What is communication? • Transmit information over unreliable channels – Wired • Telephone • Cable TV • Fiber optic
– Wireless • Mobile phone • Wireless local area network • Satellite
– Storage • Hard drive • Compact disc
Wireless Multimedia Networks Ad-hoc Network Wired LAN
Wired LAN
Backbone Network
Wireless Cellular
Wireless Cellular Wireless LAN Wireless LAN
Communication channel model Input
+
Channel Filter
Output
Noise + Interference
• • • •
Channel filter causes distortions Noise in receiver equipment Interference from the environment Limited bandwidth and power
Goal: Design signals to effectively send information over communication channels.
Digital Communications • You have already seen analog modulation • Digital modulation Amplitude
Time – Digital signals: both amplitude and time discrete • Analog to digital: Sampling and quantization
Digital Modulation • Digital information: Sequence of 0’s and 1’s: 001101….. • One bit every T seconds. During 0 < t < T s0 (t ) = A cos(2πf c t ) – To send a 0, send s1 (t ) = − A cos(2πf c t )
– To send a 1, send
• Input signal 0
• Modulated signal
0
1
1
0
1
Simple Representation of Digital Modulation Signals • In s0 (t ) and s1 (t ) the term cos(2πf c t ) is common – Equivalently
