Analyzing and Mitigating Narrow-Band Channel Estimation Errors in 5G Systems

In orthogonal frequency-division multiplexing (OFDM)-based systems, such as 5 G, precise channel estimation (CE) is crucial for reliable connectivity and high data rates. However, in 5G, the sub-band-specific precoding structure of pilot signals, known as demodulation reference signals (DMRS), limits the number of pilot samples per sub-band, which can lead to significant CE errors. This paper provides an in-depth analysis of the influence of CE errors on pilot and data subcarriers in OFDM systems. We rigorously demonstrate that CE errors on data subcarriers can be modeled as independent additive noise, validating assumptions made in previous works but not formally proven. Additionally, we analyze how CE errors on pilot subcarriers introduce bias in noise variance estimation and derive closed-form expressions for this bias under both perfect and imperfect MMSE CE conditions. We propose practical bias removal schemes tailored for residual power-based noise variance estimation. Numerical simulations confirm the accuracy of our theoretical findings and show that the proposed noise variance estimation method significantly reduces the performance gap between narrow-band and wide-band CE.