Distributed Video Coding (DVC), based on the theorems proposed by Slepian-Wolf and Wyner-Ziv, is attracting attention as a new paradigm for video compression. Some of the DVC systems use intra-frame compression based on discrete cosine transform (DCT). Unfortunately, conventional DVC systems have low affinity with DCT. In this paper, we propose a wavelet-based DVC scheme that utilizs current JPEG 2000 standard. Accordingly, the scheme has scalability with regard to resolution and quality. In addition, we propose two methods to increase the coding gain of the new DVC scheme. One is the introduction of a Gray code, and the other method involves optimum quantization. An interesting point is that though our proposed method uses Gray code, it still achieves quality scalability. Tests confirmed that the PSNR is increased about 5 [dB] by the two methods, and the PSNR of the new scheme (with methods) is about 1.5-3 [dB] higher than that of conventional JPEG 2000.

We introduce an adaptive subchannel, bit, and power allocation (ASBPA) algorithm to maximize the bandwidth efficiency of the mobile communication system that use orthogonal frequency division multiplexing (OFDM). We propose a suboptimal rate adaptive ASBPA algorithm that guarantees fairness in resource allocation and overcomes inherent co-channel interference (CCI) in the cellular system. Furthermore, we evaluate the maximum possible bandwidth efficiency of the cellular OFDM system achieved by the ASBPA algorithm which is practical to implement. Our simulation results show that the proposed algorithm outperforms the existing ones and achieves the cellular bandwidth efficiency of up to 5 b/s/Hz/cell. We also investigate some of the conditions that govern the bandwidth efficiency of the cellular OFDM system using the proposed ASBPA algorithm.

This paper proposes an iterative maximum a posteriori probability (MAP) receiver for multiple-input-multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) mobile communications. For exploiting the space, time, and frequency diversity, the low-density parity-check code (LDPC) is used as a channel coding with a built-in interleaver. The receiver employs the expectation maximization (EM) algorithm so as to perform the MAP symbol detection with reasonable computational complexity. The minimum mean square error (MMSE), recursive least squares (RLS), and least mean square (LMS) algorithms are theoretically derived for the channel estimation within this framework. Furthermore, the proposed receiver performs a new scheme called backward symbol detection (BSD), in which the signal detection uses the channel impulse response that is estimated one OFDM symbol later. The advantage of BSD, which is explained from the viewpoint of the message passing algorithm, is that BSD can exploit information on the both precedent and subsequent OFDM symbols, similarly to RLS with smoothing and removing (SR-RLS) [25]. In comparison with SR-RLS, BSD reduces the complexity at the cost of packet error rate (PER) performance. Computer simulations show that the receiver employing RLS for the channel estimation outperforms the ones employing MMSE or LMS, and that BSD can improve the PER performance of the ones employing RLS or LMS.

Recently, the Doherty amplifier technique has been the focus of attention not only for base stations but also for mobile terminals because of its high power-added efficiency in the large back-off region. In this paper, we present a miniaturized Doherty power amplifier (PA) module for W-CDMA mobile terminals. The developed Doherty PA module consists of a 4-mm-square ceramic substrate (4.0 mm4.0 mm1.5 mm, alumina, dielectric constant = 8.8), a 1-mm-square GaAs MMIC (1.0 mm1.0 mm0.1 mm), and 0603-size SMD passive components. To miniaturize the module size, the optimal designed quarter-wavelength transmission lines, which are used for impedance conversion for carrier amplifier output and phase compensation for peak amplifier input, are embedded in the ceramic module substrate. Two GaAs HBTs for a carrier amplifier and a peak amplifier and base bias circuits for each amplifier are integrated onto a single-chip GaAs MMIC. Measurement results at 1950 MHz in a W-CDMA uplink signal indicate that 27 dBm of the maximum output power, 45% of the power-added efficiency (PAE), 11 dB of power gain, and 43% of PAE at 6 dB back-off, i.e. 24 dBm output power, are obtained with the developed Doherty PA. In other words, the PAE is improved from the theoretical PAE of a conventional class B amplifier, namely, from 23% to 43%. This is the smallest Doherty amplifier developed in the form of a module for mobile terminals.

In road-vehicle communication systems, the transmission rate between user terminals in the vehicle and the access points degrades due to changing path-loss and time-varying fading. In this paper, we used an inter-vehicle packet relay technique to improve channel quality in road-vehicle communication systems. We evaluated this method using numerical analysis to validate our method.

Mobile-agent-based distributed computing is one of the most promising paradigms to support autonomic computing in a large-scale of distributed system with dynamics and diversity: mobile agents traverse the distributed system and carry out a sophisticated task at each node adaptively. In mobile-agent-based systems, a larger number of agents generally require shorter time to complete the whole task but consume more resources (e.g., processing power and network bandwidth). Therefore, it is indispensable to keep an appropriate number of agents for the application on the mobile-agent-based system. This paper considers the mobile agent population control problem in dynamic networks: it requires adjusting the number of agents to a constant fraction of the current network size. This paper proposes algorithms inspired by the single species population model, which is a well-known population ecology model. These two algorithms are different in knowledge of networks each node requires. The first algorithm requires global information at each node, while the second algorithm requires only the local information. This paper shows by simulations that the both algorithms realize self-adaptation of mobile agent population in dynamic networks, but the second algorithm attains slightly lower accuracy than the first one.

This letter proposes a hierarchical key management scheme based on hash key chain for authentication of roaming mobile nodes in both intra-domain and inter-domain. The key management scheme uses a local master key concept for reducing the latency of the authentication procedure and the communication overhead between a home authentication server and an access point in the foreign domain. The proposed scheme also supports secure separation of the authentication key among local authentication servers using hash key chain.

In ubiquitous computing environments supporting mobile agents, agent anonymity is a critical issue in protecting the privacy of users. Agent anonymity means that no other entity can identify the identity of the agent performing an action. For agent anonymity, the information, that the user creates or contributes to, and the agent itself should not be revealed, which can be accomplished by hiding the identity of the agent working on behalf of the user. In this paper, an anonymity framework is described for mobile agent systems, providing agent anonymity facilities using agent identity encryption and access control facilities, based on partially blind signature. It is possible to service anonymous mobile agents in ubiquitous computing environments while reducing the abuse resulting from anonymity, by deploying the proposed agent anonymity framework.

In this letter, an analytic model for real-time flow connections in a Wireless Mobile Internet (WMI) is developed, and then performance measures are derived. Some examples are also presented in order to show the call-blocking ratio and the number of connections admitted into a WMI.

As a result of the growth of sensor-enabled mobile devices, in recent years, users can utilize diverse digital contents everywhere and anytime. However, the interfaces of mobile applications are often unnatural due to limited computational capability, miniaturized input/output controls, and so on. To complement the poor user interface (UI) and fully utilize mobility as feature of mobile devices, we explore possibilities for a new UI of mobile devices. This paper describes the method for recognizing and analyzing a user's continuous action including the user's various gestures and postures. The application example we created is mobile game called AM-Fishing game on mobile devices that employ the accelerometer as the main interaction modality. The demonstration shows the evaluation for the system usability.

Paging extensions for Mobile Internet Protocol (P-MIP) decreases only the number of registration, but it does not much improve the method of registration, which still gives rise to a lot of lost packets and long handoff latency, and may also waste the data buffering and time during registration. In the active state, P-MIP behaves in the same way as Mobile Internet Protocol (MIP), thus, in this state, the packet loss rate of P-MIP is the same as that of MIP. However, the packet loss rate of P-MIP is lower than that of MIP, when changing from idle state to active state, because P-MIP buffers packets at the registered FA. We propose an improvement method for the registration delay, while the mobile node is entering the active state to decrease the mobile node waiting time for data packets. The proposed method can reduce the requirement of data buffering and also improve the method of registration to decrease lost packets and handoff latency when the mobile node moves across the cell in the same paging area during active state.

For mobile visual communications, the development of more robust and efficient video traffic control and transmission techniques remains one of the most important issues. Foveated video originates from visual entropy reduction by removing undetectable high visual frequencies that occur at a distance from the fixation point. In this paper, compression gain is defined and measured to quantify the enhanced performance when the visual throughput of the regions of interest (ROI) is increased over a capacity-limited channel.

Receiver enhancement at mobile terminals such as using receiver diversity is a way of achieving greater downlink capacity. The enhancement, however, is achieved not instantaneously by a network operator but gradually by the individual users that choose and purchase their own mobile terminals. We investigate in this letter the effect of gradually introducing enhanced receivers at mobiles in different locations. With greedy scheduling, capacity, fairness and coverage are quantified and numerically compared according to locations of enhanced mobiles. The results show that the enhancement made at mobiles nearer to the base provides the greater capacity but this capacity-driving introduction of the enhancement makes the fairness and the coverage poorer.

The default server strategy is commonly used to manage the location and state of mobile hosts in cellular networks. With this strategy, connections can be established after the client obtains the location information of the mobile host by querying the default server. Unfortunately, the communication cost increases if the query requests are frequent and the distance between the default server and the client is long. Still more, no connection to a mobile host can be established when the default server of the destination mobile host fails. These problems can be solved by replicating the default servers and by letting the nearest replicated default server process the query request which is sent from a client [9]. It is important to allocate replicated default servers efficiently in networks and determine the number of replicated default servers. In this paper, we suggest and evaluate a default server replication strategy to reduce communication costs and to improve service availabilities. We consider optimal replication degree as well as location for replicating the default servers in n-grid and tree networks.

For point-to-point mobile visual communications, layered video has been utilized to adapt to time-varying channel capacity over noisy environments. From the perspective of the HVS (Human Visual System), it is necessary to minimize the loss of visual quality by specifically maintaining the throughput of visually important regions, objects and so on. Utilizing the prioritized bitstreams generated according to each layer, the throughput can be improved for given channel statistics. In this paper, we define the transmission gain and measure the improved performance when the throughput of ROI (Regions Of Interest) is increased relative to visually unimportant regions over a capacity limited mobile channel.

Network Mobility (NEMO) Basic Support is the standard protocol to provide continuous network connectivity and movement transparency to a group of nodes moving together, as in a vehicle. However, the protocol suffers from sub-optimal routing and packet overhead caused by a bi-directional tunnel between the Mobile Router (MR) connecting the mobile network to the Internet and its Home Agent (HA). When a nested NEMO is formed, these inefficiencies become intolerable for real-time multimedia applications. To optimize the delivery of these packets, this study proposes Optimized NEMO (ONEMO) that is capable of providing an optimal path with minimum packet overhead in various scenarios with nested mobility. The protocol is designed to offer the path with minimum signaling overhead and functional requirements are limited to its MRs. Evaluation through measurements against NEMO Basic Support and comparison among other solutions showed effectiveness of the protocol.

In heterogeneous mobile networks, infrastructure multihop techniques enable mobile stations (MSs) with only a single wireless interface to connect with other networks via multiple-interface MSs (MMSs). That is, MMSs can become gateways between two different mobile networks. Cooperation between different mobile networks linked by MMSs can yield many benefits, including coverage expansion, load balancing, and throughput improvement. We studied how to control these cooperative benefits. We developed a network control mechanism, Cooperative Networking, which controls the cooperative benefits in heterogeneous infra-multihop networks. The proposed mechanism assigns a cooperation rule to MSs. By following the rule, every MS chooses a path to a base station, such as direct connection to 3G networks or infra-multihop connection to wireless local area networks (WLANs). Cooperation rules are designed according to the cooperative benefits, which are selected based on the needs of network operators or users. We call a selected cooperative benefit a networking policy. In our proposed cooperative networking mechanism, network operators can adaptively select a networking policy appropriate for network conditions and the needs of users. Computer simulation results validated our proposed mechanism.

To support multimedia applications effectively in mobile networks, the handover latency or packet losses during handover should be very small. Addressing this issue, we present a cooperative mobile router-based handover (CoMoRoHo) scheme for long-vehicular multihomed mobile networks. The basic idea behind CoMoRoHo is to enable different mobile routers to access different subnets during a handover and cooperatively receive packets destined for each other. In general, packet losses are directly proportional to handover latency; however, the overlapped reception of packets from different subnets makes possible to minimize packet losses even without reducing handover latency. To evaluate the scheme, we carried out performance modeling of the CoMoRoHo scheme in comparison with the Fast Handover for Mobile IPv6 (FMIPv6) protocol in regard to the handover latency, packet loss, signaling overhead, and packet delivery overhead in access networks. The analysis results show that CoMoRoHo outperforms FMIPv6 by reducing the packet losses as well as signaling overheads by more than 50%. Moreover, CoMoRoHo imposes lower packet delivery overheads required for preventing packets from being dropped from access routers. We thus conclude that CoMoRoHo is a scalable scheme because its performance remains intact even when the access network is overloaded.

Internet engineering task force (IETF) has proposed hierarchical mobile IPv6 (HMIPv6) in order to reduce a frequent location registration of a mobile node in mobile IPv6 (MIPv6). All traffics toward a mobile node must be transmitted through a MAP in HMIPv6. This brings unnecessary packet latency because of the increased processing cost of packet at the MAP. At this point, the processing cost of packet at the MAP is influenced by the packet arrival rate for a mobile node, cell mobility rate and the number of mobile nodes in MAP domain. In this paper, we analyze the MAP's performance considering the above elements. For this, we compare total cost of HMIPv6 with total cost of MIPv6 as MAP's capability after we define Markov chain model for performance analysis. Also, we define network's total profit as total cost of MIPv6 minus total cost of HMIPv6. Then, we can find optimal capability of MAP such that total profit has maximum value. Also, we use the blocking probability by the MAP's capability as performance estimation element. As a conclusion, we can observe both HMIPv6's performance by the MAP's capability and optimal capability of the MAP, and blocking probability form a relationship of trade off between them.

Lam, Chung, Gu and Sun (2003) proposed a lightweight security mechanism for mobile commerce transactions to meet the security needs in the face of the resource constraints of mobile devices. End-to-end security between the mobile device and the mobile commerce provider is established. However, its security builds on the assumption that customers can confirm every mobile commerce provider's public key by themselves before each transaction. Moreover, the mechanism still produces high overhead on the mobile device. This paper elucidates the causes of these drawbacks, and an enhanced mechanism is also proposed to protect mobile commerce transactions more effectively and efficiently.