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Spherical Co-doped SiO2/Cu-grafted TiO2 hybrid particles were prepared using organic spherical monolith particles as a template. Rutile was crystallized in the monolith particles impregnated with a TiO2 precursor solution by hydrothermal treatment in a strong acid condition (2M HCl). Subsequent UV illumination assisted efficient decomposition of organic compounds in the particles during firing. The...
Cognitive radio (CR) is viewed as a possible solution to the problem of radio spectrum congestion. CR is the promising radio technology which aims to detect and utilize the temporally unused spectrum bands by sensing its radio environment in order to improve spectrum utilization. To enhance the sensing performance, cooperative spectrum sensing has been proposed. However, when the number of cognitive...
Cognitive radio has been considered as an efficient approach to opportunistic spectrum sharing between primary users and cognitive radio users. The most important challenge of a cognitive radio system is to identify the primary users over a wide rage of the spectrum. Considering that the existing sensing techniques would be time-consuming and wasteful of power, Holland etc. give the concept of Resource...
Recently, multi-hop networks have obtained a growing interest in the applications in which the network needs to be deployed rapidly. In order to achieve high capacity packet transmission in wireless multi-hop networks, many medium access control (MAC) schemes have been proposed to maximize the system throughput. Besides, energy efficiency is a critical issue since the battery power of the mobile terminals...
Radio spectrum is one of the most scarce and valuable resources for wireless communications. Cognitive radio has been considered as an efficient means to opportunistic spectrum sharing between primary (licensed) users and cognitive radio users. In this paper, based on the two-phase channel and power allocation scheme proposed by A. T. Hoang etc., we present an opportunistic spectrum access approach...
In ad hoc networks, the throughput of the network and energy efficiency depends largely upon the performance of the medium access control (MAC) algorithm. Especially, energy efficiency is an important issue since the battery power of the mobile terminals is limited. In this paper, we propose a new scheduling MAC scheme. In the scheme, the TDMA frame consists of N time slots, and each node is assigned...
Recently, the technology of cognitive radio (CR) has captured the attention of many researchers in that it promises an effective way of enhancing spectrum usage and solving the problem of heterogeneity of radio devices. For the CR network, a fundamental issue is how to identify the spectrum opportunities. To improve the sensing performance, cooperative spectrum sensing has been proposed. With the...
The scarcity of spectrum has become a major bottleneck of the development of next generation radio systems. Cognitive radio (CR) is a promising solution to improve the utilization of the radio spectrum. That is, spectrum efficiency can be increased significantly by giving opportunistic access of the frequency bands to a group of cognitive users to whom the band has not been licensed. In this paper,...
Multicarrier code-division multiple-access (MC-CDMA) is one of the effective techniques to gain its multiple access capability, robustness against fading, and to mitigate the ISI. The paper proposes a dynamic subchannel and power allocation algorithm for MC-CDMA system. In the proposed scheme, data is transmitted over the user's best subcarrier and power control is applied for the selected subcarrier,...
In the paper, the bit error rate (BER) performance for mobile ad hoc networks is evaluated based on the scheme proposed. In G. Ferrari et al.) (2003) proposes a new TDMA MAC transmission scheme and analyzes the BER performance and connectivity characteristics of multi-hop ad hoc networks. However, G. Ferrari's analysis is under the ideal assumption of no inter-node interference (INI). In fact, timing...
Multicarrier code-division multiple-access (MC-CDMA) is one of the effective techniques to gain its multiple access capability, robustness against fading, and to mitigate the ISI. The conventional MC CDMA system is to transmit identical narrowband direct-sequence (DS) waveform in parallel over a number of subchannels uniformly. While in this paper, allowing for different quality-of-service (QoS) requirements...
In ad hoc networks, the hidden and exposed terminal problems can severely reduce the system throughput in MAC layer. To address these problems, a channel access method exploiting joint detection of overlapping packets is proposed by Kota in P. Kota and C. Schlegel, (2003). In this paper, we propose an improvement on the method, which uses CSMA/CD medium access protocol for the RTS/CTS control packets...
The paper discusses the significance and development foreground of integration between wireless local area network (WLAN) and B3G mobile cellular network in composite radio context. The concept of composite reconfigurable wireless network is introduced in the paper, and the development of future wireless communication systems is also discussed. The basic configuration framework of network interoperation...
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