322,847 research outputs found
TCP/IP Services Over ATM Satellite Link – Integration With DVB-S Services Using the Multiresolution Modulation
No full textWe propose to exploit the energy margin that can exist in satellite links to deliver multimedia traffic using multiresolution modulation techniques over the DVB-S. We propose an asymmetrical architecture, formed by a satellite forward link and a narrowband terrestrial reverse link, based on the N-ISDN. The ATM cell transport technique is adopted to support different QoS for different fluxes. In order to deliver the TCP/IP traffic, the additional delay on message delivery time suggests to modify the slow start and the congestion avoidance of the TCP. Our approach is based on the combination of a fixed window flow control at the transport layer with the ATM congestion control. The analysis shows that the system performance is satisfactory if some bounds on the transmit buffer size are respected and the spacing of the resource management cells is within a given range of values
Probability of error of OFDM systems with carrier frequency offset in frequency-selective fading channels
No full textThis paper presents an analytical approach to evaluate the error probability of orthogonal frequency-division multiplexing (OFDM) systems subject to carrier frequency offset (CFO) in frequency-selective channels, characterized by Rayleigh or Rician fading. By exploiting the Gaussian approximation of the intercarrier interference (ICI), we show that the bit-error rate (BER) for quadrature amplitude modulation (QAM) can be expressed by the sum of few integrals, whose number depends on the constellation size. Each integral can be evaluated numerically, or, in Rayleigh fading, by using a series expansion that involves generalized hypergeometric functions. Simulation results illustrate that the theoretical analysis is quite accurate, especially for Rayleigh channels
DSP Based OFDM Demodulator and Equalizer for Professional DVB-T Receivers
No full textThis work treats the design of base-band processing subsystems for professional DVB-T receivers using 1600 MIPS, fixed point DSPs. We show the results about the implementation of OFDM demodulation, channel estimation and equalization functional blocks, for the 2k/8k modes. The adoption of general purpose DSPs provides a great flexibility in the development of different configurations of the receiver. Furthermore, it enables the feasibility of adaptive equalization schemes, where the quality of the channel estimation varies according to both channel characteristics and speed of the channel variations. The 16/32 bit fixed point architecture leads to a very low implementation loss, and a carefull optimization of the pipeline architecture of the processor allows the receiver to obtain short processing delays. The flexibility of the software approach along with the obtained performance make the proposed implementation very interesting in professional and high-end receivers for interactive, multimedia applications of DVB-T
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
