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). A competing encoding technique in the ISDN basic rate U interface, mainly used in Europe, is 4B3T.
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. Symbol rate is half of data rate.
References
- Whitham D. Reeve (1995). Subscriber Loop Signaling and Transmission Handbook. IEEE Telecommunications Handbook Series. IEEE Press. ISBN 0780304403.
Line coding (digital baseband transmission) | ||
|---|---|---|
| Main articles |  | |
| Basic line codes | ||
| Extended line codes | ||
| Optical line codes | ||
| ||
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.