Simulation of Communication for Power constrained Embedded Systems - PowerPoint PPT Presentation

Simulation of Communication for Power constrained Embedded Systems

By Samir Govilkar

Under the guidance of Dr. Alex Dean

• Rapid Prototyping Tool for Embedded Communication Systems
• Aid development of embedded communication systems by non-specialists
• Targeted at study of crabs using acoustic biotelemetry and health monitoring of bridges using wireless sensor networks

• Blue crabs, Callinectes sapidus, are robust enough to carry a transmitter
• Allows study of physiological and biological parameters
• Power efficiency required because of weight restrictions on the battery
• Ideal evaluation platform for RaPTEX

• Electromagnetic waves cannot be used because of a conductive medium and high scattering
• Acoustic waves provide a good solution
• Lesser dissipation
• Lower scattering
• Communication over hundreds of kilometres possible

• Testing of underwater communication systems requires frequent trips to a water body
• Simulation environment to cut down on the number of such trips by providing a good estimation to the actual conditions
• Provide RaPTEX with performance estimation data

• Spreading Losses
• Geometrical divergence loss
• Effect of the Law of Conservation of Energy
• Dependent on range
• Absorption Losses
• Viscosity of pure water
• Molecular relaxation of Magnesium Sulphate and Boric Acid
• Dependent on temperature, depth and frequency of the acoustic wave

• Multiple paths are followed by the acoustic wave from Tx to Rx
• Reflections from air-water boundary
• Reflections from the water body bed
• Gives rise to multipath fading
• Echoes
• Interference patterns
• The delayed paths have lesser power than the LOS component

• Multipath fading is simulated using a tapped delay line channel model
• The first tap is the LOS component
• The other taps have a gain given by a Rice process

• Surface Agitation Noise caused by wind
• Bursting of bubbles of air at the air-water boundary
• Dependent on wind speed and frequency of the acoustic wave
• Thermal Noise caused by random motion of molecules in water
• Dependent on the frequency

• Snapping Shrimp cause noise by the snapping of their claws
• No mathematical model
• Model was built using observed data
• Dependent on frequency
• Rain Noise caused by impact of rain drops on surface of water
• Dependent on rate of rainfall and wind speed

• Enables use of different sources of data
• For this thesis, two sources are the simulator and data from the field data capture unit

• Avrora – AVR Simulator
• Cycle accurate simulator for AVR microcontrollers
• Highly extensible
• Relatively fast compared to other AVR simulators
• IT++ - Signal Processing Library
• Multipath fading channel classes
• Channel profiles

• Based on the Avrora simulator
• Platform consisting of AVR microcontroller, DAC and Ultrasonic Transducer
• Generates and transmits acoustic signal
• Works as a server, to which other programs can connect to, for obtaining data

• Input is a program in assembly or the output of the avr-objdump facility
• Output is streamed over a TCP connection as pairs of data and timing information

• Attempts to simulate the effects of propagation losses, noise and multipath fading.
• The carrier frequencies are selectively attenuated according to the appropriate noise models
• Noise is filtered and added to the carrier frequency components
• Multipath fading simulation is done using complex numbers

• The input to the WCS is from the ESS via a TCP connection or from a file
• The output is to standard output which can be redirected to a file
• The WCS can record data received over the TCP connection for later playback

• Consists of the Sampling Rate Converter, Receiver Filter array and the demodulator array
• The sampling rate converter will resample the input file to the required sampling frequency
• The receiver filters are 6th order elliptic IIR filters with a 2 kHz bandwidth centered around the carrier frequencies
• The default demodulation scheme is Amplitude Shift Keying (ASK)

• Used to display the RS output waveforms and the demodulated data
• Can be launched from the RS via a command line switch
• Can be launched independently and file can be loaded using the GUI

• This window displays the plots and the corresponding demodulated data

• Simple modulation scheme
• Uses amplitude of the carrier wave to encode the binary data
• Special case is On-Off Keying (OOK)
• Uses presence or absence of the carrier wave to signify a binary ‘1’ and binary ‘0’ respectively.
• Highly susceptible to noise
• Simplicity allows for easier debugging of the system

• Transmission of carrier wave
• Uses a timer interrupt based routine in assembly to ensure operation at 5 MHz sampling rate
• Profile settings
• Wind Speed
• Rainfall Rate
• Temperature
• Salinity
• Depth
• Range

• Sample underwater multipath profiles to be used by the tapped delay line model

• Clear advantage observed in using ‘Recorded’ mode for the WCS over the ‘Live’ mode
• Correlation observed as expected between the channel profiles and the simulation speeds, based on their computational complexity.

• Aim of thesis was to provide a simulation solution for underwater acoustic communication by embedded systems
• Effect of various factors were explored
• Models based on recent research were used to simulate the system

• Integration with RaPTEX needs to be performed in order to use this system efficiently.
• Water body profiles need to be built up by performing measurements of the relevant parameters for the target water bodies
• The Visualization Module can be improved to include more information about the received signal, based on the modulation scheme used.
• Support for multiple modulation schemes can be added to the receiver, in order to evaluate their pros and cons.
• Support for a network of ESS platforms simultaneuously talking to a single WCS.