# Cognitive Interference Cancellation with Digital Channelizer for Satellite Communication
## 1 Introduction  
As an emerging wireless network technology, wireless sensor networks, especially Internet of Things (IoT) networks, have gathered a lot of attention as a solution to various applications, such as an environmental monitoring and data collection for a smart community like smart city [1, 2]. Because there are needs for data transmission from isolated and wide areas in IoT networks, the wide cell coverage of the IoT is a key requirement. Therefore, the integrated networks of the existing wireless sensor network and satellite communications is an essential component for achieving the goal of the various IoT applications [3, 4, 5]. As shown in Figure 1, two different satellite links can be considered: Direct and indirect access links. To gather the information in the remote areas, e.g., ocean and desert, a sink node (terminal station) collects the information from sensors and forwards this collected information to a monitoring station (Earth station) via a satellite using an indirect access link. Therefore, the satellite link is considered as a backbone link for the wireless sensor networks. On the other hand, a terminal station can be a sensor node and it transmits its own data to the Earth station via a satellite. Because the wide network coverage, e.g., global coverage, of wireless sensor networks, such as IoT, is one of their most significant requirements, satellites have become an important part of wireless communication systems. Moreover, a satellite is not a dedicated resource but is rather shared by service providers with their own services because it is one of the most expensive network entities. The assigned bandwidth for a given satellite communication service is called a transponder. Transponder bandwidth is typically fixed in the satellite during the design process and is not finely controllable after the satellite is launched. Each transponder provides a connection with dedicated bandwidth and transmission power between two points, i.e., Earth and terminal stations. With such a fixed transponder, there are major disadvantages in terms of bandwidth efficiency and transmit power control. For example, if a satellite customer needs a slightly wider bandwidth than a provided transponder bandwidth, the customer should purchase one more transponder, which is a waste of bandwidth. To solve such a problem, the bandwidth of the subchannel in the digital channelizer is minimized for fine granularity of the transponder. In general, for efficient implementation, a digital filter bank is used for a digital channelizer [6; 7; 8]. Because of their wide transmission coverage, satellite communication systems are more vulnerable to interference that is generated in a wide area [9; 10; 11]. Interference is a threat for satellite communication systems and services because they are used for various significant purposes including military wireless communication networks. There are many different sources of interference: It can be generated by malicious users or generated unintentionally by nonlinear analog components in transceivers. Self-interference, which is an echo version of the transmitted signal, can be generated in a full-duplex operation [12]. The capability of interference mitigation in a satellite is an important issue because without it, the quality of service cannot be guaranteed and a satellite can be useless in an environment with interference. To mitigate this interference problem, cognitive interference detection and cancellation techniques are required [9; 13; 14; 15]. Various approaches are adopted for interference cancellation, depending on the properties of the target signal. As cognitive radios have attracted much attention from researchers to improve spectrum utilization, various detection methods to sense primary signals in cognitive radios have been proposed [16; 17; 18]. If the signal waveform is unknown, an energy detection method, which is one of the simplest detection schemes, is generally used to detect the signal [19; 20; 21].