Delay encoding
Encyclopedia
In telecommunication
s, delay encoding is the encoding of binary
data
to form a two-level signal such that (a) a "0" causes no change of signal level unless it is followed by another "0" in which case a transition to the other level takes place at the end of the first bit
period; and (b) a "1" causes a transition from one level to the other in the middle of the bit period.
Delay
encoding is used primarily for encoding radio
signals because the frequency
spectrum of the encoded signal contains less low-frequency energy than a conventional non-return-to-zero
(NRZ) signal and less high-frequency energy than a biphase signal.
Delay encoding is an encoding using only half the bandwidth as biphase encoding but has all the advantages of biphase encoding:
To be rewritten: It is guaranteed to have transitions every other bit, meaning that decoding systems can adjust their clock/DC threshold continuously.
One drawback is human readability (e.g. on an oscilloscope).
Delay encoding is also known as Miller encoding (named after Armin Miller, its inventor).
Some RFID cards, in particular EPC UHF Gen 2 RF cards, use a variant called "Miller sub-carrier coding".
Such cards include the CharlieCard
. In this system, 2, 4 or 8 cycles of a subcarrier square wave are transmitted for each bit time. The Miller encoding transitions are indicated by 180° phase shifts in the subcarrier, i.e. the subcarrier pauses for 1/2 of a cycle at each transition. (The resultant binary subcarrier is itself either ASK
or PSK
modulated on another carrier.)
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
s, delay encoding is the encoding of binary
Binary numeral system
The binary numeral system, or base-2 number system, represents numeric values using two symbols, 0 and 1. More specifically, the usual base-2 system is a positional notation with a radix of 2...
data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
to form a two-level signal such that (a) a "0" causes no change of signal level unless it is followed by another "0" in which case a transition to the other level takes place at the end of the first bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
period; and (b) a "1" causes a transition from one level to the other in the middle of the bit period.
Delay
Propagation delay
Propagation delay is a technical term that can have a different meaning depending on the context. It can relate to networking, electronics or physics...
encoding is used primarily for encoding radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
signals because the frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
spectrum of the encoded signal contains less low-frequency energy than a conventional 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...
(NRZ) signal and less high-frequency energy than a biphase signal.
Delay encoding is an encoding using only half the bandwidth as biphase encoding but has all the advantages of biphase encoding:
To be rewritten: It is guaranteed to have transitions every other bit, meaning that decoding systems can adjust their clock/DC threshold continuously.
One drawback is human readability (e.g. on an oscilloscope).
Delay encoding is also known as Miller encoding (named after Armin Miller, its inventor).
Some RFID cards, in particular EPC UHF Gen 2 RF cards, use a variant called "Miller sub-carrier coding".
Such cards include the CharlieCard
CharlieCard
The CharlieCard is a MIFARE-based, contactless, stored value smart card used for electronic ticketing as part of the Automated Fare Collection system installed by the Massachusetts Bay Transportation Authority at its stations and on its vehicles...
. In this system, 2, 4 or 8 cycles of a subcarrier square wave are transmitted for each bit time. The Miller encoding transitions are indicated by 180° phase shifts in the subcarrier, i.e. the subcarrier pauses for 1/2 of a cycle at each transition. (The resultant binary subcarrier is itself either ASK
Amplitude-shift keying
Amplitude-shift keying is a form of modulation that represents digital data as variations in the amplitude of a carrier wave.Any digital modulation scheme uses a finite number of distinct signals to represent digital data. ASK uses a finite number of amplitudes, each assigned a unique pattern of...
or PSK
Phase-shift keying
Phase-shift keying is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal ....
modulated on another carrier.)