  We consider general multi-antenna fading channels with coarsely quantized
outputs, where the channel is unknown to the transmitter and receiver. This
analysis is of interest in the context of sensor network communication where
low power and low cost are key requirements (e.g. standard IEEE 802.15.4
applications). This is also motivated by highly energy constrained
communications devices where sampling the signal may be more energy consuming
than processing or transmitting it. Therefore the analog-to-digital converters
(ADCs) for such applications should be low-resolution, in order to reduce their
cost and power consumption. In this paper, we consider the extreme case of only
1-bit ADC for each receive signal component. We derive asymptotics of the
mutual information up to the second order in the signal-to-noise ratio (SNR)
under average and peak power constraints and study the impact of quantization.
We show that up to second order in SNR, the mutual information of a system with
two-level (sign) output signals incorporates only a power penalty factor of
almost 1.96 dB compared to the system with infinite resolution for all channels
of practical interest. This generalizes a recent result for the coherent case.
