Protection of primary users in dynamically varying radio environment: practical solutions and challenges
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RESEARCH
Open Access
Protection of primary users in dynamically varying radio environment: practical solutions and challenges Pawel Kryszkiewicz1, Hanna Bogucka1* and Alexander M Wyglinski2
Abstract One of the primary objectives of deploying cognitive radio (CR) within a dynamic spectrum access (DSA) network is to ensure that the legacy rights of incumbent licensed (primary) transmissions are protected with respect to interference mitigation when unlicensed (secondary) communications are simultaneously operating within the same spectral vicinity. In this article, we present non-contiguous orthogonal frequency division multiplexing (NCOFDM) as a promising and practical approach for achieving spectrally agile wireless data transmission that is suitable for secondary users (SUs) to access fragmented spectral opportunities more efficiently. Furthermore, a review of the current state-of-the-art is conducted with respect to methods specifically designed to protect the transmissions of the primary users (PUs) from possible interference caused by nearby SU transceivers employing NC-OFDM. These methods focus on the suppression of out-of-band (OOB) emissions resulting from the use of NCOFDM transmission. To achieve the required OOB suppression, we present two practical approaches that can be employed in NC-OFDM, namely, the insertion of cancellation carriers and windowing. In addition to the theoretical development and proposed improvements of these approaches the computer simulation results of their performance are presented. Several real-world scenarios regarding the coexistence of both PU and SU signals are also studied using actual wireless experiments based on software-defined radio. These simulation and experimental results indicate that OOB suppression can be achieved under real-world conditions, making NC-OFDM transmission a viable option for CR usage in DSA networks. 1 Introduction The idea of cognitive radio (CR) encompasses opportunistic and dynamic access to spectrum resources that might be available at a certain location and time. These resources, called spectrum holes, especially in metropolitan areas, can potentially be fragmented with several non-contiguous spectral bands of different width. Moreover, the availability of these spectrum holes may dynamically change over time, as the licensed users (primary users–PUs) enter into and depart from a given location. There has been a substantial amount of research conducted with respect to finding suitable technologies capable of aggregating the available spectrum adaptively according to dynamics of spectrum holes availability, and to support the transmissions of the secondary users * Correspondence: [email protected] 1 Chair of Wireless Communications, Poznan University of Technology, Poznan, Poland Full list of author information is available at the end of the article
(SUs) in a spectrally efficient manner. In order to use the fragmented spectrum, an SU radio transceiver must be able to shape its emission to make best use of available resources while s
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