Mobile collaborative systems, which allow collaboration through wireless networks and mobile devices, have influenced and changed the quality of our lives over the past decade. Meanwhile, the explosive growth of data traffic for user services threatens the current mobile systems. Especially, mobility models, architectures, and application services have posed various challenges to those in academia and industry. In particular, the key challenges for improving efficiency, scalability, and reliability are the development of mobile collaborative systems and the measurement of precise performance of mobile collaborative systems. These challenges allow us to design and develop new models, architectures, and services for future mobile systems.

This special issue covers the following main topics:

• Mobile Internet architectures for collaborative systems

• Mobility models and performance evaluation

• Collaborative technologies for fast creation and deployment of new mobile services

• Collaborative location aware mobile systems

• Handoff, mobile networks and wireless web

• Mobile learning and groupware systems

• Mobile and ubiquitous applications exploiting semantics

• Context-aware environments for work and enterprises

• Synchronization algorithms for mobile collaborative systems

• Mobile social networking

• Evaluation of the usability of mobile collaborative applications

• Mobile technology and system for real time collaboration in enterprises.

These subjects, as well as some others, are the focus of this special issue of “Advances on Mobile Collaborative Systems”. The special issue is organized as follows:

The first paper by Fei Song, Huachun Zhou, Sidong Zhang, Hongke Zhang, and Ilsun You, presents a throughput critical condition study for reliable multipath transport. Specific analytical mechanisms are proposed to analyze the potential problems which may lead to serious performance decrease. They investigate how to use multiple paths legitimately when network environments are fluctuating. In their simulation, the results have revealed some throughput critical conditions and could be helpful in designing scheduling schemes for multipath protocols.

The second paper by Chin-Ling Chen, Yu-Ting Tsai, Aniello Castiglione, and Francesco Palmieri, proposes a dynamic location-aware key management scheme based on the bivariate polynomial key pre-distribution, where the aggregation cluster nodes can easily find their best routing path to the base station, by containing the energy consumption, storage and computation demands in both the cluster nodes and the sensor nodes. This scheme is robust from the security point of view and able to work efficiently, despite the highly constrained nature of sensor nodes.

The third paper by Jinjing Zhao and Yan Wen, describes the relation between prefix hijacking and the Internet hierarchy. The Internet is classified into three tiers based on the power-law and commercial relations of autonomous systems. The relation between network topology and prefix hijacking influence is presented for all sorts of hijacking events in different layers. The results assert that the hierarchical nature of network influences the prefix hijacking greatly.

The fourth paper by Byungha Choi and Kyungsan Cho, proposes an improved detection scheme to protect a web server from detoured attacks, which disclose confidential/private information or disseminate malware codes through outbound traffic. Its scheme has a two-step hierarchy, whose detection methods are complementary to each other. The first step is a signature-based detector that uses Snort and detects the marks of disseminating malware, XSS, URL Spoofing and information leakage from the web server. The second step is an anomaly-based detector which detects attacks by using the probability evaluation in HMM, driven by both payload and traffic characteristics of outbound packets. Through the verification analysis under the attacked web server environment, they show that their proposed scheme improves the false positive rate and detection efficiency for detecting detoured attacks to a web server.

The fifth paper by Der-Chen Huang, Yi-Wei Lee, and Hsiang-Wei Wu, proposes a guarantee time slot mechanism to enhance the performance and utilization by using CFP. Their proposed method ensures each device has the authority to access the radio channel without any additional step. By comparing with the method of IEEE 802.15.4, the experimental results show that data average transmission delay and energy consumption can be reduced dramatically. In addition, the bandwidth and performance of network is improved since the pre-allocation mechanism can reduce the number of control packets.

The sixth paper by Jianfeng Wang, Hua Ma, Qiang Tang, Jin Li, Hui Zhu, Siqi Ma, and Xiaofeng Chen, describes a new verifiable fuzzy keyword search scheme based on the symbol-tree which not only supports the fuzzy keyword search, but also enjoys the verifiability of the searching result. Through rigorous security and efficiency analysis, they show that thier proposed scheme is secure under the proposed model, while correctly and efficiently realizing the verifiable fuzzy keyword search. The extensive experimental results demonstrate the efficiency of the proposed scheme.

The seventh paper by Ho-Seok Kang, Sung-Ryul Kim, and Pankoo Kim, presents a method to efficiently defend against DoS attacks by modifying routing protocols in the WSN. This method uses a location based routing protocol that is simple and easy to implement. In the WSN environment where the location-based routing protocol is implemented, this method disperses the DoS attack concentration of traffic by using the traffic deflection technique and blocks it out before arriving at the target destinations. To find out the number of traffic redirection nodes proper for this method, they have performed a few experiments, through which the number of such nodes was optimized.

The eighth paper by Taerim Lee, Hun Kim, Kyung-Hyune Rhee, and Sang Uk Shin, describes a new type of E-Discovery Service Structure based on Cloud Computing called EDaaS(E-Discovery as a Service) to make the best usage of its advantages and overcome the limitations of the existing E-Discovery solutions. EDaaS enables E-Discovery participants to smoothly collaborate by removing constraints on working places and minimizing the number of direct contact with target systems. What those who want to use the EDaaS need is only a network device for using the Internet. Moreover, EDaaS can help to reduce the waste of time and human resources because no specific software to install on every target system is needed and the relatively exact time of completion can be obtained from it according to the amount of data for the manpower control. As a result of it, EDaaS can solve the litigant’s cost problem.

In the ninth paper by Jinhai Huo, Bowen Deng, Shuhang Wu, Jian Yuan, and Ilsun You, a topographic-awareness and situational-perception based mobility model with path optimization for tactical MANET is proposed. Firstly, a formalized process is constructed to generate a random acceleration on nodes as the disturbance caused by small-scale topographic factors in the battlefield. Secondly, a path optimization method with the artificial bee colony algorithm is introduced to mimic the trace planning when the nodes possess the terrain information of battlefield. Thirdly, a topographic-awareness based bypass strategy is proposed to simulate the action of nodes facing large-scale terrain factors in the case when the terrain information is lacking. Finally, a situational-perception based avoidance strategy is built to simulate the process of cognition and decision when there is an encounter with the enemies on the march. The mobility model consists of the four parts above and imitates the dynamic characteristics of tactical nodes in military environment.

The tenth paper by Hae-Duck J. Jeong, Jiyoung Lim, WooSeok Hyun, and Arisu An, proposes a new location-based SNS application for the disabled population (except those who are visually impaired or the disabled who are not able to use a smartphone) with three major characteristics of this application to be considered as follows: (i) the person uses a Social Networking Service (SNS) by constructing a friend matching system such as Facebook or Twitter, which are the most widely used SNS in the world; (ii) the general population registers real-time information for a specific location on the map for the disabled population using SNS. This information with photos and messages is given and evaluated by users; and (iii) this system makes it easier to see that the menu in the GUI was implemented.

The eleventh paper by Myunggwon Hwang, Do-Heon Jeong, Jinhyung Kim, Sa-kwang Song, and Hanmin Jung, describes activity inference for constructing user intention model. User intention modeling is a key component for providing appropriate services within ubiquitous and pervasive computing environments. Intention modeling should be concentrated on inferring user activities based on the objects a user approaches or touches. In order to support this kind of modeling, they propose the creation of object–activity pairs based on relatedness in a general domain. They also show their method for achieving this and evaluate its effectiveness.

The twelfth paper by Hsing-Chung Chen, Marsha Anjanette Violetta, Chien-Erh Weng, and Tzu-Liang Kung, presents a novel Cognitive RBAC (Role-Based Access Control) scheme which can be applied to Mobile Heterogeneous Networks (MHNs). The MHNs consist of mobile communication systems and Wi-Fi systems. The required new definitions for the RBAC model are proposed in this paper. They can improve the ability of conventional RBAC model to meet new challenges. In their scheme, they assume that a Cognitive Server (CS) provides and manages the permissions of services, and Network Providers support and manage a variety CRs and CNs, individually. For more efficiently managing CR and CN and meeting the large scale heterogeneous networks, they let mobile user can perceive network candidate actively to access services, in which the permissions are depending to the contract made by CS with each Network Provider. In this paper, the new generalized cognitive RBAC model and their definitions are proposed, and could be applied to new applications in an MHNs environment.

The thirteenth paper by Yong-Hwan Lee, Bonam Kim, and Sang-Burm Rhee, proposes a new efficient and effective mobile image retrieval method that applies a weighted combination of color and texture utilizing spatial-color and second order statistics. The prototype system for mobile image searches runs in real-time on an iPhone and can easily be used to find a specific image. In order to evaluate the performance of the new method, they assessed the Xcode simulation’s performance in terms of average precision and F-score using several image databases and compare the results with those obtained using existing methods such as MPEG-7. Experimental trials revealed that the proposed descriptor exhibited a significant improvement of over 13% in retrieval effectiveness compared to the best of the other descriptors.

The fourteenth paper by Jen-Wei Hu, Chu-Sing Yang, and Te-Lung Liu, describes integrating management functions of virtual network in their testbed. In this paper, they design and create a Future Internet testbed in Taiwan over TWAREN Research Network. This testbed evolves into an environment for programmable network and cloud computing. This paper also presents several finished and ongoing experiments on the testbed for multiple aspects including topology discovery, multimedia streaming, and virtual network integration.

The fifteenth paper by Inshil Doh, Jiyoung Lim, and Kijoon Chae, proposes an energy-efficient and secure channel group key establishment and rekeying management scheme for mobile open IPTV services. Their scheme provides the data authentication between an Evolved Node B (eNB) or a Base Station and the mobile devices for the security enhancement and efficiently rekeys the group key when the membership changes. Additionally, it proposes a pairwise key establishment mechanism for open IPTV services through eNBs. Their proposal can cope with the security vulnerability in mobile open IPTV services and guarantee the secure group key rekeying in addition to decreasing the storage and communication overhead.

The sixteenth paper by Bing Bai, Zhenqian Feng, Baokang Zhao, and Jinshu Su, presents a community-based single-copy forwarding protocol for DTNs routing, which efficiently utilizes the community structure to improve the forwarding efficiency. Simulation results are presented to support the effectiveness of their scheme.

In the seventeenth paper by Jyh-Horng Wen, Yung-Cheng Yao, and Ying-Chih Kuo, a Wiener-based successive interference cancellation (SIC) scheme is proposed to detect the OFDM signals. It provides good ICI cancellation performance; however, it suffers large computation complexity. Therefore, a modified Wiener-based SIC scheme is further proposed to reduce the computation complexity. Simulation results show the performance of the Wiener-based SIC scheme is better than those of zero forcing, zero forcing plus SIC and original Wiener-based schemes. Furthermore, with the modified Wiener-based SIC scheme, the performance is still better than the others. Although the performance of the modified Wiener-based SIC scheme suffers little degradation compared to Wiener-based SIC scheme, the computation complexity can be dramatically reduced.

The eighteenth paper by Satoshi Tanaka, Takashi Nishide, and Kouichi Sakurai, proposes an efficient implementation of computing multivariate polynomial systems for multivariate cryptography on GPU and evaluate efficiency of the proposal. GPU is considered to be a commodity parallel arithmetic unit. Moreover, they give an evaluation of their proposal. Their proposal parallelizes an algorithm of multivariate cryptography, and makes it efficient by optimizing the algorithm with GPU.

Finally, in the last paper by Tianhan Gao, Nan Guo, Kangbin Yim, they leverage the combination of PKI and certificate-based cryptography and propose a hierarchical security architecture for the HMIPv6 roaming service. Under this architecture, they present a mutual authentication protocol based on a novel cross-certificate and certificate-based signature scheme. Mutual authentication is achieved locally during the mobile node’s handover. In addition, they propose a key establishment scheme and integrate it into the authentication protocol which can be utilized to set up a secure channel for subsequent communications after authentication. their approach is the first addressing the security of HMIPv6 networks using such a hybrid approach. In comparison with PKI-based and IBC-based schemes, their solution has better overall performance in terms of authenticated handover latency.

We strongly believe that the papers presented in this special issue make significant contributions to the work and studies conducted by academic researchers, industry professionals, students, and everyone in the areas of advances on mobile collaborative systems.

We would like to thank all the authors for their valuable contributions. Our special thanks go to prof. Mirjana Ivanović, Editor in Chief of the Computer Science and Information Systems (ComSIS) Journal, for inviting us to prepare this special issue and for his productive comments and great support throughout the entire publication process.

Editors of the special issue
Hae-Duck Joshua Jeong,
Fatos Xhafa,
Makoto Takizawa