  The capacity of a discrete-time multi-input multi-output (MIMO) Gaussian
channel with output quantization is investigated for different receiver
architectures. A general formulation of this problem is proposed in which the
antenna outputs are processed by analog combiners while sign quantizers are
used for analog-to-digital conversion. To exemplify this approach, four analog
receiver architectures of varying generality and complexity are considered: (a)
multiple antenna selection and sign quantization of the antenna outputs, (b)
single antenna selection and multilevel quantization, (c) multiple antenna
selection and multilevel quantization, and (d) linear combining of the antenna
outputs and multilevel quantization. Achievable rates are studied as a function
of the number of available sign quantizers and compared among different
architectures. In particular, it is shown that architecture (a) is sufficient
to attain the optimal high signal-to-noise ratio performance for a MIMO
receiver in which the number of antennas is larger than the number of sign
quantizers. Numerical evaluations of the average performance are presented for
the case in which the channel gains are i.i.d. Gaussian.
