164,508 research outputs found
Dual-Mode Vector-Quantised Low-Rate Cordless Videophone Systems for Indoors and Outdoors Applications
No full textDual-mode reconfigurable wireless videophone transceivers are proposed for noise-, rather than interference-limited indoors and outdoors applications and their video quality, bit rate, robustness, and complexity issues are analyzed. A suite of fixed, but arbitrarily programmable low-rate, perceptually weighted vector quantized (VQ) codecs with and without run-length compression (RLC) are contrived for quarter common intermediate format (QCIF) videophone sequences. The 11.36-kb/s Codec 1 is Bose–Chaudhuri–Hochquenghem (BCH) (127,71,9) coded to a rate of 20.32 kb/s and this arrangement is comparatively studied along with the 8-kb/s Codec 2 and BCH(127,50,13) scheme, which has the same 20.32-kb/s overall rate. The source-sensitivity matched Systems 1–6 characterized in Table IV were contrived to comparatively study the range of system design options. For example, using Codec 1 in System 1 and coherent pilot symbol assisted 16-level quadrature amplitude modulation (16-PSAQAM), an overall signaling rate of 9 kBd was yielded, if the noise-limited channel had a signal-to-noise ratio (SNR) in excess of about 22 dB in the vicinity of the basestation or in indoors scenarios. In contrast, over lower quality outdoors channels near the fringes of the cell, the more robust 4-QAM mode of operation had to be invoked, which required twice as many time slots to accommodate the resulting 18-kBd stream and hence, reduced the total number of users supported. The robustness of Systems 2–4, and 6 was increased using automatic repeat requests (ARQ), again, inevitably reducing the number of users supported, which was between 6 and 16. In a bandwidth of 200 kHz, similarly to the Pan-European GSM mobile radio system’s speech channel, using systems 1, 3, 4, or 5, for example, 16 and eight videophone users can be supported in the 16- and 4-QAM modes, respectively, while in dual-mode cells the number of users is between eight and 16. The basic system characteristics are highlighted in Table IV. Index Terms—Fixed-rate video coding, QAM video communications, vector-quantized video coding, wireless video telephony
Multi-Mode Wireless Videophony
No full textA comparative study of arbitrarily programmable, but fixed-rate videophone codecs using quarter common intermediate format (QCIF) video sequences scanned at 10 frames/s is offered. These codecs were designed to allow direct replacement of mobile radio voice codecs in second generation wireless systems, such as the Pan-European GSM, the American IS-54 and IS-95 as well as the Japanese systems, operating at 13, 8, 9.6 and 6.7 kbps, respectively, although better video quality is maintained over higher-rate, 32kbps cordless systems, such as the Japanese PHS and the European DECT and CT2 systems. Best overall performance was achieved by our vector-quantised codecs, followed by the discrete cosine transformed and the quadtree-based schemes, which were characterised by the bit allocation schemes of Table 1. The associated video Peak Signal-to-Noise Ratio (PSNR) was around 30 dB, while the subjective quality can be viewed under http://www-mobile.ecs.soton.ac.uk. A range of multimode wireless transceivers were also proposed, which are characterised by Table 2
Wilson's map operations on regulat dessins and cyclotomic fields of definition
No full textDessins d’enfants can be seen as bipartite graphs embedded in compact orientable surfaces. According to Grothendieck and others, a dessin uniquely determines a complex structure on the surface, even an algebraic structure as a projective algebraic curve defined over a number field. Combinatorial properties of the dessin should therefore determine the equations and also structural properties of the curve, such as the field of moduli or the field of definition. However, apart from a few series of examples, very few general results concerning such correspondences are known. As a step in this direction, we present a graph theoretic characterisation of certain quasiplatonic curves defined over cyclotomic fields, based on Wilson's operations on maps: these leave invariant the graph but change the cyclic ordering of edges around the vertices, therefore they change the embeddings, and hence the dessins, and hence the conformal and algebraic structure of the underlying curves. Under suitable assumptions, satisfied by many series of regular dessins, these changes coincide with the effect of Galois conjugation. This coincidence allows one to draw conclusions about Galois orbits and fields of definition of dessins. The possibilities afforded by these techniques, and their limitations, are illustrated by a new look at some known examples and a study of dessins based on the regular embeddings of complete graphs. <br/
[Siegmund Streit]
No full textPorträt von Sigismund Streit (1687-1775), radiert nach BardouBardou del. ; H. Lips sculp.Datierung gemäss Lips' chronologischem InventarBeim vorliegenden Blatt handelt es sich um einen Zustandsdruck, da die Bezeichnung des Dargestellten noch nicht in der Schrifttafel zu sehen istAuf Blatt handschriftliche Notiz "ō Brun"Auf Rückseite des Blattes handschriftliche Notiz "Prof. Sigmund Streit in Padua"Auf Unterlagenblatt handschriftliche Notiz "Prof. J. Streit"Auf Unterlagenblatt und Rückseite des Blattes Nummerierung nach Lips' Inventarisierung übernommen: Nr. 773, Album I
A Fractal Video Communicator
No full textThe image quality and compression ratio trade-offs of five different 176 × 144 pels quarter common intermediate format (QCIF) fractal image codes are investigated by simulation. The average peak signal-to-noise ratio (PSNR) ranges from 29 dB to 37 dB, while the coding rate from 0.24 bit/pel (bpp) to 1.22 bit/pel, as seen in Table 1. Two of the candidate codecs, a 0.28 bit/pel and a 1.1 bit/pel codec, were subjected to bit-sensitivity analysis and projected by the source-sensitivity matched shortened binary BCH(122,80,6) and BCH (122,52,11) codes and transmitted using coherent pilot symbol assisted (PSAM) square-constellation 16-level quadrature amplitude modulation (16-QAM). The proposed fractal video communications required a channel signal-to-noise ratio (SNR) and signal-to-interference ratio (SIR) of about 15 dB in order to maintain a video peak SNR (PSNR) of 31 dB and 35 dB at signaling rate of 39 kBaud and 156 kBaud, respectively, over Rayleigh-fading channels having a propagation frequency of 1800 MHz and a pedestrian speed of 2 mph
Quadtree-Based Reconfigurable Cordless Videophone Systems
No full textAbstract - Arbitrarily programmable, but fixed-rate quadtree (QT) decomposed. parametrically enhanced videophone codecs using quarter common intermediate format (QCIF) video sequences are proposed as a direct replacement for mobile radio voice codecs In second generation systems, such as the Pan-European GSM, the American IS-54 and IS-95, as well as the Japanese systems. The corresponding bit rates are 13, 8, 9.6 and 6.7 kb/s, respectively. As an example, the proposed 11.36 kb/s prototype Codec 1 and the 11 kb/s Codee 2 are embedded in the adaptively reconfigurable wireless videophone Systems 1-4 featured in Table IV and their video quality, bit rate, robustness, and complexity Issues are investigated. Coherent reconfigurable 16 or four-level pilot symbol assisted quadrature amplitude modulation (PSAQAM) is used and the system's robustness is Improved by a combination of diversity and automatic repeat request (ARQ) techniques. When using a bandwidth of 200 kHz, as In the Pan-European GSM mobile radio system, the number of videophone users supported varies between three and 16, while the minimum required channel signal to noise ratio over Gausslan and Rayleigh channels is in excess of 6 and 8 dB, respectively, assuming a noise-limited, rather than interference-limited scenario. The salient system features are summarized in Table 1V
Vector-quantised Cordless Videophone Transceivers
No full textA variety of adaptively re-configurable wireless videophone transceivers are proposed and their video quality, bit rate, robustness and complexity issues are analysed. A suite of fixed but arbitrarily programmable low-rate, perceptually weighted vector quantised (VQ) codecs with and without run-length compression (RLC) are contrived for quarter common intermediate format (QCIF) videophone sequences. The 11.36 kbps Codec 1 is BCH(127,71,9) coded to a rate of 20.32 kbps and this arrangement is comparatively studied along with the 8 kbps Codec 2 and BCH(127,50,13) scheme, which has the same 20.32 kbps overall rate. The source-sensitivity matched Systems 1-6 characterised in Table 3 were contrived to comparatively study the range of system design options. For example, using Codec 1 in System 1 and coherent pilot symbol assisted 16-level quadrature amplitude modulation (16-PSQAM), an overall signalling rate of 9kBd was yielded. Over lower quality channels the 4QAM mode of operation had to be invoked, which required twice as many time slots to accommodate the resulting 18kBd stream. The robustness of Systems 2,3,4 and 6 was increased using Automatic Repeat Requests (ARQ), inevitably reducing the number of users supported, which was between 6 and 16. In a band-width of 200kHz, similarly to the Pan European GSM mobile radio systems's speech channel, using Systems 1, 3, 4 or 5 for example, 16 and 8 videophone users can be supported in the 16QAM and 4QAM modes, respectively. The basic system characteristics are highlighted in Table 3
An Adaptive Discrete Cosine Transformed Videophone Communicator for Mobile Applications
No full textA highly bandwidth efficient, fixed but arbitrarily programmable rate, perceptually weighted Discrete Cosine Transfor (DCT) based video communicator for quarter common intermediate format (QCIF) videophone sequences is presented. Perceptually weighted cost/gain controlled motion compensation and quad-class DCT-based compression is applied without variable rate compression techniques and without adaptive buffering in order to maintain a fixed transmission rate, which can be adjusted to any required value. in this treatise we opted for a source coded rate of 11.36 kbps and the sensitivity-matched forward error correction (FEC) coded rate became 20.32 kbps. A partial forced update technique was invoked in order to keep transmitter and receiver aligned amongst hostile channel conditions. When using coherent pilot symbol assisted 16-level quadrature amplitude modulation (16-PSAQAM), an overall signalling rate of 9 kBd was yielded. OVer lower quality channels 4QAM had to be invoked, which required twice as many time slots to accommodate the resulting 18 kBd stream. Over the best Gaussian and worst Rayleigh channels signal-to-noise ratio (SNR) values in the range of 7 to 20 dB were needed for these modems in order to maintain near-unimpaired image quality. In a bandwidth of 200 kHz, similarly to the GSM speech channel, 16 and 8 videophone users can be supported, when using the 16QAM and 4QAM systems, respectively
Wireless Videophone Schemes
No full textA range of 5-11.36 kbps videophone codecs are proposed and the 11.36 kbps codec 1, the 8.52 kbps Codecs 2 and the 8 kbps Codec 2a are embedded in the intelligent re-configurable systems 1-3. After sensitivity-matched binary Bose-Chaudhuri-Hocquenghem (BCH) forward error correction (FEC) coding the data rate associated with Codec 1 and Codec 2a became 20.32 kbps, while that of Codec 2 was 15.24 kbps. When using Codec 1 in System 1 and coherent pilot symbol assisted 16-level quadrature amplitude modulation (16-PSAQAM), an overall signalling rate of 9 kBd was yielded. Over lower quality channels the 4QAM mode of operation had to be invoked, which required twice as many time slots to accommodate the resulting 18 kBd stream. In a bandwidth of 200 kHz, similarly to the Pa-European GSM mobile radio system’s speech channel, using Systems 1 and 3 for example, 126 and 8 videophone users can be supported in the 16QAM and 4QAM modes, respectively. All system features are summarised in Table 3
A 9/18 kBd Wireless Videophone Scheme
No full textA highly bandwidth efficient, fixed but arbitrarily programmable rate, perceptually weighted Discrete Cosine Transform (DCT) based video communicator for quarter common intermediate format (QCIF) videophone-sequences is presented. Perceptually weighted cost/gain controlled motion compensation and quad-class DCT-based compression is applied without variable rate compression techniques and without adaptive buffering in order to maintain a fixed transmission rate, which can be adjusted to any required value. In this treatise we opted for a source coded rate of 11.36 kbps and the sensitivity matched forward error correction (FEC) coded rate became 20.32 kbps. A partial forced update technique was invoked in order to keep transmitter and receiver aligned amongst hostile channel conditions. When using coherent pilot symbol assisted 16-level quadrature amplitude modulation (16-PSAQAM), an overall signalling rate of 9 kBd was yielded. Over lower quality channels 4QAM had to be invoked, which required twice as many time slots to accommodate the resulting 18 kBd stream. Over the best Gaussian and worst Rayleigh channels signal-to-noise ratio (SNR) values in the range of 7 to 20 dB were needed for these modems in order to maintain near-unimpaired image quality. In a bandwidth of 200 kHz, similarly to the GSM speech channel, 16 and 8 videophone users can be supported, when using the 16QAM and 4QAM systems, respectively
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