Younghwan Yoo

Airtime Fairness for IEEE 802.11 Multirate Networks

Under a multirate network scenario, the IEEE 802.11 DCF MAC fails to provide airtime fairness for all competing stations since the protocol is designed for ensuring max-min throughput fairness. As such, the maximum achievable throughput by any station gets bounded by the slowest transmitting peer. In this paper, we present an analytical model to study the delay and throughput characteristics of such networks so that the rate anomaly problem of IEEE DCF multirate networks could be mitigated. We call our proposal time fair CSMA (TFCSMA) which utilizes an interesting baseline property for estimating a target throughput for each competing station so that its minimum contention window could be adjusted in a distributed manner. As opposed to the previous work in this area, TFCSMA is ideally suited for practical scenarios where stations frequently adapt their data rates to changing channel conditions. In addition, TFCSMA also accounts for packet errors due to the time varying properties of the wireless channel. We thoroughly compare the performance of our proposed protocol with IEEE 802.11 and other existing protocols under different network scenarios and traffic conditions. Our comprehensive simulations validate the efficacy of our method toward providing high throughput and time fair channel allocation.

User Activity Recognition in Smart Homes Using Pattern Clustering Applied to Temporal ANN Algorithm

This paper discusses the possibility of recognizing and predicting user activities in the IoT (Internet of Things) based smart environment. The activity recognition is usually done through two steps: activity pattern clustering and activity type decision. Although many related works have been suggested, they had some limited performance because they focused only on one part between the two steps. This paper tries to find the best combination of a pattern clustering method and an activity decision algorithm among various existing works. For the first step, in order to classify so varied and complex user activities, we use a relevant and efficient unsupervised learning method called the K-pattern clustering algorithm. In the second step, the training of smart environment for recognizing and predicting user activities inside his/her personal space is done by utilizing the artificial neural network based on the Allen’s temporal relations. The experimental results show that our combined method provides the higher recognition accuracy for various activities, as compared with other data mining classification algorithms. Furthermore, it is more appropriate for a dynamic environment like an IoT based smart home.

A Partition-Based LEACH Algorithm for Wireless Sensor Networks

Wireless sensor networks (WSN) have been considered as a promising method for reliably monitoring both civil and mili-tary environments under hazardous or dangerous conditions. Due to such environments, the power supplies for sensors in the network are not usually rechargeable or replaceable. There-fore, the energy efficiency is critical for the lifetime and cost of WSN. Numerous mechanisms have been proposed to reduce the impact of communication protocols on the overall energy dissipation of WSN. The low-energy adaptive clustering hierarchy (LEACH) deploys randomized rotation of cluster-heads to evenly distribute the energy load among all sensors in a WSN. This paper proposes an improved LEACH algorithm called partition-based LEACH (pLEACH), which firstly parti-tions the network into optimal number of sectors, and then selects the node with the highest energy as the head for each sector, using the centralized calculations. The simulation re¬sults and analysis show that pLEACH could achieve much better performance of WSN in terms of the energy dissipation and network lifetime.

A Bit collision detection based Query Tree protocol for anti-collision in RFID system

Anti-collision algorithms in the RFID system can be divided into two categories: ALOHA based and binary tree based algorithm. Each of them has its own advantages or disadvantages. The QT protocol, as a classic binary tree based algorithm, was proposed to achieve the reliable throughput of identification by using prefix to avoid collisions. This paper proposes an improved QT protocol called Bit collision detection based Query Tree (BQT) by adopting individual bit collision detection, which can detect the collision in each bit. It can reduce the collision for the tags which have the same prefix and accelerate identification process. The simulation results and analysis show that our BQT protocol could reduce the collisions and achieve much better performance on tag identification.

Mobile Sensor Relocation to Prolong the Lifetime of Wireless Sensor Networks

The wireless sensor network (WSN) has recently attracted considerable attention due to the low price and ease to deploy it. In particular, in a hostile or harsh regions where sensors cannot be deployed manually, WSNs can be established just by dropping sensors from the air. In this case, however, most likely sensors are not placed at optimal positions, although the location of sensors does have a drastic impact on the WSN performance. Moreover, randomized deployment algorithm can leave holes in terms of coverage in the sensing area. This paper proposes a sensor relocation scheme where mobile sensors move to patch up the holes by appropriate coverage. Simulation results show that the proposed algorithm outperforms prior existing schemes in terms of coverage and lifespan of WSNs.

Multiple shared backup cycles for survivable optical mesh networks

This paper proposes a backup network planning method for survivable WDM mesh networks. The proposed method centers around multiple backup cycles where each network link is assigned m backup cycles and each cycle protects 1/m of the working capacity of a target link. Distributed link restoration is performed using preplanned cycles, in which both the backup paths and the spare capacity can be shared. The preconfiguration of the cycles and the spare capacity placement are derived directly from the network topology off-line, which is independent of the primary traffic status or its dynamic changes over time. The proposed method provides efficiency and simplicity to survivable network design and management, and also to runtime recovery operation. Experimental results show that the proposed method needs on average under 60% of spare capacity redundancy for single link failure while preserving the speed of cycle-based restoration.

A Simple Load-Balancing Approach in Secure Ad Hoc Networks

Most ad-hoc routing protocols such as AODV and DSR do not try to search for new routes if the network topology does not change. Hence, with low node mobility, traffic may be concentrated on several nodes, which results in long end-to-end delay due to congestion at the nodes. Furthermore, since some specific nodes are continuously used for long duration, their battery power may be rapidly exhausted. Expiration of nodes causes connections traversing the nodes to be disrupted and makes many routing requests be generated at the same time. Therefore, we propose a load balancing approach called Simple Load-balancing Approach (SLA), which resolves the traffic concentration problem by allowing each node to drop RREQ or to give up packet forwarding depending on its own traffic load. Meanwhile, mobile nodes may deliberately give up forwarding packets to save their own energy. To make nodes volunteer in packet forwarding we also suggest a payment scheme called Protocol-Independent Fairness Algorithm (PIFA) for packet forwarding. To evaluate the performance of SLA we compare two cases where AODV employs SLA or not. Simulation results show that SLA can distribute traffic load well and improve performance of entire ad-hoc networks.

Impact of a simple load balancing approach and an incentive-based scheme on MANET performance

Most reactive mobile ad hoc network (MANET) routing protocols such as AODV and DSR do not perform search for new routes until the network topology changes. But, low node mobility does not affect the MANET connectivity and the same routes may be used for a long time. This may cause concentration of traffic on few mobile stations (MSs), which results in congestion and hence longer end-to-end delay. In addition, continuous use of MSs may cause their battery power to get exhausted rapidly. Expiration of MS energy causes disruption of connections traversing through the MSs and could generate many simultaneous new routing requests. Therefore, we propose a load balancing approach called Simple Load Balancing Approach (SLBA), which can be transparently added to any current reactive routing protocol such as AODV and DSR. SLBA minimizes the traffic concentration by allowing each MS to drop RREQ or to give up packet forwarding depending on its own traffic load. Meanwhile, MSs may deliberately give up forwarding packets to save their own energy. For encouraging MSs to volunteer in forwarding packets, we introduce a reward scheme for packet forwarding, named Protocol-Independent Fairness Algorithm (PIFA). We compare the performance of AODV and DSR with and without SLBA and PIFA. Simulation results indicate that SLBA can distribute traffic very well and improve the MANET performance. PIFA is also observed to prevent MANET partitioning and any performance degradation due to selfish nodes.

A partition-based centralized LEACH algorithm for wireless sensor networks using solar energy

Wireless Sensor Network (WSN) has been considered as a promising method for reliably monitoring both civil and military environments under hazardous conditions. Due to such condition, the power supply for sensor in the network cannot be usually rechargeable or replaceable. Thus, instead of battery replacement, we develop a solar energy recharging hardware to charge the battery of sensors to prolong the lifetime of each sensor recharging in the network. The proposed method, however, has a problem. Each node cannot be charged with the same amount of power depending on its physical location. The classic LEACH protocol deploys the randomize rotation of cluster-heads to evenly distribute the energy load among sensors without considering the unbalanced residual energy of each node. So some enhanced solar aware LEACH protocols have been proposed, but it is not much efficient for prolonging the lifetime of network. This paper proposes an advanced LEACH algorithm which prioritizes each sensor for the cluster--head election according to its current energy and rate of energy harvesting. The simulation results and analysis show that our proposed algorithm could outperform existing methods in terms of the number of alive nodes.

Impact of Node Density and Sensing Range on Intrusion Detection in Wireless Sensor Networks

Wireless sensor networks present a feasible and economic solution to some of the most challenging problems such as intrusion detection. In this paper, we establish relationship between node density, sensing range, and the possible intrusion distance before the intruder is detected by any of the sensors. We also extend our model to the multi-sensor joint detection case where an event can only be detected by k (k > 1) sensors simultaneously. Furthermore, we consider the effect of node heterogeneity on the intrusion detection in wireless sensor network, where two types of sensors with different sensing ranges are deployed. All the analytical results are validated via simulations. Our analysis can provide very useful insights in choosing network design parameters of sensor networks so that specified performance requirements can be met, thereby enhancing the acceptance of sensor networks.