单词 | 2B1Q (2 Binary 1 Quaternary) |
释义 | 2B1Q (2 Binary 1 Quaternary) A line coding technique, with echo cancellation, used in North America for ISDN basic rate interface (BRI). 2B1Q is a form of pulse amplitude modulation (PAM) that uses four (i.e., quaternary) levels of amplitude (i.e., voltage), each of which represents two adjacent bits in a bit stream, and is accomplished by varying the voltage at nominal levels of ±1 (actually 0.833) and ±3 (actually 2.5) volts, as illustrated in the accompanying figure. As 2B1Q impresses two bits on each baud, the baud rate is halved, and a baud rate of 80 kilobaud will support a signaling rate of 160 kbps. Because statistics force the line voltage to be positive half the time and negative half the time, on average, the signal power lies at a frequency of 40 kHz, which is half the baud rate. 2B1Q also is the electrical line coding technique used in high-bit-rate digital subscriber line (HDSL). 2B1Q also is known as 4-level pulse amplitude modulation (4 PAM). In European and many other countries, the line coding technique employed is 4 Binary 3 Ternary (4B3T). See also 4B3T, baud rate, bit rate, BRI, echo cancellation, HDSL, ISDN, and PAM. 0 1 0 0 1 1 1 0 Baseband Digital Signal 0 1 0 0 1 1 1 0 +3V +1V 0V -1V -3V 2B1Q Line Coding |
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