  Amplitude-coherent (AC) detection is an efficient detection technique that
can simplify the receiver design while providing reliable symbol error rate
(SER). Therefore, this work considers AC detector design and SER analysis using
M-ary amplitude shift keying (MASK) modulation over Rician fading channels.
More specifically, we derive the optimum, near-optimum and a suboptimum AC
detectors and compare their SER to the coherent, noncoherent and the heuristic
AC detectors. Moreover, the analytical SER of the heuristic detector is derived
using two different approaches for single and multiple receiving antennas. One
of the derived expressions is expressed in terms of a single integral that can
be evaluated numerically, while the second approach gives a closed-form
analytical expression for the SER, which is also used to derive a simple
formula for the asymptotic SER at high signal-to-noise ratios (SNRs). The
obtained analytical and simulation results show that the SER of the AC and
coherent MASK detectors are comparable, particularly for high values of the
Rician K-factor, and small number of receiving antennas. Moreover, the obtained
results show that the SER of the optimal AC detector is equivalent to that of
the coherent detector. However, the optimal AC detector complexity is
prohibitively high, particularly at high SNRs. In most of the scenarios, the
heuristic AC detector significantly outperforms the optimum noncoherent
detector, except for the binary ASK case at low SNRs. Moreover, the obtained
results show that the heuristic AC detector is immune to phase noise, and thus,
it outperforms the coherent detector in scenarios where system is subject to
considerable phase noise.
