Unipolar encoding
Encyclopedia
Unipolar encoding is a line code
. A positive voltage represents a binary
1, and zero volts indicates a binary 0. It is the simplest line code, directly encoding the bitstream, and is analogous to on-off keying
in modulation.
Its drawbacks are that it is not self-clocking
and it has a significant DC component, which can be halved by using return-to-zero
, where the signal returns to zero in the middle of the bit period. With a 50% duty cycle
each rectangular pulse is only at a positive voltage for half of the bit period. This is ideal if one symbol is sent much more often than the other and power considerations are necessary, and also makes the signal self-clocking.
Traditionally, a unipolar scheme was designed as a non-return-to-zero
scheme, in which the positive voltage defines bit 1 and the zero voltage defines bit 0. It is called NRZ because the signal does not return to zero at the middle of the bit.
Compared with its polar counterpart, Polar NRZ, this scheme is very expensive. The normalized power (power required to send 1 bit per unit line resistance) is double that for polar NRZ. For this reason, this scheme is not normally used in data communications today.
In a unipolor encoding, all signal levels are on one side of the axis, either above or below.
NRZ(Non-Return-Zero) Traditionally, a unipolor coding was designed as a non-return-zero(NRZ) coding in which the positive voltage defines bit 1 and the zero voltage defines bit 0. It is called NRZ because the signal does not return to zero at the middle of the bit. Compared with the counterpart, this coding is very costly. Hence, this scheme is normally not used in data communications today.
Line code
In telecommunication, a line code is a code chosen for use within a communications system for baseband transmission purposes...
. A positive voltage represents a binary
Binary logic
Binary logic could refer to:* any two-valued logic, especially in social sciences* classical propositional two-valued logic, also called boolean logic in engineering, which is the logical foundation of digital electronics...
1, and zero volts indicates a binary 0. It is the simplest line code, directly encoding the bitstream, and is analogous to on-off keying
On-off keying
On-off keying the simplest form of amplitude-shift keying modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binary one, while its absence for the same duration represents a...
in modulation.
Its drawbacks are that it is not self-clocking
Self-clocking signal
In telecommunications and electronics, a self-clocking signal is one that can be decoded without the need for a separate clock signal or other source of synchronization...
and it has a significant DC component, which can be halved by using return-to-zero
Return-to-zero
For the Delp/Goudreau band, see RTZReturn-to-zero describes a line code used in telecommunications signals in which the signal drops to zero between each pulse. This takes place even if a number of consecutive 0's or 1's occur in the signal. The signal is self-clocking...
, where the signal returns to zero in the middle of the bit period. With a 50% duty cycle
Duty cycle
In engineering, the duty cycle of a machine or system is the time that it spends in an active state as a fraction of the total time under consideration....
each rectangular pulse is only at a positive voltage for half of the bit period. This is ideal if one symbol is sent much more often than the other and power considerations are necessary, and also makes the signal self-clocking.
Traditionally, a unipolar scheme was designed as a non-return-to-zero
Non-return-to-zero
In telecommunication, a non-return-to-zero line code is a binary code in which 1's are represented by one significant condition and 0's are represented by some other significant condition , with no other neutral or rest condition. The pulses have more energy than a RZ code...
scheme, in which the positive voltage defines bit 1 and the zero voltage defines bit 0. It is called NRZ because the signal does not return to zero at the middle of the bit.
Compared with its polar counterpart, Polar NRZ, this scheme is very expensive. The normalized power (power required to send 1 bit per unit line resistance) is double that for polar NRZ. For this reason, this scheme is not normally used in data communications today.
See also
- Bipolar encodingBipolar encodingIn telecommunication, bipolar encoding is a type of line code . A duobinary signal is such an encoding.- Advantages :...
- Bipolar violationBipolar violationA bipolar violation, bipolarity violation, or BPV, is a violation of the bipolar encoding rules where two pulses of the same polarity occur without an intervening pulse of the opposite polarity. This indicates an error in the transmission of the signal.T-carrier and E-carrier signals are...
- On-off keyingOn-off keyingOn-off keying the simplest form of amplitude-shift keying modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binary one, while its absence for the same duration represents a...
In a unipolor encoding, all signal levels are on one side of the axis, either above or below.
NRZ(Non-Return-Zero) Traditionally, a unipolor coding was designed as a non-return-zero(NRZ) coding in which the positive voltage defines bit 1 and the zero voltage defines bit 0. It is called NRZ because the signal does not return to zero at the middle of the bit. Compared with the counterpart, this coding is very costly. Hence, this scheme is normally not used in data communications today.