2B1Q
Two-binary, one-quaternary (2B1Q) is a line code used in the U interface of the Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) and the high-bit-rate digital subscriber line (HDSL).[1] 2B1Q is a four-level pulse-amplitude modulation (PAM-4) scheme without redundancy, mapping two bits (2B) into one quaternary symbol (1Q). Symbol rate is half of data rate.
A competing encoding technique in the ISDN basic rate U interface, mainly used in Europe, is 4B3T.
Encoding
To minimize error propagation, bit pairs (dibits) are assigned to voltage levels according to a Gray code, as follows:
Dibit | Signal level |
---|---|
10 | +450 mV |
11 | +150 mV |
01 | −150 mV |
00 | −450 mV |
If the voltage is misread as an adjacent level, this causes only a 1-bit error in the decoded data. 2B1Q code is not DC-balanced.
References
- ^ Reeve, Whitham D. (1995). Subscriber Loop Signaling and Transmission Handbook. IEEE Telecommunications Handbook Series. IEEE Press. ISBN 0780304403.
- v
- t
- e
- Unipolar encoding
- Bipolar encoding
- On-off keying
- Mark and space
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/95/Digital_signal_encoding_formats-en.svg/240px-Digital_signal_encoding_formats-en.svg.png)
- See also: Baseband
- Baud
- Bit rate
- Digital signal
- Digital transmission
- Ethernet physical layer
- Pulse modulation methods
- Pulse-amplitude modulation (PAM)
- Pulse-code modulation (PCM)
- Serial communication
- Category:Line codes
![]() | This article related to telecommunications is a stub. You can help Wikipedia by expanding it. |
- v
- t
- e