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Base Station Cooperation on the Downlink: Large System Analysis

IEEE TRANSACTIONS ON INFORMATION THEORY 2012年第4期58卷 2079-2106页

作者： Zakhour, Randa Hanly, Stephen V. Univ Melbourne Dept Elect & Elect Engn Parkville Vic 3052 Australia Natl Univ Singapore Dept Elect & Comp Engn Singapore Singapore

This paper considers maximizing the network-wide minimum supported rate in the downlink of a two-cell system, where each base station (BS) is endowed with multiple antennas. This is done for different levels of cell cooperation. At one extreme, we consider single cell processing where the BS is oblivious to the interference it is creating at the other cell. At the other extreme, we consider full cooperative macroscopic beamforming. In between, we consider coordinated beamforming, which takes account of inter-cell interference, but does not require full cooperation between the BSs. We combine elements of Lagrangian duality and large system analysis to obtain limiting SINRs and bit-rates, allowing comparison between the considered schemes. The main contributions of the paper are theorems which provide concise formulas for optimal transmit power, beamforming vectors, and achieved signal to interference and noise ratio (SINR) for the considered schemes. The formulas obtained are valid for the limit in which the number of users per cell,, and the number of antennas per base station, N, tend to infinity, with fixed ratio beta = K/N. These theorems also provide expressions for the effective bandwidths occupied by users, and the effective interference caused in the adjacent cell, which allow direct comparisons between the considered schemes.

关键词： Base station cooperation cellular systems intercell interference interference channel linear precoding MIMO broadcast channel multicell processing regularized zero forcing

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Achieving "Massive MIMO" Spectral Efficiency with a Not-so-Large Number of Antennas

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2012年第9期11卷 3226-3239页

作者： Huh, Hoon Caire, Giuseppe Papadopoulos, Haralabos C. Ramprashad, Sean A. Samsung Elect Co Ltd Media Lab Suwon 443742 Gyeonggi Do South Korea Univ So Calif Dept Elect Engn Los Angeles CA 90089 USA Docomo Innovat Palo Alto CA 94304 USA

Time-Division Duplexing (TDD) allows to estimate the downlink channels for an arbitrarily large number of base station antennas from a finite number of orthogonal uplink pilot signals, by exploiting channel reciprocity. Based on this observation, a recently proposed "Massive MIMO" scheme was shown to achieve unprecedented spectral efficiency in realistic conditions of distance-dependent pathloss and channel coherence time and bandwidth. The main focus and contribution of this paper is an improved Network-MIMO TDD architecture achieving spectral efficiencies comparable with "Massive MIMO", with one order of magnitude fewer antennas per active user per cell (roughly, from 500 to 50 antennas). The proposed architecture is based on a family of Network-MIMO schemes defined by small clusters of cooperating base stations, zero-forcing multiuser MIMO precoding with suitable inter-cluster interference mitigation constraints, uplink pilot signals allocation and frequency reuse across cells. The key idea consists of partitioning the users into equivalence classes, optimizing the Network-MIMO scheme for each equivalence class, and letting a scheduler allocate the channel time-frequency dimensions to the different classes in order to maximize a suitable network utility function that captures a desired notion of fairness. This results in a mixed-mode Network-MIMO architecture, where different schemes, each of which is optimized for the served user equivalence class, are multiplexed in time-frequency. In order to carry out the performance analysis and the optimization of the proposed architecture in a systematic and computationally efficient way, we consider the large-system regime where the number of users, the number of antennas, and the channel coherence block length go to infinity with fixed ratios.

关键词： Channel training downlink scheduling frequency reuse inter-cell cooperation large-system analysis linear precoding Massive MIMO pilot contamination time-division duplex

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Optimal linear precoding strategies for wideband noncooperative systems based on game theory - Part I: Nash equilibria

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2008年第3期56卷 1230-1249页

作者： Scutari, Gesualdo Palomar, Daniel P. Barbarossa, Sergio Univ Roma La Sapienza Dept INFOCOM I-00184 Rome Italy Hong Kong Univ Sci & Technol Dept Elect & Comp Engn Hong Kong Hong Kong Peoples R China

In this two-part paper, we propose a decentralized strategy, based on a game-theoretic formulation, to find out the optimal precoding/multiplexing matrices for a multipoint-to-multipoint communication system composed of a set of wideband links sharing the same physical resources, i.e., time and bandwidth. We assume, as optimality criterion, the achievement of a Nash equilibrium and consider two alternative optimization problems: 1) the competitive maximization of mutual information on each link, given constraints on the transmit power and on the spectral mask imposed by the radio spectrum regulatory bodies;and 2) the competitive maximization of the transmission rate, using finite order constellations, under the same constraints as above, plus a constraint on the average error probability. In this first part of the paper, we start by showing that the solution set of both noncooperative games is always nonempty and contains only pure strategies. Then, we prove that the optimal precoding/multiplexing scheme for both games leads to a channel diagonalizing structure, so that both matrix-valued problems can be recast in a simpler unified vector power control game, with no performance penalty. Thus, we study this simpler game and derive sufficient conditions ensuring the uniqueness of the Nash equilibrium. Interestingly, although derived under stronger constraints, incorporating for example spectral mask constraints, our uniqueness conditions have broader validity than previously known conditions. Finally, we assess the goodness of the proposed decentralized strategy by comparing its performance with the performance of a Pareto-optimal centralized scheme. To reach the Nash equilibria of the game, in Part II, we propose alternative distributed algorithms, along with their convergence conditions.

关键词： ad hoc networks cognitive radio game theory linear precoding mutual information Nash equilibrium

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Compressed Sensing Based Channel Estimation for Two-Way Relay Networks

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IEEE WIRELESS COMMUNICATIONS LETTERS 2012年第3期1卷 201-204页

作者： Cheng, Peng Gui, Lin Rui, Yun Guo, Y. Jay Huang, Xiaojing Zhang, Wenjun Shanghai Jiao Tong Univ Dept Elect Engn Shanghai 200240 Peoples R China Chinese Acad Sci Shanghai Adv Res Inst Beijing 100864 Peoples R China CSIRO ICT Ctr Marsfield NSW 2122 Australia

In this letter, a novel channel estimation scheme based on compressed sensing (CS) theory is proposed for two-way relay networks (TWRN) in sparse frequency-selective fading channels. Unlike point-to-point systems, applying CS theory to sparse channel estimation in TWRN is much more challenging since the equivalent channels (terminal-relay-terminal) may be no longer sparse due to the linear convolutional operation. To solve this problem, instead of directly estimating the equivalent channels, a linear precoding based method is designed to firstly separate the individual channels between the terminals and the relay from the equivalent channels. CS theory is then applied to the time-domain channel estimation with much smaller number of pilot symbols. This scheme enables accurate channel estimation for TWRN with significant overhead reduction. Extensive numerical results are provided to substantiate the effectiveness of the proposed method.

关键词： Compressed sensing (CS) linear precoding sparse channel estimation two-way relay networks (TWRN)

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Statistical Eigenmode-Based SDMA for Two-User Downlink

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2012年第10期60卷 5371-5383页

作者： Wang, Jue Jin, Shi Gao, Xiqi Wong, Kai-Kit Au, Edward Southeast Univ Natl Mobile Commun Res Lab Nanjing 210096 Jiangsu Peoples R China UCL Dept Elect & Elect Engn London WC1E 7JE England Huawei Technol Shenzhen Peoples R China

This paper proposes a statistical-eigenmode space-division multiple-access (SE-SDMA) transmission approach for a two-user downlink system where two transmit antennas are deployed at the base station and each mobile user has only one receive antenna, assuming that only statistical channel state information (SCSI) is available at the transmitter. By maximizing a lower bound of the ergodic signal-to-leakage-and-noise ratio (SLNR), the proposed SE-SDMA approach selects two users with orthogonal principal statistical eigen-directions and then transmits to each user along the corresponding eigenmode. For this approach, we derive an exact expression of the achievable ergodic rate, and compare it with the zero-forcing beamforming (ZFBF) system exploiting instantaneous CSI. We show that SE-SDMA can achieve the maximum ergodic sum-rate of the two selected users, and provide significant user selection gains. For comparison with ZFBF, we show that the rate gap between SE-SDMA and ZFBF with perfect CSI at the transmitter (CSIT) tends to zero in highly correlated channels. Further, when ZFBF is implemented with inaccurate CSIT, the operating regions of SE-SDMA and ZFBF are investigated for different ranges of signal-to-noise ratio (SNR), instantaneous CSIT accuracy levels, and spatial correlation levels. Numerical results confirm the analytically derived conclusions, and physical insights are provided.

关键词： Broadcast channel correlation linear precoding rate space-division multiple-access (SDMA)

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Asymmetric Cooperation among Wireless Relays with linear precoding

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2008年第12期7卷 5420-5430页

作者： Devroye, Natasha Mehta, Neelesh B. Molisch, Andreas F. Univ Illinois Dept Elect & Comp Engn Chicago IL 60680 USA Indian Inst Sci Dept Elect Commun Engn Bangalore 560012 Karnataka India MERL Cambridge England Lund Univ Dept Electrosci S-22100 Lund Sweden

Wireless relays extend coverage, improve spectral efficiency, and enhance reliability and rates of wireless cellular communication systems. In this work, we introduce the fundamental notion of asymmetric cooperation among cooperating relays in cellular downlinks - different relays are party to different but overlapping knowledge about the messages transmitted from the base station. We argue that asymmetric cooperation arises naturally in most two-phase protocols In which the base station first transmits information to multiple relays that then cooperatively forward the information to the recipient mobile stations in the cell. For a system in which two relays are of the decode-and-forward type and cooperate using linear precoding to communicate with two mobile stations, we formulate the general, but complicated, throughput optimization problem and derive several results that considerably simplify the optimization. We show that under different channel configurations and fairness criteria, asymmetric cooperation is often the throughput-maximizing option. Under typical configurations, a 20-30% throughput enhancement is achieved compared to conventional full-cooperation systems.

关键词： Relays fading channels cooperation linear precoding asymmetry SDMA MIMO

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An Iterative Precoder Design for Successive Zero-Forcing Precoded Systems

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IEEE COMMUNICATIONS LETTERS 2012年第1期16卷 16-18页

作者： Le-Nam Tran KTH Royal Inst Technol Signal Proc Lab ACCESS Linnaeus Ctr SE-10044 Stockholm Sweden

Successive zero-forcing (SZF) is a precoding technique for broadcast channels that partially precancels the multiuser interference. Due to the residual interference, the optimal precoder design for SZF is difficult to find, and currently unknown. This letter proposes a suboptimal iterative precoder design for the sum rate maximization problem for SZF, using a local optimization method. In each iteration, the precoders are updated to maximize a first-order approximation of the sum rate, which can be easily solved since the approximation is concave with the precoders. By initializing the precoders with zero matrices, we analytically prove that the iterative design can achieve a larger sum rate than the block diagonalization (BD) approach. Moreover, numerical results demonstrate the superior sum-rate performance of the proposed design over the existing scheme, which is based on a heuristic method.

关键词： MIMO downlink channel linear precoding

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An Efficient Method for MSE Transceiver Design With Imperfect CSIat Both Ends of a MIMO Link

An Efficient Method for MSE Transceiver Design With Imperfec...

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International Conference on Communication Technology and System Design

作者： Sudhir, A. Ch. Rajasekhar, Ch. PrabhakaraRao, B. Krishnachaitanaya, M. Saimdhuri, P. JignashReddy, K. GITAM Univ GIT Dept ECE Visakhapatnam Andhra Pradesh India JNTU Univ Dept ECE Kakinada Andhra Pradesh India

Multiple transmit and receive antennas can be used to form multiple-input multiple-output (MIMO) channels to increase the capacity by a factor of the minimum number of transmit and receive antennas. In this paper, we propose a novel joint linear transceiver design for single-user multiple-input, multiple-output (SU-MIMO) systems employing improper signal constellations. In particular, improved minimum mean square error (MMSE) transceiver is designed based on modified cost functions, with channel mean as well as both transmit and receive correlation information at both ends. The joint design is formulated into an optimization problem. The optimum closed-form precoder and decoder are derived. Compared to the case with perfect channel state information (CSI), linear filters are added at both ends to balance the suppression of channel noise and the noise from imperfect channel estimation. The superiority of the proposed joint linear transceiver design over the conventional solutions is verified by simulation results. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICCTSD 2011

关键词： Channel state information (CSI) mean-square error (MSE multiple-input multiple-output (MIMO) linear precoding spatial multiplexing

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Joint precoding and Decoding in MU-MIMO Downlink Systems with Perfect Channel State Information (CSI)

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Procedia Technology 2012年 6卷 708-715页

作者： M.Raja P. Muthuchidambaranathan Department of Electronics and Communication Engineering National Institute of Technology Tiruchirappalli India

In this paper, we propose an joint optimization of precoder and decoder for downlink transmissions in multiuser multiple-input, multiple-output (MU-MIMO) systems with perfect channel state information (CSI). This paper focuses on the scenario when an improper constellation such as binary phase shift-keying (BPSK) or M -ary amplitude shift-keying ( M -ASK) is employed. The proposed joint design aims to minimize all the users total mean-squared-error (TMSE) under the constraint of total transmit power. Simulation results show that the proposed joint linear precoder and decoder designs improves BER performance of MU-MIMO downlink systems and verify its effectiveness.

关键词： Multiple-input multiple-output (MIMO) Total mean square error (TMSE) Channel state information (CSI) linear precoding Diversity Improper modulations

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Optimal multi-user MIMO linear precoding based on particle swarm optimization

Optimal multi-user MIMO linear precoding based on particle s...

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IEEE International Conference on Communications (ICC 2008)

作者： Shu, Fang Li Lihua Ping, Zhang Beijing Univ Posts & Telecommun Key Lab Universal Wireless Commun Minist Educ Beijing 100876 Peoples R China

ISBN: (纸本)9781424420742

An optimal multi-user MIMO linear precoding scheme based on particle swarm optimization is proposed in this paper. The proposed scheme aims to maximize the system capacity of multi-user MIMO system. This paper explores a simplified function to measure the optimal problem. With the adoption of particle swarm optimization algorithm, the optimal linear precoding vector could he easily searched according to the simplified function. The proposed scheme outperforms the multi-user MIMO linear precoding schemes based on channel inversion and channel block digonolization methods.

关键词： multi-user MIMO particle swarm optimization linear precoding

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