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.

Cellular and Network MIMO architectures: MU-MIMO spectral efficiency and costs of channel state information

Abstract: Cooperative Multi-User MIMO signaling across cells, also known as Network MIMO, has recently received a great deal of attention as a potential physical layer technique for future high-throughput wireless systems. Indeed, cooperative signaling is able to reduce inter-cell interference within groups of coordinated cells thereby improving system throughput. Such benefits, however, are often assessed ignoring inherent overheads such as those required to obtain channel state information (CSI) to enable downlink signaling by MU-MIMO. In fact CSI estimation does take physical layer resources from data and thus should be accounted for in assessing the net benefits of any cooperative signalling strategy. The paper characterizes some elements of this overhead and its effect on CSI estimation error and MU-MIMO efficiency. The results show that, when CSI overheads are taken into account, conventional cellular architectures, with no coordination across cells, can be quite attractive relative to Network MIMO.

Applying Ontology and Probabilistic Model to Human Activity Recognition from Surrounding Things

Abstract: This paper proposes human activity recognition based on the actual semantics of the human's current location. Since no predefined semantics of location can adequately identify human activity, we automatically identify the semantics from things by focusing on the association between things and human activities with the things. Ontology is used to deal with the various possible representations (terms) of each thing, identified by a RFID tag, and a multi-class Naive Bayesian approach is applied to detect multiple actual semantics from the terms. Our approach is suitable for automatically detecting possible activities even given a variety of object characteristics including multiple representations and variability. Simulations with actual thing datasets and experiments in an actual environment demonstrate its noise tolerance and ability to rapidly detect multiple actual semantics from existing things.

Downlink mimo transmission control method and base station device

Abstract: A method of controlling downlink transmission from a base station having multiple antennas to a mobile station having multiple antennas includes the steps of applying open loop-type MIMO diversity to one or more common control channels, an MBMS channel, and an L1/L2 control channel; and applying closed loop-type MIMO multiplexing and/or MIMO diversity to a shared data channel.

Toward network coding-based protocols for data broadcasting in wireless Ad Hoc networks

Abstract: In this paper we consider practical dissemination algorithms exploiting network coding for data broadcasting in ad hoc wireless networks. For an efficient design, we analyze issues related to the use of network coding in realistic network scenarios. In detail, we quantify the impact of random access schemes, as used by IEEE 802.11, on the performance of network coding. In such scenarios, deadlock situations may occur where the delivery process stops and some of the nodes never gather the required packets. To tackle this problem, we propose a proactive mechanism (called proactive network coding) which adapts its transmission schedule according to the decoding status of neighboring nodes. This scheme can detect when nodes need additional packets in order to decode and acts accordingly. We finally investigate the behavior of network coding schemes in multi-rate environments, where we propose a distributed heuristic approach for the selection of data rates.

μSleep: a technique for reducing energy consumption in handheld devices

Abstract: Energy management has become one of the great challenges in portable computing. This is the result of the increasing energy requirements of modern portable devices without a corresponding increase in battery technology. uSleep is an energy reduction technique for handheld devices that is most effective when the handheld's processor is lightly loaded, such as when the user is reading a document or looking at a web page. When possible, rather than using the processor's idle mode, uSleep tries to put the processor in sleep mode for short periods (less than one second) without affecting the user's experience. To enhance the perception that the system is on, an image is maintained on the display and activity is resumed as a result of external events such as touch-screen and button activity. We have implemented, analyzed and evaluated uSleep on a prototype pocket computer, where it has reduced energy consumption by up to 60%.