On the Use of Spatial Diversity under Highly Challenging Channels for Ultra Reliable Communications

The Industry 4.0 concept is the result of latest technical advances that have completely changed the existing industrial vision, not only from the mechanical point of view, but also from the Machine-to-Machine (M2M) communication perspective. This revolution encompasses wireless communication technologies that are expected to be the replacement for traditional wired and fixed communication systems. However, industrial propagation channels are still a challenge for wireless industrial network deployments. This paper addresses this problem by proposing spatial diversity based retransmissions. Two general retransmission schemes have been tested: default and smart. Moreover, specific time scheduling choices have been proposed. The impact of the number of transmitters in relation to communication reliability has been analyzed. Results show that the use of spatial diversity based retransmissions makes restrictive reliability values feasible under realistic conditions. In fact, in the case of smart retransmissions, adding a second transmitter the reliability increases around 8 dB. Moreover, whereas the channel coherence time is a critical parameter for time based retransmissions, in the case of spatial diversity, the reliability performance has no dependency on the channel coherence time.