{
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   "source": [
    "# Pulling radio data out of thin air\n",
    "\n",
    "## Yuval Adam"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
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   },
   "source": [
    "## Yuval Adam\n",
    "\n",
    " - Full stack developer and systems architecture consultant\n",
    " - Using Python for **everything** for 10+ years\n",
    " - https://yuv.al\n",
    " - [@yuvadm](https://twitter.com/yuvadm)\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## This talk\n",
    "\n",
    " - I never learned physics, RF engineering or signal processing\n",
    " - But radios are pretty cool!\n",
    " - Hopefully I can show you some neat things\n",
    " - Slides and code @ https://github.com/yuvadm/radio-pyconil-2018"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Radio\n",
    "\n",
    "![static/waves.gif](static/waves.gif)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Radio Waves\n",
    "\n",
    "![static/dipole.gif](static/dipole.gif)\n",
    "\n",
    "*Source: https://en.wikipedia.org/wiki/Antenna_(radio)*\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Hardware Radio\n",
    "\n",
    "![static/radio.jpg](static/radio.jpg)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## Hardware Radio\n",
    "\n",
    "![static/gsm.jpg](static/gsm.jpg)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Software-Defined Radio\n",
    "\n",
    "![rtlsdr.jpg](static/rtlsdr.jpg)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## What's it good for\n",
    "\n",
    " - Digital TV broadcast (\"Idan+\", DVB-T)\n",
    " - Airplane tracking (ADS-B)\n",
    " - Weather satellites\n",
    " - IoT project integration\n",
    " - FM radio broadcast"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## Airplane Location Tracking (ADSB)\n",
    "\n",
    "![static/adsb.png](static/adsb.png)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## Weather Satellites\n",
    "\n",
    "![static/noaa.jpg](static/noaa.jpg)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## Internet of Things\n",
    "\n",
    "![static/iot.jpg](static/iot.jpg)\n",
    "\n",
    "*Source: https://blog.hackster.io/iot-devices-may-be-susceptible-to-replay-attacks-with-a-raspberry-pi-and-rtl-sdr-dongle-de6eca268fbf*"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "# I/Q Sampling\n",
    "\n",
    "![static/cosample.png](static/cosample.png)\n",
    "\n",
    "*Source: http://whiteboard.ping.se/SDR/IQ*"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## I/Q Sampling\n",
    "\n",
    "![static/corkscrew.png](static/corkscrew.png)\n",
    "\n",
    "*Source: http://whiteboard.ping.se/SDR/IQ*"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Modulations\n",
    "\n",
    "![static/amfm2.gif](static/amfm2.gif)\n",
    "\n",
    "*Source: http://mriquestions.com/signal-squiggles.html*"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## GQRX"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
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   },
   "outputs": [],
   "source": [
    "# pyrtlsdr provides us bindings to work with the RTL-SDR driver\n",
    "\n",
    "from rtlsdr import RtlSdr\n",
    "\n",
    "sdr = RtlSdr()\n",
    "sdr.sample_rate = 1.2e6       # 1,200,000 samples per second\n",
    "sdr.center_freq = 91.8e6      # 91,800,000 Hz frequency for the radio station\n",
    "sdr.gain = 'auto'             # tune the gain (AKA \"volume\") automatically\n",
    "\n",
    "samples = sdr.read_samples(1.2e6 * 10)\n",
    "sdr.close()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
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   },
   "outputs": [],
   "source": [
    "# Alternatively, load previously captured samples from rtl_sdr\n",
    "# and convert them from unsigned 8-bit samples to a complex IQ array\n",
    "\n",
    "import numpy as np\n",
    "\n",
    "raw = np.fromfile('/tmp/samples.in', np.uint8).astype(np.float64)\n",
    "raw += -127\n",
    "raw /= 2**7\n",
    "samples = (raw[0::2] + 1j * raw[1::2]).astype(np.complex64)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "# We captured too many samples so we need to apply a low pass filter\n",
    "# In other words, we have a too large window and we want to make it smaller\n",
    "\n",
    "import scipy.signal as signal\n",
    "\n",
    "BANDWIDTH = 200e3\n",
    "DECIMATION_RATE = int(1.2e6 / BANDWIDTH)  # Decimation factor of 6\n",
    "\n",
    "samples = signal.decimate(samples, DECIMATION_RATE)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "# Apply the Frequency DEmodulation\n",
    "# We use something called a polar discriminator\n",
    "\n",
    "samples = np.angle(samples[1:] * np.conj(samples[:-1]))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
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   },
   "outputs": [],
   "source": [
    "# De-emphasis filter\n",
    "# Even I'm not sure exactly how/why this works\n",
    "\n",
    "# MAKE THINGS SOUND BETTER\n",
    "\n",
    "d = BANDWIDTH * 75e-6\n",
    "x = np.exp(-1/d)\n",
    "b, a = [1-x], [1,-x]\n",
    "samples = signal.lfilter(b, a, samples)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "# Decimate the signal down to something an audio driver can handle\n",
    "# We only catch the mono part of the signal\n",
    "\n",
    "AUDIO_RATE = 50e3\n",
    "DECIMATION_RATE = int(BANDWIDTH / AUDIO_RATE)  # Decimation factor of 4\n",
    "\n",
    "samples = signal.decimate(samples, DECIMATION_RATE)\n",
    "\n",
    "# Amplify the signal volume\n",
    "samples *= 10000\n",
    "samples = samples.astype('int16')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "# HIT IT\n",
    "\n",
    "import alsaaudio\n",
    "\n",
    "device = alsaaudio.PCM(alsaaudio.PCM_PLAYBACK, device='default')\n",
    "device.setchannels(1)\n",
    "device.setrate(50000)\n",
    "device.setformat(alsaaudio.PCM_FORMAT_S16_LE)\n",
    "device.setperiodsize(120)\n",
    "\n",
    "# Write data in chunks\n",
    "for s in np.array_split(samples, 120):\n",
    "    device.write(s)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Review\n",
    "\n",
    " - Took a fixed set of samples, did some math on them\n",
    " - Python, NumPy and SciPy are very good at doing fast processing of **static** data\n",
    " - When handling **real-time** data, buffering becomes a serious issue\n",
    "  - How do you synchronize different input/ouput sample rates on the same flow?"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## GNU Radio\n",
    "\n",
    "- Comprehensive signal processing framework\n",
    "- Implemented many DSP primivites\n",
    "- Has a great scheduling engine\n",
    "- *Actually* generates flowgraphs in Python"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Where to go from here\n",
    "\n",
    " - Buy an RTL-SDR dongle, they start at less than $10\n",
    "  - eBay, AliExpress\n",
    " - Learn more about SDR, signal processing\n",
    "  - https://osmocom.org/projects/sdr/wiki/rtl-sdr\n",
    "  - https://www.reddit.com/r/RTLSDR/wiki/index\n",
    "  - Michael Ossmann's video course - https://greatscottgadgets.com/sdr/\n",
    " - But you don't really need do know math\n",
    "  - Lots of code is already written\n",
    " - Explore the radio waves!"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Thank you! Questions?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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