Simulation of Communication for Power constrained Embedded Systems

1. Simulation of Communication for Power constrained Embedded Systems By Samir Govilkar Under the guidance of Dr. Alex Dean

2. The RaPTEX Project • 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

3. Studying Crabs using acoustic biotelemetry • 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

4. Underwater communication • 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

5. A simulation environment • 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

6. Propagation Losses • 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

7. Multiple Paths • 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

8. Modeling Multiple Paths • 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

9. Ambient Noise • 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

10. Intermittent Noise • 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

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

12. Related Work • 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

13. System Block Diagram

14. Embedded System Simulator (ESS) • 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

15. ESS Block Diagram • 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

16. Water Channel Simulator (WCS) • 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

17. WCS Block Diagram • 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

18. Receiver Simulator • 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)

19. RS Block Diagram

20. Visualization Module • 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

21. VM Graph Window • This window displays the plots and the corresponding demodulated data

22. Amplitude Shift Keying (ASK) • 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

23. Implementation • 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

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

25. Simulation Speed Comparison

26. Results • 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.

27. Waveforms and Power Spectra

28. Observations • 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

29. Future Work • 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.

30. Thank You