This paper shows that wirelessly powered backscatter communications is
subject to a fundamental tradeoff between the harvested energy at the tag and
the reliability of the backscatter communication, measured in terms of SNR at
the reader. Assuming the RF transmit signal is a multisine waveform adaptive to
the channel state information, we derive a systematic approach to optimize the
transmit waveform weights (amplitudes and phases) in order to enlarge as much
as possible the SNRenergy region. Performance evaluations confirm the
significant benefits of using multiple frequency components in the adaptive
transmit multisine waveform to exploit the nonlinearity of the rectifier and a
frequency diversity gain.Comment: submitted for publicatio
