Search results for "coding"
showing 10 items of 920 documents
Link Adaptation Thresholds for the IEEE 802.16 Base Station
2008
The IEEE 802.16 technology defines a number of modulation and coding schemes that the base station can use to achieve the best tradeoff between the spectrum efficiency and the resulting application level throughput. However, the 802.16 specification does not define any particular link level adaptation algorithm, neither does it specify the SNR thresholds to switch between modulation and coding schemes. In this paper we consider a link adaptation model and conduct a number of simulation runs to find transition thresholds for ARQ and HARQ retransmission mechanisms. All the simulations are done with the 802.16 extension for the NS-2 simulator.
Increasing the VoIP Capacity through MAP Overhead Reduction in the IEEE 802.16 OFDMa Systems
2010
One of the main issues with supporting VoIP service over 802.16 networks is the signalling overhead caused by the downlink MAP messages due to frequent transmissions and small packets. To decrease the MAP overhead, the 802.16 standard proposes some mechanisms, such as the compressed MAP and sub-MAPs. In this paper, we show by means of extensive dynamic simulations that sub-MAPs can reduce dramatically the signalling overhead associated with VoIP traffic and significantly improve overall VoIP capacity. At the same time, since sub-MAPs are more sensitive to packet drops, they tend to increase the number of HARQ retransmissions in downlink and transmission delays in the uplink direction.
ARQ parameters for VoIP in IEEE 802.16 networks
2009
IEEE 802.16 standard defines two data retransmission mechanisms. HARQ provides fast retransmissions in cost of slightly increased overhead. On the contrary, ARQ has less overhead in cost of bit longer delays. It is therefore often used with BE connections. In addition to delay tolerant applications, BE can also be used for real-time services. Therefore, in this paper we analyze the ARQ mechanism and provide guidelines on how to set the ARQ parameters to achieve a good balance between the VoIP delay and packet loss.
Wavelet-based video compression: A glimpse of the future?
2004
Masteroppgave i informasjons- og kommunikasjonsteknologi 2004 - Høgskolen i Agder, Grimstad Even though wavelet-based video compression has been an area of research for more than a decade, motion estimation and compensation has been considered complex and inefficient until recently. We have carried out a thorough investigation of existing research work in this field, and found that fundamental problem with wavelet-based temporal removal while obtaining highly scalability (the wavelet-properties of multiresolution structure in combination with embedded coding), has been solved by performing motion compensated temporal filtering within the wavelet domain of a overcomplete three-dimensional li…
Development of a Matlab Toolbox for Mobile Fading Channel Simulators
2007
Masteroppgave i informasjons- og kommunikasjonsteknologi 2007 – Høgskolen i Agder, Grimstad Knowledge of channel behaviours in mobile radio communication is extensively recommended for the study of transmitter/receiver performances. Our intention in this master's thesis is to develop various kinds of mobile fading channel simulators using Matlab. The developed channel simulators were combined into a user-friendly toolbox from which users can easily select well-known channel models to test and to study the performance of mobile communication systems. The toolbox can be integrated into the new release of Matlab software. The toolbox contains channel simulators for spatial shadowing processes,…
Analysis of audio coding algorithms for networked embedded systems
2004
Masteroppgave i informasjons- og kommunikasjonsteknologi 2004 - Høgskolen i Agder, Grimstad Today there are many different audio coding algorithms, some of them standardized by the ITU, like G.711, G.726 and G.728, and several other codecs by other organizations like Fraunhofer (mp3) and Microsoft (WMA). All these algorithms differ in several important features, like speech quality, bit or compression rate, robustness, delay, sampling frequency, complexity and range of use. The past decade we have witnessed a great progress towards application of low-rate speech/music coders as well as computer related voice/music applications. Central to this progress has been the development of speech cod…
An Iconic Framework for Learning the Art of Programming
2016
The integration of programming teachings, in all levels of education, highlights the need to acquire the art of programming for each individual student through versatile tools based on specific cognitive methods. Diversified linguistic metaphors have to be adopted by the developing frame, in order to highlight the qualities of each student. Therefore, a framework, oriented to learning the art of programming, must foster polychrome constructs representations, a number of data structures and an intuitive interfaces in order to make easier to understand the evolution of the algorithm that have to be developed. The following contribution will present a theoretical formalization of a framework f…
Comparative study of multi-2D, Full 3D and hybrid strategies for multi/hyperspectral image compression
2009
In this paper, we investigate appropriate strategies for multi/hyperspectral image compression. In particular, we compare the classic multi-2D compression strategy and two different implementations of 3D strategies (Full 3D and hybrid). All strategies are combined with a PCA decorrelation stage to optimize performance. For multi-2D and hybrid strategies, we propose a weighted version of PCA. Finally, for consistent evaluation, we propose a larger comparison framework than the conventionally used PSNR. The results are significant and show the weaknesses and strengths of each strategy.
The role of perceptual contrast non-linearities in image transform quantization
2000
Abstract The conventional quantizer design based on average error minimization over a training set does not guarantee a good subjective behavior on individual images even if perceptual metrics are used. In this work a novel criterion for transform coder design is analyzed in depth. Its aim is to bound the perceptual distortion in each individual quantization according to a non-linear model of early human vision. A common comparison framework is presented to describe the qualitative behavior of the optimal quantizers under the proposed criterion and the conventional rate-distortion based criterion. Several underlying metrics, with and without perceptual non-linearities, are used with both cr…
Super resolving optical system based on spectral dilation
2004
Time multiplexing is a common approach for achieving super resolution. The basic method involves moving two grating one is in front of the object and the other one in front of the camera. In this paper, we present a novel approach for obtaining super resolution not by shifting a grating, but by using its various dilations for obtaining the required encoding and decoding of information.