## 2 Literature Review
The main issue with simple FFT is that frequency samples are calculated just based on one window of the data stream, which makes the estimated power spectrum noisy with less precision. Such detectors are suitable for powerful interference detection not for weak power RFIs. The Welch method can enhance PSD estimation with arithmetic averaging over several FFT packets [26]. However, complexity and required random access memory (RAM) for saving the previous FFT packets increase by the number of involved FFT packets in averaging. The complexity limits the hardware implementation of the Welch method. Another issue happens when the system needs to track hopping interference, in this case, Welch method does not have enough flexibility to support the detector. Smaller and end user devices also need to have access to a high-quality spectrum and a fixable detector. Most of the available detectors use complex algorithms and circuitry to protect an especial application against a type of interference. It mostly results in an expensive and heavy device which may be unpractical for smaller devices and complex to implement. The recently simplified Welch method [16] is introduced as a promising candidate for enhanced PSD estimation. Benefiting from simple and practical design, it can convert an academic SDR to a worthy spectrum analyzer. It gives the end user flexibility to adjust the degree of averaging by simply tuning one feedback level. Thus, it motivates us to design a new detector based on that algorithm. IIR notch filters are widely used with mitigation systems to protect different communication protocols like wireless local area network (WLAN) standard (IEEE 802.11a/g/n/ac) [27; 28], GNSS [13], and discrete multi-tone (DMT) system [29; 30]. 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. After mitigation, performance enhancement is explained as BER improvement. Mentioned algorithms can improve performance compared to the unprotected system; however, for a narrowband modulated signal, QoS is more sensitive to spectrum manipulation and solid criteria must be used for notch filter bandwidth adjustment [10]. The current article tries to cover the shortcoming in the research area by deploying the following points:  
* As the main element of spectrum monitoring and detection, a smooth and flexible PSD is extracted from the input signal based on the simplified Welch method [16]. Flexibility of this method allows the detector to tune the PSD smoothness from the degree equivalent to 100 averaging of previous FFT packet to a simple FFT. In this way, the detector can change its mode from very low power interference detection to low power interference with hopping center frequency detection. * By the smart design based on the basic logic elements, the proposed detector can extract necessary information about the mixed RFI in the desired signal: (1) grouping the abnormality points in PSD as individual interferences and gives the number of required notch filter; (2) Start, end, center, and bandwidth of each interference; (3) Power of each interference. * A criterion based on the interference power (JSR) and optimum reception SNR is proposed for notch filter bandwidth adjustment. * By mixing the chain of notch filters with the multiplexer, the variable number of notch filters can be activated equal to the detected number of interferences. It minimizes removed useful information from signal spectrum.