  We present new insightful results on the uplink data detection for massive
multiple-input multiple-output systems with 1-bit analog-to-digital converters.
The expected values of the soft-estimated symbols (i.e., after the linear
combining and prior to the data detection) have been recently characterized for
multiple user equipments (UEs) and maximum ratio combining (MRC) receiver at
the base station. In this paper, we first provide a numerical evaluation of the
expected value of the soft-estimated symbols with zero-forcing (ZF) and minimum
mean squared error (MMSE) receivers for a multi-UE setting with correlated
Rayleigh fading. Then, we propose a joint data detection (JD) strategy, which
exploits the interdependence among the soft-estimated symbols of the
interfering UEs, along with its low-complexity variant. These strategies are
compared with a naive approach that adapts the maximum-likelihood data
detection to the 1-bit quantization. Numerical results show that ZF and MMSE
provide considerable gains over MRC in terms of symbol error rate. Moreover,
the proposed JD and its low-complexity variant provide a significant boost in
comparison with the single-UE data detection.
