Cell Site Power Characterization for Multi-rate Wireless CDMA Data Networks Using Lognormal Approximation

An analytical model is developed to solve the power-rate assignment problem for multi-rate CDMA systems and calculate the probability density function (PDF) for the downlink traffic power as a function of the bit rate assignment scheme, the target link quality figure, and the other network parameters. This paper proposes the use of the lognormal random variable as an approximation for an empirical parameter (denoted herein by fi) that is needed to solve the energy per-bit to noise spectral power density equation for scheduled data bursts. The approximation depends on matching the mean and standard deviation of the lognormal variable to the mean and standard deviation of the empirical parameter fi where the matching depends only the radio frequency (RF) path loss model and the shadowing process standard deviation. The paper presents example calculations for the cumulative probability distribution (CDF) of the downlink traffic power and outage probabilities for a general CDMA system assuming specific scenarios of data bit rate assignments. The study also compares between analytical results and those obtained using conventional Monte-Carlo simulations. Comparisons indicate that the developed model provides an appropriate mechanism to approximate both the PDF or CDF, and the outage probability for the cell site total downlink traffic power.