amplitudivaihemodulaatio

Amplitudivaihemodulaatio, often abbreviated as APM or QAM, is a modulation scheme that combines both amplitude modulation and phase modulation to transmit information. In essence, it encodes data by varying both the amplitude and the phase of a carrier signal. This allows for more data to be transmitted on a single carrier frequency compared to simple amplitude modulation (AM) or phase modulation (PM) alone.

The technique works by using a carrier wave and modifying two of its properties: its amplitude and its phase. By choosing discrete levels for both amplitude and phase, a multitude of distinct signal states can be created. Each of these states represents a specific bit pattern or symbol. For example, in 16-QAM, there are 16 possible combinations of amplitude and phase, allowing each symbol to carry 4 bits of information (since 2^4 = 16).

APM is widely used in digital communication systems, including Wi-Fi, cellular networks (like 4G and 5G), and cable modems. Its efficiency in utilizing bandwidth makes it a crucial technology for modern high-speed data transmission. The higher the order of QAM (e.g., 64-QAM, 256-QAM), the more bits can be transmitted per symbol, leading to higher data rates, but also requiring more complex circuitry and a cleaner signal to avoid errors. The selection of the appropriate QAM order depends on the signal quality and the desired data throughput.