Analytical Studies of Fragmented-Spectrum Multi-Level OFDM-CDMA Technique in Cognitive Radio Networks

In this paper, we present a multi-user resource allocation framework using fragmented-spectrum synchronous OFDM-CDMA modulation over a frequency-selective fading channel. In particular, given pre-existing communications in the spectrum where the system is operating, a channel sensing and estimation method is used to obtain information of subcarrier availability. Given this information, some real-valued multi-level orthogonal codes, which are orthogonal codes with values of $\{\pm1,\pm2,\pm3,\pm4, ... \}$, are provided for emerging new users, i.e., cognitive radio users. Additionally, we have obtained a closed form expression for bit error rate of cognitive radio receivers in terms of detection probability of primary users, CR users' sensing time and CR users' signal to noise ratio. Moreover, simulation results obtained in this paper indicate the precision with which the analytical results have been obtained in modeling the aforementioned system.Comment: 6 pages and 3 figure

Identifying the Most Appropriate Cultivar for Sustainability of Rice Production System Using Analytic Hierarchy Process (AHP)

In general, the ultimate goal of a sustainable system is to maximize the benefits of existing resources and to minimize the threats to the environment that occur due to the present conventional agricultural activities. Meanwhile, seed, as a rice cultivar in the present study, is presented as an important factor in sustainability. Therefore, identifying the most suitable cultivar of rice for sustaining the rice cultivation system is considered to be the main goal of the research. The population of the present study involves all specialists who have enough knowledge on components of sustainability and rice cultivars. To this end, 16 people were identified and studied through non-probability sampling method (purposeful and snowball). Face and content validity was used to determine the validity of the questionnaire. In addition, to assess the reliability, inconsistency ratio was used. Analytical Hierarchy Process (AHP) technique was used in order to achieve the main objective, which is to identify the most suitable varieties for sustainable rice cultivation system. Expert Choice 2000 software was applied to calculate the data.The prerequisite of applying AHP technique is to consider the criteria (sustainability of rice cultivation system) which include: economical, ecological, technical, social, and policy sustainability and their sub-criteria in the one hand, and decision alternatives (rice cultivars) including: Hashemi, Tarom, Neda, Fajr, Khazar and Shirudi in the other hand. The results of prioritizing the criteria of rice cultivation stability showed that the economical (32%), ecological (23.9%) and technical (21.1%) stability are more important than the stability of social (14.8%) and policy (8.3%) aspects. Likewise, research findings showed that the cultivars of Hashemi (20.6%) and Tarom (20.1%) with a slight difference against each other are the most proper cultivars, respectively, in the sustainability of rice cultivation system