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Veciana, “Transmission capacity of CDMA ad hoc networks employing successive interference cancellation
 in Proc. IEEE Globecom
, 2004
"... Abstract — Spread spectrum technologies are appropriate for ad hoc networking because they permit interference averaging and tolerate colocated simultaneous transmissions. We develop analytic results on the transmission capacity of a CDMA ad hoc network. Transmission capacity is defined as the maxi ..."
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Abstract — Spread spectrum technologies are appropriate for ad hoc networking because they permit interference averaging and tolerate colocated simultaneous transmissions. We develop analytic results on the transmission capacity of a CDMA ad hoc network. Transmission capacity is defined as the maximum permissible density of simultaneous transmissions that allows a certain probability of successful reception. Three models of increasing generality are analyzed: a trivial model with two transmitters, a Poisson point process model where each node transmits with fixed power, and a Poisson point process model where nodes use variable transmission powers. We obtain upper and lower bounds on the transmission capacity for both frequency hopped (FHCDMA) and direct sequence (DSCDMA) implementations of CDMA for the latter two models. Our analysis shows that FHCDMA obtains a higher transmission capacity than DSCDMA on the order of M 1 − 2 α, where M is the spreading factor and α> 2 is the path loss exponent. The interpretation is that FHCDMA is generally preferable to DSCDMA for ad hoc networks, particulary when the path loss exponent is large. I.
Antijamming for embedded wireless networks
 IN PROCEEDINGS OF THE 2009 INTERNATIONAL CONFERENCE ON INFORMATION PROCESSING IN SENSOR NETWORKS
, 2009
"... Resilience to electromagnetic jamming and its avoidance are difficult problems. It is often both hard to distinguish malicious jamming from congestion in the broadcast regime and a challenge to conceal the activity patterns of the legitimate communication protocol from the jammer. In the context of ..."
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Resilience to electromagnetic jamming and its avoidance are difficult problems. It is often both hard to distinguish malicious jamming from congestion in the broadcast regime and a challenge to conceal the activity patterns of the legitimate communication protocol from the jammer. In the context of energyconstrained wireless sensor networks, nodes are scheduled to maximize the common sleep duration and coordinate communication to extend their battery life. This results in welldefined communication patterns with possibly predictable intervals of activity that are easily detected and jammed by a statistical jammer. We present an antijamming protocol for sensor networks which eliminates spatiotemporal patterns of communication while maintaining coordinated and contentionfree communication across the network. Our protocol, WisperNet, is timesynchronized and uses coordinated temporal randomization for slot schedules and slot durations at the link layer and adapts routes to avoid jammers in the network layer. Through analysis, simulation and experimentation we demonstrate that WisperNet reduces the efficiency of any statistical jammer to that of a random jammer, which has the lowest censorshiptolink utilization ratio. WisperNet has been implemented on the FireFly sensor network platform.
Optimized PRQMF Based Codes For Multiuser Communications
 SPIE Proceedings  Wavelet Applications
, 1995
"... In communications systems, the message signal is sometimes spread over a large bandwidth in order to realize performance gains in the presence of narrowband interference, multipath propagation, and multiuser interference. The extent to which performance is improved is highly dependent upon the sprea ..."
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In communications systems, the message signal is sometimes spread over a large bandwidth in order to realize performance gains in the presence of narrowband interference, multipath propagation, and multiuser interference. The extent to which performance is improved is highly dependent upon the spreading code implemented. Traditionally, the spreading codes have consisted of pseudonoise (PN) sequences whose chip values are limited to bipolar values. Recently, however, alternatives to the PN sequences have been studied including wavelet based and PRQMF based spreading codes. The spreading codes implemented are the basis functions of a particular wavelet transform or PRQMF bank. Since the choice of available basis functions is much larger than that of PN sequences, it is hoped that better performance can be achieved by choosing a basis tailored to the system requirements mentioned above. In this paper, a design method is presented to construct a PRQMF bank which will generate spreading...
A PrQmf (wavelet) Based Spread Spectrum Communications System
 In The Proceedings of the IEEE Conference on Military Communications
, 1994
"... A new spread spectrum technique is introduced whereby the spreading and despreading is achieved using PRQMF filter banks. The transmitted signal is generated using a synthesis filter bank while an analysis filter bank performs the demodulation process. This paper describes the implementation of thi ..."
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A new spread spectrum technique is introduced whereby the spreading and despreading is achieved using PRQMF filter banks. The transmitted signal is generated using a synthesis filter bank while an analysis filter bank performs the demodulation process. This paper describes the implementation of this technique, its use as a multiuser CDMA system, and its performance against narrowband interference. Monte Carlo simulation is used to determine bit error rate (BER) performance for AWGN, pulse interference, and narrowband (tone) interference. The AWGN BER is then compared to theoretical performance while the jammer suppression results are compared to standard spreading techniques. 1. INTRODUCTION In the past decade, the use of signal analysis and compression via subband decomposition has pervaded the fields of audio/image coding [1], feature detection and extraction [2], signal excision [3], and other areas. Much of this has been fueled by the recent popularity of the wavelet transform....
Orthogonal polynomials associated with root systems,Preprint(1988
 the IEEE Journal on Selected Areas in Communications
, 2006
"... Recent research in wireless CDMA systems has shown that adaptive rate/power control can considerably increase network throughput relative to systems that use only power or rate control. In this paper, we consider joint power/rate optimization in the context of orthogonal modulation (OM) and investig ..."
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Recent research in wireless CDMA systems has shown that adaptive rate/power control can considerably increase network throughput relative to systems that use only power or rate control. In this paper, we consider joint power/rate optimization in the context of orthogonal modulation (OM) and investigate the additional performance gains achieved through adaptation of the OM order. We show that such adaptation can significantly increase network throughput while simultaneously reducing the perbit energy consumption relative to fixedorder modulation systems. The optimization is carried out under two different objective functions: minimizing the maximum service time and maximizing the sum of user rates. For the first objective function, we prove that the optimization problem can be formulated as a generalized geometric program (GGP). We then show how this GGP can be transformed into a nonlinear convex program, which can be solved optimally and efficiently. For the second objective function, we obtain a lower bound on the performance gain of adaptive OM (AOM) over fixedmodulation systems. Numerical results indicate that relative to an optimal joint rate/power control fixedorder modulation scheme, the proposed AOM scheme achieves significant throughput and energy gains. I.
A Study on the Design of LargeScale Mobile Recording and Tracking Systems �
"... Mobile inventory control system involves large number of highly mobile and dispersed databases in the form of RFID �radio frequency ID � tag devices. Radio tags have limited communication range, bandwidth, computing power and storage. We examine some critical impact of these characteristics on desig ..."
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Mobile inventory control system involves large number of highly mobile and dispersed databases in the form of RFID �radio frequency ID � tag devices. Radio tags have limited communication range, bandwidth, computing power and storage. We examine some critical impact of these characteristics on design of facilities and techniques required for supporting integrated mobile distributed databases and computing environment. We analyze the performance of RF tags protocols and database mechanisms using processoriented discreteevent simulation tools. We present the results of experiments on three simulation models for RF tag protocols: slotted ALOHA�TDMA, Id arbitration and CDMA. The performance results shows that packet direct sequence �DS � CDMA gives superior performance compared to slotted ALOHA�TDMA and IDArbitration. The main performance result of experiments on mobile databases shows that optimistic concurrency control performs better for situations where tag transaction probability and write percentage is high. This scenario is found in many active intransit visibility recording and tracking systems. 1
On the Frequency Domain Approach for Spread Spectrum Receivers: Towards a Convergence
 of DSCDMA, MCCDMA and OFDM,” in IEEE SPAWC
, 2004
"... Abstract — The RAKE receiver is suboptimal when noise is non white, as in wideband CDMA systems. Frequency domain processing provides an efficient way to eliminate narrowband interference or exploit colored noise and it can significantly outperform the RAKE receiver. Additionally, other functions ca ..."
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Abstract — The RAKE receiver is suboptimal when noise is non white, as in wideband CDMA systems. Frequency domain processing provides an efficient way to eliminate narrowband interference or exploit colored noise and it can significantly outperform the RAKE receiver. Additionally, other functions can be carried out directly in frequency domain, such as despreading, synchronization that is crucial for performance and equalization, which can mitigate multiuser interference. In this paper we discuss the frequency domain processing for DSCDMA and potential gains are assessed by simulation results. An additional and important feature is that the frequency domain receiver for DSCDMA also provides a common platform for MCCDMA and OFDM, paving the way for an universal receiver. I.
Block QIM watermarking games
 IEEE Transactions on Information Forensics and Security
, 2006
"... While binning is a fundamental approach to blind data embedding and watermarking, an attacker may devise various strategies to reduce the effectiveness of practical binning schemes. The problem analyzed in this paper is design of worstcase noise distributions against Ldimensional lattice Quantizat ..."
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While binning is a fundamental approach to blind data embedding and watermarking, an attacker may devise various strategies to reduce the effectiveness of practical binning schemes. The problem analyzed in this paper is design of worstcase noise distributions against Ldimensional lattice Quantization Index Modulation (QIM) watermarking codes. The cost functions considered are (1) probability of error of the maximumlikelihood decoder, and (2) the more tractable Bhattacharyya upper bound on error probability, which is tight at low embedding rates. Both problems are addressed under the following constraints on the attacker’s strategy: the noise is independent of the marked signal, blockwise memoryless with block length L, and may not exceed a specified quadraticdistortion level. The embedder’s quadratic distortion is limited as well. Three strategies are considered for the embedder: optimization of the lattice inflation parameter (aka Costa parameter), dithering, and randomized lattice rotation. Critical in this analysis are the symmetry properties of QIM nested lattices and convexity properties of probability of error and related functionals of the noise distribution. We derive the minmax optimal embedding and attack strategies and obtain explicit solutions as well as numerical solutions for the worstcase noise. The role of the attacker’s memory is investigated; in particular, we demonstrate the remarkable effectiveness of impulsivenoise attacks as L increases. The formulation proposed in this paper is also used to evaluate the capacity of lattice QIM under worstnoise conditions.
THE SYMMETRIC RUDINSHAPIRO TRANSFORM AN EASY, STABLE, AND FAST CONSTRUCTION OF MULTIPLE ORTHOGONAL SPREAD SPECTRUM SIGNALS
"... A method for constructing spread spectrum sequences is presented. The method is based on a linear, orthogonal, symmetric transform, the RudinShapiro transform (RST), which is in many respects quite similar to the Haar wavelet packet transform. The RST provides the means for generating large sets of ..."
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A method for constructing spread spectrum sequences is presented. The method is based on a linear, orthogonal, symmetric transform, the RudinShapiro transform (RST), which is in many respects quite similar to the Haar wavelet packet transform. The RST provides the means for generating large sets of spread spectrum signals. This presentation provides a simple definition of the symmetric RST that leads to a fast N log(N) and numerically stable implementation of the transform. 1.
CDMA Ad Hoc Networks: Design and Performance Tradeoffs Committee:
"... My sincere thanks to my supervisor Professor Gustavo de Veciana for his tremendous efforts on my behalf over the five years that we have worked together. What I have learnt in these five years is not only how to do pure research, but also being a confident speaker, a rigorous researcher, a responsib ..."
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My sincere thanks to my supervisor Professor Gustavo de Veciana for his tremendous efforts on my behalf over the five years that we have worked together. What I have learnt in these five years is not only how to do pure research, but also being a confident speaker, a rigorous researcher, a responsible instructor, a good collaborator and much more. I would also thank Professors Andrews, Baldick, Shakkottai and Vin for participating my Ph.D. committee and providing me many valuable suggestions and directions on my research. I must particularly thank Professor Andrews and, my former colleague, Professor Weber for their collaboration and contributions to my work. I would not have been able to work on so many interesting problems without them. I also would like to thank my friends Jay, Xun, Jangwon, Seungjun, Alex, Shailesh and Balaji for making a friendly, open minded and creative research group to work in. I also want to thank my former supervising Professors Yujin Zhang, Qingmin Liao and Xinggang Lin, from whom I learnt elements of serious and rigorous research. My special thanks go to Mr. and Mrs. Chujo, Mr. Takeo, Chingfong, Hungying and Richard at Fujitsu Labs of America for their tutoring and collaboration when I was intern