Performance of Energy and Spectrally Efficient AF Relay-Aided Incremental CDRT NOMA-Based IoT Network With Imperfect SIC for Smart Cities

High spectral and energy efficiencies are vital for the implementation of smart cities. To this end, this article investigates the performance of an amplify-and-forward (AF) relay-aided coordinated direct and relay transmission (CDRT) protocol in a downlink nonorthogonal multiple access (NOMA)-based Internet of Things (IoT) network in which the source shares the direct as well as the relayed links to the IoT near-user (NU) and the far-user (FU). Different from the existing literature, we exploit incremental relaying (IR) along with combining at the NU (and not just at the FU) to achieve a 20% increase in FU throughput while ensuring the desired performance at NU. Considering practical imperfect successive interference cancelation (SIC), we analyze the throughput performance. Both NU and FU accrue large throughput gains, and doubling of the energy efficiency (EE) is achieved over the nonincremental AF CDRT NOMA scheme and its relayed orthogonal multiple access counterpart. We accomplish this by intelligently exploiting feedback bits in the second phase of signalling to avoid unwanted relaying, which saves energy and improves EE, which is very much required from the perspective of IoT-based energy-efficient smart cities. It is seen that the proper choice of the power allocation coefficient and the target information rate is crucial for maximizing the sum throughput and EE of the considered IoT Network. Finally, we validate the correctness of the theoretical analysis and the superiority of the proposed scheme through Monte Carlo simulations.