Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 6 Articles
Developing an effective cooperative spectrum sensing (CSS) scheme in cognitive radio (CR), which is considered as\r\npromising system for enhancing spectrum utilization, is necessary. In this paper, a cluster-based optimal selective CSS\r\nscheme is proposed for reducing reporting time and bandwidth while maintaining a certain level of sensing\r\nperformance. Clusters are organized based on the identification of primary signal signal-to-noise ratio value, and the\r\ncluster head in each cluster is dynamically chosen according to the sensing data qualities of CR users. The cluster\r\nsensing decision is made based on an optimal threshold for selective CSS which minimizes the probability of sensing\r\nerror. A parallel reporting mechanism based on frequency division is proposed to considerably reduce the time for\r\nreporting decision to fusion center of clusters. In the fusion center, the optimal Chair-Vashney rule is utilized to obtain\r\na high sensing performance based on the available cluster�s information....
Cooperative spectrum sensing in cognitive radio (CR) networks is studied in which each CR performs energy\r\ndetection to obtain a binary decision on the absence/presence of the primary user. The problem of interest is how to\r\nefficiently report and combine the local decisions to/at the fusion center under fading channels. In order to reduce\r\nthe required transmission bandwidth in the reporting phase, the paper examines nonorthogonal transmission of local\r\ndecisions by means of on-off keying. Proposed and analyzed is a novel decoding-based fusion rule that essentially\r\nperforms in three steps: (1) estimating minimum mean-square error of the transmitted information from cognitive\r\nradios, (2) making hard decisions of the transmitted bits based on the estimated information, and (3) combining the\r\nhard decisions in a linear manner. Simulation results support the theoretical analysis and show that the added\r\ncomplexity of the decoding-based fusion rule leads to a considerable performance gain over the simpler\r\nenergy-based fusion rule when the reporting links are reasonably strong....
In a data transmission system, the transmission medium is the physical path between transmitter and receiver. Recall from Chapter 3 that for guided media, electromagnetic waves are guided along a solid medium, such as copper twisted pair, copper coaxial cable, and optical fiber. For unguided media, wireless transmission occurs through the atmosphere, outer space, or water. The characteristics and quality of a data transmission are determined both by the characteristics of the medium and the characteristics of the signal. In the case of guided media, the medium itself is more important in determining the limitations of transmission. For unguided media, the bandwidth of the signal produced by the transmitting antenna is more important than the medium in determining transmission characteristics. One key property of signals transmitted by antenna is directionality. In general, signals at lower frequencies are omni directional; that is, the signal propagates in all directions from the antenna. At higher frequencies, it is possible to focus the signal into a directional beam. In considering the design of data transmission systems, key concerns are data rate and distance: the greater the data rate and distance the better....
In intelligent transportation systems, the cooperation between vehicles and the road side units is essential to bring\r\nthese systems to fruition. Vehicular ad hoc networks (VANETs) are a promising technology to enable the\r\ncommunications among vehicles on one hand and between vehicles and road side units on the other hand.\r\nHowever, it is a challenging task to develop a reliable routing algorithm for VANETs due to the high mobility and\r\nthe frequent changes of the network topology. Communication links are highly vulnerable to disconnection in\r\nVANETs; hence, the routing reliability of these ever-changing networks needs to be paid special attention. In this\r\npaper, we propose a new vehicular reliability model to facilitate the reliable routing in VANETs. The link reliability is\r\ndefined as the probability that a direct communication link between two vehicles will stay continuously available\r\nover a specified time period. Furthermore, the link reliability value is accurately calculated using the location,\r\ndirection and velocity information of vehicles along the road. We extend the well-known ad hoc on-demand\r\ndistance vector (AODV) routing protocol to propose our reliable routing protocol AODV-R. Simulation results\r\ndemonstrate that AODV-R outperforms significantly the AODV routing protocol in terms of better delivery ratio and\r\nless link failures while maintaining a reasonable routing control overhead....
In this paper, the challenging problem of joint channel estimation and data detection for multiple-input\r\nmultiple-output orthogonal frequency division multiplexing systems operating in time-frequency dispersive channels\r\nunder unknown background noise is investigated. Based on two different but equivalent signal models, two\r\nexpectation-maximization algorithm-based iterative schemes for joint data detection and channel and noise variance\r\nestimation are proposed. The first scheme jointly detects data and estimates the channel and noise variance, but the\r\ncomputational complexity is high, owing to the simultaneous detection and estimation for all antennas. To reduce\r\nthe computational complexity, a complexity-reduced scheme that is detecting data and estimating channel for only\r\none antenna during each iteration and holding the unknown quantities of other antennas to their last values is\r\nproposed, whose performance only slightly degrades compared to the first scheme. Moreover, both schemes are\r\nderived as closed-form expressions, and therefore, our proposed schemes are free of exhaustive search. Simulation\r\nresults demonstrate quick convergence of the proposed algorithm, and after convergence, the performance of the\r\nproposed algorithm is close to that of the optimal channel estimation and data detection case, which assumes full\r\ntraining and perfect channel state information....
Cooperative communication has been considered as a promising technique to improve communication quality of\r\nservice (QoS) in wireless networks, including mobile ad hoc networks (MANETs). Due to their unorganized and\r\ndecentralized infrastructure, cooperative MANETs (CO-MANETs) are vulnerable to attacks initiated on relays. Although\r\nencryption and authentication protocols may prevent compromised data transmission when a selected relay is\r\nattacked, their cost is high. In this paper, we propose a game-theoretic approach to quantitatively analyze the attack\r\nstrategies of the attacker so as to make a rational decision on relay selection and the authentication parameter\r\nadaptation to reach a trade-off between security and QoS in CO-MANETs. Simulation results show the effectiveness of\r\nthe proposed approach for security and QoS co-design in CO-MANETs....
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