It Is Declared that the Rate Can Reach Up to 1.3 Gbit/s in a Scenario with 802.11ac, HT80 Frequency Bandwidth, and 3x3 MIMO. However, Why Is the Tested Rate Far Lower Than 1.3 Gbit/s?

Bandwidth loss from the physical layer to the service layer includes time consumption of the process required by 802.11 MAC layer communication, and header and trailer overheads of data frames on different layers.

Specifically, bandwidth provided by the communications system can be calculated using the number of bits transmitted per unit time, that is, number of bits/time.

• Number of valid bits transmitted

  In the preceding figure, A-MSDU Subfrm1 marked in dashed lines is the packet sent from the Ethernet, where the MSDU field is the service packet sent from the upper layer (packet described in the test result of Chariot). The entire 802.11 packet also has other headers including PLCP Preamble, PLCP Header, and 802.11 Header.

• Time for transmitting the preceding bits

  The following figure shows the protocol process through which each data packet transmitted on the 802.11 air interface goes.

  The transmitter sends a data frame after Distributed Interframe Space (DIFS) times out and waits for the backoff time. After receiving the data frame, the receiver waits until Short Interframe Space (SIFS) times out and sends an ACK frame to the transmitter. It can be considered that a data packet is successfully sent only after the entire process is correctly completed.

Service packet rate = Number of bits in service packets/Total packet transmission time

Due to communication loss described above, the actual service rate is less than the PHY rate of the air interface.