Fuzzy Based PC-PUSH in CR-MANETs

Hindawi Publishing Corporation Mathematical Problems in Engineering Volume 2014, Article ID 926709, 15 pages http://dx.doi.org/10.1155/2014/926709 Research Article Fuzzy Based PC-PUSH in CR-MANETs S. Nejatian,1,2 S. K. Syed Yusof,1 N. M. Abdul Lattif,1 V. Rezaie,3 and V. Asadpour4 1 UTM-MIMOS Center of Excellence, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia Department of Electrical Engineering, Faculty of Engineering, Islamic Azad University, Yasuj Branch, Yasuj, Kohgiluyeh and Boyer-Ahmad Province 7591483587, Iran 3 Department of Mathematics, Faculty of Science, Islamic Azad University, Yasuj Branch, Yasuj, Kohgiluyeh and Boyer-Ahmad Province 7591483587, Iran 4 Department of Electrical Engineering, University of North Dakota, Grand Forks, ND 58202, USA 2 Correspondence should be addressed to S. Nejatian; Received 29 August 2014; Accepted 22 October 2014; Published 26 November 2014 Academic Editor: Ezzat G. Bakhoum Copyright © 2014 S. Nejatian et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In cognitive radio (CR), the secondary user (SU) needs to hand off its ongoing communication to an idle channel in order to avoid interference to the primary user (PU). Spectrum hand off issue becomes challenging in CR mobile ad hoc networks (CR-MANETs) because of the uncertainty in spectrum availability, broad range of spectrum bands and lack of central entity. The purpose of this study is to design a unified spectrum handoff (USH) scheme for CR-MANETs that considers the spectrum heterogeneity and its availability over time and space. A local flow hand off is performed when spectrum hand off cannot be carried out due to the SUs mobility. To improve further USH, preemptive unified spectrum handoff (PUSH) algorithm is proposed in which two different preemptive hand off threshold regions are defined. The PUSH algorithm also predicts the cognitive link availability considering the PU interference boundary. Although the PUSH scheme improves the hand off performance, the number of spectrum hand offs due to the PU activity should be reduced in this scheme. Therefore, the PC-PUSH (Power Controller-PUSH) scheme is proposed in which the fuzzy logic is used to improve the PUSH in terms of the number of spectrum handoffs because of the PU activity. The PC-PUSH decreases the interference to the PUs, while reducing the number of spectrum handoffs. The results show that the proposed scheme improves the link maintenance probability, decreases the hand off delay, and reduces the number of spectrum handoffs. 1. Introduction Over the last few decades, the huge success of wireless applications has caused some spectrum bands being heavily used, especially unlicensed bands, such as ISM bands. This can be attributed to interference and poor network performance. On the other hand, recent studies by the Federal Communications Commission (FCC) have shown that a large amount of the licensed spectrum bands allocated through static assignment policies remains underutilized and inefficient. In fact, researchers have concluded that the traditional fixed spectrum allocation approach cannot continue to efficiently regulate the spectrum access. To address this situation, wireless devices operating in unlicensed bands can dynamically identify currently unused licensed spectrum bands for data communications and opportunistically access the unoccupied spectrum called spectrum holes or white spaces. Cognitive capability with the enabling technology of cognitive radio (CR) allows wireless devices to use the spectrum holes. CR has the capability of completely changing its transmitter parameters (operating spectrum, modulation, and transmission power) based on interactions with the surrounding spectral environment. CR users, called secondary users (SUs) or unlicensed user, sense a wide spectrum range, identify the spectrum holes, and opportunistically access them when primary (or licensed) users (PUs) are idle [1]. PUs have been licensed to use the spectrum band and SUs must access the spectrum in a nonintrusive manner [2]. The latest trend in CR research area has seen an extensive research interest in mobile ad hoc networks (MANETs) to improve the spectrum efficiency by novel design techniques 2 that simultaneously address the communication problems through various layers of the protocol stack. Enabling the CR technology in MANETs introduces the cognitive radio mobile ad hoc networks (CR-MANETs). The uncertainty in the availability of spectrum holes is caused by the random appearance of PUs as well as the unpredictability of the SUs demand. The spectrum holes may shift over time and over space. In a CR system, the shifting of spectrum holes can be defined as spectrum mobility, which is cohesive to spectrum handoff. Spectrum handoff refers to the transfer of an ongoing data transmission of a CR user to another available spectrum band. In heterogeneous CR networks, a channel may be available over vast, mutually exclusive spectrum bands that present remarkable heterogeneity in terms of channel transmission range [3]. Spectrum handoff is extremely challenging in CR networks, especially in CR-MANETs, because of frequent topologic variations, limited power, limited channel transmission range, bandwidth constraints, and lack of the central controlling entity [4]. On the other hand, the available spectrum bands vary over time and space, while they are distributed nonadjacently over a broad frequency range. In a CR-MANET system, SU mobility and channel heterogeneity lead to performance degradation and frequent spectrum handoff during communication. Hence, the fluctuation of PU activity and the SU mobility in CR-MANETs have made the issue of maintaining optimal routes more complex. Route failure has strong relationship with spectrum handoff. The route failure can be caused by spectrum mobility (PU activity), SU mobility, and channel heterogeneity. According to the failure type, different route recovery strategies need to be applied. Previous works on spectrum handoff in CRMANETs only consider the effect of PUs activity. Therefore, a unified spectrum handoff (USH) management for CRMANETs must be proposed that considers the effects of all of the factors mentioned above. In this work, a preemptive unified spectrum handoff (PUSH) method for CR-MANETs is proposed. PUSH considers the effects of mentioned factors on handoff initiation and management. In PUSH, two different preemptive handoff threshold regions were introduced and defined. A preemptive local flow handoff is performed when spectrum handoff cannot be carried out due to the SUs mobility. The PUSH algorithm also predicts the cognitive link availability and estimates the maximum link availability time considering the PU interference boundary. Alth (...truncated)