Predicting and Verifying Cellular Network Coverage

Recent investigations have shown that cell radius is a much better metric of RF coverage than area reliability. Given the maximum allowable path loss of the radio equipment and assuming a Hata path loss model, cell radius predictions are shown to be a monotonically decreasing function of the desired area reliability. A useful, technology independent nomograph is given that predicts the cell radius as a function of the desired area reliability for both 800MHz and 1.9 GHz propagation. Validating cellular coverage involves sampling a subset of the desired coverage area and quantifying cell radius accuracy as a quality of coverage. The linear distance that must be driven to verify that the cell radius is achieved is also approximated. 1. RF COVERAGE BACKGROUND Coverage prediction is the forecast of signal strength over an area of interest in lieu of any measurements. Coverage validation is the measurement and verification of the desired signal strength throughout an area of interest. Area reliability is the probability that the RF signal strength measured throughout the cell will meet or exceed a desired quality threshold (e.g.,over 90% of the area the signal strength is greater than -90 dBm). Cell edge reliability is the probability that the RF signal strength measured on a circular contour at the cell edge will meet or exceed the same threshold (e.g.,over 75% of the cell edge the signal strength is greater than -90 dBm). In Reudink’s path loss model [17], the median signal strength, P (dBm), is considered to be a linear function of the logarithm of the distance from the base station, and the azimuthal path loss changes due to shadowing are modeled by adding a single lognormal random variable, X, with standard deviation dB): ) , 0 ( ~ where ; log10 N X X R R B P P o R O Using linear regression this concept was used to define the “effective radius”, R (km), of a cell and was shown to be a better metric of coverage than area reliability [6][9]: R 10 (P THRESH FM A ) / B 1) where PTHRESH is the desired signal strength at the receiver A’ (the intercept) is the signal strength at 1 km, B is path loss slope (dB/decade of distance, e.g., 40) is the standard deviation of the lognormal shadowing (e.g., = 8dB) The fade margin is given by z FM ensures the desired cell edge reliability