Unipolar encoding is a

line code In telecommunications, a line code is a pattern of voltage, current, or photons used to represent digital data transmission (telecommunications), transmitted down a communication channel or written to a storage medium. This repertoire of signal ...

. A positive voltage represents a

binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two values (0 and 1) for each digit * Binary function, a function that takes two arguments * Binary operation, a mathematical op ...

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 or Onoff may refer to: * On-off control, a type of feedback controller * On-off keying, a type of line modulation * On-off relationship, a form of personal relationship * On-Off Singles, a type of tennis game * On-off switch, a type of e ...

in modulation. Its drawbacks are that it is not

self-clocking 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 (computer science), synchronization. This is usually done by including embedd ...

and it has a significant

DC component In signal processing, when describing a periodic function in the time domain, the DC bias, DC component, DC offset, or DC coefficient is the mean value of the waveform. A waveform with zero mean or no DC bias is known as a ''DC balanced'' or ''DC ...

, which can be halved by using

return-to-zero Return-to-zero (RZ or RTZ) describes a line code used in telecommunications signals in which the signal drops (returns) to zero between pulses. This takes place even if a number of consecutive 0s or 1s occur in the signal. The signal is se ...

, where the signal returns to zero in the middle of the bit period. With a 50%

duty cycle A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. As a for ...

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. NRZ (Non-Return-to-Zero) - Traditionally, a unipolar scheme was designed as a

non-return-to-zero In telecommunications, a non-return-to-zero (NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a ne ...

(NRZ) 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, as instead happens in other line coding schemes, such as

Manchester code In telecommunications and data storage, Manchester code (also known as phase encoding, or PE) is a line code in which the encoding of each data bit is either low then high, or high then low, for equal time. It is a self-clocking signal with no ...

. Compared with its polar counterpart, polar NRZ, this scheme applies a DC bias to the line and unnecessarily wastes power – The normalized power (power required to send 1 bit per unit line resistance) is double that for polar NRZ. For this reason, unipolar encoding is not normally used in data communications today. An Optical Orthogonal Code (OOC) is a family of (0,1) sequences with good

auto Auto may refer to: Vehicles * An automobile, or car * An autonomous car, a self-driving car * An auto rickshaw Mechanisms * Short for automatic * An automaton * An automatic transmission Media * Auto (art), a form of Portuguese dramatic play * ...

- and

cross-correlation In signal processing, cross-correlation is a measure of similarity of two series as a function of the displacement of one relative to the other. This is also known as a ''sliding dot product'' or ''sliding inner-product''. It is commonly used f ...

properties for ''unipolar'' environments. They differ from codes developed for electrical communication which are usually ''bipolar''. i.e. (−1,1) sequences. They are used in optical communications to enable

CDMA Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...

in optical fiber transmission.

References

{{Bit-encoding Encodings Line codes

See also

References