• Journal of Digital Convergence
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• v.11 no.12
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• pp.367-380
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• 2013

A secure data gathering in a Wireless Sensor Network(WSN) has given attention to one of security issues. In general, the process of secure data gathering causes difficulties: one process is exchanging the secured data and the other is constructing secured data path. The previous studies have been resolving the difficulties in terms of two problems: security and data gathering in WSNs. However, a WSN requires a protocol that has to guarantee a security of path between sensors and sink, or a cluster head. Thus how to gather data securely is an important issue. In this paper, we propose a secure data gathering protocol over WSNs, which consists of hierarchical key settlement and secure path construction, and aims at tackling two problems. The proposed protocol causes little overhead to sensor nodes for secured key settlement and path construction. This work provides security analysis focused on the key settlement protocol and evaluates network performance for the proposed data gathering protocol through simulation.

• Journal of Korea Multimedia Society
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• v.12 no.7
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• pp.997-1005
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• 2009

In this paper, we suggest an energy-efficient clustering scheme based on cross-layer design in wireless sensor networks. The proposed scheme works adequately for the characteristic environment of the networks. In the proposed clustering scheme, we separate clusters composed of sensor nodes in the event area from clusters of the other area when an event occurs by using an application layer information. We can save energy from multiple paths through multiple clusters to deliver the same event. We also suggest TDMA scheduling for non-evented clusters. In the scheduling, we allocate one time slot for each node to save energy. The suggested clustering scheme can increase the lifetime of the entire network. We show that our scheme is energy efficient through simulation in terms of the frequency of event occurrences, the event continual time and the scope.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.3
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• pp.243-257
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• 2010

Rapid developments in wireless sensor networks have extended many applications, hence, many studies have developed wireless sensor network positioning systems for indoor environments. Among those systems, the Global Position System (GPS) is unsuitable for indoor environments due to Line-Of-Sight (LOS) limitations, while the wireless sensor network is more suitable, given its advantages of low cost, easy installation, and low energy consumption. Due to the complex settings of indoor environments and the high demands for precision, the implementation of an indoor positioning system is difficult to construct. This study adopts a low-cost positioning method that does not require additional hardware, and uses the received signal strength (RSS) values from the receiver node to estimate the distance between the test objects. Since many objects in indoor environments would attenuate the radio signals and cause errors in estimation distances, knowing the path loss exponent (PLE) in an environment is crucial. However, most studies preset a fixed PLE, and then substitute it into a radio propagation loss model to estimate the distance between the test points; such method would lead to serious errors. To address this problem, this study proposes a Path Loss Exponent Estimation Algorithm, which uses only four beacon nodes to construct a radio propagation loss model for an indoor environment, and is able to provide enhanced positioning precision, accurate positioning services, low cost, and high efficiency.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.1
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• pp.62-77
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• 2010

Emerging applications with high data rates will need to transport bulk data reliably in wireless sensor networks. ARQ (Automatic Repeat request) or Forward Error Correction (FEC) code schemes can be used to provide reliable transmission in a sensor network. However, the naive ARQ approach drops the whole frame, even though there is a bit error in the frame and the FEC at the bit level scheme may require a highly complex method to adjust the amount of FEC redundancy. We propose a bulk data transmission scheme based on erasure-resilient code in this paper to overcome these inefficiencies. The sender fragments bulk data into many small blocks, encodes the blocks with LT codes and packages several such blocks into a frame. The receiver only drops the corrupted blocks (compared to the entire frame) and the original data can be reconstructed if sufficient error-free blocks are received. An incidental benefit is that the frame error rate (FER) becomes irrelevant to frame size (error recovery). A frame can therefore be sufficiently large to provide high utilization of the wireless channel bandwidth without sacrificing the effectiveness of error recovery. The scheme has been implemented as a new data link layer in TinyOS, and evaluated through experiments in a testbed of Zigbex motes. Results show single hop transmission throughput can be improved by at least 20% under typical wireless channel conditions. It also reduces the transmission time of a reasonable range of size files by more than 30%, compared to a frame ARQ scheme. The total number of bytes sent by all nodes in the multi-hop communication is reduced by more than 60% compared to the frame ARQ scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.5
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• pp.772-778
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• 2018

Due to the recent advances in computing, communication and micro-electromechanical technology, Wireless Sensor Networks (WSNs) applications have been extended from military to many commercial areas such as object tracking, wire detection, and vehicular sensor networks. In some applications bursty data from many sensor nodes may be generated and the generated data from the monitoring area may be sent in a limited time to the final destination, sink node. In this paper, we present a BTF-MAC protocol adequate for WSNs applications in which bursty data packets are required to be transmitted in a limited time. The BTF-MAC is a synchronous duty-cycle MAC protocol and uses a slot-reserved and operational period extension mechanism adapted to the traffics. Our numerical analysis and simulation results show that BTF-MAC outperforms other related protocols such as DW-MAC and SR-MAC in terms of energy consumption and transmission delay.

• KIPS Transactions on Software and Data Engineering
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• v.2 no.11
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• pp.747-756
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• 2013

It is important to reduce unnecessary overhead in sensor network using battery. In addition encryption is important because of necessity of security. Since unavoidable overhead occurs in case of encryption, security and overhead are in trade-off condition. In this paper, we use a concept called trust to reduce the encryption overhead. We reduce overhead by controlling encryption key sizes while maintaining the security level where high and low trust nodes are mixed. We simulated and compared normal encryption and trust value based encryption. As a result, the latter has lower execution time and overhead. If we define a standard of trust levels considering purpose and circumstances of real network, we can use constrained resources efficiently in sensor network.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.7
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• pp.2414-2434
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• 2015

Among numerous localization schemes proposed specifically for Wireless Sensor Network (WSN), the range-free localization algorithms based on the received signal strength indication (RSSI) have attracted considerable research interest for their simplicity and low cost. As a typical range-free algorithm, Approximate Point In Triangulation test (APIT) suffers from significant estimation errors due to its theoretical defects and RSSI inaccuracy. To address these problems, a novel localization method called FIAPIT, which is a combination of an improved APIT (IAPIT) and a fuzzy logic system, is proposed. The proposed IAPIT addresses the theoretical defects of APIT in near (it's defined as a point adjacent to a sensor is closer to three vertexes of a triangle area where the sensor resides simultaneously) and far (the opposite case of the near case) cases partly. To compensate for negative effects of RSSI inaccuracy, a fuzzy system, whose logic inference is based on IAPIT, is applied. Finally, the sensor's coordinates are estimated as the weighted average of centers of gravity (COGs) of triangles' intersection areas. Each COG has a different weight inferred by FIAPIT. Numerical simulations were performed to compare four algorithms with varying system parameters. The results show that IAPIT corrects the defects of APIT when adjacent nodes are enough, and FIAPIT is better than others when RSSI is inaccuracy.

• Journal of Biosystems Engineering
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• v.27 no.3
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• pp.259-266
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• 2002

It is crucial to know spatial soil variability for precision farming. However, it is time-consuming, and difficult to measure spatial soil properties. Therefore, there are needs fur sensing technology to estimate spatial soil variability, and for electronic mapping technology to store, manipulate and process the sampled data. This research was conducted to develop a real-time soil organic matter sensor and an electronic mapping system. A soil organic matter sensor was developed with a spectrophotometer in the 900∼1,700 nm range. It was designed in a penetrator type to measure reflectance of soil at 15cm depth. The signal was calibrated with organic matter content (OMC) of the soil which was sampled in the field. The OMC was measured by the Walkeley-Black method. The soil OMCs were ranged from 0.07 to 7.96%. Statistical partial least square and principle component regression analyses were used as calibration methods. Coefficient of determination, standard error prediction and bias were 0.85 0.72 and -0.13, respectively. The electronic mapping system was consisted of the soil OMC sensor, a DGPS, a database and a makeshift vehicle. An algorithm was developed to acquire data on sampling position and its OMC and to store the data in the database. Fifty samples in fields were taken to make an N-fertilizer dosage map. Mean absolute error of these data was 0.59. The Kring method was used to interpolate data between sampling nodes. The interpolated data was used to make a soil OMC map. Also an N-fertilizer dosage map was drawn using the soil OMC map. The N-fertilizer dosage was determined by the fertilizing equation recommended by National Institute of Agricultural Science and Technology in Korea. Use of the N-fertilizer dosage map would increase precision fertilization up to 91% compared with conventional fertilization. Therefore, the developed electronic mapping system was feasible to not only precision determination of N-fertilizer dosage, but also reduction of environmental pollution.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.12
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• pp.933-937
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• 2009

This paper proposes a dynamic timeout scheduling for energy efficient and accurate aggregation by analyzing the single hop delay in wireless sensor networks based on IEEE 802.15.4. The proposed scheme dynamically configures the timeout value depending on both the number of nodes sharing a channel and the type of wireless media, with considering the results of delay analysis of the single hop delay. The timeout of proposed scheme is much smaller than the maximum single hop delay which is used as the timeout of traditional data aggregation schemes. Therefore the proposed scheme considerably reduces the energy consumption of idle monitoring for waiting messages. Also, the proposed scheme maintains the data accuracy by guaranteeing the reception ratio required by the sensor network applications. Extensive simulation has revealed that proposed scheme enhances energy consumption by 30% with maintaining data accuracy, as compared with the TAG data aggregation.

• Journal of Korea Multimedia Society
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• v.11 no.5
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• pp.633-640
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• 2008

Sensor node clustering is one of the most popular research topics to reduce the energy of sensor nodes in wireless sensor networks. Previous researches, however, did not consider prediction effects of sensed environment information on TDMA scheduling of a cluster, resulting energy inefficiency. In this paper, we suggest an energy efficient cluster-based scheduling scheme that can be applied flexibly to many environment information systems. This scheme reflects the environment information obtained at the application layer to the MAC layer to set up the schedule of a cluster. The application layer information sets up the scheduling referring to the similarity of sensed data of cluster head. It determines the data transmission considering the result of similarity. We show that our scheme is more efficient than LEACH and LEACH-C in energy, which are popular clustering schemes, through simulation.