Young-myoung Kang

Robust Sybil attack defense with information level in online Recommender Systems

As the major function of Recommender Systems (RSs) is recommending commercial items to potential consumers (i.e., system users), providing correct information of RS is crucial to both RS providers and system users. The influence of RS over Online Social Networks (OSNs) is expanding rapidly, whereas malicious users continuously try to attack the RSs with fake identities (i.e., Sybils) by manipulating the information in the RS adversely. In this paper, we propose a novel robust recommendation algorithm called RobuRec which exploits a distinctive feature, admission control. RobuRec provides highly trusted recommendation results since RobuRec predicts appropriate recommendations regardless of whether the ratings are given by honest users or by Sybils thanks to the power of admission control. To demonstrate the performance of RobuRec, we have conducted extensive experiments with various datasets as well as diverse attack scenarios. The evaluation results confirm that RobuRec outperforms the comparable schemes such as PCA and LTSMF significantly in terms of Prediction Shift (PS) and Hit Ratio (HR).

PSD: Practical Sybil detection schemes using stickiness and persistence in online recommender systems

The main function of recommender systems (RSs) is to recommend user-customized information to customers or system users. Correct and useful information is crucial for both customers and service providers. The influence of RSs is expanding over the Internet. However, criminal users try to manipulate the results of RSs with fake identities (i.e., Sybils) for financial gain. Effective metrics are consequently required for defense against Sybil attack. In this paper, we first explore two metrics, stickiness and persistence, from the perspective of the RS security domain. We then propose practical detecting schemes, Dynamic Sybil Attack Monitoring on Recommender Systems (DySy-Rec) and Fuzzy rule-based DySy-Rec (FDySy-Rec), which apply stickiness and persistence in two real datasets from real movie RSs. To demonstrate the effectiveness and potential of DySy-Rec and FDySy-Rec, we conducted extensive experiments on the inclusion of more diverse and smart types of attacks. The experimental results show that the proposed schemes achieve substantial performance improvement compared with previous statistical approaches in terms of precision and recall. Finally, the results confirm the practical possibilities of exploiting stickiness and persistence in the fight against dynamic Sybil attacks in online RSs.

Opportunities of MIM capture in IEEE 802.11 WLANs: analytic study

Physical layer capture in WLANs makes a receiver to decode a relatively strong packet in a collision. According to recent works, an augmented physical layer capture handles interference better and facilitates more concurrent transmissions. This newly discovered physical layer capability is called Message in Message (MIM). It is a well-known fact that MIM capture capability can improve the throughput of wireless network. The MIM capture, however, only happens when a later packet has higher SINR (>=10dB). Furthermore, how likely MIM capture will happen has not been analyzed precisely. This paper analyzes that how likely such a MIM capture condition will take place in varying geometrical locations of nodes. It is the first analytical approach towards quantifying possibilities of performance gain from exploiting MIM capture capability in IEEE 802.11 WLANs. The result from our analysis shows that MIM capture and physical layer capture combined has maximum of 40% probability of occurrence. Moreover, we introduce several applications that harness MIM capture capability such as AP Placement Problem, AP Power Control, and Opportunistic Concurrent Transmission.

Design, Analysis and Implementation of Energy-efficient Broadcast MAC Protocols for Wireless Sensor Networks

In wireless sensor networks (WSNs), most energy saving asynchronous MAC protocols are custom tailored for unicast communications only. However, broadcast protocols are very commonly used in WSNs for a variety of functionalities, such as gathering network topology information, event monitoring and query processing. In this paper, we propose a novel low-power asynchronous broadcast MAC protocol called Alarm Broadcast (A-CAST). A-CAST employs the strobe preamble that specifies the residual waiting time for the following data transmission. Each receiver goes back to sleep upon hearing the strobe preamble for the residual time duration, to conserve energy and to wake up just before data transmission starts. We compute the energy consumption of A-CAST via rigorous mathematical analysis. The analytic results show that A-CAST outperforms B-CAST, a simple broadcast extension of the well-known B-MAC. We also implement A-CAST on sensor motes and evaluated its performance through real experiments. Our experimental results show that A-CAST reduces the energy consumption by up to 222% compared to the previously proposed protocols.

802.11mc: Using Packet Collision as an Opportunity in Heterogeneous MIMO-Based Wi-Fi Networks

Multiple-input-multiple-output (MIMO) technology boosts 802.11 Wi-Fi system capacities by using concurrent transmission of multiple streams from multiple antennas. The MIMO system in 802.11 Wi-Fi, however, typically requires request-to-send/clear-to-send (RTS/CTS)-like control message exchanges to fully realize the advantages of MIMO, although they incur nontrivial overhead. Furthermore, uncontrolled packet collisions severely limit the concurrent transmission gain of the MIMO nodes and the throughput of legacy single-input-single-output (SISO) nodes. In this paper, we propose a new distributed medium access control (MAC) protocol called 802.11 MIMO-based collision resolution (802.11mc). The 802.11mc protocol not only resolves the packet collisions but actually extracts channel information from collided frames as well to use it for concurrent MIMO transmissions. In particular, 802.11mc attaches a postamble after an RTS frame such that the channel information can be obtained, even when RTS frames collide. This information is used for interference alignment (IA) and cancelation for the interpretations of simultaneous frames. To show the feasibility of our proposal, we prototyped the scheme on the Universal Software Radio Peripheral (USRP) N210 testbed. Through both USRP experiments and NS-2-based simulations, we prove that 802.11mc improves the throughput gain of both MIMO and SISO nodes significantly.

Design, Analysis and Evaluation of A New Energy Conserving MAC Protocol for Wireless Sensor Networks

Low power listening (LPL) MAC protocols based on duty-cycling mechanism have been studied extensively to achieve ultra low energy consumption in wireless sensor networks (WSNs). Especially, recent ACK-based LPL schemes such as X-MAC employ strobe preambles and an early ACK, and show fair performances in communications and energy efficiencies. However, the state-of-the-art ACK-based LPL scheme still suffers from collision problems due to the protocol incompleteness. These collision effects are not trivial and make WSNs unstable, aggravate energy consumptions. In this paper, we propose two novel schemes; (i) ?-duration CCA to mitigate the collision problem in ACK-based LPL MAC protocols. (ii) Short Preamble Counter (SPC) to conserve more energy by reducing unnecessary overhearing. We demonstrate the performance improvement of our scheme via a mathematical analysis and real-time experiments. Both analysis and experimental results confirm that our proposed scheme saves energy by up to 36% compared to the naive ACK-based LPL MAC protocol thanks to ?-duration CCA and SPC.

A distributed message in message aware concurrent transmission protocol in IEEE 802.11 WLANs

The IEEE 802.11 distributed coordination function (DCF) employs the carrier sense technology to avoid frame collisions. However, recent measurement studies demonstrate that the physical layer (PHY) capture effect frequently occurs; even when frames collide, one of them can be decoded successfully if its relative signal strength is high enough. Furthermore, a new wireless PHY technology, called Message In Message (MIM), adopts an advanced preamble detection function to enhance the PHY capture effect. To fully exploit MIM in multi-collision environments, frame transmission orders have to be carefully scheduled. It also requires tight time synchronization at multiple access points (APs), thus induces large overheads. In this article, we propose an opportunistic concurrent transmission protocol called DistributedO pportunistic M IM-aware C oncurrent T ransmission (DOMCT) which exploits the MIM functionality in a distributed manner obliterating the centralized control. In DOMCT, APs first prepare interference MAPs to discover the possible simultaneous MIM transmission opportunities. Detecting the inadvertent frame transmission from a neighboring AP, an AP transmits another frame intentionally if both frames can successfully be decoded at destination nodes by the MIM capture effect. Through both analysis and extensive ns-2 simulations, we show that DOMCT outperforms the legacy DCF by up to 61% and observe comparable performance to that of the centralized approach.

An MIM-aware association control scheme for openflow access points in NOX architectures

Message In Message (MIM) is an emerging wireless technology to improve the capacity of wireless networks, which augments concurrent transmission opportunities of contending wireless nodes. In a MIM-capable communication system, however, the challenging problem is that the concurrent transmission opportunity is restricted by underlying network topologies. In this paper, we propose an MIM-aware association control scheme (MIMAC) that can greatly increase concurrent transmission opportunities by regulating the association among OpenFlow APs in NOX-based wireless systems. MIMAC exploits the distinctive features of NOX architectures, such as maintaining a global view of the network topology and controlling the association among OpenFlow APs in a centralized way. Using simulation-based evaluations, we demonstrate that MIMAC achieves high throughput enhancement by up to 200% compared to legacy WLAN systems.