A sampling resource allocation problem formulation for determining the optimal sample size for each of multiple sampling activities competing for a single sampling resource is described. The problem is formulated as a nonlinear knapsack problem with lower and upper binding restrictions. The objective function based on the squared coefficient of variation is used for the real-time performance monitoring of digital signals. This formulation is an extension of the classical method of determining the minimum sample size for a single sampling activity. A solution procedure is also provided. >