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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 ...
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.
So each sample encodes one of a finite number of "symbols", which in turn represent one or more binary digits (bits) of information. Each symbol is encoded as a different combination of amplitude and phase of the carrier, so each symbol is represented by a point on the constellation diagram, called a constellation point. The constellation ...
Constellation shaping is an energy efficiency enhancement method for digital signal modulation that improves upon amplitude and phase-shift keying (APSK) and conventional quadrature amplitude modulation (QAM) by modifying the continuous uniform distribution of the data symbols to match the channel.
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.
The following are core features that have been approved as of Draft 3.0: 4096-QAM (4K-QAM) enables each symbol to carry 12 bits rather than 10 bits, resulting in 20% higher theoretical transmission rates than WiFi 6's 1024-QAM.
Differential coding: In order to get a rotation-invariant constellation, this unit shall apply a differential encoding of the two Most Significant Bits (MSBs) of each symbol. QAM Mapper: the bit sequence is mapped into a base-band digital sequence of complex symbols. There are 5 allowed modulation modes: 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM.
DMT allocates from 2 to 15 bits per channel (bin). As line conditions change, bit swapping allows the modem to swap bits around different channels, without retraining, as each channel becomes more or less capable. If bit swapping is disabled then this does not happen and the modem needs to retrain in order to adapt to changing line conditions.