Hello everyone,
Today I will share with you the Extended Range (ER).
As with cellular networks, the bottleneck in wireless coverage is the uplink. On a Wi-Fi network, APs have higher transmit power and more antennas and provide long downlink coverage. In addition, APs are connected to power supplies and do not need to worry about power consumption. However, for mobile phones, tablets, and other IoT terminals, the transmit power and number of antennas are limited, affecting uplink coverage. In addition, the battery life must be optimized.
802.11ax introduces a longer OFDM symbol time of 12.8 μs, which is four times longer than the legacy symbol time of 3.2 μs. Subcarrier spacing is equal to the reciprocal of the symbol time. As a result of the longer symbol time, the subcarrier size and spacing decrease from 312.5 kHz to 78.125 kHz. The narrow subcarrier spacing allows better equalization and therefore enhanced channel robustness. Because of the 78.125 kHz spacing, an OFDMA 20 MHz channel consists of a total of 256 subcarriers (tones) as depicted in Figure 1. The data transmission duration increases from 3.2 us to 12.8 us. A longer transmission time can reduce the packet loss rate of STAs.
Figure 1 Subcarrier spacing
In addition, Wi-Fi 6 optimizes uplink signal coverage. That is, a terminal concentrates its energy on a narrower 2 MHz channel and improves uplink coverage by increasing uplink power spectral density.
802.11ax can use only 2 MHz bandwidth for narrowband transmission, which reduces noise interference on the frequency band, improves the receiver sensitivity of STAs, and increases the coverage range.
Figure 2 Range increase brought by a long OFDM symbol and narrowband transmission
Extended Distance PPDU Transmission Mode
1. 802.11ax proposes to improve transmission performance in an outdoor scenario. Therefore, for a single-user format, the preamble part is repeatedly transmitted (from two symbols in another format to four symbols) on the HE-SIG-A, thereby enhancing the robustness of and.
2. Power boosting is performed on the conventional preamble, the HE-STF, and the HE-LTF to further expand the transmission range of the preamble.
3. A transmission range of a data part is extended by using a manner such as dual-carrier modulation (Dual Carrier Modulation, DCM) and band suffocation transmission of a 106-tone RU.
Figure 3 802.11ax packet structure-single user format with extended range
That is all I want to share with you! Thank you!
