  In this paper, we propose a novel splitting receiver, which involves joint
processing of coherently and non-coherently received signals. Using a passive
RF power splitter, the received signal at each receiver antenna is split into
two streams which are then processed by a conventional coherent detection (CD)
circuit and a power-detection (PD) circuit, respectively. The streams of the
signals from all the receiver antennas are then jointly used for information
detection. We show that the splitting receiver creates a three-dimensional
received signal space, due to the joint coherent and non-coherent processing.
We analyze the achievable rate of a splitting receiver, which shows that the
splitting receiver provides a rate gain of $3/2$ compared to either the
conventional (CD-based) coherent receiver or the PD-based non-coherent receiver
in the high SNR regime. We also analyze the symbol error rate (SER) for
practical modulation schemes, which shows that the splitting receiver achieves
asymptotic SER reduction by a factor of at least $\sqrt{M}-1$ for $M$-QAM
compared to either the conventional (CD-based) coherent receiver or the
PD-based non-coherent receiver.
