Applying Analytical Hierarchy Process to a WiMAX Performance Evaluation Model

Evaluating performance of individual features of WiMAX technology is a topic of widespread discussion. Currently, there is no quantitative way of measuring WiMAX technology so that wireless operators can meet their design objectives. This paper outlines a set of design criteria for WiMAX and provides a decision-making aid that ranks the importance of criteria using Analytic Hierarchy Process （AHP）. This ranking should sufficiently reflect market expectations of the relative importance of various design criteria. A model integrating AHP priorities with enhanced Data Envelopment Analysis （DEA） is the basis for formulating a technological value in simple, comparable format. A case study is provided to show how this technological value is used to evaluate a three year network deployment plan. In the future, this model could be extended to WiMAX equipment suppliers for the purpose of validating performance targets of individual criteria, and enhancing supplier roadmaps for future network development.

Nonlinear dynamic analysis and fatigue damage assessment for a deepwater test string subjected to random loads

The deepwater test string is an important but vulnerable component in offshore petroleum exploration,and its durability significantly affects the success of deepwater test operations.Considering the influence of random waves and the interaction between the test string and the riser,a time-domain nonlinear dynamic model of a deepwater test string is developed.The stress-time history of the test string is obtained to study vibration mechanisms and fatigue development in the test string.Several recommendations for reducing damage are proposed.The results indicate that the amplitude of dynamic response when the string is subjected to random loads gradually decreases along the test string,and that the von Mises stress is higher in the string sections near the top of the test string and the flex joints.In addition,the fatigue damage fluctuates with the water depth,and the maximum damage occurs in string sections adjacent to the lower flex joint and in the splash zone.Several measures are proposed to improve the operational safety of deepwater test strings：applying greater top tension,operating in a favorable marine environment,managing the order of the test string joints,and performing nondestructive testing of components at vulnerable positions.

Investigation on performance of special-shaped 8-quadrature amplitude modulation constellations applied in visible light communication

Light-emitting diode(LED)-based visible light communication(VLC) has become a potential candidate for nextgeneration ultra-high-speed indoor wireless communication. In this paper, four special-shaped 8-quadrature amplitude modulation(QAM) constellations are investigated in a single-carrier VLC system. It is numerically verified and experimentally demonstrated that circular(7,1) shows obvious superiority in the performance of the dynamic range of signal voltage peak-to-peak(vpp) value and bit error rate(BER). Next best is rectangular, followed by triangular; circular(4,4) has the worst performance. A data rate of 1.515 Gbit/s is successfully achieved by circular(7,1) employing a red chip LED over 0.5 m indoor free space transmission below a BER threshold of3.8 × 10^(-3). Compared with circular(4,4), the traditional 8-QAM constellation, circular(7,1) provides a wider dynamic range of signal vpp, a higher data rate, and a longer transmission distance. To the best of our knowledge,this is the first investigation into the performance differences of special-shaped 8-QAM constellations in a highspeed, single-carrier VLC system, and the results comprehensively demonstrate that circular(7,1) is the optimal option.