Multipath Delay Profile Prediction On A Workstation For Urban Mobile Radio Communications

Abstract

A multipath delay profile prediction system without any field measurement is proposed. The applied method is purely theoretical one assuming a direct-diffracted wave from transmitting antenna and the waves scattered on the walls visible from transmitting antenna as incident waves at a receiving point. The prediction system has been realized on a workstation. Comparison with measured results shows good agreement with the predicted. 1.0 Introduction Digital mobile radio communication provides various changes in the mobile telecommunications [ 13. However, its performance is greatly dependent on the multipath delay characteristics, because the bit error is due to the channel distortion caused by frequency selective fading. The multipath delay characteristics of service area is an important information for the system design. Generally, field measurement is conducted to investigate the multipath delay, which is time-consuming and uneconomical. A deterministic approach, such as the prediction of multipath propagation environment for the concerned place can be quite worthwhile to design the mobile radio system, if the topological information is available. There have been some works to estimate the statistical characteristics of mobile radio channel according to building map data [21[3]. However, they have not predicted the exact multipath delay profile at arbitrary receiving point, which will sometimes good information to evaluate the service area and system performance. This paper proposes a method to predict multipath delay profiles in urban areas assuming building-wall-scattered waves and direct-diffixted waves based on a building topological database, where the delay profile prediction system was realized on a workstation. And it is shown that the predicted power delay profiles are coincide with the measured ones, 2.0 Principle The proposed method predicts direct-dz$acted waves (diffracted wave travels on the line connecting between the transmitting and the receiving antennas) and building-wall-scattered wuves arriving at a receiving point based on a building topological database. 2.1 Building topological database The building topological database contains the building positions and heights expressed by wall-vectors representing the outline of the building by rounding counterclockwise [4]. The data were digitized from building maps scaled 1/2500, and its accuracy is 1 m. The height of building, H , is calculated by the equation H = [3.8N + 2.51 (m), where [ ] denote the Gauss symbols and N is the number of story observed in the field inspection. In the prediction, it is assumed that all the buildings stand on a flat surface. 2.2 Delay profile prediction The propagation model assumed for delay profile prediction is composed of direct-diffracted waves and buildingwall-scattered waves. The direct-diffracted wave is the wave travels on the line connecting the transmitting and the receiving antennas, which becomes a direct wave when no diffracting objects exist on the line. The buildingwall-scattered waves are the waves scatters on the building wall. For saving the computing time, only the buildingscattered-waves scattering on the wall visible from the transmitting antenna spre predicted. The signal strength of directdiffracted waves is calculated for each receiving point by counting the Wfraction loss caused by all the buildings on the line between the transmitting and the receiving antennas, using multiple knife edge model. On the other hand, in the case of building-wall-scattered wave, the calculation is complicated. The signal strength of the wave scattering on the wall is calculated by following radar equation, where P,, is the received power from w, scattering wall, Pi is transmitting power, Gt is the transmitting antenna gain, U, is the bistatic cross-section of TIth scattering wall, A, is an effective section of the receiving antenna, and dl and d2 are the distance between the transmitting antenna and the scattering wall, and the distance between scattering wall and the receiving antenna, respectively. The bistatic cross-section U,, is calculated by following equation according to the approximation of physical optics assuming that the building wall is a smooth metal plate [51, where IC = 2n/A, A is wave length, W and L are the width and the height of the visible portion of the wall, respectively, 4in, ( b, , e,,, and Or, are the angles shown in the Fig. 1. Generally the U, has a mainlobe to the