Replicated Server Placement with QoS Constraints

The network planning problem of placing replicated servers with QoS constraints is considered. Each server site may consist of multiple server types with varying capacities and each site can be placed in any location among those belonging to a given set. Each client can be served by more than one location as long as the round-trip delay of data requests satisfies predetermined upper bounds. Our main focus is to minimize the cost of using the servers and utilizing the link bandwidth, while serving requests according to their delay constraint. This is an NP-hard problem. A pseudopolynomial and a polynomial algorithm that provide guaranteed approximation factors with respect to the optimal for the problem at hand are presented.     

On the base stations antenna system design for mobile communications

The design of a base station antenna for mobile communications is presented. The orthogonal method (OM) is applied under constraints on nulls of the radiation pattern. In the synthesis process the mutual coupling between the elements of the antenna array could be taken into account. Beam tilting and direction of arrival are also considered. The whole design is completed by implementing a special architecture of the antenna. Finally, some examples show the applicability of our technique.     

On the beam tilting and bit rate selection in mobile systems

Beam tilting of a mobile Base Station (BS), as a technique that limits the transmitted signals to each cell, introduces a way of increasing the system bit rate over a wider range than that without beam tilting. In this paper, the general approach of a BS antenna is being evaluated giving the system's response for different half power beamwidths (HPBW) and different types of propagation environments. The critical rate of the system versus the level of diffuse reflection, the communication distance, the excess distance and the height of the BS antenna are being examined.     

On the design of switched-beam wideband base stations

A switch beam base-station antenna is presented. The antenna is an improvement on the Butler matrix. The input ports of the antenna are excited with equal or unequal amplitudes. The feed network is analyzed and presented in a simple manner. The antenna comprises the main part of a base station, and is useful for broadband communications. The architecture of the base station is described, and the services that can be provided are given. Finally, comments are made about the tradeoffs and benefits of the antenna in comparison to the classical Butler-matrix switched-beam and adaptive arrays.     

Algorithms for precomputing constrained widest paths and multicast trees

We consider the problem of precomputing constrained widest paths and multicast trees in a communication network. Precomputing and storing of the relevant information minimizes the computational overhead required to determine an optimal path when a new connection request arrives. We evaluate algorithms that precompute paths with maximal bandwidth (widest paths), which in addition satisfy given end-to-end delay constraints. We analyze and compare both the worst case and average case performance of the algorithms. We also show how the precomputed paths can be used to provide computationally efficient solutions to the constrained widest multicast tree problem. In this problem, a multicast tree with maximal bandwidth (widest multicast tree) is sought, which in addition satisfies given end-to-end delay constraints for each path on the tree from the source to a multicast destination.     

On mobile communications smart base-station system design

A design technique for mobile base-station antennas is presented. Beam tilting to avoid intersymbol interference is considered, and the orthogonal method (OM) under constraints on the radiation pattern is applied. The adaptive architecture of the mobile system, in conjunction with the direction of arrival (DoA) and the least mean square algorithms, is explained. A set of useful examples shows the applicability of the whole design.