Issue link: https://resources.mouser.com/i/1207833
22 Wait or Sleep Times: What Are the Challenges for the RF Front End? One thing 802.11ax adds is target wait time (TWT)—also known as sleep times—which allows a device to stay in a sleep state longer before transmitting data. This resource scheduling improves battery life and means a better experience for a consumer. However, latency in turn-on mode could be an underlying challenge. TWT also brings the following: • High susceptibility to frequency and clock offsets in OFDMA. Unlike LTE base station technologies, 802.11ax doesn't have a synchronized clock signal. As a result, devices will rely on the access point to keep all the devices on the network synchronized. Additionally, 11ax uses longer orthogonal frequency-division multiplexing (OFDM) symbols than 11ac, which means more data comes through. In short, the access point will have to work harder—and be more accurate—than in the past. • Flatness maintained over a longer time period. The specs we've received from some of our chipset partners show that the initial power amplifier (PA) turn-on time has not changed in 802.11ax; it's still 200-400 nanoseconds. However, the gain flatness has been extended, guaranteeing the front-end module (FEM) has no gain expansion or gain droop for the duration of the packet. Indoor vs. Outdoor Wi-Fi: What Are the Similarities and Differences? For 802.11ax to work across all environments, both indoor Wi-Fi and outdoor base stations or small cells will be required. The front-end development is very similar for indoor and outdoor environments. The coexistence strategy—out-of-band rejection, harmonic filtering, and frequency range—is similar. The main differences between indoor and outdoor environments include: • A new data packet structure for outdoor. As we mentioned earlier, 802.11ax adds an entirely new data packet format for outdoor Wi-Fi, the HE-xSU PPDU format (shown in the PPDU figure at the end of this article). The extended range of the outdoor PPDU format allows the Wi-Fi signal to travel longer distances, as is typical for an outdoor Wi-Fi environment. ©2018 Qorvo, Inc. Target Wait Time (TWT) 802.11 ax