Multiple-access interference

Dramatic growth rates in capacity demands in wireless and other broadband systems have resulted in a rise in the use of communication networks in which multiple users share common communication resources. A significant consequence of this trend is the increasing presence of multiple-access interference (MAI), which arises in communication systems employing non-orthogonal multiplexing, that is, in multiple-access systems. This issue arises naturally, for example, in code-division multiple-access (CDMA) communication systems using nonorthogonal spreading codes. It also arises in orthogonally multiplexed wireless channels, such as time-division multiple-access (TDMA) and orthogonal frequency division multiple-access (OFDMA) channels, due to effects such as multipath or nonideal frequency channelization, and in wireline channels such as those arising in digital subscriber line (DSL) systems or powerline communications (PLCs) in which crosstalk and other types of interference are major impairments. MAI also arises in optical wave-division multiplexing (WDM) systems due to mode interactions caused by nonlinearities.