Novel wireless modulation technique based on noise

In this paper, a new RF modulation technique is presented. Instead of using sinusoidal carriers as information bearer, pure noise is applied. This allows very simple radio architectures to be used. Spread-spectrum based technology is applied to modulate the noise bearer. Since the transmission bandwidth of the noise bearer can be made very wide, up to ultra-wideband regions, extremely large processing gains can be obtained. This will provide robustness in interference-prone environments. To avoid the local regeneration of the noise reference at the receiver, the Transmit-Reference (TR) concept is applied. In this concept, both the reference noise signal and the modulated noise signal are transmitted, together forming\ud the bearer. The reference and modulated signals are separated by applying a time offset. By applying different delay times for different channels (users) a new multiple access scheme results based on delay: Delay Division Multiple Access (DDMA). A theoretical analysis is given for the link performance of a single-user and a multi-user system. A testbed has been built to demonstrate the concept. The demonstrator operates in a 50 MHz bandwidth centered at 2.4 GHz. Processing gains ranging from 10¿30 dB have been tested. The testbed confirms the basic behavior as predicted by the theory

A low-cost time-hopping impulse radio system for high data rate transmission

We present an efficient, low-cost implementation of time-hopping impulse radio that fulfills the spectral mask mandated by the FCC and is suitable for high-data-rate, short-range communications. Key features are: (i) all-baseband implementation that obviates the need for passband components, (ii) symbol-rate (not chip rate) sampling, A/D conversion, and digital signal processing, (iii) fast acquisition due to novel search algorithms, (iv) spectral shaping that can be adapted to accommodate different spectrum regulations and interference environments. Computer simulations show that this system can provide 110Mbit/s at 7-10m distance, as well as higher data rates at shorter distances under FCC emissions limits. Due to the spreading concept of time-hopping impulse radio, the system can sustain multiple simultaneous users, and can suppress narrowband interference effectively.Comment: To appear in EURASIP Journal on Applied Signal Processing (Special Issue on UWB - State of the Art

Ultra Wideband Communications: from Analog to Digital

Ultrabreitband-Signale (Ultra Wideband [UWB]) können einen signifikanten Nutzen im Bereich drahtloser Kommunikationssysteme haben. Es sind jedoch noch einige Probleme offen, die durch Systemdesigner und Wissenschaftler gelöst werden müssen. Ein Funknetzsystem mit einer derart großen Bandbreite ist normalerweise auch durch eine große Anzahl an Mehrwegekomponenten mit jeweils verschiedenen Pfadamplituden gekennzeichnet. Daher ist es schwierig, die zeitlich verteilte Energie effektiv zu erfassen. Außerdem ist in vielen Fällen der naheliegende Ansatz, ein kohärenter Empfänger im Sinne eines signalangepassten Filters oder eines Korrelators, nicht unbedingt die beste Wahl. In der vorliegenden Arbeit wird dabei auf die bestehende Problematik und weitere Lösungsmöglichkeiten eingegangen. Im ersten Abschnitt geht es um „Impulse Radio UWB”-Systeme mit niedriger Datenrate. Bei diesen Systemen kommt ein inkohärenter Empfänger zum Einsatz. Inkohärente Signaldetektion stellt insofern einen vielversprechenden Ansatz dar, als das damit aufwandsgünstige und robuste Implementierungen möglich sind. Dies trifft vor allem in Anwendungsfällen wie den von drahtlosen Sensornetzen zu, wo preiswerte Geräte mit langer Batterielaufzeit nötigsind. Dies verringert den für die Kanalschätzung und die Synchronisation nötigen Aufwand, was jedoch auf Kosten der Leistungseffizienz geht und eine erhöhte Störempfindlichkeit gegenüber Interferenz (z.B. Interferenz durch mehrere Nutzer oder schmalbandige Interferenz) zur Folge hat. Um die Bitfehlerrate der oben genannten Verfahren zu bestimmen, wurde zunächst ein inkohärenter Combining-Verlust spezifiziert, welcher auftritt im Gegensatz zu kohärenter Detektion mit Maximum Ratio Multipath Combining. Dieser Verlust hängt von dem Produkt aus der Länge des Integrationsfensters und der Signalbandbreite ab. Um den Verlust durch inkohärentes Combining zu reduzieren und somit die Leistungseffizienz des Empfängers zu steigern, werden verbesserte Combining-Methoden für Mehrwegeempfang vorgeschlagen. Ein analoger Empfänger, bei dem der Hauptteil des Mehrwege-Combinings durch einen „Integrate and Dump”-Filter implementiert ist, wird für UWB-Systeme mit Zeit-Hopping gezeigt. Dabei wurde die Einsatzmöglichkeit von dünn besetzten Codes in solchen System diskutiert und bewertet. Des Weiteren wird eine Regel für die Code-Auswahl vorgestellt, welche die Stabilität des Systems gegen Mehrnutzer-Störungen sicherstellt und gleichzeitig den Verlust durch inkohärentes Combining verringert. Danach liegt der Fokus auf digitalen Lösungen bei inkohärenter Demodulation. Im Vergleich zum Analogempfänger besitzt ein Digitalempfänger einen Analog-Digital-Wandler im Zeitbereich gefolgt von einem digitalen Optimalfilter. Der digitale Optimalfilter dekodiert den Mehrfachzugriffscode kohärent und beschränkt das inkohärente Combining auf die empfangenen Mehrwegekomponenten im Digitalbereich. Es kommt ein schneller Analog-Digital-Wandler mit geringer Auflösung zum Einsatz, um einen vertretbaren Energieverbrauch zu gewährleisten. Diese Digitaltechnik macht den Einsatz langer Analogverzögerungen bei differentieller Demodulation unnötig und ermöglicht viele Arten der digitalen Signalverarbeitung. Im Vergleich zur Analogtechnik reduziert sie nicht nur den inkohärenten Combining-Verlust, sonder zeigt auch eine stärkere Resistenz gegenüber Störungen. Dabei werden die Auswirkungen der Auflösung und der Abtastrate der Analog-Digital-Umsetzung analysiert. Die Resultate zeigen, dass die verminderte Effizienz solcher Analog-Digital-Wandler gering ausfällt. Weiterhin zeigt sich, dass im Falle starker Mehrnutzerinterferenz sogar eine Verbesserung der Ergebnisse zu beobachten ist. Die vorgeschlagenen Design-Regeln spezifizieren die Anwendung der Analog-Digital-Wandler und die Auswahl der Systemparameter in Abhängigkeit der verwendeten Mehrfachzugriffscodes und der Modulationsart. Wir zeigen, wie unter Anwendung erweiterter Modulationsverfahren die Leistungseffizienz verbessert werden kann und schlagen ein Verfahren zur Unterdrückung schmalbandiger Störer vor, welches auf Soft Limiting aufbaut. Durch die Untersuchungen und Ergebnissen zeigt sich, dass inkohärente Empfänger in UWB-Kommunikationssystemen mit niedriger Datenrate ein großes Potential aufweisen. Außerdem wird die Auswahl der benutzbaren Bandbreite untersucht, um einen Kompromiss zwischen inkohärentem Combining-Verlust und Stabilität gegenüber langsamen Schwund zu erreichen. Dadurch wurde ein neues Konzept für UWB-Systeme erarbeitet: wahlweise kohärente oder inkohärente Empfänger, welche als UWB-Systeme Frequenz-Hopping nutzen. Der wesentliche Vorteil hiervon liegt darin, dass die Bandbreite im Basisband sich deutlich verringert. Mithin ermöglicht dies einfach zu realisierende digitale Signalverarbeitungstechnik mit kostengünstigen Analog-Digital-Wandlern. Dies stellt eine neue Epoche in der Forschung im Bereich drahtloser Sensorfunknetze dar. Der Schwerpunkt des zweiten Abschnitts stellt adaptiven Signalverarbeitung für hohe Datenraten mit „Direct Sequence”-UWB-Systemen in den Vordergrund. In solchen Systemen entstehen, wegen der großen Anzahl der empfangenen Mehrwegekomponenten, starke Inter- bzw. Intrasymbolinterferenzen. Außerdem kann die Funktionalität des Systems durch Mehrnutzerinterferenz und Schmalbandstörungen deutlich beeinflusst werden. Um sie zu eliminieren, wird die „Widely Linear”-Rangreduzierung benutzt. Dabei verbessert die Rangreduzierungsmethode das Konvergenzverhalten, besonders wenn der gegebene Vektor eine sehr große Anzahl an Abtastwerten beinhaltet (in Folge hoher einer Abtastrate). Zusätzlich kann das System durch die Anwendung der R-linearen Verarbeitung die Statistik zweiter Ordnung des nicht-zirkularen Signals vollständig ausnutzen, was sich in verbesserten Schätzergebnissen widerspiegelt. Allgemeine kann die Methode der „Widely Linear”-Rangreduzierung auch in andern Bereichen angewendet werden, z.B. in „Direct Sequence”-Codemultiplexverfahren (DS-CDMA), im MIMO-Bereich, im Global System for Mobile Communications (GSM) und beim Beamforming.The aim of this thesis is to investigate key issues encountered in the design of transmission schemes and receiving techniques for Ultra Wideband (UWB) communication systems. Based on different data rate applications, this work is divided into two parts, where energy efficient and robust physical layer solutions are proposed, respectively. Due to a huge bandwidth of UWB signals, a considerable amount of multipath arrivals with various path gains is resolvable at the receiver. For low data rate impulse radio UWB systems, suboptimal non-coherent detection is a simple way to effectively capture the multipath energy. Feasible techniques that increase the power efficiency and the interference robustness of non-coherent detection need to be investigated. For high data rate direct sequence UWB systems, a large number of multipath arrivals results in severe inter-/intra-symbol interference. Additionally, the system performance may also be deteriorated by multi-user interference and narrowband interference. It is necessary to develop advanced signal processing techniques at the receiver to suppress these interferences. Part I of this thesis deals with the co-design of signaling schemes and receiver architectures in low data rate impulse radio UWB systems based on non-coherent detection.● We analyze the bit error rate performance of non-coherent detection and characterize a non-coherent combining loss, i.e., a performance penalty with respect to coherent detection with maximum ratio multipath combining. The thorough analysis of this loss is very helpful for the design of transmission schemes and receive techniques innon-coherent UWB communication systems.● We propose to use optical orthogonal codes in a time hopping impulse radio UWB system based on an analog non-coherent receiver. The “analog” means that the major part of the multipath combining is implemented by an integrate and dump filter. The introduced semi-analytical method can help us to easily select the time hopping codes to ensure the robustness against the multi-user interference and meanwhile to alleviate the non-coherent combining loss.● The main contribution of Part I is the proposal of applying fully digital solutions in non-coherent detection. The proposed digital non-coherent receiver is based on a time domain analog-to-digital converter, which has a high speed but a very low resolution to maintain a reasonable power consumption. Compared to its analog counterpart, itnot only significantly reduces the non-coherent combining loss but also offers a higher interference robustness. In particular, the one-bit receiver can effectively suppress strong multi-user interference and is thus advantageous in separating simultaneously operating piconets.The fully digital solutions overcome the difficulty of implementing long analog delay lines and make differential UWB detection possible. They also facilitate the development of various digital signal processing techniques such as multi-user detection and non-coherent multipath combining methods as well as the use of advanced modulationschemes (e.g., M-ary Walsh modulation).● Furthermore, we present a novel impulse radio UWB system based on frequency hopping, where both coherent and non-coherent receivers can be adopted. The key advantage is that the baseband bandwidth can be considerably reduced (e.g., lower than 500 MHz), which enables low-complexity implementation of the fully digital solutions. It opens up various research activities in the application field of wireless sensor networks. Part II of this thesis proposes adaptive widely linear reduced-rank techniques to suppress interferences for high data rate direct sequence UWB systems, where second-order non-circular signals are used. The reduced-rank techniques are designed to improve the convergence performance and the interference robustness especially when the received vector contains a large number of samples (due to a high sampling rate in UWB systems). The widely linear processing takes full advantage of the second-order statistics of the non-circular signals and enhances the estimation performance. The generic widely linear reduced-rank concept also has a great potential in the applications of other systems such as Direct Sequence Code Division Multiple Access (DS-CDMA), Multiple Input Multiple Output (MIMO) system, and Global System for Mobile Communications (GSM), or in other areas such as beamforming

UWB System Performance Improvement Using Smart Interference Rejection Filter

In this paper we proposed a smart interference rejection filter in TH-PPM UWB system, which improves the system\'s error probability for an order of magnitude in case of high power OFDM interference. The smart filter is based on an adaptive transversal filter. Based on the fulfillment of certain conditions, the filter activates or deactivates some parts of it

A General Framework for Analyzing, Characterizing, and Implementing Spectrally Modulated, Spectrally Encoded Signals

Fourth generation (4G) communications will support many capabilities while providing universal, high speed access. One potential enabler for these capabilities is software defined radio (SDR). When controlled by cognitive radio (CR) principles, the required waveform diversity is achieved via a synergistic union called CR-based SDR. Research is rapidly progressing in SDR hardware and software venues, but current CR-based SDR research lacks the theoretical foundation and analytic framework to permit efficient implementation. This limitation is addressed here by introducing a general framework for analyzing, characterizing, and implementing spectrally modulated, spectrally encoded (SMSE) signals within CR-based SDR architectures. Given orthogonal frequency division multiplexing (OFDM) is a 4G candidate signal, OFDM-based signals are collectively classified as SMSE since modulation and encoding are spectrally applied. The proposed framework provides analytic commonality and unification of SMSE signals. Applicability is first shown for candidate 4G signals, and resultant analytic expressions agree with published results. Implementability is then demonstrated in multiple coexistence scenarios via modeling and simulation to reinforce practical utility

Spektralno-efikasna zelena bežična komunikacija pomoću kognitivnog UWB signalnog modela

This paper focuses on spectral lines suppression for non-coherent impulse-radio ultra-wideband (IR-UWB) signals in the presence of pulse attenuation and timing jitter. Particular attention is devoted to severely unbalanced (i.e. non-uniform distributed) data sources where a unified spectral analysis is considered for both uncorrelated and correlated M-ary biorthogonal data-stream scenarios. Indeed, the specific novelty insights of this paper are as follows: i) Proposal of a new spectral-efficient signal model as a modified version of transmitted-reference (TR) approach, where each transmitted symbol is represented by a preamble Data-based Statistical Reference (DSR) followed by a set of transmitted data pulses and within this context, the preamble signal is designed to eliminate spectral lines via an adaptive monitoring of data-stream statistics as the optimal spectral policy; ii) Performance analysis in order to derive optimal signal parameters; iii) Evaluation of the system capabilities over different predefined operational modes.Ovaj rad se fokusira na prigušenje spektralnih linija kod ne-koherentnih radio-impulsnih ultra-širokopojasnih (IR-UWB) signala prilikom slabljenja pulsa i vremenskog podrhtavanja. Posebna pažnja je pridana značajno neuravnoteženim (npr. ne-unifornmno distribuiranim) izvorima podataka gdje je jedinstvena spektralna analiza razmatrana za nekorelirane i korelirane M-arne biortogonalne scenarije prijenosa podataka. Novine predstavljene u ovom radu su: i) Novi spektralno-efikasni signalni model koji je modificirana verzija pristupa prijenosom-reference (TR), gdje se svaki preneseni simbol prikazuje pomoću preambule definirane statistikom reference podataka (DSR) koju slijedi skup prenesenih podatkovnih pulseva, te je u tom kontekstu preambula signala dizajnirana kako bi se eliminirale spektralne linije pomoću optimalnog spektralnog kriterija definiranog adaptivnim praćenjem statistike poslanih podataka; ii) Analiza performansi kako bi se dobili optimalni parametri signala i iii) Evaluacija sposobnosti sustava prilikom rada u različitim predefiniranim stanjima

Performance Enhancement of Ultra Wideband WPAN using Narrowband Interference Mitigation Techniques

A new promising technique adopted by 4G community is ultra-wideband technology, which offers a solution for high bandwidth, high data rate, low cost, low power consumption, position location capability etc. A conventional type of UWB communication is impulse radio, where very short transient pulses are transmitted rather than a modulated carrier. Consequently, the spectrum is spread over several GHz, complying with the definition of UWB. Currently, the Rake receiver used for spread spectrum is considered a very promising candidate for UWB reception, due to its capability of collecting multipath components. Since UWB signals occupy such a large bandwidth, they operate as an overlay system with other existing narrowband (NB) radio systems overlapping with their bands. In order to ensure a robust communication link, the issue of coexistence and interference of UWB systems with current indoor wireless systems must be considered. Ultra Wideband technology with its application, advantages and disadvantages are discussed in detail. Design of UWB short pulse and a detail study IEEE 802.15.3a UWB channel models statistical characteristics have been analyzed through simulation. Simulation studies are performed and improved techniques are suggested for interference reduction in both Impulse Radio based UWB and Transmitted Reference type of UWB system. Modified TR-UWB receiver with UWB pulse design at transmitter end and notch filtering at receiver’s front end proved to be more efficient in single NBI, multiple NBI and WBI suppression. Extensive simulation studies to support the efficacy of the proposed schemes are carried out in the MATLAB. Bit error rate (BER) performance study for different data rates over different UWB channel models are also analyzed using proposed receiver models. Performance improvement of TR-UWB system is noticed using the proposed techniques

Transceiver design and system optimization for ultra-wideband communications

This dissertation investigates the potential promises and proposes possible solutions to the challenges of designing transceivers and optimizing system parameters in ultra-wideband (UWB) systems. The goal is to provide guidelines for UWB transceiver implementations under constraints by regulation, existing interference, and channel estimation. New UWB pulse shapes are invented that satisfy the Federal Communications Commission spectral mask. Parameters are designed to possibly implement the proposed pulses. A link budget is quantified based on an accurate frequency-dependent path loss calculation to account for variations across the ultra-wide bandwidth of the signal. Achievable information rates are quantified as a function of transmission distance over additive white Gaussian noise and multipath channels under specific UWB constraints: limited power spectral density, specific modulation formats, and a highly dispersive channel. The effect of self-interference (SI) and inter-symbol interference (ISI) on channel capacity is determined, and modulation formats that mitigate against this effect is identified. Spreading gains of familiar UWB signaling formats are evaluated, and UWB signals are proved to be spread spectrum. Conditions are formulated for trading coding gain with spreading gain with only a small impact on performance. Numerical results are examined to demonstrate that over a frequency-selective channel, the spreading gain may be beneficial in reducing the SI and ISI resulting in higher information rates. A reduced-rank adaptive filtering technique is applied to the problem of interference suppression and optimum combining in UWB communications. The reduced-rank combining method, in particular the eigencanceler, is proposed and compared with a minimum mean square error Rake receiver. Simulation results are evaluated to show that the performance of the proposed method is superior to the minimum mean square error when the correlation matrix is estimated from limited data. Impact of channel estimation on UWB system performance is investigated when path delays and path amplitudes are jointly estimated. Cramér-Rao bound (CRB) expressions for the variance of path delay and amplitude estimates are formulated using maximum likelihood estimation. Using the errors obtained from the CRB, the effective signal-to-noise ratio for UWB Rake receivers employing maximum ratio combining (MRC) is devised in the presence of channel path delay and amplitude errors. An exact expression of the bit error rate (BER) for UWB Rake receivers with MRC is derived with imperfect estimates of channel path delays and amplitudes. Further, this analysis is applied to design optimal transceiver parameters. The BER is used as part of a binary symmetric channel and the achievable information rates are evaluated. The optimum power allocation and number of symbols allocated to the pilot are developed with respect to maximizing the information rate. The optimal signal bandwidth to be used for UWB communications is determined in the presence of imperfect channel state information. The number of multipath components to be collected by Rake receivers is designed to optimize performance with non-ideal channel estimation