A New Approximation for Average Symbol Error Probability over Log-Normal Channels

The average symbol error probability(ASEP) is an important measure to evaluate the performance of different modulation techniques over fading channels. The phenomenon of both shadowing and slow fading in wireless communication system is generally characterized by log-normal probability distribution. Approximating log-normal integrals by constructing Taylor series expansion of second order, a simple tight closed-form approximation for ASEP over log-normal fading channel is derived. This expression facilitates the computation of average symbol error rate for a broader class of coherent digital modulation schemes. The efficiency of the expression is numerically examined and comparison of the results is carried out in relation to the existing approximate expressions.