Low-Complexity Joint Estimation Algorithm for Carrier Frequency Offset and Sampling Frequency Offset in 5G-NTN Low Earth Orbit Satellite Communications

GONG Xianfeng; LI Ying; LIU Mingyang; ZHAI Shenghua

doi:10.11999/JEIT251086

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GONG Xianfeng, LI Ying, LIU Mingyang, ZHAI Shenghua. Low-Complexity Joint Estimation Algorithm for Carrier Frequency Offset and Sampling Frequency Offset in 5G-NTN Low Earth Orbit Satellite Communications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT251086

Citation:

GONG Xianfeng, LI Ying, LIU Mingyang, ZHAI Shenghua. Low-Complexity Joint Estimation Algorithm for Carrier Frequency Offset and Sampling Frequency Offset in 5G-NTN Low Earth Orbit Satellite Communications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT251086

Citation:

GONG Xianfeng, LI Ying, LIU Mingyang, ZHAI Shenghua. Low-Complexity Joint Estimation Algorithm for Carrier Frequency Offset and Sampling Frequency Offset in 5G-NTN Low Earth Orbit Satellite Communications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT251086

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Low-Complexity Joint Estimation Algorithm for Carrier Frequency Offset and Sampling Frequency Offset in 5G-NTN Low Earth Orbit Satellite Communications

doi: 10.11999/JEIT251086 cstr: 32379.14.JEIT251086

GONG Xianfeng^{1, 2},
LI Ying^{1
,
,},
LIU Mingyang^{1, 2},
ZHAI Shenghua²

1.
School of Telecommunications Engineering, Xidian University, Xi’an 710071, China
2.
China Academy of Space Technology (CAST)-Xi’an Institute of Space Radio Technology, Xi’an 710010, China

Funds: The National Natural Science Foundation of China(62131016, 62471363)

Accepted Date: 2025-12-02
Rev Recd Date: 2025-12-02

Available Online: 2025-12-05

Abstract

Abstract

Objective The Doppler effect presents a major impairment in Low Earth Orbit (LEO) satellite communications within 5G Non-Terrestrial Networks (5G-NTN), introducing Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO), and Inter-Subcarrier Frequency Offset (ISFO) across subcarriers. Although existing estimation algorithms focus mainly on CFO and SFO, the effect of ISFO remains inadequately addressed. ISFO becomes particularly detrimental to receiver performance when OFDM systems utilize a large number of subcarriers and high-order modulation. Moreover, under joint CFO and SFO conditions, conventional maximum likelihood estimation (MLE) methods often involve one- or two-dimensional grid searches, incurring high computational complexity. To mitigate these issues, this paper proposes two novel joint estimation algorithms for CFO and SFO. Methods This paper analyzes the influence of non-ideal factors at the transmitter, receiver, and channel, such as local oscillator offset, sampling frequency offset in Digital-to-Analog and Analog-to-Digital converters, and Doppler effect. A mathematical model for the received OFDM signal is developed, and the mechanism through which SFO and ISFO distort the phase of frequency-domain subcarriers is derived. Leveraging the pilot structure of 5G-NTN, two joint CFO and SFO estimation algorithms are introduced: (1) Algorithm 1 exploits the sequence correlation between the received frequency-domain DMRS signal vectors, denoted as and . After phase pre-compensation is applied to , the normalized cross-correlation vector is computed. An objective function is constructed based on this vector, and its unimodal property within the main lobe is utilized to efficiently estimate the parameters via a bisection search. (2) Algorithm 2 treats the estimation parameters as analogous to carrier frequency offsets in single-carrier systems and adopts an L&R-based autocorrelation approach to derive approximate closed-form expressions. Results and Discussions A computational complexity analysis is performed comparing the proposed algorithms with conventional one-dimensional (1D-ML) and two-dimensional (2D-ML) grid-search MLE methods. Numerical results demonstrate that Algorithm 1 achieves substantial complexity reduction. Specifically, the number of complex multiplications—the dominant computational cost—is only 4% of that of the 2D-ML method, 8% of that of Algorithm 2, and 44% of that of the 1D-ML method. Although Algorithm 2 is computationally heavier, it provides a closed-form estimation expression. The performance of each algorithm is evaluated in terms of the mean square error (MSE) of the estimated parameters. Simulations show that for a subcarrier number of 3072, the 1D-ML algorithm slightly outperforms others at SNRs below 5 dB. However, since robust modulation schemes (e.g., BPSK, QPSK) typically used at low SNRs can tolerate larger offsets, the medium-to-high SNR regime is of greater practical interest, where all four algorithms exhibit comparable estimation performance. Conclusions This paper addresses the impact of Doppler effect in 5G-NTN LEO satellite communications by analyzing the mechanism and influence of ISFO and proposing two joint estimation algorithms for CFO and SFO. First, a mathematical model of the received signal is established considering non-ideal factors such as CFO, SFO, and ISFO. It is derived that the combined effect of SFO and ISFO on OFDM signals is equivalent to their linear superposition, effectively expanding the range of the equivalent SFO. Second, the objective function is defined using the cross-correlation vector of two DMRS sequences. Leveraging its unimodal characteristic within the main lobe, a binary search algorithm is employed to achieve rapid convergence. Subsequently, the parameter to be estimated—determined by SFO and ISFO—is analogized to the carrier frequency offset in single-carrier systems. An approximate closed-form solution for parameter estimation is derived using the L&R algorithm. Finally, complexity analysis and performance simulations are conducted. The results demonstrate that the proposed algorithms not only significantly reduce computational complexity but also exhibit excellent estimation performance. The outcomes of this research can be applied to the development of 5G-NTN LEO satellite payloads and terminal products, demonstrating promising potential for widespread application.

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References(17)

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