Fundamentals of Digital Communication

Digital communication system Input Signal Analog/ Digital Low Pass Filter Sampler Quantizer Source Encoder Channel Encoder Multiplexer Carrier Modulator Pulse Shaping Filters Line Encoder To Channel De- Modulator Receiver Filter Detector From Channel Carrier Ref. Signal at the user end Digital-to-Analog Converter Channel Decoder De- Multiplexer

Goal of Modulation Techniques Modulation is difficult task in hostile channels like the mobile radio channels Small-scale fading and multi-path conditions. The goal of a modulation scheme is: To transport the message signal through the radio channel with best possible quality. To occupy least amount of radio (RF) spectrum.

Multipath Propagation signal at sender signal at receiver LOS pulses multipath pulses   short term fading long term fading t power

Wireless channel Effective channel depends on both physical environment and bandwidth!