Protocols for dynamic spectrum access in cognitive radio networks

Spectrum access protocols permit secondary users to transmit on frequency bands that are not being utilized by the primary owners. A cognitive radio that wishes to transmit in a band must first decide if the band is available (i.e., not being used by the owner) and then it must periodically re-evaluate the band\u27s availability once it begins transmitting in the band to ensure that a signal from a primary owner has not emerged. To accomplish these tasks, spectrum access protocols employ periodic sensing of the channel. Frequent sensing intervals are required to ensure that cognitive radios wishing to access the band are not disrupting transmissions by the owners of the band. Because spectrum sensing requires that radios cease transmission to observe the channel, the potential for throughput by the secondary users is reduced. A proposed enhancement to standard spectrum access protocols is presented that permits secondary users to monitor the frequency bands while communicating. This capability increases the amount of time that radios can transmit on the band and it decreases the amount of time required to detect the emergence of transmissions by a primary owner. Both improvements are obtained via a protocol that observes statistics obtained in the receiver of the cognitive radio during packet reception. The statistics are obtained with little or no additional hardware and do not require complicated channel measurements or pilot symbols. The proposed protocol for spectrum access is applicable to both single-link networks and multi-link cooperative networks

A cross-layer approach to increase spatial reuse and throughput for ad hoc networks

Ad hoc networks employing adaptive-transmission protocols can alter transmission parameters to suit the channel environment. Channel-access mechanisms are used to govern temporal use of the transmission medium amongst nodes. Effective operation of a channel-access mechanism can improve the ability of an adaptive-transmission protocol to accommodate changing channel conditions. The interoperability of these two mechanisms motivates cross-layer design of adaptive-transmission protocols. In this thesis we examine the integration of a new channel-access mechanism with a physical-layer adaptive-transmission protocol to create a cross-layer protocol with enhanced capabilities. We derive specific physical-layer measurements which are used to control channel-access behavior in a distributed manner. We propose a distributed heuristic using cross-layer information to drive a channel-access protocol which works in conjunction with an adaptive-transmission protocol. We show that the new protocol outperforms statically configured transmission protocols as well as protocols which act independently of cross-layer enhancements

Essential Personal Attributes, Skills and Abilities Needed by Aspiring Community College Presidents

The community college presidency is in critical state of evolution. Boggs (2003) stated that the rate of presidential retirements appears to be on the rise, with 79% of presidents planning to retire by 2012. Weisman and Vaughn (2007) in a 2006 survey found the number of presidents planning to retire within ten years is 84%. The most likely candidates to fill these presidential vacancies are the senior administrators. This presents a challenge because the senior administrators are at the same age as the retiring presidents and they too are preparing for retirement. The previous generations of community college presidents, the pioneers, laid a solid foundation. The yet undefined and new generation of presidents is responsible for assuming the mantle of leadership in the future. The purpose of this study was to explore essential attributes and abilities needed by future community college presidents as defined by current community college board members and presidents. To generate data, semi-structured interviews were used to investigate the respondent’s views regarding the needed personal attributes and skills of future presidents. Through a qualitative data analysis, the community college presidents and board of trustee members identified personal attributes, skills and abilities, other factors, presidential leadership potential and challenges for aspiring presidents. The primary recommendations stemming from this study include additional research to gain the perspectives of community college trustees in other states. The perspective of community college presidents in other states regarding the personal attributes, abilities, and professional experiences are vital for future community college presidents. Additionally, it is recommended to define the best practices for identifying and nurturing educational administrators who possess the personal attributes and skills to become future presidents; and best practices for those who possess the personal attributes and skills to become future presidents