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Digital 16-QAM with example symbols Constellation points for 4-QAM, 16-QAM, 32-QAM, and 64-QAM overlapped As in many digital modulation schemes, the constellation diagram is useful for QAM. In QAM, the constellation points are usually arranged in a square grid with equal vertical and horizontal spacing, although other configurations are ...
A diagram with four points, for example, represents a modulation scheme that can separately encode all 4 combinations of two bits: 00, 01, 10, and 11, and so can transmit two bits per symbol. Thus in general a modulation with N {\displaystyle N} constellation points transmits log 2 N {\displaystyle \log _{2}N} bits per symbol.
The history of modems is the attempt at increasing the bit rate over a fixed bandwidth (and therefore a fixed maximum symbol rate), leading to increasing bits per symbol. For example, ITU-T V.29 specifies 4 bits per symbol, at a symbol rate of 2,400 baud, giving an effective bit rate of 9,600 bits per second.
QAM is a digital television standard using quadrature amplitude modulation. It is the format by which digital cable channels are encoded and transmitted via cable television providers. QAM is used in a variety of communications systems such as Dial-up modems and WiFi.
In digital signal modulation, information bits modulate the carrier electromagnetic wave signal to a set of desired phase, frequency and amplitude states. This set of allowed states is called a constellation. Typically, the probability of an information bit to be a 0 is the same as that of a 1, leading to all states from the constellation to ...
The link spectral efficiency of a digital communication system is measured in bit/s/Hz, [2] or, less frequently but unambiguously, in (bit/s)/Hz.It is the net bit rate (useful information rate excluding error-correcting codes) or maximum throughput divided by the bandwidth in hertz of a communication channel or a data link.
Up to 15 bits per symbol can be encoded in a bin on a good quality line. The frequency layout can be summarised as: 30 Hz-4 kHz, voice. 4–25 kHz, unused guard band. 25–138 kHz, 25 upstream bins (7-31). 138–1104 kHz, 224 downstream bins (32-255).
In telecommunications and computing, bit rate (bitrate or as a variable R) is the number of bits that are conveyed or processed per unit of time. [1]The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction with an SI prefix such as kilo (1 kbit/s = 1,000 bit/s), mega (1 Mbit/s = 1,000 kbit/s), giga (1 Gbit/s = 1,000 Mbit/s) or tera (1 Tbit/s = 1,000 Gbit/s). [2]