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ABSTRACT: We give a model for the performance impact on wireless systems of the limitations of certain resources, namely, the base-station power amplifier and the available OVSF codes. These limitations are readily modeled in the loss model formulation as a stochastic knapsack. A simple and well-known recurrence of Kaufman and Roberts allows the predictions of the model to be efficiently calculated. We discuss the assumptions and approximations we have made that allow the use of the model. We have included the model in Ocelot, an Alcatel-Lucent tool for modeling and optimizing cellular phone systems. The model is fast to compute, differentiable with respect to the relevant parameters, and able to model broad ranges of capacity and resource use. These conditions are critical to our application of optimization.
Vehicular Technology Conference, 2007. VTC-2007 Fall. 2007 IEEE 66th; 11/2007
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ABSTRACT: We investigate models for uplink interference in wireless systems. Our models account for the effects of outage probabilities. Such an accounting requires a nonlinear, even nonconvex model, since increasing interference at the receiving base station increases both mobile transmit power and outage probability, and this results in a complex interaction. Our system model always has at least one solution, a fixed point, and it is provably unique under certain reasonable conditions. Our main purpose is to model real wireless systems as accurately as possible, and so we test our models on realistic scenarios using data from a sophisticated simulator. Our algorithm for finding a fixed point works very well on such scenarios, and is guaranteed to find the fixed point when we can prove it is unique. A slightly simplified model reduces the main data structure for a K -sector market to 16 K <sup>2</sup> bytes of memory.
Vehicular Technology Conference, 2007. VTC-2007 Fall. 2007 IEEE 66th; 11/2007
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ABSTRACT: We introduce a simple model of the effect of temporal variation in signal strength on active-set membership, for cellular phone systems that use the soft-handoff algorithm of IS-95a. This model is based on a steady-state calculation, and its applicability is confirmed by computational studies.
Vehicular Technology Conference, 2004. VTC 2004-Spring. 2004 IEEE 59th; 06/2004
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ABSTRACT: For 3G cellular networks, capacity is an important objective, along with coverage, when characterizing the performance of high-data-rate services. In live networks, the effective network capacity heavily depends on the degree that the traffic load is balanced over all cells, so changing traffic patterns demand dynamic network reconfiguration to maintain good performance. Using a four-cell sample network, and antenna tilt, cell power level and pilot fraction as adjustment variables, we study the competitive character of network coverage and capacity in such a network optimization process, and how it compares to the CDMA-intrinsic coverage-capacity tradeoff driven by interference. We find that each set of variables provides its distinct coverage-capacity tradeoff behavior with widely varying and application-dependent performance gains. The study shows that the impact of dynamic load balancing highly depends on the choice of the tuning variable as well as the particular tradeoff range of operation.
Vehicular Technology Conference, 2003. VTC 2003-Fall. 2003 IEEE 58th; 11/2003
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ABSTRACT: We present an algorithm based on lattice reduction for the fast
decoding of diagonal differential modulation across multiple antenna.
While the complexity of the maximum-likelihood (ML) algorithm is
exponential both in the number of antenna and the rate, the complexity
of our approximate lattice algorithm is polynomial in the number of
antennas and the rate. We show that the error performance of our lattice
algorithm is very close to the ML algorithm
IEEE Transactions on Communications 03/2001; · 1.68 Impact Factor
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ABSTRACT: We give a practical and provably good Monte Carlo algorithm for approximating center points. Let P be a set of n points in IR d . A point c 2 IR d is a fi-center point of P if every closed halfspace containing c contains at least fin points of P . Every point set has a 1=(d + 1)-center point; our algorithm finds an OmegaGamma/ =d 2 )-center point with high probability. Our algorithm has a small constant factor and is the first approximate center point algorithm whose complexity is subexponential in d. Moreover, it can be optimally parallelized to require O(log 2 d log log n) time. Our algorithm has been used in mesh partitioning methods and can be used in constructing high breakdown estimators for multivariate datasets in statistics. It has the potential to improve results in practice for constructing weak ffl-nets. We derive a variant of our algorithm whose time bound is fully polynomial in d and linear in n, and show how to combine our approach with previous techniques to ...
03/1995;
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K.L. Clarkson
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ABSTRACT: A simple idea for speeding up the computation of extrema of a
partially ordered set turns out to have a number of interesting
applications in geometric algorithms; the resulting algorithms generally
replace an appearance of the input size n in the running time by an
output size A⩽n. In particular, the A coordinate-wise minima of a
set of n points in R<sup>d</sup> can be found by an algorithm needing
O(nA) time. Given n points uniformly distributed in the unit square, the
algorithm needs n+O(n<sup>5/8</sup>) point comparisons on average. Given
a set of n points in R<sup>d</sup>, another algorithm can find its A
extreme points in O(nA) time. Thinning for nearest-neighbor
classification can be done in time O(n log n)Σ<sub>i</sub> A<sub>i
</sub>n<sub>i</sub>, finding the A<sub>i</sub> irredundant points among
n<sub>i</sub> points for each class i, where n=Σ<sub>i</sub>
n<sub>i</sub> is the total number of input points. This sharpens a more
obvious O(n<sup>3</sup>) algorithm, which is also given here. Another
algorithm is given that needs O(n) space to compute the convex hull of n
points in O(nA) time. Finally, a new randomized algorithm finds the
convex hull of n points in O(n log A) expected time, under the condition
that a random subset of the points of size r has expected hull
complexity O(r). All but the last of these algorithms has polynomial
dependence on the dimension d, except possibly for linear programming
Foundations of Computer Science, 1994 Proceedings., 35th Annual Symposium on; 12/1994
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K.L. Clarkson
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ABSTRACT: The problem of evaluating the sign of the determinant of a small matrix aries in many geometric algorithms. Given an n×n matrix A with integer entries, whose columns are all smaller than M in Euclidean norm, the algorithm given evaluates the sign of the determinant det A exactly. The algorithm requires an arithmetic precision of less than 1.5n+2lgM bits. The number of arithmetic operations needed is O(n<sup>3 </sup>)+O(n<sup>2</sup>) log OD(A)/β, where OD(A)|det A| is the product of the lengths of the columns of A, and β is the number of `extra' bits of precision, min{lg(1/u)-1.1n-2lgn-2,lgN-lgM-1.5n-1}, where u is the roundoff error in approximate arithmetic, and N is the largest representable integer. Since OD(A)⩽M<sup>n</sup>, the algorithm requires O(n<sup>3</sup>lgM) time, and O(n<sup>3</sup>) time when β=Ω(logM)
Foundations of Computer Science, 1992. Proceedings., 33rd Annual Symposium on; 11/1992
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K.L. Clarkson
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ABSTRACT: An algorithm for solving linear programming problems is given. The
expected number of arithmetic operations required by the algorithm is
given. The expectation is with respect to the random choices made by the
algorithm, and the bound holds for any given input. The technique can be
extended to other convex programming problems
Foundations of Computer Science, 1988., 29th Annual Symposium on; 11/1988
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ABSTRACT: The authors study both the incidence counting and the many-faces problem for various kinds of curves, including lines, pseudolines, unit circles, general circles, and pseudocircles. They also extend the analysis to three dimensions, where they concentrate on the case of spheres, which is relevant for the three-dimensional unit-distance problem. They obtain upper bounds for certain quantities. The authors believe that the techniques they use are of independent interest
Foundations of Computer Science, 1988., 29th Annual Symposium on; 11/1988
