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Fundamental concepts in wireless networks
Sharing Ressources
Cellular concepts (reuse re sources)
WLAN (shared space)
Ad hoc (shared resources)
Sensor (shared resources, large space)
WIRELESS COMMUNICATION TECHNOLOGY
Fundamentals
Electromagnetic waves—characterized by frequency or wavelength, relationship: c=λf
Fundamental concepts in wireless networks
Sharing Ressources
Cellular concepts (reuse re sources)
WLAN (shared space)
Ad hoc (shared resources)
Sensor (shared resources, large space)
WIRELESS COMMUNICATION TECHNOLOGY
Fundamentals
Electromagnetic waves—characterized by frequency or wavelength, relationship: c=λf
The electro magnetic spectrum
SPECTRUM ALLOCATION
Done by Governments
Internationally by ITU-R (WARC) World Administrative Radio Conference
Methods
Beauty contest method
Lottery system
Auctioning
Unlicensed usage
ISM, for industrial scientific and medicinal
In US & Canada 900Mhz and 5Ghz
Radio Propagation Mechanisms
Reflection
Diffraction
Scattering
Characteristics of wireless channel
Transmission impediments
Path loss
Fading
Interference
Doppler shift
Transmission rate constraints
Nyquist’s theorem
Shannon’s theorem
Ratio of transmitted signal power to the received signal power.
Models: free space, two-ray
Free space : Pr =Pt Gt Gr (λ/4∏d)2
Two ray model Pr =Pt Gt Gr (hthr/d2)2
Fading
Fluctuation in signal strength when received at the receiver.
Fast fading—due to propagation mechanisms (delay spread—time difference b/w reception of first version of the signal and last signal)
Slow fading (shadow fading)—due to blocks in the path (eg building)—lasts for long time
Diversity
providing multiple channels between Tx and Rx which may differ in space, time or frequency & send parts of the signals in each channel.
Adaptive modulation
Get feedback from Rx and Tx acts accordingly.
Adjacent channel interference: components of the signal which are outside the allocated range between two nearby signal frequencies may interfere. Avoid by providing guard band
Co-channel / narrowband interference–due to other nearby systems using same frequency.
Inter symbol interference- due to temporal spreading and the consequent overlapping of individual signal.
Change/shift in frequency when transmitter and receiver are mobile with respect to each other.
Given by fd= v/λ where v is the relative velocity between Tx and Rx.
Capacity of the channel :
C= 2 * B * log 2 L b/s. L=number of voltage values or signals used
for noiseless channel
C= B * log 2 (1+ S/N)
for noisy channel