208,206 research outputs found
An Analysis of Packet Fragmentation Impact in LPWAN
Packet fragmentation has mostly been addressed in the literature when
referring to splitting data that does not fit a frame. It has received
attention in the IoT community after the 6LoWPAN working group of IETF started
studying the fragmentation headers to allow IPv6 1280 B MTU to be sent over
IEEE 802.15.4 networks supporting a 127 B MTU. In this paper, and following
some of the recent directions taken by the IETF LPWAN WG, an analysis of packet
fragmentation in LPWANs has been done. We aim to identify the impact of sending
the data in smaller fragments considering the restrictions of industrial
duty-cycled networks. The analyzed parameters were the energy consumption,
throughput, goodput and end to end delay introduced by fragmentation. The
results of our analysis show that packet fragmentation can increase the
reliability of the communication in duty-cycle restricted networks. This is of
especial relevance when densifying the network. We observed relevant impact in
energy consumption and extra latency, and identified the need for
acknowledgements from the gateway/sink to exploit some of the benefits raised
by fragmentation.Comment: paper accepted and presented at IEEE Wireless Communications and
Networking Conference, 15-18 April, Barcelona, Spai
General analytical framework for cooperative sensing and access trade-off optimization
In this paper, we investigate the joint cooperative spectrum sensing and
access design problem for multi-channel cognitive radio networks. A general
heterogeneous setting is considered where the probabilities that different
channels are available, SNRs of the signals received at secondary users (SUs)
due to transmissions from primary users (PUs) for different users and channels
can be different. We assume a cooperative sensing strategy with a general
a-out-of-b aggregation rule and design a synchronized MAC protocol so that SUs
can exploit available channels. We analyze the sensing performance and the
throughput achieved by the joint sensing and access design. Based on this
analysis, we develop algorithms to find optimal parameters for the sensing and
access protocols and to determine channel assignment for SUs to maximize the
system throughput. Finally, numerical results are presented to verify the
effectiveness of our design and demonstrate the relative performance of our
proposed algorithms and the optimal ones.Comment: arXiv admin note: text overlap with arXiv:1404.167
Microarray Analysis of Late Response to Boron Toxicity in Barley (Hordeum vulgare L.) Leaves
DNA microarrays, being high-density and high-throughput, allow quantitative analyses of thousands of genes and their expression patterns in parallel. In this study, Barley1 GereChip was used to investigate transcriptome changes associated with boron (B) toxicity in a sensitive barley cultivar (Hordeum vulgare L. cv. Hamidye). Eight-day-old aseptically grown seedlings were subjected to 5 or 10 mM boric acid (B(OH)(3)) treatments for 5 days and expression profiles were determined with DNA microarrays using total RNA from leaf tissues. Among the 22,840 transcripts - each represented with a probe set on the GeneChip - 19,424 probe sets showed intensity values greater than 20(th) percentile in at least one of the hybridizations. Compared to control (10 mu M B(OH)(3)), 5 mM B(OH)(3) treatment resulted in differential expression of 168 genes at least by twofold. Moreover, 10 mM B(OH)(3) treatment resulted in at least twofold induction or reduction in expression of 312 transcripts. Among these genes, 37 and 61 exhibited significantly (P <0.05) altered levels of expression under 5 and 10 mM B(OH)(3) treatments, respectively. Differentially expressed genes were characterized using expression-based clustering and HarvEST:Barley. Investigations of expression profiles revealed that B toxicity results in global changes in the barley transcriptome and networks of signaling or molecular responses. A noticeable feature of response to 8 was that it is highly interconnected with responses to various environmental stresses. Additionally, induction of jasmonic acid related genes was found to be an important late response to B toxicity. Determination of responsive genes will shed light on successive studies aiming to elucidate molecular mechanism of B toxicity or tolerance. To the best of our knowledge, this is the first report on global expression analysis of barley seedlings under B toxicity
A methodology to benchmark flexible payload architectures in a megaconstellation use case
International audienceThis paper proposes a methodology to benchmark satellite payload architectures and find the optimal trade-offs between high flexibility and low complexity. High flexibility would enable the satellite to adapt to various distributions of user terminals on the ground and fulfill the data rate demand of these users. Besides, low complexity is required to keep satellite networks competitive in the context of emerging 5G networks. To estimate the flexibility of a payload, an indicator to characterize the non-uniformity of user distributions is proposed. Each benchmarked payload may be characterized by a graph relating the throughput to this parameter further denoted mu. The payload provides the same throughput trends for different scenarios of user distributions with the same mu parameter. As a consequence, the average capacity of the system may be estimated by (a) calculating the probability distribution of mu over the orbit and (b) integrating the throughput based on this payload response. It thus results in a straightforward way for benchmarking payloads directly on an estimation of the averaged capacity, accounting for the user distribution over the earth. A simulation platform has been developed to characterize the payload throughput including the implementation of a resource allocation algorithm that accounts for constraints of various payloads. Using this definition and the developed tool, we benchmark a bent-pipe architecture, a beam hopping architecture and a hybrid beam-steering architecture for a LEO megaconstellation use case. The methodology showcases the interest for investigating different payload architectures depending on realistic traffic scenario analysis
On Capacity and Delay of Multi-channel Wireless Networks with Infrastructure Support
In this paper, we propose a novel multi-channel network with infrastructure
support, called an MC-IS network, which has not been studied in the literature.
To the best of our knowledge, we are the first to study such an MC-IS network.
Our proposed MC-IS network has a number of advantages over three existing
conventional networks, namely a single-channel wireless ad hoc network (called
an SC-AH network), a multi-channel wireless ad hoc network (called an MC-AH
network) and a single-channel network with infrastructure support (called an
SC-IS network). In particular, the network capacity of our proposed MC-IS
network is times higher than that of an SC-AH network and an
MC-AH network and the same as that of an SC-IS network, where is the number
of nodes in the network. The average delay of our MC-IS network is times lower than that of an SC-AH network and an MC-AH network, and
times lower than the average delay of an SC-IS network, where
and denote the number of channels dedicated for infrastructure
communications and the number of interfaces mounted at each infrastructure
node, respectively. Our analysis on an MC-IS network equipped with
omni-directional antennas only has been extended to an MC-IS network equipped
with directional antennas only, which are named as an MC-IS-DA network. We show
that an MC-IS-DA network has an even lower delay of compared with an SC-IS network and our
MC-IS network. For example, when and , an
MC-IS-DA network can further reduce the delay by 24 times lower that of an
MC-IS network and reduce the delay by 288 times lower than that of an SC-IS
network.Comment: accepted, IEEE Transactions on Vehicular Technology, 201
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