On the Throughput and Energy Efficiency of Cognitive MIMO Transmissions

In this paper, throughput and energy efficiency of cognitive multiple-input multiple-output (MIMO) systems operating under quality-of-service (QoS) constraints, interference limitations, and imperfect channel sensing, are studied. It is assumed that transmission power and covariance of the input signal vectors are varied depending on the sensed activities of primary users (PUs) in the system. Interference constraints are applied on the transmission power levels of cognitive radios (CRs) to provide protection for the PUs whose activities are modeled as a Markov chain. Considering the reliability of the transmissions and channel sensing results, a state-transition model is provided. Throughput is determined by formulating the effective capacity. First derivative of the effective capacity is derived in the low-power regime and the minimum bit energy requirements in the presence of QoS limitations and imperfect sensing results are identified. Minimum energy per bit is shown to be achieved by beamforming in the maximal-eigenvalue eigenspace of certain matrices related to the channel matrix. In a special case, wideband slope is determined for more refined analysis of energy efficiency. Numerical results are provided for the throughput for various levels of buffer constraints and different number of transmit and receive antennas. The impact of interference constraints and benefits of multiple-antenna transmissions are determined. It is shown that increasing the number of antennas when the interference power constraint is stringent is generally beneficial. On the other hand, it is shown that under relatively loose interference constraints, increasing the number of antennas beyond a certain level does not lead to much increase in the throughput

The coexistence of cognitive radio and radio astronomy

An increase of the efficiency of spectrum usage requires the development of new communication techniques. Cognitive radio may be one of those new technique, which uses unoccupied frequency bands for communications. This will lead to more power in the bands and therefore an increasing level of Radio Frequency Interference (RFI), which would cause loss of operation particularly for passive users of the spectrum, such as radio astronomy. This paper will address this issue and will present calculations indicating that the impact of cognitive radio on radio astronomy observations is considerable. The signal levels resulting from cognitive radio systems indicate that spectral bands used for cognitive radio applications cannot be used for radio astronomical research

The influence of a collaborative procurement approach using integrated design in construction on project team performance

Purpose – The purpose of the paper is to study the influence of procurement on the performance of integrated design teams. Design/methodology/approach – The research paradigm is based on Russian socio-constructivist approach to activity theory. Activity theory, as opposed to natural or social science, is a design science approach that focuses on the context aspect of project. A triangulation of qualitative research methods is used to investigate the dynamic of integrated teams in two different procurement contexts. Findings – The paper is conclusive regarding the influence of procurement on team efficiency. It demonstrates that traditional procurement processes reinforce socio-cognitive barriers that hinder team efficiency. It also illustrates how new procurement modes can transform the dynamic of relationships between the client and the members of the supply chain, and have a positive impact on teamperformance. Practical implications – The paper demonstrates first that problems with integrated design team efficiency are related to context and not process – they are not technical but socio-cognitive; second that fragmented transactional contracting increases socio-cognitive barriers that hinder integrated design team performance; third that new forms of relational contracting may help to mitigate socio-cognitive barriers and improve integrated design team performance, fourth that changing the context through procurement does not address the problem of obsolete design practices. Originality/value – The paper brings together theories of production in lean construction and social learning as a rival approach to traditional project management theory for demonstrating the importance of context on team performance

The role of cognitive abilities in laparoscopic simulator training

Learning minimally invasive surgery (MIS) differs substantially from learning open surgery and trainees differ in their ability to learn MIS. Previous studies mainly focused on the role of visuo-spatial ability (VSA) on the learning curve for MIS. In the current study, the relationship between spatial memory, perceptual speed, and general reasoning ability, in addition to VSA, and performance on a MIS simulator is examined. Fifty-three laparoscopic novices were tested for cognitive aptitude. Laparoscopic performance was assessed with the LapSim simulator (Surgical Science Ltd., Gothenburg, Sweden). Participants trained multiple sessions on the simulator until proficiency was reached. Participants showed significant improvement on the time to complete the task and efficiency of movement. Performance was related to different cognitive abilities, depending on the performance measure and type of cognitive ability. No relationship between cognitive aptitude and duration of training or steepness of the learning curve was found. Cognitive aptitude mediates certain aspects of performance during training on a laparoscopic simulator. Based on the current study, we conclude that cognitive aptitude tests cannot be used for resident selection but are potentially useful for developing individualized training programs. More research will be performed to examine how cognitive aptitude testing can be used to design training programs