This document provides an overview of key concepts in mobile computing. It discusses: 1) Modes of evaluation including problem-based learning, continuous assessments, and term-end exams. 2) Types of mobility including user mobility (e.g. Vodafone services) and device mobility (e.g. mobile phones). 3) Characteristics of communication devices ranging from fixed/wired to mobile/wireless and applications of mobile technologies in various domains like vehicles, emergencies, and replacing wired networks.

1. ITA503-Mobile Computing

2. • Mode of evaluation
– PBL
– CAT1
– CAT2
– Term end

3. • Text Book:”Mobile communication” Schiller
2ed Pearson education
– “Computer networks” A Tanenbaum 4ed
• Reference:”wireless communications “ T S
Rappaport 2ed pearson

4. Types of mobility
1)User mobility
eg: vodofone service
2)Device mobility
eg:mobile phones

5. Characteristic of communication devices
• Fixed & wired eg:Desktop
• Mobile & wireless eg:Laptop
• Fixed & wireless eg:wireless on historical
buildings
• Mobile and wireless eg:GSM

6. Applications
• Vehicles
• Emergencies
• Business
• Replacement of wired networks- sensor
networks
• Infotainment

7. Mobile & wireless devices
• Sensors
• Embedded Controllers
• Pagers
• Mobile phones
• Personal digital assistance
• Pocket computers
• Notepad/lap tops

8. Simple n/w & reference Model

9. Frequency Spectrum

10. Frequency Allocations(in MHz)

12. Signals
• Signals are function of time & location
• Signal Parameters represent the data values.
• Carrier signals
• Periodic signals(sine waves)
• A-amplitude
• F-frequency
• ϕ-phase swift

14. Time domain

15. Signal reconstruction by Fourier
• C-determine direct current component of
signal
• an & bn amplitudes of nth sine & cosine
functions

16. Frequency domain &Phase domain
M - Amplitude Of Signal
I – In-Phase(phase 0)
Q - Quadrature(90’ Phase Shift)
Representation of Signals

17. Antennas
• It couples electromagnetic energy to and from
space to and from a wire or a coaxial cable
• Theoretical reference : it is isotropic radiator
• i.e – a point in a space radiating equal power
in all directions
• Radiation pattern is symmetric in all directions

18. • Isotropic antennas does not exist in reality
• Real antennas exhibit directive effect(intensity
is not same in all directions)
• Types of antennas
– Dipole
– Omni directional
– Directional
– Sectorized
– Diversity

19. • Dipole antennas
– Consist of two collinear conductors of equal
length , separated by small gap

20. • Omni – directional
– Radiation pattern in one plane
– This is used to overcome environmental
challenges by boosting power level of signal
– Challenges could be mountains, valley, building etc

21. • Directional antennas
– Radiation pattern only in x-axis
– Special eg: Satellite dishes

22. • Sectorized antennas
– Several directional antennas combined on a single
pole

23. • Diversity combining
– Constitutes a power of all signals to produce gain
– Phase is corrected to avoid cancellation

24. Signal propagation
• One can determine the behavior of a signal
travelling along wire, e.g., received power
depending on the length of wire
• For wireless ,the above prediction is valid only
in vacuum

25. • Transmission Range: with this radius of the sender
transmission is possible
• Detection range: within a second radius , detection
of transmission is possible.
i.e transmitted power is large enough to differ from
background noise
• Interference range:background noise is added with
the transmission.

26. Path Loss of radio signals
• Line-of-sight
• Path loss in vacuum
– Received energy pr =1/d2
– d is distance between sender & receiver
• Sender in a space radiate energy in spherical
shape,surface area is s=4πd2 increasing results
loss
• Received power depends on the wavelength,
gain of the receiver & transmitter antennas

27. • Penetration of signal on object depends on
the frequency
• Lower frequency better penetration
3 fundamental behavior of radio waves
• Ground waves
• Sky waves
• Line of sight

28. Ground waves(<2MHz)
– It follows earths surface and propagate long
distance
Sky waves (2-30 MHz)-(short waves)
– Reflected by ionosphere
Line of sight (>30MHz)
– Follows straight line of sight
– No reflection in ionosphere
– Cable of bending due to refraction
– Mobile phone system, satellite system, cordless
phone

29. Additional Signal propagation effects
• Blocking or shadowing of radio signals due to
large obstacles
• Reflection
• Refraction-bending effect of signal

30. • Scattering :size of obstacle is in order of the
wavelength or less,radio waves get scattered
• Diffraction: Deflection at the edge of object
and propagate in different direction

31. Multi-path propagation

32. • Along with direct transmission from a sender
to a receiver the propagation effects like
scattering, reflection, difraction leads to one
of the severe effect called Multi-path
propagation

33. • signals travelling along different paths with
different lengths arrive at the receiver at
different times
• This effect is called delay spread
• Typical values for delay spread are
approximately 3 μs in cities, up to 12 μs
• GSM, for example, can tolerate up to 16 μs of
delay spread, i.e., almost a 5 km path
difference

34. Effects of spread delay
• A short impulse will be smeared out into a
broader impulse, or rather into several weaker
impulses.
• Inter-symbol-Interference(ISI) - At the
receiver, both impulses interfere, i.e., they
overlap in time

35. Avoiding ISI
• Knowing the channel characteristic
• If sender knows the delay of different path ,it
can compensate the distortion caused by the
channel
• How?
– sender may first transmit a training sequence
known by the receiver. The receiver then
compares the received signal to the original
training sequence and programs an equalizer that
compensates for the distortion

36. Fading
• The power of the received signal changes
considerably over time
• Short time fading-quick changes in the
received power are called short-term fading
– signals may have a different phase due to different
paths and cancel each other

37. • Long term fading:
– The average power over time, is caused by, for
example, varying distance to the sender
– senders can compensate for long-term fading by
increasing/decreasing sending power

38. MULTIPLEXING
• Multiplexing describes how several users can
share a medium with minimum or no
interference
• For wireless communication, multiplexing can
be carried out in four dimensions:
– space, time, frequency, and code

39. Space Division Multiplexing (SDM)
• Guard Space

40. Frequency Division Multiplexing(TDM)
• Adjacent channel interference
• Guard Space

41. Time Division Multiplexing(TDM)
• Co-Channel Interference

42. Mix of FDM & TDM

43. Code Division Multiplexing (CDM)
• Secure
• Codes are used
• Orthogonal code
• Guard space as codes