# Effects of Interference and Mitigation Using Notch Filter for the DVB-S2 Standard
## 2 Literature Review and Related Works
However, this study does not investigate the system behavior with different interference power levels. There is a tradeoff between the remaining interference power and removed data from the spectrum of the desired signal. When the interference power is low, the important parameter is the removed frequency band from the desired spectrum. While for powerful interference, residual interference is more important and can paralyze special blocks in the chain block of the receiver. Compared to [22], the current study tries to introduce the \"remaining interference power\" after filtering. In the first section of this current study, the sensitivity of each block of a digital receiver to interference power is carefully analyzed and the critical threshold that stops that block from functioning correctly is displayed based on the simulations. Then, in another section, the residual interference power based on the notch filter bandwidth is displayed. For utilizing a notch filter, with the knowledge of the system sensitivity in critical, the user is able to discover which gap bandwidth can guaranty that the residual power does not exceed the critical threshold. In research [23], the author transfers digital data based on the IEEE 802.11 standard. Transferred data is then mixed with an AWGN channel and a CW interference with different power. The author describes the system degradation for different input interference power, based on the different BER curves. In the same way, obtained system performance is described based on the BER curves after filtering. Depictured BER curves in this study greatly expose the emergency of having an interference mitigation study for a typical digital receiver. However, adjusting the notch bandwidth adaptively based on JSR and the desired quality of service is missing from this paper. Another important point is that digital communication channels have more complicated effects that cause more system degradation in the presence of noise and add more blocks to the receiver chain. Based on the discussion above, it can be seen that the literature about protecting a digital receiver against narrowband interference is still new. Following shortcoming subjects are open and highly demand more research and attention:  
* Filter types and their effects on the quality of service: selected filter type directly determines the system limitation on interference mitigation. The amount of transmitted data that is removed by the filter gaps from the desired signal spectrum is an essential point for preserving the quality of service. * Considered channel and its effect on the transmitted signal: it should be considered that communication channels almost contain more destructive effects than a simple AWGN channel. The most frequent and famous effects are Doppler (or carrier frequency shift) and variable time delay that exist even for wireless transmitter and receiver with a very short distance. These effects, in the presence of CWI, are more significant and can cause complete packet loss and full crash of the receiver. Caring about just a simple modulator is not sufficient. * Typical digital receivers contain more blocks: to handle the real effects of a communication channel, a digital receiver must utilize different signal processing blocks to compensates for each effect individually. These blocks are sensitive to external interference and the amount of damage varies based on the interference parameters. * Criteria to adjust the filter parameters: Prior to this study, most researches are focused on the effects of a narrow band interference on the received signal's BER. Preserving QoS and also protecting all signal processing blocks require more consideration than the BER for filter adjustment. * Considering the described shortcoming, the current study tries to fulfill the following study subjects:
* This study brings the first order notch filter in the chain of a digital receiver as a protector against narrowband interference and explains how it could be utilized beside other blocks.