An Active Controller Selection Scheme for Minimizing Packet-In Processing Latency in SDN

In software-defined network, the use of distributed controllers to control forwarding devices has been proposed to solve the issues of scalability and load balance. However, the forwarding devices are statically assigned to the controllers in these distributed systems, which can overload some controllers while others are underutilized. In this paper, we propose an architecture named ASLB (active controller selection load balance), which proactively selects appropriate controllers for load balancing and minimize packet processing delays. We also present a novel active controller selection algorithm (ACS) for ASLB that efficiently schedules traffic from the switch to the controller and designs an intermediate coordinator for actively selecting a controller to serve a request. We built a system and evaluated it on a physical platform. The results show that ASLB is much better than the static allocation scheme in terms of minimizing latency, bandwidth utilization, and throughput.

Analysis and comparison of the two sectoring approaches in elevator traffic systems

Sectoring is a group control algorithm that is used in elevator traffic control systems by grouping passengers that have common destinations or common origins into elevator cars that serve these floors. The building is split into sectors usually comprising contiguous floors. Two different alternative algorithms for sectoring are discussed in this paper. The first approach is based on dynamic allocation with equal sector allocation. The second approach is based on static allocation with unequal sector sizes. Under static allocation, the same elevator car is allocated to the same sector in every round trip. Under dynamic allocation, each elevator car is allocated to a different sector in each round trip. Under the dynamic allocation scheme suggested in this paper, the elevator cars are sequenced to the various sectors in the buildings in a round-robin fashion. It is important to note that under both schemes, the provided (relative) handling capacity of different sectors is equalised. Five different buildings have been analysed using the two suggested sectoring algorithms. The building is first designed by finding the required number and speed of elevators assuming conventional control. Each building is then analysed using one of the two suggested sectoring algorithms. In order to compare the performance of the two sectoring algorithms, the provided (relative) handling capacity is calculated. The provided (relative) handling capacity of the two suggested algorithms is then compared. Very little difference was found between the two algorithms. The dynamic sectoring with equal sector sizes offers the convenience of having equal sector sizes. The static sectoring with unequal sector sizes is more convenient for passengers that are familiar with the building. Practical application: This paper analyses two different options for sectoring the control system of an elevator system in a building. Each of the two sectoring methods is suitable for different situations. The dynamic allocation method is more suitable for destination group control systems and offers the group controller more flexibility. The static allocation method with unequal sector sizes ensures that the passengers remain familiar with the elevators that they use to get to their floors. The programmer of the elevator group controller can programme both methods in the controller and allow it to switch to the most suitable algorithm depending on the prevailing conditions.

Sensing Techniques for Next Generation Cognitive Radio Networks

Cognitive radio is the technology used to solve the problem of spectrum underutilization by performing spectrum sensing, spectrum management, spectrum sharing, and spectrum mobility. The primary goal of cognitive radio is open spectrum sharing. Spectrum is a scarce and valuable natural resource that has to be used very effectively. The static allocation of spectrum to the licensed users will lead to wastage of resources when the spectrum is unused by the licensed user. Spectrum sensing methodology helps in detecting the spectrum holes and enables the unlicensed users to access the unused bands in the licensed spectrum effectively without interfering the licensed users. Cognitive thinking takes wireless communication to the next level by sensing the electromagnetic environment and dynamically adjusts its operating parameters in order to achieve maximum throughput, mitigate interference, facilitate interoperability, etc. The chapter presents the basics of cognitive radio networks, its architecture, its application, and advantages of cognitive radio networks.

WELFARE EFFECTS OF PATENT PROTECTION IN A SEMI-ENDOGENOUS GROWTH MODEL

This paper examines how strengthening patent protection affects welfare in a nonscale quality-ladder model, which was developed by Segerstrom [American Economic Review 88, 1290–1310] and generalized by Li [American Economic Review 93, 1009–1017]. In the Segerstrom–Li model, patent protection creates no distortion in static allocation among the production sectors. In order to examine the welfare effects of strengthening patent protection adequately, we incorporate a competitive outside good into the Segerstrom–Li model. In the general model, we derive the welfare-maximizing degree of patent protection analytically by utilizing a linear approximation of the transition path. The result shows that the welfare-maximizing degree of patent protection is weaker when the market share of the outside good is positive than when it is zero. In other words, disregarding the static distortion that patent protection creates leads to excessive patent protection.

Simple vs. Complex: Implications of Lags in Pollution Delivery for Efficient Load Allocation and Design of Water-quality Trading Programs

Water-quality markets that allow point-nonpoint trades assume that nonpoint best management practices (BMPs) achieve the targeted reductions as soon as they are implemented. However, changes in water quality in response to BMPs occur over time—from a few months to decades. We simulate emission allocations using static and dynamic-optimization models to determine whether a simple static allocation can produce results comparable economically and environmentally to complex multi-period designs for nitrogen emissions to Chesapeake Bay. We find that static rules provide relatively large cost savings compared to dynamic rules but result in a delay in achievement of water-quality targets.

Dynamic Thrust Allocation of Dynamic Positioning Vessel Based on Model Predictive Control

The dynamic positioning (DP) vessel maintains its position and heading by active thrusters. For safety reasons, DP vessels are typically designed with redundancy thrusters more than needed for motion control. Optimization theories are useful in finding thrust allocation solutions that minimize fuel consumption and reduce “wear and tear” on a thruster. But several challenges exist such as uncertain thruster model, thruster dynamics characters and the individual limitations of the thrusters. In this paper, a dynamic thrust allocation scheme is presented based on model predictive control (MPC) that directly takes thrusters with dynamics characters and various constraints into account. It is shown in simulations that the MPC dynamic thrust allocation scheme performs better in comparison with an existing static allocation method. Its main advantage is the ability to handle thruster dynamics characters and various constraints.