interference typically increases. There is a spreading of the spots in the constellation, decreasing the separation between adjacent states, making it difficult for the receiver to decode the signal appropriately. In other words, there is reduced noise immunity. There are several test parameter measurements which help determine an optimal QAM mode for a specific operating environment. The following three are most significant: Carrier/interference ratio Carrier-to-noise ratio Threshold-to-noise ratio See also Amplitude and phase-shift keying or asymmetric phase-shift keying (APSK) Carrierless amplitude phase modulation (CAP) In-phase and quadrature components Modulation for other examples of modulation techniques Phase-shift keying QAM tuner for HDTV Random modulation References Further reading Jonqyin (Russell) Sun "Linear diversity analysis for QAM in Rician fading channels", IEEE WOCC 2014 John G. Proakis, "Digital Communications, 3rd Edition" External links QAM Demodulation Interactive webdemo of QAM constellation with additive noise Institute of Telecommunicatons, University of Stuttgart QAM bit error rate for AWGN channel – online experiment How imperfections affect QAM constellation Microwave Phase Shifters Overview by Herley General Microwave Simulation of dual-polarization QPSK (DP-QPSK) for 100G optical transmission Radio modulation modes Data transmission