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.

Dynamic TDD Support in Macrocell-Assisted Small Cell Architecture

Abstract: Dynamic allocation of subframes to uplink (UL) or downlink (DL) in time division duplex (TDD), termed ‘Dynamic TDD,’ has been studied by the 3rd Generation Partnership Project (3GPP) since the Long Term Evolution (LTE) Release 11 timeframe. At the same time, 3GPP is also standardizing macrocell-assisted small cell heterogeneous architectures for inclusion in LTE Release 12 as a solution offering high data rate to user terminals (UEs) along with high system capacity through spatial reuse of spectrum. In this paper, we focus on a particular small cell architecture proposed by DOCOMO, known as the Phantom Cell architecture, which provides the option to support dynamic TDD. For an arbitrarily-located UE in a small cell network, we apply results from stochastic geometry to derive expressions for the distribution of DL signal to interference plus noise ratio (SINR) at an arbitrary UE and the distribution of UL SINR at its serving base station (BS). The analytical results are verified by system level simulations. These results can be used to study aspects of system design for small cells, and the sensitivity of SINR to the extent of synchronization across small cells employing dynamic TDD. In order to deal with the severe inter-cell interference (ICI) problem in dynamic TDD, we further propose a frequency domain interference coordination technique. Finally, system level simulations based on more realistic system models and assumptions are conducted to evaluate the performance of dynamic TDD systems and the proposed interference coordination technique.

System-level performance of downlink NOMA combined with SU-MIMO for future LTE enhancements

Abstract: This paper investigates the system-level performance of downlink non-orthogonal multiple access (NOMA) combined with single user MIMO (SU-MIMO) for future LTE (Long-Term Evolution) enhancements. The goal is to clarify the performance gains of NOMA combined with SU-MIMO transmission, taking into account the LTE radio interface such as frequency-domain scheduling, adaptive modulation and coding (AMC), and NOMA specific functionalities such as multi-user pairing/ordering and transmit power allocation. In particular, we propose practical schemes to efficiently combine NOMA with open-loop SU-MIMO (Transmission Mode 3: TM3) and closed-loop SU-MIMO (Transmission Mode 4: TM4) specified in LTE. Based on computer simulations, we compare NOMA performance gains for different granularities of scheduling and MCS (modulation and coding scheme) selection, for both genie-aided channel quality information (CQI) estimation and approximated CQI estimation, and using different number of power sets. Evaluation results show that NOMA can still provide a hefty portion of its expected gains even with approximated CQI estimation and limited number of power sets, and also when LTE compliant subband scheduling and wideband MCS are applied.

Fireflies as role models for synchronization in ad hoc networks

Abstract: Fireflies exhibit a fascinating phenomenon of spontaneous synchronization that occurs in nature: at dawn, they gather on trees and synchronize progressively without relying on a central entity. The present article1 reviews this process by looking at experiments that were made on fireflies and the mathematical model of Mirollo and Strogatz [1], which provides key rules to obtaining a synchronized network in a decentralized manner. This model is then applied to wireless ad hoc networks. To properly apply this model with an accuracy limited only to the propagation delay, a novel synchronization scheme, which is derived from the original firefly synchronization principle, is presented, and simulation results are given.

Usage Control Enforcement: Present and Future

Abstract: Both personal data and intellectual property must be protected for various reasons. The authors explore the state of the art in usage control, which is about controlling the use of such data after it has been given away, and identify room for improvement.

Multi-band lookup table type predistorter

Abstract: A lookup table type predistorter for reading out distortion compensation data by using a difference signal between a power amplifier input signal and an output signal as a reference signal; wherein N input side variable band signal extractors extract transmitting signals in N frequency bands from the input signal, N output side variable band signal extractors extract signals in N frequency bands from the output of power amplifier, and N difference detectors detect differences between N frequency band signals respectively detected at the input side and the output side as N reference signals, which are used to read out N compensation data from N lookup tables, the N compensation data are added to the transmitting signals in N frequency bands, and N results of addition are combined to produce an output of the predistorter.