Enhanced channel coding using source criteria in speech coders

Spectral efficiency in digital voice communications in personal communications networks is primarily provided for by advanced speech coding techniques. A threat to the quality and low bit rate requirements of these speech coders is imposed by the transmission channel. Channel coding is thus considered mandatory, but its performance is limited to specific channel conditions and system constraints like bandwidth and transmission power. The authors describe a technique for exploiting source redundancy in speech coders for further improving the performance of the channel coding scheme without the obligatory increased redundancy     

Video transmission over mobile satellite systems

Mobile satellite communication channels are characterized by long transmission delays, variation of these delays, high bit‐error‐rates, shadowing and the multipath effect which severely reduce the quality of video services. Error control techniques including feedback mechanisms, error concealment methods, forward error correction techniques and error resilience schemes are examined in this paper for achieving a high‐integrity video transmission over a mobile satellite channel. The application of three different error resilience algorithms, namely Turbo codes, error‐resilient entropy codes and two‐way decoding using reversible codes is presented. Their joint performance is also examined. Furthermore, a low‐delay and low‐complexity video transcoding algorithm which fully interconnects two very low bit rate video communication standards: MPEG‐4 and H.263 is also elaborated. This transcoder works as a gateway tool which links two heterogeneous multimedia networks, such as a mobile satellite network and a land‐based network, with negligible processing delay and complexity. Copyright © 2000 John Wiley & Sons, Ltd.     

Rate control algorithm for block-based variable rate video encoders

Bit rates generated from block-based hybrid video coding algorithms are highly variable. In some applications, constant bit rate is more desirable. A rate control algorithm making use of the prediction error of the current frame is proposed and shown to give an almost constant output bit rate. H.263 is used in simulation experiments to test the algorithm     

Closed-loop motion compensation for video coding standards

In the classical block-matching motion-estimation approach, the motion vectors which result in minimum distortion between the estimated and the actual image block are chosen. However, these motion vectors may not be optimal in terms of coding efficiency. An analysis by synthesis method which selects the optimal motion vectors, using the resulting bit rate and distortion, is presented. A significant reduction in bit rate is achieved with virtually no degradation in objective image quality. H.263 is used in simulation experiments to test the algorithm     

Rate control feedback mechanism for packet video networks

The authors incorporate a newly proposed rate control feedback mechanism (RCFM) in an H.263 video coder. RCFM adapts to network conditions to locally drop video packets and then discard corresponding macroblocks (MBs) from any further prediction process. The proposed RCFM regulates the output bitrate of an H.263 codec while keeping all encoder parameters fixed and maintaining a good QoS     

Utilisation of downsampling for arbitrary views in multi-view video coding

The effect of using downsampling for arbitrary views inside a multi- view sequence on the multi-view coding (MVC) efficiency is explored. A bit rate adaptive approach is proposed to consider downsampling certain views prior to encoding with relevant downscaling ratios. The inter-view references, if any, are downsampled to the same resolution and the decoded view is upsampled back to the original resolution. The results over several multi-view test sequences imply that up to 0.9 dB gain or 20% reduction in bit rate can be achieved, reducing the computational complexity in the encoder significantly at the same time.     

Lossy multiplexing of low bit rate speech in thin route telephony

To alleviate congestion at thin route multiplexers such as are used in VSAT systems, some transmitters are forced to drop speech packets. Receiver reconstruction of the lost speech invariably produces some degradation of quality. The authors exploit the knowledge of dropped packets at the transmitter to mitigate this degradation     

Vector-quantised transform coder for speech coding at 9-6 kbit/s and below

The transform approach to speech coding has been established for some time, and has been shown to be very efficient in controlling the bit allocation and the shape of the noise spectrum. Various transform coders have been reported which produce high-quality digital speech at around 16 kbit/s. Although these coders can maintain good quality down to about 9.6 kbit/s, they perform poorly at lower bit rates. Here we discuss how vector quantisation (VQ) can be used to improve the quality of transform coders. We describe one specific design of vector-quantised transform coder (VQTC) which follows on from earlier work, and which is capable of producing good-quality speech at as low as 4.8 kbit/s.     

Prediction of stereoscopic video quality using objective quality models of 2-D video

The timely deployment of three-dimensional (3-D) video applications requires accurate objective quality measures, so that time consuming subjective tests can be avoided. Investigated is the correlation between subjective and objective evaluations of colour plus depth map 3-D video. Subjective tests are performed to determine the overall image quality and depth perception of a range of asymmetrically coded video sequences. The subjective results are used to determine more accurate objective quality assessment metrics for colour plus depth map based stereoscopic video.     

Automatic 3D face synthesis using single 2D video frame

3D face synthesis has been extensively used in many applications over the last decade. Although many methods have been reported, automatic 3D face synthesis from a single video frame still remains unsolved. An automatic 3D face synthesis algorithm is proposed, which resolves a number of existing bottlenecks.