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.

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A stochastic MIMO radio channel model with experimental validation

The demand for wireless mobile communications services is growing at an explosive rate, with the anticipation that communication to a mobile device anywhere on the globe at all times will be available in the near future. An array of antennas mounted on vehicles, ships, aircraft, satellites, and base stations is expected to play an important role in fulfilling the increased demand of channel requirement for these services, as well as for the realization of the dream that a portable communications device the size of a wristwatch be available at an affordable cost for such services. This paper is the first of a two-part study. It provides a comprehensive treatment, at a level appropriate to nonspecialists, of the use of an antenna array to enhance the efficiency of mobile communications systems. It presents an overview of mobile communications as well as details of how an array may be used in various mobile communications systems, including land-mobile, indoor-radio, and satellite-based systems. It discusses advantages of an array of antennas in a mobile communications system, highlights improvements that are possible by using multiple antennas compared to a single antenna in a system, and provides details on the feasibility of antenna arrays for mobile communications applications.

/pdf/applications-of-antenna-arrays-to-mobile-communications-i-4vrvp7rdiu.pdf

Applications of antenna arrays to mobile communications. I. Performance improvement, feasibility, and system considerations

Multiple-input-multiple-output (MIMO) wireless systems use multiple antenna elements at transmit and receive to offer improved capacity over single antenna topologies in multipath channels In such systems, the antenna properties as well as the multipath channel characteristics play a key role in determining communication performance This paper reviews recent research findings concerning antennas and propagation in MIMO systems Issues considered include channel capacity computation, channel measurement and modeling approaches, and the impact of antenna element properties and array configuration on system performance Throughout the discussion, outstanding research questions in these areas are highlighted

/pdf/a-review-of-antennas-and-propagation-for-mimo-wireless-1xbqo9fzkp.pdf

A review of antennas and propagation for MIMO wireless communications

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.

/pdf/overview-of-spatial-channel-models-for-antenna-array-3ucqde59u0.pdf

Overview of spatial channel models for antenna array communication systems

A simple statistical model of azimuthal and temporal dispersion in mobile radio channels is proposed. The model includes the probability density function (PDF) of the delay and azimuth of the impinging waves as well as their expected power conditioned on the delay and azimuth. The statistical properties are extracted from macrocellular measurements conducted in a variety of urban environments. It is found that in typical urban environments the power azimuth spectrum (PAS) is accurately described by a Laplacian function, while a Gaussian PDF matches the azimuth PDF. Moreover, the power delay spectrum (PDS) and the delay PDF are accurately modeled by an exponential decaying function. In bad urban environments, channel dispersion is better characterized by a multicluster model, where the PAS and PDS are modeled as a sum of Laplacian functions and exponential decaying functions, respectively.

http://www2.elo.utfsm.cl/~ipd465/Papers%20y%20apuntes%20varios/A%20Stochastic%20Model,%20Ped%20Mog%20Fleury.pdf

A stochastic model of the temporal and azimuthal dispersion seen at the base station in outdoor propagation environments

A wide-band spatial model of the mobile channel has been developed. The model allows the inclusion of array antennas at the base station. The diffuse scattering is modeled using dense discrete scatterers. An algebraic power decay is used for the path loss to the scatterers of the environment and to the mobile. Results from the model are compared with experimental results obtained at 1800 MHz. The parameters that are used are delay spread, power window, and angular spread of incident power. The model elucidates the general diffuse background scattering in a rural and an urban environment. It can be extended with inclusion of spatial specular scatterers where appropriate.

Diffuse channel model and experimental results for array antennas in mobile environments

The paper deals with the problems of how different mobile propagation scenarios influence the signals received at an antenna array. The analysis of the propagation environment is based on computer simulations. Linear arrays with 1-19 elements have been simulated in a 20/spl deg/ and a 45/spl deg/ environment. A new angle diversity technique, jitter diversity, is suggested with a simple algorithm giving substantial improvement in the average gain and statistical distribution.

Mobile radio environments and adaptive arrays

The lack of capacity in mobile communication systems is an increasing problem. A channel model for the use of antenna arrays at the base station is presented. A new diversity scheme, jitter diversity, is suggested with a simple algorithm. The technique is to use an antenna array and move the main beam slightly to avoid deep fades, giving substantial improvement in the fading distribution and the mean power. Linear antenna arrays with 1-19 elements are applied to propagation environments with different scatterer spread. The influence of the environments on the received antenna pattern, such as the effective gain, is investigated. Experiments support the main findings, namely that the environments reduce the directivity of the perceived antenna diagram by several dB. Jitter diversity is a very simple approach, compared to other combining methods, as it only includes the variation of a single parameter, the phase between elements. It should therefore be simple to implement in practice.

http://ieeexplore.ieee.org/iel3/3758/10964/00504989.pdf

Jitter diversity in multipath environments

The influence of the angular dimension in mobile communications is reviewed for outdoor channels. The importance of angular spreading of the environment is stressed as it has an impact on the channel modelling for adaptive arrays. Definitions are introduced, and it is shown how the channel statistics such as delay spread and the correlation between the antenna elements are effected. Experimental results are given for highly directive antennas, and the influence on cellular capacity through reduction of interference is discussed.

http://ieeexplore.ieee.org/iel3/4268/12241/00563746.pdf

The angular aspect of wideband modelling and measurements

Optimum diversity combining in a wireless communications system using TDMA/TDD is considered. By the use of optimum diversity combining a receiving antenna array is able to suppress interference and thus the capacity of the system is increased. The results in this paper are obtained by simulations. In the simulations a DECT-like system is used as the TDMA/TDD system. The results show that in the uplink direction M-1 interferers can be suppressed by an M element array. However the downlink transmit diversity performance is much worse, due to the changes in the radio channel during the dwell time between the uplink and downlink burst. That is the reason why it is concluded that optimum diversity combining is only useful for a TDD system with a short dwell time.

O. Norklit

Papers

Diffuse channel model and experimental results for array antennas in mobile environments

Mobile radio environments and adaptive arrays

Jitter diversity in multipath environments

The angular aspect of wideband modelling and measurements

Evaluation of optimum diversity combining in DECT