the LTE physical layer and MAC functionalities. The deployment scenarios included supplemental LTE downlink operating in an unlicensed spectrum com- prising multiple contiguous 20 MHz bands. The LTE network with an uplink and downlink anchored on the licensed spectrum (up to 20 MHz) for delivering essential control signaling and synchronization related to radio resource management and connection/mobility provides reliability, mobility, and coverage, whereas the unlicensed spectrum was exclusively used for increasing the downlink data rates. LTE-U was designed to comply with the US regulations and targets other regions of the world with no LBT requirements. However, it does not necessarily meet the needs of other regions which do require LBT feature such as Europe and Japan. While LTE-U and LAA are both LTE-based solutions for operation in the unlicensed band, they differ in the way they meet the regulatory requirements. LTE-U is well suited for regions that do not require LBT and address coexistence issues with Wi-Fi using an algorithm called carrier sensing adaptive transmission (CSAT) in the LTE-U eNB, which is based on the use of duty cycle that adapts the duration of the ON period by sensing the average power in the channel as shown in Fig. 8.20. LTE-U also limits the duration of the ON period to 20 ms SO that low 880 Chapter 8 LTE in OFF period senses channel CCA success utilization by Wi-Fi Channel access by Wi-Fi when LTE is OFF LAA frame failure LTE on TE off LTE on LE off CCA failure CCA success Duty cycle Wi-Fi Wi-Fi Random backoff Carrier sensing adaptive transmission (CSAT) Licensed assisted access (LAA) Figure 8.20 Comparison of CSAT and LBT mechanisms [17,23]. latency applications can coexist. On the other hand, LAA is a global solution and includes support for LBT and a more flexible frame structure to better adapt to channel availability. LAA is generally preferred by operators as it is the only method that provides full cellular capabilities, whereas LWA or LWIP are less frequently used because t