Connecting numerous Internet of Things (IoT) devices from different sources of information with diverse Quality of Service (QoS) requirements leads to the need of new transmission techniques. In this thesis, we proposed two sets of transmission schemes that take into consideration different properties of IoT devices and the heterogeneous requirements of IoT applications. The first set of adaptive transmission schemes takes into consideration the remaining battery of each IoT sensor node to decide on the transmit power and the modulation mode to be used during each transmission slot. The second set of transmission schemes presented in Chapter 4, considers a Massive Multiple-Input Multiple-Output (Massive MIMO) system, in which the base station (BS) is equipped with a large number of antennas serving a high number of IoT nodes from different traffic types and we aim to adapt and optimize the system and transmissions parameters for each of these traffics.