The spectrum sensing performance in cooperative cognitive radio (CR) network is studied under a double threshold (DTH)-based detection with censoring of CRs, and thereafter, the study is extended for a hybrid spectrum access scheme in presence of Rayleigh faded sensing (S) and reporting (R) channels. In spectrum sensing, a CR employs an energy detection to detect the presence of primary user (PU) and compares the received energy statistics with the DTH. The CRs with energy statistics lying in fuzzy zone are not allowed to send their sensing information to the fusion centre (FC). Further, the qualified CRs are censored (rank-based and threshold-based censoring) to report their decisions based on quality of R-channel. The incorporation of DTH-based sensing and censoring of CRs not only improves the detection performance but also reduces the transmission overhead. In spectrum access, two hybrid spectrum access schemes, namely conventional hybrid spectrum access scheme (CHSAS) and a modified hybrid spectrum access scheme (MHSAS) are studied and compared.
TopIntroduction
Cognitive Radio (CR) has evolved as a smart technology to resolve the spectrum scarcity issue in the secondary network. In an overlay or underlay CR network, a CR node exploits the licensed spectrum band without creating harmful interference to the primary user (PU). In overlay network, a CR user accesses the PU band only if the PU is found to be absent, while in an underlay network, both the users (CR and the PU) share the spectrum. Thus, accuracy in sensing the presence of PU has a great importance in CR technology otherwise a PU has to face an undesirable interference (Haykin, 2005). In spectrum sensing (SS), a CR may employ an energy detector (ED) to detect PU in the given channel (Ghasemi, 2005). Each CR of a secondary network senses the status of PU and compares the received energy statistics with a predefined threshold, i.e., a single threshold based (STH) based detection (Ghasemi, 2005). Spectrum sensing can also be performed using double threshold (DTH) (Bhowmick, 2015a). It is observed that DTH based spectrum sensing reduces the transmission of sensing overhead at the cost of some performance loss (Bhowmick, 2015a; Chunhua, 2007). In DTH based sensing, the CRs with energy statistics lying in fuzzy zone (between two thresholds) are not allowed to send the sensing information to the fusion centre(FC) (Chunhua, 2007). If the R-channels are heavily faded, the overall decision, i.e., cooperative decision at FC may be affected (Bhowmick, 2015a). Thus, it is required to eliminate CRs having bad R-channels from the cooperation process. In (Nallagonda, 2013a), authors proposed censoring techniques, i.e., Threshold-based censoring (TBC) and Rank-based censoring (RBC) to combat with such type of adverse scenarios. Censoring of CRsis done in (Nallagonda, 2013a) on the basis of R-channel quality. In (Bhowmick, 2015a; Bhowmick, 2014), authors studied the censoring schemes under DTH. The incorporation of censoring of CRs with DTH based sensing improves the performance of SS and at the same time it reduces the overhead of the transmission (Bhowmick, 2015a; Bhowmick, 2014). It is shown in (Bhowmick, 2014), Reduction in overhead of the transmission improves the agility gain of the network. A cooperative SS (CSS) under DTH with censoring has been studied for perfect and imperfect estimation of channel and different fusion strategies such as Majority, and Maximal Ratio Combining (MRC) (Bhowmick, 2015a).