Showing papers on "Spread spectrum published in 2006"

Auction-based spectrum sharing

Abstract: We study auction mechanisms for sharing spectrum among a group of users, subject to a constraint on the interference temperature at a measurement point. The users access the channel using spread spectrum signaling and so interfere with each other. Each user receives a utility that is a function of the received signal-to-interference plus noise ratio. We propose two auction mechanisms for allocating the received power. The first is an auction in which users are charged for received SINR, which, when combined with logarithmic utilities, leads to a weighted max-min fair SINR allocation. The second is an auction in which users are charged for power, which maximizes the total utility when the bandwidth is large enough and the receivers are co-located. Both auction mechanisms are shown to be socially optimal for a limiting "large system" with co-located receivers, where bandwidth, power and the number of users are increased in fixed proportion. We also formulate an iterative and distributed bid updating algorithm, and specify conditions under which this algorithm converges globally to the Nash equilibrium of the auction.

The Medium is the Message

Abstract: In this paper we advocate exploiting channel descriptor information in packet data communication networks to gain transmission capacity. Besides the normal data transmission also the channel descriptor (or character of the channel) can be used to convey data. This novel access technique is suitable for wired as well as for wireless networks. By the example of a wireless spread spectrum system with pseudo?noise spreading sequences, we can report that a gain of nearly an order of magnitude in terms of capacity can be achieved compared to the standard spread spectrum transmission for a given scenario. Our approach is not limited to spread spectrum technologies, but applies to all systems with the property that the number of channel descriptors is larger than the actual number of simultaneously usable resources.

Route and spectrum selection in dynamic spectrum networks

Abstract: Efficient spectrum allocation in dynamic spectrum systems is a challenging problem, particularly for multi-hops transmissions. The inter-dependence between route selection and spectrum management makes it important to examine interaction between the two and the corresponding performance and com- plexity tradeoffs. In this paper, we explore two design method- ologies: a decoupled design where these tasks are carried out independently by different protocol layers, and a collaborative design that integrates them into a single task. Experimental results show that the collaborative design, if well-provisioned, offers significant performance improvement compared to the decoupled design. I. INTRODUCTION

Low-complexity variable step-size mechanisms for stochastic gradient algorithms in minimum variance CDMA receivers

Abstract: In this paper, the performance of blind adaptive receivers for direct sequence code division multiple access (DS-CDMA) systems that employ stochastic gradient (SG) algorithms with variable step size mechanisms is investigated. Two low complexity variable step size mechanisms are proposed for estimating the parameters of linear CDMA receivers that operate with SG algorithms. For multipath channels the novel adaptation mechanisms are also incorporated in the channel estimation algorithms, whereas for the single-path case the novel techniques are restricted to the linear receiver parameter vector estimation. Analytical expressions for the excess mean squared error (MSE) are derived and a convergence analysis of the proposed adaptation techniques is carried out for both frequency selective and flat scenarios. Finally, numerical experiments are presented for nonstationary environments, showing that the new mechanisms achieve superior performance to previously reported methods at a reduced complexity

Spread spectrum applications of universal frequency translation

Abstract: Frequency translation and spread spectrum applications of same are described herein. Such applications include, but are not limited to, unified down-conversion and de-spreading, unified up-conversion and spreading, RAKE receivers utilizing unified down-conversion and de-spreading, and Early/Late receivers utilizing unified down-conversion and de-spreading, and combinations and applications of same. Additionally, applications are included for limiting spectral growth during unified up-conversion and spreading of a baseband signal.

Model development for the wideband expressway vehicle-to-vehicle 2.4 GHz channel

Abstract: Statistical channel models for small-scale fading are presented for a frequency selective vehicle-to-vehicle or mobile-to-mobile wireless communications link in an expressway environment in Atlanta, Georgia, where both vehicles travel in the same direction. These doubly selective models were developed from measurements taken using the direct sequence spread spectrum (DSSS) technique at 2.45 GHz. The models imply a non-separable channel with a persistent Ricean behavior across multiple model taps. We also explore model dynamics by comparing BER statistics for an overall model that is fit to the entire data set with those of a collection of models, each fit to smaller, non-overlapping intervals

Spectrum Sensingwith Forward Methods

Abstract: New technologies will require effective spectrum use. Opportunistic spectrum usage that is one application of so called cognitive radio techniques enables the use of unused frequencies. One possible way to locate these free frequency bands is to use so called spectrum sensing. In this paper, energy detection based spectrum sensing methods called the forward consecutive mean excision (FCME) and forward cell averaging (CA) methods are studied in the situations where the noise power is unknown. The detection and false alarm probabilities of the studied methods are also of interest. Numerical results show that the investigated approaches have good performance.

Bandwidth extension of narrowband speech

Abstract: A system extends the bandwidth of a narrowband speech signal into a wideband spectrum. The system includes a high-band generator that generates a high frequency spectrum based on a narrowband spectrum. A background noise generator generates a high frequency background noise spectrum based on a background noise within the narrowband spectrum. A summing circuit linked to the high-band generator and the background noise generator combines the high frequency spectrum and narrowband spectrum and the high frequency background noise spectrum.

Spread Spectrum Audio Steganography Using Sub-band Phase Shifting

Abstract: This paper presents an improvement of spread spectrum audio data hiding methods. We introduce phase shifting in audio signals to reduce the correlation with PN signal per each sub-band. It allows easy detection of the embedded data signal from audio when de-spreading the compound signal. The paper reports the subjective test results and the measurements of noise resiliency. The proposed method generates the quality degradation at the same level of NMR +3dB, but accests +6dB noise, therefore, the method has 3dB benefits.

Radar-Communication Integration Based on DSSS Techniques

Abstract: With the rapidly incremental demand in electronic devices, there is something in exploring multifunctional RF systems for reducing cost, minimizing the radar cross and probability of intercept, etc. This paper presents an integration system of radar and communication based on DSSS (direct sequence spread spectrum) technique, an attractive technique which is highly secure and robust. It utilizes different PN code to spread the spectrum of radar and communication data to avoid jamming mutually. Additionally, it uses BPM to gain better performance. The simulation over an ideal AWGN channel shows that the system can work perfectly

Digital Communications Using Chaos and Nonlinear Dynamics

Abstract: An Overview of Digital Communications Techniques Using Chaos and Nonlinear Dynamics.- Digital Communication Using Self-Synchronizing Chaotic Pulse Position Modulation.- Spread Spectrum Communication with Chaotic Frequency Modulation.- Ultra-Wideband Communications Using Pseudo-Chaotic Time Hopping.- Optimum Spreading Sequences for Asynchronous CDMA System Based on Nonlinear Dynamical and Ergodic Theories.- Nonlinear Phenomena in Turbo Decoding Algorithms.- Security of Chaos-Based Communication and Encryption.- Random Finite Approximations of Chaotic Maps.- Numerical Methods for the Analysis of Dynamics and Synchronization of Stochastic Nonlinear Systems.- Dynamics and Synchronization of Semiconductor Lasers for Chaotic Optical Communications.- Performance of Synchronized Chaotic Optical Communication Systems.

On the Limits of Communication Performance with One-Bit Analog-To-Digital Conversion

Abstract: As communication systems scale up in speed and bandwidth, the power consumption and cost of high-precision (e.g., 6-12 bits) analog-to-digital conversion (ADC) becomes the limiting factor in modern receiver architectures based on digital signal processing. In this paper, we consider the effects of lowering the precision of the ADC on the performance of the communication link. We focus on the most extreme scenario, in which the receiver employs one-bit ADC at baseband. While this constraint impacts every aspect of design ranging from synchronization and channel estimation to demodulation and decoding, in this initial exposition, we focus on the Shannon-theoretic limits imposed by one-bit ADC for an ideal discrete-time real baseband Additive White Gaussian Noise (AWGN) channel. Results are obtained both for non-spread and spread spectrum systems. While binary phase shift keying (BPSK) is optimal in a non-spread system, we obtain less predictable results for spread spectrum system, including the sub-optimality of BPSK and non-monotonicity of mutual information with signal-to-noise ratio for a fixed constellation.

Adaptive modulation in ad hoc DS/CDMA packet radio networks

Abstract: This paper investigates the benefit of adaptive modulation based on channel state information (CSI) in direct-sequence/ code-division multiple-access (DS/CDMA) multihop packet radio networks. By exploiting varying channel conditions, adaptive modulation can be used in ad hoc networks to provide upper layers with higher capacity links over which to relay traffic. Using the /spl alpha/-stable interference model, the distribution of the signal-to-interference ratio (SIR) is obtained for a slotted system of randomly, uniformly distributed nodes using multilevel coherent modulation schemes. Performance is evaluated in terms of the information efficiency, which is a new progress-related measure for multihop networks. Three types of adaptivity are analyzed, differing in the level of CSI available: 1) full knowledge of the SIR at the receiver; 2) knowledge of only the signal attenuation due to fading; and 3) knowledge of only the slow fading component of the signal attenuation. The effect of imperfect channel information is also investigated. Sample results are given for interference-limited networks experiencing fourth-power path loss with distance, Ricean fading, and lognormal shadowing.

Spread spectrum radar apparatus

Abstract: It is an object of the present invention to prevent the sensitivity of radar apparatus from falling. A spread spectrum radar apparatus which detects an object, includes a carrier wave oscillator which generates a carrier wave, transmission unit which transmits a spread signal which is the carrier wave spread using a first PN code, an intermediate demodulated signal generating unit which receives a reflected wave which is the spread signal reflected from the object, and despreads the reflected wave using a delayed second PN code that has a cyclically reversed logical value of the first PN code, to generate an intermediate demodulated signal, a low-pass filter through which a specific frequency component of the intermediate demodulated signal passes, and a sampling unit which samples an output signal from the low-pass filter, and the sampling unit samples the output signal in synchronization with the cycle of the reversal.

Ultrawide bandwidth signals as shot noise: a unifying approach

Abstract: We present a shot noise based model for a large family of ultrawide bandwidth (UWB) signals. These include time-hopping and direct-sequence signaling with pulse position, interval, and amplitude modulations. Each specific signal is constructed by adding features to a basic model in a modular, simple, and tractable way. Our work unifies the contributions scattered in the literature and provides a general approach that allows various extensions of previous works as well as new results. The exact power spectrum is then evaluated using shot noise spectral theory, which provides a simpler, systematic, and rigorous approach to the spectra evaluation of complicated UWB signals. The strength of our methodology is that different features of the signal model contribute clearly and separately to the resulting spectral expressions.

Adaptive spread-spectrum multicarrier multiple-access over wirelines

Abstract: In this paper, we investigate the dynamic resource allocation adapted to spread-spectrum multicarrier multiple-access (SS-MC-MA) systems in a multiuser power line communication (PLC) context. The developed adaptive system is valid for uplink, downlink, as well as for indoor and outdoor communications. The studied SS-MC-MA system is based on classical multicarrier modulation like digital multitone (DMT), combined with a spread-spectrum (SS) component used to multiplex several information symbols of a given user over the same subcarriers. The multiple-access task is carried out using a frequency-division multiple-access (FDMA) approach so that each user is assigned one or more subcarrier sets. The number of subcarriers in each set is given by the spreading code length as in classical SS-MC-MA systems usually studied in the wireless context. We derive herein a new loading algorithm that dynamically handles the system configuration in order to maximize the data throughput. The algorithm consists in an adaptive subcarrier, code, bit, and energy assignment algorithm. Power-spectral density constraint due to spectral mask specifications is considered, as well as finite-order modulations. In that case, it is shown that SS-MC-MA combined with the proposed loading algorithm achieves higher throughput than DMT in a multiuser PLC context. Because of the finite granularity of the modulations, some residual energy is indeed wasted on each subcarrier of the DMT spectrum. The combining of a spreading component with DMT allows to merge these amounts of energy so that one or more additional bits can be transmitted in each subcarrier subset leading to significant throughput gain. Simulations have been run over measured PLC channel responses and highlight that the proposed system is all the more interesting than the signal-to-noise ratio is low.

Interference mitigation study for UWB radio using template waveform processing

Abstract: Ultra-wideband (UWB) is an effective technique that enables coexistence with other radio systems using very short pulses and spread spectrum. However, there are potential interferences among those using the same frequency bands. This paper discusses the effects of interference between pulse-based UWB (p-UWB) and other systems: continuous wave, binary phase-shift keying signal, IEEE802.11a wireless LAN using a 5-GHz band, and multiband orthogonal frequency-division multiplexing (MB-OFDM). The MB-OFDM is inferentially proposed for personal area networks, as is p-UWB. The FCC has stated that both p-UWB and MB-OFDM systems will use the same band from 3.1 to 10.6 GHz. The bit-error-rate performance is shown assuming that p-UWB and the other systems are utilized at close range. To mitigate the effects of interference to p-UWB from other radio systems, a multicarrier template wave technique is proposed. The multicarrier template wave is approximated with an ordinary pulse waveform by Gabor transform formula and is composed of several subband pulses without interfering bands. The proposed UWB receiver for MB-OFDM interferences can detect their hopping pattern without a priori knowledge from the MB-OFDM transmitter. These techniques are shown to be effective for the systems to coexist.

Space–Time Coding for Multiuser Ultra-Wideband Communications

Abstract: In this paper, we present the construction of full rate, fully diverse, and totally real space-time (ST) codes for ultra-wideband (UWB) transmissions. In particular, we construct two families of codes adapted to real carrierless UWB communications that employ pulse position modulation, pulse amplitude modulation, or a combination of the two. The first family encodes adjacent symbols and is constructed from totally real cyclic division algebras. The second family encodes the pulses used to convey one information symbol, and permits achieving high performance levels with reduced complexity. The first family of codes achieves only a fraction of the coding gain of the second one. Moreover, these coding gains are independent from the size of the transmitted constellation. For time-hopping multiple-access channels, the amplitude spreading code associated with the second family of codes is taken to be user-specific. In this case, a simple design criterion is proposed, and spreading matrices constructed according to this criterion permit reducing the level of multiple-access interference (MAI). Simulations performed over realistic indoor UWB channels verify the theoretical claims and show high performance levels and better immunity against MAI

Integrated Radar and Communication Based on DS-UWB

Abstract: Tremendous efforts have been devoted to develop the UWB technology for radar and communication applications over the past decades With the rapidly incremental demand, there is something in exploring of integrated UWB radar and communication system for reducing cost, minimizing the radar cross and probability of intercept, etc This paper presents an integration system of radar and communication based on direct sequence UWB (DS-UWB) It utilizes different PN code to spread the spectrum of radar and communication data to avoid jamming mutually The simulation over an ideal AWGN channel shows that the system can work perfectly

Orthogonal frequency coding for SAW tagging and sensors

Abstract: Surface acoustic wave (SAW)-based sensors can offer wireless, passive operation in numerous environments, and various device embodiments are used for retrieval of the sensed data information. Single sensor systems typically can use a single carrier frequency and a simple device embodiment because tagging is riot required. In a multisensor environment, it is necessary to both identify the sensor and retrieve the sensed information. This paper presents the concept of orthogonal frequency coding (OFC) for implications to SAW sensor technology. The OFC offers all advantages inherent to spread spectrum communications, including enhanced processing gain and lower interrogation power spectral density (PSD). It is shown that the time ambiguity in the OFC compressed pulse is significantly reduced as compared with a single frequency tag having the same code length, and additional coding can be added using a pseudo-noise (PN) sequence. The OFC approach is general and should be applicable to many differing SAW sensors for temperature, pressure, liquid, gases, etc. Device embodiments are shown, and a potential transceiver is described. Measured device results are presented and compared with coupling of modes (COM) model predictions to demonstrate performance. Devices then are used in computer simulations of the proposed transceiver design, and the results of an OFC sensor system are discussed.

Average channel capacity for Rayleigh fading spread spectrum MIMO systems

Abstract: In this paper, a novel approach to the problem of estimating the average channel capacity (in the Shannon sense) assigned to each user of a spread spectrum (SS) multiple-input multiple-output (MIMO) system operating in a Rayleigh fading environment, is presented. The analysis leads to a closed-form expression which fully conforms to the upper bound of the channel capacity value of a non-fading AWGN channel when the transmitted signal bandwidth tends to infinity proving the validity of the described analysis. Copyright © 2006 John Wiley & Sons, Ltd.

Fingerprint multicast in secure video streaming

Abstract: Digital fingerprinting is an emerging technology to protect multimedia content from illegal redistribution, where each distributed copy is labeled with unique identification information. In video streaming, huge amount of data have to be transmitted to a large number of users under stringent latency constraints, so the bandwidth-efficient distribution of uniquely fingerprinted copies is crucial. This paper investigates the secure multicast of anticollusion fingerprinted video in streaming applications and analyzes their performance. We first propose a general fingerprint multicast scheme that can be used with most spread spectrum embedding-based multimedia fingerprinting systems. To further improve the bandwidth efficiency, we explore the special structure of the fingerprint design and propose a joint fingerprint design and distribution scheme. From our simulations, the two proposed schemes can reduce the bandwidth requirement by 48% to 87%, depending on the number of users, the characteristics of video sequences, and the network and computation constraints. We also show that under the constraint that all colluders have the same probability of detection, the embedded fingerprints in the two schemes have approximately the same collusion resistance. Finally, we propose a fingerprint drift compensation scheme to improve the quality of the reconstructed sequences at the decoder's side without introducing extra communication overhead.

Jammer suppression in DS-CDMA arrays using independent component analysis

Abstract: We propose using Independent Component Analysis (ICA) as an advanced pre-processing tool for blind suppression of interfering jammer signals in direct sequence spread spectrum communication systems utilizing antenna arrays. The role of ICA is to provide a jammer-mitigated signal to the conventional detection. If the jammer signal is weak or absent, preprocessing by ICA is not advisable. Therefore we also consider two possible switching schemes, called pre-switching and post-switching, which activate the ICA-based jammer canceller only when it is expected to improve conventional detection. ICA-RAKE pre-switching is less complex, while post-switching performs better, especially when the jammer is pulsed in nature. Simulations are given to illustrate the achieved performance gains for single- and multi-path channels.

Clock generating method and clock generating circuit

Abstract: In a clock generating circuit, while a PLL (Phase-Locked Loop) circuit and a modulator are employed, when a frequency dividing ratio of a feedback-purpose frequency divider in the PLL circuit is changed in accordance with modulation data produced based upon a modulation profile of the modulator to perform a frequency modulation so as to spread a spectrum, a turning point of the modulation profile is moved so as to disperse a degree of frequency, so that the spread spectrum is re-spread Also, a clock generating circuit is constituted by a PLL circuit and a modulator, a multiple modulation profile generating circuit is provided in the modulator, and a turning point of a modulation profile is moved so as to disperse a degree of frequency, so that a spread spectrum is re-spread

Land-based local ranging signal methods and systems

Abstract: To provide sub-meter accuracy in a local positioning system, ranging signals with a high modulation rate of code, such as 30 MHz, or more are transmitted. Code phase measurements may be used to obtain the accuracy without requiring relative motion or real time kinematic processing. The ISM or X-band is used for the carrier of the code to provide sufficient bandwidth within available spectrums. The length of codes used is less than or about a longest length across the region of operation, such as less than 15 kilometers in an open pit mine. The spread spectrum codes from different land-based transmitters are transmitted in time slots pursuant to a time division multiple access scheme for an increase in dynamic range. To avoid overlapping of code from different transmitters, each time slot includes or is separated by a blanking period. The blanking period is selected to allow the transmitted signal to traverse a region of operation. Differential measurements of signals received at a base station and a mobile receiver may improve accuracy.

Point-to-point underwater acoustic communications using spread-spectrum passive phase conjugation

Abstract: The ocean is often a complex multipath channel and progress has been made in developing equalization algorithms to overcome this. Unfortunately, many of these algorithms are computationally demanding and not as power-efficient as one would like; in many applications it may be better to trade bit rate for longer operational life. In 2000 the U.S. Navy was developing an underwater wireless acoustic network called Seaweb, for which a number of modulation schemes were being tested in a series of SignalEx experiments. This paper discusses two modulation schemes and associated receiver algorithms that were developed and tested for Seaweb applications. These receiver designs take advantage of time reversal (phase conjugation) and properties of spread spectrum sequences known as Gold sequences. Furthermore, they are much less complex than receivers using adaptive equalizers. This paper will present results of testing these signaling and receiver concepts during two experiments at sea.

High-Rate Direct-Sequence Spread Spectrum With Error-Control Coding

Abstract: High-rate direct-sequence spread spectrum is a modulation technique in which most or all of the spreading is provided by nonbinary data modulation. For applications to mobile ad hoc wireless networks, the limited processing gain of high-rate direct-sequence spread spectrum gives only modest protection against multiple access or multipath interference, which limits the applicability of the modulation technique to fairly benign channels. In this paper, we explore the increased interference-rejection capability that can be obtained from convolutional coding with Viterbi decoding, Reed-Solomon coding with errors-and-erasures decoding, and block product coding with iterative decoding. For channels with multiple access or multipath interference, performance results are given for several soft-decision decoding metrics, the benefits of adaptive-rate coding are illustrated, and the accuracy and utility of the Gaussian approximation are described. We also show how to use the bit-error probability for a system without error-control coding to determine which modulation method will give the best packet-error probability in a system with error-control coding

An Enhanced Multiplicative Spread Spectrum Watermarking Scheme

Abstract: Watermarks can be embedded into the host contents by multiplicative spread spectrum (MSS) methods. However, the interference from the host contents hinders the successful detection of the embedded watermark. This interference can be compensated at the embedder, or be exploited at the detector to improve the detection rate. In this paper, we first derive the optimum decision rule for watermarking in the discrete cosine transform domain, and then proceed to present an enhanced MSS scheme that compensates the host interference at the embedder. In our scheme, the host interference to be compensated is a generalized correlation tailored to the optimum decision rule. Its effectiveness is validated through both theoretical analyses and experiments

Adaptive multi-channel modem

Abstract: An adaptive multi-channel (AMC) modem that can receive one or multiple spread spectrum signals simultaneously includes an adjustable filter, a ΔΣ ADC, and a digital processor. The adjustable filter filters an input signal with an adjustable bandwidth and provides an output signal comprised of a selected number of spread spectrum signals. The ΔΣ ADC digitizes the output signal and provides data samples. The sampling rate and/or the reference voltage of the ΔΣ ADC may be varied to obtain the desired performance. The digital processor processes the data samples for each spread spectrum signal to recover data sent in that signal. A controller ascertains the operating conditions (e.g., the desired signal level, the undesired signal level, and so on) and selects the number of spread spectrum signals to receive based on the operating conditions, user requirements, and possibly other factors.