ownlink and uplink. For LAA uplink, in particular, UEs would need to rely on the uplink grant from eNB for (re)transmissions. Enhanced licensed-assisted access was introduced in 3GPP Rel-14. It defines how a UE can access 5 GHz band to transmit data in the uplink direction. Because all uplink transmissions in LTE are scheduled and controlled by the serving eNB, the channel contention between devices and the LBT scheme, which was defined in LAA for downlink operation, needed to be adapted to the uplink direction. Furthermore, the regulatory requirements for access to 5 GHz band vary in different regions. For example, ETSI requires that the OCB, defined by 3GPP as the bandwidth containing 99% of the signal power, to be between 80% and 100% of the declared nominal channel bandwidth [29]. As an initial approach, multi-cluster PUSCH transmission, which was specified in 3GPP Rel-10, was considered to fulfill this 898 Chapter 8 ETSI requirement [29]. Multi-cluster PUSCH allows two clusters of resource blocks to be scheduled far enough from each other to fulfill, for example, the 80% bandwidth require- ment. However, further studies in 3GPP suggested that the latter was not an efficient solu- tion. Furthermore, the PSD limits defined for the 5G GHz band was another limitation of the multi-cluster PUSCH approach as shown in Fig. 8.34. The LTE-based eLAA supports multi-subframe scheduling, where an uplink grant can schedule PUSCH transmissions in a number of consecutive subframes ranging from two to four subframes. It further supports DCI formats 0A and 4A for single subframe scheduling and DCI formats 0B and 4B for multi-subframe scheduling for single-layer and multi-layer PUSCH transmissions, respec- tively (see Fig. 8.35). As an example, the 10 dBm/MHz defined by the ETSI over 5150-5350 MHz frequency range is shown in Fig. 8.34, where ETSI allows a PSD of 17 dBm/MHz (over 5470-5725 MHz) if TPC can be applied [29]. The US FCC defines 11 dBm/MHz PSD for 5150-5350 MHz frequency range. As a result, 3GPP adopted the principl