With ever decreasing of feature sizes, the measurement of lens aberration has become increasingly important for the
imaging quality control of projection lithographic tools. In this paper, we propose a method for in-situ aberration
measurement based on a quadratic aberration model, which represents the bilinear relationship between the aerial image
intensity and the Zernike coefficients. The concept of cross triple correlation (CTC) is introduced, so that the quadratic
model can be calculated in a fast speed with the help of fast Fourier transform (FFT). We then develop a method for the
Zernike coefficients characterization using the genetic optimization algorithm from the through focus aerial images of a
nine contacts mask pattern. Simulation results demonstrate that this method is simple to implement and will have
potential applications for in-situ metrology of lens aberration in lithographic tools.
The quadratic aberration model used in optical lithography is a natural extension of the linear model by taking into
account interactions among individual Zernike coefficients. Although the model has been tested and verified in many
applications, the effects of Zernike coefficients under partially coherent imaging are usually obtained by extensive
experiments due to complexity of the model expression. In this paper, a generalized cross triple correlation (CTC) is
introduced, and a fast algorithm to simulate the quadratic aberration model is developed. Simulations were performed by
the proposed CTC based algorithm with different input Zernike aberrations for binary and phase shift masks with
multiple pitches and orientations, which demonstrate that the proposed approach is not only accurate but also efficient
for revealing the influence of different Zernike orders on aerial image intensity distributions under partially coherent
Ensuring minimum quality-of-service levels to traffic flows and groups of flows is an important challenge for future packet networks. Admission control is an important measure for QoS provision. However, the problem of multicast admission control was much less investigated. In this paper, a reservation-based edge multicast admission control scheme is investigated, which targets high QoS level and scalability. Using a new concept, virtual link, a virtual-link-oriented quota-based resource management mechanism is proposed. Besides, a hierarchical distributed bandwidth broker architecture is also employed. In this scheme, a central bandwidth broker manages the physical link bandwidth, and allocates/reclaims the bandwidth to virtual links; edge bandwidth brokers manage the bandwidth of virtual links, make admission decisions and reserve bandwidth for each flow. Simulation results show that the scheme achieves high scalability. Furthermore, the impact of quota size on the performance and complexity is investigated. A bandwidth adaptive quota size scheme is proposed to further improve the performance and reduce the complexity.
Class-based service differentiation is provided in DiffServ networks. However, this differentiation will be disordered under dynamic traffic loads due to the fixed weighted scheduling. An adaptive weighted scheduling scheme is proposed in this paper to achieve fair bandwidth allocation among different service classes. In this scheme, the number of active flows and the subscribed bandwidth are estimated based on the measurement of local queue metrics, then the scheduling weights of each service class are adjusted for the per-flow fairness of excess bandwidth allocation. This adaptive scheme can be combined with any weighted scheduling algorithm. Simulation results show that, comparing with fixed weighted scheduling, it effectively improve the fairness of excess bandwidth allocation.