The effects of mismatched roll-off factor on the receiving performance of QAM signals

Investigating the blind roll-off factor estimation of QAM signals has great significance in non-cooperative communication. In this paper we analyze and simulate the effects of roll-off factor error and the mismatched filter order on the receiving performance for the receiver with symbol timing recovery (STR) or without receiving processing(without STR). The results show that the effect is very small. It is reasonable to set the roll-off factor of the receiving square-root raised cosine (SRRC) filter to be 0.5-0.7 without knowing the roll-off factor of the transmission SRRC filter and it has the smallest influence on receiving performance. The higher order (which means greater out-of-band attenuation) of receiving filter can not obviously improve the receiving performance. On the contrary it makes the receiver more complicated and more difficult to implement.