Fast radio wave propagation prediction is of tremendous interest for planning and optimization of cellular radio networks. We propose a cube oriented 3D ray launching algorithm for both fast and accurate field strength prediction, particularly suitable for urban scenarios. Our model allows field strength prediction for a 5 km 2 area with 5 meter resolution in about 8 sec with mean squared error of 7 dB. As urban environments cannot be completely described, we recommend a parameter calibration for different cities using measurement data from test runs.

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In this paper, discrete mathematical programming approaches are used to solve the frequency allocation and cell site selection problem in an integrated setup. Both CDMA (code division multiple access) and FD/TDMA (frequency/time division multiple access) technologies will be important for 3rd generation mobile systems. If all users share the same bandwidth, base transmitter stations should be placed such that a maximum of traffic can be carried at low interference rates. The expected traffic is represented by spatially scattered weighted nodes. The problem to select an optimal set of base station locations from a given pool of configurations is formulated as an integer linear program and solved by combinatorial optimization methods. For systems which employ FD/TDMA schemes, the cell site optimization process depends on the assignment of channels. We suggest an integrated linear programming approach to solve both objectives in a single planning step. Because of the problems' tremendous complexity, special branchand-bound procedures are developed as exact and approximate solution methods. An examples is given for a typical urban scenario with base transmitters below roof tops.

Abstract.The technique Private Information Retrieval (PIR) perfectly protects a user's access pattern to a database. An attacker cannot observe (or determine) which data element is requested by a user and so cannot deduce the interest of the user. We discuss the application of PIR on the World Wide Web and compare it to the MIX approach. We demonstrate particularly that in this context the method does not provide perfect security, and we give a mathematical model for the amount of information an attacker could obtain. We provide an extension of the method under which perfect security can still be achieved.

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