What is QAM?
QAM is a digital modulation scheme used in 5G NR that encodes data by simultaneously varying the amplitude and phase of a carrier signal. Higher-order QAM transmits more bits per symbol — increasing spectral efficiency — but requires a higher signal-to-noise ratio (lower EVM) to reliably decode the densely packed constellation points.
How Does QAM Work?
QAM maps groups of bits to complex-valued symbols plotted on an IQ (In-phase / Quadrature) diagram. 64-QAM encodes 6 bits per symbol, 256-QAM (the 5G NR standard) encodes 8 bits per symbol, and 1024-QAM (Release 16 enhancement) encodes 10 bits per symbol. The link adaptation mechanism (AMC) dynamically selects the modulation order based on reported CQI — switching to lower-order QAM when signal quality degrades.
Use Cases
Achieving peak spectral efficiency in eMBB scenarios close to the gNB, 256-QAM for all 5G NR commercial deployments, 1024-QAM for ultra-dense mmWave environments.
3GPP / Standards Reference
3GPP TS 38.214 (Physical Layer Procedures for Data — Modulation and Coding), TS 38.211
Related Terms
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