Threshold jumping and wrap-around scan techniques toward efficient tag identification in high density RFID systems

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1 DOI /s Threshold jumping and wrap-around scan techniques toward efficient tag identification in high density RFID systems Ching-Hsien Hsu & Han-Chieh Chao & Jong Hyuk Park # Springer Science + Business Media, LLC 2009 Abstract With the emergence of wireless RFID technologies, the problem of Anti-Collision has been arousing attention and instigated researchers to propose different heuristic algorithms for advancing RFID systems operated in more efficient manner. However, there still have challenges on enhancing the system throughput and stability due to the underlying technologies had faced different limitation in system performance when network density is high. In this paper, we present a Threshold Jumping (TJ) and a Wrap-Around Scan (WAS) techniques, which are query tree based approaches, aiming to coordinate simultaneous communications in high density RFID environments, to speedup tag identification, to increase the overall read rate and to improve system throughput in largescale RFID systems. The main idea of the Threshold C.-H. Hsu Department of Computer Science and Information Engineering, Chung Hua University, Hsinchu, Taiwan, Republic of China chh@chu.edu.tw H.-C. Chao Institute of Computer Science & Information Engineering, and Department of Electronic Engineering, National Ilan University, I-Lan, Taiwan, Republic of China hcc@mail.niu.edu.tw hcc@mail.ndhu.edu.tw H.-C. Chao Department of Electrical Engineering, National Dong Hwa University, Hualien, Taiwan, Republic of China J. Hyuk Park (*) Department of Computer Science and Engineering, Kyungnam University, Masan, Kyungnam, South Korea parkjonghyuk1@hotmail.com Jumping is to limit the number of collisions. When the number of collisions exceeds a predefined threshold, it reveals that tag density in RF field is too high. To avoid unnecessary enquiry messages, the prefix matching will be moved to next level of the query tree, alleviating the collision problems. The method of setting frequency bound indeed improves the efficiency in high density and randomly deployed RFID systems. However, in irregular or imbalanced RFID networks, inefficient situation may happen. The problem is that the prefix matching is performed in single direction level-order scheme, which may cause an imbalance query tree on which the right subtree always not been examined if the identification process goes to next level before scan the right sub-tree due to threshold jumping. By scanning the query tree from right to left in alternative levels, i.e., wrap-around, this flaw cold be ameliorated. To evaluate the performance of proposed techniques, we have implemented the TJ and the WAS method along with the query tree protocol. The simulation results show that the proposed techniques provide superior performance in high density environments. It is shown that the TJ and WAS are effective in terms of increasing system throughput and minimizing identification delay. Keywords Tag anti-collision. Query tree. Wrap-around scan. Threshold jumping 1 Introduction Radio Frequency Identifier (RFID) system is an automatic technology to identify objects, record metadata or control individual target through radio waves. The RFID system is mainly composed by three components, tags, readers and host system. An RFID tag is comprised of integrated circuit

2 with an antenna for storing information and communication, respectively. An RFID reader is capable of reading the information stored at tags located in its sensing range. The host system is a control center that provides services and management. The electronics in the RFID reader use an outside power resource to generate signal to drives the reader s antenna and turn into radio wave. The radio wave will be received by RFID tag which will reflect the energy in the way of signaling its identification and other related information. In matured RFID systems, the reader s RF can also instruct the memory to be read or written from which the tag contained. Many applications, such as supply chain automation, identification of products at check-out points, security and access control, localization and object tracking have been developed to take the primary function of RFID systems. Advantages of RFID technologies, such as price efficiency, fast deployment, reusable and accuracy of stock management also broaden the scope of applications of RFID systems. Advanced characteristics of recent RFID readers, like size miniaturization and capabilities of Wi-Fi or cellular also motivate the development of large scale RFID systems. In recent RFID technologies, it is motivated that an RFID system can be integrated with wireless sensor network by interfacing RFID tags with external sensing capabilities, such as light, temperature or shock sensors; forming a hybrid infrastructure that combines advantages of both technologies. Similar to wireless sensor network, RFID tags can be deployed in an ad-hoc fashion instead of pre-installed statically. As a result, RFID has gradually been applied to our daily lives so that some identification problems might be happened. When a reader simultaneously communicate with multiple tags that are in the same interrogation zone, the tags responses might be collided because the tag could not be aware the existence of neighboring tags due to it has no carrier sense ability. Therefore, efficient methods for identifying multiple tags simultaneously are of great importance for the development of large-scale wireless RFID systems. In general, the tag anti-collision techniques can be classified into two categories, aloha based and query tree based protocols. Aloha based approaches use time slot to reduce collision probability. Tags randomly select a particular slot in the time frame, load and transmit its identification to the reader. Once the transmission is collided, tags will repeatedly send its id in next interval of time to make sure its id is successfully recognized. Alohabased protocols can reduce the collision probability. However, they have the tag starvation problem that a particular tag nay not be identified for a long time. For the consideration of performance, when number of RFID tag increased, the tag collision rate will be increased as well; this may result a low tag recognition rate. The query tree based schemes use a data structure similar to a binary search algorithm. An RFID reader consecutively communicates with tags by sending prefix codes based on the query tree data structure. Only tags in the reader s interrogation zone and of which ID match the prefix respond. The reader can identify a tag if only one tag respond the inquiry. Otherwise the tags responses will be collided if multiple tags respond simultaneously. Although tree based protocols do not bring the tag starvation problem, but they have relatively long identification delay. In this paper, we present a Threshold Jumping (TJ) and a Wrap-Around Scan (WAS) techniques aim to coordinate simultaneous communications in high density RFID environments, to speedup tag identification and to increase the overall read rate and throughput in large-scale RFID systems. The main idea of the proposed technique is to limit number of collisions during the identification phase. When number of collisions larger than the predefined acceptable ratio, it reveals that the density in RF field is too high. In order to minimize unnecessary inquiry, the prefix matching will be moved to lower level of the query tree, alleviating the collision problems. The method of setting collision bound indeed improves the efficiency of large-scale RFID tag identification. Together with the concept of wrap-around scan, the tag anti-collision problem could be significantly ameliorated. To evaluate the performance of proposed techniques, we have implemented the TJ and the WAS method along with other tag identification approaches. The experimental results show that the proposed techniques present significant improvement in most circumstance. The rest of this paper is organized as follows: In Section 2, a brief survey of related work will be presented. Section 3 introduces the tree based tag identification algorithm as preliminary of this study. In section 4, two query tree based algorithms, the Threshold Jumping (TJ) and Wrap-Around Scan (WAS) are proposed. Performance comparisons and analysis of the proposed techniques will be given in Section 5. Finally, in Section 6, some concluding remarks are made. 2 Related work Many research results have been proposed in literature, such as security and privacy related research (Weis et al. 2004) focuses on methods of preserving and protecting privacy of RFID tags; the RFID reader collision avoidance and hidden terminal problems were firstly addressed in (Engels et al. 2002) aiming to enhance accuracy of RFID systems; the energy saving and coverage problems (Namboodiri and Gao 2007; Zhang and Hou 2005; Ching- Hsien et al. 2008) were extensively studied in order to improve lifetime of wireless RFID networks.

3 Research efforts for collision avoidance have been also presented in literature. Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA) and Carrier Sense Multiple Access (CSMA) (Jain and Das 2006) are four basic access methods to categorize MAC-level protocols. Standard collision avoidance protocols like RTS-CTS (Sobrinho et al. 2005) cannot be directly applied in RFID systems due to the reason, in traditional wireless networks, the CTS are sent back to the sender. Similar situation in RFID system, when a reader broadcasts an RTS, all tags in the read range need to send back CTS to the reader. It then requires another collision avoidance mechanism for CTS, and it will make the protocol more complicated. Techniques for resolving RFID reader collision problems are usually proposed as reader anti-collision techniques or tag anticollision solutions. The Colorwave (Waldrop 2003) is a scheduling-based approach prevents RFID readers from simultaneously transmitting signal to an RFID tag. The Colorwave is used as a distributed anti-collision system based on TDMA in RFID network. The Pulse protocol (Shailesh et al. 2005) is referred as a beacon broadcast and CSMA mechanism. Readers periodically send a beacon during communication with tags in separate control channels. The contend_back-off and the delay_before_ beaconing in the protocol are similar in wireless networks. If a reader receives a beacon, the residual back-off timer will be stored and kept until the next coming chance. This process is expected to achieve the fairness among all readers. A coverage-based RFID reader anti-collision mechanism was proposed in (Joongheon et al. 2546). Kim et al. (Joongheon et al. 2546) presented a localized clustering coverage protocol for solving reader collision problems occurring among homogeneous RFID readers. In (Cha et al. 2006), Cha et al. proposed two ALOHA-based algorithms with a Tag Estimation Method (TEM) for speedup object identification in RFID systems. Hsu et al. (Ching-Hsien et al. 1007) proposed a two phase dynamic modulation (TPDM) scheme to coordinate communications between multiple readers and tags. In TPDM, the scheduling is divided into two phases, the regional scheduling and the hidden terminal scheduling. The existing tag identification approaches can be classified into two main categories, the Aloha-based (Klair et al. 2007; Law et al. 2000; Roberts 1975; Vogt 2002; Zhen et al. 2005) anti-collision scheme and the tree-based scheme (Capetanakis 1979; Myung et al. 2006; Ryu et al. 2007; Zhou et al. 2004). RFID readers in the former scheme create a frame with a certain number of time slots, and then add the frame length into the inquiry message sending tags in its vicinity. Tags response the interrogation based on a random time slot. Because collisions may happen at the time slot when two or more tag response simultaneously, making those tags could not be recognized. Therefore, the readers have to send inquiries contiguously until all tags are identified. As a result, Aloha-based scheme might have long processing latency in identifying large-scale RFID systems (Law et al. 2000). In (Vogt 2002), Vogt et al. investigated how to recognize multiple RFID tags within the reader s interrogation ranges without knowing the number of tags in advance by using framed Aloha. A similar research is also presented in (Zhen et al. 2005) by Zhen et al. In (Klair et al. 2007), Klair et al. also presented a detailed analytical methodology and an in-depth qualitative energy consumption analysis of pure and slotted Aloha anti-collision protocols. Another anti-collision algorithm called enhanced dynamic framed slotted aloha (EDFSA) is proposed in (Lee et al. 2005). EDFSA estimates the number of unread tags first and adjusts the number of responding tags or the frame size to give the optimal system efficiency. In tree-based scheme, such as ABS (Myung et al. 2006), IBBT (Choi et al. 2004) and IQT (Sahoo et al. 2006), RFID readers split the set of tags into two subsets and labeled them by binary numbers. The reader repeats such process until each subset has only one tag. Thus the reader is able to identify all tags. The adaptive memoryless tag anti-collision protocol proposed by Myung et al. (Myung & Lee 2005) is an extended technique based on the query tree protocol. Choi et al. also proposed the IBBT (Improved Bit-by-bit Binary-Tree) algorithm (Choi et al. 2004) in Ubiquitous ID system and evaluate the performance along three other old schemes. The IQT protocol (Sahoo et al. 2006) is a similar work approach by exploiting specific prefix patterns in the tags to make the entire identification process. Recently, Zhou et al. (Zongheng et al. 2007) consider the problem of slotted scheduled access of RFID tags in a multiple reader environment. They developed centralized algorithms in a slotted time model to read all the tags. With the fact of NPhard, they also designed approximation algorithms for the single channel and heuristic algorithms for the multiple channel cases. Although tree based schemes have advantage of implementation simplicity and better response time compare with the Aloha based ones, they still have challenges in decreasing the identification latency. In this paper, we present two enhanced tree based tag identification techniques aim to coordinate simultaneous communications in large-scale RFID systems, to speedup minimize tag identification latency and to increase the overall read rate and throughput. 3 Query tree based tag anti-collision Radio Frequency IDentification (RFID) system is operated with the identification function through radio frequency, but

4 usually, not only one tag is applied to the identification, that means RFID reader needs to identify multiple tags at the same time. However, collision problems may happen in the process of identifying multiple tags. Binary splitting is a commonly approach applied in solving the tag collision problems. Figure 1 demonstrates a simple example of the query tree scheme. As this is a simple example, the collision only happened at nodes 0 and 01, which are represented as grid circles. The reader takes six inquiries to identify the three tags in this example. Considering when tag density becomes higher, every time when collision happened, the reader will add one bit for prefix matching at next level. In such way, it may waste too much time in scanning the entire binary tree. Due to this, a threshold of collisions could be defined as the criterion to move the identification to next level of a query tree. When the number of collisions exceeds the predefined threshold, we can predict that tag density in RF field is too high. So, the prefix matching at the current level will be skipped and jump to next level in order to save unnecessary communications of prefix enquiries. This idea motivates the design of threshold jumping. 4 The proposed techniques 4.1 Threshold Jumping (TJ) Recall that when readers stay in the environment with high tags density, collision may happen very frequently, and owing to this, a lot of query time will be wasted. In Threshold Jumping algorithm, a threshold of collisions is mainly used as the criterion of moving the identification to next level of a query tree. By means of the criterion to judge the level of tag density, if the density is high, the corresponding level of the query tree will be jumped over. As shown in Fig. 2, when the number of collisions exceeds the predefined threshold, prefix matching at the present level will be skipped in order to save unnecessary prefix inquiries for the remaining part at the same level. Through the step, the number of inquiry message could be significantly reduced. Let s take an example to clarify the above concept. Given an RFID network having 13 tags with 4-bits id length as shown in Fig. 3, the prefix matching will be conducted in level order scheme. Prefix messages are with 1-bit in level 1, two bits length in level 2, and so on. To perform a complete inquiry in different level, the number of inquiry messages will be 2 in level 1, 4 in level 2, 8 in level 3, etc. Having the threshold set to 2 I /M, where I denotes the level in the query tree and M is a pre-defined constant, if the collisions in level I exceeds 2 I /M, the prefix matching will be jumped to the next level for a new search. Figure 3 shows the example of identifying 13 RFID tags using TJ with M=3. Based on the threshold ratio 1/3, the threshold in levels 1, 2, 3 are [2/3], [4/3] and [8/3], respectively. Namely, in level 1, the identification will be moved to level 2 if 1 collision occurred; when I=2, i.e., level 2, the identification moves to level 3 if more than 2 collisions are occurred; similarly, when I=3, the identification will be jumped to level 4 if more than 3 collisions are raised in level 3, and so on. Table 1 summarizes the detail information (collision, identified or idle) using the TJ method compared to the traditional query tree scheme. The TJ uses 22 inquiries to identify all tags while the QT spent 24 inquiries. One thing worthy to mention is that although 22 inquiries is much more than the number of RFID tags, but to exhaustively scan RFID tags using full length id is not a feasible approach. This is because for RFID tags having more than 16 bits length id, the process of scanning entire query tree will lead significant large amount of inquiries, i.e., Therefore, the query tree based mechanism with prefix matching is usually considered as the feasible solution in tag anti-collision problem. Recall the example described above, it s clear that there are a lot of unnecessary broadcast in the method of query tree with binary splitting. For the TJ technique, when collision exceeds a certain proportion, it reveals that tag density is too high so there is no need to continuously launch broadcast to current level in order to save identification time. Therefore, in the Threshold Jumping method, the threshold is taken to count the collision numbers. Once collision is over the proportion, there is no need to continue the query to the current level, instead, jumping to the next level. Based on the reduction of broadcasting messages, the efficiency of identification will be enhanced. 4.2 Wrap-Around Scan (WAS) The method of setting collision limitation in TJ (Threshold Jumping) is adopted to improve identification efficiency when tag density is high. Recall that the TJ scans the query tree in a level order scheme. The direction of scan is always from left to right. Considering that the single direction scan in TJ may result very limited information of idle or collision in the right sub-tree of the query tree due to the threshold jumping. As a result, the identification of right sub-tree will be postponed to the last moment. The main reason is that if threshold is fulfilled in TJ, right sub-tree will be skipped over so that inefficiency may happen if tag density is low or meets the situation of unbalanced tree. The problem can be resolved through alternatively change the direction of prefix scan in different levels; the so-called WAS (Wrap-Around Scan). In WAS, the identification of tags in the right sub-tree could be advanced by reversing

5 Fig. 1 Example of query tree algorithm the direction of scan in each level alternatively. Figure 4 demonstrates the idea of wrap-around scan. The level ordered scans start from left to right in all odd (or even) levels and starts from right to left in all even (or odd) levels. Using wrap-around scan, the amount of prefix inquiries is expected to be decreased as the advance findings of the information of no response / collisions in the query tree could be in a balanced way. Let s use the same example that illustrated in section 4.1 to demonstrate the WAS scheme. Figure 5 gives the details of identification of the WAS method. The WAS scans the query tree from right to left in level 1, the reverse in level 2, and reverse again in level 3, and so on. Since the threshold ration is set 1/3, the threshold of collisions are 1, 2 and 3 in level 1, level 2 and level 3, respectively. The only one collision happened in level 1 is node 1, the two collision nodes appeared in level 2 are nodes 00 and 01; while the three collision nodes in level 3 are happened at nodes 111, 100 and 010 in order. It s clear that the efficiency of identification is enhanced by means of the addition of WAS (Wrap-Around Scan) in TJ (Threshold Jumping). The reason is that the WAS (Wrap-Around Scan) could identify the tags of right sub-tree and learned more information regarding no response and collision. The advanced information can significantly diminish the inquiry messages. Such phenomenon reveals that the WAS (Wrap- Around Scan) can speed up the identification efficiency, especially in unbalanced or irregular RFID networks. 5 Performance evaluation To evaluate the performance of the proposed techniques, we have implemented the TJ and WAS schemes along with the query tree protocol (QT). Figure 6 compares the number of inquiries to identify different number of RFID tags. Because Fig. 2 The paradigm of threshold jumping

6 Fig. 3 Example of threshold jumping the tag id is set 8 bits length, density=10% means that there are %=26 tags and density=20% means that there are %=51 tags, and so on. All tags are randomly generated in a uniform distribution manner. This is so called balance tree, as entitled in the figure. In this test, the threshold ratio is set 1/3. Basically, the proposed techniques TJ and WAS can reduce the amount of inquiry messages. As we expected, the WAS outperforms the TJ. Although the TJ and WAS methods do not improve the inquiry messages very much in low density network, when density increasing, both of the proposed methods present significant improvements to the traditional query tree protocol. Figure 7 uses the same configuration as that of Fig. 6 but increases the length of tag ID. Because of the long Table 1 Tag identification of three different schemes Step Binary Tree Threshold Jumping Wrap-Around Scan Broadcast Status Identified Tag Broadcast Status Identified Tag Broadcast Status Identified Tag 1 0 Collision 0 Collision 0 Collision 2 1 Collision 00 Collision 00 Collision 3 00 Collision 01 Collision 01 Collision 4 01 Collision 000 Collision 111 Collision 5 10 Collision 001 Collision 110 Identified Collision 010 Collision 101 Collision Collision 0000 Identified Collision Collision 0001 Identified Identified Collision 0010 Identified Collision Identified Identified Identified Collision 0100 Identified Identified Identified Identified Identified Identified Identified Identified Collision 0111 No Response 0100 Identified Identified Identified Identified Identified Identified Identified Identified No Response 1001 Identified Identified Identified Identified Identified Identified Identified Identified No Response Identified Identified Identified Identified Identified Identified 1111

7 Fig. 4 The paradigm of wrap-around scan simulation time for high density network with 12 bits ID length, we only report the results from density=20% to density=80%. Namely, the number of tags in this test is set from %~ %, i.e., 819~3277. This simulation has similar observations as those of Fig. 6. The TJ and WAS have better performance compare to the QT in terms of the inquiry messages. As the TJ and WAS schemes define a collision threshold to limit unnecessary inquiries, Fig. 8 examines the effects of different threshold ratio to the performance of the two schemes. Figure 8(a) is the result for density=80% and Fig. 8(b) is the results for density=50%. For high density network, we observed that lower threshold resulting less inquiry cost. Both of the TJ and WAS methods outperform the traditional query tree protocol (QT). For low density RFID network, it is obvious that TJ and WAS will reach a lower bound inquiries when threshold ratio is less than 1/5. Similar to the previous one, the TJ and WAS have better performance compare to the QT in terms of the inquiry messages. The last experiment was conducted with different distribution of tags id. The term Tree Balance Factor (TBF) defined in Fig. 9 is used to indicate the percentage of tags distributed in left sub-tree and right sub-tree of a query tree. TBF=10% means that number of tags in left sub-tree and right sub-tree are with the ratio 1:9; similarly, TBF= 20% represents the number of tags in left sub-tree and right sub-tree are with the ratio 2:8. Since the distribution of tags in a query tree is not a uniform distribution, this is so called Fig. 5 Example of wrap-around scan

8 Inquiry QT Balance Tree (8-Bits) Inquiry Balance Tree (8-Bits), density=80% QT TJ WAS TJ WAS Density(%) a Threshold Ratio (1/TR) Inquiry Balance Tree (8-Bits), density=50% Fig. 6 Performance comparison of the TJ, WAS and QT with 8 bits RFID tag imbalance tree, as titled in Fig. 9. The experiment varies tree balance factor from 10% which means a balance tree, to 50% which reflects an imbalance distribution. The density is set 80% in this test. From the experimental results, the WAS scheme outperforms the TJ and the query tree methods. For imbalanced instances, the TJ performs worse than the query tree (BT) protocol. This is because the TJ method does not scan right sub-tree in most of levels in a query tree. As a result, there is no information of collision or no response at upper levels of the right sub-tree. Consequently, when the identification goes to lower levels, the reader needs to match large number of tags id. This situation usually happened in imbalanced tree. Such phenomenon matches the results shown in Fig. 9. For the cases of TBF=40% and 50%, the TJ scheme could present noticeable improvement as compare to the QT b QT TJ WAS Threshold Ratio Fig. 8 Performance comparison of the TJ, WAS and QT with different threshold ratio a results of density=80% b results of density=50% Inquiry Balance Treee(12--Bits) 350 Inquiry QT Imbalance Tree (8-Bits) TJ WAS QT TJ WA Density(%) Tree Balance Factor (%) Fig. 7 Performance comparison of the TJ, WAS and QT with 12 bits RFID tag Fig. 9 Performance comparison of the TJ, WAS and BT in imbalanced tree

9 6 Conclusions With the emergence of wireless RFID technologies, identifying high density RFID tags is a crucial task in developing largescale RFID systems. In this paper, we have presented two enhanced tree-based tag identification techniques for minimizing tag identification cost. By setting a collision bound, the prefix matching will be jumped to lower level of the query tree in order to alleviate the collision problems. Together with the wrap-around scan technique, the efficiency of tag identification can be significantly improved. To evaluate the performance of proposed techniques, we have implemented the TJ and WAS techniques along with the query tree protocol (QT). The experimental results show that the proposed techniques provide considerable improvements on the latency of tag identification. It is also shown that the TJ and WAS are effective in terms of increasing system throughput, efficiency and easy implementation. 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10 Dr. Ching- Hsien. Hsu received the B.S. and Ph.D. degrees in Computer Science from Tung Hai University and Feng Chia University, Taiwan, in 1995 and 1999, respectively. He is currently an associate professor in the department of Computer Science and Information Engineering at Chung Hua University, Taiwan. Dr. Hsu s research interest is primarily in parallel and distributed computing, cloud and grid computing, P2P computing and services computing. Dr. Hsu has published more than 100 academic papers in journals, books and conference proceedings. He was awarded as annual outstanding researchers by Chung Hua University in 2005, 2006 and 2007 and got the excellent research award in Dr. Hsu is serving in a number of journal editorial boards, including International Journal of Communication Systems, International Journal of Computer Science, International Journal of Grid and High Performance Computing, International Journal of Smart Home and International Journal of Multimedia and Ubiquitous Engineering. He has edited more than 20 international journal special issues as a guest editor. He has severed many international conferences as various chairs and committee members. Dr. Hsu is currently an IEEE senior member and serves as an executive committee of IEEE Technical Committee on Scalable Computing (TCSC). Homepage: TEL: FAX: Han-Chieh Chao is a joint appointed Full Professor of the Department of Electronic Engineering and Institute of Computer Science & Information Engineering. He also serves as the Dean of the College of Electrical Engineering & Computer Science for National Ilan University, I-Lan, Taiwan, R.O.C. He has been appointed as the Director of the Computer Center for Ministry of Education on September 2009 as well. His research interests include High Speed Networks, Wireless Networks, IPv6 based Networks, Digital Creative Arts and Digital Divide. He received his MS and Ph.D. degrees in Electrical Engineering from Purdue University in 1989 and 1993 respectively. Dr. Chao is also serving as an IPv6 Steering Committee member and co-chair of R&D division of the NICI (National Information and Communication Initiative, a ministry level government agency which aims to integrate domestic IT and Telecom projects of Taiwan), Co-chair of the Technical Area for IPv6 Forum Taiwan, the Editor-in-Chief of the Journal of Internet Technology, Journal of Internet Protocol Technology and International Journal of Ad Hoc and Ubiquitous Computing. Dr. Chao has served as the guest editors for Mobile Networking and Applications (ACM MONET), IEEE JSAC, IEEE Communications Magazine, Computer Communications, IEE Proceedings Communications, the Computer Journal, Telecommunication Systems, Wireless Personal Communications, and Wireless Communications & Mobile Computing. Dr. Chao is an IEEE senior member and a Fellow of IET (IEE). He is a Chartered Fellow of British Computer Society. Dr. Jong Hyuk Park received his Ph.D. degree in Graduate School of Information Security from Korea University, Korea. Before August, 2007, Dr. Park had been a research scientist of R&D Institute, Hanwha S&C Co., Ltd., Korea. He is now a professor at the Department of Computer Science and Engineering, Kyungnam University, Korea. Dr. Park has published about 100 research papers in international journals and conferences. Dr. Park has served as Chairs, program committee or organizing committee chair for many international conferences and workshops; Chair of SH 06/07/08, MUE 07/08, IPC 07/07, FGCN 07/08, TRUST 07/08, SMPE 07/08, UASS 07/08, SSDU 07/ 08, UIC 07/08, Mobility 08, SUTC 08, WPS 08, SecUbiq 07, ISM 07, and PC member of PerCom 08, AINA 07/08, MOBIQU- ITOUS 07/08, ATC 08, EUC 07 and so on. Dr. Park was editor-inchief of the International Journal of Multimedia and Ubiquitous Engineering (IJMUE), the managing editor of the International Journal of Smart Home (IJSH). And he is Associate Editors / Editors of 13 international journals including seven journals indexed by SCI(E). Dr. Park s research interests include Digital Forensics, Security, Ubiquitous and Pervasive Computing, Context Awareness, Multimedia Service, etc. He is a member of the KICS, KIISC, KMS, and IEICE. Homepage: