Development of a Wireless Communications Planning Tool for Optimizing Indoor Coverage Areas A. Dimitriou, T. Vasiliadis, G. Sergiadis Aristotle University of Thessaloniki, School of Engineering, Dept. of Electrical & Computer Engineering, Telecommunications Division, 540 06 Thessaloniki, Greece Tel. +30 31 996314, e-mail: sergiadi@eng.auth.gr ABSTRACT In this paper we present some preliminary results on the subject of indoor wireless communications planning by using computer simulation of signal propagation. The goal of this simulation is to obtain an overview of the received signal strength throughout the indoor environment and then try to optimize the coverage by moving the antenna properly. The optimization is considered as a procedure of moving signal “blind spots” according to a non-standard pattern that obeys custom needs, related to specific parameters of the environment (e.g. furniture). I. INTRODUCTION Modern trends in digital communications are focusing on ways and means by which indoor wireless services will evolve even more and overcome difficulties related to signal propagation inside buildings and dense office environments. In such places, electromagnetic wave propagation suffers from deep fading, caused by multiple reflections from the room walls. The effect of fading is large variations in the received signal strength along a distance of only a few wavelengths long. The statistical properties of both fast and slow fading are well described in bibliography by Rayleigh and Rician probability functions and therefore we will not discuss them in this paper. [1-3] The major cause of multipath fading is the vectorial addition of all incoming EM wave rays at the receiving point. These rays traveled different distances and some of them have been subjected to a single or multiple wall reflections, resulting to a total number of wave rays that have different phase arguments. When added at the receiving point, these vectors may (or not) cancel out, in respect with each other’s phase. This results in deep signal variations when the receiver moves around the room. A similar effect is observed when we monitor the received signal strength at a fixed point in the room, while changing the signal’s frequency (for a CW signal propagation). This effect is often called frequency dispersion of the signal. Even though the receiver might suffer from a deep fade at a certain position and frequency, this does not mean that adjacent frequencies suffer as well. We can record such signal variations versus frequency at some points of the indoor environment. [4] An example of this behavior is well illustrated in Figure 1, where the received signal is plotted versus frequency. This measurement was taken in an empty meeting room using a spectrum analyzer, a frequency generator feeding a TX antenna while sweeping the DECT band (1880- 1900MHz) and a dipole antenna at the receiving point (RX antenna is not moving). -80 -70 -60 -50 1880 1882 1884 1886 1888 1890 1892 1894 1896 1898 1900 Ref Level : -46,3 dBm dB / Div : 3,64 dB Detection : Pos. Peak RX Power vs. Frequency at a fixed receiving point Model: MS2711 Serial #: 00006040 Date: 12/14/2000 Time: 19:37:28 Antenna: NONE RBW: 100 kHz VBW: 300 kHz Attenuation: 0 dB CF: 1890,0 MHz SPAN: 20,0 MHz Spectrum Analyzer (dBm) Frequency (1880,0 - 1900,0 MHz) Figure 1. Large signal variations versus frequency at a fixed receiving point in the room (blind spot). II. PROPAGATION SIMULATION In real conditions like these, we are currently in the process of developing a software tool for visualizing the indoors-received signal strength and then marking the positions in the room where large signal variations are observed. We characterize these points as “blind spots” in the room. By default, we consider these blind spots as points in the room in which the receiver probably might have a problem in communication and thus quite possibly will attempt a handover.