Simulation of Communication for Power constrained Embedded Systems By Samir Govilkar Under the...
-
Upload
clinton-lawson -
Category
Documents
-
view
219 -
download
0
Transcript of Simulation of Communication for Power constrained Embedded Systems By Samir Govilkar Under the...
Simulation of Communication for Power constrained Embedded Systems
By Samir GovilkarUnder the guidance of Dr. Alex Dean
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
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
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
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
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
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
Transmitter
Receiver
Air
Water
Ground
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
processdT’ dT’ dT’
+
XX Xh(0,t)dT’ h(dT’,t)dT’ h(dT’,t)dT’ …
x(t)
y(t)
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
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
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
L DLPF LPF
π/L π/D
x(n) y(n)
L DLPF
π/max(D,L)
x(n) y(n)
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
System Block Diagram
Embedded System
Simulator (ESS)
Water Channel
Simulator (WCS)
Receiver Simulator (RS)
Field Data
Visualization Module (VM)
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
ESS Block Diagram
Avrora AVR simulator 8 – bit DAC Ultrasonic Transducer
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
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
WCS Block Diagram
Propagation Losses simulator
Noise simulatorMultipath Fading
Channel simulator
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
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)
RS Block Diagram
Sampling Rate Convertor
BW = 2 kHzfc = 60 kHz
BW = 2 kHzfc = 65 kHz
BW = 2 kHzfc = 70 kHz
BW = 2 kHzfc = 75 kHz
BW = 2 kHzfc = 80 kHz
fc = 60 kHz
fc = 65 kHz
fc = 70 kHz
fc = 75 kHz
fc = 80 kHz
Receiver Filter Array Demodulator Array
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
VM Graph Window This window
displays the plots and the corresponding demodulated data
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
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
Multipath profiles Sample underwater
multipath profiles to be used by the tapped delay line model
Underwater 1
Taps 1 2 3 4
Delay(ms) 0 2 4 6
Power (dB) 0 -20 -30 -40
Underwater 2
Taps 1 2 3 4
Delay(ms) 0 2 4 6
Power (dB) 0 -20 -30 -40
Simulation Speed Comparison
0
10
20
30
40
50
60
70
80
90
Live(
Symbo
ls O
nly)
Recor
ded(
Symbo
ls O
nly)
Live(
Full D
ata)
Recor
ded
(Full
Dat
a)
Tim
e (
se
co
nd
s)
Underwater1
Underwater2
Underwater3
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.
Waveforms and Power Spectra
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
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.
Thank You