A 3D ray tracing simulator has been developed for indoor wireless networks. The simulator uses geometrical optics (GOs) to propagate the electromagnetic waves inside the buildings. The prediction technique takes into account multiple reflections and transmissions of the propagated waves. An interpolation prediction method (IPM) has been proposed to predict the propagated signal and to make the ray-tracing algorithm faster, accurate, and simple. The measurements have been achieved by using a single Wi-Fi network access point as a transmitter and a laptop as a receiver. Measured data had been collected at different positions in indoor environment and compared with predicted signals. The comparison of the predicted and measured received signals gave root mean square error of 2.96 dB and std. deviation of 2.98 dB.

The indoor wireless environments suffer from weak coverage due to the building construction and the multipath effect inside the buildings. The interest grows in the indoor coverage to serve the costumers with data and voice anytime anywhere. The ray-tracing (RT) algorithms have been used widely for accurately predicting the site-specific radio propagation characteristics [

Two-dimensional ray-tracing algorithm has been developed in [

The main purpose of our simulator is to study indoor wireless propagations for indoor wireless networks for different types of systems and building constructions to develop an indoor location update and paging algorithm. We are looking for a versatile and accurate algorithm to predict the received signal strength (RSS) inside indoor environments. This work represents the development of three-dimensional ray-tracing algorithm for indoor wireless networks followed by the measurement procedure. Comparison between predicted and measured received signals for WLAN has been achieved.

The simulator starts by creating a custom layout of the indoor environment. The user has to define the area of the building, wall locations and materials, ceiling height, and the locations of the transmitters and receiver. The system parameters such as the operating frequency, the transmitter and receiver gains, transmitter elevation angle (vertical), transmitter propagation angle (horizontal), and the number of reflections and refractions are defined by the user. The ray tracing starts with the reflection phenomena on the basis that the vast majority of the energy is contained in the reflected components followed by transmission. The other effects such as diffraction, scattering have less effect for indoor radio propagations [

Site-specific propagation model has been used with brute-force ray-tracing method, where a bundle of transmitted rays has been considered that may or may not reach the receiver. By using the concept of ray tracing, rays may be launched from a transmitter location and the interaction of the rays with partitions within a building modeled using well-known reflection and transmission theory. The transmitter (Tx) and receiver (Rx) are modeled as points at discrete locations in three-dimensional space. All the possible angles of departure and arrival at the transmitter and receiver are considered to determine all possible rays that may leave the transmitter and arrive at the receiver as shown in Figures

3D representation of the transmitter (Tx), receiver (Rx), and the reflected and transmitted rays as (a) a top view of the building and (b) a side view.

First, the model determines whether a line-of-sight (LOS) path exists. If so, it computes the received LOS signal. The averaged LOS power from the averaged LOS delay profile is represented using the free space or Friis equation [

Next, the model traces a source ray in a specified direction and detects whether an intersection occurs. If no intersection is found, the process stops and a new source ray in a direction making an angle (angle step) of 10° with the original ray initiates. Once an intersection has occurred, the received signal is computed for a reflected and transmitted ray, each of which is traced to the next intersection in the same way. This recursion continues until the number of reflections and transmissions reached maximum defined value (3 for this simulation) as shown in Figures

The averaged reflected power is assumed to be the free space value for the unfolded path length multiplied by the square of the voltage reflection coefficient (

In this model, there is no need to collect more information about the propagation constant of the medium which is varying from one place to another inside the building [

In RT algorithms, the rays propagate with a certain departure and elevation angles. The small is the angle step between each ray and its subsequent ray, the more accurate and precise is the RT algorithm. This leads to increase the time needed to propagate the rays, calculate reflective and transmission coefficients, and calculate the received signals at each intersection position [

The measurement procedure has been conducted in a five-story apartment building with cement walls and concrete floors and ceiling. Figure

Floor plan of the building showing the location of the transmitter (Tx) and the measurement positions for the receiver (numbered).

The receiver is Intel Wi-Fi Link 5100 AGN network adapter with 7 dBi gain, operates at 2.4 GHz. The receiver is moved to collect measured signals at 60 positions (numbered) throughout the flat as shown in Figure

The received signal plane view is shown in Figure

Contour of the received signal with respect to the transmitter.

Root mean square error (RMSE) and the standard deviation (

RMSE and

No. of reflections | 0 | 1 | 2 | 3 | 4 | 5 |
---|---|---|---|---|---|---|

RMSE (dB) | 6.47 | 4.80 | 4.24 | 2.96 | 3.44 | 4.95 |

4.65 | 3.41 | 3.09 | 2.98 | 3.37 | 4.22 |

The measured and the predicted signals vary with about the same slope. Figure

The measured and simulated received signals with 0° to 360° elevation angle and propagation angle for three reflections.

A three-dimensional ray-tracing simulator has been developed to study the indoor radio wave propagation for wireless communications networks. The number of the reflected rays has been optimized. The number of three reflections has been found as the optimum number of reflections with RMSE 2.96 dB and standard deviation of 2.98 dB with the consideration of reflected and transmitted rays for 10° angle step. This number was used to simulate the propagation of electromagnetic wave for wireless local area networks (WLANs) inside a building. The proposed interpolation prediction method (IPM) helps to have a complete prediction throughout the predicted area and reduce the propagation and computation process. The comparison shows that the general behavior of the predicted and measured received signals is quite similar.

The authors thank the Ministry of Science, Technology, and Innovation, Malaysia, (MOSTI) for supporting this work by the Project Grant no. 01-01-02-SF0344.