The New Challenge: Mobile Multimedia Sensor Networks ... - CiteSeerX

Int. J. Multimedia Intelligence and Security, Vol. x, No. x, xxxx

The New Challenge: Mobile Multimedia Sensor Networks Lei Shu, Takahiro Hara, Shojiro Nishio Department of Multimedia Engineering, Osaka University, Japan E-mail: {lei.shu, hara, nishio}@ist.osaka-u.ac.jp

Yuanfang Chen School of Software, Dalian University of Technology, China E-mail: yuanfang [email protected]

Manfred Hauswirth Digital Enterprise Research Institute, National University of Ireland, Galway, Ireland E-mail: [email protected] Abstract: Along with the fast development of sensor hardware, traditional scalar sensor nodes are now provided with both multimedia and mobility functions. By observing this emerging combination of these two functions into traditional wireless sensor networks (WSNs), we take the opportunity in this paper to highlight a subset of WSNs, which we name as “Mobile Multimedia Sensor Networks (MMSNs)”. Furthermore, we present a number of challenging issues that may appear in MMSNs in terms of enhancing diverse quality of services (QoS) and prolonging the network lifetime for both WSNs and multimedia communication research communities. Keywords: Mobile; Multimedia; Sensor networks; Research issues. Reference to this paper should be made as follows: Lei, S. ‘The New Challenge: Mobile Multimedia Sensor Networks’, Int. J. Multimedia Intelligence and Security, Vol. x, No. x, pp.xxx–xxx. Biographical notes: Lei Shu is a currently Specially Assigned Research Fellow in Department of Multimedia Engineering, Graduate School of Information Science and Technology, Osaka University, Japan. He has published over 90 papers in related conferences, journals, and books. He had been awarded the MASS 2009 IEEE TCs Travel Grant and the Outstanding Leadership Award of EUC 2009 as Publicity Chair, Best Paper Award in Globecom 2010. He has served as editor of several international journals, e.g., IET Communications and Wireless Communications and Mobile Computing c 2010 Inderscience Enterprises Ltd. Copyright

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Lei Shu and Yuanfang Chen (Wiley). He has served as more than 30 various Co-Chair for international conferences/workshops, e.g., ICC 2012; TPC members of more than 100 conferences. His research interests include semantic sensor networks, wireless sensor network, sensor network middleware. He is a member of IEEE. Takahiro Hara is an Associate Professor of the Department of Multimedia Engineering, Osaka University. He has published more than 100 international Journal and conference papers in the areas of databases, mobile computing, peer-to-peer systems, WWW, and wireless networking. He served and is serving as a Program Chair of MDM’06 and 10 and AINA’09. He guest edited IEEE Journal on Selected Areas in Communications, Sp. Issues on Peer-to-Peer Communications and Applications. He served and is serving as PC member of more than 120 international conferences such as IEEE ICNP, WWW, DASFAA, ACM MobiHoc, and ACM SAC. His research interests include distributed databases, peer-to-peer systems, mobile networks, and mobile computing systems. He is an IEEE Senior member and a member of four other learned societies including ACM. Manfred Hauswirth is Vice-Director of the Digital Enterprise Research Institute (DERI), Galway, Ireland and professor at the National University of Ireland, Galway (NUIG). His main research interests are on semantic sensor networks, sensor networks middleware, large-scale semantics-enabled distributed information systems and applications, peer-to-peer systems, Internet of things, self-organization and self-management, Semantic Web services, and distributed systems security. He has published over 100 papers in these domains, he has co-authored a book on distributed software architectures and several book chapters on P2P data management and semantics. He has served in over 170 program committees of international scientific conferences and was program co-chair of the P2P 2007, general chair of the ESWC 2008, and is program co-chair of the ODBASE 2011. He is a member of IEEE and ACM.

1 Introduction Wireless sensor networks (WSNs), consist of many tiny sensor nodes, have gained a lot of attention from both academic and industrial communities for nearly more than ten years. Worldwide researchers have put a huge amount of effort for designing and challenging all aspects (e.g., network communication and data management) of WSNs to prolong the network lifetime and enhance the quality of service (QoS) for diverse applications. Along with the further development of industrial technologies, both mobility function and multimedia function are merged into traditional static & scalar WSNs as two significant enhancements for the capability of WSNs, e.g., wireless mobile sensor networks Munir et al. (2007); Ren et al. (2006); Zhu et al. (2010) and wireless multimedia sensor networks Akyildiz et al. (2007); Almalkawi et al. (2010). These new emerging functions of WSNs are, of course, motivated by a large number of realistic application requirements and the previous shortcoming of traditional static & scalar WSNs.

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Figure 1

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Both mobility function and multimedia function are available in these Mobile Sensor Platforms (MSP), which can be considered as mobile multimedia sensor nodes.

For example, mobility function allows sensor nodes to self-organize the network topology by moving to the optimal locations, and the multimedia sensor nodes can help to provide more comprehensive information to reflect some difficult events, which are difficult to be reflected by traditional scalar sensory data. In this paper, one of the major focuses is to introduce a new challenging research direction, which we named as “Mobile Multimedia Sensor Networks (MMSNs)”. Paretically, we define the “Mobile Multimedia Sensor Networks” as “using a number of mobile multimedia sensor nodes in the sensor network to enhance the sensor network capability for event description”. The reasons for us to raise this special subset of WSNs are many, e.g., • Existing hardware platform had already provided the possibility for taking both mobility and multimedia functions into consideration, e.g., the Mobile Sensor Platform from AICIP laboratory at the Electrical Engineering and Computer Science Department of the University of Tennessee, USA, as shown in Fig. 1. • Many applications of WSNs actually need both mobility and multimedia functions. The merging of both mobile and multimedia functions into traditional WSNs will, of course, bring a lot of challenging research issues to both WSNs and multimedia communication research communities. In order to help future researchers to have a clear overview on the possible difficult research problems in mobile multimedia sensor networks, we gathered the expertise from people with knowledge on both the wireless mobile sensor networks and wireless multimedia sensor networks fields, and mainly scattered the possible research issues into both network communication and data management aspects. The remaining parts of this paper are organized as: Section 2 summarizes the existing research issues in both wireless mobile sensor networks and wireless multimedia sensor networks. Section 3 presents the concept of mobile multimedia sensor networks and its detailed information. Section 4 describes a number of identified research issues that exist in mobile multimedia sensor networks. Two

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examples of research issues are given in Section 5, and Section 6 concludes this paper.

2 State of the Art Research efforts on both the wireless mobile sensor networks and wireless multimedia sensor networks have been conducted for a few years. For wireless mobile sensor networks, existing research works have been investigated on a number of research issues, including: • Topology control issue Li et al. (2008). This is a problem of assigning radio powers to sensor nodes to make sure the network is connected at the minimum cost of energy consumption. • Coverage issue Bartolini et al. (2008). This is a problem of letting mobile sensor nodes to self move to optimal locations to maximize the network coverage while keeping the whole network connected. • Localization issue Xu et al. (2007). This is a problem of enhancing the localization accuracy by exploring the mobility of sensor nodes. • Target detection issue Xing et al. (2008). This is a problem of using mobile sensor nodes to assistant the target detection with the goal of low detection delay and short moving distance. • Data gathering issue Cheng et al. (2009). This is a problem of gathering sensory data from static sensor nodes while the base station can move inside the network area. • Data replication issue Hara et al. (2006). This is a problem of using data replication technology to increase the data availability which may be decreased by the movement of interested sensor nodes. For wireless multimedia sensor networks, existing research works also have been investigated on the following research issues: • Multi-path transmission issue Shu et al. (2007). This is a problem of exploring and constructing a number of transmission paths in WSN to allow parallel multimedia streaming. • Cross-layer optimization issue Shu et al. (2009). This is a problem of taking affects from each network layer into consideration to maximize the network transmission capacity. • Video-coding issue Xue et al. (2008). This is a problem of using distributed video coding technology to reduce the system delay in wireless multimedia sensor networks. • Cooperative caching issue Dimokas et al. (2008). This is a problem of letting small sensor nodes to collaborate with each other to cache multimedia data in network to satisfy some application-level Quality-of-Services.

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Major Entities of Different Sensor Networks

Traditional Static WSNs

Mobile WSNs

Multimedia WSNs

Static Base Station

Mobile Base Station Mobile Cluster Head Mobile Sensor Node Mobile Relay Node

Static Base Station

Static Cluster Head Static Scalar Sensor Node

Multimedia Cluster Head Multimedia Sensor Node Static Scalar Sensor Node

Mobile Multimedia WSNs Mobile Base Station Mobile Multimedia Cluster Head Mobile Multimedia Sensor Node Mobile Relay Node Mobile Scalar Sensor Node Static Scalar Sensor Node

• Congestion control issue Yaghmaee et al. (2009). This is a problem of giving different priorities to different kind of multimedia streams based on the importance levels of their provided information for facilitating the multimedia streaming in transport layer. • Security issue Grieco et al. (2009); Guerrero-Zapata et al. (2010). This is a big research aspect of wireless multimedia sensor networks, in which all kind of security related issues are considered, e.g., secure geographic routing, secure multimedia coding. However, to the best of our knowledge, this is no existing research work that considers both mobile and multimedia functions for WSNs at the same time, but actually, existing hardware technologies can already provide the mobile multimedia sensor node platform. This empty space gives us the motivation to carefully look into the research issues of mobile multimedia sensor networks in this paper.

3 Mobile Multimedia Sensor Networks 3.1 Applications A lot of important and useful applications had already been presented in great detail in the survey paper of wireless multimedia sensor networks Akyildiz et al. (2007), e.g., 1) Surveillance sensor networks; 2) Environmental monitoring; 3) Advanced health care delivery; 4) Person locator services; 5) Traffic avoidance, enforcement and control systems; and 6) Target tracking, etc. We believe that merging mobility function into these wireless multimedia sensor networks supported applications can further help to enhance the WSNs’ capability for gathering the most useful sensory data and reduce the energy and communication cost. For example, in the case of surveillance sensor networks, when original static multimedia sensor nodes are further provided mobility function, these nodes

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Figure 2

Mobile Multimedia Sensor Networks.

can smartly move themselves to certain desired locations to capture the best quality multimedia data, while also minimizing the multimedia streaming cost in WSNs. Furthermore, in case any sensor node has errors on operations, e.g., no data reporting or continuously sending data for a long period time, the mobile multimedia sensor node can be moved to the corresponding place to check whether the sensor node is out of energy or an outlier for attacking the WSN. From the application point of view, we particularly believe that mobile multimedia sensor networks is a subset of original wireless multimedia sensor networks, in which the mobility related research issues were not specially highlighted, and presented to research communities, as shown in Fig. 2.

3.2 Major Entity We give a list of the major entities of 1) traditional sensor networks; 2) wireless mobile sensor networks; 3) wireless multimedia sensor networks; and 4) mobile multimedia sensor networks, respectively, as shown in Table 1. It is easy to find that mobile multimedia sensor networks consist of the major entities from all previous WSNs, including: • Mobile base station. It is not mandatory for all the MMSNs applications that the base station must be mobile, but once the base station is moveable, it can help to reduce the data transmission cost and delay by moving to an optimal location in the network area. • Mobile multimedia cluster head. In the two-tier network architecture Akyildiz et al. (2007), sometimes, multimedia sensor nodes can serve as cluster heads for gathering the sensory data from other scala sensor nodes. • Mobile multimedia sensor node. These nodes provide multimedia stream data, e.g., video & image streams. • Mobile relay node. Mobile relay nodes are used to help to connect isolated parts of the network to keep all sensor nodes connected. • Mobile scalar sensor node. • Static scalar sensor node.

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Although, it is not mandatary for all of these entities to be used in the same application at the same time, but this kind of diversity of major entities in mobile multimedia sensor networks poses a lot of new challenging research issues.

3.3 Mobility Model and Paradigm There are a large number of mobility model for mobile ad hoc & sensor networks (MANET) that have been widely used in various research work Hara (2010), e.g., • Random Walk Michelini et al. (2008). This is one of the simplest mobility models. In this model, each mobile node randomly determines a movement directions and randomly determines a moving speed. • Random WayPoint (RWP) Bettstetter et al. (2003). This is one of the most popular mobility models in MANET. In this model, mobile node remains stationary for a pause time, then it selects a random destination in the entire network area and moves to the destination at a random speed. • Manhattan Mobility Chen et al. (2008). This model emulates the node movement on streets where nodes only travel on the pathways in a map. • Reference Point Group Mobility Jayakumar et al. (2008). This model is used to model group mobility. Each group has a logical “center” called a reference point and group members (nodes). Each reference point moves according to the RWP model. In each group, nodes are uniformly distributed within a radius from the reference point. • Random WayPoint with Locality Hara (2010). This model is the same as the RWP model except for the way to choose destinations. In this model, each mobile node has a home area, which is a subarea in the entire area. When determining a destination, it chooses a random destination inside the home area with high probability H and one outside the region with probability 1 - H. These mobility models can mainly be categorized into three types of mobility paradigm: • Controllable movement. The movement of mobile entities is planned and controlled. • Unpredictable movement. The movement of mobile entities is random and uncontrollable. • Predictable movement. The movement of mobile entities is uncontrollable but has clear direction or track. Most of these mobility models and paradigms can also exist in applications of mobile multimedia sensor networks.

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4 Research Issues We integrated either the mobility function or the multimedia function to previous presented existing research issues in Section 2, and identified a number of potential research issues in mobile multimedia sensor networks. In this section, we give the detailed description for each of them: • Stream data transmission issue. This issue is an extended research problem of multi-path transmission issue Shu et al. (2007) in wireless multimedia sensor networks, by taking mobility of both the single multimedia source node and sensor nodes into consideration. Multimedia stream data transmission in WSNs generally needs several reliable transmission paths to support the transmitting of stream data for a period of time. However, the mobility of both multimedia source nodes and sensor nodes will cause dynamic changing on the network topology as well as the routing paths. This kind of changing poses a huge difficulty for exploring and maintaining multiple reliable transmission paths. • Multimedia source nodes repositioning issue. This issue is an extended research problem of congestion control issue Yaghmaee et al. (2009) in wireless multimedia sensor networks, by taking mobility of multimedia source nodes into consideration. In this research problem, multiple multimedia source nodes are movable for exploring the best locations for gathering the multimedia streams with the best quality. It is challenging to fairly receive the multimedia streams from the multiple source nodes to the static base station, in terms of minimizing the transmission cost and traffic congestion. • Base station repositioning issue. This issue is an extended research problem of data gathering issue Cheng et al. (2009) in wireless mobile sensor networks. In this research problem, the base station is movable, and there are a number of static multimedia source nodes in the WSNs. Furthermore, some nature holes, e.g., water pools, also exist in the network field. The challenging difficulty here is that how to find an optimal location for the mobile base station to fairly receive the multimedia streams from the multiple source nodes and minimize the transmission cost and traffic congestion. • Localization issue. This issue is an extended research problem of localization issue Xu et al. (2007) in wireless mobile sensor networks. In this problem, the localization of sensor nodes is not only based on the radio signal strength, but also can be facilitated by using mobile image sensor nodes. Particularly, based on the captured images which include the angle/distance information between the anchor and the to be detected nodes, the detection accuracy can be drastically improved. • Continuous object tracking issue. This issue is an extended research problem of target detection issue Xing et al. (2008) in wireless mobile sensor networks. In this research problem, both mobile multimedia sensor nodes and mobile base stations can be used for tracking the continuous moving objects. The mobile multimedia sensor nodes can help to enhance the accuracy for boundary detection, and the mobile base stations can help to reduce the

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transmission cost of the updating messages. Here, the difficulty is how to efficiently organize the locations of these mobile nodes or set the random moving patterns to minimize the message transmission cost. • Coverage issue issue. This issue is an extended research problem of coverage issue Bartolini et al. (2008) in wireless mobile sensor networks. In this research problem, a number of mobile image sensor nodes can be used to monitor the network area. The goal of this kind of research work is to selforganize these mobile image sensor nodes to fairly cover the whole network area, or to collaborate with each other to monitor a huge object which cannot be monitored by only a single mobile image sensor node. The difficulty here is how to efficiently self-organize these mobile image sensor nodes. • Data replication issue. This issue is an extended research problem of both data replication issue Hara et al. (2006) in wireless mobile sensor networks and cooperative caching issue Dimokas et al. (2008) in wireless multimedia sensor networks. In this problem, multimedia data (e.g., images) of mobile source nodes are cached in a large number of small scalar sensor nodes, by having data replication of pieces of multimedia data. The challenging issue in this scenario is that how to efficiently allocate the replicas while the multimedia source node moves to reducing the data retrieval delay (or the interrupting time caused by the movement of multimedia source node.) • Security issue. Similar to wireless multimedia sensor networks Mulugeta et al. (2010), this is a big research aspect of mobile multimedia sensor networks, in which all kind of security related issues can be considered, e.g., mobile sensory stream data worthiness assessment, trust management of mobile multimedia source nodes, and detecting malicious nodes by mobile multimedia sensor nodes.

5 Two examples of research issues In this section, we give two examples of research problems in mobile multimedia sensor networks.

5.1 Example 1: multiple multimedia source nodes data gathering As shown in Fig. 3, five mobile multimedia source nodes are deployed in the network field to monitor five critical objects. For each source node, at least five transmission paths are needed for sending the large volume of multimedia stream data. When transmitting multimedia streams in WNS, the used relay nodes in the transmission paths generally cannot be shared with other source nodes for constructing new path Shu et al. (2007), and thus forming a dynamic hole when a number of closely deployed relay nodes are fully occupied. However, if all the multimedia source nodes want to transmit their stream data at the same time, some neighboring source nodes will have to compete with each other for the use of the number-limited sensor nodes as relay nodes to construct their multiple routing paths. As shown in Fig. 4, the overlapped area of neighboring source nodes’

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Figure 3

A research problem for transmitting the multimedia streams from multiple multimedia source nodes to a single base station.

Figure 4

An example of the dynamic hole and the competing area.

dynamic holes can be considered as the competing area. This kind of competition among neighboring source nodes can cause the difficulty to guarantee the global fairness, which means to equally gather the stream data from different source nodes. However, if both the multimedia source nodes and the base station can move in the WSN, we believe that some new methods can be investigated and proposed to help to relieve the heavy competition and traffic congestion for facilitating the multimedia stream data gathering.

5.2 Example 2: multiple suspicious sensor nodes checking As shown in Fig. 5, the WSN is deployed with 1000 sensor nodes, and 1% sensor nodes are suspicious nodes (black color). The suspicious nodes are detected by other security methods, because they either have errors on operations or are having malicious behaviors. Five mobile multimedia sensor nodes are randomly deployed in the network field. These mobile multimedia sensor nodes are supposed to move to the locations of suspicious sensor nodes to check them locally by taking photos to confirm the detection results of security methods. However, how to equally plan the itinerary for each mobile multimedia sensor node and eventually minimize the

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Figure 5

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Itinerary planning problem for mobile multimedia sensor nodes. In this figure, the possible itineraries for these five mobile multimedia sensor nodes are shown. Each of them will check 2 suspicious nodes.

overall cost of movement of mobile multimedia sensor node and multimedia data transmission in WSN is a challenging issue.

6 Conclusions In this paper, we highlight an interesting subset of WSNs: “Mobile Multimedia Sensor Networks (MMSNs)”. Research issues of mobile multimedia sensor networks are identified based on the survey of research issues in both wireless mobile sensor networks and wireless multimedia sensor networks. As one of its major contributions, this paper provides some new research directions for existing research community.

Acknowledgements This research work in this paper was supported: in part by Grant-in-Aid for Scientific Research (S)(21220002) of the Ministry of Education, Culture, Sports, Science and Technology, Japan, and in part by Lion project supported by Science Foundation Ireland under grant No.: SFI/08/CE/I1380 (Lion-2).

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