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The fabrication and measurement of previously proposed artificial magnetic conductor (AMC) designs are presented in this paper. The AMC ground planes were synthesized by a hybrid genetic program (HGP) and were compared with AMC designs found in the literature. The HGP designed AMCs outperformed those in the literature. The performance was determined from full-wave electromagnetic simulations. We also validate the performance of the HGP designed AMCs through fabrication and measurement.

Radio propagation modeling and prediction play an important role in the understanding of electromagnetic (EM) wave propagation in complex environments, as well as in the design of wireless communications and radar systems.

As terrestrial wireless communication systems become more ubiquitous, there is a rising need to study the propagation characteristics of every habitable environment so that effective communication systems can be established. Past research showed that open-trench drains, whose presence is prevailing in many Asian cities, make up an additional channel in which radio signal can adequately travel. In this letter, we have further our studies in the propagation characteristics of an open-trench drain to delve into areas that have not been previously reported. Specifically, we present field measurement results of an open-trench drain for line-of-sight (LoS) and non-line-of-sight (NLoS) portions at three frequencies (900 MHz, 2.4 and 5.8 GHz) for three different polarizations, namely, vertical-vertical (VV), horizontal-horizontal (HH), and horizontal-vertical (HV) polarizations. Subsequently, we have adopted K-means clustering approach to process the obtained data in deriving path loss exponent $n$ and their associated standard deviation. Comparison is made of the $n$ values, as well as the standard deviation values, before and after employing K-means clustering.

A fundamental approach in the optimal design of wireless communication systems is a proper comprehension of radio wave propagation through wireless channels. As wireless communications become more ubiquitous, new propagation environments emerge and the propagation mechanisms therein are being constantly investigated. The objectives of this chapter are twofold: firstly, to give a succinct review of new and emerging complex environments that require fine-tuning of the propagation models since traditional propagation models that simplify the propagation environment by ignoring the small and fine structures are no longer valid for such complex environments and, secondly, to recount the fundamental concepts of radio propagation modeling and its significance, as well as the basic propagation mechanisms and ray-tracing image method. These fundamental working principles of ray-tracing image method can be utilized both for indoor and outdoor environments because these two settings are governed in essence by the same propagation mechanisms.

Advanced Nodes are the main components of Physical Layer based fully-directional networks. They consist of sets of appropriately programmed antenna arrays that enable them to conform to the standards of the radio being used. This paper provides an in-depth comparison of advanced nodes implementations for the two main choices of radios: 3GPP's Long Term Evolution (LTE) and IEEE 802.11 (WiFi). Component-by-component comparison is carried out, investigating several implementation aspects as well as estimated performance (in terms of standard performance metrics such as bit error rate, data rate, capacity, coverage radius) for the two radios. Based on the comparison, the associated implementation trade-offs are analyzed which help in choosing between the two radios.

In this paper, the performance of an existing Multiuser Wireless Communication System is analyzed using accurate site specific propagation modelling data (such as path gain, angle of arrival/departure and delay spread) of a typical urban environment. For optimal utilization of realistic temporal, spectral and spatial data, obtained from the available ray-tracing tools, a novel multiple detail-level adaptive cognitive communication system is proposed. Desirable system performance in terms of bit-error rate and capacity is shown to be achievable using only AoA and path gain information of as little as 5 paths in generating the channel matrix. As a result, significant savings (85%) in computational cost are achieved, thus emphasizing the potential practical implementation of the proposed approach in cognitive communication applications.

In this paper, a low complexity hybrid smart antenna system with directional elements and reduced-size digital beamformer is proposed to combat the inter-symbol interference (ISI) problem over frequency-selective fading channels. The conventional smart antenna systems with omni-directional elements utilize the full-size digital beamformer to suppress interference and obtain the optimum performance. However, the proposed hybrid smart antenna system with directional elements can split the linear receive array into two subarrays. One subarray contains the elements with no ISI, which can be processed with a simple maximum ratio combiner (MRC). The second subarray includes the elements with the ISI interference, which require the use of a reduced-size optimum beamformer for interference suppression. Finally, the outputs of the two subarrays are combined for optimal detection of the transmitted signals. Simulation results confirm that the proposed low complexity hybrid smart antenna system can provide robust performance under the multipath fading channel with ISI, and outperform the conventional smart antenna systems due to the use of directional antennas and utilization of multipath diversity gain.

This letter presents a method for determining the required number and locations of transmit antennas to optimize wireless propagation coverage in a given indoor environment. The ray-tracing method is employed to calculate the field distribution due to one or more transmitting antennas and the genetic algorithm (GA) is used to determine the required number and the locations of these antennas to achieve optimized wireless coverage in a given area. In the ray-tracing method, detailed parameters such as thickness, dielectric constant, and the conductivity of individual walls are assigned for realistic field calculations. Obtained simulation results illustrate the feasibility of using the integrated ray-tracing/GA method in determining the optimized coverage of a wireless network.

Phased array antennas have and will continue to be a critically important component in the development of future wireless systems with applications in communications, radar, and satellite technologies. In spite of the significant advances in the design of modern phased array antennas, there continue to be significant and growing need for developing high performance systems that are also low cost and with beam steering capabilities. In this paper we describe some of the antenna array designs that focus on achieving this goal. We will start with one approach that is based on an analog phase-shifting approach and involves an integrated use of ferroelectric materials and the Continuous Transverse Stub (CTS) antenna array technologies. A complementary design which is based on digital beamforming and the utilization of the Hybrid Smart Antenna technique recently developed by our group will then be described. This will be followed with comments regarding the trade-off between the analog and digital phase shifting techniques. We will conclude the chapter with a description of a novel ultra-wideband and low profile ground plane which is based on a hybrid ferrite and Electromagnetic Band Gap (EBG) materials design. In all cases simulation results and experimental validation, whenever available, will be presented and aspects of the required future work to fully enable these technologies will be discussed.

Propagation-prediction and site-planning software for wireless communication networks has been developed. The software has a user-friendly graphical user interface (GUI), and provides calculations for large-scale and small-scale propagation parameters, including path loss (or received power) and delay profiles. Angles of arrival/departure, which are useful for the design of wireless systems employing multiple antennas, are also provided in the simulation. Some of the main features of the software include the use of a computationally efficient ray-tracing approach for simulating propagation in wireless environments, and the fact that users can upload AutoCAD .dxf files for indoor or outdoor environments. Both a single-building floor plan or an entire city layout can be simulated, and the user is provided with the ability to assign wall geometries and electrical parameters. User-defined realistic antenna radiation patterns for both the transmitting and receiving antennas are incorporated in the simulation. Broadband as well as polarization-dependent simulations are also included in the software.

A comprehensive review of the propagation prediction models for terrestrial wireless communication systems is presented in this paper. The classic empirical models are briefly described and the focus is placed on the application of ray-tracing techniques to the development of deterministic propagation models. Schemes to increase the computational efficiency and accuracy are discussed. Traditional statistical models are also briefly reviewed for completeness. New challenges to the propagation prediction are described and some new approaches for meeting these challenges are presented.

As wireless communication becomes more ubiquitous, there is a steadfast growing need to accumulate the propagation knowledge in small radio cells because they can increase the capacity of radio networks and overcome radio spectrum crowding. For these small radio cells that are intended to cover mainly indoor or very small outdoor areas their base station antennas are usually mounted inside a building or below rooftop level in an outdoor environment. In such scenarios when the lower base-station antennas are used, various objects that exist in that particular environment may affect radio propagation significantly so their effects should be studied.

The finite-difference time-domain (FDTD) technique has become increasingly popular and is being used to model extremely complex and electrically large structures. These simulations are computationally demanding and often exceed available limits on computer resources. In this paper, we present an FDTD sub-gridding technique that allows for increased resolution in regions of interest without increasing the overall computational requirements beyond the available resources. Furthermore, the formulation presented here allows for traversing dielectric boundaries using any integer refinement factor and the maximum Courant number. By allowing the coarse-/fine-grid boundary to traverse dielectric boundaries, numerical simulations that were previously either extremely difficult or impossible to perform are now possible. The technique presented here uses a weighted current value from the coarse region at the boundary between the fine- and coarse-grid regions to update the fine-region tangential fields on that boundary. The weighting function depends on the material properties and the relative position of the fine-region electric field within the current contour at the boundary. The complete formulation of this new technique is described and some results of simulation cases are presented to validate the accuracy and stability of the newly developed FDTD code. Simulations include simple cases where the analytical solution exists and more complex cases, which were impossible to model using a uniform-grid FDTD code. In some simulation examples, computer memory savings as high as 70 times what would have been necessary with a uniform-grid code were achieved. It is shown that errors of less than 2% are achievable with ratios of coarse-to-fine grid sizes exceeding ten. The new technique is expected to be used in simulating many electrically large and complex structures in the biomedical microwave processing of materials and the wireless communications areas.

Cognitive radio systems adaptively adjust their radio parameters based on the feedback from the electromagnetic environment. Therefore, it is expected that cognitive radio systems will have better performance if they are integrated with accurate site-specific propagation modeling. Our group has long standing expertise in propagation modeling utilizing geo-spatial tools and indoor building models, and has focus on integrating these models as part of the environment awareness engine in cognitive radios. In this paper, we present the preliminary results for a multi-antenna based spectrum sensing algorithm with adaptive thresholds. The results show that, an almost fixed detection rate of 85% can be achieved for a mobile cognitive radio in an urban environment when the thresholds are set based on the path loss information provided by site-specific propagation modeling. On the other hand, the spectrum sensing algorithm with a fixed threshold shows a great variability in the detection performance, going as low as 65% in regions with heavy fading, which leads to harmful interference.

This paper describes an overview of recent advances in propagation modeling with some focus on contributions in characterizing challenging communications environments in urban and costal communications scenarios. MIMO capacity is estimated for typical communication scenarios, and impact of mutual coupling and wall type effects on the estimated MIMO capacities are quantified for various numbers of antenna array elements.

The propagation characteristics in indoor stairwell differ from those of the conventional indoor signal propagation across different floors and hence, deserve independent scrutiny. In this work, the propagation characteristics in four indoor stairwells have been examined by means of extensive field measurements at two frequency bands − 2.4 and 5.8 GHz respectively. It has been found the values of the path loss exponent n for stairwell are higher than those for other indoor environments. More importantly, the standard deviation of the n-values are high, leading to less accurate propagation models. This paper proposes the use of K-means clustering for the path loss data and values of path loss exponent n of stairwells are subsequently computed. The newly-computed path loss exponents n are lowered and their standard deviation values are significantly reduced. The path loss characteristics are useful for understanding radio propagation in pico- or femto-cells that have great potential in increasing the capacity and reducing the operational cost for wireless communications systems.

A new coaxial continuous transverse stub (CTS) array is proposed, designed, constructed, and tested. It is an omni-directional low cost antenna array which provides good impedance matching characteristics and good tolerance to manufacturing errors. It can be simply fed by a coaxial connector and is particularly suitable for millimeter wave personal communication systems (PCS). It is shown that this type of radiating element provides high percentage of radiation, and for the simulated design of single- and multiple-element arrays, S/sub 11/ was below -10 dB across a 6 GHz frequency span at the Ka band. A three-element prototype coaxial CTS antenna array was designed, constructed, and tested in the X-band. Experimental results were in good agreement with the simulated performance. Potential application of this new antenna array in multiband operation is also described.

Phased array antennas have and will continue to be a critically important component in the development of future wireless systems with applications in communications, radar, and satellite technologies. In spite of the significant advances in the design of modern phased array antennas, there continue to be significant and growing need for developing high performance systems that are also low cost and with beam steering capabilities. In this paper we describe some of the antenna array designs that focus on achieving this goal. We will start with one approach that is based on an analog phase-shifting approach and involves an integrated use of ferroelectric materials and the Continuous Transverse Stub (CTS) antenna array technologies. A complementary design which is based on digital beamforming and the utilization of the Hybrid Smart Antenna technique recently developed by our group will then be described. This will be followed with comments regarding the trade-off between the analog and digital phase shifting techniques. We will conclude the chapter with a description of a novel ultra-wideband and low profile ground plane which is based on a hybrid ferrite and Electromagnetic Band Gap (EBG) materials design. In all cases simulation results and experimental validation, whenever available, will be presented and aspects of the required future work to fully enable these technologies will be discussed.

In this paper, we will first review the ray-tracing algorithms developed in our group; then examples of the exploitation of geospatial data for radio propagation and its benefits will be presented. We will discuss the techniques to extract three dimensional (3D) building structures in urban propagation environment using 2D images in cyberspace. Finally, a real-time ray tracer will be briefly described.

This paper summarizes the results of an ongoing design effort to miniaturize HF antennas for HFSWR and OTHR systems. The proposed design is based on a meander antenna described in [1]. Design modifications include a multi-element folding to increase the radiation efficiency and improve the impedance matching and also the incorporation of a back conducting plane reflector to improve the gain. Based on simulation results using the FEKO and IE3D software and experimental measurements, we were able to successfully demonstrate the anticipated advantages of the proposed prototype design.

The development of advanced phased array antennas and new propagation models that address wireless applications in challenging propagation environments have and will continue to be a critically important component in the development of future wireless systems with applications in communications, radar, and Satellite technologies. In spite of the significant advances in these technologies, challenges continue to preclude their low cost, reliable, and high speed application in tough propagation environments including urban areas, UAVs, and other DoD applications. In this paper we describe some of the ongoing research activities at the University of Hawaii in the area of advanced wireless systems. In the antenna array design technology, two complementary antenna arrays designs will be described and the development of an ultra-wideband ground plane for foliage penetrating radars will be discussed. For the propagation modeling area, new models for characterizing indoor/outdoor transmission and for evaluating wireless coverage in urban areas taking into account the radiation patterns of the transmitting and receiving antennas will be presented. In all cases simulation results will be presented and validation with experimental observations will be included whenever available.

This paper presents a new method of incorporating propagation models into wireless systems simulations. The multipath data for each transmitter-receiver pair in a realistic environment is calculated using the site-specific propagation modeling software developed at the University of Hawaii. Instead of fitting the multipath data into a statistical model, we directly use the data for the calculation of discrete channel impulse responses for each transmitter-receiver pair. The Doppler effects and the effects of pulse shaping filters on the calculation of discrete channel impulse responses are investigated. Finally, these channel impulse responses are employed in a CDMA system simulator to evaluate the output signal-to-noise ratio (SNR) and the corresponding bit error rate (BER).

The ultra-wide hand (UWB) communications systems have been evolving quickly due to the recent FCC approval of the use of 7.5 GHz band of the unlicensed spectrum. To help with the effective implementation of impulse radio it is necessary to carefully characterize propagation in complex environments. This paper reports on the numerical simulation of UWB pulse reflections and transmissions through complex wall structures that are often encountered in indoor propagation environments. The finite-difference time-domain method is employed to accurately and efficiently calculate the field responses. Simulation results show that different structures of the walls have significant effect on the propagation characteristics. It is shown that the scattering due to the complex wall structures leads to complicated reflected and transmitted signals that could result in serious challenges in the design and effective implementation of an UWB communications system.

This paper reports on simulation results for the MIMO capacity and fading characteristics for indoor/outdoor propagation environments. The finite-difference time-domain (FDTD) method is used for the calculation of the reflection and transmission characteristics through windows and metal-framed structures and the obtained diffraction-type effects were then represented by an equivalent ray-tracing model. An integrated ray tracing code that accounts for these effects is then used to calculate MIMO capacity and Rician K-factor. The obtained results are then compared with those based on available data for Gaussian channels. In related preliminary results, it is shown that for an indoor environment with realistic walls of complex structures, the MIMO capacity and the K values are very different from those calculated based on simplified wall structures.

With the growing interest in implementing wireless communication systems based on MIMO, it is important that the capacity of such a system be evaluated in typical and realistic propagation environments. The paper describes an FDTD simulation procedure for calculating MIMO capacity in some typical propagation environments, including transmission through windows and metal-framed structures, communications through tree canopies, and accounting for the walls of complex structures. Scattering and diffraction effects from metal frames, complex walls, and leaves of trees result in complex field distributions which are expected to cause varying fading characteristics and hence affect the estimation of the MIMO capacity. It is shown that scattering and diffraction effects may increase the MIMO capacity when compared with those cases based on uniform solid walls.

In a network with several transmitting nodes, array antennas at both ends of MIMO links can be exploited to have multiple links operate in the same channel. Depending on the network topology, each interfering link can transmit fewer modes than it would in an isolated environment, and use the remaining degrees of freedom to avoid or suppress interference. With interference, channel state information (CSI) must be fed back to the transmitter to reach the highest level of performance. We show that the difference between closed- and open-loop capacities when links interfere is usually much larger than with isolated links. This implies that less frequent CSI updates are sufficient to keep closed-loop MIMO performance above open-loop MIMO. We analyze the effect of CSI aging for MIMO links. To understand the effect of fading and study the feasibility of closed-loop operation in MIMO links, we utilize two models for the MIMO channels. First, we use a Rayleigh fading model, and a filtered Gaussian noise method to simulate a fading channel. Then, we consider a more realistic scenario, where we simulate propagation in a typical indoor environment using the finite-difference time-domain (FDTD) method. The results, especially with the realistic channels, indicate that, even with the overhead of CSI updates multiplied by the number of iterations, spatial multiplexing may be attractive for static and low-mobility networks, such as in indoor environments.

This paper reviews the recent progress in propagation modeling for complex and challenging wireless communications environments. As more advanced wireless communication systems are being developed, detailed propagation and channel prediction research is needed for systems designs and for evaluating their performance. Complex propagation environments such as complex walls, windows and metal framed structures, and tree canopies are examples of environments that still need more detailed and accurate propagation modeling. New parameters, such as coverage, MIMO capacity, and bit error rate are needed to better evaluate and understand the performance of these systems under realistic communication environments. The paper discusses some of the models and shows some of the recent results in this area.

Smart antenna and associated technologies are expected to play a significant role in enabling broadband wireless communication systems. Smart antennas exploit space diversity to help provide high data rates, increased channel capacity, and improved quality of service at an affordable cost. In this paper we present a new procedure for implementing smart antenna algorithms. It is a hybrid approach that integrates the features of the switched beam method and the adaptive beam forming approach. Specifically it is shown that by using high gain antenna elements and combining the switched beam process with the adaptive beam forming procedure on a limited number of elements (as low as two in an eight-element array), a performance close to that of a more complex eight-element adaptive array may be achieved. The proposed hybrid method, therefore, is fast, is computationally efficient, and provides a cost effective approach for exploiting space diversity. Even with the inclusion of interference signals, the proposed hybrid approach out-performed the switched beam method, and provided performance similar to that of an adaptive array with less number of elements (three in an eight-element array). Implementation of an adaptive array also includes estimations; hence, reducing the number of elements in an array may lead to improved accuracy, in addition to fast convergence and reduced complexity.

Continuous transverse stub (CTS) technology has been adapted for use with coaxial lines to produce effective microwave antenna structures that radiate omnidirectionally, with high efficiency, low reflection, and useful radiation patterns. In this paper, we describe the design, construction, and testing of a new type of antenna arrays, that is, a six-element multiband (4.2 and 19.4 GHz) CTS antenna array. The design of the CTS array was optimized through simulation using FDTD and then built and tested using both S-parameters and radiation pattern measurements. Simulation results agreed very well with measured data. These simple and low cost coaxial CTS structures could be adapted for base station applications in wireless communication, for satellite communication systems, and identification friend-or-foe (IFF) systems for the military.

The two-dimensional finite-difference time-domain (FDTD) method is used to calculate the electric field distributions in an indoor communication environment with realistic floor plan. Power and fading characteristics (e.g., the Rician K-factor), and MIMO capacities are then calculated. Three different wall structures, i.e., the simple slab structure, the complex structure, and the effective slab wall of the complex structure, are considered and the corresponding K-factors and MIMO capacities are compared. It is found that the mean values of K-factors of the complex wall cases are larger than that of the slab walls by around 3 to 5 dB, while the K values of effective walls are larger than those of the complex wall cases by as much as 7 dB. It is also shown that the complex wall structures give larger MIMO capacities in most cases and the effective wall structures give the lowest MIMO capacities in all cases. Based on these results, it may be concluded that the complex wall effect on the propagation characteristics and the MIMO capacity may not be appropriately approximated by those estimated based on effective wall structures.

The multigrid finite-difference time-domain (FDTD) method is more efficient and accurate in characterizing electrically large and complex electromagnetic devices and structures. Detailed results of electromagnetic fields distribution in critical areas of interest can be obtained, thus accurately identifying hot spots and potential design faults. We present results illustrating the use of multigrid FDTD for the simulation and design of microwave processing systems. A realistic microwave dryer is simulated. New designs to improve the uniformity of the power distribution pattern in the ware samples are presented. It is shown that by using a slotted waveguide with slots varying in size along the waveguide, the absorption and the power uniformity can be significantly improved. The dependence of the power distribution pattern on the number of samples and a comparison between the slotted waveguide feed and the mode stirrer design is presented.

The development of accurate propagation prediction models for outdoor/indoor communication environments is challenging and requires the development of innovative approaches to: (a) improve the accuracy of available models; (b) improve the computation efficiency; and (c) implement sufficiently general calculation procedures that would help in characterizing complicated and unique outdoor/indoor propagation features and environments. In this paper we describe a new propagation prediction model that addresses the above stated requirements. Specifically, the computational efficiency of the shooting-and-bouncing ray (SBR) was significantly improved by employing ray tracing techniques based on computer graphics approaches. The accuracy issue was addressed by employing a multi-grid FDTD method to calculate diffraction coefficients from unique and difficult to handle analytically indoor and outdoor structures. Additional improvement in accuracy was achieved by calculating reflection and transmission coefficients from walls of complex structures. Finally, the multi-grid FDTD method was used to characterize unique outdoor/indoor environments such as windows, doors, etc. The overall model was integrated, and propagation prediction results for typical outdoor/indoor communication environments are presented and compared with available data.

In this paper, we describe the development of a unified code for simulating microwave processing of materials in multimode cavities. The integrated codes include a multi-grid 3D FDTD code and a finite difference heat transfer program. The code was used to simulate various feed options for the microwave cavity to help control and improve the uniformity of heating. The heat transfer code together with knowledge of the dielectric properties of materials as a function of temperature, which is also measured in our laboratory, provide significant information that help design controlled and high-yield microwave drying processes. Simulation results from both the multi-grid FDTD and the heat transfer codes are described, and suggestions for optimizing the drying uniformity discussed.

As the search continues for low-cost and high-performance components for the front-end devices for wireless communications systems, the focus has been on the use of MEMS technology; but some attention has recently been given to exploring new and innovative designs based on the Ferroelectric and the Continuous Transverse Stubs (CTS) technologies. In this paper we present new phase shifter designs and an integrated phased array antenna system based on the use of multilayer ferroelectric materials. Simulation results show that with the appropriate selection of the materials properties and the dimensions of the multilayer dielectric system, insertion losses may be reduced by as much as a factor of 100. These results also show that while only a slight reduction (15%) in the maximum achievable tunability was observed, it was possible to achieve significant improvement in the impedance matching characteristics. A procedure to enhance the radiation efficiency from an integrated ferroelectric/CTS phased antenna array design will be described and specific array designs discussed.

A new coaxial Continuous Transverse Stub (CTS) array is proposed in this paper. It is an omni-directional low cost antenna array which provides good impedance matching characteristics and good tolerance to manufacturing errors. It can be simply fed by a coaxial connector and is particularly suitable for millimeter wave personal communication systems (PCS). It is shown that this type of radiating element provides high aperture efficiency, and for the simulated design of single- and multiple-element arrays, S/sub 11/ was below -10 dB across a 6 GHz frequency span at the Ka band. The geometry of the proposed antenna is described and its design consideration discussed.

Two fast ray tracing procedures, one using space division with uniform rectangular grid and the other using unstructured triangular grid, are combined to cope with the complex propagation environments, such as micro-and pico-cells. Basically, unstructured triangular grids are employed for the calculation of outdoor propagation and uniform rectangular grids are used for indoor cases. The combined procedure has the advantages of the rectangular and triangular methods while overcoming their disadvantages. The new method is general, easy to implement and computationally efficient for many propagation environments.

To help enable the next generation of the wireless technology, paradigm shifts in the antenna designs are needed, and significant advances in the development of computationally efficient and physics-based propagation models for channel characterization are required. In the antenna design area, high-performance and low-cost antenna array designs with full 2D steering capabilities can play a significant role in increasing the capacity, extending the range, and in improving the capabilities and quality of service in a wireless communications system. A wide variety of space diversity techniques has been proposed and the development of a low-cost adaptive antenna array is crucial in the realization and implementation of these systems. In this presentation, the design and optimization of a new low-cost phased array antenna based on the CTS technology is described. The new CTS array provides full 2D scanning capabilities using ferroelectric (BSTO) material. The design procedure is described and techniques for overcoming the significant conductor losses discussed. Two computationally efficient techniques for modeling indoor/outdoor propagation environments are described and a procedure for improving the accuracy of the ray tracing-based calculations using a multigrid FDTD method are discussed.

A new triangular-grid ray tracing (TGRT) method is proposed in this paper. It is based on dividing the propagation region into triangles. The number of triangles is decided by the number of structures' vertices, instead of their dimensions. For the 2D case, it can reduce the visible decision calculation to 2 edges for each triangle. It is shown that this method unifies the indoor and/or outdoor propagation problems and provides savings in computational time.