Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Intelligent Reflecting Surface Assisted Massive MIMO Communications   In a practical massive MIMO (multiple-input multiple-output) system, the
number of antennas at a base station (BS) is constrained by the space and cost
factors, which limits the throughput gain promised by theoretical analysis.
This paper thus studies the feasibility of adopting the intelligent reflecting
surface (IRS) to further improve the beamforming gain of the uplink
communications in a massive MIMO system. Under such a novel system, the central
question lies in whether the IRS is able to enhance the network throughput as
expected, if the channel estimation overhead is taken into account. In this
paper, we first show that the favorable propagation property for the
conventional massive MIMO system without IRS, i.e., the channels of arbitrary
two users are orthogonal, no longer holds for the IRS-assisted massive MIMO
system, due to its special channel property that each IRS element reflects the
signals from all the users to the BS via the same channel. As a result, the
maximal-ratio combining (MRC) receive beamforming strategy leads to strong
inter-user interference and thus even lower user rates than those of the
massive MIMO system without IRS. To tackle this challenge, we propose a novel
strategy for zero-forcing (ZF) beamforming design at the BS and reflection
coefficients design at the IRS to efficiently null the inter-user interference.
Under our proposed strategy, it is rigorously shown that even if the channel
estimation overhead is considered, the IRS-assisted massive MIMO system can
always achieve higher throughput compared to its counterpart without IRS,
despite the fact that the favorable propagation property no longer holds.

16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg