This work focuses on random linear packet coding as an efficient method for reliable high-speed underwater communications over acoustic links with long delay. The transmitter sends coded packets with a pre-determined ...
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ISBN:
(纸本)9781457720895
This work focuses on random linear packet coding as an efficient method for reliable high-speed underwater communications over acoustic links with long delay. The transmitter sends coded packets with a pre-determined redundancy over a simplex link with no feedback. The receiver checks each received packet, discarding packets with errors, until the necessary degrees of freedom for successful decoding have been achieved. Each coded packet is modulated using Orthogonal Frequency Division Multiplexing (OFDM) for transmission over an acoustic channel. Differentially coherent detection is employed at the receiver for symbol detection. We focus on an experimental analysis using an in-air testbed and verifying the results with signals transmitted during an experiment conducted off the coast of Kauai, HI, in July 2011.
Providing low-latency high-quality data services to mobile terminals has become a mandatory requirement for all mobile broadband standards. Therefore, effective countermeasures against mobile channel impairments, like...
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ISBN:
(纸本)9781424441471
Providing low-latency high-quality data services to mobile terminals has become a mandatory requirement for all mobile broadband standards. Therefore, effective countermeasures against mobile channel impairments, like small- and large-scale fading, are of the utmost importance whenever traditional physical layer channel codes do not provide sufficient resilience or request too much hardware resources. Among the possible countermeasures, the paper investigates the application of packet layer coding, which basically consists in applying forward error control techniques at upper layer (UL-FEC). In the paper the UL-FEC decoder performance analytical model already developed by authors is generalized and extended to include non-periodic shadowing and small-scale fading. Analytical results are then validated through numerical simulation considering a real application scenario.
In this work we analyze the average queue backlog for transmission of a single multicast flow consisting of M destination nodes in a wireless network. In the model we consider, the channel between every pair of nodes ...
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In this work we analyze the average queue backlog for transmission of a single multicast flow consisting of M destination nodes in a wireless network. In the model we consider, the channel between every pair of nodes is an independent identically distributed packet erasure channel. We first develop a lower bound on the average queue backlog achievable by any transmission strategy;for a single-hop multicast transmission, our bound indicates that the queue size must scale as at least Omega(ln(M)). Next, we generalize this result to a multihop network and obtain a lower bound on the queue backlog as it relates to the minimum-cut capacity of the network. We then analyze the queue backlog for a strategy in which random linear coding is performed over groups of packets in the queue at the source node of a single-hop multicast. We develop an upper bound on the average queue backlog for the packet-coding strategy to show that the queue size for this strategy scales as O(ln(M)). Our results demonstrate that in terms of the queue backlog for single-hop multicast, the packet coding strategy is order-optimal with respect to the number of receivers.
The paper investigates coding and encapsulation techniques for the possible extension of the Digital Video Broadcasting-Return Channel Satellite (DVB-RCS) to ensure a global coverage for mobile terminals. Specifically...
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ISBN:
(纸本)9781424416448
The paper investigates coding and encapsulation techniques for the possible extension of the Digital Video Broadcasting-Return Channel Satellite (DVB-RCS) to ensure a global coverage for mobile terminals. Specifically, Link Layer-Forward Error Correction (LL-FEC) appears to be a reliable solution, allowing to improve the C/N performance and to counteract the Doppler effect typical of mobile channels, avoiding scalability and latency issues of Automatic Repeat reQuest (ARQ) approaches. In the paper we evaluate LL-FEC performance when applied to the railway environment. It is shown how this scenario deeply affects the LL-FEC code performance both in the Multi Protocol Encapsulation (MPE), and the Generic Stream Encapsulation (GSE) cases. In order to counteract this performance reduction two different approaches are considered. In the first case, we increase the number of rows of the LL-FEC Reed Solomon (RS) matrix. In the second case we exploit the sliding encoding mechanism. We also introduce a modified version of GSE that shows reduced overhead and improved performance. Results show that DVB-RCS can greatly benefit from LL-FEC RS coding in reducing residual errors that cannot be counteracted at the physical layer for efficiency reasons.
The object of this study is the data compression of CT scans of the brain. A circle is first established which contains all pixels inside the head while minimizing the insignificant area, after which the portion outsi...
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The object of this study is the data compression of CT scans of the brain. A circle is first established which contains all pixels inside the head while minimizing the insignificant area, after which the portion outside the circle so obtained is eliminated. The data are then truncated at CT values of +/- 127 and the differences of two consecutive pixel values are converted into variable length codes. The coding algorithms employed are the well-known Huffman code and our packet coding, both of which achieved a data compression ratio of 20%.
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