Mobile computing
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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.
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
- 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
- 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