  In this paper, a backscatter cooperation (BC) scheme is proposed for
non-orthogonal multiple access (NOMA) downlink transmission. The key idea is to
enable one user to split and then backscatter part of its received signals to
improve the reception at another user. To evaluate the performance of the
proposed BC-NOMA scheme, three benchmark schemes are introduced. They are the
non-cooperation (NC)-NOMA scheme, the conventional relaying (CR)-NOMA scheme,
and the incremental relaying (IR)-NOMA scheme. For all these schemes, the
analytical expressions of the minimum total power to avoid information outage
are derived, based on which their respective outage performance, expected
rates, and diversity-multiplexing trade-off (DMT) are investigated. Analytical
results show that the proposed BC-NOMA scheme strictly outperforms the NC-NOMA
scheme in terms of all the three metrics. Furthermore, theoretical analyses are
validated via Monte-Carlo simulations. It is shown that unlike the CR-NOMA
scheme and the IR-NOMA scheme, the proposed BC-NOMA scheme can enhance the
transmission reliability without impairing the transmission rate, which makes
backscattering an appealing solution to cooperative NOMA downlinks.
