Celal Alp Tunc

Examination of existent propagation models over large inhomogeneous terrain profiles using fast integral equation solution

The accuracy of most widely used empirical models are investigated using the spectrally accelerated forward-backward (FBSA) method as a benchmark solution. First, FBSA results are obtained for propagation over large scale terrain profiles and compared with measurements to assess the accuracy of FBSA. Then, accuracy of some International Telecommunication Union (ITU) and Federal Communications Commission (FCC) propagation models are investigated. It has been observed that, for rural areas, the prediction of the most recent ITU recommended propagation model (Rec. 1546) deviates much more than older models do.

Characteristic Basis Function Method for Solving Electromagnetic Scattering Problems Over Rough Terrain Profiles

A computationally efficient algorithm, which combines the characteristic basis function method (CBFM), the physical optics (PO) approach (when applicable) with the forward backward method (FBM), is applied for the investigation of electromagnetic scattering from-and propagation over-large-scale rough terrain problems. The algorithm utilizes high-level basis functions defined on macro-domains (blocks), called the characteristic basis functions (CBFs) that are constructed by aggregating low-level basis functions (i.e., conventional sub-domain basis functions). The FBM as well as the PO approach (when applicable) are used to construct the aforementioned CBFs. The conventional CBFM is slightly modified to handle large-terrain problems, and is further embellished by accelerating it, as well as reducing its storage requirements, via the use of an extrapolation procedure. Numerical results for the total fields, as well as for the path loss are presented and compared with either measured or previously published reference solutions to assess the efficiency and accuracy of the algorithm.

Capacity of printed dipole arrays in the MIMO channel

The performance of printed dipole arrays in the MIMO channel is investigated using a channel model based on the Method of Moments solution of the electric-field integral equation. Comparisons with freestanding dipoles are given in terms of channel capacity. Effects of the electrical properties (such as the dielectric thickness and permittivity) on the MIMO capacity are explored. Various dielectric-substrate configurations yielding high-capacity MIMO arrays are presented.

On the Capacity of Printed Planar Rectangular Patch Antenna Arrays in the MIMO Channel: Analysis and Measurements [Wireless Corner]

Printed arrays of rectangular patch antennas are analyzed in terms of their MIMO performance using a full-wave channel model. These antennas are designed and manufactured in various array configurations, and their MIMO performance is measured in an indoor environment. Good agreement is achieved between the measurements and simulations performed using the full-wave channel model. Effects on the MIMO capacity of the mutual coupling and the electrical properties of the printed patches, such as the relative permittivity and thickness of the dielectric material, are explored.

Investigation of planar and conformal printed arrays for MIMO performance analysis

MIMO channel capacity of printed arrays with dipole elements is analyzed. A MIMO channel model based on electric fields is used. The effects of mutual interactions among the array elements through space and surface waves are included into the channel matrix using a full-wave hybrid Method of Moments (MoM)/Greens function technique in the spatial domain. MIMO capacity of printed arrays is then compared with that of free standing thin wire dipole arrays. Results show better performance of printed arrays.

On the Number of Clusters in Channel Model

Typically, scatterers in an environment are not distributed uniformly but rather observed to occur in clusters. Identification of clusters is an issue under discussion. To this end, we study the effect of number of clusters on channel model through computer simulations. We focus on a geometric stochastic directional channel model based on COST259. Fixing a scatterer scenario, we calculate root mean square delay and angular spreads when scatterers are grouped into varying numbers of clusters and study how sensitive these parameters are to the number of clusters used in this channel model

Fast integral equation techniques for propagation problems

In this paper, the Method of Moments (MOM) solution is achieved for scattering problems by using the stationary Spectrally Accelerated Forward-Backward method (FBSA) and the non-stationary Spectrally Accelerated BiConjugate Gradient Stabilized (SA-BiCGSTAB) method, with a storage requirement and a computational cost of O(N) per iteration where N is the number of surface unknowns in the discretized integral equation. The SA-BiCGSTAB method is applied over rough terrain profdes as well as reentrant surfaces which can not be handled by any conventional stationary iterative technique.

Propagation and coverage analysis over terrain profiles comparing empirical approaches with numerically exact solutions

Mobile radio planning requires the accurate prediction of electromagnetic field strengths over large areas and in a wide variety of environments. This present approaches to predicting field patterns present a similar behavior about the main trend in field attenuation. However, they do not give numerically or analytically exact results. The spectral acceleration forward-backward (FB/SA) is an integral equation based numerical method that obtains the exact scattering data over very undulating terrain profiles with a computational cost of O(N). In this paper, the propagation and coverage analysis problem over different terrain profiles is explored using the FB/SA. In addition, the exact solution is compared with some popular propagation models.

A model with electric fields for the inclusion of mutual coupling effects in the MIMO channel

Multiple input multiple output (MIMO) wireless communication systems have been a focus of interest, due to their ability to increase the capacity in rich scattering environments by using multi-element antenna arrays both at the transmitter and the receiver sides. However, when dealing with multi-element antenna arrays, effects of mutual coupling among the array elements become significant and should be included in the channel matrix properly. These effects were included in the MIMO channel matrix mainly for free standing linear arrays (FSLA) of uniform thin-wire dipole antennas using coupling matrices obtained from the mutual interaction matrix and terminations. These matrices reduce to the identity matrix when the interactions are ignored, because of the scaling factors related with termination impedances. Therefore, in this paper we propose a partially stochastic full-wave electromagnetic model with electric fields (MEF), to evaluate the MIMO channel matrix accurately with and/or without including effects of mutual coupling. Effects of mutual interactions among the array elements through space and surface waves (when printed arrays are considered) are included in the channel matrix using a full-wave hybrid method of moments (MoM)/Greens function technique. The stochastic part of the model comes from a local cluster of uniformly distributed scatterers. Consequently, the proposed method is exact except the scatterer scenario, thus, besides achieving the accuracy to be used as a benchmark solution for other approaches, comparisons can be made among any kind of arrays.