On the Impact of Transmitter Channel Knowledge in Energy-Efficient Machine-Type Communication

We address the problem of delivering a fixed data payload over a Rayleigh fading wireless channel, where the aim is to allocate resources to minimize the average total energy, given by the sum of the transmit energy and an overhead circuit energy. This scenario is well suited for uplink cellular machine-type communications in future 5G Internet of Things (IoT) use cases, where the focus is more on device energy efficiency than on throughput. We propose and describe the transmission policies to be used under three scenarios with different levels of channel state information (CSI) at the transmitter: non-causal CSI, causal CSI, and average CSI. For typical uplink macrocellular links, we show 1) that the strategy for causal CSI has nearly the same energy efficiency as the unachievable non-causal CSI bound, and 2) that the energy difference between this bound and the average CSI energy is about a factor of 2 to 5.