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WPSS System Architecture. Edusafe Technical Meeting Tuscania 6 June 2013. Panayiotis Mousouliotis, ECE Diploma-master. Overview. System Overview Hardware Architecture Software Architecture Software System Evaluation. Wireless Personal Surveillance System (WPSS) Overview.

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wpss system architecture

WPSS System Architecture

Edusafe Technical Meeting


6 June 2013

Panayiotis Mousouliotis, ECE Diploma-master

  • System Overview
  • Hardware Architecture
  • Software Architecture
  • Software System Evaluation
wireless personal surveillance system wpss overview
Wireless Personal Surveillance System (WPSS) Overview
  • 3 main components
    • PTU
    • Cable
    • Helmet attachment
  • Streams data over the

CERN network

    • Video
    • Audio
    • Sensor data
  • Receives audio data over the CERN network
hardware architecture
Hardware Architecture

PTU Components:

  • GumstixOveroFireSTORMCOM
    • Main Processor (Texas Instruments OMAP3730)
    • DSP Processor (C64x Fixed Point DSP 660 MHz)
    • Audio and Power Management chip (TPS65950)
    • WiFi and Bluetooth chip (Marvell 88W8686)
    • 512MB low power RAM
    • 512MB NAND flash
  • Battery
hardware architecture1
Hardware Architecture

Helmet Attachment Components:

  • Camera (Logitech C920 USB camera)
  • Omnidirectional microphone (on the camera PCB)
  • Microcontroller (ATmega168 for LED control)
  • Push-button (industrial SPST for LED control)
  • LED Driver (powered by the PTU)
  • LEDS (3x Luxeon Rebel LEDS)
  • Headphone jack (3.5mm TRS connector from PTU output)
  • Microphone jack (3.5mm TRS connector to the PTU input)
hardware architecture2
Hardware Architecture

Connecting cable:

  • For PTU and Helmet Attachment connection
  • Flexible
  • Military type connector
  • 6 wires:
software architecture
Software Architecture

Operating System of the COM module:

  • Ångström Linux distribution
  • Custom patched 2.6.34 kernel to enable:
    • Power management function (TPS65950 chip)
    • OTG USB port power override
    • Camera sensor driver for ARM ISP (Image Signal Processor) utilization
  • UBI filesystem on COM’s NAND flash memory
    • extending the memory’s life
software architecture1
Software Architecture

System boot procedure:

  • Bring up the wireless device and connect to some predefined SSID (e.g. ”CERN”)
  • Connect as a client to a VPN network that is served by the main video processing server
  • Bring up audio, video and watchdog services
software architecture2
Software Architecture

Audio Service (PTU)

  • Communication with the supervisor station
  • Linphone VoIP software
    • PCMU encoding at 8kHz
    • Optimized for the GumstixOvero sound device (TPS65950)
  • Bash script for push button -> GPIO pin interpretation:
software architecture3
Software Architecture

Audio services (Server)

  • Asterisk server
    • Telephone book register between the mobile clients. Possible connection with CERN telephone network.

Audio services (Supervision post)

  • Linphone or other VoIP solution
software architecture4
Software Architecture

Video Services Overview:

  • Streaming service
    • Executed on the PTU. Custom code based on the gstreamer framework, optimized for the ARM/DSP architecture
  • Receiving service
    • Executed on the Server. Custom code based on the gstreamer framework, possibility for optimization on GPU hardware
  • Transcoding service
    • Executed on the Server. Based on the VideoLan Client application
system architecture
System Architecture

Video Service (PTU) – Streaming service – gstreamer video pipeline:

  • Video4Linux2 source element
    • Takes images from the Logitech camera
  • Color Conversion element
    • Converts YUYV as output from the camera to UYVY for processing on the DSP.
  • H264 encoding element
    • Encodes H264 video on the DSP
  • Packetization and transmission element
    • Packetizes the video stream and transmits over the network (acknowledged transmission imposed by the ATLAS environment).
system architecture1
System Architecture

Video Service (Server) – Receiver service:

  • Reception and depacketization element
  • H264 decoding element
  • Image processing/overlaying element
    • Processes each image frame or overlays information on them
  • Input selector element
    • It’s purpose is to switch between it’s two inputs on request (when the network stream is interrupted in order to keep the pipeline alive)
  • Video4Linux2 sink element
    • Sinks the video stream into a virtual Video4Linux2 loopback device. The decoded and processed stream can be subsequently accessed by Video4Linux2 applications as a /dev/video? device
system architecture2
System Architecture

Video Service (Server) – Transcoding service:

  • VideoLan Client application
    • Input from video loopback device
    • Transcoding into
      • MJPEG served via HTTP (suitable for supervisor post)
      • H264 in MPEG4 TS (suitable for storage)
        • served as a file through HTTP
        • as an HTML5 video stream, after being split into 10 second chunks
software architecture5
Software Architecture

Watchdog Services (PTU):

  • Wireless network connection
    • Periodic checks are needed to detect loss of signal or perform roaming between access points
  • System health
    • Detection and relaunching of hanged services
  • Connection with DAQ server or supervision post
    • Detection of proper operation of data streams (audio/video/sensors)
software system evaluation
Software System Evaluation
  • Acceptable performance
  • Some gstreamer elements are bottlenecks:
    • On the PTU, color conversion and compression do not take full advantage of the hardware (ISP/DSP)
    • On the server side, some image processing elements do not take full advantage of the multiple cores and the decoding element does not use the GPU