Chapter 4 (part 1_a)
Baseband Data Transmission
EKT 357 Digital Communications
Chapter 1 (part 1_a) Overview
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Baseband data transmission
Line coding
Baseband Transmission
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A sequence of binary digits are to be
transmitted through a baseband channel.
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However, no channel can be used for the
transmission of binary digits without first
transforming the digits to waveforms that are
compatible with the channel.
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For baseband channels, compatible waveforms
are pulses.
Line Coding
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Using Digital Signals to Transmit Digital Data
 Bits must be changed to digital signal for transmission
 Unipolar encoding
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Polar encoding
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Positive or negative pulse used for zero or one
Uses two voltage levels (+ and - ) for zero or one
Bipolar encoding
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+, -, and zero voltage levels are used
Line coding and decoding
4.5
Line Coding
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The binary digits with electrical pulses in order to
transmit them through a baseband channel.
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Pulse modulation applied to binary symbol, the
resulting binary waveform is called PCM waveform.
(E.g. Line Codes)
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Four main groups of line codes
 Non return to zero (NRZ)
 Return to Zero (RZ)
 Phase encoded
 Multilevel binary
Non Return To Zero (NRZ)
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NRZ-L
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Used extensively in digital logic circuit
Binary 1 one represented by one voltage level
Binary 0 is represented by another voltage level.
Non Return To Zero (NRZ)
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NRZ-M
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Used in magnetic tape recording.
The 1 (mark) is represented by change in level
The 0 (space) is represented by no change in level
Differential encoding
Non Return To Zero (NRZ)
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NRZ-S
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Complement of NRZ-M
1 is represented by no change in level
0 is represented by a change in level
Return To Zero (RZ)
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Unipolar RZ
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1 is represented by a half bit wide pulse.
0 is represented by the absence of pulse.
Return To Zero (RZ)
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Bipolar RZ
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1 & 0 are represented by opposite level pulses that are one
half bit wide.
Pulse present in each bit interval.
Return To Zero (RZ)
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RZ-AMI
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1 is represented by equal amplitude alternating pulses.
0 is represented by the absences of pulse.
Phase Encoded
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Bi-phase-level @ Manchester coding
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1 half-bit-wide pulse positioned during the first
half of the bit interval
0 half-bit-wide pulse positioned during the
second half of the bit interval.
Phase Encoded
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Bi-phase-mark
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Transition occurs at the beginning of every bit
interval.
1 second transition one half bit interval later
0 no second transition
Phase Encoded
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Bi-phase-space
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Transition happen on the beginning of every bit
interval.
1no second transition
0 second transition one-half bit interval later.
Phase Encoded
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Delay modulation @ Miller coding
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1transition of the mid-point of the bit interval.
0 no transition, unless it is followed by another
zero.
Multilevel Binary
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Used three levels to encode the binary data.
Dicode and duo binary
Multilevel Binary
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Dicode –NRZ
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Transition happen on the beginning of every bit
interval.
1 to 0 or 0 to 1 data transition changes the pulse
polarity
without a data transition, the 0 level is sent.
Multilevel Binary
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Dicode- RZ
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Transition happen on the beginning of every bit
interval.
1 to 0 or 0 to 1 transition produces a half-duration
polarity change;
Otherwise, a 0 level is sent.
NRZ
RZ
Phase
Encoded
Multilevel
Binary