Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Practical Design for Multiple-Antenna Cognitive Radio Networks with
  Coexistence Constraint   In this paper we investigate the practical design for the multiple-antenna
cognitive radio (CR) networks sharing the geographically used or unused
spectrum. We consider a single cell network formed by the primary users (PU),
which are half-duplex two-hop relay channels and the secondary users (SU) are
single user additive white Gaussian noise channels. In addition, the
coexistence constraint which requires PUs' coding schemes and rates unchanged
with the emergence of SU, should be satisfied. The contribution of this paper
are twofold. First, we explicitly design the scheme to pair the SUs to the
existing PUs in a single cell network. Second, we jointly design the nonlinear
precoder, relay beamformer, and the transmitter and receiver beamformers to
minimize the sum mean square error of the SU system. In the first part, we
derive an approximate relation between the relay ratio, chordal distance and
strengths of the vector channels, and the transmit powers. Based on this
relation, we are able to solve the optimal pairing between SUs and PUs
efficiently. In the second part, considering the feasibility of implementation,
we exploit the Tomlinson-Harashima precoding instead of the dirty paper coding
to mitigate the interference at the SU receiver, which is known side
information at the SU transmitter. To complete the design, we first approximate
the optimization problem as a convex one. Then we propose an iterative
algorithm to solve it with CVX. This joint design exploits all the degrees of
design. To the best of our knowledge, both the two parts have never been
considered in the literature. Numerical results show that the proposed pairing
scheme outperforms the greedy and random pairing with low complexity. Numerical
results also show that even if all the channel matrices are full rank, under
which the simple zero forcing scheme is infeasible, the proposed scheme can
still work well.

4
The categories of this paper are: cond-mat
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga