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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).

Software architecture video service ptu streaming service
Software ArchitectureVideo Service (PTU) – Streaming service:

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 architecture video services server
Software ArchitectureVideo Services (Server):

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