Effects of Malicious Users on the Energy Efficiency of Cognitive Radio Networks Efe F. Orumwense 1 , Thomas J. Afullo 2 , Viranjay M. Srivastava 3 School of Electrical, Electronic and Computer Engineering, University of KwaZulu-Natal, Durban, 4041, South Africa. 1 efe.orumwense@gmail.com 2 Afullot@ukzn.ac.za 3 viranjay@ieee.org Abstract— Multiple Cognitive Radio Users (CRUs) perform local spectrum sensing independently and makes a binary decision about the spectrum occupancy. The binary decision is forwarded to a Fusion Center (FC) for fusion which leads to more accurate detection of licensed signals in the network. Some malicious users in the network may affect the decisions of other legitimate CRUs by sending wrong spectrum occupancy information to the FC so as to use the spectral band for their own selfish gain, a term known as Primary User Emulation Attack (PUEA). In this paper, the effect of malicious users on the energy efficiency of cognitive radio networks is examined. A secured energy detection cooperative spectrum sensing technique is proposed and analysed to help maximize energy efficiency and reduce the effects of these attacks on the network. Simulation results show that there is a decrease in the energy efficiency of the network when the malicious users increases, and also that our proposed secured Cooperative Spectrum Sensing (CSS) technique in the OR fusion rule provides better energy efficiency. Keywords— Cognitive Radio Networks, Energy Efficiency, Malicious Users, Primary User Emulation Attacks, Fusion Rule. I. INTRODUCTION With the recent advances in wireless communication technology, Cognitive Radio (CR) has gradually paved its way into modern day technology becoming more popular by the day and evolving to become an alluring and attractive solution to spectral congestion and shortage problems [1]. In a Cognitive Radio Network (CRN), a Cognitive Radio User (CRU) or unlicensed user can opportunistically use an unused portion of spectrum belonging to a licensed user without a license. In order to avoid interference with the licensed user during this process, the CRU should have a prior knowledge about the status of the spectrum, either it is being used or vacant before using it. This prior knowledge about the status of the spectrum is gained through a process called spectrum sensing [2]. In a spectrum sensing process, each unlicensed user is equipped with cognitive radio to detect a targeted licensed spectrum and logically decide if the spectrum is free or vacant. In the vein to enhancing the performance of the process, multiple CRU can effectively cooperate with each other to conduct spectrum sensing, a term in literature commonly known as Cooperative Spectrum Sensing (CSS) [3] [4]. Cooperative spectrum sensing allows each cognitive radio to perform local spectrum sensing independently and then makes a binary decision and forwards this decision to a Fusion Center (FC). The FC gathers the local sensing information and makes a final decision about the availability of the spectral band. It has been seen that with the introduction of cooperative spectrum sensing in cognitive radio networks, the effects of multi-path fading and shadowing experienced by CRUs are mitigated and the performance of spectrum sensing has greatly improved with a more accurate detection of licensed user signals [5]. CSS, however, is vulnerable to some misbehaving CRUs which disrupt the network and the spectrum sensing etiquette and the obtainable overall performance. The misbehaviour is caused by reporting false spectrum occupancy information in order to influence the final decision made by the FC. A malicious CRU usually sends information that the spectrum is used to the FC which helps to identify the spectrum as used in taking the final decision. The resultant effect of this is that other CRUs will identify the malicious CRU as a licensed user thereby vacating the occupied spectrum band for the malicious CRU believing it is a licensed user. This gives the malicious user an unrivalled access to the spectrum [6]. An attack in the cooperative spectrum sensing process of a cognitive radio network in which malicious users pretends to be a licensed user by sending false spectrum occupancy information in order to gain unrivalled access to a vacant spectrum is called Primary User Emulation Attacks (PUEA) [6]. One of the possible approaches in preventing PUEA in the network is to build a secure link between CRUs and FC in order to be sure that only authenticated spectrum sensing occupancy results obtained from a trusted CRU is accepted by the FC in making its final decisions. In order to build a secured link, authentication, integrity and accurate spectrum sensing mechanism, are taken into consideration. The spectrum sensing mechanism used must be able to accurately detect vacant spectrum bands. The FC receiving the spectrum occupancy information should be able to attest that information is coming from a legitimate CRU (authentication) and also that the information was not modified or changed in transit (integrity). Due to the large overhead required in most spectrum sensing mechanisms, previous works on this aspect are mainly based on licensed user detection techniques and intrusion detection techniques with cryptographic mechanisms. In [7], an authentication of the licensed user’s signal using cryptographic and wireless link signatures via a helper node which is usually placed in close proximity to the primary user is used. Chen et al [8], have investigated a cooperative spectrum sensing scenario in the presence of a Page 431 Southern Africa Telecommunication Networks and Applications Conference (SATNAC) 2015