Paul Cotae

Optimization of Sensor Locations and Sensitivity Analysis for Engine Health Monitoring Using Minimum Interference Algorithms

The global optimization of sensor locations and a sensitivity analysis based on the minimization of interferences due to wireless communications between sensors are studied in the presence of additive white Gaussian noise (AWGN). We used a Gram matrix approach for robust determination of sensor locations by minimizing the interferences (maximizing the signal strength) among sensors for engine health monitoring systems. In order to solve the problem of optimum placement, an iterative algorithm for maximizing the determinant of the Gram matrix is proposed and implemented. The sensitivity criterion proposed in this paper is the spectral number of the Frobenius norm of the Gram matrix associated with sensor readings. We derived the necessary conditions under which the number of sensors and the optimal sensor locations will remain unchanged when the data measured for sensitivity analysis is affected by AWGN. Our theoretical results are verified by simulations providing details concerning numerical implementations.

An Algorithm for Obtaining Welch Bound Equality Sequences for S-CDMA Channels

Summary In this paper we describe the properties of those sequences(matrix) that meet equality in the Welchs lower bound on total squared correlation. These sequences are called also Welch Bound Equality (WBE) sequences. The generalized WBE sequences (matrix) are defined. Same definitions on majorization are introduced in order to characterize the eigenvalues of a hermitian matrix. A new algorithm for generating WBE spreading sequence multisets is proposed. We apply the proposed algorithm when all users have different average-channel-input energy constraint in the case of synchronous CDMA channels. We obtain real optimum signature sequences that maximize the sum capacity of S-CDMA channels.

Transmitter adaptation algorithm for multicellular synchronous DS-CDMA systems with multipath

A procedure for the design of complex sequence/signature sets for a multicell system under synchronous multipath transmission is presented. The optimization criterion is the total weighted square correlation (TWSC) that incorporates transmission power and channel impulse response values. By solving an inverse eigenvalue problem related to block structured matrices, the bandwidth of initial generalized Welch bound equality signals is preserved in the extended signal space associated to multiple cell system. Numerical results for overloaded uplink multicellular direct-sequence code-division multiple-access (DS-CDMA) systems are presented in order to support our analysis.

Spreading sequence design for multiple-cell synchronous DS-CDMA systems under total weighted squared correlation criterion

An algorithm for designing spreading sequences for an overloaded multicellular synchronous DS-CDMA system on uplink is introduced. The criterion used to measure the optimality of the design is the total weighted square correlation (TWSC) assuming the channel state information known perfectly at both transmitter and receiver. By using this algorithm it is possible to obtain orthogonal generalized WBE sequences sets for any processing gain. The bandwidth of initial generalized WBE signals of each cell is preserved in the extended signal space associated to multicellular system. Mathematical formalism is illustrated by selected numerical examples.

Cognitive Radio: Time Domain Spectrum Allocation using Game Theory

The currently available unlicensed spectrum is reaching its limit and various demands for applications and data rates in wireless communications requires additional spectrum which imposes limits on spectrum access. These requirements demand for efficient and intelligent use of spectrum. The system model and the problem of the optimum spectrum allocation in cognitive radios are introduced and formulated in this paper. We derived a lower limit of the demanded allocations for all the users in the system and obtain the optimal solution which attains this lower bound. An algorithm which finds these optimum values of the demanded allocations is introduced to find the optimum spectrum allocation in time domain. The convergence of this algorithm is shown using the eigen values of the Gram matrices. Simulations are provided to support the mathematical formalism and the convergence of the algorithm to optimal solution.

Efficient power control for broadcast in wireless communication systems

Energy efficiency is a measure of performance in wireless networks. Therefore, controlling the transmitter power at a given node increases not only the operating life of the battery but also the overall system capacity by successfully admitting new nodes between a source and a destination. It is essential to find effective means of power control of point-to-point, broadcasting and multicasting scenarios. In past work A. T. Chronopoulos et al. (2002), we presented a new scheme state space-based control design (SSCD) using both the state space and optimal control methodology in discrete-time for power control in wireless systems. Further, we proved the convergence of the overall network with our algorithm using Lyapunov stability analysis. We made a comparison with a well known distributed power control (DPC) scheme. Here we present simulation results and comparisons for point-to-point communication with random node placement. We also combined the schemes SSCD and DPC with a tree based broadcast algorithm BIP to obtain broadcast tree in ad-hoc networks with power control. We show the effectiveness of the new algorithm through simulations.

Editorial: distributed signal processing techniques for wireless sensor networks

1Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843, USA 2Department of Electrical and Computer Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA 3Department of Electrical and Computer Engineering, Iowa State University, Ames, IA 50011, USA 4Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695, USA 5Department of Electrical and Computer Engineering, University of Texas at San Antonio, San Antonio, TX 78249, USA

Construction of complex-valued simplex signature sets with constant chip magnitude

A new algorithm for the design of overloaded real-valued signature sets with total-squared-correlation equal to Welch bound equality (WBE) set is presented. It is proved that if K=N+1 the normalized cross correlation between any pair of signatures in a set obtained by the proposed algorithm is either -1/(K-1) or +1/(K-1) and the entire cross correlation matrix G is obtained analytically. Using this algorithm we solved the open problem of existence of complex valued WBE sequence sets with constant chip magnitude in the simplex case. The results are derived in the context of synchronous code division multiple access (CDMA) channels and a numerical example for K=3 and N=2 is given.

Complex spreading sequence design for S-CDMA systems under total weighted squared correlation criterion

An algorithm for the design of the overloaded complex spreading sequence sets on the uplink of multicellular synchronous CDMA systems is introduced. Assuming that in each cell the number of users K is greater than the corresponding processing gain N, the total weighted squared correlation criterion is used as a performance measure. The mathematical formalism is supported with selected numerical examples in the multicellular context.

An Iterative Power Allocation Scheme for Spread Spectrum Wireless Systems

This paper formulates a new optimization problem for direct-sequence spread spectrum systems by considering the joint transmitted power and link quality in a functional form. Link quality is measured in terms of signal interference to noise ratio including the cross correlations and multipath effect. By solving this optimization problem a new distributed power control scheme is proposed which guarantees a global optimum in all practical cases. The implementation of the proposed procedure can be simply performed locally and the scheme fits well into low-power radios