Hydroelectricity in Washington State: Finding New Locations for Hydroelectric Dams

https://digitalcommons.tacoma.uw.edu/gis_projects/1041/thumbnail.jp

Designing Power-Efficient Modulation Formats for Noncoherent Optical Systems

We optimize modulation formats for the additive white Gaussian noise channel with a nonnegative input constraint, also known as the intensity-modulated direct detection channel, with and without confining them to a lattice structure. Our optimization criteria are the average electrical and optical power. The nonnegativity input signal constraint is translated into a conical constraint in signal space, and modulation formats are designed by sphere packing inside this cone. Some remarkably dense packings are found, which yield more power-efficient modulation formats than previously known. For example, at a spectral efficiency of 1 bit/s/Hz, the obtained modulation format offers a 0.86 dB average electrical power gain and 0.43 dB average optical power gain over the previously best known modulation formats to achieve a symbol error rate of 10^-6. This modulation turns out to have a lattice-based structure. At a spectral efficiency of 3/2 bits/s/Hz and to achieve a symbol error rate of 10^-6, the modulation format obtained for optimizing the average electrical power offers a 0.58 dB average electrical power gain over the best lattice-based modulation and 2.55 dB gain over the best previously known format. However, the modulation format optimized for average optical power offers a 0.46 dB average optical power gain over the best lattice-based modulation and 1.35 dB gain over the best previously known format.Comment: Submitted to Globecom 201

A Two-Dimensional Signal Space for Intensity-Modulated Channels

A two-dimensional signal space for intensity- modulated channels is presented. Modulation formats using this signal space are designed to maximize the minimum distance between signal points while satisfying average and peak power constraints. The uncoded, high-signal-to-noise ratio, power and spectral efficiencies are compared to those of the best known formats. The new formats are simpler than existing subcarrier formats, and are superior if the bandwidth is measured as 90% in-band power. Existing subcarrier formats are better if the bandwidth is measured as 99% in-band power.Comment: Submitted to IEEE Communications Letters, Feb. 201

Strictly Bandlimited ISI-Free Transmission Over Intensity-Modulated Channels

In this paper, the design and analysis of a new bandwidth-efficient signalling method over the bandlimited intensity-modulated direct-detection (IM/DD) channel is pro- posed. The channel can be modeled as a bandlimited channel with nonnegative input and additive white Gaussian noise. Due to the nonnegativity constraint, the methods previously proposed for conventional bandlimited channels cannot be applied here. We propose a method to transmit without intersymbol interference in a narrower bandwidth compared to previous works, by combining Nyquist pulses with a constant bias. In fact, we can transmit with a bandwidth equal to that of coherent transmission. A trade-off between the required average optical power and the bandwidth is investigated. At low bandwidths, the most power- efficient transmission is obtained by either the parametric linear pulse or the so-called “better than Nyquist” pulse, depending on the exact bandwidth

Power efficient subcarrier modulation for intensity modulated channels

We compare formats for optical intensity modulation limited by thermal noise with the assumption of having ideal devices. At the same bitrate and bandwidth, a hitherto unknown format turns out to be more power efficient than known formats. This new modulation, which is a hybrid between on-off keying and phase-shift keying, belongs to the subcarrier modulation family. At asymptotically high signal-to-noise ratios, this hybrid scheme has a 1.2 dB average electrical power gain and 0.6 dB average optical power gain compared to OOK, while it has a 3.0 dB average electrical power gain and 2.1 dB average optical power gain compared to subcarrier QPSK

Bandlimited Intensity Modulation

In this paper, the design and analysis of a new bandwidth-efficient signaling method over the bandlimited intensity-modulated direct-detection (IM/DD) channel is presented. The channel can be modeled as a bandlimited channel with nonnegative input and additive white Gaussian noise (AWGN). Due to the nonnegativity constraint, standard methods for coherent bandlimited channels cannot be applied here. Previously established techniques for the IM/DD channel require bandwidth twice the required bandwidth over the conventional coherent channel. We propose a method to transmit without intersymbol interference in a bandwidth no larger than the bit rate. This is done by combining Nyquist or root-Nyquist pulses with a constant bias and using higher-order modulation formats. In fact, we can transmit with a bandwidth equal to that of coherent transmission. A trade-off between the required average optical power and the bandwidth is investigated. Depending on the bandwidth required, the most power-efficient transmission is obtained by the parametric linear pulse, the so-called "better than Nyquist" pulse, or the root-raised cosine pulse.Comment: 28 pages 10 Figure

Signaling for Optical Intensity Channels

With the growing popularity of social media services, e-commerce, and many other internet-based services, we are witnessing a rapid growth in the deployment of data centers and cloud computing platforms. As a result, the telecommunications industry has to continue providing additional network capacity to meet the increasing demand for bandwidth. The use of fiber-optic communications plays a key role in meeting this demand. Coherent optical transceivers improve spectral efficiency by allowing the use of multilevel in-phase and quadrature (I/Q) modulation formats, which encode information onto the optical carrier’s amplitude and phase. However, for short-haul optical links, using noncoherent optical transceivers, also known as intensity-modulated direct-detection (IM/DD) systems, is a more attractive low-cost approach. Since only the intensity of light can carry information, designing power- and spectrally-efficient modulation formats becomes challenging. Subcarrier modulation, a concept studied in wireless infrared communications, allows the use of I/Q modulation formats with IM/DD systems at the expense of power and spectral efficiency. This thesis addresses the problem of optimizing single-subcarrier modulation formats for noncoherent fiber and wireless optical communication systems in order to achieve a good trade-off between spectral efficiency, power efficiency, and cost/complexity. For the single-subcarrier three-dimensional signal space, denoted as raised-QAM in the literature, we propose a set of 4-, 8-, and 16-level modulation formats which are numerically optimized for average electrical, average optical, and peak power. In the absence of error-correcting codes, the optimized formats offer gains ranging from 0.6 to 3 dB compared to the best known formats. However, when error-correcting codes with performance near capacity are present, the obtained modulation formats offer gains ranging from 0.3 to 1 dB compared to previously known formats. In addition, laboratory experiments using the obtained 4- and 8-ary modulation formats were carried out. The performance improvement over the previously known formats conforms with the theoretical results. To address transceiver complexity, a two-dimensional signal space for optical IM/DD systems is proposed. The resulting modulation formats have simpler modulator and demodulator structures than the three-dimensional formats. Their spectra have in general narrower main lobes but slower roll-off, which make them a good choice for single-wavelength optical systems. The three-dimensional formats are more suitable for wavelength-division multiplexing systems, where crosstalk between adjacent channels is important

Performance Trade-off Investigation of B-IFDMA

A performance trade-off investigation is carried out between different possible uplink multiple access schemes, that are based on Orthogonal Frequency Division Multiplexing (OFDM), for International Mobile Telecommunication (IMT) Advanced systems. Between the Discrete Fourier Transform (DFT) precoded systems with different subcarrier allocation mappings and systems lacking DFT-precoders, Block Interleaved Frequency Division Multiple Access (B-IFDMA) is shown to provide a good trade-off between the frequency diversity collected, envelope properties achieved, and channel estimation performance compared to the other mapping schemes. The schemes are analyzed in the presence of the different possible modules which include equalizers, modulators, interleavers, and channel codes. In particular, robust codes such as Turbo codes are able to collect the diversity provided by such schemes, and B-IFDMA systems is shown to be able to beat the other systems in bit error rate (BER) performance terms

A DMAIC Framework for Improving Software Quality in Organizations: Case Study at RK Company

Managing quality is a vital aspect in software development world, especially in the current business competition for fast delivery of feature rich products with high quality. For an organization to meet its intended level of excellence in order to ensure its success, a culture of quality should be built where every individual is responsible of quality and not just the software testing team. However, delivering software products with very few bugs is a challenging constraint that is usually sacrificed in order for a company to meet other management constraints such as cost, scope and scheduling. The purpose of this thesis is to apply six sigma DMAIC framework on 'RK’ company (name anonymized) in order to help software organizations focus on improving the quality of their software products. Different phases of DMAIC methodology are applied to one of the largest software applications for ‘RK’ company where critical to quality aspects were identified, production bugs were classified and measured, the causes of the large number of production bugs were specified leading to different improvement suggestions. Several metrics were proposed to help ‘RK’ company control its software development process to ensure the success of the project under study