Ultra-Wideband Relay Communication Systems

Impulse-radio ultra-wide-band (IR-UWB) signaling is a promising technique for high-speed, short-range relay communications networks. Depending on how the relay node retransmits the signal, there are two main relay schemes: conventional one-directional (one-way) relay model, and bi-directional (two-way) relay model. In bi-directional relay communications, wireless network coding (WNC), also called physical-layer network coding (PNC), could be applied to overcome the spectral efficiency limitation of the conventional one-way relay. In the first part of this work, we propose asynchronous, differential, and bidirectional decode and forward (ADBDF) and asynchronous, differential, and bidirectional denoise and forward (ADBDNF) UWB relay methods, where the relay node (RN) does not need to be synchronized with the end nodes (ENs). The proposed schemes are attractive for networks in which stringent/complicated synchronization between the RN and the ENs may not be feasible. The second part of this work focuses on UWB channel classification. We propose a 2-dimensional (2-D) LOS/NLOS classification scheme that uses skewness of the channel impulse/pulse response. The proposed channel classification decreases the complexity of existing channel classification methods and can be used in a variety of areas such as localization, relay communications, and cooperative communications. The final part of this work deals with compressive sensing (CS) algorithms that employ sub-Nyquist sampling for UWB communications. We develop coarse graining (CG) for the proposed CS sub-Nyquist sampling technique, which leads to: (1) reduced sampling rate at the receiver, and hence reduced use of analog-to-digital converters (ADCs) resources; and (2) low-complexity channel estimation

Performance Evaluation of 802.15.4 UWB PHY for High Speed Data Rate under IEEE Channel Mode

In modern day society the increase of data generation and transfer has been an issue that researchers are working on. This generated and shared data might have a different purpose but one thing is certain, the reception. This communication can cover continents, countries, cities or even just a few meters. For the purpose of the later, personal area networks (PAN) have been created with a main focus to lower the energy consumption. The protocol that is created under IEEE is 802.15.4 and it has multiple applications in the context of next generation sensor networks. This thesis investigates the performance IEEE 802.15.4 UWB PHY for high data rates over IEEE multipath fading channels and introduces receivers aiming to diversity and to mitigate the intersymbol interference (ISI) that might appear. We simulate the protocols highest mandatory data rate over slow, block faded, realistic IEEE channel models such as, residential, office, outdoor and industrial. The simulation includes Reed Solomon (RS) channel coding, optimal successive erasure decoding (SED), and coherent RAKE receivers. We verify that the selective RAKE (sRAKE) perform better than the nonselective RAKE (n-sRAKE) in all environments and also the increase of fingers is mandatory in order to improve performance. In cases with low number of fingers the ISI mitigation techniques like Maximum-Likehood Sequence Estimator (MLSE) & RAKE combination or Maximum Ration Combining (MRC) ISI cancellation receivers, can provide some gain in large delay spread environments. In cases with high number of ingers the MRC received employs its full diversity since the received power is arger than before. Overall the apply of optimal errors and erasures decoding can urther improve the system performance by adding a small gain, lowering existing it Error Probability (BEP) even more.A huge percentage of data has been generated in the last two years and it will grow more, as every one of us is constantly producing and releasing data. The latest years has been an extensive research on capacity maximization, bit rate increment and power optimization. That research lead to the development of various protocols for cellular and personal area networks (PAN), where they each utilizes the frequency spectrum differently. Even if cellular networks have the ability to cover large area, development of multiple personal area networks can be developed for the purpose to offload data from the cellular network. Keeping in mind the research needs, 802.15.4 UWH PHY is a solid candidate when it comes to data transfer in a small area. This protocol offers various mandatory transmission modes that can be selected depending the channel parameters and various data rate needs. Time hopping and spreading sequence offers the existence of multiuser environment where multiple transceivers can co-exist. Overall the complexity, cost and energy consumption for transmission and reception can be kept low, matching the research needs. The main issues regarding 802.15.4 UWH PHY and high speed data rates is first, the energy dispersion of the transmitted symbol to multiple bins and second, the appearance of Inter Symbol Interference (ISI) in high delay profile environments. The solution in the former problem is the necessary implementation of a RAKE receiver. Regarding the latter, literature offers multiple ways to mitigate the ISI but the aim should be to keep the lowest complexity possible regarding the implementation. In this thesis we evaluate the performance of 802.15.4 UWB PHY for high speed data rates under IEEE channel models. Various receivers has been build for the purpose of this thesis, Maximum Ratio Combining (MRC), MRC with Inter Symbol Interference and MLSE & RAKE combination receiver. The MRC is a simple RAKE receiver with maximum diversity, MRC with ISI cancellation is based on the MRC receiver with the ability to mitigate ISI, and MLSE & RAKE combination is an optimum ISI mitigation receiver without the diversity of the MRC

Design and analysis of space-time block and trellis coding schemes for single-band UWB communications systems

Ultra Wide-Band (UWB) technology has recently attracted much research interest due to its appealing features in short-range mobile communications. These features include high-data rates, low power consumption, multiple-access communications and precise positioning capabilities. Space-Time Coding (STC) techniques, such as block coding and trellis coding, are known to be simple and practical ways to increase both the spectral efficiency and the capacity in wireless communications. The the- sis aims at designing robust and efficient space-time coding schemes well adapted to single-band UWB signalling. Thus, this work incorporates a fine analysis of a stan- dard Single Input Single Output (SISO) single-band UWB system, scrutinising every important aspect of this system including transceiver structure, channel modelling, multiple-access techniques and detection process. Research also leads to the deriva- tion of a novel closed-form approximation for the average probability of bit-error for single-band UWB systems. This in-depth study highlights drawbacks inherent to UWB systems such as time-jitter effects or rake-receiver complexity and proposes schemes that benefit from spatial diversity to mitigate these problems. Thus, the thesis concentrates on the design of new multiple-antenna space-time coding systems tailored for UWB communications. As a result, this work derives and generates gen- eralised full-rate space-time block codes based on orthogonal pulses to capture both spatial and multipath diversities. Space-time trellis coded modulation is then revis- ited to further improve the spectral efficiency limit and to deliver the high-data rates promised by UWB technology. A new version of space-time trellis coding is developed for the peculiar UWB signalling structure. Finally, thanks to a novel closed-form ap- proximation, a theoretical comparison is undertaken between any SISO-UWB system and the multiple antenna UWB systems proposed in this thesis. The results clearly underline the impact of STC on a single-band UWB system in terms of enhanced robustness against timing-jitter effects, higher spectral efficiency and capacity im- provement. These advantages are finally confirmed through the numerical evaluation of the error-rate performance.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Managing Impulsive Interference in Impulse Radio UWB Networks

Wireless sensor networks are ideally built on low-cost, low-complexity nodes that have a low power consumption to guarantee a long network lifetime. These are all properties that can potentially be achieved with impulse radio ultra-wide band (IR-UWB). In addition, IR-UWB has a fine timing resolution resulting in accurate ranging and localization possible. For all these reasons, IR-UWB is an extremely interesting physical layer technology for wireless sensor networks. In this article, we consider the management of impulsive interference in IR-UWB networks. Impulsive interference is due to uncoordinated concurrent transmissions. It occurs, for instance, when several independent piconets operate in close vicinity and is also present in some MAC layer proposals that allow concurrent transmissions. If not properly addressed, impulsive interference can severely affect the throughput and energy consumption of an IR-UWB network; as such, it already needs to be taken into account in the design phase. First, we show that impulsive interference is a serious concern for IR-UWB networks. Second, we present techniques at the physical layer and at the link layer to cope with and combat such interference efficiently. Finally, we present DCC-MAC as an example of an interference-aware design

Interference management in impulse-radio ultra-wide band networks

We consider networks of impulse-radio ultra-wide band (IR-UWB) devices. We are interested in the architecture, design, and performance evaluation of these networks in a low data-rate, self-organized, and multi-hop setting. IR-UWB is a potential physical layer for sensor networks and emerging pervasive wireless networks. These networks are likely to have no particular infrastructure, might have nodes embedded in everyday life objects and have a size ranging from a few dozen nodes to large-scale networks composed of hundreds of nodes. Their average data-rate is low, on the order of a few megabits per second. IR-UWB physical layers are attractive for these networks because they potentially combine low-power consumption, robustness to multipath fading and to interference, and location/ranging capability. The features of an IR-UWB physical layer greatly differ from the features of the narrow-band physical layers used in existing wireless networks. First, the bandwidth of an IR-UWB physical layer is at least 500 MHz, which is easily two orders of magnitude larger than the bandwidth used by a typical narrow-band physical layer. Second, this large bandwidth implies stringent radio spectrum regulations because UWB systems might occupy a portion of the spectrum that is already in use. Consequently, UWB systems exhibit extremely low power spectral densities. Finally IR-UWB physical layers offer multi-channel capabilities for multiple and concurrent access to the physical layer. Hence, the architecture and design of IR-UWB networks are likely to differ significantly from narrow-band wireless networks. For the network to operate efficiently, it must be designed and implemented to take into account the features of IR-UWB and to take advantage of them. In this thesis, we focus on both the medium access control (MAC) layer and the physical layer. Our main objectives are to understand and determine (1) the architecture and design principles of IR-UWB networks, and (2) how to implement them in practical schemes. In the first part of this thesis, we explore the design space of IR-UWB networks and analyze the fundamental design choices. We show that interference from concurrent transmissions should not be prevented as in protocols that use mutual exclusion (for instance, IEEE 802.11). Instead, interference must be managed with rate adaptation, and an interference mitigation scheme should be used at the physical layer. Power control is useless. Based on these findings, we develop a practical PHY-aware MAC protocol that takes into account the specific nature of IR-UWB and that is able to adapt its rate to interference. We evaluate the performance obtained with this design: It clearly outperforms traditional designs that, instead, use mutual exclusion or power control. One crucial aspect of IR-UWB networks is packet detection and timing acquisition. In this context, a network design choice is whether to use a common or private acquisition preamble for timing acquisition. Therefore, we evaluate how this network design issue affects the network throughput. Our analysis shows that a private acquisition preamble yields a tremendous increase in throughput, compared with a common acquisition preamble. In addition, simulations on multi-hop topologies with TCP flows demonstrate that a network using private acquisition preambles has a stable throughput. On the contrary, using a common acquisition preamble exhibits an effect similar to exposed terminal issues in 802.11 networks: the throughput is severely degraded and flow starvation might occur. In the second part of this thesis, we are interested in IEEE 802.15.4a, a standard for low data-rate, low complexity networks that employs an IR-UWB physical layer. Due to its low complexity, energy detection is appealing for the implementation of practical receivers. But it is less robust to multi-user interference (MUI) than a coherent receiver. Hence, we evaluate the performance of an IEEE 802.15.4a physical layer with an energy detection receiver to find out whether a satisfactory performance is still obtained. Our results show that MUI severely degrades the performance in this case. The energy detection receiver significantly diminishes one of the most appealing benefits of UWB, specifically its robustness to MUI and thus the possibility of allowing for parallel transmissions. This performance analysis leads to the development of an IR-UWB receiver architecture, based on energy detection, that is robust to MUI and adapted to the peculiarities of IEEE 802.15.4a. This architecture greatly improves the performance and entails only a moderate increase in complexity. Finally, we present the architecture of an IR-UWB physical layer implementation in ns-2, a well-known network simulator. This architecture is generic and allows for the simulation of several multiple-access physical layers. In addition, it comprises a model of packet detection and timing acquisition. Network simulators also need to have efficient algorithms to accurately compute bit or packet error rates. Hence, we present a fast algorithm to compute the bit error rate of an IR-UWB physical layer in a network setting with MUI. It is based on a novel combination of large deviation theory and importance sampling

Secure Neighbor Discovery and Ranging in Wireless Networks

This thesis addresses the security of two fundamental elements of wireless networking: neighbor discovery and ranging. Neighbor discovery consists in discovering devices available for direct communication or in physical proximity. Ranging, or distance bounding, consists in measuring the distance between devices, or providing an upper bound on this distance. Both elements serve as building blocks for a variety of services and applications, notably routing, physical access control, tracking and localization. However, the open nature of wireless networks makes it easy to abuse neighbor discovery and ranging, and thereby compromise overlying services and applications. To prevent this, numerous works proposed protocols that secure these building blocks. But two aspects crucial for the security of such protocols have received relatively little attention: formal verification and attacks on the physical-communication-layer. They are precisely the focus of this thesis. In the first part of the thesis, we contribute a formal analysis of secure communication neighbor discovery protocols. We build a formal model that captures salient characteristics of wireless systems such as node location, message propagation time and link variability, and we provide a specification of secure communication neighbor discovery. Then, we derive an impossibility result for a general class of protocols we term "time-based protocols", stating that no such protocol can provide secure communication neighbor discovery. We also identify the conditions under which the impossibility result is lifted. We then prove that specific protocols in the time-based class (under additional conditions) and specific protocols in a class we term "time- and location-based protocols," satisfy the neighbor discovery specification. We reinforce these results by mechanizing the model and the proofs in the theorem prover Isabelle. In the second part of the thesis, we explore physical-communication-layer attacks that can seemingly decrease the message arrival time without modifying its content. Thus, they can circumvent time-based neighbor discovery protocols and distance bounding protocols. (Indeed, they violate the assumptions necessary to prove protocol correctness in the first part of the thesis.) We focus on Impulse Radio Ultra-Wideband, a physical layer technology particularly well suited for implementing distance bounding, thanks to its ability to perform accurate indoor ranging. First, we adapt physical layer attacks reported in prior work to IEEE 802.15.4a, the de facto standard for Impulse Radio, and evaluate their performance. We show that an adversary can achieve a distance-decrease of up to hundreds of meters with an arbitrarily high probability of success, with only a minor cost in terms of transmission power (few dB). Next, we demonstrate a new attack vector that disrupts time-of-arrival estimation algorithms, in particular those designed to be precise. The distance-decrease achievable by this attack vector is in the order of the channel spread (order of 10 meters in indoor environments). This attack vector can be used in previously reported physical layer attacks, but it also creates a new type of external attack based on malicious interference. We demonstrate that variants of the malicious interference attack are much easier to mount than the previously reported external attack. We also provide design guidelines for modulation schemes and devise receiver algorithms that mitigate physical layer attacks. These countermeasures allow the system designer to trade off security, ranging precision and cost in terms of transmission power and packet length

Self-concatenated coding for wireless communication systems

In this thesis, we have explored self-concatenated coding schemes that are designed for transmission over Additive White Gaussian Noise (AWGN) and uncorrelated Rayleigh fading channels. We designed both the symbol-based Self-ConcatenatedCodes considered using Trellis Coded Modulation (SECTCM) and bit-based Self- Concatenated Convolutional Codes (SECCC) using a Recursive Systematic Convolutional (RSC) encoder as constituent codes, respectively. The design of these codes was carried out with the aid of Extrinsic Information Transfer (EXIT) charts. The EXIT chart based design has been found an efficient tool in finding the decoding convergence threshold of the constituent codes. Additionally, in order to recover the information loss imposed by employing binary rather than non-binary schemes, a soft decision demapper was introduced in order to exchange extrinsic information withthe SECCC decoder. To analyse this information exchange 3D-EXIT chart analysis was invoked for visualizing the extrinsic information exchange between the proposed Iteratively Decoding aided SECCC and soft-decision demapper (SECCC-ID). Some of the proposed SECTCM, SECCC and SECCC-ID schemes perform within about 1 dB from the AWGN and Rayleigh fading channels’ capacity. A union bound analysis of SECCC codes was carried out to find the corresponding Bit Error Ratio (BER) floors. The union bound of SECCCs was derived for communications over both AWGN and uncorrelated Rayleigh fading channels, based on a novel interleaver concept.Application of SECCCs in both UltraWideBand (UWB) and state-of-the-art video-telephone schemes demonstrated its practical benefits.In order to further exploit the benefits of the low complexity design offered by SECCCs we explored their application in a distributed coding scheme designed for cooperative communications, where iterative detection is employed by exchanging extrinsic information between the decoders of SECCC and RSC at the destination. In the first transmission period of cooperation, the relay receives the potentially erroneous data and attempts to recover the information. The recovered information is then re-encoded at the relay using an RSC encoder. In the second transmission period this information is then retransmitted to the destination. The resultant symbols transmitted from the source and relay nodes can be viewed as the coded symbols of a three-component parallel-concatenated encoder. At the destination a Distributed Binary Self-Concatenated Coding scheme using Iterative Decoding (DSECCC-ID) was employed, where the two decoders (SECCC and RSC) exchange their extrinsic information. It was shown that the DSECCC-ID is a low-complexity scheme, yet capable of approaching the Discrete-input Continuous-output Memoryless Channels’s (DCMC) capacity.Finally, we considered coding schemes designed for two nodes communicating with each other with the aid of a relay node, where the relay receives information from the two nodes in the first transmission period. At the relay node we combine a powerful Superposition Coding (SPC) scheme with SECCC. It is assumed that decoding errors may be encountered at the relay node. The relay node then broadcasts this information in the second transmission period after re-encoding it, again, using a SECCC encoder. At the destination, the amalgamated block of Successive Interference Cancellation (SIC) scheme combined with SECCC then detects and decodes the signal either with or without the aid of a priori information. Our simulation results demonstrate that the proposed scheme is capable of reliably operating at a low BER for transmission over both AWGN and uncorrelated Rayleigh fading channels. We compare the proposed scheme’s performance to a direct transmission link between the two sources having the same throughput

Time reversal transmission approach for ultra wideband communications

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Communications protocols for wireless sensor networks in perturbed environment

This thesis is mainly in the Smart Grid (SG) domain. SGs improve the safety of electrical networks and allow a more adapted use of electricity storage, available in a limited way. SGs also increase overall energy efficiency by reducing peak consumption. The use of this technology is the most appropriate solution because it allows more efficient energy management. In this context, manufacturers such as Hydro-Quebec deploy sensor networks in the nerve centers to control major equipment. To reduce deployment costs and cabling complexity, the option of a wireless sensor network seems the most obvious solution. However, deploying a sensor network requires in-depth knowledge of the environment. High voltages substations are strategic points in the power grid and generate impulse noise that can degrade the performance of wireless communications. The works in this thesis are focused on the development of high performance communication protocols for the profoundly disturbed environments. For this purpose, we have proposed an approach based on the concatenation of rank metric and convolutional coding with orthogonal frequency division multiplexing. This technique is very efficient in reducing the bursty nature of impulsive noise while having a quite low level of complexity. Another solution based on a multi-antenna system is also designed. We have proposed a cooperative closed-loop coded MIMO system based on rank metric code and max−dmin precoder. The second technique is also an optimal solution for both improving the reliability of the system and energy saving in wireless sensor networks