The problem of blind channel equalization can be described using the simple system diagram shown in Figure 2.1. The complex baseband model for a typical QAM (quadrature amplitude modulated) data communication system consists of an unknown linear time-invariant (LTI) channel c(t) which represents the physi­ cal inter-connection between the transmitter and the receiver at baseband. The matched filter is also included in the LTI channel model. The baseband-equivalent transmitter generates a sequence of complex-valued random input data {$[&]}, each element of which belongs to a complex alphabet A (or constellation) of QAM sym­ bols. The data sequence [s[k]} is sent through a baseband-equivalent complex LTI channel whose output r(t) is observed by the receiver. The function of the equalizer at the receiver is to estimate the original data {s[k]} from the received signal r(t).