Optimizing Spectrum Efficiency With MIMO NOMA PD Approach in a 5G Cooperative Spectrum Sharing Environment

The fifth generation (5G) of cellular communication networks has introduced various advanced technologies to address the increasing demand for higher data rates and improved spectrum utilization. One of these technologies, non-orthogonal multiple access (NOMA), has gained significant attention due to its ability to enhance spectral efficiency by allowing multiple users to share the same time-frequency resource block. NOMA affords a number of advantageous features including increased spectrum efficiency (SE). It comes in various forms, such as power-domain (PD) NOMA and code-domain (CD) NOMA. This paper attentions mainly on enhancing the SE of downlink (DL) PD-NOMA in a 5G cooperative spectrum sharing environment using single input single output (SISO), massive MIMO (M-MIMO), and multiple input multiple output (MIMO). Two methods are approached here. In the first one, the NOMA handlers access the free/unconstrained channels using competing channel (C-Ch) approach, whereas the next one uses dedicated channel (D-Ch) approach. Five users are considered at distances of 1000, 800, 600, 400, and 200 m from the base station (BS) with different power allocation coefficients at transmitting power of 40 dBm and bandwidth of 70 MHz. Quadrature phase shift keying (QPSK) is used with successive interference cancellation (SIC) at the receiver side and superposition coding (SC) at the transmitter side under frequency selective Rayleigh fading environment. The PD DL NOMA system's results demonstrated that combining 32 × 32 MIMO, 64 × 64 MIMO, and 128 × 128 M-MIMO in a single cell and the same network with cooperative cognitive radio network (CoCRN) significantly improved the SE reliability. The user Ur5 produces an optimal SE performance of 3.753 bps/Hz/cell for PD DL NOMA with SISO, 5.77 bps/Hz/cell for CoCRN PD DL NOMA with SISO using C-Ch, and 7.45 bps/Hz/cell for CoCRN DL PDNOMA with SISO using D-Ch with a 40 dBm transmitting power. Furthermore, the SE for Ur5 (nearest user) was increased to 64%, 67%, and 69%, respectively, using PD-NOMA with 32 × 32 MIMO, PD-NOMA with 32 × 32 MIMO using C-Ch, and DL NOMA PD with 32 × 32 MIMO using D-Ch. DL PD-NOMA with MIMO(64 × 64) using D-Ch improved the SE rate by 77% having transmission power of 40 dBm in comparison with the SE outcome for DL PDNOMA with SISO; however, DL PD-NOMA with MIMO (64 × 64) most dramatically upgraded the SE rate for Ur5 by 73%. Using C-Ch and CoCRN DL PD-NOMA with MIMO (64 × 64), the SE performance was boosted by 76%. The best user, Ur5, had an 82% improvement in SE performance when DL PD-NOMA with M-MIMO (128 × 128) was compared to DL NOMA with SISO. With a 40 dBm transmission power, CoCRN DL NOMA with 128 × 128 M-MIMO using C-Ch showed an 88% improvement, whereas CoCRN DL PD-NOMA with M-MIMO (128 × 128) using D-Ch experienced an 89% improvement.