High-speed turbo-TCM-coded orthogonal frequency-division multiplexing ultra-wideband systems

One of the UWB proposals in the IEEE P802.15 WPAN project is to use a multiband orthogonal frequency-division multiplexing (OFDM) system and punctured convolutional codes for UWB channels supporting a data rate up to 480 Mbps. In this paper, we improve the proposed system using turbo TCM with QAM constellation for higher data rate transmission. We construct a punctured parity-concatenated trellis codes, in which a TCM code is used as the inner code and a simple parity-check code is employed as the outer code. The result shows that the system can offer a much higher spectral efficiency, for example, 1.2 Gbps, which is 2.5 times higher than the proposed system. We identify several essential requirements to achieve the high rate transmission, for example, frequency and time diversity and multilevel error protection. Results are confirmed by density evolution. Copyright (C) 2006 Yanxia Wang et al

Advanced Coding And Modulation For Ultra-wideband And Impulsive Noises

The ever-growing demand for higher quality and faster multimedia content delivery over short distances in home environments drives the quest for higher data rates in wireless personal area networks (WPANs). One of the candidate IEEE 802.15.3a WPAN proposals support data rates up to 480 Mbps by using punctured convolutional codes with quadrature phase shift keying (QPSK) modulation for a multi-band orthogonal frequency-division multiplexing (MB-OFDM) system over ultra wideband (UWB) channels. In the first part of this dissertation, we combine more powerful near-Shannon-limit turbo codes with bandwidth efficient trellis coded modulation, i.e., turbo trellis coded modulation (TTCM), to further improve the data rates up to 1.2 Gbps. A modified iterative decoder for this TTCM coded MB-OFDM system is proposed and its bit error rate performance under various impulsive noises over both Gaussian and UWB channel is extensively investigated, especially in mismatched scenarios. A robust decoder which is immune to noise mismatch is provided based on comparison of impulsive noises in time domain and frequency domain. The accurate estimation of the dynamic noise model could be very difficult or impossible at the receiver, thus a significant performance degradation may occur due to noise mismatch. In the second part of this dissertation, we prove that the minimax decoder in \cite, which instead of minimizing the average bit error probability aims at minimizing the worst bit error probability, is optimal and robust to certain noise model with unknown prior probabilities in two and higher dimensions. Besides turbo codes, another kind of error correcting codes which approach the Shannon capacity is low-density parity-check (LDPC) codes. In the last part of this dissertation, we extend the density evolution method for sum-product decoding using mismatched noises. We will prove that as long as the true noise type and the estimated noise type used in the decoder are both binary-input memoryless output symmetric channels, the output from mismatched log-likelihood ratio (LLR) computation is also symmetric. We will show the Shannon capacity can be evaluated for mismatched LLR computation and it can be reduced if the mismatched LLR computation is not an one-to-one mapping function. We will derive the Shannon capacity, threshold and stable condition of LDPC codes for mismatched BIAWGN and BIL noise types. The results show that the noise variance estimation errors will not affect the Shannon capacity and stable condition, but the errors do reduce the threshold. The mismatch in noise type will only reduce Shannon capacity when LLR computation is based on BIL

A Joint PHY/MAC Architecture for Low-Radiated Power TH-UWB Wireless Ad-Hoc Networks

Due to environmental concerns and strict constraints on interference imposed on other networks, the radiated power of emerging pervasive wireless networks needs to be strictly limited, yet without sacrificing acceptable data rates. Pulsed Time-Hopping Ultra-Wide Band (TH-UWB) is a radio technology that has the potential to satisfy this requirement. Although TH-UWB is a multi-user radio technology, non-zero cross-correlation between time-hopping sequences, time-asynchronicity between sources and a multipath channel environment make it sensitive to strong interferers and near-far scenarios. While most protocols manage interference and multiple-access through power control or mutual exclusion (CSMA/CA or TDMA), we base our design on rate control, a relatively unexplored dimension for multiple-access and interference management. We further take advantage of the nature of pulsed TH-UWB to propose an interference mitigation scheme that reduces the impact of strong interferers. A source is always allowed to send and continuously adapts its channel code (hence its rate) to the interference experienced at the destination. In contrast to power control or exclusion, our MAC layer is local to sender and receiver and does not need coordination among neighbors not involved in the transmission. We show by simulation that we achieve a significant increase in network throughput

High Speed Turbo Tcm Ofdm For Uwb And Powerline System

Turbo Trellis-Coded Modulation (TTCM) is an attractive scheme for higher data rate transmission, since it combines the impressive near Shannon limit error correcting ability of turbo codes with the high spectral efficiency property of TCM codes. We build a punctured parity-concatenated trellis codes in which a TCM code is used as the inner code and a simple parity-check code is used as the outer code. It can be constructed by simple repetition, interleavers, and TCM and functions as standard TTCM but with much lower complexity regarding real world implementation. An iterative bit MAP decoding algorithm is associated with the coding scheme. Orthogonal Frequency Division Multiplexing (OFDM) modulation has been a promising solution for efficiently capturing multipath energy in highly dispersive channels and delivering high data rate transmission. One of UWB proposals in IEEE P802.15 WPAN project is to use multi-band OFDM system and punctured convolutional codes for UWB channels supporting data rate up to 480Mb/s. The HomePlug Networking system using the medium of power line wiring also selects OFDM as the modulation scheme due to its inherent adaptability in the presence of frequency selective channels, its resilience to jammer signals, and its robustness to impulsive noise in power line channel. The main idea behind OFDM is to split the transmitted data sequence into N parallel sequences of symbols and transmit on different frequencies. This structure has the particularity to enable a simple equalization scheme and to resist to multipath propagation channel. However, some carriers can be strongly attenuated. It is then necessary to incorporate a powerful channel encoder, combined with frequency and time interleaving. We examine the possibility of improving the proposed OFDM system over UWB channel and HomePlug powerline channel by using our Turbo TCM with QAM constellation for higher data rate transmission. The study shows that the system can offer much higher spectral efficiency, for example, 1.2 Gbps for OFDM/UWB which is 2.5 times higher than the current standard, and 39 Mbps for OFDM/HomePlug1.0 which is 3 times higher than current standard. We show several essential requirements to achieve high rate such as frequency and time diversifications, multi-level error protection. Results have been confirmed by density evolution. The effect of impulsive noise on TTCM coded OFDM system is also evaluated. A modified iterative bit MAP decoder is provided for channels with impulsive noise with different impulsivity

Performance studies and receiver design of a MB-OFDM UWB system

Master'sMASTER OF ENGINEERIN

Location-aware and Cooperative Communication in an OFDM based Ultra-wideband Radio System

Die auf dem orthogonalen Frequenzmultiplex (OFDM, Orthogonal Frequency Division Multiplexing) basierende Ultra-Breitband-(UWB, Ultra-wideband) Technologie stellt eine verheißungsvolle Technologie dar, um hohe Datenübertragungsraten und Lokalisierungs- und deren Tracking-Anwendungen zu realisieren. Im Gegensatz zu anderen Systemen ist die Reichweite von OFDM UWB Systemen durch eine strenge Regulierung sehr stark begrenzt. Darüber hinaus ist die Lokalisierung nicht zufriedenstellend. Damit sind bereits die beiden größten Nachteile im Bezug auf bestehende OFDM UWB System benannt. Die Motivation und Hauptaufgabe dieser Arbeit ist damit die Lösung der eben genannten Nachteile. Es wird ein OFDM UWB System vorgestellt, das Space Frequency Block Coding (SFBC) und FFH OFDM miteinander verbindet. Dieses vereinte System wertet die räumliche und frequentielle Diversität eines OFDM-Symbols aus und zeigt dabei eine hohe Güte in der Punkt-zu-Punkt Kommunikation. Beim Design von kooperativen UWB-Systemen wird ein AF-(Amplify-and-Forward) basiertes echtzeitfähriges SFBC-TFC (Time Frequency Code) Protokoll vorgestellt. In Kombination mit den oben genannten Strategien, kann eine Erhöhung in den Reichweite von OFDM UWB Systemen erreicht werden. In den Ausführungen zur Ortung anhand von OFDM UWB Signalen wird ein Algorithmus entwickelt, der aufgrund einer Kanalschätzung eine Minimierung des Phasenversatzes zwischen geschätztem und realem Kanal im Frequenzbereich durchführt. Diese Minimierung erwirkt eine Unterdrückung der Energie am Ende der Kanalimpulsantwort (CIR, Channel Impulse Response) im Zeitbereich. Zum Zweck der einfachen Implementierbarkeit wird das RTT (Round-Trip-Time) Messprotokoll in WiMedia UWB Systemen dahingehend verändert, dass das mobile Gerät keine Minimierung vornimmt. Es leitet seine Informationen an das mit ihm Kommunizierende, stationäre Gerät weiter, das direkt den gesamten Zeitversatz innerhalb des RTT berechnet. Der vorgeschlagene Algorithmus und das vorgeschlagene Protokoll haben ein besseres Ortungsvermögen als bekannte UWB Lokalisierungsprozeduren und bedürfen nur etwas zusätzlicher Berechnungsleistung. Diese Arbeit zeigt, dass Systeme mit hohen Datenraten wie OFDM UWB auch eine gute Lokalisierungsgenauigkeit erreichen können. Zusätzlich ist die Schwachstelle einer limitierten Reichweite ebenso kompensiert worden. Diese Erweiterungen dienen der Entwicklung von nützlichen UWB-Applikationen und sichern den Anteil der OFDM UWB Technik im Markt der drahtlosen Kommunikationssysteme der Zukunft.The Orthogonal Frequency Division Multiplexing (OFDM) based Ultra-wideband (UWB) is one of the most promising technologies for high data rate transmission and localization and tracking applications. However, the restricted transmit power causes a shorter communication range compared to other indoor radio systems. In addition, the ranging functionality is still not well supported by the current OFDM based UWB technology. These two drawbacks are the main disadvantages existing in the current OFDM UWB systems. To get rid of the two drawbacks, is the motivation and main task of this thesis. Within the scope of this thesis, a joint design of Space Frequency Block Coding (SFBC) with Fast Frequency Hopping (FFH) OFDM scheme is investigated in a multiple antenna OFDM UWB system. The joint scheme is able to exploit spatial and frequency domain diversity within one OFDM symbol, and can improve the data transmission quality in point-to-point communication. To the cooperative communication in UWB systems, an Amplify-and-Forward (AF) based distributed SFBC-TFC (Time Frequency Code) protocol is designed. In combination with the aforementioned strategies an increase in the communication range is achieved. Within the scope of this thesis, accurate ranging schemes for the OFDM UWB systems are designed. Fine ToA detection method based on the estimated channel is developed. The fine ToA is estimated by minimizing the accumulated energy of the tail taps of the estimated Channel Impulse Response (CIR). For the purpose of a feasible implementation, the Round-Trip-Time (RTT) measurement protocol in [WiM09] is modified in a way that the complicated computational tasks are burden onto the powerful device. The proposed fine ToA detection method and modified RTT protocol provides an accurate ranging capability and ensures feasible implementation to the MB-OFDM UWB systems. In carrying out this scheme, only some computational tasks are needed, no extra hardware support is required. It is shown in this thesis, OFDM UWB systems with very high data rate transmission and good ranging capability could be achieved, and the weakness of limited communication range is also compensated. These improvements will cause the rise of more valuable UWB applications for customers and ensures a bright future for the OFDM UWB technique

Time diversity solutions to cope with lost packets

A dissertation submitted to Departamento de Engenharia Electrotécnica of Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engenharia Electrotécnica e de ComputadoresModern broadband wireless systems require high throughputs and can also have very high Quality-of-Service (QoS) requirements, namely small error rates and short delays. A high spectral efficiency is needed to meet these requirements. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation. An alternative to simple retransmission that can improve both power and spectral efficiency is to combine the signals associated to different transmission attempts. This thesis analyses two time diversity approaches to cope with lost packets that are relatively similar at physical layer but handle different packet loss causes. The first is a lowcomplexity Diversity-Combining (DC) Automatic Repeat reQuest (ARQ) scheme employed in a Time Division Multiple Access (TDMA) architecture, adapted for channels dedicated to a single user. The second is a Network-assisted Diversity Multiple Access (NDMA) scheme, which is a multi-packet detection approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This thesis combines these techniques with Single Carrier with Frequency Division Equalizer (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems. It proposes a new NDMA scheme capable of handling more Mobile Terminals (MTs) than the user separation capacity of the receiver. This thesis also proposes a set of analytical tools that can be used to analyse and optimize the use of these two systems. These tools are then employed to compare both approaches in terms of error rate, throughput and delay performances, and taking the implementation complexity into consideration. Finally, it is shown that both approaches represent viable solutions for future broadband wireless communications complementing each other.Fundação para a Ciência e Tecnologia - PhD grant(SFRH/BD/41515/2007); CTS multi-annual funding project PEst-OE/EEI/UI0066/2011, IT pluri-annual funding project PEst-OE/EEI/LA0008/2011, U-BOAT project PTDC/EEATEL/ 67066/2006, MPSat project PTDC/EEA-TEL/099074/2008 and OPPORTUNISTICCR project PTDC/EEA-TEL/115981/200

Distortion-Tolerant Communications with Correlated Information

This dissertation is devoted to the development of distortion-tolerant communication techniques by exploiting the spatial and/or temporal correlation in a broad range of wireless communication systems under various system configurations. Signals observed in wireless communication systems are often correlated in the spatial and/or temporal domains, and the correlation can be used to facilitate system designs and to improve system performance. First, the optimum node density, i.e., the optimum number of nodes in a unit area, is identified by utilizing the spatial data correlation in the one- and two-dimensional wireless sensor networks (WSNs), under the constraint of fixed power per unit area. The WSNs distortion is quantized as the mean square error between the original and the reconstructed signals. Then we extend the analysis into WSNs with spatial-temporally correlated data. The optimum sampling in the space and time domains is derived. The analytical optimum results can provide insights and guidelines on the design of practical WSNs. Second, distributed source coding schemes are developed by exploiting the data correlation in a wireless network with spatially distributed sources. A new symmetric distributed joint source-channel coding scheme (DJSCC) is proposed by utilizing the spatial source correlation. Then the DJSCC code is applied to spatial-temporally correlated sources. The temporal correlated data is modeled as the Markov chain. Correspondingly, two decoding algorithms are proposed. The first multi-codeword message passing algorithm (MCMP) is designed for spatially correlated memoryless sources. In the second algorithm, a hidden Markov decoding process is added to the MCMP decoder to effectively exploit the data correlation in both the space and time domains. Third, we develop distortion-tolerant high mobility wireless communication systems by considering correlated channel state information (CSI) in the time domain, and study the optimum designs with imperfect CSI. The pilot-assisted channel estimation mean square error is expressed as a closed-form expression of various system parameters through asymptotic analysis. Based on the statistical properties of the channel estimation error, we quantify the impacts of imperfect CSI on system performance by developing the analytical symbol error rate and a spectral efficiency lower bound of the communication system