Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cell-Free Massive MIMO Meets OTFS Modulation   We provide the first-ever performance evaluation of orthogonal time frequency
space (OTFS) modulation in cell-free massive multiple-input multiple-output
(MIMO) systems. To investigate trade-off between performance and overhead, we
apply embedded pilot-aided and superimposed pilot-based channel estimation
methods. We then derive a closed-form expression for the individual user
downlink and uplink spectral efficiencies as a function of the numbers of APs,
users and delay-Doppler domain channel estimate parameters. Based on these
analytical results, we also present new scaling laws that the AP's and user's
transmit power should satisfy, to sustain a desirable quality of service. It is
found that when the number of APs, $M_a$, grows without bound, we can reduce
the transmit power of each user and AP proportionally to $1/M_a$ and $1/M_a^2$,
respectively, during the uplink and downlink phases. We compare the OTFS
performance with that of orthogonal frequency division multiplexing (OFDM) at
high-mobility conditions. Our findings reveal that with shadowing correlation,
OTFS modulation with embedded pilot-based channel estimation provides
$30$-folds gain over the OFDM counterpart in terms of $95\%$-likely per-user
downlink rate. Finally, with superimposed pilot-based channel estimation, the
increase in the per-user throughput is more pronounced at the median rates over
the correlated shadowing channels.

18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
13
The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol