# A Relay Optimization Method for NOMA-Based Power Line Communication Systems
###### Abstract  
Power line communication (PLC) technology is investigated in this research. A PLC system model combining Orthogonal Frequency Division Multiplexing (OFDM) and Non-Orthogonal Multiple Access (NOMA) technologies is proposed to enhance spectral efficiency, extend transmission distance, and improve signal quality. We construct detailed models for the system, signal, and noise. Future Channel State Information (CSI) is predicted using a Long Short-Term Memory (LSTM) network, and an improved simulated annealing algorithm is employed to optimize power allocation and relay positioning in the system. Experiments validate the effectiveness of the LSTM model in predicting CSI data in a NOMA communication system, demonstrating generally good performance despite some prediction errors. Simulation results show that this approach significantly enhances system performance, reduces power consumption, and meets constraints on system capacity, bit error rate (BER), and signal-to-interference-plus-noise ratio (SINR) in complex PLC environments. Future research should focus on optimizing model parameters, expanding datasets, exploring alternative optimization algorithms, and testing the model in real-world scenarios to improve generalizability and practicality. In conclusion, the proposed multi-user PLC system provides an effective technical solution for future smart grid and Internet of Things (IoT) applications. p +
Footnote †: journal: applied sciences  
0000-0002-0001-9999-2246-22  
effectively suppress multipath fading in power line communication. This approach significantly improves resource utilization, quality of service, and data transmission rates [5]. Non-Orthogonal Multiple Access (NOMA), an emerging multi-user access technology, enables multiple users to share the same frequency band resources through power domain or code domain multiplexing, thus significantly improving spectrum efficiency. Compared to traditional Orthogonal Multiple Access (OMA), NOMA serves multiple users simultaneously, thereby increasing system capacity and reducing latency. NOMA significantly improves PLC system performance, better meeting the needs of future smart grids and the Internet of Things (IoT) [6; 7; 8; 9; 10]. Researchers have recently proposed various NOMA-based PLC schemes, including two-stage and cooperative relay schemes, to further enhance system performance. For instance, the two-stage NOMA scheme applies NOMA at both the source and relay modems, significantly improving system capacity compared to single-stage schemes. Additionally, cooperative NOMA strategies, where multiple PLC modems relay signals together, have shown significant improvements in reliability and throughput, especially in harsh PLC environments [3; 11]. To further optimize PLC system performance, researchers have proposed combining OFDM and NOMA technologies. These schemes enhance spectral efficiency, improve signal quality, and extend transmission distance through relay technology. In multi-hop hybrid PLC-wireless communication systems, employing decode-and-forward relays significantly enhances system reliability and coverage [3]. To address noise and fading issues in PLC systems, researchers have introduced receive diversity techniques and power optimization strategies. In receive diversity PLC systems under Nakagami-m noise environments, the minimum mean square error estimation technique is used to obtain channel gain estimates, and the maximum likelihood decision rule designs suboptimal receiver structures, improving system symbol error probability performance [12]. In three-node bidirectional relay-assisted PLC systems, power optimization algorithms considering quality of service constraints effectively reduce total system power and enhance performance [13]. Smart grid applications necessitate frequent access to PLC networks by numerous devices requesting data transmission. To meet this demand, several access protocols have been proposed.