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R.B. Ertel

Bio: R.B. Ertel is an academic researcher from University of Virginia. The author has contributed to research in topics: Smart antenna & Communication channel. The author has an hindex of 3, co-authored 4 publications receiving 1223 citations.

Papers
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Journal ArticleDOI
TL;DR: This tutorial reviews the key concepts in spatial channel modeling and presents emerging approaches, and reviews the research issues in developing and using spatial channel models for adaptive antennas.
Abstract: Spatial antenna diversity has been important in improving the radio link between wireless users. Historically, microscopic antenna diversity has been used to reduce the fading seen by a radio receiver, whereas macroscopic diversity provides multiple listening posts to ensure that mobile communication links remain intact over a wide geographic area. In later years, the concepts of spatial diversity have been expanded to build foundations for emerging technologies, such as smart (adaptive) antennas and position location systems. Smart antennas hold great promise for increasing the capacity of wireless communications because they radiate and receive energy only in the intended directions, thereby greatly reducing interference. To properly design, analyze, and implement smart antennas and to exploit spatial processing in emerging wireless systems, accurate radio channel models that incorporate spatial characteristics are necessary. In this tutorial, we review the key concepts in spatial channel modeling and present emerging approaches. We also review the research issues in developing and using spatial channel models for adaptive antennas.

917 citations

Journal ArticleDOI
TL;DR: The joint TOA/AOA, the marginal TOA, and the marginal AOA probability density functions (PDFs) are derived for the elliptical and circular scattering models to provide insight into the properties of the spatial wireless channel.
Abstract: With the introduction of antenna array systems into wireless communication networks comes the need to better understand the spatial characteristics of the channel. Scattering models provide both angle of arrival (AOA) and time of arrival (TOA) statistics of the channel. A number of different scattering models have been proposed in the literature including elliptical and circular models. These models assume that scatterers lie within an elliptical and circular region in space, respectively. In this paper, the joint TOA/AOA, the marginal TOA, and the marginal AOA probability density functions (PDFs) are derived for the elliptical and circular scattering models. These PDFs provide insight into the properties of the spatial wireless channel.

313 citations

Proceedings ArticleDOI
16 May 1999
TL;DR: A simple procedure for estimating and then compensating for the non-ideal phase shifts in the splitter using complex baseband measurements at the array output is described.
Abstract: Most direction finding algorithms require knowledge of the array manifold. The array manifold may be estimated using expensive and time consuming array calibration procedures. An alternative is to bore-sight the array and then assume that the array manifold is ideal. Bore-sighting is often achieved by injecting a common signal into the RF front-end using a signal generator followed by a signal splitter. Unknown phase shifts through the splitter will cause errors in the bore-sighting process. In this paper we describe a simple procedure for estimating and then compensating for the non-ideal phase shifts in the splitter using complex baseband measurements at the array output.

27 citations

Proceedings ArticleDOI
08 Sep 2003
TL;DR: Wideband characterization for indoor and outdoor-to-indoor channels and wideband vector channel measurements for an indoor environment shows that the coherent bandwidth of about 10 MHz associated with indoor channel can accommodate diversity operations for wideband CDMA (W-CDMA) system.
Abstract: Coherence bandwidth is an important propagation parameter that has direct impact on the design and performance of a wireless communications link contemplating performance enhancement features like smart antenna applications. This paper presents wideband characterization for indoor and outdoor-to-indoor channels and wideband vector channel measurements for an indoor environment. The results show that the coherent bandwidth of about 10 MHz associated with indoor channel can accommodate diversity operations for wideband CDMA (W-CDMA) system. In addition, a study of the envelope cross-correlation points to the feasibility of a smart antenna system. For outdoor-to-indoor channel, the coherence bandwidth indicated that some additional temporal processing would be necessary for a W-CDMA system. Existing narrowband systems, however, would suffice to use simple diversity techniques in such a channel.

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Book
01 Jan 2005

9,038 citations

Journal ArticleDOI
TL;DR: It is shown that the fading correlation affects the MEA capacity by modifying the distributions of the gains of these subchannels, which depends on the physical parameters of MEA and the scatterer characteristics.
Abstract: We investigate the effects of fading correlations in multielement antenna (MEA) communication systems. Pioneering studies showed that if the fades connecting pairs of transmit and receive antenna elements are independently, identically distributed, MEAs offer a large increase in capacity compared to single-antenna systems. An MEA system can be described in terms of spatial eigenmodes, which are single-input single-output subchannels. The channel capacity of an MEA is the sum of capacities of these subchannels. We show that the fading correlation affects the MEA capacity by modifying the distributions of the gains of these subchannels. The fading correlation depends on the physical parameters of MEA and the scatterer characteristics. In this paper, to characterize the fading correlation, we employ an abstract model, which is appropriate for modeling narrow-band Rayleigh fading in fixed wireless systems.

2,598 citations

Journal ArticleDOI
TL;DR: While the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice), and I believe that the Handbook can be useful in those laboratories.
Abstract: There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

2,493 citations

Dissertation
24 Apr 2002
TL;DR: Results show that remarkable energy and spectral efficiencies are achievable by combining concepts drawn from space-time coding, multiuser detection, array processing and iterative decoding.
Abstract: Space-time codes (STC) are a class of signaling techniques, offering coding and diversity gains along with improved spectral efficiency. These codes exploit both the spatial and the temporal diversity of the wireless link by combining the design of the error correction code, modulation scheme and array processing. STC are well suited for improving the downlink performance, which is the bottleneck in asymmetric applications such as downstream Internet. Three original contributions to the area of STC are presented in this dissertation. First, the development of analytic tools that determine the fundamental limits on the performance of STC in a variety of channel conditions. For trellis-type STC, transfer function based techniques are applied to derive performance bounds over Rayleigh, Rician and correlated fading environments. For block-type STC, an analytic framework that supports various complex orthogonal designs with arbitrary signal cardinalities and array configurations is developed. In the second part of the dissertation, the Virginia Tech Space-Time Advanced Radio (VT-STAR) is designed, introducing a multi-antenna hardware laboratory test bed, which facilitates characterization of the multiple-input multiple-output (MIMO) channel and validation of various space-time approaches. In the third part of the dissertation, two novel space-time architectures paired with iterative processing principles are proposed. The first scheme extends the suitability of STC to outdoor wireless communications by employing iterative equalization/decoding for time dispersive channels and the second scheme employs iterative interference cancellation/decoding to solve the error propagation problem of Bell-Labs Layered Space-Time Architecture (BLAST). Results show that remarkable energy and spectral efficiencies are achievable by combining concepts drawn from space-time coding, multiuser detection, array processing and iterative decoding.

2,286 citations

Journal ArticleDOI
TL;DR: A simple stochastic MIMO model channel has been developed that uses the correlation matrices at the mobile station (MS) and base station (BS) so that results of the numerous single-input/multiple-output studies that have been published in the literature can be used as input parameters.
Abstract: Theoretical and experimental studies of multiple-input/multiple-output (MIMO) radio channels are presented. A simple stochastic MIMO model channel has been developed. This model uses the correlation matrices at the mobile station (MS) and base station (BS) so that results of the numerous single-input/multiple-output studies that have been published in the literature can be used as input parameters. The model is simplified to the narrowband channels. The validation of the model is based upon data collected in both picocell and microcell environments. The stochastic model has also been used to investigate the capacity of MIMO radio channels, considering two different power allocation strategies, water filling and uniform and two different antenna topologies, 4/spl times/4 and 2/spl times/4. Space diversity used at both ends of the MIMO radio link is shown to be an efficient technique in picocell environments, achieving capacities within 14 b/s/Hz and 16 b/s/Hz in 80% of the cases for a 4/spl times/4 antenna configuration implementing water filling at a SNR of 20 dB.

1,493 citations