Optimized linear precoding for biased 2-ASK modulation in multi-user SWIPT with integrated receiver

Simultaneous wireless information and power transfer can be realized by means of an integrated receiver, where both the energy harvesting and the information detection operate on the rectified received signal. In this contribution, we consider a MU-MISO communication system where all users terminals are equipped with a current-splitting integrated receiver. Biased binary ASK modulation with zero-forcing linear precoding is used. We demonstrate that, for a given transmit power, the received signal power can be considerably increased by applying appropriate rotations of the symbols and suitable row permutations of the channel matrix at the transmitter. We present low-complexity rotation and permutation optimization algorithms, resulting in significantly higher harvested power and information rate, compared to the case where no optimization is performed. We investigate the power-rate trade-off of the optimized system by varying the amount of the rectifier output current drawn by the harvesting circuit, and study the effect of selecting the ratio of the minimum-to-maximum symbol magnitudes in the biased binary ASK constellation. A numerical example shows that the proposed optimizations and selection of the symbol magnitude ratio result in SNR gains up to about 11 dB to 21 dB (depending on the information rate) and harvested power gains up to about 14 dB.