# Effects of Interference and Mitigation Using Notch Filter for the DVB-S2 Standard
## 2 Literature Review and Related Works  
Multiple interference mitigation techniques were developed for broadband radio communication [7; 8; 15]. Most communication protocols are shielded against adjacent communication interference. Since the rise of co-channel communications, either unintentional or intentional interferences are still a possible problem for this type of communication. An interference mitigation research in 2016 was conducted to identify the effects of wideband, narrowband, and radar interferences on a standard satellite communication (SATCOM) protocol [16]. A similar study was conducted to analyze the interference mitigation methods for GNSS broadband communications [17]. To remove the interference after the detection, a discrete notch filter is used to adapt in real-time to the center frequency and to the amplitude of the interference. The use of finite impulse response filters (FIR) [18] and infinite impulse response filters (IIR) are the most common for interference removal of discrete communication signals [15]. Compared with FIR filters, IIR filters have a simpler structure and faster convergence time. More recently, a study was carried out on the effects of the CWI center frequency on an orthogonal frequency division multiplex (OFDM) signal, which is used in modern wireless devices. This digitally modulated signal is vulnerable to CWI, so it is very important to mitigate its effects. Not only that, but a small variation in the CWI center frequency could cause a huge rise in the BER of this system [19]. Research [17; 20] tries to utilize a notch filter as a computationally efficient solution for protecting the GNSS system against narrowband attacks. One of the most important shortcomings of the notch filtering literature is the usage of a second-order or bi-polar notch filter. This type of notch has two symmetric gaps and can be applied to a real input signal. This means that two bands of the input signal are removed by the filter. Telecommunication signals have \"in-phase\" and \"quadrature\" components that make the receiver able to work properly with both components as a complex number. Working with complex numbers allows the system to use complex filters. Compressed digital communication signal like DVB-S2, carries significant information in a narrow frequency band. This paper tries to utilize a first-order notch filter that has only one gap to preserve the quality of service as much as possible. In [18], a linear multistage Wiener filter is utilized to remove narrowband interference in a high data rate direct-sequence ultra-wideband (DS-UWB) system. The research benefits from the second-order statistics of the received signal for faster filter coefficient convergence. Compared to a simple IIR notch filter, this filter has more complexity that increases directly with the number of utilized filter taps. For a notch filter, there are two important parameters: center frequency of the notch and its bandwidth. Those parameters can simply be adjusted as two numbers by the external detector That makes the notch filter suitable to remove a narrowband interference with fast hopping center frequency and makes it possible to design the detector completely independently of the notch filter based on any desired statistical or non-statistical algorithms. Studies [21; 22] are great examples of trying to protect a digital communication standard against narrowband interference. The author compares the performance of null-subcarriers reservation (NSR) and an adaptive notch filter (ANF) for narrowband interference suppression utilized in intensity modulation and direct detection (IM/DD) system. This article implemented all the blockchain of the DMT standard and utilizes quadrature phase-shift keying (QPSK) symbols for data modulation. The author uses BER curves to compare the obtained system performance with two different algorithms. Based on this research, ANF outperforms the NSR scheme in narrowband interference cancellation.