Beacon-Synchronized Uplink Non-Orthogonal Multiple Access Communication System

Practical deployment of uplink Non-Orthogonal Multiple Access (NOMA) suffers from synchronization errors, device-specific carrier-frequency offsets, hardware impairments, and the complexity of Successive Interference Cancellation (SIC). This paper presents an end-to-end three-user, narrowband single-carrier power-domain uplink NOMA testbed built with low-cost ADALM Pluto Software-Defined Radios (SDR) that operate without a shared reference clock. A beacon-and-response protocol is executed directly on each radio’s native ARM processor and provides low-overhead transmission coordination. The receiver addresses any residual asynchrony among the received signals through a user-specific preamble acquisition, carrier-frequency-offset estimation and correction, matched filtering, least-squares channel estimation, pilot-aided phase tracking, soft combining of repeated packet copies, convolutional decoding, waveform reconstruction, and SIC. The designed platform is evaluated over 1000 communication rounds in both single-cell and simultaneous two-cell configurations, with three transmitting users and one central receiver per cell. In the single-cell experiment, the beacon detection success rate reaches 93.17%, while the system packet error rate is only 0.45% when all users detect the beacon. In the two-cell experiment, the combined beacon detection rate is 92.55%, and the corresponding system packet error rates are 0.12% and 1.81% for the two cells. The average receiver-side processing remains below 100 ms, while end-to-end latency stays below 0.36 s despite the host communication and file-transfer overhead. The proposed implementation closes the gap between analytical NOMA theoretical research approaches and practical over-the-air deployment, and provides a reproducible foundation for scalable multicell experimentation and future integrated real-time processing.