On scalar ambiguity in blind channel estimation for OFDM systems

Blind channel estimation is a promising technique to reduce the pilot overhead. Unfortunately, most existing algorithms suffer from the scalar ambiguity problem, and hence only achieve semi-blind identification. In this paper, we show that with the information of source constellation, the phase of the ambiguous scalar can be divided into a fractional part and an integer part. Then we propose a multiple-constellation scheme enabling totally blind identification regardless of constellation type for OFDM systems. The necessary and sufficient condition for eliminating the scalar ambiguity is given. An application example shows that our scheme can help other algorithms circumvent the annoying ambiguity.