Jieun Yu

Effect of localized optimal clustering for reader anti-collision in RFID networks: fairness aspects to the readers

This paper proposes an adaptive and dynamic localized scheme unique to hierarchical clustering in RFID networks, while reducing the overlapping areas of clusters and consequently reducing collisions among RFID readers. Drew on our LLC scheme that adjusts cluster coverage to minimize energy consumption, low-energy localized clustering for RFID networks (LLCR) addresses RFID reader anti-collision problem in this paper. LLCR is a RFID reader anti-collision algorithm that minimizes collisions by minimizing overlapping areas of clusters that each RFID reader covers. LLCR takes into account each RFID readers energy state as well as RFID reader collisions. For the energy state factor, we distinguish homogeneous RFID networks from heterogeneous ones according to computing power of each RFID reader. Therefore, we have designed efficient homo-LLCR and hetero-LLCR schemes for each case. Our simulation-based performance evaluation shows that LLCR minimizes energy consumption and overlapping areas of clusters of RFID readers.

Cooperative Bridges: Topology Control in Cooperative Wireless Ad Hoc Networks

Cooperative Communication (CC) is a technology that allows multiple nodes to simultaneously transmit the same data. It can save power and extend transmission coverage. However, prior research work on topology control considers CC only in the aspect of energy saving, not that of coverage extension. We identify the challenges in the development of a centralized topology control scheme, named Cooperative Bridges, which reduces transmission power of nodes as well as increases network connectivity. We observe that CC can bridge (link) disconnected networks. We propose two algorithms that select the most energy efficient neighbor nodes, which assist a source to communicate with a destination node; an optimal method and a greedy heuristic. In addition we consider a distributed version of the proposed topology control scheme. Our findings are substantiated by an extensive simulation study, through which we show that the Cooperative Bridges scheme substantially increases the connectivity while consuming a similar amount of transmission power compared to other existing topology control schemes.

Reducing reader collision for mobile RFID

Mobile RFID, the technology of a cellular phone equipped with a RFID reader, allows users to read RFID tags anywhere. However, signals from more than two readers can interfere with one another, i.e., reader collision problem; reliable tag reading is necessary. This paper proposes GENTLE protocol to use beacon messages and multi-channel for increasing throughput. GENTLE protocol can also put tag ID information into the beacon message and share it among close readers. In addition, we suggest LSWBT protocol that reduces reader collision without beacon messages. Simulation results show that GENTLE and LSWBT protocols outperform existing reader anti-collision protocols.

New dominating sets in social networks

Motivated by applications in social networks, a new type of dominating set has been studied in the literature. In this paper, we present results regarding the complexity and approximation in general graphs.

GENTLE: Reducing Reader Collision in Mobile RFID Networks

Mobile RFID, the technology of a cellular phone equipped with a RFID reader, allows users to read RFID tags anywhere. However, signals from more than two readers can interfere with one another, i.e., reader collision problem; reliable tag reading is necessary. This paper proposes Gentle protocol to use beacon messages and multi-channel for increasing throughput. In addition, Gentle protocol can put tag ID information into the beacon message and share it among close readers. Simulation results show that Gentle protocol outperforms existing reader anti-collision protocols.

Topology Control in Cooperative Wireless Ad-Hoc Networks

Topology control is to determine the transmission power of each node so as to maintain network connectivity and consume the minimum transmission power. Cooperative Communication (CC) is a new technology that allows multiple nodes to simultaneously transmit the same data. It can save transmission power and extend transmission coverage. However, prior research work on topology control considers CC only in the aspect of energy saving, not that of coverage extension. We observe that CC can bridge (link) disconnected networks and therefore identify the challenges in the development of a centralized topology control scheme, named shape Cooperative Bridges, which reduces transmission power of nodes as well as increases network connectivity. We propose three algorithms that select energy efficient neighbor nodes, which assist a source node to communicate with a destination node: an optimal method and two greedy heuristics. In addition, we consider a distributed version of the proposed topology control scheme. Our findings are substantiated by an extensive simulation study, through which we show that the shape Cooperative Bridges scheme substantially increases the connectivity with tolerable increase of transmission power compared to other existing topology control schemes, which means that it outperforms in terms of a connectivity-to-power ratio.

Virtual machines placement for network isolation in clouds

Performance isolation is a serious issue in multi-tenant data center because interference among tenants can cause immense service troubles. Therefore, present data center provides performance isolation among tenants. However, it is limited to system resources, not network resources, nevertheless oversubscription that is caused by network interference entails troubles. Therefore, we place virtual machines (VMs) with matching algorithm into servers based on measured traffic distribution of VMs. We present our approach named Incubating that reduces oversubscription, also increases link utilization. We also show that our work has better practicality compared with prior work because we consider traffic distribution as a time unit.

ProTaR: Probabilistic Tag Retardation for Missing Tag Identification in Large-Scale RFID Systems

Radio frequency identification (RFID) technology provides a promising solution to the problem of missing object identification in large-scale systems, such as warehouses and bookstores by employing RFID readers to communicate with numerous RFID tags, each of which is attached to a monitored object. To achieve prompt identification of missing tags/objects, extensive research is carried out while the transmission of expatiatory bits from each tag and the occurrence of substantial tag collisions critically degrade the time efficiency. Therefore, this motivates us to propose ProTaR, a probabilistic tag retardation-based protocol, which addresses the missing tag identification problem in a more time-efficient way than the prior work. Based on an improvement of conventional frame-slotted ALOHA algorithm, ProTaR aims at alleviating the tag collision problem and achieving compact tag transmissions. The novelty of ProTaR is manifested mainly in two aspects. ProTaR leverages a mask at a reader to distill partial bits from 96-bit identifier (ID) of each tag for the characterization of tag uniqueness. In this context, ProTaR averts the transmission of redundant bits from both the tags and reader. A bit vector is constructed by the reader to inform each tag of the transmissions of others. This idea successfully eliminates the tag collisions, and hence makes full utilization of tag responses. Experimental results validate that ProTaR achieves 100% identification accuracy regardless of missing tag ratio. Furthermore, extensive simulations present that ProTaR enables the time efficiency improvement of up to 88% compared with benchmarks while merely degrading the optimum by 15%.

On the Calculation of the Maximal MOT Throughput in T-DMB

Digital multimedia broadcasting (DMB) is one of burgeoning communication technologies, which can provide audio, video, and data services to mobile terminals using broadcasting infrastructures. Data services in terrestrial- digital multimedia broadcasting (T-DMB) inherently have the disadvantage of retransmitting a lot of data unnecessarily for reliability. This paper proposes a novel optimized transmission policy using segment size and repetition number variability, which maximizes the object- level throughput as well as improves reliability. The theoretical modeling and simulation results demonstrate that our policy provides a throughput gain over the conventional protocol.

Impacts of Repetitions and Segment Size Variability on Object-Level Throughput in T-DMB

Data services in terrestrial-digital multimedia broadcasting (T-DMB) inherently have the disadvantage of retransmitting data unnecessarily for reliability. This paper proposes a novel optimized transmission policy using segment size and repetition number variability, which maximizes the object-level throughput. The theoretical modeling and simulation results demonstrate that our policy provides a throughput gain over the conventional protocol.