Spectral Efficiency of Distributed Large-scale MIMO Systems with ZF Receivers

Distributed multiple-input multiple-output (DMIMO)
is a promising technique for next generation wireless
networks, which offers a remarkable spectral efficiency gain over
the conventional co-located MIMO (C-MIMO). In contrast to CMIMO,
which can be regarded as a special case of D-MIMO,
performance analysis of D-MIMO is a challenging problem. This
is because radio channels between a user and the distributed radio
ports (RPs) are characterized by non-identical path-loss and
shadowing effects which render the classical analytical methods
non-tractable. In this paper, new accurate expressions for the
uplink spectral efficiency of D-MIMO and C-MIMO systems are
presented and compared for given large-scale coefficients. We
further consider the uplink spectral efficiency for a single-cell
distributed large-scale MIMO (D-LMIMO) system with linear
zero-forcing (ZF) receivers, accounting for path loss along with
shadow fading and multi-path fading effects. Exact expressions
for the average spectral efficiency over shadow fading in the
asymptotically very large number of RPs antennas regime is
explicitly derived, and a tight closed-form lower bound on the
asymptotic spectral efficiency is presented. We demonstrate that,
the transmit power of each user in D-LMIMO can be scaled
down proportionally to the inverse of the number of RP antennas
with no performance reduction. Moreover, we study the spectral
efficiency of a D-MIMO in a multi-cell environment taking into
account accurate co-channel interference (CCI) models. These
expressions provide meaningful insights into the impact of SNR,
RPs and user positions, number of RPs antennas, shadow fading,
and out-of-cell interference on the spectral efficiency of D-MIMO
over practical scenarios. Finally, numerical results are validated
by simulation to confirm our analysis.