Performance Analysis of NOMA-Assisted Optical OFDM ISAC Systems with Clipping Distortion

TL;DR

This work analyzes a NOMA-assisted optical ISAC system using DCO-OFDM under clipping distortion, proposing clipping-before-NOMA to mitigate distortion and reduce PAPR. It derives Bussgang-based models for clipping noise, provides closed-form expression for user rates under SIC, and evaluates sensing performance via RMSE and CRB for distance estimation with a CCR-based VLC channel. Key findings show that allocating more power to the strong user improves sum-rate and sensing accuracy, while balanced power allocation offers fairness at the expense of BER and sensing performance, with clipping distortion causing saturation phenomena at high $E_b/N_0$. The results inform design choices for joint communication and sensing in multi-user VLC systems, emphasizing the trade-off between fairness and joint performance and suggesting adaptive strategies for clipping and PA in dynamic scenarios.

Abstract

This paper studies the performance of optical orthogonal frequency-division multiplexing (OFDM)-based multi-user integrated sensing and communication (ISAC) systems employing non-orthogonal multiple access (NOMA). Due to their inherent high peak-to-average power ratio (PAPR), OFDM waveforms are clipped to fit the limited dynamic range of the optical transmitters (e.g., light-emitting diodes (LEDs)), resulting in clipping distortion. To alleviate the impact of the distortion, we propose a novel transmitter architecture where the clipping processes are performed before NOMA superposition coding. We then analyze the performance of the proposed optical ISAC systems considering the effects of power allocation and clipping distortion. For the communication subsystem, we analyze the effect of NOMA on the achievable sum rate and bit error rate (BER). For the sensing subsystem, the root mean square error (RMSE) and Cramér-Rao bound (CRB) of estimating the transmission distance accuracy are obtained. Simulation results reveal that allocating more power to the strong user yields a higher sum rate, lower BER, and better sensing performance, whereas a more balanced power allocation among users results in degraded BER and sensing performance.

Figures (6)

• Figure 1: An example of NOMA-assisted multi-user optical ISAC system.
• Figure 2: Schematic diagram of the proposed NOMA-assisted DCO-OFDM optical ISAC system.
• Figure 3: PAPR comparison between two system models.
• Figure 4: BER performance of the proposed system.
• Figure 5: Sum-rate performance of the proposed system.