Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Precoding for the Sparsely Spread MC-CDMA Downlink with
  Discrete-Alphabet Inputs   Sparse signatures have been proposed for the CDMA uplink to reduce multi-user
detection complexity, but they have not yet been fully exploited for its
downlink counterpart. In this work, we propose a Multi-Carrier CDMA (MC-CDMA)
downlink communication, where regular sparse signatures are deployed in the
frequency domain. Taking the symbol detection point of view, we formulate a
problem appropriate for the downlink with discrete alphabets as inputs. The
solution to the problem provides a power-efficient precoding algorithm for the
base station, subject to minimum symbol error probability (SEP) requirements at
the mobile stations. In the algorithm, signature sparsity is shown to be
crucial for reducing precoding complexity. Numerical results confirm
system-load-dependent power reduction gain from the proposed precoding over the
zero-forcing precoding and the regularized zero-forcing precoding with
optimized regularization parameter under the same SEP targets. For a fixed
system load, it is also demonstrated that sparse MC-CDMA with a proper choice
of sparsity level attains almost the same power efficiency and link throughput
as that of dense MC-CDMA yet with reduced precoding complexity, thanks to the
sparse signatures.

14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
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The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
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The categories of this paper are: eess
10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: funct-an