Power saving is an important issue in the mobile computing environment. In this paper, we propose a broadcast mechanism that constructs the broadcast channels according to the access frequency of each type of message in order to save power in mobile stations. The pinwheel scheduling algorithm presented in this paper is used to organize all types of messages in the broadcast channels in the most symmetrical distribution in order to reduce both the tuning and access time. The multichannel broadcast mechanism is also discussed for use when the number of message types increases. The performance of the proposed mechanism is analyzed, and the improvement over existing methods is demonstrated numerically. The results show that the proposed mechanism is capable improving both the tuning and access time due to the presence of skewness in the access distribution among the disseminated messages. When the number of message types increase, both the tuning and access time can be further improved as long as a small number of broadcast channels are added.

In advanced ITS, on-board intelligent systems by the Inter-Vehicle Communications (IVC) is essential technology to achieve a safe automotive society. We aim to avoid the vehicular collisions under almost all situations such as intersections, highways, and blind corners by using IVC technology through wireless ad hoc networks. The objectives of this paper are to develop Vehicular Collision Avoidance Support System (VCASS), and to show its performance by various experiments with two real vehicles. We have installed personal computers, telecommunication equipments, and GPS in two vehicles. In this system, the vehicles exchange the location information and the velocity vectors by the UDP broadcast with each other, and calculate the relative position/speed. The vehicles make the warning for drivers with the possibility of the collision. We verify the validity and the effectiveness of VCASS by the experiments.

Recently, the integration of wired and wireless networks has become an interesting issue. The introduction of extending Mobile IP to mobile ad hoc networks not only helps the mobile nodes connect to the Internet but also broadens the scope of the ad hoc networks and increases their application. However, these hybrid schemes faces several security problems from the inherent weakness of ad hoc routing. In this paper, we propose a hybrid authentication scheme of Mobile IP assistance for ad hoc routing security. The regular Mobile IP registration scheme has been refined to an ad hoc key-aided version and now incorporates a novel routing packet authentication mechanism in the ad hoc routing operation. A distinct character of this hybrid scheme is that a Mobile Agent can form a secure ad hoc network where the mobile hosts can be authorized and authenticated by the refined Mobile IP registration scheme. In these findings, we shall propose that the mobile hosts can follow a novel routing packet authentication mechanism to secure the routing packets by using the cryptography of the simple geometric properties of lines. Since the novel routing authentication mechanism does not need digital signatures for completing the routing packet integrity, in this hybrid authentication scheme, the cryptographic computation cost on the mobile hosts' side is relatively minimized.

We propose a modified Hidden Markov Model (HMM) with a view to improve gesture recognition using a moving camera. The conventional HMM is formulated so as to deal with only one feature candidate per frame. However, for a mobile robot, the background and the lighting conditions are always changing, and the feature extraction problem becomes difficult. It is almost impossible to extract a reliable feature vector under such conditions. In this paper, we define a new gesture recognition framework in which multiple candidates of feature vectors are generated with confidence measures and the HMM is extended to deal with these multiple feature vectors. Experimental results comparing the proposed system with feature vectors based on DCT and the method of selecting only one candidate feature point verifies the effectiveness of the proposed technique.

To overcome the mobility impact on RSVP, many schemes have been proposed based on Mobile IP regional registration and passive reservation in advance. Although the regional registration and in advance reservation reduce the QoS interruption time, the latter may demand intolerable bandwidth. This letter introduces a novel approach to reduce the QoS interruption time by maximizing the localization of QoS re-establishment in the regional registration environment. The proposed scheme identifies the exact path segment affected by mobility. The QoS interruption time of the proposed scheme is comparable to its low bound without in advance reservation.

Nowadays more people have started using their mobile phone to access information they need from anywhere at anytime. In advanced mobile technology, Location Service allows users to quickly pinpoint their location as well as makes a recommendation to fascinating events. However, users desire more appropriate recommendation services. In other words, the message service should push a message at a proper place in time. In consequence, customers obtain a higher level of satisfaction. In this paper, we propose a framework of time, place, purpose and personal profile based recommendation service. We illustrate scenarios in "push", "pull" and "don't disturb" services, where our DB queries can recommend the relevant message to users. The three factors: time, place and purpose are mutually dependent and the basic rules to analyze the essential data are summarized. We also create algorithms for DB query. We are filtering messages by one important factor: personal profile such as user's preference and degree of preference. Furthermore, we discuss an implementation of the prototype system, including results of experimental evaluation.

We formally define the mobile agent allocation problem from a system-wide viewpoint and then prove that it is strongly NP-complete even if each agent communicates only with two agents. This is the first formal definition for scheduling mobile agents from the viewpoint of load balancing, which enables us to discuss its properties on a rigorous basis. The problem is recognized as preemptive scheduling with independent tasks that require mutual communication. The result implies that almost all subproblems of mobile agent allocation, which require mutual communication of agents, are strongly NP-complete.

When an application code is downloaded from an unknown server to the mobile device, it is important to authenticate the code. Usually, code execution is overlapped with downloading to reduce transfer/invocation delay. In this letter, we present an efficient code authentication scheme that permits overlapping of execution and downloading when the sequence of code execution is determined during the execution time. The proposed scheme is based on authentication trees. Compared with the tree chaining scheme, the proposed scheme has lower communication overhead and shorter average verification delay. Also, the computation cost of the proposed scheme on the receiver is much smaller than that of the tree chaining scheme.

In this paper, we focus on the problem that in an ad hoc network, how to send a message securely between two users using the certificate dispersal system. In this system, special data called certificate is issued between two users and these issued certificates are stored among the network. Our final purpose on this certificate dispersal problem is to construct certificate graphs with lower dispersability cost which indicates the average number of certificates stored in each node in an ad hoc network. As our first step, when a certificate graph is given, we construct two efficient certificate dispersal algorithms for strongly connected graphs and directed graphs in this paper. We can show that for a strongly connected graph G =(V, E) and a directed graph H =(V ′, E ′), new upper bounds on dispersability cost on the average number of certificates stored in one node are O(DG +|E|/|V|) and O(pG dmax +|E ′|/|V ′|) respectively, where DG is the diameter of G, dmax is the maximum diameter of strongly connected components of H and pG is the number of strongly connected components of H. Furthermore, we give some new lower bounds for the problem and we also show that our algorithms are optimal for several graph classes.

In this paper, we propose the design of a scalable reliable mobile multicast scheme--SRMoM. SRMoM uses well-known Scalable Reliable Multicast (SRM) in the wired networks and a NAK-based ARQ with adaptive Forward Error Correction (AFEC) in the wireless networks. In AFEC, the probability of needing retransmission of original multicast packets after FEC recovery is selectable. This selective property enables the control of channel utilization in the wireless segment for different numbers of Mobile Hosts (MHs). Using this property, the channel utilization of SRMoM is made to be virtually independent of the number of MHs, thus making it extremely scalable. The performance of SRMoM is analyzed with three adaptive FEC algorithms based on three wireless loss models, namely a Gilbert-Elliott channel, a simplified Gilbert-Elliott channel, and a binary symmetric channel, analytically as well as through simulation. Furthermore, the performance of SRMoM is compared with SRM and MRMoM (NAK-based protocol without FEC) through simulation. Using the average number of transmissions per original multicast packet, and wireless link utilization as metrics, we demonstrate that the performance of SRMoM is indeed virtually independent of the number of MHs, and that it results in the lowest number of packet transmissions and lowest channel utilization of reliable mobile multicast protocols that have been proposed to date.

Recent advancement in personal communication services (PCS) provides wireless multimedia services for users on the move. For establishing the convenient access environment, the evolution of IP-based integrated scheme becomes very urgent for public wireless access systems. In this paper, we clarify the well-known issues of integrating the general packet radio service (GPRS) network and IEEE 802.11 wireless local area network (WLAN). These issues include the inconsistence in transmission rate and coverage area, the difficulty in seamless handoff, the complexities of mobile IP and address translations, and so on. Based on classified cases, we propose the circular probe strategy (CPS) to solve the IP translations and measure the precise handoff latency of a mobile node roaming from one network to another. This latency information helps a mobile node and its home agent (HA) to decide the appropriate handoff timing, to maximize the data transmission rate, and to perform seamless handoff in the heterogeneous system. We also proposed the smart access point (AP) mechanism to reduce the overhead of CPS and to provide precise handoff latency information for mobile nodes (MNs) to select the most appropriate AP for association. Experiment results demonstrate that the proposed smart handoff scheme performs better than traditional algorithms in terms of handoff time in the integrated network.

One of the remaining issues of Mobile IP is a mobile host (MH) needs to update its location each time it moves from one subnet to another, even when it is in dormant mode while roaming. This practice is apparently not efficient in terms of location update cost and power consumption. Recent research works have attempted to address that problem by extending Mobile IP with a layer 3 paging mechanism so-called IP paging. Particularly, IP Individual Paging schemes, which are customized to each MH, have attracted considerable interest of researchers. The employment of adaptability in some manner to MH parameters in order to enhance the efficiency of IP paging schemes is probably a promising approach. In this paper, we present an analysis on the effects of both host-adaptability and time-adaptability to MH parameters in Individual Paging schemes by comparing the signaling cost of an adaptive Individual Paging scheme to that of a non-adaptive counterpart. From our analysis, specifying the optimal paging area (PA) is critical in saving signaling cost of IP paging. Thus, our investigation is focused on the adaptability of PA to maintain its optimality.

On the Internet, two different IP protocols are deployed such as IPv4 and IPv6. The Mobile Router uses the basic NEMO protocol which is IPv6 protocol specific. During the early period of time that IPv6 transition is occurring it is very likely that a Mobile Router will move to an IPv4 only access network. When this occurs the Mobile Router will no longer be able to operate using the basic NEMO protocol. There has already been some earlier work to provide IPv6 capability over an IPv4 access network for a Mobile Router. This paper provides a capability by to maintain IPv6 connectivity for the Mobile Router via its Home Agent with IPv4-in-IPv6 encapsulation with no special boxes to be deployed elsewhere in the network.

This paper proposes a new ad hoc routing protocol using route redundancy as one of route selection criteria. It is important to provide redundancy for the route from source to destination in mobile ad hoc networks that are susceptible to failure. Route redundancy implies the relative possibility that redundant paths will exist on a route to be built up. Our proposal aims to establish a route that contains more redundant paths toward a destination node by involving intermediate nodes with relatively more adjacent nodes in a possible route. Our approach can localize the effects of route failures, and reduce control traffic overhead and route reconfiguration time by enhancing the reachability to the destination node without source-initiated route rediscoveries at route failures. We show the route setup procedure considering link redundancy and the route reconfiguration procedures employing redundant path information at the intermediate nodes. Further, this paper presents a new route maintenance protocol. Most of existing ad hoc routing protocols re-initiate a route query procedure when a destination node moves away and a route failure occurs. However, our scheme makes the destination node find a neighbor node that knows the way to the source node and establish a partial route to the neighbor node. If the destination node can find any and connect to it, the route will be recovered. This produces less control overhead than a source-initiated route discovery. We show the performance of our routing schemes through simulations using the Network Simulator 2 (ns-2).

In this paper, we propose an efficient route discovery scheme for mobile ad hoc networks called Hop-Wise Limited broadcast (HoWL). Since nodes do not identify the location of other nodes, some of the routing protocols proposed for mobile ad hoc networks use network-wide broadcasts to discover a route. In contrast, HoWL limits the area of a route discovery by predicting the current location of the destination node using history of hop counts of previously used routes. We also introduce Characterized Environmental Indicators (CEI) which characterize environments for networks of mobile nodes. Specifically, environments can be characterized by three indicators: node density, average hop count of utilized routes, and frequency of link failure. We have implemented HoWL as an extension to DSR on GloMoSim network simulator. Quantitative and qualitative performance comparisons were evaluated between HoWL and its related work, Expanding Ring Search (RING) and LAR. The simulations show that HoWL performs best when low communication overhead is desired where up to 20% decrease over RING and three-fold decrease over LAR in the overhead were demonstrated. Thus, HoWL is most effective in overhead sensitive environments such as battery-limited sensor networks.

In this paper, we propose an advanced location-based service that we call a direction-based service, which utilizes both the position and direction of a user. The direction-based service enables a user to point to an object of interest for command or investigation. We also describe the design, implementation and evaluations of a direction-based service system named Azim. With this system, the direction of the user can be obtained by a magnetic-based direction sensor. The sensor is also used for azimuth-based position estimation, in which a user's position is estimated by having the user point to and measure azimuths of several markers or objects whose positions are already known. Because this approach does not require any other accurate position sensors or positive beacons, it can be deployed cost-effectively. Also, because the measurements are naturally associated with some degree of error, the position is calculated as a probability distribution. The calculation considers the error of direction measurement and the pre-obtained field information such as obstacles and magnetic field disturbance, which enables robust position measurements even in geomagnetically disturbed environments. For wide-area use, the system also utilizes a wireless LAN to obtain rough position information by identifying base stations. We have implemented a prototype system for the proposed method and some applications for the direction-based services. Furthermore, we have conducted experiments both indoors and outdoors, and exemplified that positioning accuracy by the proposed method is precise enough for a direction-based service.

Existing reliable multicast protocols are designed to perform well in wired networking environments. However, in mobile networking environments, these reliable mobile multicast protocols are not optimal as they do not take into account the limitations of power (energy), storage capacity, processing power, impairments of wireless communication channels, and the frequent changes of location and the resulting loss of network connectivity. This paper analyses four hybrid reliable multicast schemes, namely NAK-based schemes, ACK-based schemes, ACK-based schemes with FEC (Forward Error Correction), and NAK-based schemes with FEC that are suitable for mobile networking environments and quantifies their performance. These four schemes differ from the generic sender-initiated and receiver-initiated reliable multicast protocols in that they rely on a mixture of multicasting and unicasting for providing reliability. This analysis is used to show that NAK-based schemes with FEC is best suited for reliable multicasting in mobile environments as they provide excellent performance in terms of average wireless channel utilization and average processing time, independently of the number of MHs.

In a ubiquitous computing environment, people are surrounded by hundreds of mobile or embedded computers each of which may be used to support one or more user applications due to limitations in their individual computational capabilities. We need an approach to coordinating heterogeneous computers that acts as a virtual computer around a mobile and ubiquitous computing environment and supports various applications beyond the capabilities of single computers. This paper presents a framework for building and aggregating distributed applications from one or more mobile components that can be dynamically deployed at mobile or stationary computers during the execution of the application. Since the approach involves mobile-transparent communications between components and component relocation semantics, it enables a federation of components to adapt its structure and deployment on multiple computers whose computational resources, such as input and output devices, can satisfy the requirement of the components in a self-organized manner. This paper also describes a prototype implementation of the approach and its application.

In this paper, we improve the performance analysis of the Rake receiver for the DS-CDMA forward link using long random spreading sequences (RSS's) by more accurately evaluating the correlation between the various interference terms. We also extend the analysis to the case of short (periodic) RSS. The accuracy of the expressions obtained in our analysis is verified by computer simulation. We show that for a given normalized spreading factor, the bit error rate (BER) performance of the Rake receiver is the same for BPSK and QPSK data modulation. We also show that when the channel delay spread is smaller than a data symbol duration, the CDMA receiver has similar BER performance for long and short RSS's. However, for large delay spread, the employment of short RSS's may result in severe performance degradation.

In this Letter, a frequency-domain pre-rake transmission is presented for a direct sequence spread spectrum with time division duplex (DSSS/TDD) system under a frequency-selective fading channel. The mathematical relationship between frequency-domain and time-domain pre-rake transmissions is discussed. It is confirmed by the computer simulation that, similar to the time-domain pre-rake transmission, frequency-domain pre-rake transmission can improve the bit error rate (BER) performance. The frequency-domain pre-rake transmission shows only slight performance degradation compared to the frequency-domain rake reception for large SF.