Biomedical subjects

Pamela C Cosman

Publications and source records attributed to Pamela C Cosman.

5 recordsLinked to original sources

PubMed2006

Video coding with fixed-length packetization for a tandem channel.

A robust scheme is presented for the efficient transmission of packet video over a tandem wireless Internet channel. This channel is assumed to have bit errors (due to noise and fading on the wireless portion of the channel) and packet erasures (due to congestion on the wired portion). First, we propose an algorithm to optimally switch between intracoding and intercoding for a video coder that operates on a packet-switched network with fixed-length packets. Different re-synchronization schemes are considered and compared. This optimal mode selection algorithm is integrated with an efficient channel encoder, a cyclic redundancy check outer coder concatenated with an inner rate-compatible punctured convolutional coder. The system performance is both analyzed and simulated. Last, the framework is extended to operate on a time-varying wireless Internet channel with feedback information from the receiver. Both instantaneous feedback and delayed feedback are evaluated, and an improved method of refined distortion estimation for encoding is presented and simulated for the case of delayed feedback.

Algorithms↗

PubMed2006

A cross-layer diversity technique for multicarrier OFDM multimedia networks.

Diversity can be used to combat multipath fading and improve the performance of wireless multimedia communication systems. In this work, by considering transmission of an embedded bitstream over an orthogonal frequency division multiplexing (OFDM) system in a slowly varying Rayleigh faded environment, we develop a cross-layer diversity technique which takes advantage of both multiple description coding and frequency diversity techniques. More specifically, assuming a frequency-selective channel, we study the packet loss behavior of an OFDM system and construct multiple independent descriptions using an FEC-based strategy. We provide some analysis of this cross-layer approach and demonstrate its superior performance using the set partitioning in hierarchical trees image coder.

Algorithms↗

PubMed2006

Drift-resistant SNR scalable video coding.

We address the problem of enhancement layer drift estimation for fine granular scalable video. An optimal per-pixel drift estimation algorithm is introduced. The encoder assumes that there is some truncation of the enhancement layer, which does not allow the enhancement layer reference to be properly reconstructed, and the encoder recursively estimates the associated drift and chooses coding modes accordingly. The approach yields performance gains of about 1 dB across low to medium rates. In addition, we investigate dual frame prediction, for both base and enhancement layer, with pulsed-quality allocation in the base

Algorithms↗

PubMed2006

Error-resilient video communications over CDMA networks with a bandwidth constraint.

We present an adaptive video transmission scheme for use in a code-division multiple-access network, which incorporates efficient bandwidth allocation among source coding, channel coding, and spreading under a fixed total bandwidth constraint. We derive the statistics of the received signal, as well as a theoretical bound on the packet drop rate at the receiver. Based on these results, a bandwidth allocation algorithm is proposed at the packet level, which incorporates the effects of both the changing channel conditions and the dynamics of the source content. Detailed simulations are done to evaluate the performance of the system, and the sensitivity of the system to estimation error is presented.

Algorithms↗

PubMed2004

Video compression for lossy packet networks with mode switching and a dual-frame buffer.

Video codecs that use motion compensation benefit greatly from the development of algorithms for near-optimal intra/inter mode switching within a rate-distortion framework. A separate development has involved the use of multiple-frame prediction, in which more than one past reference frame is available for motion estimation. In this paper, we show that using a dual-frame buffer (one short-term frame and one long-term frame available for prediction) together with intra/inter mode switching improves the compression performance of the coder. We improve the mode-switching algorithm with the use of half-pel motion vectors. In addition, we investigate the effect of feedback in making more informed and effective mode-switching decisions. Feedback information is used to limit drift errors due to packet losses by synchronizing the long-term frame buffers of both the encoder and the decoder.

Algorithms↗