No description available.

Abstract Spread spectrum technique modifies the signal spectrum to spread it out and increase its bandwidth. There are two major methods in spread spectrum technique: direct sequence and frequency hopping. The resistance capability of jamming signal for frequency hopping system is better than that for direct sequence system. Two types of frequency hopping techniques can be distinguished. In ¡§fast frequency hopping¡¨ the period of a frequency-hop is smaller than a data symbol-period while in ¡§slow frequency hopping¡¨ the period of a frequency-hop is larger than a data symbol-period. Fast frequency hopping systems have the advantages that the error correction codes are not needed and diversity can be applied. The disadvantage of fast frequency hopping system is that coherent data detection is not possible because of phase discontinuities. Traveling wave tube amplifier is often used in satellite communications. It has nonlinear characteristics which can be classified as nonlinear amplitude and phase distortions toward the output signals. Certain backoff input power makes the amplifier work within the linear region. However, in order to have more output power, the amplifier usually operates in the saturation region and in consequence serious nonlinear signal distortion would be introduced. In this thesis, the effect of nonlinear amplifier on a frequency hopping multiple access (FHMA) system with binary frequency shift keying is discussed. In the simulation, two types of nonlinear amplifiers, traveling wave tube amplifier and solid state power amplifier, are applied to the FHMA system. Tradeoff between power efficiency and performance degradation is determined by the index of total performance degradation, which is obtained from simulation. With known single carrier output power, third-order intermodulation, and same input power, the bit error rate performance is also analyzed.

In frequency-hopping (FH) system, the signal is not only impaired by receiver thermal noise, but also impaired by jamming, interference or multipath fading. Therefore, diversity techniques are used to reduce these impairments. Two systems are considered in this thesis, the first one is fast frequency-hopping/M-ary frequency-shift-keying (FFH/MFSK) System and the second one is fast frequency-hopping multiple access/M-ary frequency-shift-keying system (FFHMA/MFSK) System. In the first system, we consider three cases, multitone jamming (MTJ), broad-band noise jamming (BBN) and partial-band noise jamming (PBN).In the second system, we consider multiuser cases with multiple access interference, frequency-selective fading, and AWGN channels. In this thesis, two modified diversity combining methods are proposed. These methods are modified product and Order Statistics-Normalized Envelope Detection (OSNED) methods by adding the reliable order statistics. From simulation results, these methods can effectively combat multitone jamming and partial-band noise jamming. When comparing with product and OSNED in multiple access interference channel and frequency-selective fading channels, the proposed methods have better performance at high SNR. The proposed methods also do not need the additional side information as hard limiting majority vote (HLMV) and soft limiting combiner (SLC) needed.

Universiẗat, Diss., 2004--Bremen.

Indiana University-Purdue University Indianapolis (IUPUI) / Leg-Spring Stiffness (LSS) is the measure of the musculoskeletal, neuromuscular, and biomechanical functions of the human body, and an appropriate evaluation metric for changes brought on by Anterior Cruciate Ligament Reconstruction (ACLr). ACLr can lead to flexion and extension loss, resulting in increased stiffness of the musculotendinous units of the ACLr leg and thus changes in LSS. LSS can be measured using Kleg, but little is known about the validity and reliability of the different methods of LSS and Kleg calculations. The purpose of this study was to determine if ACLr leads to a change in LSS (as measured by Kleg) during hopping, and to compare results of the Spring-Mass calculation and knee Joint Torsional stiffness methods in the computation of the overall Kleg. Video data synchronize with GRF were used to compute the kinematic and kinetic variables. Mann-Whitney U tests were used to determine significant differences between the control and experimental group for the Spring-Mass method of calculation (p = 0.004), Joint Torsional method (p =0.44), Kknee (p = 0.29), and Kankle (p = 0.17). Cohen’s effect calculations showed small to medium effects for the KKnee, (d = 0.383) but moderate effect size for the KAnkle, (d = 0.541). Wilcoxon Signed Rank comparison for all the legs and (N=42) between computational methods were significant differences between computational methods (Z = 5.65, p = 0.000), and with a large effect size (Cohen’s d = 3.14). Similar results were found when comparing only the ACLr leg values (p = 0.005, Cohen’s d = 4.88). The comparison between ACL Leg vs Non-ACL leg for experimental group subjects was not significant in either calculation method (Spring-Mass p = 0.20, Z = -1.27; torque calculation p = 0.96, Z = -0.05). The spring-mass method was more stable and able to detect differences between the control and ACLr group. The lack of statistical differences in the joint torsion calculation method, as well as in comparing the unaffected leg to the ACLr leg in the experimental group, suggests that LSS may not be a precise enough measurement to determine the effects of an ACLr.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Sensor technology is continually advancing to meet demands of a wide range of potential applications. Many of these applications could be better served by distributed sensing than by traditional centralized sensing. To support these emerging applications, it is important to design and develop a unified framework for communication and network infrastructure capable of supporting various sensing functions. A research prototype operating in the 915 MHz Industrial, Scientific, and Medical band (ISM band) has been developed as potentially the core component of this infrastructure. In this paper, we will present the design and optimization of the system, data processing procedures, system parameters, network protocols, and experimental results.

No description available.

No description available.

Stuttgart, Univ., Diss., 2004.

No description available.