# Primary User Localization Algorithm Based on Compressive Sensing in Cognitive Radio Networks
## 1 Introduction  
At the present stage, the static spectrum allocation scheme greatly hinders the development of wireless communication technology and the expansion of the mobile communication business. The concept of dynamic spectrum access arises on this occasion. On the premise of not causing interference to primary users (PUs), secondary users in wireless network can adaptively change its communication parameters, access licensed band in order to communicate effectively through a sensing wireless environment, thus improving the spectrum utilization. As an effective technique to ease the contradiction among limited spectrum resources, increasing spectrum requirement and low frequency spectrum utilization, cognitive radio (CR) [1] technology has attracted wide attention. In cognitive radio networks, PUs have priority rights to access the licensed band. During the process of using spectrum holes to communicate, CRs should be able to quickly detect the emergence of PU, in order to withdraw from an occupied spectrum in a timely manner [2]. However, in an unauthentic network, malicious users (MUs) may easily fake the features of PUs and transmit within the cognitive network sensing band by reconfiguring the air interface of CR. Based on cognitive-etiquette [3] of spectrum access priority, CRNs would mistakenly consider MU as legal PU and shift scanning band, thus remarkably reducing the available spectrum resource in CRNs, which is called primary user emulation attack (PUEA) [4]. It is apparent that such attacks will cause numerous SUs to lose access to the network services. In particular, information about PUs location could enable several key capabilities in CR networks, including improved spatio-temporal sensing, intelligent location-aware routing, as well as aiding spectrum policy enforcement [5]. Fortunately, with the restriction of the transmitting power, it is hard for MUs to imitate energy level and position information of PUs at the same time. Thus, combining the energy level with position information ofsource signal, and further confirm the identity of detection signal can prevent PUEA when MUs has successfully simulated the signal features of PUs. In addition, the positioning mechanism based on signal source can also be integrated into the CRNs spectrum sensing process, in order to enhance the credibility of the sensing results of SUs, which prevents spectrum sensing data falsification (SSDF) attacks to a certain extent. Therefore, research about signal source localization algorithm within the authorized frequency band is of important significance. As FCC has considered opening free TV band for cognitive users in dynamic spectrum access [6]. Thus, existing research on signal source localization algorithm in CRNs usually assumes that the authorized user networks are the TV tower with fixed position. In order to facilitate the process of obtaining the source position in CRNs, CRNs can be regarded as wireless sensor networks [7] (WSNs), then the source in the sensing spectrum band becomes a goal node in WSN, and SU is a beacon node in WSN [8]. The existing localization algorithms in WSN can be divided into range-based [9] and range-free [10] localization algorithms according to the different means of measurement. Range-based techniques such as multi-alteration require high hardware demand and are sensitive to noise. In contrast, range-free localization schemes locate the target nodes depending on the correlation among network nodes, among which the centroid scheme is a classic one [11]. Centroid scheme equally treats influence of normal nodes acting on the goal nodes, leading to ordinary localization performance. The WCL algorithm and the RR-WCL algorithm based on centroid scheme were proposed in [12; 13]. These research papers introduced different methods to calculate the weights of beacon nodes through received signal strength (RSS), thus reflecting the influence extent of beacon nodes exerting to centroid position.