There has been extensive research on large scale multi-user multiple-input
multiple-output (MU-MIMO) systems recently. Researchers have shown that there
are great opportunities in this area, however, there are many obstacles in the
way to achieve full potential of using large number of receive antennas. One of
the main issues, which will be investigated thoroughly in this paper, is timing
asynchrony among signals of different users. Most of the works in the
literature, assume that received signals are perfectly aligned which is not
practical. We show that, neglecting the asynchrony can significantly degrade
the performance of existing designs, particularly maximum ratio combining
(MRC). We quantify the uplink achievable rates obtained by MRC receiver with
perfect channel state information (CSI) and imperfect CSI while the system is
impaired by unknown time delays among received signals. We then use these
results to design new algorithms in order to alleviate the effects of timing
mismatch. We also analyze the performance of introduced receiver design, which
is called MRC-ZF, with perfect and imperfect CSI. For performing MRC-ZF, the
only required information is the distribution of timing mismatch which
circumvents the necessity of time delay acquisition or synchronization. To
verify our analytical results, we present extensive simulation results which
thoroughly investigate the performance of the traditional MRC receiver and the
introduced MRC-ZF receiver