  Harvesting the gain of a large number of antennas in a mmWave band has mainly
been relying on the costly operation of channel state information (CSI)
acquisition and cumbersome phase shifters. Recent works have started to
investigate the possibility to use receivers based on energy detection (ED),
where a single data stream is decoded based on the channel and noise energy.
The asymptotic features of the massive receiver array lead to a system where
the impact of the noise becomes predictable due to a noise hardening effect.
This in effect extends the communication range compared to the receiver with a
small number of antennas, as the latter is limited by the unpredictability of
the additive noise. When the channel has a large number of spatial degrees of
freedom, the system becomes robust to imperfect channel knowledge due to
channel hardening. We propose two detection methods based on the instantaneous
and average channel energy, respectively. Meanwhile, we design the detection
thresholds based on the asymptotic properties of the received energy.
Differently from existing works, we analyze the scaling law behavior of the
symbol-error-rate (SER). When the instantaneous channel energy is known, the
performance of ED approaches that of the coherent detection in high SNR
scenarios. When the receiver relies on the average channel energy, our
performance analysis is based on the exact SER, rather than an approximation.
It is shown that the logarithm of SER decreases linearly as a function of the
number of antennas. Additionally, a saturation appears at high SNR for PAM
constellations of order larger than two, due to the uncertainty on the channel
energy. Simulation results show that ED, with a much lower complexity, achieves
promising performance both in Rayleigh fading channels and in sparse channels.
