High reliability will be required even in Internet of Things (IoT) communications in the near future for control purposes. To enhance reliability, both uplink (UL) and downlink (DL) communication quality must be considered. In this paper, we focus on the improvement of DL physical layer communication. To enhance the reliability of DL, the use of spatial diversity is a promising technique. We deal with two transmit diversity (TD) techniques, space-time block coding (STBC) and cyclic delay

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... ty (CDD), which are evaluated by experimentations in real environments. From the results of the experiments, we confirmed that STBC and CDD could improve frame error ratio (FER). CDD can achieve almost the same performance as STBC by setting the amount of cyclic shift (ACS) appropriately. For example, in a non-line-of-sight (NLOS) area where shadowing happens due to hillock, FER could be improved from 5.11 × 10 −2 to 1.59 × 10 −2 in STBC and 1.00 × 10 −2 in CDD.