A Novel NOMA Scheme for Uplink Heterogeneous Network Using QR Decomposition-Based Projection

This paper proposes a novel non-orthogonal multiple access (NOMA) scheme for the uplink heterogeneous network (HetNet) using QR decomposition. In a HetNet employing NOMA, femtocell users (FUs) share the same spectrum as that of the macrocell users (MUs). While it increases the system capacity, this reuse results in new cases of cross-tier and co-tier interference. Cross-tier interference at the femtocell causes severe performance degradation due to the high transmit power of undesired macrocell users (MUs). Hence efficient interference management is essential to garner the benefits promised by NOMA-HetNet combination. In the proposed NOMA scheme, the cross-tier interference in the femtocell is mitigated by QR decomposition-based decoding. This decomposition carried out at the femtocell base station (FBS) extracts the desired NOMA users' signal from the received composite signal. In contrast to the NOMA schemes in literature based on successive interference cancellation (SIC), the proposed scheme does not require any user pairing or power control schemes on the user equipment (UE) to decode FUs' data at the FBS. Besides, it does not require any information exchange to the transmitter (UE) side for decoding, thereby significantly reducing the computational complexity as well as the signaling overhead at the FBS. Performance of the proposed scheme is evaluated through simulation studies and also compared with a prevailing SIC algorithm to establish its superiority.