Source-Channel Diversity for Parallel Channels

We consider transmitting a source across a pair of independent, non-ergodic channels with random states (e.g., slow fading channels) so as to minimize the average distortion. The general problem is unsolved. Hence, we focus on comparing two commonly used source and channel encoding systems which correspond to exploiting diversity either at the physical layer through parallel channel coding or at the application layer through multiple description source coding. For on-off channel models, source coding diversity offers better performance. For channels with a continuous range of reception quality, we show the reverse is true. Specifically, we introduce a new figure of merit called the distortion exponent which measures how fast the average distortion decays with SNR. For continuous-state models such as additive white Gaussian noise channels with multiplicative Rayleigh fading, optimal channel coding diversity at the physical layer is more efficient than source coding diversity at the application layer in that the former achieves a better distortion exponent. Finally, we consider a third decoding architecture: multiple description encoding with a joint source-channel decoding. We show that this architecture achieves the same distortion exponent as systems with optimal channel coding diversity for continuous-state channels, and maintains the the advantages of multiple description systems for on-off channels. Thus, the multiple description system with joint decoding achieves the best performance, from among the three architectures considered, on both continuous-state and on-off channels.Comment: 48 pages, 14 figure

Advanced Telecommunications and Signal Processing Program

Contains an introduction and reports on seven research projects.Advanced Telecommunications Research ProgramAT&T FellowshipGEM FellowshipU.S. Federal Bureau of InvestigationLucent Technologies FellowshipCharles S. Draper LaboratoryU.S. Navy - Office of Naval Research NDSEG Graduate Fellowshi

Advanced Telecommunications and Signal Processing Program

Contains an introduction, and reports on seven research projects.Advanced Telecommunications Research ProgramAT&T FellowshipINTEL FellowshipU.S. Navy - Office of Naval Research NDSEG Graduate FellowshipMaryland Procurement Office Contract MDA904-93-C-418

Structural Comparison of Allogeneic and Syngeneic T Cell Receptor–Peptide-Major Histocompatibility Complex Complexes: A Buried Alloreactive Mutation Subtly Alters Peptide Presentation Substantially Increasing Vβ Interactions

The crystal structures of the 2C/H-2Kbm3–dEV8 allogeneic complex at 2.4 Å and H-2Kbm3–dEV8 at 2.15 Å, when compared with their syngeneic counterparts, elucidate structural changes that induce an alloresponse. The Asp77Ser mutation that imbues H-2Kbm3–dEV8 with its alloreactive properties is located beneath the peptide and does not directly contact the T cell receptor (TCR). However, the buried mutation induces local rearrangement of the peptide itself to preserve hydrogen bonding interactions between the peptide and the α1 77 residue. The COOH terminus of the peptide main chain is tugged toward the α1-helix such that its presentation to the TCR is altered. These changes increase the stability of the allogeneic peptide-major histocompatibility complex (pMHC) complex and increase complementarity in the TCR–pMHC interface, placing greater emphasis on recognition of the pMHC by the TCR β-chain, evinced by an increase in shape complementarity, buried surface area, and number of TCR–pMHC contacting residues. A nearly fourfold increase in the number of β-chain–pMHC contacts is accompanied by a concomitant 64% increase in β-chain–pMHC shape complementarity. Thus, the allogeneic mutation causes the same peptide to be presented differently, temporally and spatially, by the allogeneic and syngeneic MHCs

Structure and stability of the Lukash plane-wave spacetime

We study the vacuum, plane-wave Bianchi $VII{}_{h}$ spacetimes described by the Lukash metric. Combining covariant with orthonormal frame techniques, we describe these models in terms of their irreducible kinematical and geometrical quantities. This covariant description is used to study analytically the response of the Lukash spacetime to linear perturbations. We find that the stability of the vacuum solution depends crucially on the background shear anisotropy. The stronger the deviation from the Hubble expansion, the more likely the overall linear instability of the model. Our analysis addresses rotational, shear and Weyl curvature perturbations and identifies conditions sufficient for the linear growth of these distortions.Comment: Revised version, references added. To appear in Class. Quantum Gra

JPSEC for secure imaging in JPEG 2000

People v. Wood, 12 N.Y.2d 69, 187 N.E.2d 116, 236 N.Y.S.2d 44 (1962)

Advanced Television and Signal Processing Program

Contains an introduction and reports on two research projects.Advanced Television Research Progra

Advanced Telecommunications and Signal Processing Program

Contains an introduction and reports on eleven research projects.Advanced Telecommunications Research Progra

Advanced Telecommunications and Signal Processing Program

Contains an introduction and reports on twelve research projects.AT&T FellowshipAdvanced Telecommunications Research ProgramINTEL FellowshipU.S. Navy - Office of Naval Research NDSEG Graduate FellowshipMaryland Procurement Office Contract MDA904-93-C-418