Towards Accurate Throughput Analysis for Dense Heterogeneous Networks with Cooperative NOMA

In a heterogeneous cellular network (HetNet) consisting of M tiers of densely-deployed base stations (BSs), we consider that each BS in the HetNet associated with multiple users is able to simultaneously schedule and serve at most K users in a downlink time slot by performing the (power-domain) non-orthogonal multiple access (NOMA) scheme. This paper aims to provide accurate analyses for the link throughput of a (NOMA) user for the non-cooperative and the proposed cooperative NOMA schemes. The link throughput of the users is first studied for the non-cooperative NOMA scheme in which no BSs are coordinated to jointly transmit the NOMA signals for a particular BS and its tight and accurate lower bound is derived. We show that the link throughput performance can be largely degraded if allocated transmit powers for the users are not satisfied with certain constraints. To improve the link throughput of the users, we propose a cooperative NOMA scheme in which the void BSs that are not tagged by any users are coordinated to enhance the farthest user in a particular cell. The accurate approximated expression of the link throughput of a user is found for this cooperative NOMA scheme. We show that cooperative NOMA is able to significantly improve the link throughput of all users as long as the transmit powers are appropriately allocated among the users.