  To improve the system throughput, this paper proposes a network
non-orthogonal multiple access (N-NOMA) technique for the uplink coordinated
multi-point transmission (CoMP). In the considered scenario, multiple base
stations collaborate with each other to serve a single user, referred to as the
CoMP user, which is the same as for conventional CoMP. However, unlike
conventional CoMP, each base station in N-NOMA opportunistically serves an
extra user, referred to as the NOMA user, while serving the CoMP user at the
same bandwidth. The CoMP user is typically located at the cell-edge, whereas
users close to the base stations are scheduled as NOMA users. Hence, the
channel conditions of the two kind of users are very distinctive, which
facilitates the implementation of NOMA. Compared to the conventional orthogonal
multiple access based CoMP scheme, where multiple base stations serve a single
CoMP user only, the proposed N-NOMA scheme can support larger connectivity by
serving the extra NOMA users, and improve the spectral efficiency by avoiding
the CoMP user solely occupying the spectrum. A stochastic geometry approach is
applied to model the considered N-NOMA scenario as a Poisson cluster process,
based on which closed-form analytical expressions for outage probabilities and
ergodic rates are obtained. Numerical results are presented to show the
accuracy of the analytical results and also demonstrate the superior
performance of the proposed N-NOMA scheme.
