Performance of Trellis Coded Modulation with 8PSK through TDRSS

The need to increase data-rate capabilities of the Tracking and Data Relay Satellite System (TDRSS) has prompted NASA to investigate bandwidth-efficient modulation schemes. Based upon current technology the most promising scheme is Trellis-Coded Modulation (TCM) operating with Octal Phase Shift Keying (8 PSK). In conjunction with NASA, New Mexico State University\u27s Manuel Lujan Jr. Center for Space Telemetering and Telecommunications Systems has constructed a system to test this new candidate TDRSS modulation scheme, TCM 8 PSK. This system was tested through the TDRSS channel to demonstrate that this coding scheme operates as well over the actual channel as it has in lab experiments and simulations. Two interchangeable codecs, implementing separate TCM techniques, were tested. The results of this experiment and subsequent data analysis are presented in this paper

The Internet in India and China

This article compares the diffusion of the Internet in China and India. Using a six–dimension framework for characterizing the state of the Internet in a nation, we observe that, while both nations have made significant progress since our last comparison (in 1999), China enjoys a substantial lead over India. We also examine determinants of Internet diffusion. We find that the Chinese Internet has benefited from economic and trade reform begun in the late 1980s, a strong government commitment to the Internet, complementary human and capital resources, etc. The two nations have very different governments and policies, leading to differing approaches to the introduction of telecommunication competition and infrastructure development. China has pursued a strategy of competition among government–owned organizations while India has set policy via recommendations of publicly visible task forces. It remains to be seen whether India’s relatively transparent and market driven approach to Internet policy (and access) will prove effective in the long run. India and China have approximately 40 percent of the world population, and most of their inhabitants live in rural villages that lack basic telephone service. If the Internet is to succeed in raising the level of human development and curtailing migration to teeming urban centers, it must succeed in India and China. What we learn there may enable us to provide communication and information to the world\u27s 1.5 million unconnected villages

Data Rate Determination for Fixed, Matched Filter Channels

In today\u27s world, with ever rising data rate requirements and ever shrinking budgets, the use of existing equipment to perform new tasks is highly desirable. Often the need to increase the data transmission rates through an existing system is clear, yet financial or logistical constraints do not permit complete redesign of the system. Other situations do not allow the designer access to all of the system components, as in satellite systems. Whatever the circumstances, the desirable result is to maximize the data rates through existing channels. This paper presents a method for determination of the allowable data rates in existing channels. In addition, a measure of the expected degradation associated with the use of a pre-existing receive filter and matched transmit filter pair at increased transmit data rates is determined. Examples are given for different filter types and data modulation formats

A Comparison of Modulation Schemes in Bandlimited AWGN Channels

In recent years, as data rates rise for seemingly decreasing available bandwidths, a great deal of research has been directed toward finding bandwidth efficient modulation schemes. Two such methods are partial-response signaling and trellis-coded modulation. Both of which promise performance gains in a bandlimited channel when compared to uncoded systems. This paper will compare the performance of these schemes, when applied to a QPSK system over various channel bandwidths

Uplink-Noise Limited Satellite Channels

Many applications, current and emerging, are faced with a relatively new and interesting channel model. Systems which transmit data through a nonlinear relay, such as a satellite, must deal with a composite channel that can be separated into two distinct channels - the uplink channel between the user and the relay, and the downlink channel between the relay and the final destination. If the system has a strict power limitation and high data rate demands, such as a small satellite transmitting through NASA\u27s TDRSS Network, the dominant noise is present on the uplink rather than the downlink channel. Such a system is deemed to be uplink-noise limited and presents the designer with a number of problems not encountered in a more typical downlink-noise limited channel. Whereas the transmitted signal constellation can be pre-distorted to take into account the effect of the nonlinearity in the down-link limited channel, no amount of pre-distortion will solve the problems encountered when the majority of the noise is present before the nonlinearity. Instead, the receiver must be modified to reflect the non- Gaussian noise due to the operation of the nonlinearity on Gaussian noise. Under three assumptions - there is no downlink-noise present, the downlink channel is wideband relative to the data, and the filter proceeding the nonlinearity meets both matched filter and Nyquist requirements - such modifications can be made based on the nature of the nonlinearity. By mapping the ideal decision region through the nonlinearity, performance almost identical to that of a linear-wideband AWGN channel can be achieved. This paper will develop the theoretical performance of the receiver described for a nonlinearity typical of a satellite channel. Performance curves will be presented for QPSK, SPSK, 16PSK and 16QAM modulation schemes

Cost Effectiveness of the US Geological Survey\u27s Stream-gaging Program in New York

The U.S. Geological Survey conducted a 5-year nationwide analysis to define and document the most cost effective means of obtaining streamflow data. This report describes the stream gaging network in New York and documents the cost effectiveness of its operation; it also identifies data uses and funding sources for the 174 continuous-record stream gages currently operated (1983). Those gages as well as 189 crest-stage, stage-only, and groundwater gages are operated with a budget of $1.068 million. One gaging station was identified as having insufficient reason for continuous operation and was converted to a crest-stage gage. Current operation of the 363-station program requires a budget of$1.068 million/yr. The average standard error of estimation of continuous streamflow data is 13.4%. Results indicate that this degree of accuracy could be maintained with a budget of approximately $1.006 million if the gaging resources were redistributed among the gages. The average standard error for 174 stations was calculated for five hypothetical budgets. A minimum budget of$970,000 would be needed to operated the 363-gage program; a budget less than this does not permit proper servicing and maintenance of the gages and recorders. Under the restrictions of a minimum budget, the average standard error would be 16.0%. The maximum budget analyzed was $1.2 million, which would decrease the average standard error to 9.4%. (Author \u27s abstract

Scientific Computing in the Soviet Union

In the last decade, the Soviet Union has placed increased emphasis on the development of high-speed computers and networks for use in scientific, economic, and military applications. When Communist Party General Secretary Mikhail Gorbachev labeled supercomputer development a top priority task for our science and economy in April, 1987, he added new urgency to the production of machines that would both support activities in these applications and also serve as high-profile standard-bearers for perestroika, his program of restructuring and modernization for the nation. The Soviets have also undertaken some major projects in networking, including the creation of a nationwide packet-switched network for the Academy of Sciences, work on network access to databases on scientific literature, and local area networks at a number of institutes

Morphology of wood species affecting wood-thermoplastic interaction: Microstructure and mechanical adhesion

The main objective of the research presented here was to relate anatomical features of wood species that affect the interactions between polymeric phases and performance of wood plastic composites (WPC). These interactions were related to the probable interlocking volume and surface area for stress transfer in a WPC. Composites were produced from different wood species and analyzed using SEM (scanning electron microscopy). Results showed that wood species with high interfacial areas may increase mechanical interlocking, reflected in the viscous constant of the Maxwell model. A complicating factor was that the relation of cell wall thickness-lumen diameter and the interconnectivity between wood cells in a wood, affect the potential for cell collapse. When wood cells collapse, the penetration of the thermoplastic into the wood structure was almost always ceased. The collapse of wood cells during extrusion-injection molding processes reduced the potential surface for stress transfer between phases affecting the mechanical properties of composites. Undamaged wood cells may potentially be filled with HDPE thermoplastic enhancing modulus and increase the strength of WPC

Becoming a Champion of Orientation

New student orientation programs are one of the most important high impact practices for student success. These introductory programs not only empower students to be able to selfidentify how their academic support needs can be met, they also provide the critically important introduction to building social support networks. College presidents must embrace the critical role of new student orientation programs, understand their complexities, and find ways to illustrate the role of these programs to faculty, staff, and students