Millimeter-wave (mmWave) communications is a promising enabling technology for high rate (Giga-bit) multimedia applications. However, because oxygen absorption peaks at 60 GHz, mmWave signal power degrades significantly over long distances. Therefore, a traffic flow transmitting over multiple short hops is preferred to improve the flow throughput. In this thesis, we first design a hop selection metric for the piconet controller (PNC) to select appropriate relay hops for a traffic flow, aiming to improve the flow throughput and balance the traffic loads across the network. We then propose a multi-hop concurrent transmission (MHCT) scheme to exploit the spatial diversity of the mmWave WPAN by allowing multiple communication links to transmit simultaneously. By deriving the probability that two links can transmit simultaneously as a function of link length, the MHCT scheme is capable of improving spatial multiplexing gain in comparison with the single hop concurrent transmission (SHCT) scheme. We theoretically demonstrate that by properly breaking a single long hop into multiple short hops, the time resource can be utilized more efficiently, thus supporting more traffic flows in the network within the same time interval. In addition, the per-flow throughput is obtained analytically. Extensive simulations are conducted to validate the analysis and demonstrate that the proposed MHCT scheme can significantly improve the average traffic flow throughput.

In recent years, the miniaturization of cell phones and computers has led to a requirement for antennas to be small and lightweight. Antennas, desired to operate in the WLAN frequency range, often possess physical sizes that are too large for integration with radio-frequency (RF) devices. When integrating antennas into three-dimensional (3D) system-on-package (SOP) transceivers, the maintenance of a compact size also provides isolation from other devices, hence, surface wave propagation or high dielectric constant materials such as low temperature cofired ceramics (LTCC) does not affect nearby components of the transceiver such as filters, baluns, and other embedded passives. Therefore, the application of design methods is necessary for realizing compact antennas in the wireless community that can be integrated to RF packages. Furthermore, it is essential that these compact antennas maintain acceptable performance characteristics, such as impedance bandwidth, low cross-polarization, and high efficiency. In addition, the analysis of circuit modeling techniques that could be used to obtain a better understanding of the physical phenomena of the antenna is quite necessary as modules become more and more complex. Based on these requirements, the focus of this research is to improve the design of compact antennas for wireless communications, wireless local area networks (WLAN), and millimeter-wave applications by using time-domain electromagnetic and circuit modeling techniques and optimizations. These compact antenna designs are applied to practical wireless communications systems such as global system of mobile communications (GSM), Bluetooth Industrial-Scientific-Medical (ISM) devices, IEEE802.11a WLAN, and Local Multipoint Distribution Systems (LMDS) applications. Parametric analyses are conducted to study critical parameters that may affect the antenna designs. Moreover, optimizations are performed to optimize the structures, and measured results are presented to validate design techniques.

The small carrier wavelength at millimeter-wave (mm-Wave) frequencies allows the possibility of implementing a large number of antennas on a single chip. This work uses the potential of large antenna arrays at these frequencies to develop a low-complexity directional modulation technique: Antenna Subset Modulation (ASM) for point-to-point secure wireless communication. The main idea in ASM is to communicate information by modulating the far-field radiation pattern of the array at the symbol rate. By driving only a subset of antennas and changing the subset used for each symbol transmission the far-field pattern is modulated. Two techniques for implementing antenna subset selection are proposed. The first technique is simple where the antenna subset to be used is selected at random for every symbol transmission. While randomly switching antenna subsets does not affect the symbol modulation for a desired receiver along the main lobe direction, it effectively randomizes the amplitude and phase of the received symbol for an eavesdropper along a sidelobe. Using a simplified statistical model for random antenna subset selection, an expression for the average symbol error rate (SER) is derived as a function of observation angle for linear arrays. To overcome the problem of large peak sidelobe level in random antenna subset switching, an optimized antenna subset selection procedure based on simulated annealing is then discussed. Finally, numerical results comparing the average SER performance of the proposed techniques against conventional array transmission are presented. While both methods produce a narrower information beam-width in the desired direction, the optimized antenna subset selection technique is shown to offer better security and array performance. / text

Millimeter-wave (mmWave) communications is a promising enabling technology for high rate (Giga-bit) multimedia applications. However, because oxygen absorption peaks at 60 GHz, mmWave signal power degrades significantly over long distances. Therefore, a traffic flow transmitting over multiple short hops is preferred to improve the flow throughput. In this thesis, we first design a hop selection metric for the piconet controller (PNC) to select appropriate relay hops for a traffic flow, aiming to improve the flow throughput and balance the traffic loads across the network. We then propose a multi-hop concurrent transmission (MHCT) scheme to exploit the spatial diversity of the mmWave WPAN by allowing multiple communication links to transmit simultaneously. By deriving the probability that two links can transmit simultaneously as a function of link length, the MHCT scheme is capable of improving spatial multiplexing gain in comparison with the single hop concurrent transmission (SHCT) scheme. We theoretically demonstrate that by properly breaking a single long hop into multiple short hops, the time resource can be utilized more efficiently, thus supporting more traffic flows in the network within the same time interval. In addition, the per-flow throughput is obtained analytically. Extensive simulations are conducted to validate the analysis and demonstrate that the proposed MHCT scheme can significantly improve the average traffic flow throughput.

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No description available.

Photonic generation of ultra-low phase noise and frequency-tunable microwave or millimeter-wave (mm-wave) signals has been a topic of interest in the last few years. Advanced photonic techniques, especially the recent advancement in photonic components, have enabled the generation of microwave and mm-wave signals at high frequencies with a large tunable range and ultra-low phase noise. In this thesis, techniques to generate microwave and mm-wave signals in the optical domain are investigated, with an emphasis on system architectures to achieve large frequency tunability and low phase noise. The thesis consists of two parts. In the first part, techniques to generate microwave and mm-wave signals based on microwave frequency multiplication are investigated. Microwave frequency multiplication can be realized in the optical domain based on external modulation using a Mach-Zehnder modulator (MZM), but with limited multiplication factor. Microwave frequency multiplication based on external modulation using two cascaded MZMs to provide a larger multiplication factor has been proposed, but no generalized approach has been developed. In this thesis, a generalized approach to achieving microwave frequency multiplication using two cascaded MZMs is presented. A theoretical analysis leading to the operating conditions to achieve frequency quadrupling, sextupling or octupling is developed. The system performance in terms of phase noise, tunability and stability is investigated. To achieve microwave generation with a frequency multiplication factor (FMF) of 12, a technique based on a joint operation of polarization modulation, four-wave mixing and stimulated-Brillouin-scattering-assisted filtering is also proposed. The generation of a frequency-tunable mm-wave signal from 48 to 132 GHz is demonstrated. The proposed architecture can even potentially boost the FMF up to 24. In the second part, techniques to generate ultra-low phase noise and frequency-tunable microwave and mm-wave signals based on an optoelectronic oscillator (OEO) are studied. The key component in an OEO to achieve low phase noise and large frequency-tunable operation is the microwave bandpass filter. In the thesis, we first develop a microwave photonic filter with an ultra-narrow passband and large tunability based on a phase-shifted fiber Bragg grating (PS-FBG). Then, an OEO incorporating such a microwave photonic filter is developed. The performance including the tunable range and phase noise is evaluated. To further increase the frequency tunable range, a technique to achieve microwave frequency multiplication in an OEO is proposed. An mm-wave signal with a tunable range more than 40 GHz is demonstrated.

Three 40/60-GHz optical-wireless bidirectional architectures are designed with a centralized light source in the central office based on wavelength reuse. Three super-broadband access networks are proposed and experimentally demonstrated for simultaneously delivering wired and wireless services over an optical fiber and an air link in a single transport platform. The transport feasibility in metro and wide-area access networks with multiple reconfigurable optical add-drop multiplexers (ROADMs) nodes is explored for 40-GHz and 60-GHz optical millimeter-wave signals. Additionally, the optical-wireless systems using the orthogonal frequency division multiplexing (OFDM) modulation format are analytically and experimentally demonstrated to mitigate the chromatic dispersion in optical fiber. This thesis also successfully implements the testbed trial for the delivery of uncompressed 270-Mb/s standard-definition television (SDTV) and 1.485-Gb/s high-definition television (HDTV) video signals over optical fiber and air links. The demonstration represents the first ever reported real applications over hybrid wired and wireless access networks, showing that our developed up-conversion schemes and designed architectures are highly suitable for super-broadband applications in next-generation optical-wireless access networks.

Thesis (doctoral)--Helsinki University of Technology, 2009. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--University of Cambridge, 1998. / Includes bibliographical references (p. 197-201).