okay, that makes sence, the only thing thats bothering me now is this.
the question i should really ask is what should i see happening in the tap weight vector.
a while ago i did a simulation of an adaptive filter. (a plain and simple FIR feed forward filter.) the input signal was a sine wave with noise, and hence the desired signal was a pure sine wave. after the coefficients adapted, they remain the same, i thought that this was due to the single being a periodic signal. so if the ideal signal is removed, and the coefficients are unchanged, then the system will still work.
in my DFE, im using randomly generated bits that will form symbols for DQPSK. because its random, whenever i look at the tap coefficient vector, its always changing. i assume this is happening because the signal isnt periodic. but so far, im only getting a relativly correct output becuase i have the known signal.
so what exactly is used when the desired signal is unknown?