ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / A critical element of the proposed iNET architecture is the development of a telemetry network that provides two-way communication between multiple nodes on both the ground and in the air. Conventional airborne telemetry is based on IRIG-106 Chapter 4 and provides only a serial streaming data path from the aircraft to the ground. The network-centric architecture of iNET requires not only a duplex communication link between the ground and the test article, but also a communication link that provides higher bandwidth performance, higher spectrum efficiency, and a transport environment that is capable of fully packetized Internet Protocol. This paper describes the development path followed by TTC in the implementation of its nXCVR-2000G, an OFDM 802-11a-based iNET-ready IP transceiver.

Optical wireless communication (OWC) is a promising alternative to radio frequency (RF) communication with a significantly larger and unregulated spectrum. Impairments in the physical layer, such as the non-linear transfer characteristic of the transmitter, the dispersive optical wireless channel and the additive white Gaussian noise (AWGN) at the receiver, reduce the capacity of the OWC system. Single-carrier multi-level pulse position modulation (M-PPM) and multilevel pulse amplitude modulation (M-PAM) suffer from inter-symbol interference (ISI) in the dispersive channel which reduces their capacity even after channel equalization. Multi-carrier modulation such as optical orthogonal frequency division multiplexing (O-OFDM) with multilevel quadrature amplitude modulation (M-QAM) is known to maximize the channel capacity through bit and power loading. There are two general signal structures: bipolar Gaussian signal with a direct current (DC) bias, i.e. DC-biased O-OFDM (DCO-OFDM), or unipolar half- Gaussian signal, employing only the odd subcarriers, i.e. asymmetrically clipped O-OFDM (ACO-OFDM). In this thesis, the signal distortion from the transmitter nonlinearity is minimized through pre-distortion, optimum signal scaling and DC-biasing. The optical front-ends impose minimum, average and maximum optical power constraints, as well as an average electrical power constraint, on the information-carrying signals. In this thesis, the optical signals are conditioned within these constraints through optimum signal scaling and DC-biasing. The presented analysis of the optical-to-electrical (O/E) conversion enables the derivation of the electrical signal-to-noise ratio (SNR) at the receiver, including or excluding the additional DC bias power, which is translated into bit-error rate (BER) performance. In addition, a generalized piecewise polynomial model for the non-linear transfer characteristic of the transmitter is proposed. The non-linear distortion in O-OFDM is translated by means of the Bussgang theorem and the central limit theorem (CLT) into attenuation of the data-carrying subcarriers at the receiver plus zero-mean complex-valued Gaussian noise. The attenuation factor and the variance of the non-linear distortion noise are derived in closed form, and they are accounted towards the received electrical SNR. Through pre-distortion with the inverse of the proposed piecewise polynomial function, the linear dynamic range of the transmitter is maximized, reducing the non-linear distortion to double-sided signal clipping. Finally, the OWC schemes are compared in terms of spectral efficiency and electrical SNR requirement as the signal bandwidth exceeds the coherence bandwidth of the optical wireless channel for a practical 10 dB linear dynamic range. Through optimum signal scaling and DCbiasing, DCO-OFDM is found to achieve the highest spectral efficiency for a target SNR, neglecting the additional DC bias power. When the DC bias power is counted towards the signal power, DCO-OFDM outperforms PAM with linear equalization, approaching the performance of the more computationally intensive PAM with non-linear equalization. In addition, the average optical power in O-OFDM is varied over dynamic ranges of 10 dB, 20 dB and 30 dB. When the additional DC bias power is neglected, DCO-OFDM is shown to achieve the Shannon capacity, while ACO-OFDM exhibits a 3 dB gap which grows with higher SNR targets. When the DC bias power is included, DCO-OFDM outperforms ACO-OFDM for the majority of average optical power levels with the increase of the SNR target or the dynamic range.

Relay techniques have the potential to enhance capacity and coverage of a wireless network. Due to rapidly increasing number of smart phone subscribers and high demand for data intensive multimedia applications, the useful radio spectrum is becoming a scarce resource. For this reason, two way relay network and cognitive radio technologies are required for better utilization of radio spectrum. Compared to the conventional one way relay network, both the uplink and the downlink can be served simultaneously using a two way relay network. Hence the effective bandwidth efficiency is considered to be one time slot per transmission. Cognitive networks are wireless networks that consist of different types of users, a primary user (PU, the primary license holder of a spectrum band) and secondary users (SU, cognitive radios that opportunistically access the PU spectrum). The secondary users can access the spectrum of the licensed user provided they do not harmfully affect to the primary user. In this thesis, various resource allocation and optimization techniques have been investigated for wireless relay and cognitive radio networks.

In today’s modern society, we are surrounded by a multitude of digital devices.The number of available digital devices is set to grow even more. As the trendcontinues, product life-cycle is a major issue in mass production of these devices.Testing and verification is responsible for a significant percentage of the productioncost of digital devices. Time efficient procedures for testing and characterization aretherefore sought for. Moreover, the need for flexible and low-cost solutions in thedesign architecture of radio frequency devices coupled with the demand for highdata rate has presented a challenge caused by interferences from the analog circuitparts. Study of digital signal processing based techniques which would alleviate theeffects of the analog impairments is therefore a pertinent subject. In the first part of this thesis, we address parameter estimation based on wave-form fitting. We look at the sinewave model for parameter estimation which iseventually used to characterize the performance of a device. The underlying goal isto formulate and analyze a set of new parameter estimators which provide a moreaccurate estimate than well known estimators. Specifically, we study the maximum-likelihood (ML) SNR estimator employing the three-parameter sine fit and derivealternative estimator based on its statistical distribution. We show that the meansquare error (MSE) of the alternative estimators is lower than the MSE of the MLestimator for a small sample size and a few of the new estimators are very close tothe Cramér-Rao lower bound (CRB). Simply put, the number of acquired measure-ment samples translate to measurement time, implying that the fewer the numberof samples required for a given accuracy, the faster the test would be. We alsostudy a sub-sampling approach for frequency estimation problem in a dual channelsinewave model with common frequency. Coprime subsampling technique is usedwhere the signals from both channels are uniformly subsampled with coprime pairof sparse samplers. Such subsampling technique is especially beneficial to lower thesampling frequency required in applications with high bandwidth requirement. TheCRB based on the co-prime subsampled data set is derived and numerical illus-trations are given showing the relation between the cost in performance based onthe mean squared error and the employed coprime factors for a given measurementtime. In the second part of the thesis, we deal with the problem of phase-noise (PHN).First, we look at a scheme in orthogonal frequency-division multiplexing (OFDM)system where pilot subcarriers are employed for joint PHN compensation, channelestimation and symbol detection. We investigate a method where the PHN statis-tics is approximated by a finite number of vectors and design a PHN codebook. Amethod of selecting the element in the codebook that is closest to the current PHNrealization with the corresponding channel estimate is discussed. We present simula-tion results showing improved performance compared to state-of-the art techniques.We also look at a sequential Monte-Carlo based method for combined channel im-pulse response and PHN tracking employing known OFDM symbols. Such techniqueallows time domain compensation of PHN such that simultaneous cancellation ofthe common phase error and reduction of the inter-carrier interference occurs. / <p>QC 20150529</p>

The growing demand for wireless communication capacity and the overutilisation of the conventional radio frequency (RF) spectrum have inspired research into using alternative spectrum regions for communication. Using optical wireless communications (OWC), for example, offers significant advantages over RF communication in terms of higher bandwidth, lower implementation costs and energy savings. In OWC systems, the information signal has to be real and non-negative. Therefore, modifications to the conventional communication algorithms are required. Multicarrier modulation schemes like orthogonal frequency division multiplexing (OFDM) promise to deliver a more efficient use of the communication capacity through adaptive bit and energy loading techniques. Three OFDM-based schemes – direct-current-biased OFDM (DCO-OFDM), asymmetrically clipped optical OFDM(ACO-OFDM), and pulse-amplitude modulated discrete multitone (PAM-DMT) – have been introduced in the literature. The current work investigates the recently introduced scheme subcarrier-index modulation OFDM as a potential energy-efficient modulation technique with reduced peak-to-average power ratio (PAPR) suitable for applications in OWC. A theoretical model for the analysis of SIM-OFDMin a linear additive white Gaussian noise (AWGN) channel is provided. A closed-form solution for the PAPR in SIM-OFDM is also proposed. Following the work on SIM-OFDM, a novel inherently unipolar modulation scheme, unipolar orthogonal frequency division multiplexing (U-OFDM), is proposed as an alternative to the existing similar schemes: ACO-OFDMand PAM-DMT. Furthermore, an enhanced U-OFDMsignal generation algorithm is introduced which allows the spectral efficiency gap between the inherently unipolar modulation schemes – U-OFDM, ACO-OFDM, PAM-DMT – and the conventionally used DCO-OFDM to be closed. This results in an OFDM-based modulation approach which is electrically and optically more efficient than any other OFDM-based technique proposed so far for intensity modulation and direct detection (IM/DD) communication systems. Non-linear distortion in the optical front-end elements is one of the major limitations for high-speed communication in OWC. This work presents a generalised approach for analysing nonlinear distortion in OFDM-based modulation schemes. The presented technique leads to a closed-form analytical solution for an arbitrary memoryless distortion of the information signal and has been proven to work for the majority of the known unipolar OFDM-based modulation techniques - DCO-OFDM, ACO-OFDM, PAM-DMT and U-OFDM. The high-speed communication capabilities of novel Gallium Nitride based μm-sized light emitting diodes (μLEDs) are investigated, and a record-setting result of 3.5Gb/s using a single 50-μm device is demonstrated. The capabilities of using such devices at practical transmission distances are also investigated, and a 1 Gb/s link using a single device is demonstrated at a distance of up to 10m. Furthermore, a proof-of-concept experiment is realised where a 50-μm LED is successfully modulated using U-OFDM and enhanced U-OFDM to achieve notable energy savings in comparison to DCO-OFDM.

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No. of bitstreams: 1 Diss_Helder_Robelcio_Junior.pdf: 2504827 bytes, checksum: 6687d65850121aa2895c1fa972749363 (MD5) Previous issue date: 2017-08-30 / Conselho Nacional de Pesquisa e Desenvolvimento Cient?fico e Tecnol?gico - CNPq / The wireless communication channel has severe signal degradation effects resulting from the usual multiplicity of propagation paths originated by reflection of the electromagnetic wave at specific points along the path of the digital transmitter-receiver link. Metallic building structures, for example, are points of reflection of the wave. This multiplicity of propagation paths, called multipath, generates signal interference on itself when multiple signals arrive at the receiver, degrading signal intelligibility, which increases the bit error rates of the link, reducing a reliability. This interference is called intersymbol interference (ISI) because, in the baseband signal at the receiver, overlapping of the digital modulation symbols occurs, resulting in a failure to detect the binary words associated with the symbols. In this context, the channel estimation and compensation process plays an important role in the wireless receiver. The increasing demand for systems with higher transmission capacities, robustness and less computational complexity, has driven several researches in the scope of the algorithms used in the channel estimation process. In recent years, data transmission technique through Orthogonal Frequency Division Multiplexing (OFDM) has been highlighted by resistance to ISI, good spectral efficiency and transmission capacity of high data rates. OFDM is a multi-carrier modulation technique that consists of dividing the total bandwidth into smaller subchannels by using orthogonal subcarriers spectrally superimposed. Despite its robustness, it is still required channel estimation techniques, in OFDM receiver, due to the multipath effect characteristic of a wireless communication channel. This work proposes the implementation of a channel estimator, based on a complex Radial Basis Function (RBF) network. The proposed network is trained from the impulse response of the channel obtained through the pilot carriers sent and known by the receiver. The simulation results show that the proposed network obtained better results than the classical estimators used for channel estimation in OFDM systems. / O canal de comunica??o sem fio (wireless) apresenta severos efeitos de degrada??o de sinal resultantes da usual multiplicidade de caminhos de propaga??o originados por reflex?o da onda eletromagn?tica em pontos espec?ficos ao longo do caminho do enlace entre transmissor e receptor digital. Estruturas met?licas de constru??es civis, por exemplo, constituem pontos de reflex?o da onda. Esta multiplicidade de caminhos de propaga??o, denominada multipercurso, gera interfer?ncia do sinal sobre ele mesmo quando os m?ltiplos sinais chegam ao receptor, degradando a inteligibilidade do sinal recebido em consequ?ncia dos m?ltiplos ecos do sinal, o que aumenta a taxa de erro de bits do enlace, reduzindo a confiabilidade. Denomina-se esta interfer?ncia de interfer?ncia intersimb?lica (ISI, do ingl?s intersymbol interference) porque, no sinal em banda-base no receptor, ocorre superposi??o dos s?mbolos da modula??o digital, resultando em falha na detec??o das palavras bin?rias associadas aos s?mbolos. Neste contexto, o processo de estima??o e compensa??o dos efeitos do canal desempenha um papel importante em um receptor de comunica??o wireless. A crescente demanda por sistemas de maiores capacidades de transmiss?o, robustez e menor complexidade computacional, tem impulsionado v?rias pesquisas no ?mbito dos algoritmos utilizados no processo de estima??o de canal. Nos ?ltimos anos a t?cnica de transmiss?o de dados atrav?s da Multiplexa??o por Divis?o Ortogonal de Frequ?ncia (OFDM) tem ganhado destaque por apresentar resist?ncia ? ISI, boa efici?ncia espectral e capacidade de transmiss?o de altas taxas de dados. OFDM ? uma t?cnica de modula??o por multiportadoras que consiste na divis?o da largura de banda total em subcanais menores, utilizando subportadoras ortogonais sobrepostas espectralmente. N?o obstante a sua robustez, faz-se ainda necess?rio aplicar t?cnicas de estima??o de canal no receptor OFDM, devido ao efeito de m?ltipercurso caracter?stico de um canal de comunica??o wireless. Neste trabalho ? proposto a implementa??o de um estimador de canal, baseado em uma rede neural com fun??o de base radial (RBF, do ingl?s Radial Basis Function) complexa. A rede proposta ? treinada a partir da resposta ao impulso do canal obtida atrav?s de portadoras piloto enviadas e conhecidas pelo receptor. Os resultados da simula??o mostram que a rede proposta obteve melhores resultados do que os estimadores cl?ssicos utilizados para estima??o de canal em sistemas OFDM.

Due to the ever increasing dependency on existing wireless technologies and the growing usage of sophisticated wireless devices, the demand for bandwidth is rising exponentially. Also, the Federal Communications Commission (FCC) has reserved a considerable amount of spectrum for licensed users. As a result, the unlicensed spectrum usage is constrained to the overcrowded unlicensed spectrum. Various spectral management surveys have indicated inefficient spectrum utilization in the licensed spectral bands. The congested unlicensed spectrum and inefficiently used licensed frequency bands calls for an approach to use the available spectrum opportunistically. Therefore, the concept of "Spectrum Pooling", which is based on Dynamic Spectrum Access (DSA), was proposed to make the unused sections of licensed spectrum available to the unlicensed users. In Spectrum Pooling, an empty section of licensed spectrum is borrowed by a secondary user for certain period of time without interfering with the licensed user. Orthogonal Frequency Division Multiplexing (OFDM) is a transmission scheme that is a candidate for Spectrum Pooling since it is capable of forming an adaptive spectral shape that allows coexistence of licensed and unlicensed users while attemting to minimize any interference. Subcarriers in the OFDM signal can be deactivated to generate Non-Contiguous OFDM (NC-OFDM). Even though NC-OFDM allows efficient use of available spectrum, it causes out of band (OOB) radiation, which adversely affects the performance of adjacent user. This thesis presents two novel techniques for combat the effects of OOB radiation generated by NC-OFDM. The proposed techniques employ a filtering-based approach combined with the technique of windowing in order to suppress the unwanted sidelobes by around 35dB-40dB. The attenuation is achieved without affecting other transmission parameters of the secondary user significantly.

Land mobile radio technology (LMR) has existed since the early 1920's. The most visible manifestation of this technology is the handheld VHF/UHF radios also referred to as 'walkie-talkie'. These handheld devices are one of the most ubiquitous forms of radio communication systems. Most of them are designed for transmitting analog voice signals. Due to an increase in the amount of digitized analog signals over the past few years complemented by a need for transmitting pure digital data, there has been a desire to transmit digital data. There are methods which allow the analog radios to transmit digital data without any modifications; however the data rate achievable using these methods is very low. In contrast, the digital variants of these hand-held radios are capable of transmitting digital data at comparatively higher data rates. However they are expensive and require major infrastructure overhauls. In this thesis, a prototype modem was developed which interfaces with an analog radio without any modifications to the radio. Furthermore, the data rates achievable are comparable with those achieved using digital radios. The modem uses Orthogonal Frequency Division Multiplexing (OFDM) technique to generate an audio band signal which is fed to the radio. The OFDM technique used to generate the audio band signal from data bits ensures maximum bandwidth efficiency. The developed modem is capable of communicating over Ethernet connection. It uses a RJ 45 interface to connect to a data source.

Water occupies three fourth of earth's surface. The remaining one fourth is land. Although human habitats reside on land, there is no denying of the vital connection between land and water. The future sustainability of human species on this planet depends on wise utilization of all available resources, including that provided by the vast water world. Therefore, it is imperative to explore, understand, and define this massive, varying, and in many areas, unexplored water domain. The water domain exploration and data collection can be conducted using manned or unmanned vehicles, as allowed by the water environment. This dissertation addresses three of the key difficulties that occur during underwater acoustic communication among manned and/or unmanned vehicles and proposes feasible solutions to resolve those difficulties. The focus and the contributions of this research involve the following perspectives: 1) Representation of Underwater Acoustic Communication (UAC) Channels: Providing a comprehensive classification and representation of the underwater acoustic communication channel based on the channel environment. 2) Estimation and Compensation of Doppler Shift: Providing compensation algorithm to mitigate varying Doppler shift effect over subcarriers in UAC Orthogonal Frequency Division Multiplexing (OFDM) systems. 3) Mitigation of Inter-symbol Interference (ISI): Providing feasible solution to long delay spread causing ISI in Ultra-wideband channels.

Zugl.: Dresden, Techn. Univ., Diss., 2007