Showing papers by "Wai-Choong Wong published in 1991"
11 Jun 1991
TL;DR: In this article, an ordered dynamic channel assignment with reassignment (ODCAR) scheme is proposed for highway microcellular radio environment where the microcells are shaped to segments of the highway.
Abstract: The authors propose an ordered dynamic channel assignment with reassignment (ODCAR) scheme and study its performance in a highway microcellular radio environment where the microcells are shaped to segments of the highway. Channels are assigned on an ordered basis in conjunction with a minimax algorithm to provide high capacity and to alleviate worst case channel congestion in each microcell. Simulation results show significant performance improvements in terms of channel utilization and probability of call failure. The load sharing feature of this improved scheme is demonstrated in a highway microcellular radio network with an asymmetrical teletraffic load condition. The authors examine how load sharing is accomplished under such circumstances. >
22 citations
01 Feb 1991
TL;DR: A robust speech communications system over a digital mobile radio channel using 12 Kbit/s embedded subband coding of speech and rate compatible punctured convolutional (RCPC) codes with generalised Viterbi decoding with combined error detection and correction is considered.
Abstract: A robust speech communications system over a digital mobile radio channel is considered We examine a system using 12 Kbit/s embedded subband coding of speech and rate compatible punctured convolutional (RCPC) codes with generalised Viterbi decoding for combined error detection and correction System performance is improved by exploiting the frame-toframe redundancy in the subband energy profile used for adaptive bit allocation in the subband coder Unreliable subband side information about the energy profile is identified through a two-stage process comprising the channel error detector and a source-based subband energy profile error detector The subband side information deemed unreliable is replaced with the estimates based on frame-to-frame redundancy This improved error detection capability in the subband side information allows a judicious reassignment of channel error protection bits to the subband main information, leading to an overall improvement in system performance Using a realistic simulation model of a digital mobile radio communication system, an improvement of up to 44 dB in recovered speech segmental SNR is obtained at a channel SNR of 6 dB, compared with a system with only channel error protection
7 citations
TL;DR: In this paper, a dynamic load sharing scheme based on a reconfigurable overlapped cellular coverage is investigated for various teletraffic conditions in a highway microcellular structure, accidents and road works result in localised congestions contributing to asymmetrical traffic load situations.
Abstract: In a highway microcellular structure, accidents and road works result in localised congestions contributing to asymmetrical teletraffic load situations. A dynamic load-sharing scheme based on a reconfigurable overlapped cellular coverage is investigated for various teletraffic conditions. System performance in terms of the probabilities of new calls blocked and handoff failure are improved significantly with this scheme.
6 citations
11 Jun 1991
TL;DR: The authors describe a hybrid image coding scheme called the classified hybrid image coder (CHIC), which combines the classified vector quantization (CVQ) and the discrete cosine transform (DCT) coding schemes to achieve a better performance than would be possible if they were to be used separately.
Abstract: The authors describe a hybrid image coding scheme called the classified hybrid image coder (CHIC). CHIC combines the classified vector quantization (CVQ) and the discrete cosine transform (DCT) coding schemes to achieve a better performance than would be possible if they were to be used separately. The image is subdivided into 16*16 pixel blocks (vectors) and transformed using DCT. Each vector is classified into an edge vector and a shade vector. Classification is based on the distribution and value of the DCT coefficients in each vector. Shade vectors are coded using CVQ. Edge vectors are further classified according to their edge strengths. In each of these classes, the coefficients are quantized and then coded with an adaptive arithmetic coder (AAC). The performance of the AAC is further improved by further classifying the DCT coefficients into different groups, based on their different frequency ranges. The AAC uses a set of training images to generate the initial histogram tables. >
3 citations