Exploiting Heterogeneous Networks model for Cluster Formation and Power Allocation in Uplink NOMA

Non-orthogonal multiple access (NOMA) enables the next generation mobile communication systems to achieve extremely high data rate with better connectivity and higher spectral efficiency. In downlink NOMA, multiple user-equipments (UEs) are grouped in a single cluster so that a single composite power signal can be transmitted from the evolved nodeB (eNB) for all UEs belong to that cluster. Each UE in the cluster then retrieves its own signal from the composite power signal while implementing successive interference cancellation (SIC). However, in NOMA uplink transmission, each UE is unaware about the transmission of other UEs in the cell. Hence each UE is considered as a unique individual entity in uplink and therefore transmits power independently. Therefore in uplink, multiple UEs cannot be grouped into a single cluster so as to transmit a single composite power signal to the eNB. In order to achieve spectral efficiency in uplink NOMA, in this paper we exploit the concept of Heterogeneous network (HetNet) model and propose a two-step power allocation scheme. UEs belong to a specific geographical area are grouped in a small cell alike cluster and a cluster-eNB (ceNB) is defined for each cluster. UEs inside the cluster transmits individually and independently to the ceNB during the first step and afterwards the ceNB multiplex multiple UEs in a single superimposed composite power signal while allocating distinct power levels to different users in the second step. Finally, the ceNB then transmits the superimposed composite power signal to the eNB. The numerical results demonstrate that the proposed technique outperforms the conventional orthogonal multiple access (OMA) technique.