A NOMA Scheme Using Oblique Projection for HetNet Uplink Under Perfect and Imperfect CSIR

The emerging non-orthogonal multiple access (NOMA) technique for fifth-generation (5G) heterogeneous network (HetNet) yields performance improvement specifically by boosting the network capacity and spectral efficiency. This paper proposes a new NOMA scheme for the uplink HetNet using oblique projection (OP) under perfect and imperfect channel state information at the receiver (CSIR). In this scheme, the OP operation performed at the femtocell base station (FBS) recovers the desired NOMA users' signal from the composite received signal. Unlike the existing successive interference cancellation (SIC) based NOMA schemes, the proposed scheme does not demand any power control or user clustering techniques for decoding NOMA users' data at the receiver side. Further, it does not need information exchange between users for decoding and hence the computational complexity and the signaling overhead of the system gets reduced significantly. To evaluate the performance of the proposed scheme under perfect CSIR analytically, we derive the closed-form expression for the probability of error and outage probability at the FBS receiver. We also derive the diversity order, sum-rate, and perform the computational complexity analysis of the NOMA-HetNet system employing the proposed scheme. Simulation results illustrate that the derived analytical results accurately describe the proposed NOMA scheme. We compare the performance of the proposed technique with a prevailing SIC based NOMA scheme and establish its superiority. Performance of the proposed NOMA scheme under imperfect CSIR is also studied and established that the scheme works well under this scenario also.