This thesis presents novel communication schemes between independent clock domains. The clock domains are equipped with synchronizers for adaptation to an asynchronous communication channel. We propose two synchronization schemes: one for interfacing a fixed-frequency clock domain to a pausible clock domain and one for interfacing two independent fixed-frequency clock domains. In the first scheme, the sender uses a fixed-frequency clock and the receiver uses a pausible clock. In the second scheme, both the sender and the receiver use fixed-frequency clocks, but their frequencies are uncorrelated. Metastability-related failures are reduced by converting failures in the data path into failures in the control path, where they can be more easily accommodated. Throughputs are improved by using the asP* handshaking protocol. We demonstrate applicability of the proposed schemes on two case studies: a parity detector circuit for memory operation, and a cross-bar switch. Hspice simulations using 0.18 technology demonstrates proper operation of all proposed designs.

The demand for wireless devices is increasing, new standards are constantly evolving and the operating frequencies are spreading towards higher spectrums. The stress on lowering the voltage supply, the power consumption, the cost and increasing level of integration are the driving forces behind today's RF microelectronics research. / The goal of this thesis is to show the possibility of standard CMOS technology replacing the traditional technologies in RFIC applications, specifically in the design and implementation of frequency synthesizers for 5GHz WLAN applications. The frequency synthesizer is a key building block of WLAN transceivers. To generate multiple frequencies with the resolution required by 5GHz WLAN standards, a fractional-N frequency synthesizer architecture was successfully implemented in 1.8V 0.18mum CMOS technology. To be able to cover the lower and upper 5GHz bands of both HiperLan and 802.11a standards, a wide tuning range quadrature voltage controlled oscillator (VCO), providing a 4-phase output and operating from 5GHz to 6GHz, was used in the phase lock loop (PLL) design. The 5GHz WLAN standards are targeted since they are the most promising, they have few interferers and large data throughputs. / This thesis presents one of the few frequency synthesizers having a large bandwidth of operation and a small resolution reported to-date for this type of application. Also, the digital components used in this frequency synthesizer, namely the fractional-N divider and prescaler have the lowest power consumption reported to-date.

This thesis considers simplified decoding for a type of full-rate non-orthogonal complex space-time block codes (STBCs) over Rayleigh fading channels. More precisely, we propose a decision feedback symbol-by-symbol decoding algorithm for the Quasi-Orthogonal code family, that comprises the Quasi-Orthogonal code and the Improved Quasi-Orthogonal code, by using the QR decomposition. Compared to optimal joint decoding, this algorithm significantly reduces complexity. For performance evaluations of the simplified decoding algorithm for the Quasi-Orthogonal code family over Rayleigh fading channels, we derive upper and lower bounds for symbol error rate. Furthermore, by using high SNR asymptotics we investigate the diversity orders provided by different decoding algorithms. The analysis shows that because of the relative constellation rotation, the diversity order provided by optimal decoding for the Improved Quasi-Orthogonal code is 4. Also, because of the error propagation in the decision feedback, the diversity order provided by the simplified decoding for the Improved Quasi-Orthogonal code is reduced to 2. All analytical results match well the associated computer simulations. Finally, we compare the performances of the simplified and optimal decoding for the Improved Quasi-Orthogonal code over correlated Rayleigh fading channels by using the "one-ring" channel model. Through computer simulations we show that the relative performance loss between the simplified and optimal decoding decreases as channel correlation increases. Therefore, the simplified decoding algorithm is suitable for highly spatially correlated Rayleigh fading channels.

Co-channel interference is the main source that limits the performance in a cellular network. Accurate interference estimation is useful for resource allocation, network planning and performance assessment in cellular systems. If the individual interference power caused by a single interferer can be approximated by a lognormal distribution due to the predominant effect of shadowing, evaluation of the total interference distribution boils down to the problem of the sum of lognormal distributed random variables. However, the problem of the sum of independent lognormal distributions is well known to be difficult due to the non-existence of closed form expressions. Many approximation methods have been proposed to solve this problem. This thesis presents the Log Shifted Gamma (LSG) approximation method, which provides high accuracy for the entire sum of lognormal distributions with all combinations of individual lognormal parameters. The probability density function (PDF) of Log Shifted Gamma random variable is in closed-form expression and is fully characterized by its parameters. By comparing results in outage probability and capacity evaluation, guideline of resource allocation, and typical value estimation, LSG approximation is found to be a better tool of analysis with higher accuracy than other methods, including the classical lognormal and Gaussian approximation.

The performance of a device, for certain design parameters, can be modeled using finite element analysis (FEA); however, this can be computationally complex and time consuming. But because this performance can be modeled as a continuous function over the parameter ranges, it is efficient to combine FEA with interpolation to rapidly estimate the performance for any variables. While there exists many interpolation techniques, FEA can provide sensitivities at little extra cost, so these methods should take advantage of this information. In this thesis, a new adaptive interpolation scheme is proposed which uses radial basis functions (multiquadrics) while making use of sensitivities. Results demonstrate the greater accuracy of the new scheme compared to a previous multiquadric algorithm without sensitivities. Test cases include artificial functions, and an example combining FEA and the interpolation of the reflection coefficient for a rectangular waveguide containing a partial height metallic post.

The development and growth of new communication services and emerging applications requires high-performance access networks capable of providing high-bandwidth interconnections to end-users. In recent years, optical code-division multiple access (OCDMA) has been proposed as a means for providing flexible access to high-bandwidth applications and offering different levels of quality of service. This thesis explores the impact of encoder/decoder mismatch on system performance for 2 dimensional wavelength-time (2D lambda-t) OCDMA and the implementation of a multi-user 2D lambda-t OCDMA direct detection demonstrator system. Our analysis and experimental demonstrations are based on depth-first search codes (DFSCs) which have previously been shown to be attractive in OCDMA applications. We have developed an OCDMA system simulation model that quantifies the BER performance as wavelength and/or time misalignments (which cause mismatch in the encoder/decoder) increase. Furthermore, we have succeeded in encoding and decoding DFSCs as well as in demonstrating a 4-user system which has been implemented using standard commercially available off-the-shelf optical components.

Tandem coding and decoding has been demonstrated to yield arbitrarily low error rates provided a sufficiently large block length is used. When applied to practical systems that are inherently limited to a finite complexity and therefore to finite block lengths, such a strategy may be largely suboptimal. Indeed, a tandem decoding strategy ignores two types of information: the source memory and the residual redundancy of the source coder. Moreover, conventional source decoders, within a tandem decoding strategy, are designed to perform the inverse operation of the source coder and may severely decrease performance if errors are still present at their input. One viable alternative, that has been demonstrated to yield gains, is the design of a joint source-channel decoding scheme that would take the additional sources of redundancies---the source memory and the source coder's residual redundancy---into account. / In this context, we propose a novel, iterative joint source-channel decoding algorithm. The proposed scheme is derived from a Bayesian network representation of the coding chain and incorporates three types of information: the source memory; the residual redundancy of the source coder; and finally the redundancy introduced by the channel coder. Specifically, we modify an existing algorithm by first deriving a new, equivalent Bayesian network representation of the coding chain. Next, we derive a fully consistent methodology, within the framework of Bayesian networks, for performing the iterations. The proposed algorithm is shown to yield significant gains along with a drastic reduction in computational complexity when compared with the existing one. Finally, we outline additional possible improvements on the proposed algorithm. They include methods for further reductions in computational complexity at no cost in performance in one case, and at a slight cost in performance in the other.

Error correcting codes are of paramount importance for reliable communications. By adding redundancy to the transmitted data they allow the decoder to detect and correct errors. However in favorable channel conditions, a part of this redundancy can be removed in order to increase throughput. Unfortunately most coding schemes are poorly adapted to these higher coding rates. For example, the decoding of block codes grows exponentially with code length. In this thesis we propose a novel solution to this problem: selective trellis pruning. / Selective trellis pruning reduces decoding complexity by removing certain codewords from the trellis. This reduction is accomplished by making hard decisions on the values of bits in the received sequence above the certainty threshold. This method can produce near-optimal results with only a fraction of the operation required by full decoding thanks to the reduced trellis size. In this work we also introduce an innovative way of obtaining the pruned trellis directly from a simplified version of the generator matrix. By using this method we avoid the long process of constructing and then pruning the full trellises, thus making the selective trellis pruning algorithm an efficient decoding tool. Finally we apply this algorithm to the parallel concatenated turbo block code decoder in order to reduce its complexity.

The maturing of the telecommunications industry has seen the development and implementation of devices that work at high frequencies of the electromagnetic spectrum. With the rapid deployment of optical networks, there is an increasing demand for low-cost and efficient communications circuitry. In order to interface with such high frequency signals at lower cost, there has been a recent push for very high frequency circuits using low-cost fabrication technologies like digital CMOS. / This thesis investigates the usage of legacy architectures and the implementation of different topologies using digital CMOS technology. Various Clock and Data Recovery Phase-Locked Loops have been implemented using a 0.18mum CMOS technology, and the process from modeling to actual implementation will be presented. The design of the components of the loop, layout issues, and the performance of the various designs will be discussed. New fully-differential CMOS designs that are optimized for high-speed operation, yet providing stable lock with minimal jitter, with a targeted operation range from 1 GHz to 7 GHz, will be described in detail, as well as their operation and optimization.

This thesis considers the application of the principles of distributed signal detection to the uplink of a mobile communication unit engaged in soft handoff, when all base stations involved are equipped with multiple receiving antennas. The system consists of a local detector at each base station and a fusion center at the Mobile Switching Center (MSC). Optimum decision rules are derived for systems without channel coding, as well as for systems using channel coding, over a quasi-static spatially uncorrelated Rayleigh fading channel. Two different cases are considered. In the first case, accurate estimates of the base station channel states are available at the MSC, while in the second case only the statistics of the channels are known. For both cases, when the system is not using channel coding the optimum local decision rules are likelihood ratio quantizers for which the defining thresholds are optimized numerically with respect to the probability of bit error at the output of the MSC. With channel coding it is shown that the complexity of either the implementation or the optimization of the optimum decision rules increases exponentially with the frame size. Hence, for coded systems, sub-optimum alternatives are proposed where the local decision rules are likelihood ratio quantizers. The performances of these systems are investigated. For the uncoded systems the probability of bit error is evaluated numerically, and for coded systems the probability of bit error and frame error are estimated through computer simulations. Finally, it is demonstrated that by carefully selecting the thresholds defining the local decision rules, 8 quantization levels are sufficient to make the performances almost identical to the performances of an optimum centralized system, implementing at the MSC a maximum likelihood test using the actual signals received at the involved base stations.* / *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation).