  The PAMELA satellite experiment has measured the cosmic-ray positron fraction
between 1.5 GeV and 100 GeV. The need to reliably discriminate between the
positron signal and proton background has required the development of an ad hoc
analysis procedure. In this paper, a method for positron identification is
described and its stability and capability to yield a correct background
estimate is shown. The analysis includes new experimental data, the application
of three different fitting techniques for the background sample and an estimate
of systematic uncertainties due to possible inaccuracies in the background
selection. The new experimental results confirm both solar modulation effects
on cosmic-rays with low rigidities and an anomalous positron abundance above 10
GeV.
