NTT DoCoMo

About: NTT DoCoMo is a based out in . It is known for research contribution in the topics: Base station & Mobile station. The organization has 4032 authors who have published 8655 publications receiving 160533 citations.

Network architecture for mobile communications systems beyond IMT-2000

Abstract: This article describes a suitable network architecture for the mobile communications system beyond IMT-2000. The rapid developments in mobile communication services have significantly altered the lifestyles of many people. With the increasing demand for access to the Internet, the amount of data traffic in mobile communication networks has significantly increased and will dominate these networks. Therefore, mobile networks beyond IMT-2000 should offer higher bit rate channels and adapt to multimedia traffic more efficiently. This article first forecasts market trends in mobile communications in order to identify requirements of the mobile communications system beyond IMT-2000. Then the article considers the network architecture of the mobile communications system beyond IMT-2000 that will satisfy those requirements.

Wireless Network Virtualization as A Sequential Auction Game

Abstract: We propose a virtualization framework to separate the network operator (NO) who focuses on wireless resource management and service providers (SP) who target distinct objectives with different constraints. Within the proposed framework, we model the interactions among SPs and NO as a stochastic game, each stage of which is played by SPs (on behalf of the end users) and is regulated by the NO through the Vickrey-Clarke-Groves (VCG) mechanism. Due to the strong coupling between the future decisions of SPs and lack of global information at each SP, the stochastic game is notoriously hard. Instead, we introduce conjectural prices to represent the future congestion levels the end users potentially will experience, via which the future interactions between SPs are decoupled. Then, the policy to play the dynamic rate allocation game becomes selecting the conjectural prices and announcing a strategic value function (i.e., the preference on the rate) at each time. We prove that there exists one Nash equilibrium in the conjectural prices and, given the conjectural prices, the SPs have to truthfully reveal their own value function. We further prove that this Nash equilibrium results in efficient rate allocation in our virtualized wireless network. In other words, there are enough incentives for NO to advertise such a conjectural price and SPs to follow this advice.

Image decoding apparatus, image decoding program, image decoding method, image encoding apparatus, image encoding program, and image encoding method

Abstract: An image decoding apparatus has a video data decoder for receiving and decoding encoded video data to acquire a plurality of reconstructed images; a subsidiary data decoder for receiving and decoding subsidiary data to acquire subsidiary motion information; and a resolution enhancer for generating motion vectors representing time-space correspondences between the plurality of reconstructed images, based on the subsidiary motion information acquired by the subsidiary data decoder, and for generating a high-resolution image with a spatial resolution higher than that of the plurality of reconstructed images, using the generated motion vectors and the plurality of reconstructed images acquired by the video data decoder

Advanced LOS path-loss model in microcellular mobile communications

Abstract: This paper proposes an advanced line-of-sight path-loss model incorporating characteristics of an actual urban environment. Accurate results are obtained by using a two-path model with shadowing caused by obstacles that would appear in an actual urban environment and rising reflection area caused by vehicular traffic. By applying the model in an urban environment, microcellular path loss can be predicted from ultra-high-frequency to microwave bands.

A comparative study of different deployment modes for femtocell networks

Abstract: Femtocell networks have the potential of significantly improving the capacity of next-generation cellular systems. However, interference to/from the macrocell network is a critical problem affecting the capacity. Co-channel operation with closed-subscriber group (CSG) access offers a large bandwidth to be shared by the users of the femtocell network; however, it also introduces significant interference to/from the macrocell network. On the other hand, femtocell networks using dedicated spectrum assignment and open access mode have insignificant interference concerns, with the trade-off of available spectrum limitations. In this study, we investigate interference vs. bandwidth tradeoffs in different types of femtocell network deployments through the help of channel capacity formulations. Related downlink simulation results are provided to compare the capacities of different deployment modes and the impact of key system parameters.