wei zhang, xianghua xu , qinchao zhang , jian wan, naixue xiong

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Network Coding Data Collecting Mechanism based on Prioritized DegreeDistribution in Wireless Sensor Network

Wei Zhang, Xianghua Xu, Qinchao Zhang ,Jian Wan, Naixue Xiong

2011 Ninth IEEE/IFIP International Conference on Embedded and Ubiquitous Computing

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Outline

• Introduction• Network Model• PLTCDS Algorithm • PLTCDS Analysis• PLTCDS TYPE Ⅱ• Result and Performance• Conclusion and Future Work

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Introduction

• Goal– To develop an effective data collecting mechanism

based on network coding to quickly recover source data while collecting. i.e., cliff effect.

• Main idea– The predefined node broadcasts a beacon to stimulate

the nodes to form the network with degree distribution priority.

– Introducing a class of cumulative counter scheme to avoid empty storage.

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Network Model• WSN consists of – n nodes that there are k source nodes and is not

very large, and that are uniformly distributed at random in a M*M region.

– collector S, usually at themarginal region of the network.

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Network Model

• The k source nodes disseminate the sensed data to the storage nodes by simply replication or coding, improving the network data persistency and reliability.

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Network Model

• Description of our scheme：1) The position of collector S is known.2) The source nodes act both a sensing and storage

node.3) Each node has limited knowledge of global

information, such as neighbor nodes, n, k but does not know the maximum degree of the network, and no routing table is maintained.

4) Each node has limited storage, assuming it can only store one encoded packet.

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PLTCDS Algorithm

• We present a prioritized LT Codes based distributed storage (PLTCDS) algorithm to improve decoding efficiency while collecting.

• The source packets are disseminated throughout the network by simple random walks, and nodes use the coding strategy to do its encoding operation.

• We use a simple way to grade the network finding out the nodes with prioritized degree level.

• The PLTCDS algorithm consists of 4 main phases: initialization, encoding, storage and decoding.

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PLTCDS Algorithm

1) Initialization phase• Packet header fields:

– Flag: indicating whether the data is new or an update of a previous value.

– Set C( to to guarantee the source packet visits each node in the network at least once.

𝑰𝑫 𝒗𝒊 𝑿𝒗𝒊 C(

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PLTCDS Algorithm

1) Initialization phase• Constructing network with degree level:

Initial : the degree level of every node is 0.The nodes receiving the beacon which the collector

broadcasts adjust the degree level to 1. We make these nodes as prioritized nodes.

• Nodes producing code degree:The nodes of degree level one : .The rest nodes draw a random number according to

the Ideal Soliton distribution .

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PLTCDS Algorithm2) Encoding phase

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PLTCDS Algorithm

3) Storage phase• The node(recoding all of sources’ ID) finishes its

encoding phase would not update the storage.• When all nodes satisfied these conditions,

network coding phase is completed.4) Decoding phase• The collector gets into the network from the

entry of the network and visits the nodes on a certain path.

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PLTCDS Analysis

• In this scenario, the collector firstly visits the nodes around it, it can quickly gather the encode packets with low degree, accelerating the decoding speed.

• Considering the worst case, that is, all of prioritized nodes failed before the collector get into the network, the performance would decline, but it can still maintain the performance of directly application of LT codes.

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PLTCDS TYPE Ⅱ• The nodes with degree priority are distributed

around the network instead of concentrated together near the entry of the network.

• Compared to PLTCDS, this algorithm is particularly effective for data collecting in disaster-prone areas and suitable for those areas that are difficult to access to the interior of the network.

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PLTCDS TYPE Ⅱ• There are some differences from the previous

PLTCDS in the initialization phase and decoding phase.

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PLTCDS TYPE ⅡInitialization phase• Constructing network with degree level:

Initial : the degree level of every node is 0.The node nearest to the middle of the network broadcasts a

beacon.All nodes hear it mark the degree level to one, and

rebroadcast it to their neighbors.A node hears the beacon with i but its degree is still zero,

update itself to i+1.We should find nodes with priority, so we define that the

nodes with the highest two degree level are prioritized nodes.

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PLTCDS TYPE ⅡDecoding phase

The collector moves a circle around the network first and then gets into the interior zone.

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Result and Performance

• The nodes are uniformly distributed in a field at random, and the hop count coefficient of the source packet C = 3.

• The location of the collector is (0,0).

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Data collecting in a random network

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Data collecting in a random network

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Data collecting in a disaster network

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Network connectivity

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PLTCDS TYPE Ⅱ

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CONCLUSION AND FUTURE WORK• Unlike previous schemes, PLTCDS considered

the data decoding efficiency.• PLTCDS can efficiently collect source data in

disaster scenarios, especially when the collector only can gather a small part of all nodes.

• we will improve this algorithm in more disaster scenarios and ease the influence on data persistence.