When the number of users in a service area increases in mobile multimedia services, no individual user can obtain satisfactory radio resources such as bandwidth and signal power because the resources are limited and shared. A solution for such a problem is user-position control. In the user-position control, the operator informs users of better communication areas (or spots) and navigates them to these positions. However, because of subjective costs caused by subjects moving from their original to a new position, they do not always attempt to move. To motivate users to contribute their resources in network services that require resource contributions for users, incentive-rewarding mechanisms have been proposed. However, there are no mechanisms that distribute rewards appropriately according to various subjective factors involving users. Furthermore, since the conventional mechanisms limit how rewards are paid, they are applicable only for the network service they targeted. In this paper, we propose a novel incentive-rewarding mechanism to solve these problems, using an external evaluator and interactive learning agents. We also investigated ways of appropriately controlling rewards based on user contributions and system service quality. We applied the proposed mechanism and reward control to the user-position control, and demonstrated its validity.

This paper introduces a communication system model with renewable power supply. As we assumed a battery-free microgrid system with conventional power as a backup power supply, we propose a method of power state and data transmission scheduling for delay-tolerant communication networks, which reduces conventional power consumption by operating adaptively to changes in renewable power. We found through computer simulations that the proposed method efficiently reduced conventional power consumption.

In this paper, we propose a novel solution to improving wireless channel quality of wireless local area networks (WLANs) in fast-mobile environments, which uses a media-access-control (MAC) layer approach: adaptive frame-length control and block acknowledgement (ACK). In fast-mobile environments, using short frame lengths can suppress channel estimation error and decrease frame errors. However, it increases the MAC overhead, resulting in decreased throughput. To solve this tradeoff, we combined block ACK, which is specified in IEEE802.11e as an optional function, with adaptive frame-length control. Although adaptive frame-length control considering this tradeoff has previously been investigated, the targets were different from WLANs using orthogonal frequency division multiplexing (OFDM) in fast-mobile environments. The MAC-overhead reduction using block ACK is suitable for our frame-length control because it does not change the frame format in the physical layer. Also, it is a new idea to use block ACK as a solution to improving channel quality in fast-mobile environments. In this paper, we evaluate our method through computer simulations and verify the effectiveness of adaptive frame-length control that can accommodate relative speeds.

This paper proposes ABdis, a new active measurement method for estimating the available bandwidth on a communication network path. Due to the recent explosion in multimedia applications, it is becoming increasingly important to manage network QoS, and tools that can measure network quality precisely are necessary to do this. Many conventional active measurement methods/tools, however, can measure/estimate only the average of the available bandwidth in a given period but cannot measure its distribution. If the distribution of the bandwidth over short intervals can be measured, the information would be useful for network management, proxy selection, and end-to-end admission control. We propose an end-to-end active measurement method called ABdis, which can estimate the distribution of the available bandwidth in a network path. ABdis employs multiple probes having different rates and a parameter-matching technique for estimating distribution. Furthermore, we present the results of simulations and verify ABdis's performance under various conditions by changing probe parameters, amount of cross traffic, and network models.

A switching network construction scheme for a fast packet switching system, which is expected to provide multi-media services efficiently and economically, is proposed. The proposed packet switch has RAM as a shared buffer. Its access is assigned to input and output ports dynamically in order to fully utilize limited memory time. This enables packet switches to flexibly accommodate packet links having different bit-rates. An asynchronous data transfer technique is also incorporated into inter-switch links. This switching network can dynamically alter the inter-switch link speed, according to the demanded flow. The dynamism of this simple hardware contributes greatly to better packet transfer quality. This paper describes switch architecture, multi-stage packet switching network construction which can handle any combination of packet flow without centralized switch resource management, and simulated packet transport characteristics of a multi-stage switching network. The simulation results show that the proposed switching network gives good packet transport quality, in terms of packet delay and loss. Finally, the congestion mechanism is analyzed.

Information-centric networking (ICN) has been investigated as a new communication model that is optimal for data registration and retrieval. A promising application of ICN is mobile machine-to-machine (M2M) communication in which data are registered by M2M terminals, such as vehicles, and retrieved by other M2M terminals. One of the most difficult challenges with ICN is achieving data mobility in which the data are registered by moving terminals and the location of the data changes constantly. To gain access to moving data, the data retrieval messages must access the routing information, which results in a high volume of message transaction loads of high-tier nodes such as the name resolution nodes. We previously proposed a scheme called data-centric network (DCN), which mitigates this problem by allocating multiple intermediate nodes that act as route aggregation points and by establishing optimized routes. In this paper, we compare the transaction load of DCN with those of conventional ICN schemes using theoretical evaluation based on probability calculation. We also compare the amount of route information and transaction loads using a simulator against binary tree and ISP backbone topologies. From these evaluations, we clarify the characteristics of each ICN scheme in different terminal distribution and communication patterns and show that DCN reduces the transaction loads of high-tier nodes when the terminals are communicating locally.

The demand of using applications that assume bidirectional communication such as voice telephony and peer-to-peer using wireless stations has been increasing and especially, the rapid increase of uplink traffic from wireless terminals is expected. However, in uplink WLANs, the hidden-station problem remains to be solved. In this paper, we point out this hidden-station problem and clarify the following unfairness between UDP and TCP uplink flows: 1) the effect of collision caused by hidden-station relationship on throughput and 2) the instability of the throughput depending on the number of hidden stations. To solve these problems, we propose a virtual multi-AP access mechanism. Our mechanism first groups stations according to the hidden-station relationship and type of transport protocol they use then assigns a virtually isolated channel to each group, which enables STAs to communicate as if STAs in different groups are connected to different isolated APs (virtual APs: VAPs). It can mitigate the effect caused by collisions between hidden stations and eliminate the contention between UDP and TCP uplink flows. Its performance is shown through simulation.

Mobile virtual network operators (MVNOs) are mobile operators without their own infrastructure or government issued spectrum licenses. They purchase spectrum resources from primary mobile network operators (MNOs) to provide communication services under their own brands. MVNOs are expected to play an important role in mobile network markets, as this will increase the competition in retail markets and help to meet the demand of niche markets. However, with the rapidly increasing demand of mobile data traffic, efficient utilization of the limited spectrum resources owned by MVNOs has become an important issue. We propose here a resource sharing mechanism between MVNOs against the background of network functions virtualization (NFV). The proposed mechanism enables MVNOs to improve their quality of service (QoS) by sharing spectrum resources with each other. A nash bargaining solution based decision strategy is also devised to ensure the fairness of resource sharing. Extensive numerical evaluation results validate the effectiveness of the proposed models and mechanisms.

In conventional road-vehicle communication systems, user terminals in the vehicles have to directly connect to wireless access points (APs). However, vehicle speeds are so fast that the channel condition between the terminals and the APs constantly changes because of changing path loss and time-varying fading. In this paper, to compensate for such deterioration, we propose to reduce the relative speed between the terminals and the APs by an inter-vehicle packet relay technique. If a terminal can send data via other vehicles running at lower speeds, the relative speed will decrease, which suppresses the dynamic range of path loss and deterioration by fading. We, first, validate our method by a numerical analysis using a statistical path-loss model. The numerical analysis verifies that our method is able to suppress deterioration caused by path loss and time-varying fading. However, in the numerical analysis, geometric propagation of paths is not considered; instantaneous and rapid loss changes are not considered. Therefore, we evaluate our method by computer simulations using a geometric propagation model. In the simulations, phase difference between multiple paths and loss fluctuation within one frame duration affect the performance. From the results of the simulations, we validate our method. Furthermore, we investigate the combination of our method and the selection diversity technique, which can suppress channel fluctuation and may enhance the performance of our method. Moreover, we measure interference in the overlapped zone between two AP areas. From the measurement, we show that our packet relays do not cause a problem in interference between areas.

Analyzing short-interval-traffic behaviors is important for network performance management to realize high quality multimedia applications. However, it is difficult to measure short-interval-traffic volumes because there are complications in collecting short-interval-traffic data from routers. An example is a heavy load on routers or inaccurate measurement by the short-polling interval; it even demands expensive measurement tools. To resolve these disadvantages, an estimating method of short-interval-traffic distribution (EMSIT) has been proposed. This method estimates short-interval-traffic distributions using MIB (Management Information Base) data, which collects traffic volumes in cycles of several minutes. In this paper, we propose a new estimation method (EMSIT-LD) based on EMSIT, which applies to the case of long-term-traffic dynamics. We evaluate it using computer simulations and actual traffic data.

Conventional mechanisms proposed for enhancing quality of service (QoS) in 802.11 networks suffer from a lack of backward compatibility and fairness with and to legacy devices. In this paper, we present a cooperative mechanism, called TXOP (transmission opportunity) Exchange, that provides a legacy-neutral solution in which only stations (STAs) participating in TXOP Exchange cooperatively use their available bandwidth to satisfy their required throughputs, while other legacy devices continue to get the same throughput performance as before. Specifically, we discuss the implementation of TXOP Exchange in legacy 802.11 networks. We show that this mechanism can be realized with minor modifications to the RTS (request-to-send) frames of only the STAs participating in TXOP Exchange and without any replacement of legacy access points or STAs. We show an example of a proportional fair algorithm for fair and efficient MAC cooperation using a Nash bargaining solution (NBS). A simulation study using a realistic simulator verifies that the TXOP Exchange mechanism ensures legacy neutrality and fair and efficient cooperation even when a large number of legacy STAs coexist.

The market growths of smart-phones and thin clients have been significantly increasing communication traffic in mobile networks. To handle the increased traffic, network operators should consider how to leverage distributed wireless resources such as distributed spots of wireless local access networks. In this paper, we consider the system where multiple moving users share distributed wireless access points on their traveling routes between their start and goal points and formulate as an optimization problem. Then, we come up with three algorithms as a solution for the problem. The key idea here is 'longcut route instruction', in which users are instructed to choose a traveling route where less congested access points are available; even if the moving distance increases, the throughput for users in the system would improve. In this paper, we define the gain function. Moreover, we analyze the basic characteristics of the system using as a simple model as possible.

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.

Searching mechanisms employed in unstructured overlay networks typically hit multiple peers for the desired content. We propose the use of a simple method that raises the hit rates of unpopular contents and balances the loads by choosing the peer holding the least contents as the provider when multiple candidates exist.

The demand for data/audio streaming/video streaming multicast services in large scale networks has been increasing. Moreover, the improved transmission speed and mobile-device capability in wireless access networks enable people to use such services via their personal mobile devices. Peer-to-peer (P2P) architecture ensures scalability and robustness more easily and more economically than server-client architecture; as the number of nodes in a P2P network increases, the amount of workload per node decreases and lessens the impact of node failure. However, mobile users feel much larger psychological cost due to strict limitations on bandwidth, processing power, memory capacity, and battery life, and they want to minimize their contributions to these services. Therefore, the issue of how we can reduce this psychological cost remains. In this paper, we consider how effective a social networking service is as a platform for mobile P2P multicast. We model users' cooperative behaviors in mobile P2P multicast streaming, and propose a social-network based P2P streaming architecture for mobile networks. We also measured the psychological forwarding cost of real users in mobile P2P multicast streaming through an emulation experiment, and verify that our social-network based mobile P2P multicast streaming improves service quality by reducing the psychological forwarding cost using multi-agent simulation.

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.

Multihop techniques in CDMA radio access networks, enable dead-spot mobile stations, which cannot communicate with base stations directly, to send data to them via other mobile stations. In this paper, we propose a mechanism for establishing connections and relaying packets between mobile stations. In this mechanism, the mobile stations are connected to one another and relay packets through a random access channel, which is an uplink common channel. In addition, our mechanism satisfies the requirements for applying multihop techniques to third generation radio access networks. Moreover, we also discuss our evaluation of the performance of the mechanism through computer simulations. The results we obtained reveal that it is capable of reducing dead-spot mobile stations and improving throughput with only limited modifications to conventional systems. Furthermore, we propose an adaptive transmission power control to enhance our mechanism and also evaluate this method through computer simulations.

Machine-to-Machine (M2M) communication is expected to grow in networks of the future, where massive numbers of low cost, low function M2M terminals communicate in many-to-many manner in an extremely mobile and dynamic environment. We propose a network architecture called Data-centric Network (DCN) where communication is done using a data identifier (ID) and the dynamic data registered by mobile terminals can be retrieved by specifying the data ID. DCN mitigates the problems of prior arts, which are large size of routing table and transaction load of name resolution service. DCN introduces concept of route attraction and aggregation in which the related routes are attracted to an aggregation point and aggregated to reduce routing table size, and route optimization in which optimized routes are established routes to reduce access transaction load to the aggregation points. These allow the proposed architecture to deal with ever increasing number of data and terminals with frequent mobility and changes in data.

In peer-to-peer (P2P) content sharing, users can share their content by contributing their own resources to one another. However, since there is no incentive for contributing contents or resources to others, users may attempt to obtain content without any contribution. To motivate users to contribute their resources to the service, incentive-rewarding mechanisms have been proposed. On the other hand, emerging wireless technologies, such as IEEE 802.11 wireless local area networks, beyond third generation (B3G) cellular networks and mobile WiMAX, provide high-speed Internet access for wireless users. Using these high-speed wireless access, wireless users can use P2P services and share their content with other wireless users and with fixed users. However, this diversification of access networks makes it difficult to appropriately assign rewards to each user according to their contributions. This is because the cost necessary for contribution is different in different access networks. In this paper, we propose a novel incentive-rewarding mechanism called EMOTIVER that can assign rewards to users appropriately. The proposed mechanism uses an external evaluator and interactive learning agents. We also investigate a way of appropriately controlling rewards based on the system service's quality and managing policy.