Fading Channel Modeling via Variable-Length Markov Chain Technique

Channel characterization and modeling are essential to the wireless communication system design. A model that optimally represents a fading channel with a variable-length Markov chain (VLMC) is proposed in this paper. A VLMC offers a general class of Markov chains whose structure has a variable order and a parsimonious number of transition probabilities. The proposed model consists of two main components: 1) the optimal fading partition under the constraint of a transmission policy and 2) the derivation of the best VLMC representation with respect to the Kullback-Leibler (K-L) distance of fading samples. The fading partition is used to discretize a continuous fading channel gain. The optimal discretization criterion is developed based on the cost function of fading channel statistics and the transmission policy used in the system. Once a continuous fading channel gain is discretized, a VLMC is then used to model the channel. To obtain the optimal VLMC representation, we use the K-L distance of the discretized fading samples as the optimization criterion. The K-L distance of the discretized fading samples is used to determine the appropriate transition probabilities characterizing the optimal VLMC. Last, we show simulation results that demonstrate the accuracy and the effectiveness of the proposed fading channel representation in modeling the Rayleigh fading as well as the lognormal fading.     

Dynamic Probabilistic Caching Algorithm with Content Priorities for Content‐Centric Networks

This paper presents a caching algorithm that offers better reconstructed data quality to the requesters than a probabilistic caching scheme while maintaining comparable network performance. It decides whether an incoming data packet must be cached based on the dynamic caching probability, which is adjusted according to the priorities of content carried by the data packet, the uncertainty of content popularities, and the records of cache events in the router. The adaptation of caching probability depends on the priorities of content, the multiplication factor adaptation, and the addition factor adaptation. The multiplication factor adaptation is computed from an instantaneous cache‐hit ratio, whereas the addition factor adaptation relies on a multiplication factor, popularities of requested contents, a cache‐hit ratio, and a cache‐miss ratio. We evaluate the performance of the caching algorithm by comparing it with previous caching schemes in network simulation. The simulation results indicate that our proposed caching algorithm surpasses previous schemes in terms of data quality and is comparable in terms of network performance.     

Robust scalable video multi-cast with multiple sources and inter-source network decoding in lossy networks

This paper presents a robust scalable video multi-cast scheme with source diversity and inter-source network decoding in lossy networks. The source diversity technique gives path diversity, providing a better quality of layered video transmission under hostile environments. For each source, an optimization formulation is set up to find the best transmission route of each transmitting video layer. The objectives of the formulation are to maximize the total information values of video layers reflecting the end-to-end video quality and transmission reliability. The source providing the best overall achievable data rate, which is the data rate destination can expect to receive from the transmission, is selected to be the primary source, while the rest will be secondary sources. When the Quality-of-Service (QoS) guarantees of some transmitting video layers cannot be fulfilled by the primary source, the secondary source with the best QoS parameters is selected to transmit the layers to destinations. The number of secondary sources used for transmissions is increased until the QoS guarantees of all transmitting video layers are satisfied or all network resources are utilized. Network coding is deployed to multi-cast video layers from the same source for efficient resource usage. Network coded data from different sources can be used to decode the transmitting video data. In other words, at each destination, it needs only a sufficient number of video packets from different sources to recover all transmitting video data. Simulations with different network topologies show the improvement in both objective and subjective qualities of layered video multi-cast under lossy environments.     

A cross-Layer quality-of-service mapping architecture for video delivery in wireless networks

Providing quality-of-service (QoS) to video delivery in wireless networks has attracted intensive research over the years. A fundamental problem in this area is how to map QoS criterion at different layers and optimize QoS across the layers. In this paper, we investigate this problem and present a cross-layer mapping architecture for video transmission in wireless networks. There are several important building blocks in this architecture, among others, QoS interaction between video coding and transmission modules, QoS mapping mechanism, video quality adaptation, and source rate constraint derivation. We describe the design and algorithms for each building block, which either builds upon or extend the state-of-the-art algorithms that were developed without much considerations of other layers. Finally, we use simulation results to demonstrate the performance of the proposed architecture for progressive fine granularity scalability video transmission over time-varying and nonstationary wireless channel.     

Outage probability analysis of antenna array using maximum ratio combining in spherically invariant fading environment

In this paper, the outage probability of maximum ratio combining (MRC) in the spherically invariant fading environment was analyzed. The study was done with and without consideration of the effect of noise. First, the probability density functions (pdf) of signal‐to‐interference plus noise ratio (SINR) and signal‐to‐interference ratio (SIR) were derived. In our derivation, the characteristic pdfs of spherically invariant random process (SIRP) corresponding to the interferences were assumed to be both different and identical. Moreover, both equal and different mean powers of interferences were considered. With the derived pdfs of SINR and SIR, the expressions of outage probability were computed. Numerical analysis was done using three numerical methods known as Gauss–Laguerre, Gauss–Hermite, and Gauss–Legendre integrations. It should be noted that SIRP, the generalization of Gaussian random process, is assumed to have K‐distribution, which is the generalization of Rayleigh. Our analysis was verified by comparing the outage probabilities of the considered environments with those of Rayleigh fading channel. From the numerical results, the derived outage probability converges to that of Rayleigh fading, when the shape parameter of characteristic pdf approaches infinity. Copyright © 2006 John Wiley & Sons, Ltd.     

Spatial error concealment with sequence-aligned texture modeling and adaptive directional recovery

A spatial error concealment technique based on the sequence-aligned texture modeling and the adaptive directional recovery is proposed in this work. The sequence alignment technique captures the local variation and the global trend of image textures with surrounding uncorrupted pixels, and provides the best texture model under a given cost function. With the derived texture model, geometric interpolation is used to recover lost pixels adaptively based on pixel locations. There are four candidate modes of pixel sequences to recover lost pixels, and one of them is selected for the concealment purpose. The selection criterion is based on the texture pattern modes of surrounding uncorrupted blocks. The pixel sequences used for error concealment can be obtained from the computation of the decoder or the side information from the encoder. Extensive experimental results are given to demonstrate that our error concealment technique outperforms several benchmark methods in both objective and subjective tests.