Overflow Probability of Variable-length Codes with Codeword Cost

Lossless variable-length source coding with codeword cost is considered for general sources. The problem setting, where we impose on unequal costs on code symbols, is called the variablelength coding with codeword cost. In this problem, the infimum of average codeword cost have been determined for general sources. On the other hand, overflow probability, which is defined as the probability of codeword cost being above a threshold, have not been considered yet. In this paper, we determine the infimum of achievable threshold in the first-order sense and the secondorder sense for general sources and compute it for some special sources such as i.i.d. sources and mixed sources. A relationship between the overflow probability of variable-length coding and the error probability of fixed-length coding is also revealed. Our analysis is based on the informationspectrum methods.