Paul Cotae | University of the District of Columbia (original) (raw)

Papers by Paul Cotae

Energy efficiency is a measure of performance in wireless networks. Therefore, controlling the tr... more 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 [9], 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 in [3,4]. 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.

Aeu-international Journal of Electronics and Communications, Nov 1, 2006

We focus on the application of unit norm tight frames to design code division multiple (CDMA) sys... more We focus on the application of unit norm tight frames to design code division multiple (CDMA) systems spreading sequences with constant chip magnitude. An algorithm for the design of the overloaded real-valued signature sets with minimum total-squared-correlation equal to the Welch bound equality (WBE) set is presented. By using this algorithm we solved the open problem of existence of complex-valued

The paper is about the topology of a network. Find a center is always important in geometry. Ther... more The paper is about the topology of a network. Find a center is always important in geometry. There are different kinds of center but in general centers minimize or maximize a property of the geometrical figure. The ranking tool is just a way to figure out how far or close to a center is a particular node in the network. Node centrality is the crucial importance in different areas like transportation, wireless communication, Internet, virology and more. Each time when we have a network, knowing where are the centers locations in a network is the crucial importance to improve, optimize, protect or attack a network.

We characterize the Total Weighted Squared Correlation (TWSC) criterion used in uplink synchronou... more We characterize the Total Weighted Squared Correlation (TWSC) criterion used in uplink synchronous code division multiple access (S-CDMA) as a payoff function in the context of the game theoretical framework. By using the majorization theory we proved that the value of the game for two players is a saddle-point corresponding to the minimum of TWSC (Stackelberg equilibrium point). The optimal mixed strategies for transmitter and jammer are derived.

We characterize the Total Weighted Squared Correlation (TWSC) used in uplink synchronous code div... more We characterize the Total Weighted Squared Correlation (TWSC) used in uplink synchronous code division multiple access (S-CDhfA) as a payoff function in the context of the game theoreHc framework. We proved that the value of the game for two players is a saddle-point corresponding to the minimum of TWSC {I]. The optimal solution is the Stackelberg equilibrium and is achieved by players choosing generalized Welch Bound Equality (WBE) sequences as spreading signatures. We propose an algorithm of minimizing TWSC in the presence of multipath and cdlored noise when channel state information i s known perfectly at both transmitter and receiver. A comparison of our method in terms of BER (bit error rate) and water-filling procedure with the previous known methods is also given.

In this paper, we analyze the mutual information of sensor networks in an underwater wireless com... more In this paper, we analyze the mutual information of sensor networks in an underwater wireless communication system by placing the acoustic sensor nodes at different location in order to achieve optimum mutual information. The performances of acoustic sensors nodes are observed and analyzed by placing the sensors in collaborative and parallel channel network system. Different numerical calculation and experimental observation for both network systems such as information loss, bit error rate, mutual information, and channel capacity are considered.

In this paper we explore the possibility of sending a steganographically hidden message through a... more In this paper we explore the possibility of sending a steganographically hidden message through a digital communication channel. We view the hidden (em- bedded) information as additional noise added to a cover message, in conjunction with the inherent additive white Gaussian noise (AWGN). We use the bit error rate as a function of signal-to-noise ratio, and investigate whether the hidden message is truly steganographic in the sense that it cannot be distinguished from the usual noise in the channel. In addition we show that the hidden message is harder to detect when the information is encoded with an error- correcting code, and we present limits on the stegano- graphic payload.

A new algorithm for the design of overloaded real-valued signature sets with total-squared-correl... more 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.

Manufacturing Engineer, Apr 6, 2005

A definition of total weighted square correlation (TWSC) for an overloaded multicellular synchron... more A definition of total weighted square correlation (TWSC) for an overloaded multicellular synchronous DS-CDMA system in the presence of multipath on the uplink is introduced. We assume the channel state information is known perfectly both at transmitter and receiver. The optimum solutions for minimizing TWSC are the orthogonal generalized WBE (Welch bound equality) spreading sequences. The design of such sequences

We focus on the detection of Low Rate Denial of Service Attacks (LR DoS) based on their spectral ... more We focus on the detection of Low Rate Denial of Service Attacks (LR DoS) based on their spectral properties. We revised the Fisher g-statistic test and Siegel test for detection of LR DoS attacks such as Shrew and New Shrew attacks. Our results reveal that these attacks can be effectively identified by using Fisher g-statistic test for one dominant periodicity as in the case of Shrew attacks. When multiple (compound) dominant periodicities exist in the case of New Shrew attacks, Siegel test can identify the attack better than Fisher g-statistic test. Our contribution consists in developing a new methodology for rejecting the null hypothesis or identifying LR DoS attacks. Numerical examples for a confidence interval at significance level of α = 0.01 and α = 0.05 are given for Shrew and New Shrew attacks.

We characterize total weighted square correlation (TWSC) for a given signature set used in synchr... more We characterize total weighted square correlation (TWSC) for a given signature set used in synchronous code division multiple access (S-CDMA) systems. A new theorem for TWSC and a new algorithm for obtaining real sequences that meet Welch inequality with equality are presented. Using this algorithm optimal sequences, which achieve sum capacity for overload S-CDMA systems are obtained. Numerical examples for unitary power constraint case and for arbitrary (unequal) power sets are given.

We analyze the extended total weighted squared correlation (ETWSC) for a given signature sequence... more We analyze the extended total weighted squared correlation (ETWSC) for a given signature sequence set used in slow flat multipath channels and in the presence of colored noise. extended total square correlation (ETSC) and total squared correlation (TSC) are particular cases of ETWSC and are considered as well. The main results of this paper are: 1) the conditions on the channel such that the received multipath sequences are WBE (Welch bound Equality) sequences and 2) an iterative distributed method for obtaining real sequences that meet the Welch's lower bound on ETWSC. The method is based on majorization theory decreasing the weighted Frobenius norm associated with users' Sylvester channel matrices and noise covariance matrix. Numerical results for overloaded DS-CDMA systems are presented in order to support our analysis.

2022 IEEE 19th Annual Consumer Communications & Networking Conference (CCNC), Jan 8, 2022

We present a distributed algorithm for a multiagent system in a collaborative setting including t... more We present a distributed algorithm for a multiagent system in a collaborative setting including the cost of actions. We revise the distributed Max-Plus algorithm by presenting a new Cost Distributed Max-Plus (CD Max-Plus) algorithm by including the cost of actions in the interactions of agents, named Factored Value-MCTS-CD Max-Plus algorithm. The proposed Factored Value-MCTS-CD Max-Plus algorithm is online, anytime, distributed, and scalable in number of agents and their interactions. Our contribution is an alternative solution for solving cost Dec-POMDPs competing with the state of art methods and algorithms using MCTS and Max-Plus algorithms to exploit the locality of agent interactions for planning and acting.

15. NUMBER OF PAGES 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 5c. PROGRAM ELEMENT N... more 15. NUMBER OF PAGES 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 5c. PROGRAM ELEMENT NUMBER 5b. GRANT NUMBER 5a. CONTRACT NUMBER Form Approved OMB NO. 0704-0188 3. DATES COVERED (From-To)-Approved for public release; distribution is unlimited.

Distributed Denial of Service attacks are become one of the most serious security threats to our ... more Distributed Denial of Service attacks are become one of the most serious security threats to our society. In this paper, we presented Distributed Denial of Service (DDoS) attacks detection in low and slow rate attack scenarios. Attackers generate low rate packets and try congested the TCP. After a user enters in the retransmission timeout (RTO) phase, attackers synchronize with the RTO period and they over-control legitimate users. In this paper, we focus on attacks detection in frequency domain. We tested, analyzed, and simulated different types of flows in a computer network by using MATLAB and Fisher statistical methods for detection of DDoS attack components in multiple times series. This paper intends to present applications of theoretical lectures and lab sessions to solve real engineering problems. It is a groundbreaking work in applying Fisher methods to cybersecurity and gives a new perspective to use MATLAB and other software to preprocess and simulating our data.

Robustness and resilience are often thought of in terms of a system's capacity to maintain functi... more Robustness and resilience are often thought of in terms of a system's capacity to maintain functionality in the face of external perturbations. Robustness is one of the major issues for complex networks. The robustness of the network is evaluating if the network's normal functions are affected in case of an external perturbation. Improving the robustness of any network system requires analysis of its vulnerability to external perturbations 1. The outcome of the analysis would be the solution for random failures or adversarial attacks happening to an element of the network. The main focus of this paper is to study the evolution of evaluating the robustness of complex networks, specifically, the vulnerability of the clustering of the network to the failure of the network element. Our specific focus is to identify vertices whose failure will cause critically damage to the network by corrupting its clustering 3. Identifying the real problem is key to discovering the solution because any significant change made to the clustering, resulting from element-wise failures, could reduce network performance. By using the mathematical algorithms, we can formulate the vulnerability analysis as an optimization problem, prove its NP-completeness and non-monotonicity, and the algorithms that we formulate will identify the vertices most important to clustering.

Abstract : We investigated different methods for blind Doppler shift estimation and compensation ... more Abstract : We investigated different methods for blind Doppler shift estimation and compensation in underwater acoustic wireless sensor networks. Our study is based on the data collected from our underwater experiments. We analyzed the data collected by using non-data aided techniques such as Power Spectrum analysis, Autocorrelation, and Squaring Time Phase Recovery (Oerder & Meyr) to estimate Doppler shift in collaborative distributed underwater sensor networks. We also extensively investigated optimal sensor placement in a tree structured multi-hop hierarchical network. We focused on a symmetric tree like multi-hop hierarchical routing topology, which can potentially cover larger areas as we go deeper in the water than flat placement of underwater sensor networks. We used information theoretic tools such as entropy, conditional entropy, probability mass function etc. of input and output data signal to analyze the mutual information, information loss, bit error rate, and channel capacity. We focused on the optimizing mutual information between transmitted data and received data for a specific sensor network in underwater channel. Specifically, we used multiple sensor nodes in a relay network to transfer the data into long distance looking for maximum mutual information. In addition, we studied the relationship of channel capacity to transmitted power, bandwidth and carrier frequency.

In previous papers we solved the problem of the sensor location optimization based on the minimiz... more In previous papers we solved the problem of the sensor location optimization based on the minimization of interferences due to wireless communications between sensors. We assumed that each sensor has wireless communication capabilities, in that each sensor reading is characterized in terms of signal to noise ratio. In this paper we extend the previous work in the system of systems context by studying the robustness of the optimized sensor location in the presence of white additive Gaussian Noise (AWGN). We address the question on weather the optimized sensor locations remain the same if the initial reading sensors are only affected by additive white Gaussian noise (AWGN). The analysis results are verified trough computer simulations.

A comparison of the optimal power allocation for a Gaussian vector channel subject to sum power c... more A comparison of the optimal power allocation for a Gaussian vector channel subject to sum power constraint under water filling principle and inverse eigenvalue problem is given. We focus on the overloaded multipath DS - CDMA systems when the channel information is known at both transmitter and receiver. We generalize the sum of power constraint for each cell by considering

IEEE Transactions on Vehicular Technology, Jul 1, 2007

We generalize the total square correlation and the total weighted square correlation (TWSC) for a... more We generalize the total square correlation and the total weighted square correlation (TWSC) for a given signature set used in synchronous code division multiple access (S-CDMA) systems. We define the extended TWSC measure for multipath channels in the presence and the absence of the colored noise. The main results of this paper are the following: 1) the necessary and sufficient conditions of the received Gram matrix to maximize the sum capacity in the presence of multipath; 2) the conditions on the channel such that the received multipath sequences in the presence of the colored noise are Welch bound equality (WBE) sequences; 3) a decentralized method for obtaining generalized WBE sequences that minimize the TWSC in the presence of multipath and colored noise. Using this method, the optimal sequences, which achieve sum capacity for overloaded S-CDMA systems, in the presence of multipath are obtained. Numerical examples that illustrate the mathematical formalism are also included. Index Terms-Code division multiple access (CDMA) multipath, codeword optimization, interference avoidance, total squared correlation (TSC), total weighted squared correlation (TWSC), Welch bound equality (WBE) sequences. I. INTRODUCTION T HE MOBILE wireless environment provides several unique challenges to reliable communication. These include scarce bandwidth, limited transmit power, interference between users, and time varying conditions. A central problem in the design of the wireless network is how to use the limited resources most efficiently in order to meet some performance criteria like sum information capacity, user capacity, and the quality of service requirements of application [9]. Recently, there has been a considerable interest in exploring the fundamental limits of direct-sequence code division multiple access (DS-CDMA) systems and their dependence on the choice of the spreading sequences. The recent literature on designing codes for uplink overloaded CDMA systems can be divided into two general categories: those that assume random signature sequences and those that target the optimization

Energy efficiency is a measure of performance in wireless networks. Therefore, controlling the tr... more 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 [9], 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 in [3,4]. 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.

Aeu-international Journal of Electronics and Communications, Nov 1, 2006

We focus on the application of unit norm tight frames to design code division multiple (CDMA) sys... more We focus on the application of unit norm tight frames to design code division multiple (CDMA) systems spreading sequences with constant chip magnitude. An algorithm for the design of the overloaded real-valued signature sets with minimum total-squared-correlation equal to the Welch bound equality (WBE) set is presented. By using this algorithm we solved the open problem of existence of complex-valued

The paper is about the topology of a network. Find a center is always important in geometry. Ther... more The paper is about the topology of a network. Find a center is always important in geometry. There are different kinds of center but in general centers minimize or maximize a property of the geometrical figure. The ranking tool is just a way to figure out how far or close to a center is a particular node in the network. Node centrality is the crucial importance in different areas like transportation, wireless communication, Internet, virology and more. Each time when we have a network, knowing where are the centers locations in a network is the crucial importance to improve, optimize, protect or attack a network.

We characterize the Total Weighted Squared Correlation (TWSC) criterion used in uplink synchronou... more We characterize the Total Weighted Squared Correlation (TWSC) criterion used in uplink synchronous code division multiple access (S-CDMA) as a payoff function in the context of the game theoretical framework. By using the majorization theory we proved that the value of the game for two players is a saddle-point corresponding to the minimum of TWSC (Stackelberg equilibrium point). The optimal mixed strategies for transmitter and jammer are derived.

We characterize the Total Weighted Squared Correlation (TWSC) used in uplink synchronous code div... more We characterize the Total Weighted Squared Correlation (TWSC) used in uplink synchronous code division multiple access (S-CDhfA) as a payoff function in the context of the game theoreHc framework. We proved that the value of the game for two players is a saddle-point corresponding to the minimum of TWSC {I]. The optimal solution is the Stackelberg equilibrium and is achieved by players choosing generalized Welch Bound Equality (WBE) sequences as spreading signatures. We propose an algorithm of minimizing TWSC in the presence of multipath and cdlored noise when channel state information i s known perfectly at both transmitter and receiver. A comparison of our method in terms of BER (bit error rate) and water-filling procedure with the previous known methods is also given.

In this paper, we analyze the mutual information of sensor networks in an underwater wireless com... more In this paper, we analyze the mutual information of sensor networks in an underwater wireless communication system by placing the acoustic sensor nodes at different location in order to achieve optimum mutual information. The performances of acoustic sensors nodes are observed and analyzed by placing the sensors in collaborative and parallel channel network system. Different numerical calculation and experimental observation for both network systems such as information loss, bit error rate, mutual information, and channel capacity are considered.

In this paper we explore the possibility of sending a steganographically hidden message through a... more In this paper we explore the possibility of sending a steganographically hidden message through a digital communication channel. We view the hidden (em- bedded) information as additional noise added to a cover message, in conjunction with the inherent additive white Gaussian noise (AWGN). We use the bit error rate as a function of signal-to-noise ratio, and investigate whether the hidden message is truly steganographic in the sense that it cannot be distinguished from the usual noise in the channel. In addition we show that the hidden message is harder to detect when the information is encoded with an error- correcting code, and we present limits on the stegano- graphic payload.

A new algorithm for the design of overloaded real-valued signature sets with total-squared-correl... more 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.

Manufacturing Engineer, Apr 6, 2005

A definition of total weighted square correlation (TWSC) for an overloaded multicellular synchron... more A definition of total weighted square correlation (TWSC) for an overloaded multicellular synchronous DS-CDMA system in the presence of multipath on the uplink is introduced. We assume the channel state information is known perfectly both at transmitter and receiver. The optimum solutions for minimizing TWSC are the orthogonal generalized WBE (Welch bound equality) spreading sequences. The design of such sequences

We focus on the detection of Low Rate Denial of Service Attacks (LR DoS) based on their spectral ... more We focus on the detection of Low Rate Denial of Service Attacks (LR DoS) based on their spectral properties. We revised the Fisher g-statistic test and Siegel test for detection of LR DoS attacks such as Shrew and New Shrew attacks. Our results reveal that these attacks can be effectively identified by using Fisher g-statistic test for one dominant periodicity as in the case of Shrew attacks. When multiple (compound) dominant periodicities exist in the case of New Shrew attacks, Siegel test can identify the attack better than Fisher g-statistic test. Our contribution consists in developing a new methodology for rejecting the null hypothesis or identifying LR DoS attacks. Numerical examples for a confidence interval at significance level of α = 0.01 and α = 0.05 are given for Shrew and New Shrew attacks.

We characterize total weighted square correlation (TWSC) for a given signature set used in synchr... more We characterize total weighted square correlation (TWSC) for a given signature set used in synchronous code division multiple access (S-CDMA) systems. A new theorem for TWSC and a new algorithm for obtaining real sequences that meet Welch inequality with equality are presented. Using this algorithm optimal sequences, which achieve sum capacity for overload S-CDMA systems are obtained. Numerical examples for unitary power constraint case and for arbitrary (unequal) power sets are given.

We analyze the extended total weighted squared correlation (ETWSC) for a given signature sequence... more We analyze the extended total weighted squared correlation (ETWSC) for a given signature sequence set used in slow flat multipath channels and in the presence of colored noise. extended total square correlation (ETSC) and total squared correlation (TSC) are particular cases of ETWSC and are considered as well. The main results of this paper are: 1) the conditions on the channel such that the received multipath sequences are WBE (Welch bound Equality) sequences and 2) an iterative distributed method for obtaining real sequences that meet the Welch's lower bound on ETWSC. The method is based on majorization theory decreasing the weighted Frobenius norm associated with users' Sylvester channel matrices and noise covariance matrix. Numerical results for overloaded DS-CDMA systems are presented in order to support our analysis.

2022 IEEE 19th Annual Consumer Communications & Networking Conference (CCNC), Jan 8, 2022

We present a distributed algorithm for a multiagent system in a collaborative setting including t... more We present a distributed algorithm for a multiagent system in a collaborative setting including the cost of actions. We revise the distributed Max-Plus algorithm by presenting a new Cost Distributed Max-Plus (CD Max-Plus) algorithm by including the cost of actions in the interactions of agents, named Factored Value-MCTS-CD Max-Plus algorithm. The proposed Factored Value-MCTS-CD Max-Plus algorithm is online, anytime, distributed, and scalable in number of agents and their interactions. Our contribution is an alternative solution for solving cost Dec-POMDPs competing with the state of art methods and algorithms using MCTS and Max-Plus algorithms to exploit the locality of agent interactions for planning and acting.

15. NUMBER OF PAGES 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 5c. PROGRAM ELEMENT N... more 15. NUMBER OF PAGES 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 5c. PROGRAM ELEMENT NUMBER 5b. GRANT NUMBER 5a. CONTRACT NUMBER Form Approved OMB NO. 0704-0188 3. DATES COVERED (From-To)-Approved for public release; distribution is unlimited.

Distributed Denial of Service attacks are become one of the most serious security threats to our ... more Distributed Denial of Service attacks are become one of the most serious security threats to our society. In this paper, we presented Distributed Denial of Service (DDoS) attacks detection in low and slow rate attack scenarios. Attackers generate low rate packets and try congested the TCP. After a user enters in the retransmission timeout (RTO) phase, attackers synchronize with the RTO period and they over-control legitimate users. In this paper, we focus on attacks detection in frequency domain. We tested, analyzed, and simulated different types of flows in a computer network by using MATLAB and Fisher statistical methods for detection of DDoS attack components in multiple times series. This paper intends to present applications of theoretical lectures and lab sessions to solve real engineering problems. It is a groundbreaking work in applying Fisher methods to cybersecurity and gives a new perspective to use MATLAB and other software to preprocess and simulating our data.

Robustness and resilience are often thought of in terms of a system's capacity to maintain functi... more Robustness and resilience are often thought of in terms of a system's capacity to maintain functionality in the face of external perturbations. Robustness is one of the major issues for complex networks. The robustness of the network is evaluating if the network's normal functions are affected in case of an external perturbation. Improving the robustness of any network system requires analysis of its vulnerability to external perturbations 1. The outcome of the analysis would be the solution for random failures or adversarial attacks happening to an element of the network. The main focus of this paper is to study the evolution of evaluating the robustness of complex networks, specifically, the vulnerability of the clustering of the network to the failure of the network element. Our specific focus is to identify vertices whose failure will cause critically damage to the network by corrupting its clustering 3. Identifying the real problem is key to discovering the solution because any significant change made to the clustering, resulting from element-wise failures, could reduce network performance. By using the mathematical algorithms, we can formulate the vulnerability analysis as an optimization problem, prove its NP-completeness and non-monotonicity, and the algorithms that we formulate will identify the vertices most important to clustering.

Abstract : We investigated different methods for blind Doppler shift estimation and compensation ... more Abstract : We investigated different methods for blind Doppler shift estimation and compensation in underwater acoustic wireless sensor networks. Our study is based on the data collected from our underwater experiments. We analyzed the data collected by using non-data aided techniques such as Power Spectrum analysis, Autocorrelation, and Squaring Time Phase Recovery (Oerder & Meyr) to estimate Doppler shift in collaborative distributed underwater sensor networks. We also extensively investigated optimal sensor placement in a tree structured multi-hop hierarchical network. We focused on a symmetric tree like multi-hop hierarchical routing topology, which can potentially cover larger areas as we go deeper in the water than flat placement of underwater sensor networks. We used information theoretic tools such as entropy, conditional entropy, probability mass function etc. of input and output data signal to analyze the mutual information, information loss, bit error rate, and channel capacity. We focused on the optimizing mutual information between transmitted data and received data for a specific sensor network in underwater channel. Specifically, we used multiple sensor nodes in a relay network to transfer the data into long distance looking for maximum mutual information. In addition, we studied the relationship of channel capacity to transmitted power, bandwidth and carrier frequency.

In previous papers we solved the problem of the sensor location optimization based on the minimiz... more In previous papers we solved the problem of the sensor location optimization based on the minimization of interferences due to wireless communications between sensors. We assumed that each sensor has wireless communication capabilities, in that each sensor reading is characterized in terms of signal to noise ratio. In this paper we extend the previous work in the system of systems context by studying the robustness of the optimized sensor location in the presence of white additive Gaussian Noise (AWGN). We address the question on weather the optimized sensor locations remain the same if the initial reading sensors are only affected by additive white Gaussian noise (AWGN). The analysis results are verified trough computer simulations.

A comparison of the optimal power allocation for a Gaussian vector channel subject to sum power c... more A comparison of the optimal power allocation for a Gaussian vector channel subject to sum power constraint under water filling principle and inverse eigenvalue problem is given. We focus on the overloaded multipath DS - CDMA systems when the channel information is known at both transmitter and receiver. We generalize the sum of power constraint for each cell by considering

IEEE Transactions on Vehicular Technology, Jul 1, 2007

We generalize the total square correlation and the total weighted square correlation (TWSC) for a... more We generalize the total square correlation and the total weighted square correlation (TWSC) for a given signature set used in synchronous code division multiple access (S-CDMA) systems. We define the extended TWSC measure for multipath channels in the presence and the absence of the colored noise. The main results of this paper are the following: 1) the necessary and sufficient conditions of the received Gram matrix to maximize the sum capacity in the presence of multipath; 2) the conditions on the channel such that the received multipath sequences in the presence of the colored noise are Welch bound equality (WBE) sequences; 3) a decentralized method for obtaining generalized WBE sequences that minimize the TWSC in the presence of multipath and colored noise. Using this method, the optimal sequences, which achieve sum capacity for overloaded S-CDMA systems, in the presence of multipath are obtained. Numerical examples that illustrate the mathematical formalism are also included. Index Terms-Code division multiple access (CDMA) multipath, codeword optimization, interference avoidance, total squared correlation (TSC), total weighted squared correlation (TWSC), Welch bound equality (WBE) sequences. I. INTRODUCTION T HE MOBILE wireless environment provides several unique challenges to reliable communication. These include scarce bandwidth, limited transmit power, interference between users, and time varying conditions. A central problem in the design of the wireless network is how to use the limited resources most efficiently in order to meet some performance criteria like sum information capacity, user capacity, and the quality of service requirements of application [9]. Recently, there has been a considerable interest in exploring the fundamental limits of direct-sequence code division multiple access (DS-CDMA) systems and their dependence on the choice of the spreading sequences. The recent literature on designing codes for uplink overloaded CDMA systems can be divided into two general categories: those that assume random signature sequences and those that target the optimization