On the Combined Effect of Directional Antennas and Imperfect Spectrum Sensing upon Ergodic Capacity of Cognitive Radio Systems

We consider a cognitive radio system, consisting of a primary transmitter (PUtx), a primary receiver (PUrx), a secondary transmitter (SUtx), and a secondary receiver (SUrx). The secondary users (SUs) are equipped with steerable directional antennas. We assume the SUs and primary users (PUs) coexist and the SUtx knows the geometry of network. We find the ergodic capacity of the channel between SUtx and SUrx , and study how spectrum sensing errors affect the capacity. In our system, the SUtx first senses the spectrum and then transmits data at two power levels, according to the result of sensing. The optimal SUtx transmit power levels and the optimal directions of SUtx transmit antenna and SUrx receive antenna are obtained by maximizing the ergodic capacity, subject to average transmit power and average interference power constraints. To study the effect of fading channel, we considered three scenarios: 1) when SUtx knows fading channels between SUtx and PUrx, PUtx and SUrx, SUtx and SUrx, 2) when SUtx knows only the channel between SUtx and SUrx, and statistics of the other two channels, and, 3) when SUtx only knows the statistics of these three fading channels. For each scenario, we explore the optimal SUtx transmit power levels and the optimal directions of SUtx and SUrx antennas, such that the ergodic capacity is maximized, while the power constraints are satisfied

Analysis of Indicators of Health Status in Provinces and Ten Regions of Iran

Background: Health sector is one of the most important management sectors that improvement of its indicators, leads to increased wellbeing of people, costs reduction and ultimately sustainable development. The purpose of this study was to investigate health status indicators of Iran provinces and to rank the provinces and ten regions of Iran accordingly. Methods: The method of study was descriptive and analytical. The population of the study included 31 provinces and ten regions of Iran. In this study, 20 health indicators were selected. Entropy method was used for weighting. In order to rank provinces and regions of the country, TOPSIS was used and finally for mapping Arc GIS 10.1 was used. Results: According to the results, Gilan, Semnan and Yazd provinces gained respectively the first ranks and Sistan and Baluchestan, Kermanshah and Khuzestan provinces were respectively ranked as the last ones. In the ranking of regions, in terms of development, north coastal regions and central areas gained respectively the first and the second ranks and the southeastern region was in the last place. Conclusion: Most of the provinces were grouped as deprived and relatively deprived and in terms of health status indicators were in a state of instability. Political and administrative centralization are the main factors causing this situation. In order to improve the distribution of health sectors and to reduce losses resulting from deprivation, the large south-east region and the provinces of Sistan and Baluchestan, Khuzestan, Kermanshah, Kurdistan and West Azerbaijan should be considered in investment and planning priorities

EMBEDDING FINITE FIELDS INTO ELLIPTIC CURVES

Many elliptic curve cryptosystems require an encoding function from a finite field Fq into Fq-rational points of an elliptic curve. We propose a uniform encoding to general elliptic curves over Fq. We also discuss about an injective case of SWU encoing for hyperelliptic curves of genus 2. Moreover we discuss about an injective encoding for elliptic curves with a point of order two over a finite field and present a description for these elliptic curves

Beam Selection and Discrete Power Allocation in Opportunistic Cognitive Radio Systems with Limited Feedback Using ESPAR Antennas

We consider an opportunistic cognitive radio (CR) system consisting of a primary user (PU), secondary transmitter (SUtx), and secondary receiver (SUrx), where SUtx is equipped with an electrically steerable parasitic array radiator (ESPAR) antenna with the capability of choosing one beam among M beams for sensing and communication, and there is a limited feedback channel from SUrx to SUtx. Taking a holistic approach, we develop a framework for integrated sector-based spectrum sensing and sector-based data communication. Upon sensing the channel busy, SUtx determines the beam corresponding to PU's orientation. Upon sensing the channel idle, SUtx transmits data to SUrx, using the selected beam corresponding to the strongest channel between SUtx and SUrx. We formulate a constrained optimization problem, where SUtx-SUrx link ergodic capacity is maximized, subject to average transmit and interference power constraints, and the optimization variables are sensing duration, thresholds of channel quantizer at SUrx, and transmit power levels at SUtx. Since this problem is non-convex we develop a suboptimal computationally efficient iterative algorithm to find the solution. Our results demonstrate that our CR system yields a significantly higher capacity, and lower outage and symbol error probabilities, compared with a CR system that its SUtx has an omni-directional antenna.Comment: This paper has been submitted to IEEE Transactions on Cognitive Communications and Networkin