Narrowband Interference Cancellation Using a Fine Frequency Shift in Single-Carrier Frequency Domain Equalization (SC-FDE) Systems  
[PERSON]  
1 Department of Artificial Intelligence, Hanbat National University, Sejong 34158, Republic of Korea; [EMAIL_ADDRESS]  
[PERSON]  
2 Satellite System Team 4, Hanwha Systems, Seongnam 13591, Republic of Korea; [EMAIL_ADDRESS] (Y.-B.R. ): [EMAIL_ADDRESS] (D.-H.S.) [PERSON]  
2 Satellite System Team 4, Hanwha Systems, Seongnam 13591, Republic of Korea; [EMAIL_ADDRESS] (Y.-B.R. ): [EMAIL_ADDRESS] (D.-H.S.) [PERSON]  
1 Department of Artificial Intelligence, Hanbat National University, Sejong 34158, Republic of Korea; [EMAIL_ADDRESS]  
Footnote 1: email: {j  
required to reduce PAPR can introduce a significant burden. However, the presence of narrowband interference (NBI), whether intentional or unintentional, can severely degrade receiver performance. SC-FDE systems, in particular, are more vulnerable to NBI compared to OFDM [8]. In military communications, NBI is often deliberately introduced as a form of jamming attack [11]. Addressing this vulnerability is crucial for ensuring reliable communication in such scenarios. This paper introduces a novel NBI cancellation method specifically designed for SC-FDE systems operating in NBI-prone environments. Existing NBI removal techniques are broadly categorized into time-domain cancellation techniques [12; 13] and frequency-domain cancellation techniques [14; 15; 16; 17; 18; 19; 20; 21; 22; 23]. While time-domain techniques, such as adaptive filters, are generally more complex, frequency-domain cancellation methods are simpler and can be further classified into interference reconstruction [14; 15; 16; 17] and frequency nulling [18; 19; 20; 21; 22; 23]. Among these, FFT-based frequency nulling has been recognized for its simplicity and low computational complexity, making it suitable for SC-FDE systems. However, conventional FFT nulling faces challenges when the interference frequency does not align with the FFT grid frequency [24], often necessitating the nulling of multiple FFT grids. This approach not only increases the damage to the desired signal but also results in significant performance degradation. Although techniques like the direct-sequence spread spectrum (DSSS) [24; 25; 26] can mitigate this issue, they come at the cost of reduced spectral efficiency and do not provide a fundamental solution. To overcome these limitations, this paper proposes an innovative interference cancellation technique based on FFT nulling in [22]. In [22], it was observed that NBI cancellation can be achieved by nulling only a single FFT grid when the NBI frequency aligns with the FFT grid frequency. Building on this observation, the proposed method introduces a fine frequency shift to align the interference frequency with the nearest FFT grid frequency. By doing so, the interference can be effectively canceled by nulling only a single FFT grid, thereby minimizing the damage to the desired signal. The key steps of the proposed method are as follows: First, the exact NBI frequency is identified from the received signal. The difference between the NBI frequency and the nearest FFT grid frequency is then calculated, and the received signal's frequency is shifted accordingly. After nulling the interference at the aligned FFT grid, the signal's frequency is shifted back to its original state for further processing. This novel approach retains the simplicity of FFT nulling while addressing its limitations, providing a more effective and spectrally efficient solution for NBI cancellation. The proposed method's efficacy is validated through computer simulations. Simulation results demonstrate that in scenarios with a signal-to-interference ratio (SIR) of 5 dB and 0 dB, the proposed technique significantly outperforms conventional methods, showing minimal degradation in reception performance.