25-05-2012, 03:13 PM
Introduction to Wireless
Introduction to Wireless.ppt (Size: 1.72 MB / Downloads: 69)
What is wireless communication?
Any form of communication that does not require the transmitter and receiver to be in physical contact through guided media
Electromagnetic wave propagated through free-space
Radar, RF, Microwave, IR, Optical
Simplex: one-way communication (e.g., radio, TV)
Half-duplex: two-way communication but not simultaneous (e.g., push-to-talk radios)
Full-duplex: two-way communication (e.g., cellular phones)
Frequency-division duplex (FDD)
Time-division duplex (TDD): simulated full-duplex
Why use wireless communication?
Provides mobility
A user can send and receive messages no matter where he/she is located
Added convenience / reduced cost
Enables communications without adding expensive infrastructure
Can easily setup temporary wireless LANs (disaster situations)
Developing nations use cellular telephony rather than laying wires to each home
Use resources only when sending or receiving signal
Why is wireless different than wired?
Noisy, time-varying channel
BER varies by orders of magnitude
Enviromental conditions affect transmission
Shared medium
Other users create interference
Must develop ways to share the channel
Bandwidth is limited
TÜK, FCC determines the frequency allocation
ISM band for unlicensed spectrum (902-928 MHz, 2.4-2.5 GHz, 5.725-5.875 GHz)
Requires intelligent signal processing and communications to make efficient use of limited bandwidth in error-prone environment