Time-Varying Components for Enhancing Wireless Transfer of Power and Information

Temporal modulation of components of electromagnetic systems provides an exceptional opportunity to engineer the response of those systems in a desired fashion, both in the time and frequency domains. For engineering time-modulated systems, one needs to thoroughly study the basic concepts and understand the salient characteristics of temporal modulation. In this paper, we carefully study physical models of basic bulk circuit elements—capacitors, inductors, and resistors—as frequency dispersive and time-varying components and study their effects in the case of periodical time modulations. We develop a solid theory for understanding these elements, and apply it to two important applications: wireless power transfer and antennas. For the first application, we show that, by periodically modulating the mutual inductance between the transmitter and receiver, the fundamental limits of classical wireless power transfer systems can be overcome. Regarding the second application, we consider a time-varying source for electrically small dipole antennas and show how time modulation can enhance the antenna performance. The developed theory of electromagnetic systems engineered by temporal modulation is applicable from radio frequencies to optical wavelengths.

Optical Signal Processing and Pulse Shaping for Wavelength Multiplexed High Speed Communication Systems

Mohammad Amin Shoaie

The steady growth of capacity demand in telecommunication networks has sparked the development of various photonic devices for ultrafast optical signal processing functions to meet the requirements of future flexible fiber networks in general and backbone in particular. Although these photonic devices expand the electrical bandwidth operation, they mostly operate at single wavelength and hence remain non-viable solutions for practical implementation in WDMnetworks that are considered as the major technology for high speed communications. Another key challenge of future optical networks is the ability tomerge channels in time and frequency domain in the most efficient way in order to reach the theoretical Nyquist limit of transmission links. A promising technique is the use of sinc-shaped Nyquist pulses that enable multiplexing channels in time domain with no inter-symbol interference (ISI) while exhibiting a rectangular spectrumthat alleviates the need for guard-band. The sinc pulse is indeed the basic building block in most theoretical papers that have estimated overall capacity limits, and intense efforts are being made to generate optical Nyquist pulses beyond the limit of electronics that can directly be used at the physical layer. Within the above context, two approaches, referred to as optical signal processing of WDM networks and generation/detection of Nyquist superchannels, have been studied in this thesis. The first addressed problem is simultaneous signal processing of WDMchannels. We present two principal blocks required for routing and transporting data in WDM networks, both based on dual-pump fiber optical parametric amplifier (FOPA) with (sinusoidally) modulated pumps. We show that this scheme can be designed to operate simultaneously on WDM channels at any desired wavelength range. The former block enables simultaneous wavelength conversion and time compression which is a necessary functionality in connecting dissimilar rate WDM networks. The latter processing block is all-optical 3R regeneration (reamplification, reshaping, retiming) which is crucial for maintaining pulse quality along long-haul WDMlinks. We use theoretical analysis supported by experimental results to demonstrate the efficiency of the proposed technique. The second problem that we investigate is the generation and detection of WDM-Nyquist superchannels. We developed a simple technique based onMach-Zehnder modulators (MZM) to generate a sinc-shaped Nyquist time window by direct synthesis of a rectangular, phase locked frequency comb. We show the produced pulses have exceptional quality as well as high tunability in terms of pulse width and repetition rate. We also further demonstrate a noncoherent method based on the proposed technique to performreal-time demultiplexing of WDM-Nyquist superchannels, simultaneously in time and frequency. The experimental results that are proved by mathematical analysis are employed to demonstrate the effectiveness of the proposed methods.

EPFL2016

Efficient error correction solutions for OFDM based digital video

Mauro Lattuada

The robustness of the delivery of digital compressed video streams has always been one of the main topic of the standardization bodies to assure the Quality of the Service (QoS). The MPEG standard which is nowadays the reference for digital television defines how to format the various component parts of a multimedia program and how they are combined into a single transmission bit stream. Although the MPEG stream may be directly used over a wide variety of media, it may also be used over a communication network and it is already packetized into short data packets. The multiplexed stream can be transmitted over a variety of communication networks such as Radio Frequency links (UHF/VHF), Digital Satellite links, Cable TV Networks, Standard Terrestrial Communication Links (PDH, SDH) or Packet/Cell Links (ATM, IP, IPv6, Ethernet). In critical and error prone channels the robustness of the stream has to be granted by employing strong error correction schemes. Depending on the used media the transmission has its own coding scheme and modulation methods designed for the particular environment. For example, in the case of IP based links the transfer protocol accepts loss of data and the problem can be easily overcome by retransmission. Wireless simplex transmission cannot exploit the same approach. Wireless transmission always means variable channel conditions especially when one or both terminals are moving on the outfield. The channel fading evolution and the signal impairments increase the error rate and corrupt the data. In the recent past the standardization of the DVB-T shows the possibility to provide a robust service for digital video delivery. This standard provides superior picture quality with the opportunity to view pictures in standard format or wide screen (4/3 or 16/9) formats, services including subtitling, multiple audio tracks, interactive content, multimedia content where, for instance, programs may be linked to world wide web material. Beside the provided services and features the standard offers also a modulation and transmission scheme capable to cope with the impairments of the terrestrial channel and to provide a BER after forward-error correction below 10-12. Unfortunately, these performances are guaranteed only for fixed reception, since the standard was originally aimed to replace classical analog television broadcasting in the UHF band. This thesis addresses the study of enhanced error-correction schemes in the scope of a compact, flexible and robust high-throughput real time video transmission system able to cope with high mobility channels. The study of a transmission system and error correction scheme tailored for this kind of application is here presented. The system exploits the OFDM modulation technique. This modulation scheme has already proven to be very effective in hostile environments. A flexible modulation scheme is employed to obtain variable bandwidth transmission and enhanced performances especially for mobile applications. The main topic of this research is the study of an effective error correction scheme adapted to this application. While nowadays the digital television standards use a concatenated error correction scheme based on convolutional inner coder, in this work the proposed solution is based on a turbo inner coder. Turbo codes has already shown good performances compared to convolutional codes. These results are here applied to a concatenated scheme to obtain very low BER. A comparison of the performances of various turbo coding techniques under certain implementation constraints is done in this work.The second element of the error correction scheme is the channel interleaver used to average the channel fading in time and frequency. This mechanism is conceived to be adapted to the modulated bandwidth and is optimized for high throughput real time video. This study shows that the proposed system proves to be very effective in high mobile channels because of the deep averaging strategies in conjunction with the high efficiency turbo based concatenated error correction scheme.

EPFL2005

Computational Analysis and Methods for Electromagnetic Exposure Limits, Antenna Optimization and Cell Phone Design

Chen Xi Lin

In recent years, the advancements of wireless technologies have led to rapid developments in the field of telecommunication, power delivery and bio-medical applications. During the evolution of a wireless technology, the electromagnetic compatibility (EMC) between a radiating source (e.g., an antenna) and nearby active or passive elements (e.g., a closely integrated electronic component or a human body) often introduces challenging design requirements. This thesis focuses on the applications of state-of-the-art computational electromagnetic compatibility (CEMC) techniques in multidisciplinary engineering design tasks, with an emphasis on computational bio-electromagnetic compatibility (CBEMC). The analyses reported in this thesis span practical applications from power frequency (Hz) to radio frequency (GHz), providing research outcomes which significantly benefit the understandings of low-frequency human body exposure safety and radio-frequency antenna integration and optimization. The research aspect of the thesis is initiated with a thorough review of the existing low-frequency exposure safety guidelines recommended by international regulatory committees. The subsequent analyses suggest essential scientific basis for the update and revision of the existing exposure limits. Practical exposure scenarios (e.g., magnetic resonant wireless power transfer) are investigated with novel assessment techniques. Subsequently, a computer-aided optimization scheme based on network-distributed genetic algorithms is applied to highly detailed numerical mobile phone model and human body phantoms. The investigated optimization technique is proven to be superior than traditional empirical approaches. Finally, the CEMC techniques are applied in the context of non-dosimetry related engineering design environment by investigating the integration of a miniature loudspeaker (acoustic component) and a mobile device antenna (radio frequency component). Based on simulation and measurement data, the coupling mechanisms are determined to establish the fundamental design guidelines for optimum antenna-speaker co-existence and performance. In summary, this thesis details several novel applications of CEMC in the most stringent and complex industrial design environments. The presented research findings serve as indispensable basis for future research oriented towards the exposure-compliant and electromagnetic- compatible designs for novel wireless technologies.

EPFL2013