 in the downlink to combine an LTE carrier in the unlicensed spectrum with LTE carrier(s) in the licensed spectrum (see Fig. 8.12). This aggregation of spectrum provides higher data rates, improved indoor connectivity, and network capacity. This is done by maintaining a persis- tent anchor in the licensed spectrum that carries the control and signaling information and combining it with one or more carriers from the unlicensed spectrum. The LAA has been designed as a single global solution that can adapt to unique regional regulatory require- ments while coexisting with Wi-Fi and other unlicensed-band radios. For regulatory compli- ance and coexistence with other devices operating in the unlicensed band, devices supporting LAA must utilize LBT, which is mandated in Europe and Japan. The LBT used in LAA is similar to the method used by Wi-Fi nodes. A new frame structure (type 3) was defined exclusively for LAA cells, supporting discontinuous time-limited transmissions to ensure that the LTE access nodes do not dominate the channel. It also enables the use of incomplete subframes below 1 ms for more flexible adaptation to transmission opportunities after a successful LBT. The enhanced LAA (eLAA) in Rel-14 extended the downlink-only LAA to the uplink. For LAA operation in some geographical regions (e.g., Japan), 868 Chapter 8 + (TMCOTIT|-1) Tjs (us) Tjs = 34 us ;=4ms Transmit Transmit Is the channel idle during this period? Is the detected energy below a threshold? Figure 8.11 Discontinuous transmission in LAA [22]. discontinuous transmission is part of the specification. An eNB can transmit again on the LAA SCell for a maximum duration of T=ms immediately after sensing the channel to be idle for a sensing interval of Tjs=34 us as shown in Fig. 8.11. The Rel-13 LAA functionality relies on LBT, frame structure type 3 along with discontinu- ous transmission with limited use of channel, use of incomplete subframes, downlink only, no PBCH (PBCH is not transmitted within frame structure type 3), use of Band 46 (5.150-5.92