Sequencing signals is as necessary for computers as sequencing sound for humans. With the horizontal axis signifying the in-phase signal and the vertical axis signifying the quadrature signal, constellation diagrams are a method of visualizing possible bit sequences symbols. Placement for plots on these diagrams communicate the level of adjustment in amplitude and phase for each bit sequence: amplitude is measured in distance from the center intersection of the axes, while phase is measured in degrees shifted from the horizontal in-phase axis.
QAM specifications on radiofrequency devices are notated with a prefixed number , used to indicate the amount of mathematically possible outcomes for binary bit strings a QAM modulator can handle in a given data transmission.
This means there are only four possible binary outcomes for the modulator to communicate: 00, 01, 10, and Furthermore, 16QAM processes four bits at a time, causing 16 possible binary outcomes.
This naming convention continues through the other QAM specifications, communicating the amount of binary data a modulator can handle calculated as 2 to the power of the number of bits per transmission.
Basically, the higher the number, the more data that can be handled per modulation cycle. As is the tradeoff with most networking technology, the benefits of faster speeds or superior data handling come at the cost of a decreased range of c apability.
Each advancement of QAM technology packs more readings tightly together in each quadrant of a constellation diagram, which shorte ns the distance between each point and creates a more delicate process for accurate interpretation. The margin of acceptable error shrinks incredibly as the amount of possible binary sequences increases.
Quality transmissions become reliant on the stability of shorter distances. Consider the metaphor of sound again. Gorilla Glass is an alkali-aluminosilicate glass developed by Corning that's primarily used as cover glass for mobile devices.
Because it's resilient, durable and remarkably thin, it has been made to safeguard displays and touch screens without compromising the screen or adding bulkiness to the View Full Term. By clicking sign up, you agree to receive emails from Techopedia and agree to our Terms of Use and Privacy Policy. By: Justin Stoltzfus Contributor, Reviewer. By: Satish Balakrishnan. Dictionary Dictionary Term of the Day. It is written to help depict and describe aspects of QAM in a way that is hopefully easy to grasp.
What is Quadrature Amplitude Modulation? Quadrature Amplitude Modulation, QAM is a form of modulation that is a combination of phase modulation and amplitude modulation. The QAM scheme represents bits as points in a quadrant grid know as a constellation map. It combines phase modulation and amplitude modulation. When used for Wi-Fi digital signal modulation, QAM can achieve a higher rate than common amplitude modulation and phase modulation, which support only two types of symbols to distinguish 0 and 1.
For example, QAM can modulate symbols into 16 different waveforms, representing , , and so on, as shown in the following figure. This means that a total of 16 types of symbols are available, each of which may transmit 4-bit information. QAM loads signals to two orthogonal carriers typically sine and cosine , adjusts the amplitudes of the carriers, and superimposes their amplitudes to generate the signals modulated by both the phase and amplitude.
The two carriers are usually referred to as I and Q signals. Therefore, this modulation mode is also known as IQ modulation.
QAM is also considered a combination of phase modulation and amplitude modulation because QAM-modulated signals involve the conversion of both the phase and amplitude.
In digital signal modulation, a constellation diagram is typically used to represent a two-dimensional QAM modulation graph.
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