOAPY_SDR_CS16, [0])   # Setup data stream
sdr.activateStream(stream)                      # Turn on the radio
for i in range(10):                             # Receive 10x16384 windows
    sr = sdr.readStream(stream, [buff], 16384)  # Read 16384 samples
    rc = sr.ret                                 # Number of samples read
    assert rc == 16384, 'Error code = %d!' % rc # Make sure no errors
    s0 = buff.astype(float) / np.power(2.0, 15) # Scaled interleaved signal
    s = s0[::2] + 1j*s0[1::2]                   # Complex signal data
    # <Insert code here that operates on s>
sdr.deactivateStream(stream)                    # Stop streaming samples
sdr.closeStream(stream)                         # Turn off radio

UHD

A key feature of SoapySDR is its ability to translate to/from other popular SDR APIs, such as UHD. The SoapyUHD plugin is included with AirStack and enables developers to create applications using UHD or execute existing UHD-based applications on the AIR-T. This interface is described in the figure below.

 

UHD Support Overview
 

Signal Processing

Python Interfaces

The figure below illustrates supported Python APIs that can be used to develop signal processing applications on both the CPU and GPU of the AIR-T. In general, these have been selected because they have modest overhead compared to native code and are well suited to rapid prototyping. In addition, C++ interfaces are provided for many control and processing interfaces to the AIR-T for use in performance-critical applications.

 

Python Software Suite for DSP on the AIR-T
 

The table below outlines the common data processing APIs that are natively supported by AirStack, along with the supported GPP for each API. Some of these are included with AirStack, while some are available via the associated URL.

 

Table 15
API

GPP

Description
numpy CPU numpy is one a common data analysis and processing Python module.
URL: https://numpy.org/
scipy.signal CPU SciPy is a scientific computing library for Python that contains a signal processing library, scipy.signal.
URL: https://docs.scipy.org/doc/scipy/reference/signal.html
cupy GPU Open-source matrix library accelerated with NVIDIA CUDA that is semantically compatible with numpy.
URL: https://cupy.chainer.org/
cuSignal GPU Open-source signal processing library accelerated with NVIDIA CUDA based on scipy.signal.
URL: https://github.com/rapidsai/cusignal
PyCUDA / numba GPU Python access to the full power of NVIDIA’s CUDA API
URL: https://documen.tician.de/pycuda/
Custom CUDA Kernels GPU Custom CUDA kernels may be developed and executed on the AIR-T

 

GNU Radio

The AIR-T also supports GNU Radio, one of the most widely used open-source toolkits for signal processing and SDR. Included with AirStack, the toolkit provides modules for the instantiation of bidirectional data streams with the AIR-T’s transceiver (transmit and receive) and multiple DSP modules in a single framework. GNU Radio Companion may also be leveraged for a graphical programming interface, as shown in the figure below. GNU Radio is written in C++ and has Python bindings.

 

GNU Radio Companion GUI executing a CUDA kernel
 

Like the majority of SDR applications, most functions in GNU Radio rely on CPU processing. Since many DSP engineers are already familiar with GNU Radio, two free and open source modules have been created for AirStack to provide GPU acceleration on the AIR-T from within GNU Radio. Gr-Cuda and gr-wavelearner, along with the primary GNU Radio modules for sending and receiving samples to and from the AIR-T, are shown in the table below and included with AirStack.

 

Table 16
GNU Radio Module

Description
gr-cuda A detailed tutorial for incorporating CUDA kernels into GNU Radio.
URL: https://github.com/deepwavedigital/gr-cuda
gr-wavelearner A framework for running both GPU-based FFTs and neural network inference in GNU Radio.
URL: https://github.com/deepwavedigital/gr-wavelearner
gr-uhd The GNU Radio module for supporting UHD devices.
URL: https://github.com/gnuradio/gnuradio/tree/master/gr-uhd
gr-soapy Vendor neutral set of source/sink blocks for GNU Radio.
URL: https://gitlab.com/librespacefoundation/gr-soapy

 

Deep Learning

The workflow for creating a deep learning application for the AIR-T consists of three phases: training, optimization, and deployment. These steps are illustrated in the figure below and covered in the proceeding sections.

AirPack is an add-on software package (not included with the AIR-T) that provides source code for the complete training-to-deployment workflow described in this section. More information about AirPack may be found here: https://deepwavedigital.com/airpack/.

 

Deep learning training-to-deployment workflow for the AIR-T
 

Training Frameworks

The primary inference library used on the AIR-T is NVIDIA’s TensorRT. TensorRT allows for optimized interference to run on the AIR-T’s GPU. TensorRT is compatible with models trained using a wide variety of frameworks as shown below.

 

Table 17
Deep Learning Framework


Description

TensorRT Support

Programming Languages
TensorFlow Google’s deep learning framework
URL: www.tensorflow.org/
UFF, ONXX Python, C++, Java
PyTorch Open source deep learning framework maintained by Facebook
URL: www.pytorch.org/
ONNX Python, C++
MATLAB MATLAB has a Statistics and Machine Learning Toolbox and a Deep Learning Toolbox
URL: www.mathworks.com/solutions/deep-learning.html
ONNX MATLAB
CNTK Microsoft’s open source Cognitive Toolkit.
URL: docs.microsoft.com/cognitive-toolkit/
ONNX Python, C#, C++

 

When training a neural network for execution on the AIR-T, make sure that the layers being used are supported by your version of TensorRT. To determine what version of TensorRT is installed on your AIR-T, open a terminal and run:

$ dpkg -l | grep TensorRT

The supported layers for your version of TensorRT may be found in the TensorRT SDK Documentation under the TensorRT Support Matrix section.

Optimization Frameworks

Once a model is trained (and saved in the file formats listed in the table above), it must be optimized to run efficiently on the AIR-T. The primary function of the AIR-T is to be an edge-compute inference engine for the real-time execution of deep learning applications. This section discusses the supported framework(s) for optimizing a DNN for deployment on the AIR-T.

TensorRT - The primary method for executing a deep learning algorithm on the AIR-T’s GPU is to use NVIDIA’s TensorRT inference accelerator software. This software will convert a trained neural network into a series of GPU operations, known as an inference engine. The engine can then be saved and used for repeated inference operations.

Deployment on the AIR-T

After the neural network has been optimized, the resulting inference engine may be loaded into a user’s inference application using either the C++ or Python TensorRT API. The user’s inference application is responsible for passing signals from the radio to the inference engine and reading back the results of inference. If using GNU Radio, the GR-Wavelearner library provides a mechanism for building an inference application within a GNU Radio flowgraph.


Last update: July 29, 2020