Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains x, 139 p. : ill. Includes abstract. Includes bibliographical references (p. 132-139).

The demand for access to information when and where you need has motivated the transition of wireless communications from a fixed infrastructure based cellular communications technology to a more pervasive adhoc wireless networking technology. Challenges still remain in wireless adhoc networks in terms of meeting higher capacity demands, improved reliability and longer connectivity before it becomes a viable widespread commercial technology. Present day wireless mesh networking uses node-to-node serial multi-hop communication to convey information from source to destination in the network. The performance of such a network depends on finding the best possible route between the source and destination nodes. However the end-to-end performance can only be as good as the weakest link within a chosen route. Unlike wired networks, the quality of point-to-point links in a wireless mesh network is subject to random fluctuations. This adversely affects the performance resulting in poor throughput and poor energy efficiency. In recent years, a new paradigm for communication called cooperative communications has been proposed for which initial information theoretic studies have shown the potential for improvements in capacity over traditional multi-hop wireless networks. Cooperative communication involves exploiting the broadcast nature of the wireless medium to form virtual antenna arrays out of independent single-antenna network nodes for transmission. In this research we explore the fundamental performance limits of cooperative communication under more practical operating scenarios. Specifically we provide a framework for computing the outage and ergodic capacities of non identical distributed MIMO links, study the effect of time synchronization error on system performance, analyze the end-to-end average bit error rate (ABER) performance under imperfect relaying, and study range extension and energy efficiency offered by the system when compared to a traditional system. / Ph. D.

Video transmission over noisy wireless channels leads to errors on video, which degrades the visual quality notably and makes error concealment an indispensable job. In the literature, there are several error concealment techniques based on estimating the lost parts of the video from the available data. Utilization of data hiding for this problem, which seems to be an alternative of predicting the lost data, provides a reserve information about the video to the receiver while unchanging the transmitted bit-stream syntax / hence, improves the reconstruction video quality without significant extra channel utilization. A complete error resilient video transmission codec is proposed, utilizing imperceptible embedded information for combined detecting, resynchronization and reconstruction of the errors and lost data. The data, which is imperceptibly embedded into the video itself at the encoder, is extracted from the video at the decoder side to be utilized in error concealment. A spatial domain error recovery technique, which hides edge orientation information of a block, and a resynchronization technique, which embeds bit length of a block into other blocks are combined, as well as some parity information about the hidden data, to conceal channel errors on intra-coded frames of a video sequence. The errors on inter-coded frames are basically recovered by hiding motion vector information along with a checksum into the next frames. The simulation results show that the proposed approach performs superior to conventional approaches for concealing the errors in binary symmetric channels, especially for higher bit rates and error rates.

<p>In this thesis we study the complexity of data recovery from synchronization errors, namely insertion and deletion (insdel) errors.</p> <p>Insdel Locally Decodable Codes (Insdel LDCs) are error-correcting codes that admit super-efficient decoding algorithms even in the presence of many insdel errors. The study of such codes for Hamming errors have spanned several decades, whereas work on the insdel analogue had amounted to only a few papers before our work. This work initiates a systematic study of insdel LDCs, seeking to bridge this gap through designing codes and proving limitations. Our upper bounds essentially match those for Hamming LDCs in important ranges of parameters, even though insdel LDCs are more general than Hamming LDCs. Our main results are lower bounds that are exponentially stronger than the ones inherited from the Hamming LDCs. These results also have implications for the well-studied variant of relaxed LDCs. For this variant, besides showing the first results in the insdel setting, we also answer an open question for the Hamming variant by showing a strong lower bound.</p> <p>In the trace reconstruction problem, the goal is to recover an unknown source string x \in {0,1}n from random traces, which are obtained by hitting the source string with random deletion/insertions at a fixed rate. Mean-based algorithms are a class of reconstruction algorithms whose outputs depend only on the empirical estimates of individual bits. The number of traces needed for mean-based trace reconstruction has already been settled. We further study the performance of mean-based algorithms in a scenario where one wants to distinguish between two source strings parameterized by their edit distance, and we also provide explicit construction of strings that are hard to distinguish. We further establish an equivalence to the Prouhet-Tarry-Escott problem from number theory, which ends up being an obstacle to constructing explicit hard instances against mean-based algorithms.</p>

Terrestrial Digital Video Broadcasting (DVB-T) is a standard for wireless broadcast of MPEG-2 video. DVB-T is based on channel coding algorithms and uses Orthogonal Frequency Division Multiplexing (OFDM) as a modulation scheme. In this thesis, we have implemented the standard of ETSI EN 300 744 for Digital Video Broadcasting in MATLAB. This system is composed of the certain blocks which include OFDM modulation, channel estimation, channel equalization, frame synchronization, error-protection coding, to name a few of such blocks. We have investigated the performance of the complete system for different wireless broadcast impairments. In this performance analysis, we have considered Rayleigh fading multi-path channels with Doppler shift and framing synchronization errors and obtained the bit error rate (BER), and channel minimum square error performances versus different maximum Doppler shift values, different channel equalization techniques and different channel estimation algorithms. Furthermore, we have investigated different interpolations methods for the interpolation of channel response. It is shown that minimum mean-square error (MMSE) type equalization has a better performance in symbol estimation compared to zero forcing (ZF) equalizer. Also linear interpolation in time and low pass frequency interpolation, for time frequency interpolation of channel response can be used for practical application.

In this master thesis project, a new protocol called the Round Trip Time (RTT) protocol is implemented and verified. It helps determine the Ethernet clock frequency offset between two communicating nodes. The detection of this offset between nodes is a way to reduce the clock synchronization error. Ethernet is the basis on which a large amount of communication takes place in the world. Either it is used for exchanging data from one device to another or to connect devices to the internet. Due to the absence of clocks being exchanged between the various Ethernet communicating nodes, clock phase and frequency offsets can be present which leads to clock de-synchronization between the various nodes and results in lower system throughput. In the telecommunication industry, synchronization error between base stations can lead to lower throughput, performance degradation and packet loss. Also, with the introduction of 5G, stringent requirements will be placed on the clock synchronization errors.Currently, the Precision Time Protocol (PTP) is used to detect and correct clock synchronization errors. The PTP implementation reduces the clock synchronization error but it is still quite large. Hence, it is necessary to find a protocol which can work together with the PTP protocol to reduce this error. This thesis will introduce a new way to determine the clock frequency offset between nodes through the implementation of the RTT protocol. Through the course of this project, the clock frequency offset was determined by the RTT protocol. By comparing the expected and the theoretical clock offsets, it was concluded that the two values were very similar. The error between the offsets was in the range of 2.349-15.687 parts per billion (ppb) of the link frequency. Thus, the RTT protocol accurately and precisely determined the clock frequency offset between two Ethernet communicating nodes. This protocol is also extended to determine the clock frequency offset between two nodes transmitting periodic signals. For future works, this protocol can be combined with the PTP protocol and a way to determine the clock phase offset will be investigated. / I detta examensarbete implementerades och verifierades ett nytt protokoll, kallat Round Trip Time (RTT)-protokollet, som hjälper till att bestämma Ethernets klockfrekvensförskjutning mellan två kommunicerande noder. Denna fastställda förskjutning mellan de två noderna är ett sätt att reducera klocksynkroniseringsfelet. Ethernet är grunden i en stor del av dagens kommunikation i världen. Antingen används det för informationsutbyte mellan två enheter, eller för att ansluta till internet. Då det saknas ett utbyte av referensklocka mellan de olika kommunikationsnoderna på Ethernet, kan det uppstå klockfasoch frekvensförskjutning som leder till att klockan desynkroniseras mellan de olika noderna och därmed ger ett minskat dataflöde. I telekommunikationsindustrin kan ett synkronisationsfel mellan basstationer leda till minskat dataflöde, sämre prestanda och paketförlust. I och med introduktionen av 5G kommer stränga krav att ställas på klocksynkronisationsfelen.För närvarande används Precision Time Protocol (PTP) för att upptäcka och korrigera klocksynkroniseringsfelen. Implementationen av PTP reducerar klocksynkroniseringsfelet, men det är fortfarande relativt stort. Därav är det nödvändigt att hitta ett protokoll som kan arbeta tillsammans med PTP för att reducera detta fel. Detta arbete kommer att introducera ett nytt sätt att bestämma klockfrekvensförskjutningen genom implementation av RTT-protokollet. I detta arbete bestämdes klockfrekvensförskjutningen av RTT-protokollet. Genom att jämföra det förväntade och faktiska värdet på klockförskjutningen kunde slutsatsen dras att de två värdena var väldigt lika. Felet var i storleksordningen av 2,349-15,687 parts per billion (ppb) i linkfrekvensen. Således bestämmer RTT-protokollet korrekt och exakt klockfrekvensförskjutningen mellan de två kommunikationsnoderna i Ethernet. Protokollet utökas också för att bestämma klockfrekvensförskjutningen mellan två noder som sänder en periodisk signal. För framtida arbete kan detta protokoll kombineras med PTP-protokollet, och det ska även undersökas ett sätt för att bestämma klockfasförskjutningen.