1,721,080 research outputs found
A Mobile Speech, Video and Data Transceiver Scheme
No full textThe complexity, robustness, image and speech quality as well as packet multiplexing issues of a re-configurable multi-media mobile communicator are addressed. The proposed moderate complexity motion-compensated Discrete Cosine Transform (DCT) based image communicator provides an image peak signal-to-noise ratio (PSNR) of 38 dB at an average bit rate of about 25 kbits/s. The speech codec used is a low-complexity 32 kbit/s CCITT G721 standard scheme. Bandwidth efficient 16 or 64 level quadrature amplitude modulation (QAM) combined with embedded low-complexity binary Bose-Chaudhuri-Hocquenghem (BCH) forward error correction (FEC) coding is deployed. The 20-slot packet reservation multiple access (PRMA) scheme used supports an extra 2.4 kbit/s low-rate data channel for each speech user in addition to providing 5-6 videophone channels. The ADPCM/DCT/BCH/16-QAM and ADPCM/DCT/BCH/64-QAM schemes provide nearly unimpaired speech and image quality for channel SNRs in excess of 30 dB and 38 dB, respectively
Transmission of Subband-Coded Images via Mobile Channels
No full textAbstract - The feasibility of a mobile video handset is investigated via Rayleigh-fading channels, where transmissions must be confined to the channel's coherence bandwidth to avoid the deployment of complex high-power-consumption channel equalizers. This necessitates the utilization of a low-bit-rate image codec error protected by embedded low-complexity Bose-Chaudhuri-Hoequenghem (BCH) codecs and spectrally efficient 16-level quadrature amplitude modulation (16-QAM). Motion-compensated onuniform 7-band subband coding (SBC) with subband-specific scanning, adaptive quantization (Q), run-length coding (RLO, and adaptive buffering to equalize bit-rate fluctuations offer good objective and subjective image quality at moderate complexity and a bit rate of 55 kbit/s. Using a twin-class embedded-BCH error protection as well as pilot symbol and diversity-assisted 16-QAM, our 22-kBd candidate system yields unimpaired image quality for average channel signal-to-noise ratios (SNR) in excess of about 16-18 dB, when the mobile speed is 4 mi/h, an SNR value readily maintained in personal-communications mobile systems characterized by small cells
A 22KBd Mobile Video Telephone Scheme
No full textThe complexity, image quality, bandwidth efficiency and robustness issues of a mobile video telephone scheme for personal communications networks (PCN) are addressed. Our motion-compensated 55 Kbit/s subband codec (SBC) using seven non-uniformly spaced active bands with band specific scanning and runlength coding achieves image peak signal to noise ratios (SNR) of around 38dB associated with good communications quality for monochrome common intermediate format (CIF) images sampled at 10 frames per second. The motion dependent bitrate fluctuations are smoothed out by buffering with adaptive quantiser control feedback. The video bits are then sorted into two sensitivity classes and error protected by a twin-class binary Bose-Chaudhuri-Hocquenghem (BCH) scheme. The separately BCH-encoded more significant bits (MSB) and less significant bits (LSB) are transmitted via separate subchannels of the 16-level quadrature amplitude modulator (16-QAM), having different integrity. The overall signalling rate becomes 22KBd, sufficiently low for typical microcells to fulfil the narrowband channel condition. Clearly, no equaliser has to be used, which considerably reduces the system’s complexity, yet unimpaired image quality is achieved for channel SNRs in excess of 20dB
A wireless multimedia system
No full textThe complexity, robustness, image and speech quality as well as packet multiplexing issues of a reconfigurable multi-media mobile communicator are addressed. The proposed moderate complexity motion-compensated Discrete Cosine Transform (DCT) based image communicator provides an image peak signal-to-noise ratio (PSNR) of 38 dB at an average bit rate of about 25 kbits/s. The speech codec used is a low-complexity 32 kbit/s CCITT G721 standard scheme. Bandwidth efficient 16 or 64level quadrature amplitude modulation (QAM) combined with embedded low-complexity binary Bose-Chaudhuri-Hocquenghem (BCH) forward error correction coding is deployed. The 20-slot packet reservation multiple access (PRMA) scheme used supports an extra 2.4 kbit/s low-rate data channel for each speech user, in addition to providing 5-6 video-phone channels. The ADPCM/DCT/BCH/16-QAM as well as 64QAM schemes provide nearly unimpaired speech and image quality for channel SNRs in excess of 30 dB and 38 dB, respectively
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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