Relationship between maximum access delay and the R.M.S delay spread

Abstract

Currently, the orthogonal frequency division multiplexing (OFDM) systems use a predetermined cyclic prefix (CP) that is conservatively designed for the longest anticipated delay spread to overcome the multipath propagation delays. The most important parameter for determining the CP is power delay profile which is widely accepted to be following a negative exponentially decaying pattern. In this paper, the key parameter root mean square (r.m.s) delay spread of the power delay profile is mathematically derived based on the exponentially decaying power delay profile. The 3rd Generation Partnership Project (3GPP) power delay profiles are fitted into the exponentially decaying power delay profile (EDPDP). The performance measure bit error rate (BER) is used to evaluate the effectiveness of the EDPDP and its r.m.s delay spread. The findings show that EDPDP can be used to characterize the most of the power delay profiles. Subsequently, a mathematical formula to calculate CP estimation is derived. As a result, it is found that the CP is the natural logarithm of the ration of maximum power to minimum power of a particular power delay profile multiplied by its r.m.s delay spread. This finding gives the relationship between the maximum access delay and r.m.s delay spread as far as CP is concerned.