Performance Degradation Analysis of Downlink NOMA Systems Under Carrier Frequency Offsets

Abstract

In this paper, we analyze the impact of carrier frequency offset (CFO) on downlink non-orthogonal multiple access (NOMA) systems. Our research objectives are to quantify performance degradation due to CFO and develop mitigation strategies for practical deployments. Using analytical modeling and closed-form derivations, we establish explicit mathematical relationships between CFO magnitude, power allocation coefficients, and system performance metrics. Our results reveal that users with higher power allocations experience quadratically increasing SNR degradation with CFO magnitude, with up to a 45% sum rate reduction at high CFO values. The core innovation of this work is twofold: first, we provide comprehensive closed-form expressions for SNR, achievable rate, and outage probability under various fading models; second, we develop an adaptive power allocation algorithm that dynamically adjusts coefficients based on real-time CFO estimates and channel conditions. This algorithm demonstrates significant performance improvements, reducing sum rate degradation by up to 25% compared to fixed allocation schemes while maintaining quality-of-service requirements.