No description available.

No description available.

No description available.

No description available.

<p> Due to the high cost, telephone and cable television companies can only justify installing fiber optical networks to remote sites which serve up to a few hundred customers. For customers located at variable distances from the transmitting station, they will receive signals at different strengths. The signal stability and system reliability of FTTH network affected largely by the distance. We propose an effective solution for the enhancement of signal stability of FTTH network, which uses a semiconductor optical amplifier (SOA) coupled with an optical receiver.</p> <p> Before the signal reaches the optical receiver at the user end, signal strength is automatically adjusted through a semiconductor optical amplifier (SOA). Due to the special saturation property of SOA, the output optical signal will have very small fluctuation regardless the input optical signal power, the signal stability of FTTH network will be improved significantly. A set of simplified governing equations of SOA has been proposed and the corresponding numerical solver has been implemented. Although the main focus is primarily the SOA, a simplified optical receiver is also simulated, which comprises a PIN photodetector and a low pass filter (LPF). All simulations have been carried out in the time-domain with the frequency domain low pass filter modeled by a digital filter.</p> / Thesis / Master of Applied Science (MASc)

CMOS technology is particularly attractive for commercialization of ultra wideband (UWB) radios due to its low power and low cost. In addition to CMOS implementation, UWB radios would also significantly benefit from a radio architecture that enables digital communications. In addition to the normal challenges of CMOS RFIC design, there are two major technical challenges for the implementation of CMOS digital UWB radios. The first is building RF and analog circuitry covering wide bandwidth over several GHz. The second is sampling and digitizing high frequency signals in the UWB frequency range of 3 GHz to 10 GHz, which is not feasible for existing CMOS analog-to-digital converters. In this dissertation, we investigate the two technical challenges at the circuit level and the system level. We propose a systematic approach at the circuit level for optimal transistor sizing and biasing conditions that result in optimal noise and power matching over a wide bandwidth. We also propose a general scheme for wideband matching. To verify our methods, we design two single-stage low noise amplifiers (LNAs) in TSMC 0.18µm CMOS technology. Measurement results from fabricated chips indicate that the proposed LNAs could achieve as high as 16 dB power gain and as low as 2.2 dB noise figure with only 6.4 mA current dissipation under a supply voltage of 1.2 V. At the system level, we propose a unique frequency domain receiver architecture. The receiver samples frequency components of a received signal rather than the traditional approach of sampling a received signal at discrete instances in time. The frequency domain sampling leads to a simple RF front-end architecture that directly samples an RF signal without the need to downconvert it into a baseband signal. Further, our approach significantly reduces the sampling rate to the pulse repetition rate. We investigate a simple, low-power implementation of the frequency domain sampler with 1-bit ADCs. Simulation results show that the proposed frequency-domain UWB receiver significantly outperforms a conventional analog correlator. A digital UWB receiver can be implemented efficiently in CMOS with the proposed LNA as an RF front-end, followed by the frequency domain sampler. / Ph. D.

The objective of this research is the' development and evaluation of a new style of integrated optoelectronics. The approach combines the selectivity of traditional hybrid integration with the "internal" interconnection capabilities of monolithic integration, through the use of low temperature cofireable ceramic (LTCC) tape systems. This new integration technique is applied to a fiber optic receiver system, and focuses on three main tasks. The first task involves the realization, and eventual hybridization, of the receiver electronics, including the photodetector and the associated amplifier circuitry. Second, materials and techniques for the processing of planar optical waveguides are investigated, in order to expand the potential applications of the technique. Finally, a new technique of integrating an optical fiber with the above components is introduced and evaluated. Multichip module (MCM) technology has become the new standard in the field of electronic packaging. Much of the success of MCM packaging may be attributed to the development of LTCC systems. LTCC materials utilize their multilayer (3-dimensional) nature to achieve a higher level of electronic circuit density within a hermetic module. The goal of this research effort is to expand this capability to include optical components, in addition to the traditional electronics. The optical counterpart to the printed electrical wiring within an LTCC package is the planar waveguide. Much of this research is therefore devoted to an investigation of materials and processing techniques used to develop planar optical waveguide structures. This research discusses the production and evaluation of both thin film and thick film structures based on germanium oxide (GeO₂) - a material with promising photosensitivity characteristics. As has been seen with optical fibers, the optimization of planar optical waveguides is also not a trivial task. Aside from the material and processing concerns, there is also the compatibility with cofireable ceramic materials that must be addressed. Once these planar optical waveguides are able to be incorporated within the internal layers of the multichip module, there must be a means of accessing them from the outside of the package. Thus this research work also investigates the ability to integrate optical fibers within LTCC materials. Traditional optical fiber connectors are not suitable for this application, since the interface between fiber and waveguide will be inside a hermetic module. This research discusses the techniques used to· achieve this novel integration capability. The planar optical waveguides developed in this work are not yet optimized for full integration within cofireable ceramic materials. Thus, the interface between fiber and waveguide is theoretically. analyzed from the perspective of coupling efficiency. Nevertheless, the ability to integrate an optical fiber within an LTCC module is demonstrated through the development of a fiber optic receiver module. One of the benefits of the integration technique proposed in this research work is selectivity. This feature is demonstrated through the evaluation and selection of individual components of the receiver system. This work demonstrates that the selection of receiver components is not dictated by the integration technology, but is determined instead by individual performance characteristics. Through the hybridization of the receiver circuitry and the successful integration of an optical fiber within the LTCC material, a functional integrated fiber optic receiver module has been completed. In addition, this research into the development of both thick and thin film planar optical waveguide materials is an important step toward the eventual integration of these devices. / Ph. D.

This research investigates the application of multiuser detection to Code Division Multiple Access for cellular communications. This investigation focuses on the use of multiuser receivers at the base station of mobile radio systems. The first two chapters are dedicated to multiuser detection in general. An extensive literature survey is performed on the research concerning multiuser receivers to date. Six major receiver structures are chosen for extensive simulation studies. The bit error rate performance of these receivers is investigated in several system environments. Additionally, practical issues are considered such as computational complexity and robustness to code tracking errors. From this work, one receiver structure is identified for further study, namely multistage interference cancellation. The theoretical performance of this receiver is analyzed using a standard Gaussian Approximation and an Improved Gaussian Approximation for AWGN and fading environments. Additionally, the resistance of the receiver to interference energy levels is explored. Parameter estimation is an important issue for interference cancellation. Simple methods of improving parameter estimation are examined, as is the effect of parameter estimation error on system performance. A baseband hardware implementation is detailed and several design challenges are presented. Results are given for the performance of the implemented receiver and shown to match well with theory and computer simulation. Finally, the implications of this research are discussed. / Ph. D.

Recently, ultra-wideband (UWB) technology based on the transmission of short duration pulses has gained much interest for its application to wireless communications. This thesis covers a range of topics related to the analysis of indoor UWB channels for communications and to system level design issues for UWB receivers. Measurement based UWB small scale modeling and characterization efforts as well as UWB communications system analysis and simulation are presented. Relevant background material related to UWB communications and wireless channel modeling is presented. The details of the small scale channel modeling work, including statistical characterization and potential models, are discussed. A detailed analysis of the CLEAN algorithm, which was used to process all the measurement data, is also given, and some limitations of the algorithm are presented. The significance of the channel impulse response model chosen for the simulation of UWB communications systems is also evaluated. Three traditional models are found to be useful for modeling NLOS UWB channels, but not LOS channels. A new model for LOS UWB channels is presented and shown to represent LOS channels much more accurately than the traditional models. Receiver architectures for UWB systems are also discussed. The performance of correlation receivers and energy detector receivers are compared as well as Rake diversity forms of each of these types to show tradeoffs in system complexity with performance. Interference to and by UWB signals is considered. A narrowband rejection system for UWB receivers is shown to offer significant system improvement is the presence of strong interferers. / Master of Science

Power consumption and battery life are of critical importance for medical implant devices. For this reason, devices for Wireless Body Area Network (WBAN) applications must consume very little power. To save power, it is desirable to turn off or put to sleep a device when not in use. However, a transceiver, which is the most power hungry block of a wireless sensor node, needs to listen for the incoming signal continuously. An alternative scheme, is to listen for the incoming signal at a predetermined internal, which saves power at the cost of increased latency. Another and more sophisticated scheme is to provide a wake-up receiver, which listens for the incoming signal continuously, and upon detection of an incoming signal, it wakes the primary transceiver up. A wake-up receiver is typically simple and dissipates little power to make the scheme useful. This thesis proposes a low-power wake-up receiver, which listens for a wake-up signal, identifies the target node, and wakes up the primary receiver only when that specific node is called upon. When a wake up signal is transmitted to all of the nodes on a network, our wake-up receiver allows all the nodes on a network except the targeted node to remain asleep to save power. Several wake-up receiver topologies have been proposed. This work uses a passive Cockcroft-Walton multiplier circuit as an RF envelope detector followed by a simple detector circuit. A novel serial code detector is then used to decode the pulse width modulated input signal to wake-up the designated node. A passive RF front end and simple decoding circuit reduce power consumption substantially at the cost of low sensitivity. The sensitivity of the wake-up receiver can be improved though the addition of an RF amplifier, but at the cost of increased power consumption. / Master of Science