Dissertations & Student Research in Computer Electronics & Engineering

Design and Implementation of a Hybrid Technology Networking System

Sushanta Mohan Rakshit — Tue, 23 Apr 2013 06:35:24 PDT

The safety of rail transport has always been the top priority for the Federal
Railroad Administration (FRA). Legacy technology, like wayside monitoring, is still
in place and is largely relied upon for detection of faults. Modern technology like
Radio Frequency Identification (RFID) has been introduced recently. However, this
is largely used to detect a particular railcar rather than to monitor it for problems.
Wireless Sensor Network (WSN) technology is being evaluated by the railroads for real-time or near real-time monitoring of the status of railcars for timely response to problems and also for trend analysis.

ZigBee has been the networking protocol of choice for the railroads for its low
power consumption and cost of implementation. The railroad scenario presents a long linear-chain like network topology which ZigBee was not designed to handle. It has been found that a ZigBee-only network in the railroad environment suffers from drawbacks like long synchronization delays, severe problems with route discovery and maintenance, aggregation of data errors leading to unacceptable packet loss rates, lack of a mechanism to decide traffic priority for critical packets, like alarm, so that they can reliably traverse the network to the collecting node in the locomotive etc.

Hybrid Technology Networking (HTN) protocol has been suggested which
addresses the shortcomings of ZigBee in the railroad scenario. It proposes a
standards-based multi-protocol approach that is well-suited for the railroad scenario. The current crop of sensor platforms does not provide an integrated environment for the implementation of HTN.

In this research work an integrated hardware platform for the implementation
of the HTN protocol is designed and implemented. The guiding principle has been the adherence to standards. The test results using the hardware show that it provides inter-operability with available sensor platforms, can interface with other sensing hardware using standard protocols and provides communication capabilities exceeding that needed by HTN.

Advisor: Hamid R. Sharif-Kashani

Analysis of the Feasibility of Utilizing Wakeup Radios to Optimize Energy and Latency Performance of Wireless Sensor Networks

Benjamin D. Parks — Fri, 19 Apr 2013 11:17:19 PDT

Wireless sensor networks (WSNs) have the potential to radically improve our lives by pervasive environmental monitoring in many applications. However, there are many applications that would be ideal for WSNs, but where reportable events occur with long (days, weeks) or unpredictable durations between occurrences. These uses are hampered by the high energy and latency costs of always-on and periodic wakeup networks, which waste energy on node synchronization and idle monitoring of the RF channel, and exhibit unacceptably high latency for urgent events, e.g., alarms. This thesis proposes, designs, assembles and tests, in a multi-hop WSN test bed, a wakeup receiver (WUR) and associated medium access control (MAC) protocol that can be added to WSNs to make the communications functionality of the network “on-demand”. When not required to communicate, a node’s main radio is shut down, while the wakeup radio remains active, consuming 1.85μW to continuously monitor for wakeup signals. Each node has a transmitter to broadcast the wakeup signal to adjacent nodes and establish communications when required. -40dBm of sensitivity was measured on assembled receiver prototypes, allowing wakeup ranges up to 15 feet with low-power -10dBm 433MHz testing transmitters and a predicted 90 feet with +10dBm transmitters. The WUR prototypes were successfully tested in a multi-hop WSN, becoming the first known example of incorporating fully functional WURs into a multi-hop network. Latency of one second per hop was measured when waking from deep sleep. WSN node energy consumption decreased as much as 1500-fold compared to always-on WSNs, and 15-fold compared to typical periodic wakeup WSNs when 10 hours occurs between wakeup events. At shorter wakeup intervals, the energy improvements are reduced, with performance equivalent to a 1% duty cycle periodic wakeup network at approximately 10 minutes of mean time between wakeup events. The MAC protocol developed to support WSN wake-on-demand allows basic demonstration and performance testing and establishes a foundation for future refinement of wakeup-based MAC protocols.

Advisor: Hamid Sharif-Kashani

AN INVESTIGATION OF SECURITY CHALLENGES IN COGNITIVE RADIO NETWORKS

Deepraj S. Vernekar — Thu, 06 Dec 2012 13:15:15 PST

The recent advances in wireless communication have led to the problem of growing spectrum scarcity. The available wireless spectrum has become scarcer due to increasing spectrum demand for new wireless applications. The large portion of the allocated spectrum is sporadically used leading to underutilization of significant amount of spectrum. To improve the spectrum efficiency, the idea of cognitive radio technology was introduced. This concept of cognitive radio provides a promising solution for the spectrum scarcity issues in wireless networks. Meanwhile, the security issues of cognitive radio have received more attentions recently since the inherent properties of CR networks would pose new challenges to wireless communications. In this MS thesis, general concepts of security threats to the cognitive radio networks are briefly reviewed. Performances for primary user emulation attacks are studied from Neyman-Pearson criterion point of view. A novel system model with different configurations of the primary users has been proposed and studied. Our experimental results demonstrate the statistical characteristics of the probability of false alarm and miss detection in the proposed system. I will make performance comparison with others’ research in the future.

Adviser: Yaoqing Yang

AN ULTRA-LOW POWER COMMUNICATION PROTOCOL FOR A SELF-POWERED WIRELESS SENSOR BASED ANIMAL MONITORING SYSTEM

Tao Ma — Thu, 06 Dec 2012 12:50:17 PST

To prevent and control the outbreak of contagious animal disease, many countries have developed animal identification and tracking systems. However, the current animal identification and tracking system, which is based on passive RFID technology, has many limitations such as the short communication range and incapability of automatically monitoring the animal. To overcome these limitations, our Advanced Telecommunications Engineering Laboratory (TEL) in Department of Computer and Electronics Engineering (CEEN), University of Nebraska-Lincoln took the mission of developing a more advanced monitoring system for animal identification and tracking. This dissertation work as a part of this mission was focusing on developing an ultra-low power communication protocol for our animal monitoring system. Our animal monitoring system utilizes the energy harvesting wireless sensor technology, aiming to offer a solar energy powered ad hoc network where all tags are actively collecting all the concerning information of livestock, and automatically passing the information through multi-hop to the hub. To meet the requirements of such an animal monitoring system, this dissertation had carefully designed and thoroughly implemented an ultra-low power communication protocol, which is able to provide multi-hop routing capability with an overall duty cycle level as low as 0.1%. Both lab tests and field tests were also conducted to verify the developed communication protocol. Furthermore, the two essential elements of this communication protocol: the synchronization error and the throughput, were analytically formulated and analyzed. The validity of these formulations was verified by the lab tests. Currently, the developed ultra-low power communication protocol has been successfully used in our energy harvesting wireless sensor based animal monitoring system.

Adviser: Hamid Sharif

CONDUCTIVE CONCRETE FOR ELECTROMAGNETIC SHIELDING – METHODS FOR DEVELOPMENT AND EVALUATION

Aaron P. Krause — Mon, 03 Dec 2012 12:13:32 PST

This research investigates the development and evaluation innovative methods for the use of conductive concrete as an electromagnetic shield. New testing methods are developed to determine the best conductive components to use in the design of a concrete mixture for shielding that shows the best promise. The conductive concrete mixture has the potential to provide electromagnetic shielding that is cost-effective in terms of construction, operation, and maintenance compared to conventional approaches. Two testing methods, Small Sample Testing and Large Slab Testing, are developed based on standardized testing methods that have been modified for the testing of conductive concrete mixtures. As a result of these innovative testing methods, a promising conductive concrete design has been chosen and the testing methods validated.

Adviser: Lim Nguyen

Energy Efficiency Analysis and Optimization on Mobile Video Wireless Delivery

Jianxin Sun — Fri, 27 Jul 2012 08:33:57 PDT

Micro-electronic industry has been boosting the capability of wireless mobile devices on full-scale. However, battery, as the only power source of most mobile devices, is experiencing a relatively slow development. Therefore, how to optimally utilize the limited battery energy on mobile devices under a predefined performance requirement becomes a critical issue. On the other hand, it is still unclear that how the battery capacity consumption is allocated on different working pattern of a specific video codec under various tempo-spatial scales and parameters, which has posed a design challenge on power management on multimedia communication system. Furthermore, an optimization method is needed to be proposed and experimentally tested to achieve the tradeoff between the computational complexity and the distortion of multimedia delivery in order to discover the relationship and interaction between computational parameters of multimedia communication and battery capacity consumption. From point of view of battery-aware system design and optimization, batteries discharging characteristics and a precise model under different thermal condition still need an exhaustive investigation. In this paper, we proposed a dynamic frequency scaling algorithm to optimize the energy efficiency on each sensor node under the different ambient thermal condition. A new battery model with thermal parameter is proposed and analyzed in order to predict the scheduling of dynamic frequency scaling. Experiment results indicate the efficiency and effectiveness of the proposed optimization framework, and the insight of the relationship between scheduling of dynamic frequency scaling and battery discharging curves under different environmental temperature.

Adviser: Song Ci

A Multi-Modal Sensing and Communication Platform for Continental-Scale Migratory Bird Tracking

David J. Anthony — Thu, 26 Apr 2012 07:01:05 PDT

This thesis presents a novel platform for tracking migratory birds on a continental scale. Cellular technology is used to augment the short-range radios that have traditionally been used in wireless sensor networks. The platform utilizes multiple sensors, including a GPS and solid state compass. By using these sensors, the platform is capable of not only tracking a bird’s migration path, but also provides information on a bird’s behavior during its life-cycle. Testing methodology utilizing simulations and aspect-oriented programming is used to reveal faults in the platform prior to deployment on wild animals. In collaboration with the International Crane Foundation, and the Crane Trust, the platform is evaluated on multiple species of birds (Wild Turkeys, Siberian Cranes, Sandhill Cranes), over 6 months, to evaluate its effectiveness. These deployments reveal that the system is capable of not only tracking birds, but monitoring their behavior. By utilizing cellular technology, the system is capable of delivering information about a bird within 24 hours, which is much faster than current systems used to track Whooping Cranes.

Advisers: Mehmet C. Vuran and Matthew B. Dwyer

A Study of Correlations between the Definition and Application of the Gene Ontology

Yuji Mo — Mon, 05 Dec 2011 08:06:04 PST

When using the Gene Ontology (GO), nucleotide and amino acid sequences are annotated by terms in a structured and controlled vocabulary organized into relational graphs. The usage of the vocabulary (GO terms) in the annotation of these sequences may diverge from the relations defined in the ontology. We measure the consistency of the use of GO terms by comparing GO's defined structure to the terms' application. To do this, we first use synthetic data with different characteristics to understand how these characteristics influence the correlation values determined by various similarity measures. Using these results as a baseline, we found that the correlation between GO's definition and its application to real data is relatively low, suggesting that GO annotations might not be applied in a manner consistent with its definition. In contrast, we found a sub-ontology of GO that correlates well with its usage in UniProtKB. We also study how terms from different ontologies in GO relate to each other, Such relationships can be helpful in refining term definitions. In order to identify such ``cross-terms", we propose a generalized semantic measure which can be used to identify related terms across GO ontologies. Results based on Saccharomyces Genome Database show that the measure is correlated with the degree of co-occurrence for term pairs. By thresholding the level of similarity, we found a list of highly correlated cross ontology term pairs. These term pairs show a high level of biological correlation.

Adviser: Stephen Scott

A NOVEL TELECOMMUNICATIONS-BASED APPROACH TO MATHEMATICAL MODELING OF HIV INFECTION

Aaron T. Sharp — Fri, 02 Dec 2011 07:24:59 PST

It is well known that biological systems utilize communication in some form, one prolific example of this is the propagation of HIV (Human Immunodeficiency Virus) in the human body. By modeling HIV infection as a communication system, we hope to gain a unique insight into HIV and biological communication systems in general. Such a model would provide researchers a platform for experimenting and simulating various biological communication systems. We have previously developed a layered communication protocol for interpreting biological communication systems using telecommunications paradigms and will apply said model to HIV proliferation. We will also demonstrate the effectiveness of the model by formulating a telecommunications-based mathematical model, and by implementing a simulation of HIV infection based on direct interpretation of this layered protocol.

Adviser: Tadeusz Wysocki

A Quantitative Performance Analysis of 2.5 GHz and 3.65 GHz Mobile WiMAX

Pradhumna L. Shrestha — Mon, 28 Nov 2011 14:22:22 PST

Mobile WiMAX has emerged as a prime contender for the de-facto ITU’s 4G standard. It provides high data rate with large coverage and vehicular mobility support. It has been, and is being, widely deployed in diverse applications like video streaming, broadcasting and data service. The FCC (Federal Communications Commission) issues licenses to operate Mobile WiMAX services in several spectrums, among which 2.5 GHz and 3.65 GHz are the most common. Because the 2.5 GHz spectrum suffers the least propagation losses, it has been widely applied commercially. For this reason, academic and industrial researchers have given it particular attention. However, in some cases, the 3.65 GHz is often a better choice, in spite of having a lower coverage, particularly due to its favorable licensing requirements. Due to limited amount of work published in the 3.65 GHz spectrum, the concerned parties do not have sufficient data to reliably select the spectrum. In this research work, a thorough quantitative analysis of the two Mobile WiMAX spectrums, 2.5 GHz and 3.65 GHz, are presented and compared. Actual physical testing of commercial equipment in real-world settings has been done to provide a generic overview of the performance of the two spectrums. The results presented serve multiple purposes. First, they provide reliable technical data for decision-making. Second, they can be used for link budget analysis. Finally, they can be utilized as benchmarks for future testing and quality control of equipment production. It is shown that the maximum achievable downlink throughput for the 2.5 GHz and the 3.65 GHz systems is around 22 Mbps and 21 Mbps respectively. Assuming an average user bandwidth demand of Mbps, they can both reliably serve 40 to 45 users within a coverage radius of 12 km and 8 km respectively. Other than the lower coverage, opting for the 3.65 GHz spectrum over the 2.5 GHz spectrum will cause no significant performance loss and should be preferred if the loss of coverage can be tolerated.

Advisor: Hamid R. Sharif-Kashani

STUDY OF CELLULAR PHONE DETECTION TECHNIQUES

Nicholas W. Scott — Wed, 22 Jun 2011 08:21:27 PDT

This thesis studies techniques for detecting cellular phones. It examines existing technology currently available on the open market, an existing design that utilizes mostly discrete components, and a design approach using a down converter in conjunction with a bandpass filter.

The existing technologies available on the open market are examined and discussed. These technologies are not adequate, because they are inaccurate and expensive.

The first signal detection technique, an existing design utilizing discrete components is difficult to implement. They are very affordable to construct, but require precision tuning. This design is analyzed and found to be inaccurate.

The second signal detection technique, a design using a down converter, voltage controlled oscillator (VCO), and a bandpass filter was investigated for cellular phone detection. The performance of this technique through hardware and computer modeling is discussed and the results are presented. The new system is accurate and a practical solution for detecting cellular phones in a secure facility.

Exploration of Spatial Diversity in Multi-Antenna Wireless Communication Systems

Shichuan Ma — Mon, 25 Apr 2011 07:15:48 PDT

With increasing demand on wireless internet and personal multimedia, the data rate of wireless communications is expected to increase dramatically. Future wireless networks face challenges of supporting data rates higher than one gigabits per second. Among various technologies, multi-antennas, also known as multiple-input multiple-output (MIMO), are undoubtedly the most promising to enable higher data rates. By employing the extra degrees of freedom in the spatial domain, multi-antenna techniques enhance the wireless communication systems through array gain, spatial diversity, and spatial multiplexing. Although multi-antenna systems have been utilized for more than ten years, a thorough analysis of various aspects of multi-antenna systems and the potential applications of MIMO technology need to be explored.

In this dissertation, we explore some new features of multi-antenna systems. After introducing the fundamentals of radio propagations, we first study long-range channel prediction and the I/Q imbalance compensation in MIMO-OFDM systems. A novel multi-block linear channel predictor is proposed for limited feedback precoded spatial multiplexing MIMO-OFDM systems, and a new virtual channel method is proposed to analyze the I/Q imbalances in a MIMO-OFDM wireless communication system over multipath fading channels. We then provide a detailed study of recent advances in distributed MIMO technologies in cooperative wireless networks. We also utilize the MIMO technique to enhance the self-encoded spread spectrum (SESS) systems, resulting in a robust MIMO-SESS system. Finally, we present a novel physical-layer technique to secure wireless communications by transmitting artificially generated jamming noise signals that can deteriorate the signal quality at the eavesdroppers.

Advisor: Yaoqing (Lamar) Yang

OPTIMIZED DELAY-SENSITIVE MULTIMEDIA COMMUNICATIONS OVER WIRELESS NETWORKS

Haiyan Luo — Tue, 19 Apr 2011 10:34:39 PDT

Multimedia communication is expected to be the major application of the next-generation wireless networks. However, providing delay-sensitive, loss-tolerant and resource-guzzling multimedia services over the current resource-limited wireless networks is still a very challenging task. In addition to their heterogeneous nature and resource limitation, wireless networks also suffer from channel variations and environmental changes. In this dissertation, we study the optimization techniques for wireless multimedia communications and address the issues from different theoretical and practical perspectives.

To solve the issues resulting from the increasingly heterogeneous wireless networks, we propose a framework for error resilient source coding and distributed application-layer error control, where the encoder calculates source encoding options, enabling globally optimal rate allocation between source and channel bits for all the hops considered in the end-to-end path.

Further, we propose content-aware video communications to differentiate the region of interest (ROI) from the less important background area so that resources can be classified, prioritized and more efficiently utilized for encoding and transmission. We also apply the theories by proposing a wireless e-healthcare system.

To take into consideration of channel variations and to provide a framework that can dynamically adapt to the instant channel changes, we propose a cross-layer optimized framework which jointly optimizes different functions residing at different network layers, including video encoding, network congestion, retransmission and link adaptation. We also demonstrate how this design can be widely used in wireless environments by presenting our research on the scheduling algorithm of wireless peer-to-peer (P2P) multimedia networks.

At last, we move one step further on dynamic adaptation to many other ``context" information such as user preference, location, weather, etc. By providing the design of an adaptive multimedia communications system based on context-aware services, we study how to retrieve and utilize all the context data to better serve the users with significantly-improved video quality.

The proposed optimization techniques are usually discussed within certain application scenarios to demonstrate the practicality, efficacy and efficiency. However, these research findings can be widely used in other wireless networks and applications.

A COMPREHENSIVE ANALYSIS OF LTE PHYSICAL LAYER

Fahimeh Rezaei — Mon, 06 Dec 2010 08:07:53 PST

The 3rd Generation Partnership Project (3GPP) introduced Long Term Evolution (LTE) as the 3rd generation of mobile communication standards. LTE Release 8 describes a mobile communication standard which supports up to 300 Mbps of data transmission in downlink using the OFDM scheme as well as up to 75 Mbps throughput for uplink using the SC-FDMA modulation. In this thesis, an in-depth study of LTE performance based on Release 8 is conducted for uplink and downlink under different scenarios. The main objective of this study is to investigate a comprehensive analysis of physical layer throughput of LTE Release8 based on standard parameters for different channel bandwidths, duplex schemes, antenna diversity and other scenarios. Our study of the FDD operation mode shows that the maximum throughput for downlink data is 299.122 by using 4 antenna ports with the least possible control overhead (one OFDM symbol assigned to PDCCH), 64-QAM data modulation scheme, the maximum code rate (0.92), and the maximum channel bandwidth (20 MHz). This throughput result is based on PDSCH that is used for data transmission only and does not include control information (PDCCH, PHICH, and PCFICH), broadcast channel (PBCH), reference signals, and Synchronization Signals (P-SS and S-SS). Our study also shows that the maximum uplink throughput for the FDD operation is 71.97 Mbps excluding control channel information (PUCCH), and reference signals (demodulation reference signals and sounding reference signal). This maximum throughput result is based on assuming 64-QAM data modulation, maximum bandwidth (20 MHz), and 0.85 code rate.

This study also presents other throughput results based on different parameters. Overall, this thesis provides a comprehensive investigation of the LTE performance analysis based on detailed physical layer parameters to fill the existing gap in current literature in performance study of LTE.

QUALITY-DRIVEN CROSS LAYER DESIGN FOR MULTIMEDIA SECURITY OVER RESOURCE CONSTRAINED WIRELESS SENSOR NETWORKS

Wei Wang — Thu, 02 Dec 2010 13:17:25 PST

The strong need for security guarantee, e.g., integrity and authenticity, as well as privacy and confidentiality in wireless multimedia services has driven the development of an emerging research area in low cost Wireless Multimedia Sensor Networks (WMSNs). Unfortunately, those conventional encryption and authentication techniques cannot be applied directly to WMSNs due to inborn challenges such as extremely limited energy, computing and bandwidth resources. This dissertation provides a quality-driven security design and resource allocation framework for WMSNs. The contribution of this dissertation bridges the inter-disciplinary research gap between high layer multimedia signal processing and low layer computer networking. It formulates the generic problem of quality-driven multimedia resource allocation in WMSNs and proposes a cross layer solution. The fundamental methodologies of multimedia selective encryption and stream authentication, and their application to digital image or video compression standards are presented. New multimedia selective encryption and stream authentication schemes are proposed at application layer, which significantly reduces encryption/authentication complexity. In addition, network resource allocation methodologies at low layers are extensively studied. An unequal error protection-based network resource allocation scheme is proposed to achieve the best effort media quality with integrity and energy efficiency guarantee. Performance evaluation results show that this cross layer framework achieves considerable energy-quality-security gain by jointly designing multimedia selective encryption/multimedia stream authentication and communication resource allocation.

Cross-Layer Optimized Wireless Multimedia Networking

Dalei Wu — Thu, 02 Dec 2010 13:16:00 PST

Multimedia communications, especially real-time video communications, is expected to be the major application of the next-generation wireless networks. However, bringing delay-sensitive and loss-tolerant multimedia services based on the current wireless Internet is a very challenging task. In this dissertation, we address cross-layer optimized wireless multimedia networking from both theoretical and practical perspectives.

In the first part of the dissertation, we propose cross-layer optimization frameworks for real-time video communications over wireless networks, where the expected received video quality is adopted as the objective function. With the user-centric objective function, we first study content-aware video communications in single-hop wireless networks by exploring the transmission of video summaries. Then, we investigate the routing issue for real-time video streaming over multi-hop wireless networks. Lastly, we study the performance of video summary transmission over cooperative wireless networks to exploit the spatial diversity of cooperative communications. Extensive theoretical and experimental results demonstrate that significant performance gains are obtained by our solutions.

In the second part of the dissertation, we theoretically study the methodology of cross-layer design and optimization. Despite rich literature in cross-layer design and optimization schemes, most current research on cross-layer design has been carried out in various piecemeal approaches and lacks a methodological foundation to gain in-depth understanding of complex cross-layer behaviors. We focus on the quantitative analysis of the interactions among design variables towards to the design objective. The interaction measure is calculated based on the non-additive measure theory with network observation data. We conduct a case study on cross-layer optimized wireless multimedia communications to illustrate the major cross-layer design tradeoffs and validate the proposed theoretical framework. The proposed framework can significantly enhance our capability for cross-layer behavior characterization and provide insights for future design.

Study of Physical Layer Security in Wireless Communications

Mustafa Duruturk — Fri, 05 Mar 2010 11:03:41 PST

This thesis has investigated security in wireless communications at physical layer. Security is an important issue for wireless communications and poses many challenges. Most security schemes have been applied to the upper layers of communications networks. Since in a typical wireless communication, transmission of data is over the air, third party receiver(s) may have easy access to the transmitted data. This work discusses a new security technique at the physical layer for the MIMO (802.11n) transmitters. For this project, the wireless medium is secured by transmitting a noise signal that is only recoverable by the receiver. This report includes an analysis of a wireless system that shows the bit error rate (BER) of the data signal in a two dimensional map. The map is a view of the free space, which has a receiver and transmitter at the ends. This work demonstrates that the proposed security technique can significantly complement other security approaches implemented in the upper layers of the communication network.
Advisers: Hamid Sharif and Michael Hempel

PERFORMANCE OF SELF-ENCODED SPREAD SPECTRUM UNDER WORST-CASE JAMMING

Casey L. Deyle — Thu, 18 Feb 2010 09:41:19 PST

Performance of Self-Encoded Spread Spectrum Under Worst-Case Jamming Casey Deyle, M.S University of Nebraska 2009 Advisor: Lim Nguyen Spread Spectrum Communications uses m-sequences (sometimes referred to as Pseudo Noise or PN sequences) modulated with a data signal to create a transmission signal that takes up more bandwidth than the original information signal. Self-Encoded Spread Spectrum (SESS) uses spreading codes generated by the transmitted signal, eliminating the need to synchronize m-sequences between the transmitter and receiver, thus making the channel more secure. This paper will discuss the performance of SESS system in Additive White Gaussian Noise (AWGN) and Rayleigh fading channels, as well as the use of an iterative detection to increase the performance of the system. Introduced in this paper is pulsed noise jammer (PNJ) to a SESS system, which is the worst-case jamming scenario for a SESS system, and possible ways to overcome these jamming conditions. The performance of the SESS system in this paper is analyzed using simulations that measure the probability of error (sometimes called Bit Error Rate or BER) vs signal-to-noise ratio (also called SNR or Eb/No).

ROBUST IMAGE AND VIDEO CODING WITH ADAPTIVE RATE CONTROL

Hongqiang Wang — Fri, 24 Apr 2009 14:30:13 PDT

This dissertation is focused on the problem of rate allocation in a resource constrained environment and robustness of video coding over noise channels. A new rate allocation scheme that combines the traditional PCRD-Opt algorithm with the rho domain analysis is proposed for wavelet based image coders. The proposed scheme provides competitive performance as compared with the optimal PCRD-Opt algorithm, while with great reduction on complexity and computational costs.

Rate allocation is developed for the Region-Of-Interest (ROI) in the wavelet transform domain for image coding. A recursive region growing method that deter mines the ROI in the transform domain is proposed. With excellent coding performance, robustness of the coder is improved as well because the ROI is allocated more bit resources and better protected. In addition, as intra-frame video coding is less vulnerable to errors than inter-frame video coding, we proposed rate allocation methods for several intra-frame video coding scenarios based on the proposed rate allocation algorithm for image coding.

A coding method based on the principles of distributed source coding in the wavelet transform domain is proposed in order to achieve a good compromise between compression performance and robustness. 8x8 blocks in the wavelet transform domain are classified and coded by either distributed source coding or intra-frame video coding depending on the amount of correlation between co-located blocks in two consecutive frames. The regions that contain motion blocks are extracted and then intra coded with higher priority and more rate resources. The background regions are coded based on the principle of distributed video coding. The approach exploits inter-frame redundancy without explicitly using inter-frame video coding and demonstrated both a better robustness than the traditional intra-frame video coder H.263+ and improved compression performance over the image coder based intra-frame video coding.

SELF-ENCODED SPREAD SPECTRUM SYNCHRONIZATION AND COOPERATIVE DIVERSITY

Kun Hua — Mon, 04 Aug 2008 16:02:25 PDT

This dissertation research concerns a novel self-encoded spread spectrum. It provides a feasible practical implementation for random spreading codes. The traditional transmit and receive PN code generators are not needed. Instead, the spreading codes are extracted from the user's information bits itself. Comparing to conventional CDMA, SESS completely abandons the use of pseudo-random spreading codes. The code variability doesn't depend on the spreading length like pseudo-random codes.

But because the self-encoded spreading sequence is random and time varying, data recovery requires that the despreading sequence be identical with the spreading sequence at the start of the transmission. Synchronization is one of the key techniques in SESS which seeks to recover the initial spreading sequence at the receiver without any prior knowledge. It includes two phases: initial acquisition and tracking. We consider initial acquisition as a global optimization problem and employ genetic search algorithm for converging to the global optimization efficiently. In the tracking phase, we use Markov chain analysis to examine the mean tracking time. We can verify them by simulation results as sequence length N=8. By comparing the analytical and simulation results, we can conclude that the Genetic model and Markov chain analysis can describe the process of the synchronization of SESS system reliably. We extended such synchronization model of SESS to longer sequence length as N=64 and achieved the shortest synchronization time by setting an optimum threshold. Optimal parameters are also considered to improve the synchronization time.

We also consider incorporating SESS with cooperative diversity technique to achieve spatial diversity gain with the number of relays. We observe the system’s stability in highly correlated rayleigh channels as well as in severe fading channels. Meanwhile, we also consider channel coding for time diversity gain (together with the soft decision Viterbi detection in receiver). Notice that we achieve both time diversity and special diversity while maintaining the same average power as the maximum ratio combiner.

Adviser: Lim Nguyen