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.

A Flexible Multiple Description Coding Framework for Adaptive Peer-to-Peer Video Streaming

Abstract: Efficient peer-to-peer (P2P) video streaming is a challenging task due to time-varying nature of both the number of available peers and network/channel conditions. This paper proposes a novel adaptive P2P video streaming system, which features: (i) a new flexible multiple-description coding (F-MDC) framework, such that the number of base and enhancement descriptions, and the rate and redundancy level of each description can be adapted on the fly (by only post-processing of the encoded bitstream), and (ii) a new adaptive TCP-friendly rate-controlled (TFRC), on-demand, many-to-one P2P video streaming solution based on the proposed F-MDC framework. We extend the highly scalable video coder , to MDC within the proposed F-MDC framework. Optimization of the design parameters of the proposed F-MDC method is discussed within the context of the proposed adaptive P2P streaming solution, where the number and quality of available streaming peers/paths are a priori unknown and vary in time. Experimental results, by means of NS-2 network simulation of a P2P video streaming system, show that adaptation of the number, type of descriptions and the rate and redundancy level of each description according to network conditions yields significantly superior performance when compared to other scalable MDC schemes using a fixed number of descriptions/layers with fixed rate and redundancy level.

Improved Lower Bounds on Time-of-Arrival Estimation Error in Realistic UWB Channels

Abstract: This paper investigates lower bounds on time-of-arrival (ToA) estimation error for ultrawide bandwidth ranging systems operating in realistic multipath environments Based on the Ziv-Zakai lower bound, we derive a lower bound for the ToA estimation error using both the IEEE 802154a channel models and experimentally measured data It is shown that for practical signal-to-noise values the classical Cramer-Rao lower bound is too optimistic when operating in dense multipath environments

Frequency Selective Reflectarray Using Crossed-Dipole Elements With Square Loops for Wireless Communication Applications

Abstract: A new frequency selective reflectarray (FSR) comprising a crossed-dipole array and a frequency selective surface (FSS) of square loops printed on both sides of a dielectric substrate is presented for wireless communication applications. The reflectarray functions as a reflector, and generates the desired reflected beam shape while steering the primary wave source in the desired direction. Moreover, the FSR should be partially transparent for propagation channels of other communication systems working in other frequency bands. Some new FSR designs comprising 11 by 7 elements for dual-source and dual-polarized operation are given and verified by simulation and experiment. Furthermore, the FSR is applied to a WCDMA system to eliminate blind spots in communications between the base station and mobile users. A practical link budget analysis demonstrates the effectiveness of the FSR to improve the quality of communications. Finally, the proximity effect of concrete wall on the FSR is discussed to illustrate the applicability and flexibility of the proposed frequency selective reflectarray.

Multipath interference canceller for high-speed packet transmission with adaptive modulation and coding scheme in W-CDMA forward link

Abstract: This paper proposes a multipath interference canceller (MPIC) associated with orthogonal code-multiplexing that achieves much higher peak throughput than 2 Mbit/s with adaptive data modulation for high-speed packet transmission in the wideband direct sequence-code division multiple access (W-CDMA) forward link, and evaluates its throughput performance by computer simulation. The simulation results elucidate that sufficient multipath interference (MPI) suppression is achieved by a four-stage MPIC with 6-12 orthogonal code-multiplexing using one iterative channel estimation with pilot and decision feedback data symbols and further that the interference rejection weight control according to the number of observed multipaths is effective in improving the throughput. It is also demonstrated that MPIC exhibits a superior MPI suppression effect to a chip equalizer in the lower received signal energy per bit-to-background noise spectrum density (E/sub b//N/sub 0/) channel around 0-3 dB owing to the successive channel estimation at each stage. We show that the maximum peak throughput using MPIC is approximately 2.1 fold that without MPIC in a two-path and three-path Rayleigh fading channel and that the peak throughput of 8.0 Mbit/s is achieved using 64 QAM data modulation in a two-path fading channel within a 5 MHz bandwidth. Furthermore, the required average E/sub b//N/sub 0/ for satisfying the same throughput with MPIC is decreased by more than 2.0 dB.

Method and apparatus at the physical and link layer for mobile communications

Abstract: In a cellular telecommunications network, a mobile communication system to offload data traffic from base stations to small-node devices, includes a radio base station, a plurality of small-node devices, a macro-base-station-to-the-small-node-device (BS2D) communication section configured to receive a first control-plane message from the radio base station over a BS2D communication link, a small-node-device-to-user-equipment (D2UE) communication section configured to transmit user-plane data to a user equipment over a wireless D2UE communication link established responsive to the first control-plane message, and a center small-node device. The center small-node device includes a buffer section, a backhaul communication section configured to receive the user-plane traffic data from a server over a backhaul link, and is configured to manage D2UE connections between the plurality of small-node devices and the mobile station, buffer data to be transmitted in downlink and uplink for the plurality of small-node devices, and conduct a link adaptation for the D2UE connections.