Estimating coverage of radio transmission into and within buildings at 900, 1800, and 2300 MHz

Investigations of propagation into and within buildings at 900, 1800, and 2300 MHz have been undertaken, using buildings both in the University of Liverpool precinct and in the commercial center of the city of Liverpool, United Kingdom. The emphasis of this article is the modeling of radio transmission into buildings that uses the measured penetration loss values in order to adjust the propagation models developed for the outside areas, and the modeling of radio transmission within buildings, starting with the simple distance-power law. Those models are very useful for economical reasons and are sufficiently fast for rapidly estimating coverage regions. However, more accurate models have been developed from experimental results, and are presented here. For those more precise models to work properly, it is necessary to know the environment and all the variables that may influence the propagation of the radio signals. Estimating Coverage of ANTONIO FISCHER DE TOLEDO, TELESP-TELECOMMUNICASOES ADEL M. D. TURKMANI A N D J. D A V I D P A R S O N S , UNIV. OF LIVERPOOL physical understanding and consequent mathematical modeling of the radio propagation inside buildings is very important because it facilitates a more accurate prediction of system performance and provides the mechanism to test and evaluate methods for mitigating the deleterious effects caused by the radio channel in such environments. This article reports the results of narrowband measurements into buildings at 900, 1800, and 2300 MHz, with the transmitter located on the roof of one building and the receiver located in a different building. It also describes measurements that have been undertaken with both transmitter and receiver situated within the same building. These latter measurements are classified as propagation within buildings. The experiments were conducted in order to determine statistics related to the random variation of a continuous wave (CW) signal received in indoor environments [l-31. Empirical models which allow the path loss between the transmitting and receiving antennas to be predicted have also been developed and are presented in this article. The use of radio equipment inside buildings involves a radio propagation environment that differs from the more familiar street-level situation so extensively studied in connection with vehicle-borne transceivers [4, 51. Propagation models that adequately describe the signal in open and urban areas are no longer adequate, since there will be a building penetration loss associated with the indoor environment [6-81. This additional loss will depend on a large number of factors with various degrees of importance. Among them are the transmission frequencies, the distance between the transmitter and receiver, the building construction material, and the nature of the surrounding buildings. Several researchers have studied the problem of receiving radio signals inside buildings and model it as the distance dependency of the path loss when the mobile is outside a building, plus a building loss factor. The building loss factor is included in the model to account for the increase in attenuation of the received signal observed when the mobile is moved from outside a building to inside. This model was first proposed by Rice 191 in 1959, and has been used in most subsequent investigations. In addition to penetration loss, system designers are also interested in learning about the received signal variability and the effects of building height, conditions of transmission, construction materials, and frequency of operation. Several research activities that deal with these aspects have been reported in the literature [l, 3, 9-11]. The general conclusions for the propagation into buildings are: Small-scale signal variation is Rayleigh distributed. 0 Large-scale signal variation is log-normally distributed with a standard deviation related to the condition of transmission and area of the floor. For non-line-of-sight transmissions, the standard deviation is approximately 4 dB. For partial to complete line-of-sight conditions, the standard deviation increases to 6-9 dB. 0 The penetration loss decreases at higher frequencies: 14.2 dB at 900 MHz, 13.4 dB at 1800 MHi, and 12.8 dB at 2300 M E . 0 In general, the rate of change of penetration loss with height was found to decrease with height by 1.4 dB1floor on average (1.38, 1.36, and 1.50 dB/floor for signals at 900, 1800, and 2300 MHz respectively). In the within buildings propagation case, most of the research activities that have been reported in the literature [l , 7, 12, 131 are mainly concerned with the investigation of the smalland large-scale statistics of the received signal and the variability of the floor’s mean signal level. The significant conclusions related to propagation within buildings are as follows: 0 Small-scale signal variations are Rayleigh distributed. * Large-scale signal variations are, reasonably, log-normally distributed with a standard deviation value of about 16 dB. 0 The rate of change of mean signal per floor was, on average, approximately 8.5 dB. However, careful examination of the results [ l ] reveals three different slopes: 6.5, 6.1, and 6.7 dB/floor, respectively, for 900, 1800, and 2300 MHz, when considering floors below that on which the transmitter was located; and similarly, -10.5,-10.4 and -10.8 dBIfloor, when considering the measurements conducted on floors above the transmission location. Of importance also is the dependence of the overall signal 4