17-03-2014, 04:53 PM
Baseband Transmission (1): Line coding and Power Spectrum Analysis
Objectives
z Learn various types of baseband signal encoding (line coding), which
converts bits into electrical signals for transmission over a baseband
channel.
z Learn how to determine the PSD of a baseband signal.
Baseband Encoding/Modulation
Transform (“modulate
modulate”) binary symbols (0, 1) to an electrical
waveform (signal) for transmission over a baseband channel.
Digital waveforms = baseband pulses, also called “line codes” in
telephony applications.
Each digital symbol is mapped into one of baseband waveforms g1(t), g2(t),
..., gM(t)
z
Desired attributes for line codes
Timing Information
z Receiver must determine the sampling times for signal decoding.
z A separate clock signal is expensive.
z The waveform must contain adequate timing (clock) information
Sufficient number of signal transitions for clock recovery at receiver.
Otherwise, the receiver may lose clock synchronization.
Therefore, a signal should not contain a long period of single signal
level for a long string of 0’s or 1’s (static data).