- background
Wireless local area network (WLAN), also known as Wi-Fi, is widely used to provide low-cost, high-throughput and convenient wireless communication services. Basic service set (BSS, basic service set) is the basic component of WLAN. A station (STA, station) in a certain coverage area and a wireless access point (AP, access point) dedicated to managing the BSS form a BSS, and the STA is said to be associated with the AP. Common APs include wireless routers, WiFi hotspots, etc. Mobile phones, laptops, IoT devices, etc. are STAs. The data sent by the AP to the STA is called the downlink direction, and vice versa. This article refers to the AP and STA as nodes. The sending and receiving of each node cannot occur at the same time. Each node shares the channel and avoids conflicts through the carrier sense multi-access and collision avoidance (CSMA/CA) mechanism, which is called distributed coordination function (DCF).
Figure 1.1 WLAN network
1.1 Distributed channel access and binary exponential backoff
The DCF mechanism provides a distributed, competition-based channel access function. The process of each node accessing the channel for data transmission can be divided into three stages: channel availability assessment (CCA, clear channel assessment), random backoff, and data transmission.
(1) CCA: When a node intends to send