Abstract
The cognitive radio paradigm for developing next-century wireless communication systems is rapidly entering the mainstream, and various aspects of it are currently being applied in 5G technology, aeronautical engineering, military communications, emergency, and public safety applications, satellite communication, and healthcare. Cognitive radio focuses on the existence of software defined radio architectures that allow dynamic reconfiguration. Many researchers have taken initiatives in the last decade to achieve the reconfiguration ability in cognitive radio systems to support the concept of dynamic spectrum access. As cognitive radio adapts dynamic spectrum allocation for its users, the physical implementation requires reconfigurable filters that can alter the carrier frequencies and bandwidth. Although there are many ways to reconfigure filter operation, diode based reconfiguration has received utmost attention among researchers because of its shorter response delay and easy implementation. In the last decade, researchers have reported several diode-based reconfigurable filters, including their characteristics such as filter function, filter combination, tuning range, variation in bandwidth, isolation, and resonance. However, to examine the potential of these filters in the application of cognitive radio, a comprehensive review needs to be pursued. In this review article, the descriptions of several diode based reconfigurable filters are illustrated with their exhibiting characteristics. The detailed information provided in this article has disclosed that primarily three different types diode based reconfigurable filters have been reported by researchers: Tunable, Switchable, and Hybrid (Both Tunable and Switchable). It is also found that each type of reconfiguration can further be segregated in terms of filter function, centre frequency variation, and bandwidth variation. The detailed categorization of the reconfiguration presented in this paper provides a systematic approach to select the correct reconfigurable filter for the desired frequency reconfiguration in cognitive radio.
Highlights
Cognitive Radio (CR) is considered to have tremendous potential to alleviate the spectrum scarcity problem in wireless communication [1]–[3]
This article has addressed a comprehensive survey on diode based reconfigurable filters for cognitive radio applications
Three different types of reconfigurable filters based on diode were primarily reviewed: Tunable filter, Switchable filter, and Hybrid reconfigurable filter
Summary
Cognitive Radio (CR) is considered to have tremendous potential to alleviate the spectrum scarcity problem in wireless communication [1]–[3]. The secondary user has to be adaptive as spectrum holes are dynamic, and it must be reconfigurable to maintain its communication all the time. Reconfigurable filters can provide the secondary user the ability to adapt to the dynamic nature of spectrum holes and avoid the interference caused by congested communication applications. Reconfigurable microwave filters are the filters which can adapt multiple bands of operation with a single filter structure [13] It will be highly desirable in future wireless communication with the increase in number of multifunctional devices. A study on diode based reconfigurable filter has been considered in this article for exploring spectrum reconfiguration in CR implementation. Second is PIN diode based discrete variation or switchable reconfigurable filters. To assist the reader in choosing the suitable method for designing appropriate reconfigurable filters as per the requirement, a well-organized summary diagram of diode based filter reconfiguration and a probable research direction on diode based reconfigurable filter designing for the implementation of CR is presented
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