published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / This paper analyzes the probability of bit error for PCM-FM over a standard IRIG channel subject to multipath interference modeled by the aeronautical fading channel. The aeronautical channel model assumes a mobile transmitter and a stationary receiver and specifies the correlation of the fading component. This model describes fading which is typical of that encountered at military test ranges. An expression for the bit error rate on the fading channel with a delay line demodulator is derived and compared with the error rate for the Gaussian channel. The increase in bit error rate over that of the Gaussian channel is determined along with the power penalty caused by the fading. In addition, the effects of several channel parameters on the probability of bit error are determined.

With the fast development of today’s multimedia services, engineers face a huge hurdle that is, the overwhelming need of highly reliable communication over long distances. Cooperative communication is a novel concept which tackles this problem effectively. The direct link is assisted by nodes called relays, which also reduce shadowing and pathloss effects in wireless networks. An added advantage of such a cooperative communication network is that when combined with multiple-input multiple-output (MIMO) antenna systems and cognitive radio networks (CRN), the system performance in terms of spectral efficiency and reliability, can be extremely enhanced without any extra power and spectrum.The concept of cooperative communications in MIMO and CRN systems has gained immense interest in the literature. Most of the research works have assumed Rayleigh fading conditions. In this thesis, the performance of cooperative communications with practical constraints of shadowing is studied. Analytical expressions for the outage probability of cooperative networks under different relaying protocols with selection combining are presented under the assumption of κ − µ shadowing fading. Specifically, the relaying protocols that are investigated are incremental relaying, opportunistic relaying, adaptive amplify-and-forward and decode-and-forward. Furthermore, this system model is simulated and the simulation results are compared with the analytical results. Mathematica, a technical computing tool, is used for numerical estimations using stochastic processes and probability theory. Simulation is done in MATLAB.In this thesis, along with the analytical framework for evaluating outage probability for the system is presented. Simulations are performed for various fading parameters and the results closely match with analytical results which validate the derivations.

Sucrose fading and intermittent access are two common procedures that induce alcohol consumption in rodents. Sucrose fading procedures involve exposing ethanol naïve rats to a mixture of ethanol and sucrose and gradually reducing the concentration of sugar. Intermittent access procedures involve providing rats with access to ethanol on alternating days. Given that rats will consume ethanol without sucrose, the role of sugar in the sucrose fading procedure is unclear. Rats must be ethanol naïve when they are exposed to treatment with sucrose fading, so there is no point of comparison to show that exposure to sugar in sucrose fading produces higher levels of drinking. There has yet to be any work that isolates the effects of sugar on the consumption of alcohol. The purpose of the present experiment was to examine the effects of sucrose on ethanol consumption in rats with different alcohol histories. Two groups of six rats were exposed to two successive sucrose fading procedures, 30 days apart and their drinking was measured 30 days after each one. One group was exposed to an intermittent access procedure to establish drinking prior to treatment with sucrose fading, the other was ethanol naïve. Following sucrose fading, all rats drank pharmacologically active doses of ethanol. For both groups consumption correlated with the concentration of sucrose and decreased in a step-wise manner as it was faded. For the ethanol experienced rats, consumption dropped below baseline levels as sucrose was faded and decreased further with the second exposure. In contrast, the ethanol-naïve rats did not decrease consumption from the first sucrose fading procedure to the second. Slight differences in peak force of responses were also observed.

The present study was designed to analyze the transfer of stimulus control in temporal fading procedures. Several aspects of temporal fading procedures were manipulated including sources of inhibitory stimulus control, delays of reinforcement, and rates of increase in the temporal parameter of a fading procedure. In Experiment I, previous research producing transfer of stimulus control in a temporal fading procedure was directly replicated and controls were implemented for the operation of inhibition. The results showed that inhibitory stimulus control is not necessary in order to produce a transfer as participants with neutral stimulus backgrounds also transferred from one dimension to another without errors. However, positive stimulus backgrounds in the fading procedure prohibited the participants from achieving an errorless transfer of discrimination learning. In Experiment II, a fixed trial duration was employed with a constant and equal delay of reinforcement for both new and original stimulus dimensions. In this condition, participants did not transfer from one dimension to another with up to 30-second delays. Control participants were yoked to participants exposed to delayed and fading procedures to examine response latencies under delayed reinforcement for a simultaneous discrimination. There were no discernible response patterns under this condition except that participants continued to emit relatively short response latencies with a 40-second delay of reinforcement. In Experiment III, the effects of different steps of temporal fading on transfer were examined. The results showed that as the step of delay increased (10 sec. per trial), subjects transferred earlier in the fading series. Also, subjects with extremely low steps of delay (.1 sec. per trial) tended to remain with the original stimulus dimension. Experiments I through III demonstrated the necessity of either inhibitory or neutral stimulus backgrounds, differential delays of reinforcement correlated with each stimulus dimension, and relatively rapid increments in delay of the original stimulus dimension to obtain transfers of stimulus control in temporal fading procedures. When excitatory stimulus backgrounds were employed, or no differential delay of reinforcement was present, or the delay of the original stimulus dimension increased slowly, errorless transfers were not obtained. Overall, the results indicate that temporal fading procedures are a reliable, although complexly controlled, means of obtaining transfer between two stimulus dimensions.

Previous researchers conducted activity schedule studies and used them on unstructured areas such as the playground. This study investigates the ability of fading procedures on the effects of using activity schedules on the playground. This study displayed that fading procedures can be used and determined based on the level of the individual. The results showed that two participants were able to fade to more portable forms of activity schedules from the typical activity schedule binder. This study provides many possibilities for conducting future research involving the use of fading procedures on activity schedules.

This dissertation presents a study that explores a specific implementation of concreteness fading used in a serious game that teaches programming. Concreteness fading consists of first presenting concepts with concrete representations before swapping them gradually with their concrete, normal counterparts. The goal is to figure out how concreteness fading should be applied to a programming game to have it increase learning. Expert interviews are performed to discuss different aspects of how the technique is utilized in the game Reduct. Participants also play through the game before discussing it. Results show that some found the individual representations of mechanics within the game to be the biggest flaw while others pointed to how it handled the fading aspect. These generally come down to a lack of clarity, and should be considered when developing future games of this style.

In recent years, millions of customers all over the world have been subscribing to mobile telephony services which are based on modern digital transmission. At the high transmission bit rates that these systems use, the mobile radio channel exhibits frequency-selective fading characteristics. Under such conditions, the received signal could experience significant intersymbol interference (ISI) from severe distortion to the waveform of the received baseband signal. Therefore, such techniques as adaptive waveform equalisation or adaptive maximum likelihood sequence estimation (MLSE) are used in modern digital mobile radio telephone systems to combat this undesirable ISI. These adaptive schemes have almost always been used in conjunction with coherent demodulation in the receivers.This study examines the application of noncoherent demodulation, in the form of frequency discriminator detection, as an alternative to coherent demodulation. The GSM (Global System for Mobile Communications) standard has been used as the basis for this investigation. It has been shown analytically that in the presence of frequency-selective fading, a propagation environment common to the GSM system, the use of frequency discriminator detection gives rise to nonlinear ISI in the demodulated signal. It has also been shown that frequency-selective fading could cause large unwanted "spikes" to appear in the demodulated signal, thus leading to a severe degradation in the bit-error-rate (BER) performance. Consequently, several waveform distortion cancellation schemes for combatting the nonlinear ISI have been formulated. The BER performances of these proposed schemes, under various propagation conditions, have been studied by computer simulation.Furthermore, it has been observed that the undesirable "spikes", that occur in the demodulated signal due to frequency-selective fading, could be ++ / suppressed by the use of inverse-limiting in conjunction with frequency discriminator detection. As a result, an effective adaptive detection scheme has been formulated, based on modelling the combination of the GMSK modulator, the mobile channel, the frequency discriminator, and any transmit and receive fitters, as a finite-state machine. The transmitted data is then detected using an MLSE. The BER performance of this proposed adaptive detection scheme has been extensively investigated by computer simulation. This has been carried out assuming various propagation conditions, including the two-ray fading channel model with equal path powers and relative delays of up to four bit periods, the maximum relative delay considered in the GSM system. Also, the effectiveness of the proposed adaptive detection scheme in combatting IS] has been investigated by computer simulation based on the six-ray GSM empirical propagation models for typical urban (TU), hilly terrain (HT) and rural area (RA) environments. The computer simulated results confirm that the voice grade performance required for the GSM system could be achieved by the proposed adaptive detection scheme in all the recommended GSM propagation models considered. Furthermore, the BER performance of the receiver remains unaffected by a carrier frequency offset of up to 2 kHz.

Mobile robots have found numerous applications in recent years, in areas such as consumer robotics, environmental monitoring, security and transportation. For information dissemination, multi-robot cooperation or operator intervention, reliable communications are important. The combination of communication constraints with other requirements in robotics, such as navigation and obstacle avoidance is called communication-aware motion planning. To facilitate integration, communication-aware methods should fit into traditional layered architectures of motion planning. This thesis contains two main contributions, applicable to such an architecture. The first contribution is to develop strategies for exploiting multipath fading while following a reference trajectory. By deviating from the reference, a robot can stop and communicate at positions with high signal strength, trading tracking performance for link quality. We formulate this problem in three different ways: First we maximize the link quality, subject to deterministic bounds on the tracking error. We control the velocity based on the position and channel quality. Second, we consider probabilistic tracking error bounds and develop a cascaded control architecture that performs time-triggered stopping while regulating the tracking error. Third, we formulate a hybrid optimal control problem, switching between standing still to communicate and driving to improve tracking. The resulting channel quality is analyzed and we perform extensive experiments to validate the communication model and compare the proposed methods to the nominal case of driving at constant velocity. The results show good agreement with the model and improvements of over 100% in the throughput when the channel quality is low. The second contribution is to plan velocities for a group of N robots, moving along pre-determined paths through an obstacle field. Robots can only communicate if they have an unobstructed line of sight, and the problem is to maintain connectivity while traversing the paths. This is mapped to motion planning in an N-dimensional configuration space. We propose and investigate two solutions, using a rapidly exploring random tree (RRT) and an exact method inspired by cell decomposition. The RRT method scales better with the problem size than the exact method, which has a worst-case time complexity that is exponential in the number of obstacles. But the randomization in the RRT method makes it difficult to set a timeout for the solver, which runs forever if a problem instance is unsolvable. The exact method, on the other hand, detects unsolvable problem instances in finite time. The thesis demonstrates, both in theory and experiments, that mobile robots can improve communications by planning trajectories that maintain visual connectivity, or by exploiting multipath fading when there is no line of sight. The proposed methods are well suited for integration in a layered motion planning architecture. / QC 20120117

In wireless communication systems, transmitted signals are corrupted by fading as well as noise. The receiver can benefit from the estimates of fading channels to detect the transmitted symbols. However, in practical wireless systems channel information cannot be estimated perfectly at the receiver. Therefore, it is crucial to examine the effect of channel estimation error on the structure and performance of the receivers. In the first part of the thesis, we study single-user systems with single-antenna reception over fading channels in the presence of Gaussian-distributed channel estimation error. By using the statistical information of the channel estimation error, we will derive the structure of maximum-likelihood receivers for a number of different modulation formats and then analyze their performance over fading channels. In the second part of the thesis, we consider the uplink of multi-user wireless systems with multi-antenna reception. For conventional diversity combining techniques such as maximal ratio combining and optimum combining we analyze the performance degradation due to imperfect channel estimates in the presence of multiple interfering users for several fading channels. By investigating the probability density function of the output signal-to-interference ratio, we will derive analytical expressions for several performance measures such as the average signal-to-interference ratio, outage probability and average bit-error probability. These expressions quantify performance degradation due to channel estimation error.