## 1 Introduction
Consequently, either the UWB wireless sensors network designer needs to consider how to avoid the transmission of the UWB wireless signal over the frequencies of strong narrow band interferences or the UWB receivers need to utilize narrow band interference suppression techniques to elevate the reception performance, the transmitted range, the system capacity and the data rate of the UWB radio devices. In recent years, the significant progress in UWB wireless communications and electronics has enabled the development of low-cost, low-power, multi-functional sensors nodes that are small in size and communicate untethered in a short range [28; 29; 30; 31]. Compared with traditional narrow band and broadband wireless communication systems, interferences suppression in UWB wireless sensor networks is a more challenging issue due to the rather restricted PSD transmission and the extremely wide frequency band occupied [3; 32]. Given the low power consumed and low cost requirements in practical UWB wireless senors applications, at the same time noticing other basic limitations such as low computation complexity in both hardware and software, the in-band narrow band interferencesissue should be disposed of more specifically, and some appropriate approaches that are able to deal with narrow band interference need to be developed [33; 34; 35; 36]. A universal consideration for narrow band interferences' alleviation is avoiding the interferences at the transmitter. The work in [37; 38] presented the methods via designing the optimal time-hopping sequences or direct spread spectrum codes with the proper waveform to mitigate the narrow band interferences. If the statistic characteristics of the narrow band interference are known, the narrow band interferences can be avoided by means of adjusting the transmission parameters at the transmitter appropriately, since the impacts of interferences can be directly related to the spectral characteristics of the impulse UWB waveform at the receiver. Once the sub-band of frequency spectrum where narrow band interferences are present can be avoided, the impacts of in-band narrow band interferences on the UWB wireless sensors can be alleviated. A good example for the implementation of the above ideal is designing a proper pulse shape via combination and optimization of a number of the basic Gaussian waveform and the \(n\)-th order derivative of the Gaussian monocycle [39]. In addition, interference avoiding can be realized by some physical solutions. In [40], a narrow band interference avoidance strategy based on frequency notch antenna design is presented. The basic consideration is to create frequency notches by adding a slight resonant module to the ultra-wide band antenna, which makes it insensitive to some featured frequencies. In the above approach, we should note that the reception performance of the ultra-wide band antenna will deteriorate with the number of notches increasing. Therefore, the idea of the frequency notched antenna is not practical enough at avoiding a number of strong in-band narrow band interferences in the same UWB wireless sensor networks. Another interference alleviation approach is canceling the interferences at the UWB receiver [41; 42; 43]. Interference detection and avoiding in the frequency domain are common considerations [44]. In addition, the front end analog frequency domain notch fixed filtering strategy at the ultra-wide band wireless sensor networks seems to have high feasibility. The main deficiencies of the above-mentioned NBI-avoiding algorithms are that they are heavily dependent on the precision of a priori knowledge of the central frequency and the bandwidth of the NBIs and channel state information [45; 46]. Without obtaining the exact information on the central frequencies of the interferences, the analog filter will become unavailable for interference canceling.