The integration of VANETs with Internet is required if vehicles are to access IP-based applications. A vehicle must have an IP address, and the IP mobility service should be supported during the movement of the vehicle. VANET standards such as WAVE or C-ITS use IPv6 address auto configuration to allocate an IP address to a vehicle. In C-ITS, NEMO-BS is used to support IP mobility. The vehicle moves rapidly, so reallocation of IP address as well as binding update occurs frequently. The vehicle' communication, however, may be disrupted for a considerable amount of time, and the packet loss occurs during these events. Also, the finding of the home address of the peer vehicle is not a trivial matter. We propose a network based identifier locator separation scheme for VANETs. The scheme uses a vehicle identity based address generation scheme. It eliminates the frequent address reallocation and simplifies the finding of the peer vehicle IP address. In the scheme, a network entity tracks the vehicles in its coverage and the vehicles share the IP address of the network entity for their locators. The network entity manages the mapping between the vehicle's identifier and its IP address. The scheme excludes the vehicles from the mobility procedure, so a vehicle needs only the standard IPv6 protocol stack, and mobility signaling does not occur on the wireless link. The scheme also supports seamlessness, so packet loss is mitigated. The results of a simulation show that the vehicles experience seamless packet delivery.

In this work, we address the stationary target localization problem by using Doppler frequency shift (DFS) measurements. Based on the measurement model, the maximum likelihood estimation (MLE) of the target position is reformulated as a constrained weighted least squares (CWLS) problem. However, due to its non-convex nature, it is difficult to solve the problem directly. Thus, in order to yield a semidefinite programming (SDP) problem, we perform a semidefinite relaxation (SDR) technique to relax the CWLS problem. Although the SDP is a relaxation of the original MLE, it can facilitate an accurate estimate without post processing. Simulations are provided to confirm the promising performance of the proposed method.

High availability is crucial for industrial Ethernet networks and Ethernet-based control systems, such as automation networks and substation automation systems. Because the standard Ethernet does not support fault tolerance capability, the high availability of Ethernet networks can be increased by using redundancy protocols. Various redundancy protocols for Ethernet networks have been developed and standardized, such as rapid spanning tree protocol (RSTP), media redundancy protocol (MRP), parallel redundancy protocol (PRP), high-availability seamless redundancy (HSR), and others. RSTP and MRP provide redundancy in the network, whereas PRP and HSR provide redundancy in the end nodes. RSTP and MRP have a disadvantage in switchover delay. PRP and HSR provide zero recovery time, but PRP requires a duplicate network infrastructure, and HSR is mainly used in ring-based topologies. Additionally, PRP and HSR provide seamless redundancy in the end nodes and are applied in dedicated HSR networks with dedicated HSR nodes. In this paper, we present a novel seamless redundancy protocol for Ethernet networks, which is called the Redundancy Protocol for Ethernet (RPE). The RPE provides seamless redundancy in the network. This protocol not only provides seamless communications with zero switchover time in case of failure but also supports all topologies. The RPE is transparent and compatible with standard Ethernet nodes. These features make the RPE very useful in time-critical and mission-critical systems, such as substation automation systems, automation networks, and other industrial Ethernet networks.

Target determination based on Doppler frequency shift (DFS) measurements is a nontrivial problem because of the nonlinear relation between the position space and the measurements. The conventional methods such as numerical iterative algorithm and grid searching are used to obtain the solution, while the former requires an initial position estimate and the latter needs huge amount of calculations. In this letter, to avoid the problems appearing in those conventional methods, an effective solution is proposed, in which two best linear unbiased estimators (BULEs) are employed to obtain an explicit solution of the proximate target position. Subsequently, this obtained explicit solution is used to initialize the problem of original maximum likelihood estimation (MLE), which can provide a more accurate estimate.

The high-availability seamless redundancy (HSR) protocol is a representative protocol that fulfills the reliability requirements of the IEC61850-based substation automation system (SAS). However, it has the drawback of creating unnecessary traffic in a network. To solve this problem, a dual virtual path (DVP) algorithm based on HSR was recently presented. Although this algorithm dramatically reduces network traffic, it does not consider the substation timing requirements of messages in an SAS. To reduce unnecessary network traffic in an HSR ring network, we introduced a novel packet transmission (NPT) algorithm in a previous work that considers IEC61850 message types. To further reduce unnecessary network traffic, we propose an extended dual virtual paths (EDVP) algorithm in this paper that considers the timing requirements of IEC61850 message types. We also include sending delay (SD), delay queue (DQ), and traffic flow latency (TFL) features in our proposal. The source node sends data frames without SDs on the primary paths, and it transmits the duplicate data frames with SDs on the secondary paths. Since the EDVP algorithm discards all of the delayed data frames in DQs when there is no link or node failure, unnecessary network traffic can be reduced. We demonstrate the principle of the EDVP algorithm and its performance in terms of network traffic compared to the standard HSR, NPT, and DVP algorithm using the OPNET network simulator. Throughout the simulation results, the EDVP algorithm shows better traffic performance than the other algorithms, while guaranteeing the timing requirements of IEC61850 message types. Most importantly, when the source node transmits heavy data traffic, the EDVP algorithm shows greater than 80% and 40% network traffic reduction compared to the HSR and DVP approaches, respectively.

In this paper we propose an adaptive bitrate (ABR) algorithm that selects the video rates by observing and controlling the playback buffer. In a Hypertext Transfer Protocol (HTTP) adaptive streaming session, buffer dynamics largely depend on the chunk sizes. First, we present the algorithm that selects the next video rates based on the current buffer level, while considering the upcoming chunk sizes. We aim to exploit the variation of chunk sizes of a variable bitrate (VBR) encoded video to optimize the tradeoff between the video rate and buffer underflow events while keeping a low frequency of video rate changes. To evaluate the performance of the proposed algorithm, we consider three scenarios: (i) the video flow does not compete with any cross traffic, (ii) the video flow shares the bottleneck link with competing TCP traffic, and (iii) two HTTP clients share the bottleneck. We show that the proposed algorithm selects a high playback video rate and avoids unnecessary rebuffering while keeping a low frequency of video rate changes. Furthermore, we show that the proposed algorithm changes the video quality gradually to guarantee the user's viewing experience.

This letter presents a novel phase synchronization algorithm for a MIMO radar system in order to overcome the limitation of the existing algorithms relying on channel reciprocity, or line-of-sight, assumption between radar elements. The proposed algorithm is capable of synchronizing local oscillator phases among radar elements even if line-of-sight communication links are not available. Furthermore, the proposed algorithm exhibits robust MSE performance in the presence of frequency estimation error. The performance of the proposed algorithm was analyzed theoretically and verified by simulations.

We propose a novel approach to the target localization problem using Doppler frequency shift measurements. We first reformulate the maximum likelihood estimation (MLE) as a constrained weighted least squares (CWLS) estimation, and then perform the semidefinite relaxation to relax the CWLS problem as a convex semidefinite programming (SDP) problem, which can be efficiently solved using modern convex optimization methods. Finally, the SDP solution can be used to initialize the original MLE which can provide estimates achieve the Cramer-Rao lower bound accuracy. Simulations corroborate the good performance of the proposed method.

Proxy Mobile IPv6 (PMIPv6) has been proposed in order to overcome the limitations of host-based mobility management in IPv6 networks. However, packet losses during doing handover are still a problem. To solve this issue, several schemes have been developed, and can be classified into two approaches: predictive and reactive handover. Both approaches commonly use bi-directional tunnel between mobile access gateways (MAGs). In predictive schemes especially, mobility support for a mobile node (MN) is triggered by simplified link signal strength. Thereafter, the MN sends handover notification to its serving MAG, and is then able to initiate packet forwarding. Therefore, if the MN moves toward an unexpected MAG that does not have any pre-established tunnel with the serving MAG, it may lead to packet losses. In this paper, we define this problem as Early Packet Forwarding (EPF). As a solution, we propose an enhanced PMIPv6 scheme using two-phase tunnel control based on the IEEE 802.21 Media Independent Handover (MIH).

With the increasing deployment of mobile devices and the advent of broadband wireless access systems such as WiBro, mWiMAX, and HSDPA, an efficient IP mobility management protocol becomes one of the most important technical issues for the successful deployment of the broadband wireless data networking service. IETF has proposed the Mobile IPv6 as the basic mobility management protocol for IPv6 networks. To enhance the performance of the basic MIPv6, researchers have been actively working on HMIPv6 and FMIPv6 protocols. In this paper, we propose a new mobility management protocol, HIMIPv6 (Highly Integrated MIPv6), which tightly integrates the hierarchical mobility management mechanism of the HMIPv6 and the proactive handover support of the FMIPv6 to enhance the handover performance especially for the cellular networking environment with high frequent handover activities. We have performed extensive simulation study using ns2 and the results show that the proposed HIMIPv6 outperforms FMIPv6 and HMIPv6. There is no packet loss and consequent service interruption caused by IP handover in HIMIP.

Channel scanning is an important aspect of seamless handovers since it is required in order to find a target point of attachment (PoA). However, channel scanning in single radio devices may cause severe service disruptions with the current PoA so that the provided QoS will be further degraded during a handover. In this letter, we propose a dynamic channel scanning algorithm that supports QoS. Simulation results show that the proposed mechanism reduces the service disruptions and provides the desired QoS to users during the scanning period.

The authors propose a user-centric seamless handover (HO) scheme, which is a kind of a vertical HO from a new perspective, toward a next generation network where heterogeneous access networks converge. The users' experience-oriented scheme allows users to enjoy the optimal service quality for real-time applications in respective access networks. In addition, the scheme sustains on-going sessions during the vertical HO. The proposed scheme consists of two methods -- the bicasting of Different Quality-level Streams (DiffQS) and the Delay Difference Absorption (DDA) method. Initially, the authors propose two plausible methods for the SIP-based bicasting of DiffQS. This document introduces a SIP-capable network element named the HO Assistive Server (HOAS). HOAS controls bicasting of DiffQS and provides users with the optimal service quality for real-time applications via respective access networks as well as avoiding packet loss during HO. The DDA method is also proposed to prevent a service interruption and smoothly continue a real-time service during HO. Evaluation results show that the scheme achieves the seamless service continuity from the users' perspective for HO between cellular and high-speed wireless access via the implementation of a prototype system.

We propose a new mobility management scheme using Label Switched Path (LSP) of Multi Protocol Label Switching (MPLS) for seamless service in Broadband Convergence Network (BcN) in Korea, and verify that the proposed scheme has lower latency time than the existing ones through the separation of control plane from data plane for handover signaling.

This paper presents a Maximum Likelihood Location Estimation (MLLE) algorithm for the home network environments. We propose a deployment of cluster-tree topology in the ZigBee networks and derive the MLE under the log-normal models for the Received Signal Strength (RSS) measurements. Experiments are also conducted to validate the effectiveness of the proposed algorithm.

A transport layer mobility management scheme for handling seamless handoffs between appropriate networks is presented. The future mobile environment will be characterized by multimodal connectivity with dynamic switching. Many technologies have been proposed to support host mobility across diverse wireless networks, and operate in various layers of the network architecture. Our major focus is on the transport protocol that recovers packets lost during handoffs and controls transmission speed to achieve efficient communication. Majority of the existing technologies can maintain the connection by updating the information of a single connection around a handoff. Moreover, none of the studies extensively examine the handoff latencies and focus how an appropriate network is selected, during the handoff. In this paper, we first extensively investigate the various handoff latencies and discuss the limited performance of existing technologies based on the single connection. We then propose a new scheme resolving the problems by the transport protocol enabling the adaptive selection of an appropriate interface based on communication condition among all available interfaces. Finally, we demonstrate that the proposed scheme promptly and reliably selects the appropriate interface, and achieves excellent goodput performance by comparing with the existing technologies.

A new seamless symbol rate switchable modem for multi-rate FDMA systems is proposed in this paper. In the new modem, a novel clock phase compensation algorithm makes it possible to switch the symbol rate synchronously between the transmitter and the receiver, with no degradation in BER when the symbol rate is changed. In addition, by matching the interpolation filter to the symbol rate, this modem is capable of operating at lower clock speeds, which greatly reduces the consumption power. Computer simulations confirm its fundamental performance. Simulation results show that the proposed power-efficient symbol rate switchable modem can change the symbol rate without degrading BER performance.

Multi-projector technology has been under consideration in recent years. This technology allows the generation of wide field of view and high-resolution images in a cost-effective manner. It is expected to be applied extensively to training simulators where vivid immersive sensations and precision are required. However, in many systems the viewing frustums cannot be automatically assigned for distributed rendering, and the required manual setup is complicated and difficult. This is because the camera should be coincide exactly with a desired eye point to avoid perspective distortions. For the actual applications, the camera is seldom able to be set up at the desired eye point because of physical constraints, e.g., a narrow cockpit with many instruments. To resolve this issue, we have developed a "virtual camera method" that yields high-precision calibration regardless of the camera position. This method takes advantage of the quadratic nature of the display surface. We developed a practical real-time multi-projector display system for applications such as training simulators, that require high-accuracy in geometry and rapid response time.

A sampling frequency offset estimation scheme for MB-OFDM UWB systems is proposed based on technical specification and multi-band utilization of the MB-OFDM. An estimation scheme using simple weighting factor based on the received signal power of each sub-channel is also introduced to efficiently combine estimates obtained from all the sub-carriers and to improve the estimation performance.

In order to apply the mobile multimedia communication to the road information system, a seamless handover scheme is needed. Therefore, we present a novel micro-mobility scheme based on explicit multicast (Xcast) in this article. In our proposal, the mobile traffic of its forward direction is sent to the potential access routers of a mobile node (MN) by including IP addresses of the access routers explicitly in the IP headers. As for 802.11 wireless LAN, because it is difficult to know the potential ARs of a mobile node, a new trigger, called as the Candidate AR Trigger (CAT), is introduced to get this information from the link layer. The handover mechanism of our proposed scheme is depicted in detail and the merits of this scheme are also discussed. Finally, by using a combination of performance evaluation and simulation, we argue that our architecture is capable of providing seamless handover while introducing limited network overhead.

In this paper, we propose the Synchronized Mobile Multicast (SMM) scheme for the real-time multimedia service to achieve three most important characteristics that the traditional Home Subscription (HS) and Remote Subscription (RS) mobile schemes cannot support. First, the SMM scheme supports the scalable one-to-many and many-to-many synchronized multimedia multicast on mobile IP networks to achieves seamless playback of continuous media streams even when both the mobile sender and receivers handoff simultaneously. Second, it analyzes the minimal buffer requirements of the mobile sender, the core router, the foreign agents and the mobile receivers in the multicast tree and formulates the initial playback delay within a handoff Guarantee Region (GR). Further, combined with the fine granularity scalability (FGS) encoding approach in the MPEG-4 standard, the SMM scheme achieves superior multimedia QoS guarantees and unlimited numbers of handoffs of the mobile sender and receivers only at the cost of degraded video quality for a short period after handoff with minimal extra bandwidth.