Adaptive RAKE receiver structures for ultra wide-band systems

Ultra wide band (UWB) is an emerging technology that recently has gained regulatory approval. It is a suitable solution for high speed indoor wireless communications due to its promising ability to provide high data rate at low cost and low power consumption. Another benefit of UWB is its ability to resolve individual multi-path components. This feature motivates the use of RAKE multi-path combining techniques to provide diversity and to capture as much energy as possible from the received signal. Potential future and rule limitation of UWB, lead to two important characteristics of the technology: high bit rate and low emitting power. Based on the power emission limit of UWB, the only choice for implementation is the low level modulation technology. To obtain such a high bit rate using low level modulation techniques, significant inter-symbol interference (ISI) is unavoidable. Three N (N means the numbers of fingers) fingers RAKE receiver structures are proposed: the N-selective maximal ratio combiner (MRC), the N-selective MRC receiver with least-mean-square (LMS) adaptive equalizer and the N-selective MRC receiver with LMS adaptive combiner. These three receiver structures were all simulated for N=8, 16 and 32. Simulation results indicate that ISI is effectively suppressed. The 16-selective MRC RAKE receiver with LMS adaptive combiner demonstrates a good balance between performance, computation complexity and required length of the training sequence. Due to the simplicity of the algorithm and a reasonable sampling rate, this structure is feasible for practical VLSI implementations

Ultra Wideband

Ultra wideband (UWB) has advanced and merged as a technology, and many more people are aware of the potential for this exciting technology. The current UWB field is changing rapidly with new techniques and ideas where several issues are involved in developing the systems. Among UWB system design, the UWB RF transceiver and UWB antenna are the key components. Recently, a considerable amount of researches has been devoted to the development of the UWB RF transceiver and antenna for its enabling high data transmission rates and low power consumption. Our book attempts to present current and emerging trends in-research and development of UWB systems as well as future expectations

Façonnement de l'Interférence en vue d'une Optimisation Globale d'un Système Moderne de Communication

A communication is impulsive whenever the information-bearing signal is burst-like in time. Examples of the impulsive concept are: impulse-radio signals, that is, wireless signals occurring within short intervals of time; optical signals conveyed by photons; speech signals represented by sound pressure variations; pulse-position modulated electrical signals; a sequence of arrival/departure events in a queue; neural spike trains in the brain. Understanding impulsive communications requires to identify what is peculiar to this transmission paradigm, that is, different from traditional continuous communications.In order to address the problem of understanding impulsive vs. non-impulsive communications, the framework of investigation must include the following aspects: the different interference statistics directly following from the impulsive signal structure; the different interaction of the impulsive signal with the physical medium; the actual possibility for impulsive communications of coding information into the time structure, relaxing the implicit assumption made in continuous transmissions that time is a mere support. This thesis partially addresses a few of the above issues, and draws future lines of investigation. In particular, we studied: multiple access channels where each user adopts time-hopping spread-spectrum; systems using a specific prefilter at the transmitter side, namely the transmit matched filter (also known as time reversal), particularly suited for ultrawide bandwidhts; the distribution function of interference for impulsive systems in several different settings.Une communication est impulsive chaque fois que le signal portant des informations est intermittent dans le temps et que la transmission se produit à rafales. Des exemples du concept impulsife sont : les signaux radio impulsifs, c’est-à-dire des signaux très courts dans le temps; les signaux optiques utilisé dans les systèmes de télécommunications; certains signaux acoustiques et, en particulier, les impulsions produites par le système glottale; les signaux électriques modulés en position d’impulsions; une séquence d’événements dans une file d’attente; les trains de potentiels neuronaux dans le système neuronal. Ce paradigme de transmission est différent des communications continues traditionnelles et la compréhension des communications impulsives est donc essentielle. Afin d’affronter le problème des communications impulsives, le cadre de la recherche doit inclure les aspects suivants : la statistique d’interférence qui suit directement la structure des signaux impulsifs; l’interaction du signal impulsif avec le milieu physique; la possibilité pour les communications impulsives de coder l’information dans la structure temporelle. Cette thèse adresse une partie des questions précédentes et trace des lignes indicatives pour de futures recherches. En particulier, nous avons étudié: un système d'accès multiple où les utilisateurs adoptent des signaux avec étalement de spectre par saut temporel (time-hopping spread spectrum) pour communiquer vers un récepteur commun; un système avec un préfiltre à l'émetteur, et plus précisément un transmit matched filter, également connu comme time reversal dans la littérature de systèmes à bande ultra large; un modèle d'interférence pour des signaux impulsifs

Virtual SATCOM, Long Range Broadband Digital Communications

The current naval strategy is based on a distributed force, networked together with high-speed communications that enable operations as an intelligent, fast maneuvering force. Satellites, the existing network connector, are weak and vulnerable to attack. HF is an alternative, but it does not have the information throughput to meet the distributed warfighting need. The US Navy does not have a solution to reduce dependency on space-based communication systems while providing the warfighter with the required information speed. Virtual SATCOM is a solution that can match satellite communications (SATCOM) data speed without the vulnerable satellite. It is wireless communication on a High Frequency (HF) channel at SATCOM speed. We have developed an innovative design using high power and gain, ground-based relay systems. We transmit extremely wide-wideband HF channels from ground stations using large directional antennas. Our system starts with a highly directional antenna with a narrow beam that enables increased bandwidth without interfering with other spectrum users. The beam focus and power provide a high SNR across a wideband channel with data rates of 10 Mbps; 1000 times increase in HF data speed. Our modeling of the ionosphere shows that the ionosphere has more than adequate bandwidth to communicate at 3000 km and high speeds while avoiding detection. We designed a flexible structure adjustable to the dynamic ionosphere. Our design provides a high-speed communications path without the geo-location vulnerability of legacy HF methods. Our invention will benefit mobile users using steerable beam forming apertures with wide bandwidth signals. This dissertation will focus on three areas: an examination of the ionosphere’s ability to support the channel, design of a phased array antenna that can produce the narrow beam, and design of signal processing that can accommodate the wideband HF frequency range. Virtual SATCOM is exciting research that can reduce cost and increase access to long-range, high data rate wireless communications

Optical Switching for Scalable Data Centre Networks

This thesis explores the use of wavelength tuneable transmitters and control systems within the context of scalable, optically switched data centre networks. Modern data centres require innovative networking solutions to meet their growing power, bandwidth, and scalability requirements. Wavelength routed optical burst switching (WROBS) can meet these demands by applying agile wavelength tuneable transmitters at the edge of a passive network fabric. Through experimental investigation of an example WROBS network, the transmitter is shown to determine system performance, and must support ultra-fast switching as well as power efficient transmission. This thesis describes an intelligent optical transmitter capable of wideband sub-nanosecond wavelength switching and low-loss modulation. A regression optimiser is introduced that applies frequency-domain feedback to automatically enable fast tuneable laser reconfiguration. Through simulation and experiment, the optimised laser is shown to support 122×50 GHz channels, switching in less than 10 ns. The laser is deployed as a component within a new wavelength tuneable source (WTS) composed of two time-interleaved tuneable lasers and two semiconductor optical amplifiers. Switching over 6.05 THz is demonstrated, with stable switch times of 547 ps, a record result. The WTS scales well in terms of chip-space and bandwidth, constituting the first demonstration of scalable, sub-nanosecond optical switching. The power efficiency of the intelligent optical transmitter is further improved by introduction of a novel low-loss split-carrier modulator. The design is evaluated using 112 Gb/s/λ intensity modulated, direct-detection signals and a single-ended photodiode receiver. The split-carrier transmitter is shown to achieve hard decision forward error correction ready performance after 2 km of transmission using a laser output power of just 0 dBm; a 5.2 dB improvement over the conventional transmitter. The results achieved in the course of this research allow for ultra-fast, wideband, intelligent optical transmitters that can be applied in the design of all-optical data centres for power efficient, scalable networking

Intelligent Processing in Wireless Communications Using Particle Swarm Based Methods

There are a lot of optimization needs in the research and design of wireless communica- tion systems. Many of these optimization problems are Nondeterministic Polynomial (NP) hard problems and could not be solved well. Many of other non-NP-hard optimization problems are combinatorial and do not have satisfying solutions either. This dissertation presents a series of Particle Swarm Optimization (PSO) based search and optimization algorithms that solve open research and design problems in wireless communications. These problems are either avoided or solved approximately before. PSO is a bottom-up approach for optimization problems. It imposes no conditions on the underlying problem. Its simple formulation makes it easy to implement, apply, extend and hybridize. The algorithm uses simple operators like adders, and multipliers to travel through the search space and the process requires just five simple steps. PSO is also easy to control because it has limited number of parameters and is less sensitive to parameters than other swarm intelligence algorithms. It is not dependent on initial points and converges very fast. Four types of PSO based approaches are proposed targeting four different kinds of problems in wireless communications. First, we use binary PSO and continuous PSO together to find optimal compositions of Gaussian derivative pulses to form several UWB pulses that not only comply with the FCC spectrum mask, but also best exploit the avail- able spectrum and power. Second, three different PSO based algorithms are developed to solve the NLOS/LOS channel differentiation, NLOS range error mitigation and multilateration problems respectively. Third, a PSO based search method is proposed to find optimal orthogonal code sets to reduce the inter carrier interference effects in an frequency redundant OFDM system. Fourth, a PSO based phase optimization technique is proposed in reducing the PAPR of an frequency redundant OFDM system. The PSO based approaches are compared with other canonical solutions for these communication problems and showed superior performance in many aspects. which are confirmed by analysis and simulation results provided respectively. Open questions and future Open questions and future works for the dissertation are proposed to serve as a guide for the future research efforts

MAP detection for impairment compensation in coherent WDM systems

We propose a novel recursive-algorithm based maximum a posteriori probability (MAP) detector in spectrally-efficient coherent wavelength division multiplexing (CoWDM) systems, and investigate its performance in a 1-bit/s/Hz on-off keyed (OOK) system limited by optical-signal-to-noise ratio. The proposed method decodes each sub-channel using the signal levels not only of the particular sub-channel but also of its adjacent sub-channels, and therefore can effectively compensate deterministic inter-sub-channel crosstalk as well as inter-symbol interference arising from narrow-band filtering and chromatic dispersion (CD). Numerical simulation of a five-channel OOK-based CoWDM system with 10Gbit/s per channel using either direct or coherent detection shows that the MAP decoder can eliminate the need for phase control of each optical carrier (which is necessarily required in a conventional CoWDM system), and greatly relaxes the spectral design of the demultiplexing filter at the receiver. It also significantly improves back-to-back sensitivity and CD tolerance of the system

Compact and Efficient Millimetre-Wave Circuits for Wideband Applications

Radio systems, along with the ever increasing processing power provided by computer technology, have altered many aspects of our society over the last century. Various gadgets and integrated electronics are found everywhere nowadays; many of these were science-fiction only a few decades ago. Most apparent is perhaps your ``smart phone'', possibly kept within arm's reach wherever you go, that provides various services, news updates, and social networking via wireless communications systems. The frameworks of the fifth generation wireless system is currently being developed worldwide. Inclusion of millimetre-wave technology promise high-speed piconets, wireless back-haul on pencil-beam links, and further functionality such as high-resolution radar imaging. This thesis addresses the challenge to provide signals at carrier frequencies in the millimetre-wave spectrum, and compact integrated transmitter front-ends of sub-wavelength dimensions. A radio frequency pulse generator, i.e. a ``wavelet genarator'', circuit is implemented using diodes and transistors in III--V compound semiconductor technology. This simple but energy-efficient front-end circuit can be controlled on the time-scale of picoseconds. Transmission of wireless data is thereby achieved at high symbol-rates and low power consumption per bit. A compact antenna is integrated with the transmitter circuit, without any intermediate transmission line. The result is a physically small, single-chip, transmitter front-end that can output high equivalent isotropically radiated power. This element radiation characteristic is wide-beam and suitable for array implementations