Trellis-coded pulse-amplitude modulation (TC-PAM) is the modulation format that is used in HDSL2 and G.SHDSL. It is a variant of trellis coded modulation (TCM) which uses a one-dimensional

pulse-amplitude modulation Pulse-amplitude modulation (PAM) is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulse ...

(PAM) symbol space, as opposed to a two-dimensional

quadrature amplitude modulation Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signa ...

(QAM) symbol space.Johannes Huber
"Multilevel-Codes: Distance Profiles and Channel Capacity"
Compared to the

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). 2B1Q is a four-level pulse-amplitude modulat ...

scheme used in the older

HDSL High-bit-rate digital subscriber line (HDSL) is a telecommunications protocol standardized in 1994. It was the first digital subscriber line (DSL) technology to use a higher frequency spectrum over copper, twisted pair cables. HDSL was developed to ...

and SDSL standards, TC-PAM improves range at a given bit-rate and provides enhanced spectral compatibility with

ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ...

. TC-PAM is also known as 4B1H, because it uses 16 levels to represents a 4 digit binary, 4

Binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that ta ...

1 Hexadecimal.

References

Quantized radio modulation modes {{telecomm-stub