Hệ thống 3G và mạng không dây thông minh P3

Adaptive beamforming wasinitially developed in the 1960s for the military applications of sonar andradar, in order to remove unwanted noise and jamming from output. The related the literature of the past 40 years is extremely rich [201-2371 and since this book is mainly concerned with the networking aspects of wireless systems, rather than with specific antenna array designs, here we will restrict our discussionson the topic to a rudimentaryoverview.
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Hệ thống 3G và mạng không dây thông minh P3 Third-Generation Systems and Intelligent Wireless Networking J.S. Blogh, L. Hanzo Copyright © 2002 John Wiley & Sons Ltd ISBNs: 0-470-84519-8 (Hardback); 0-470-84781-6 (Electronic)Intelligent Antenna Arrays andBeamforming3.1 IntroductionAdaptive beamforming wasinitially developed in the 1960s for the military applications ofsonar andradar, in order to remove unwanted noise and jamming from output. The related theliterature of the past 40 years is extremely rich [201-2371 and since this book is mainlyconcerned with the networking aspects of wireless systems, rather than with specific antennaarray designs, here we will restrict our discussionson the topic to a rudimentaryoverview. The first fully adaptive array was conceived in 1965 by Applebaum [238], which wasdesigned to maximise the Signal-to-Noise Ratio (SNR)at the array’s output. An alternativeapproach to cancelling unwanted interference is the Least Mean Squares (LMS) error algo-rithm of Widrow [239]. While a simple idea, satisfactory performance can be achieved underspecific conditions. Further work onthe LMS algorithm, by Frost [240] and Griffiths [241J,introduced constraints to ensure that the desired signals were not filtered out along with theunwanted signals. The optimisation process takes place as before, but the antenna gain ismaintained constant in the desired direction. For stationary signals, both algorithms con-verge to the optimum Wiener solution [3,240,242]. A different technique was proposedin 1969 by Capon [243] using a Minimum-Variance Distortionless Response (MVDR) orthe Maximum Likelihood Method (MLM).In 1974, Reed et d . demonstrated the power ofthe Sample-Matrix Inversion (SMI) technique, which determines the adaptive antennaarrayweights directly [244]. Unlikethe algorithms of Applebaum [238]and Widrow [239], whichmay suffer from slow convergence if the eigenvalue spread the received sample of correlationmatrix is relatively large, the performance of the SMI technique is virtually independent ofthe eigenvalue spread. In recent years the tight frequency reuse of cellular systems has stimulated renewed re-search interests in the field [3,6,242,245]. In this book we will attempt to review the recentliterature and highlight the most important research issues for UMTS, HiperLAN and WATMapplications, while providing some performance results. We commence in Section 3.2 by 123124 CHAPTER 3. INTELLIGENT AND ANTENNA ARRAYS BEAMFORMINGreviewing beamformingand its potential benefits, then we provide a genericsignal model inSection 3.2.3 and we describe the processes of element and beam space beamforming. InSection 3.3 we highlight a range of adaptive beamforming algorithmsand consider the lesscommonly examined downlink scenario Section 3.3.5. Lastly in Section 3.3.6 we provide insome performanceresults and outline our future work.3 2 Beamforming .The signals induced in different elements of an antenna array are combined to form a sin-gle output of the array. This process of combining the signals from the different elements isknown as beamforming. Thissection describes the basic characteristics of an antenna, the ad-vantages of using beamforming techniques a mobile in radio environment [3,6], and a genericsignal model foruse inbeamforming calculations. For further details on the associated issuesthe reader isreferred to [3,6,8,238-242,244-2501.3.2.1 AntennaArrayParametersBelow we provide a few definitions used throughout this report in order to describe antennasystems: Radiation Pattern The radiation pattern of an antenna is the relative distribution of theradiated power as a function of direction in space. The radiation pattern of an antenna arrayis the product of the element pattern and the array factor, both of which are defined below. Iff ( O , $ ) is the radiation pattern of each antenna element andF(O,$) is the array factor, thenthe arrays radiation pattern, G(8, d), which is also referred to as the beam pattern, is givenby G(O,$) = f(8,$ ) F ( @4). , (3.1) Figure 3.1 gives an example of a stylised antenna e ...