Energy and Spectral Efficient Wireless Communications

Energy and spectrum are two precious commodities for wireless communications. How to improve the energy and spectrum efficiency has become two critical issues for the designs of wireless communication systems. This dissertation is devoted to the development of energy and spectral efficient wireless communications. The developed techniques can be applied to a wide range of wireless communication systems, such as wireless sensor network (WSN) designed for structure health monitoring (SHM), medium access control (MAC) for multi-user systems, and cooperative spectrum sensing in cognitive radio systems. First, to improve the energy efficiency in SHM WSN, a new ultra low power (ULP) WSN is proposed to monitor the vibration properties of structures such as buildings, bridges, and the wings and bodies of aircrafts. The new scheme integrates energy harvesting, data sensing, and wireless communication into a unified process, and it achieves significant energy savings compared to existing WSNs. Second, a cross-layer collision tolerant (CT) MAC scheme is proposed to improve energy and spectral efficiency in a multi-user system with shared medium. When two users transmit simultaneously over a shared medium, a collision happens at the receiver. Conventional MAC schemes will discard the collided signals, which result in a waste of the precious energy and spectrum resources. In our proposed CT-MAC scheme, each user transmits multiple weighted replicas of a packet at randomly selected data slots in a frame, and the indices of the selected slots are transmitted in a special collision-free position slot at the beginning of each frame. Collisions of the data slots in the MAC layer are resolved by using multiuser detection (MUD) in the PHY layer. Compared to existing schemes, the proposed CT-MAC scheme can support more simultaneous users with a higher throughput. Third, a new cooperative spectrum sensing scheme is proposed to improve the energy and spectral efficiency of a cognitive radio network. A new Slepian-Wolf coded cooperation scheme is proposed for a cognitive radio network with two secondary users (SUs) performing cooperative spectrum sensing through a fusion center (FC). The proposed scheme can achieve significant performance gains compared to existing schemes

Clean relaying aided cognitive radio under the coexistence constraint

We consider the interference-mitigation based cognitive radio where the primary and secondary users can coexist at the same time and frequency bands, under the constraint that the rate of the primary user (PU) must remain the same with a single-user decoder. To meet such a coexistence constraint, the relaying from the secondary user (SU) can help the PU's transmission under the interference from the SU. However, the relayed signal in the known dirty paper coding (DPC) based scheme is interfered by the SU's signal, and is not "clean". In this paper, under the half-duplex constraints, we propose two new transmission schemes aided by the clean relaying from the SU's transmitter and receiver without interference from the SU. We name them as the clean transmitter relaying (CT) and clean transmitter-receiver relaying (CTR) aided cognitive radio, respectively. The rate and multiplexing gain performances of CT and CTR in fading channels with various availabilities of the channel state information at the transmitters (CSIT) are studied. Our CT generalizes the celebrated DPC based scheme proposed previously. With full CSIT, the multiplexing gain of the CTR is proved to be better (or no less) than that of the previous DPC based schemes. This is because the silent period for decoding the PU's messages for the DPC may not be necessary in the CTR. With only the statistics of CSIT, we further prove that the CTR outperforms the rate performance of the previous scheme in fast Rayleigh fading channels. The numerical examples also show that in a large class of channels, the proposed CT and CTR provide significant rate gains over the previous scheme with small complexity penalties.Comment: 30 page

IFPOC Symposium:Discovering antecedents and consequences of complex change recipients' reactions to organizational change.

IFPOC symposium: Discovering antecedents and consequences of complex change recipients' reactions to organizational change Chairs: Maria Vakola (Athens University of Economics and Business) & Karen Van Dam (Open University) Discussant: Mel Fugate (American University, Washington, D.C) State of the art Organisations are required to continuously change and develop but there is a high failure rate associated with change implementation success. In the past two decades, change researchers have started to investigate change recipients' reactions to change recognizing the crucial role of these reactions for successful change. This symposium aims at identifying and discussing the complex processes that underlie the relationships among antecedents, reactions and outcomes associated with organizational change. New perspective / contributions This symposium consists of five studies that extend our knowledge in the field by (i) providing an analysis of change recipients' reactions going beyond the dichotomous approaches (acceptance or resistance) (ii) revealing understudied antecedents-reactions and reactions-consequences patterns and relationships (iii) shedding light on the role of contextual factors i.e team climate and individual factors i.e emotion regulation on the adaptation to change. This symposium is based on a combination of both quantitative (i.e diary, survey) and qualitative (i.e interviews) research methodology. Research / practical implications This symposium aims to increase our understanding of the complex processes associated with change recipients' reactions to change. Discovering how these reactions are created and what are their results may reveal important contingencies that can explain how positive organizational outcomes during times of change can be stimulated which is beneficial for both researchers and practitioners

Qigong at Work: Where East Meets West

State of the Art Qigong is part of Traditional Chinese Medicine (TMC) and aims to balance body and mind. The roots of Qigong lie in China, where Confucian and Daoist scholars (500-400 B.C.) noted that one must learn to balance and relax one’s thoughts and emotions to avoid illness (Yang, 1997). In the Western world, Qigong is best known for its slow and coordinated movements. According to TCM, these movements will help regulate one’s ‘qi’, or life energy, through the body to improve the health and harmony of mind and body. During the practice of Qigong, one’s breathing, attention and movement are aligned. As such, Qigong is sometimes considered Mindfulness in movement (although there are many important differences). New perspectives / contributionsQigong has many positive outcomes on health and wellness. In both patient groups and healthy individuals, Qigong has been shown to improve psychological well-being, quality of life, immune function, balance and related risk-factors, and bone density (Jahnke et al., 2010). As such, Qigong offers a validated way to reduce the physical and mental activation that results from a person's work. While recent research has demonstrated how important it is to take short breaks at work, there is still little attention for Qigong exercises as a means to recover at work.Practical Implications In this presentation, we will explain and practice several Qigong exercises. These movements can be used at work (and at home) to recover from (hormonal) activation, ‘empty’ one’s head, and restore the body-mind balance. <br/