Chapter 4 (part 1_a) Baseband Data Transmission EKT 357 Digital Communications

Chapter 1 (part 1_a) Overview Baseband data transmission Baseband data transmission Line coding Line coding

Baseband Transmission A sequence of binary digits are to be transmitted through a baseband channel. A sequence of binary digits are to be transmitted through a baseband channel. 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. 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. For baseband channels, compatible waveforms are pulses. For baseband channels, compatible waveforms are pulses.

Line Coding Using Digital Signals to Transmit Digital Data Using Digital Signals to Transmit Digital Data Bits must be changed to digital signal for transmission Bits must be changed to digital signal for transmission Unipolar encoding Unipolar encoding Positive or negative pulse used for zero or one Positive or negative pulse used for zero or one Polar encoding Polar encoding Uses two voltage levels (+ and - ) for zero or one Uses two voltage levels (+ and - ) for zero or one Bipolar encoding Bipolar encoding +, -, and zero voltage levels are used +, -, and zero voltage levels are used

Line coding and decoding 4.5

Line Coding The binary digits with electrical pulses in order to transmit them through a baseband channel. The binary digits with electrical pulses in order to transmit them through a baseband channel. Pulse modulation applied to binary symbol, the resulting binary waveform is called PCM waveform. (E.g. Line Codes) Pulse modulation applied to binary symbol, the resulting binary waveform is called PCM waveform. (E.g. Line Codes) Four main groups of line codes Four main groups of line codes Non return to zero (NRZ) Non return to zero (NRZ) Return to Zero (RZ) Return to Zero (RZ) Phase encoded Phase encoded Multilevel binary Multilevel binary

Non Return To Zero (NRZ) NRZ-L NRZ-L Used extensively in digital logic circuit Used extensively in digital logic circuit Binary 1 one represented by one voltage level Binary 1 one represented by one voltage level Binary 0 is represented by another voltage level. Binary 0 is represented by another voltage level.

Non Return To Zero (NRZ) NRZ-M NRZ-M Used in magnetic tape recording. Used in magnetic tape recording. The 1 (mark) is represented by change in level The 1 (mark) is represented by change in level The 0 (space) is represented by no change in level The 0 (space) is represented by no change in level Differential encoding Differential encoding

Non Return To Zero (NRZ) NRZ-S NRZ-S Complement of NRZ-M Complement of NRZ-M 1 is represented by no change in level 1 is represented by no change in level 0 is represented by a change in level 0 is represented by a change in level

Return To Zero (RZ) Unipolar RZ Unipolar RZ 1 is represented by a half bit wide pulse. 1 is represented by a half bit wide pulse. 0 is represented by the absence of pulse. 0 is represented by the absence of pulse.

Return To Zero (RZ) Bipolar RZ Bipolar RZ 1 & 0 are represented by opposite level pulses that are one half bit wide. 1 & 0 are represented by opposite level pulses that are one half bit wide. Pulse present in each bit interval. Pulse present in each bit interval.

Return To Zero (RZ) RZ-AMI RZ-AMI 1 is represented by equal amplitude alternating pulses. 1 is represented by equal amplitude alternating pulses. 0 is represented by the absences of pulse. 0 is represented by the absences of pulse.

Phase Encoded Manchester coding Manchester coding 1  half-bit-wide pulse positioned during the first half of the bit interval 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. 0  half-bit-wide pulse positioned during the second half of the bit interval.

Phase Encoded Bi-phase-mark Bi-phase-mark Transition occurs at the beginning of every bit interval. Transition occurs at the beginning of every bit interval. 1  second transition one half bit interval later 1  second transition one half bit interval later 0  no second transition 0  no second transition

Phase Encoded Bi-phase-space Bi-phase-space Transition happen on the beginning of every bit interval. Transition happen on the beginning of every bit interval. 1  no second transition 1  no second transition 0  second transition one-half bit interval later. 0  second transition one-half bit interval later.

Phase Encoded Delay Miller coding Delay Miller coding 1  transition of the mid-point of the bit interval. 1  transition of the mid-point of the bit interval. 0  no transition, unless it is followed by another zero. 0  no transition, unless it is followed by another zero.

Multilevel Binary Used three levels to encode the binary data. Used three levels to encode the binary data. Dicode and duo binary Dicode and duo binary

Multilevel Binary Dicode –NRZ Dicode –NRZ Transition happen on the beginning of every bit interval. Transition happen on the beginning of every bit interval.  1 to 0 or 0 to 1 data transition changes the pulse polarity  1 to 0 or 0 to 1 data transition changes the pulse polarity  without a data transition, the 0 level is sent.  without a data transition, the 0 level is sent.

Multilevel Binary Dicode- RZ Dicode- RZ Transition happen on the beginning of every bit interval. Transition happen on the beginning of every bit interval. 1 to 0 or 0 to 1 transition produces a half-duration polarity change; 1 to 0 or 0 to 1 transition produces a half-duration polarity change; Otherwise, a 0 level is sent. Otherwise, a 0 level is sent.

NRZ RZ Phase Encoded Multilevel Binary