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.

Recognition Among OFDM-Based Systems Utilizing Cyclostationarity-Inducing Transmission

Abstract: This paper presents cyclostationarity-inducing transmission techniques that enable the receiver to distinguish among different systems employing OFDM (Orthogonal Frequency Division Multiplexing) as a common air interface. Several systems using different air interfaces may have different properties of cyclostationarity that can be utilized to distinguish among them. However, this is usually not possible when the same air interface is used. To address this problem for systems using OFDM as an air interface, we consider methods that induce different properties of cyclostationarity in the transmitter of different systems. Specifically, we configure the OFDM signal before transmission such that its cyclic autocorrelation function (CAF) has peaks at certain pre-chosen cycle frequencies. The difference in the cycle frequencies, at which the CAF peaks occur for the configured OFDM signals, is utilized to distinguish among several systems even when OFDM is used as a common air interface. Two configuration methods for the OFDM signal are proposed. The first proposed method inserts a specific preamble at the head of each OFDM frame. Each preamble is configured such that only a selected subset of subcarriers is used for transmission. A different subset of subcarriers results in the occurrence of CAF peaks at different cycle frequencies for the OFDM signal. The second proposed method is based on dedicating a few subcarriers in an OFDM frame to the transmission of specific signals so that the whole frame exhibits cyclostationarity at pre-chosen cycle frequencies. For this method, we introduce a method for generating signals on the dedicated subcarriers and describe their relation to the cycle frequencies of the configured OFDM frame. Both proposed methods are evaluated by computer simulation in a multipath Rayleigh fading environment. Simulation results show that system recognition based on the proposed methods exhibits excellent detection probability.

Iterative channel estimation and data detection in frequency-selective fading MIMO channels†

Abstract: Signals transmitted through multiple-input multiple-output (MIMO) wireless channels buffer from multiple-access interference (MAI), multipath propagation and additive noise. Iterative multiuser algorithms mitigate these signal impairments. while offering a good tradeoff between performance and complexity. The receiver presented in this paper performs channel estimation. multiuser detection and decoding in an iterative manner. The estimation of the frequeucy selective. block-fading channel is initiated with the pilot symbols. In subsequent iterations. soft decisions of all the data symbols are used in an appropriate way to improve the channel estimates. This approach leads, to significant Improvement of the overall receiver performance, compared to other schemes. The bit-error-rate (BER) performance of the receiver is evaluated by simulations for different parameter setups. Copyright (C) 2004 AEI. (Less)

Radio resource allocation method and base station using the same

Abstract: In a radio resource allocation method of the present invention, use-state information of radio resources and priority information of mobile stations using the same radio resources of both a base station of concern and neighboring base stations is detected at the base station of concern. A new radio resource is allocated to a link between the base station of concern and a requesting mobile station in a cell site of the base station of concern based on the use-state information and the priority information of both the base station and the neighboring base stations.

MIMO broadcast channel optimization under general linear constraints

Abstract: The optimization of the transmit parameters (power allocation and steering vectors) for the MIMO BC under general linear constraints is treated under the optimal DPC coding strategy and the simple suboptimal linear zero-forcing beamforming strategy. In the case of DPC, we show that “SINR duality” and “min-max duality” yield the same dual MAC problem, and compare two alternatives for its efficient solution. In the case of zero-forcing beamforming, we provide a new efficient algorithm based on the direct optimization of a generalized inverse matrix. In both cases, the algorithms presented here address the problems in the most general form and can be applied to special cases previously considered, such as per-antenna and per-group of antennas power constraints, “forbidden interference direction” constraints, or any combination thereof.

Design and Analysis of a Short-Term Sensing-Based Resource Selection Scheme for C-V2X Networks

Abstract: The cellular vehicle-to-everything (C-V2X) networks can support direct vehicle-to-vehicle (V2V) communications via sidelink/PC5 interface without cellular infrastructure support. The sensing-based semipersistent scheduling (SPS) scheme is to allow vehicles to autonomously reserve and select radio resources. However, the common sensing nature of the distributed SPS algorithm gives rise to that C-V2X distributed communications can be challenged by the resource selection collisions, especially in aperiodic traffic, which results in low reliability. In this article, we propose a short-term sensing-based resource selection (STS-RS) scheme to reduce packet collisions due to resource contention, where a short-term sensing duration is configured at the beginning of the resource unit right before resource selection, and whether the packet is ultimately transmitted on the selected resource depends on the sensing result. Furthermore, analysis models of the performance for the proposed STS-RS scheme and SPS scheme defined in C-V2X mode 4 are investigated. Finally, simulations and numerical results show that the STS-RS scheme significantly reduces the packet collisions and increases the C-V2X direct communication performance compared to the SPS scheme.