An innovative minimal paths algorithm based on operator calculus in graded semigroup algebras is described. Classical approaches to routing problems invariably require construction of trees and the use of heuristics t...
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ISBN:
(纸本)9781467309202
An innovative minimal paths algorithm based on operator calculus in graded semigroup algebras is described. Classical approaches to routing problems invariably require construction of trees and the use of heuristics to prevent combinatorial explosion. The operator calculus approach presented herein, however, allows such explicit tree constructions to be avoided. Moreover, the implicit tree structures underlying the problem are pruned automatically by the inherent properties of the semigroup algebras used in this approach. The operator calculus algorithm proposed here is applied to the problem of precomputed routing in a store-and-forward (S&F) satellite constellation, which provides message communication services by relaying messages between satellites through gateways on the ground. The minimum end-to-end delay paths obtained are compared with the best existing heuristics-based results. The best existing results were obtained from a greedy algorithm designed to explore only a portion of the solution space in order to avoid combinatorial explosion and memory overload. In all test cases, the operator calculus is shown to return paths whose minimum end-to-end delay is either equal to or less than that of the best existing result. In some cases, in which the tree pruning algorithm did not find a solution, the operator calculus does. These results correspond to a one-single constraint case considering the end-to-end delay as the cost of the links, if the case of multi constraints is considered (e.g. bandwidth, rapidity,...) the operator calculus approach can be similarly used.
The aim of this paper is to research an existing just-in-time scheduling problems. Moreover, we propose a new algorithm for a just-in-time scheduling problem, and perform a comparison between it and an existing algori...
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The aim of this paper is to research an existing just-in-time scheduling problems. Moreover, we propose a new algorithm for a just-in-time scheduling problem, and perform a comparison between it and an existing algorithm. The proposed algorithm has been based on the greedy algorithm. The greedy algorithm is the search method updating a solution in the direction where the improvement effect of the purpose function is the most remarkable only based on local information. As a result, we succeeded in introducing a new algorithm with a faster processing time than an existing algorithm.
In an orthogonal frequency division multiplexing (OFDM) communication system, data bits carried by each sub-carrier are not delivered at an equal error probability due to the effect of multipath fading. The effect can...
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ISBN:
(纸本)9781479902286
In an orthogonal frequency division multiplexing (OFDM) communication system, data bits carried by each sub-carrier are not delivered at an equal error probability due to the effect of multipath fading. The effect can be exploited to provide unequal error protections (UEP) to wireless data by carefully mapping bits into subcarriers. Previous works have shown that this frequency-aware approach can improve the throughput of wireless data delivery significantly over conventional frequency-oblivious approaches. We are inspired to explore the frequency-aware approach to improve the quality of wireless streaming, where video frames are naturally not of equal importance. In this work, we present FAVICS, a Frequency-Aware Video Communication System. In particular, we propose three techniques in FAVICS to harvest the frequency-diversity gain. First, FAVICS employs a searching algorithm to identify and provide reliable subcarrier information from a receiver to the transmitter. It effectively reduces the channel feedback overhead and decreases the network latency. Second, FAVICS uses a series of special bit manipulations at the MAC layer to counter the effects that alter the bits-to-subcarrier mapping at the PHY layer. In this way, FAVICS does not require any modifications to wireless PHY and can benefit existing wireless systems immediately. Third, FAVICS adopts a greedy algorithm to jointly deal with channel dynamics and frequency diversity, and thus can further improve the system performance. We prototype an end-to-end system on a software defined radio (SDR) platform that can stream video real-time over wireless medium. Our extensive experiments across a range of wireless scenarios demonstrate that FAVICS can improve the PSNR of video streaming by 5～10 dB.
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