Influence of the laser diode nonlinearity in fiber-fed microcellular networks

Abstract

In this paper, the use of an optical fiber-based fixed infrastructure for code division multiple access (CDMA) mobile networks is considered. One of the major problems associated with optical subcarrier multiplexing (SCM) is the nonlinearity of the laser diodes (LD). The LD is modeled by a memoryless nonlinearity, and the effect of the nonlinearity on the SCM transmission of CDMA signals is evaluated. The behavior departs significantly from what happens in frequency division multiple access (FDMA), and depends critically on the nonlinearity being compressing or expanding. In the former case, significant performance degradation may occur, whereas for the latter this is usually not dramatic. When compared against FDMA, the major advantage of CDMA comes from the tight power control function that must be built in such systems, which means that situations of a weak signal corrupted by strong signals do not occur, unlike what happens in FDMA.