Internet of Things Based on Cell-Free Massive MIMO

We consider Internet of Things (IoT) organized on the principles of Cell-Free Massive MIMO. Since the number of things is very large, orthogonal pilots cannot be assigned to all of them even if the things are stationary. This results in an unavoidable pilot contamination problem, which is severe for IoT since the things are operating at very low transmit power. To mitigate this problem and achieve a high uplink throughput we use Cell-Free systems with optimal LMMSE channel estimation, while traditionally simple suboptimal estimators have been used in such systems. We further derive an analytical SINR expression for this scenario, which depends only on large scale fading coefficients. This allows us to design new power control algorithms that require only infrequent transmit power adaptation. Simulation results show a 40% improvement over existing Cell-Free wireless systems and a 10-fold improvement over known IoT systems based on small-cell systems.